National Ambient Air Quality Standards for Particulate Matter, 3085-3287 [2012-30946]
Download as PDF
Vol. 78
Tuesday,
No. 10
January 15, 2013
Part II
Environmental Protection Agency
tkelley on DSK3SPTVN1PROD with
40 CFR Parts 50, 51, 52 et al.
National Ambient Air Quality Standards for Particulate Matter; Final Rule
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
PO 00000
Frm 00001
Fmt 4717
Sfmt 4717
E:\FR\FM\15JAR2.SGM
15JAR2
3086
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
40 CFR Parts 50, 51, 52, 53 and 58
[EPA–HQ–OAR–2007–0492; FRL–9761–8]
RIN 2060–AO47
National Ambient Air Quality
Standards for Particulate Matter
Environmental Protection
Agency (EPA).
ACTION: Final rule.
AGENCY:
Based on its review of the air
quality criteria and the national ambient
air quality standards (NAAQS) for
particulate matter (PM), the EPA is
making revisions to the suite of
standards for PM to provide requisite
protection of public health and welfare
and to make corresponding revisions to
the data handling conventions for PM
and to the ambient air monitoring,
reporting, and network design
requirements. The EPA also is making
revisions to the prevention of significant
deterioration (PSD) permitting program
with respect to the NAAQS revisions.
With regard to primary (health-based)
standards for fine particles (generally
referring to particles less than or equal
to 2.5 micrometers (mm) in diameter,
PM2.5), the EPA is revising the annual
PM2.5 standard by lowering the level to
12.0 micrograms per cubic meter (mg/
m3) so as to provide increased
protection against health effects
associated with long- and short-term
exposures (including premature
mortality, increased hospital admissions
and emergency department visits, and
development of chronic respiratory
disease), and to retain the 24-hour PM2.5
standard at a level of 35 mg/m3. The EPA
is revising the Air Quality Index (AQI)
for PM2.5 to be consistent with the
revised primary PM2.5 standards. With
regard to the primary standard for
particles generally less than or equal to
10 mm in diameter (PM10), the EPA is
retaining the current 24-hour PM10
standard to continue to provide
protection against effects associated
with short-term exposure to thoracic
coarse particles (i.e., PM10-2.5). With
regard to the secondary (welfare-based)
PM standards, the EPA is generally
retaining the current suite of secondary
standards (i.e., 24-hour and annual
PM2.5 standards and a 24-hour PM10
standard). Non-visibility welfare effects
are addressed by this suite of secondary
standards, and PM-related visibility
impairment is addressed by the
secondary 24-hour PM2.5 standard.
DATES: The final rule is effective on
March 18, 2013.
tkelley on DSK3SPTVN1PROD with
SUMMARY:
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
Section X.B requests
comments on an information collection
request regarding changes to the
monitoring requirements. Submit your
comments, identified by Docket ID No.
EPA–HQ–OAR–2007–0492, to the EPA
by one of the following methods:
• www.regulations.gov: Follow the
on-line instructions for submitting
comments.
• Email: a-and-r-Docket@epa.gov.
• Fax: 202–566–9744.
• Mail: Docket No. EPA–HQ–OAR–
2007–0492, Environmental Protection
Agency, Mail code 6102T, 1200
Pennsylvania Ave. NW., Washington,
DC 20460. Please include a total of two
copies.
• Hand Delivery: Docket No. EPA–
HQ–OAR–2007–0492, Environmental
Protection Agency, EPA West, Room
3334, 1301 Constitution Ave. NW.,
Washington, DC. Such deliveries are
only accepted during the Docket’s
normal hours of operation, and special
arrangements should be made for
deliveries of boxed information.
Instructions: Direct your comments to
Docket ID No. EPA–HQ–OAR–2007–
0492. The EPA’s policy is that all
comments received will be included in
the public docket without change and
may be made available online at
www.regulations.gov, including any
personal information provided, unless
the comment includes information
claimed to be Confidential Business
Information (CBI) or other information
whose disclosure is restricted by statute.
Do not submit information that you
consider to be CBI or otherwise
protected through www.regulations.gov
or email. The www.regulations.gov Web
site is an ‘‘anonymous access’’ system,
which means the EPA will not know
your identity or contact information
unless you provide it in the body of
your comment. If you send an email
comment directly to the EPA without
going through www.regulations.gov your
email address will be automatically
captured and included as part of the
comment that is placed in the public
docket and made available on the
Internet. If you submit an electronic
comment, the EPA recommends that
you include your name and other
contact information in the body of your
comment and with any disk or CD–ROM
you submit. If the EPA cannot read your
comment due to technical difficulties
and cannot contact you for clarification,
the EPA may not be able to consider
your comment. Electronic files should
avoid the use of special characters, any
form of encryption, and be free of any
defects or viruses. For additional
information about EPA’s public docket
visit the EPA Docket Center homepage
ADDRESSES:
ENVIRONMENTAL PROTECTION
AGENCY
PO 00000
Frm 00002
Fmt 4701
Sfmt 4700
at http://www.epa.gov/epahome/
dockets.htm. Comments on this
information collection request should
also be sent to the Office of Management
and Budget (OMB). See section X.B
below for additional information
regarding submitting comments to OMB.
Docket: The EPA has established a
docket for this action under Docket No.
EPA–HQ–OAR–2007–0492. All
documents in the docket are listed on
the www.regulations.gov Web site. This
includes documents in the rulemaking
docket (Docket ID No. EPA–HQ–OAR–
2007–0492) and a separate docket,
established for 2009 Integrated Science
Assessment (Docket No. EPA–HQ–
ORD–2007–0517), that has have been
incorporated by reference into the
rulemaking docket. All documents in
these dockets are listed on the
www.regulations.gov Web site. Although
listed in the index, some information is
not publicly available, e.g., CBI or other
information whose disclosure is
restricted by statute. Certain other
material, such as copyrighted material,
is not placed on the Internet and may be
viewed, with prior arrangement, at the
EPA Docket Center. Publicly available
docket materials are available either
electronically in www.regulations.gov or
in hard copy at the Air and Radiation
Docket and Information Center, EPA/
DC, EPA West, Room 3334, 1301
Constitution Ave. NW., Washington,
DC. The Public Reading Room is open
from 8:30 a.m. to 4:30 p.m., Monday
through Friday, excluding legal
holidays. The telephone number for the
Public Reading Room is (202) 566–1744
and the telephone number for the Air
and Radiation Docket and Information
Center is (202) 566–1742. For additional
information about EPA’s public docket
visit the EPA Docket Center homepage
at: http://www.epa.gov/epahome/
dockets.htm.
FOR FURTHER INFORMATION CONTACT: Ms.
Beth M. Hassett-Sipple, Health and
Environmental Impacts Division, Office
of Air Quality Planning and Standards,
U.S. Environmental Protection Agency,
Mail code C504–06, Research Triangle
Park, NC 27711; telephone: (919) 541–
4605; fax: (919) 541–0237; email:
hassett-sipple.beth@epa.gov.
SUPPLEMENTARY INFORMATION:
General Information
Availability of Related Information
A number of the documents that are
relevant to this rulemaking are available
through the EPA’s Office of Air Quality
Planning and Standards (OAQPS)
Technology Transfer Network (TTN)
Web site at http://www.epa.gov/ttn/
naaqs/standards/pm/s_pm_index.html.
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
These documents include the Plan for
Review of the National Ambient Air
Quality Standards for Particulate Matter
(U.S. EPA, 2008a), available at http://
www.epa.gov/ttn/naaqs/standards/pm/
s_pm_2007_pd.html, the Integrated
Science Assessment for Particulate
Matter (U.S. EPA, 2009a), available at
http://www.epa.gov/ttn/naaqs/
standards/pm/s_pm_2007_isa.html, the
Quantitative Health Risk Assessment for
Particulate Matter (U.S. EPA, 2010a),
available at http://www.epa.gov/ttn/
naaqs/standards/pm/
s_pm_2007_risk.html, the Particulate
Matter Urban-Focused Visibility
Assessment (U.S. EPA 2010b), available
at http://www.epa.gov/ttn/naaqs/
standards/pm/s_pm_2007_risk.html,
and the Policy Assessment for the
Review of the Particulate Matter
National Ambient Air Quality
Standards (U.S. EPA, 2011a), available
at http://www.epa.gov/ttn/naaqs/
standards/pm/s_pm_2007_pa.html.
These and other related documents are
also available for inspection and
copying in the EPA docket identified
above.
tkelley on DSK3SPTVN1PROD with
Table of Contents
The following topics are discussed in this
preamble:
I. Executive Summary
A. Purpose of This Regulatory Action
B. Summary of Major Provisions
C. Costs and Benefits
II. Background
A. Legislative Requirements
B. Review of the Air Quality Criteria and
Standards for PM
1. Previous PM NAAQS Reviews
2. Litigation Related to the 2006 PM
Standards
3. Current PM NAAQS Review
C. Related Control Programs To Implement
PM Standards
D. Summary of Proposed Revisions to the
PM NAAQS
E. Organization and Approach to Final PM
NAAQS Decisions
III. Rationale for Final Decisions on the
Primary PM2.5 Standards
A. Background
1. General Approach Used in Previous
Reviews
2. Remand of Primary Annual PM2.5
Standard
3. General Approach Used in the Policy
Assessment for the Current Review
B. Overview of Health Effects Evidence
C. Overview of Quantitative
Characterization of Health Risks
D. Conclusions on the Adequacy of the
Current Primary PM2.5 Standards
1. Introduction
a. Evidence- and Risk-based Considerations
in the Policy Assessment
b. CASAC Advice
c. Administrator’s Proposed Conclusions
Concerning the Adequacy of the Current
Primary PM2.5 Standards
2. Comments on the Need for Revision
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
3. Administrator’s Final Conclusions
Concerning the Adequacy of the Current
Primary PM2.5 Standards
E. Conclusions on the Elements of the
Primary Fine Particle Standards
1. Indicator
2. Averaging Time
3. Form
a. Annual Standard
b. 24-Hour Standard
4. Level
a. General Approach for Considering
Standard Levels
b. Proposed Decisions on Level
i. Consideration of Alternative Standard
Levels in the Policy Assessment
ii. CASAC Advice
iii. Administrator’s Proposed Decisions on
the Primary PM2.5 Standard Levels
c. Comments on Standard Levels
i. Annual Standard Level
ii. 24-Hour Standard Level
d. Administrator’s Final Conclusions on
the Primary PM2.5 Standard Levels
F. Administrator’s Final Decisions on the
Primary PM2.5 Standards
IV. Rationale for Final Decision on Primary
PM10 Standard
A. Background
1. Previous Reviews of the PM NAAQS
a. Reviews Completed in 1987 and 1997
b. Review Completed in 2006
2. Litigation Related to the 2006 Primary
PM10 Standards
3. General Approach Used in the Current
Review
B. Health Effects Related to Exposure to
Thoracic Coarse Particles
C. Consideration of the Current and
Potential Alternative Standards in the
Policy Assessment
1. Consideration of the Current Standard in
the Policy Assessment
2. Consideration of Potential Alternative
Standards in the Policy Assessment
D. CASAC Advice
E. Administrator’s Proposed Conclusions
Concerning the Adequacy of the Current
Primary PM10 Standard
F. Public Comments on the Administrator’s
Proposed Decision To Retain the Primary
PM10 Standard
G. Administrator’s Final Decision on the
Primary PM10 Standard
V. Communication of Public Health
Information
VI. Rationale for Final Decisions on the
Secondary PM Standards
A. Background
1. Approaches Used in Previous Reviews
2. Remand of 2006 Secondary PM2.5
Standards
3. General Approach Used in the Policy
Assessment for the Current Review
B. Proposed Decisions on Secondary PM
Standards
1. PM-related Visibility Impairment
a. Nature of PM-related Visibility
Impairment
i. Relationship Between Ambient PM and
Visibility
ii. Temporal Variations of Light Extinction
iii. Periods During the Day of Interest for
Assessment of Visibility
iv. Exposure Durations of Interest
v. Periods of Fog and Rain
PO 00000
Frm 00003
Fmt 4701
Sfmt 4700
3087
b. Public Perception of Visibility
Impairment
c. Summary of Proposed Conclusions
i. Adequacy
ii. Indicator
iii. Averaging Time
iv. Form
v. Level
vi. Administrator’s Proposed Conclusions
vii. Related Technical Analysis
2. Other (Non-Visibility) PM-related
Welfare Effects
a. Evidence of Other Welfare Effects
Related to PM
b. CASAC Advice
c. Summary of Proposed Decisions
Regarding Other Welfare Effects
C. Comments on Proposed Rule
1. Comments on Proposed Secondary PM
Standard for Visibility Protection
a. Overview of Comments
b. Indicator
i. Comments on Calculated vs. Directly
Measured Light Extinction
ii. Comments on Specific Aspects of
Calculated Light Extinction Indicator
c. Averaging Time
d. Form
e. Level
i. Comments on Visibility Preference
Studies
ii. Specific Comments on Level
f. Need for a Distinct Secondary Standard
g. Legal Issues
h. Relationship With Regional Haze
Program
2. Comments on the Proposed Decision
Regarding Non-Visibility Welfare Effects
D. Conclusions on Secondary PM
Standards
1. Conclusions Regarding Secondary PM
Standards To Address Non-Visibility
Welfare Effects
2. Conclusions Regarding Secondary PM
Standards for Visibility Protection
E. Administrator’s Final Decisions on
Secondary PM Standards
VII. Interpretation of the NAAQS for PM
A. Amendments to Appendix N:
Interpretation of the NAAQS for PM2.5
1. General
2. Monitoring Considerations
3. Requirements for Data Use and
Reporting for Comparison With the
NAAQS for PM2.5
4. Comparisons with the PM2.5 NAAQS
B. Exceptional Events
C. Updates for Data Handling Procedures
for Reporting the Air Quality Index
VIII. Amendments to Ambient Monitoring
and Reporting Requirements
A. Issues Related to 40 CFR Part 53
(Reference and Equivalent Methods)
1. PM2.5 and PM10-2.5 Federal Equivalent
Methods
2. Use of Chemical Speciation Network
(CSN) Methods to Support the Proposed
New Secondary PM2.5 Visibility Index
NAAQS
B. Changes to 40 CFR Part 58 (Ambient Air
Quality Surveillance)
1. Terminology Changes
2. Special Considerations for
Comparability of PM2.5 Ambient Air
Monitoring Data to the NAAQS
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
3088
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
a. Revoking Use of Population-Oriented as
a Condition for Comparability of PM2.5
Monitoring Sites to the NAAQS
b. Applicability of Micro- and Middle-scale
Monitoring Sites to the Annual PM2.5
NAAQS
3. Changes to Monitoring for the National
Ambient Air Monitoring System
a. Background
b. Primary PM2.5 NAAQS
i. Addition of a Near-road Component to
the PM2.5 Monitoring Network
ii. Use of PM2.5 Continuous FEMs at
SLAMS
c. Revoking PM10-2.5 Speciation
Requirements at NCore Sites
d. Measurements for the Proposed New
PM2.5 Visibility Index NAAQS
4. Revisions to the Quality Assurance
Requirements for SLAMS, SPMs, and
PSD
a. Quality Assurance Weight of Evidence
b. Quality Assurance Requirements for the
Chemical Speciation Network
c. Waivers for Maximum Allowable
Separation of Collocated PM2.5 Samplers
and Monitors
5. Revisions To Probe and Monitoring Path
Siting Criteria
a. Near-road Component to the PM2.5
Monitoring Network
b. CSN Network
c. Reinsertion of Table E–1 to Appendix E
6. Additional Ambient Air Monitoring
Topics
a. Annual Monitoring Network Plans and
Periodic Assessment
b. Operating Schedules
c. Data Reporting and Certification for CSN
and IMPROVE Data
d. Requirements for Archiving Filters
IX. Clean Air Act Implementation
Requirements for the PM NAAQS
A. Designation of Areas
1. Overview of Clean Air Act Designations
Requirements
2. Proposed Designations Schedules
3. Comments and Responses
4. Final Intended Designations Schedules
B. Section 110(a)(2) Infrastructure SIP
Requirements
C. Implementing the Revised Primary
Annual PM2.5 NAAQS in Nonattainment
Areas
D. Prevention of Significant Deterioration
and Nonattainment New Source Review
Programs for the Revised Primary
Annual PM2.5 NAAQS
1. Prevention of Significant Deterioration
a. Transition Provision (Grandfathering)
i. Proposal
ii. Comments and Responses
iii. Final Action
b. Modeling Tools and Guidance
Applicable to the Revised Primary
Annual PM2.5 NAAQS
c. PSD Screening Tools: Significant
Emissions Rates, Significant Impact
Levels, and Significant Monitoring
Concentration
d. PSD Increments
e. Other PSD Transition Issues
2. Nonattainment New Source Review
E. Transportation Conformity Program
F. General Conformity Program
X. Statutory and Executive Order Reviews
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
A. Executive Order 12866: Regulatory
Planning and Review and Executive
Order 13563: Improving Regulation and
Regulatory Review
B. Paperwork Reduction Act
C. Regulatory Flexibility Act
D. Unfunded Mandates Reform Act
E. Executive Order 13132: Federalism
F. Executive Order 13175: Consultation
and Coordination With Indian Tribal
Governments
G. Executive Order 13045: Protection of
Children From Environmental Health
and Safety Risks
H. Executive Order 13211: Actions that
Significantly Affect Energy Supply,
Distribution, or Use
I. National Technology Transfer and
Advancement Act
J. Executive Order 12898: Federal Actions
To Address Environmental Justice in
Minority Populations and Low-Income
Populations
K. Congressional Review Act
References
I. Executive Summary
A. Purpose of This Regulatory Action
Sections 108 and 109 of the Clean Air
Act (CAA) govern the establishment,
review, and revision, as appropriate, of
the national ambient air quality
standards (NAAQS) to protect public
health and welfare. The CAA requires
periodic review of the air quality
criteria—the science upon which the
standards are based—and the standards
themselves. This rulemaking is being
done pursuant to these statutory
requirements. The schedule for
completing this review is established by
a court order.
In 2006, the EPA completed its last
review of the PM NAAQS. In that
review, the EPA took three principal
actions: (1) With regard to fine particles
(generally referring to particles less than
or equal to 2.5 micrometers (mm) in
diameter, PM2.5), at that time, the EPA
revised the level of the primary 24-hour
PM2.5 standard from 65 to 35 mg/m3 and
retained the level of the primary annual
PM2.5 standard; (2) With regard to the
primary standards for particles less than
or equal to 10 mm in diameter (PM10),
the EPA retained the primary 24-hour
PM10 standard to continue to provide
protection against effects associated
with short-term exposure to thoracic
coarse particles (i.e., PM10-2.5) and
revoked the primary annual PM10
standard; and (3) the EPA also revised
the secondary standards to be identical
in all respects to the primary standards.
In subsequent litigation, the U.S.
Court of Appeals for the District of
Columbia Circuit remanded the primary
annual PM2.5 standard to the EPA
because the Agency had failed to
explain adequately why the standard
provided the requisite protection from
PO 00000
Frm 00004
Fmt 4701
Sfmt 4700
both short- and long-term exposures to
fine particles, including protection for
at-risk populations such as children.
The court remanded the secondary
PM2.5 standards to the EPA because the
Agency failed to explain adequately
why setting the secondary standards
identical to the primary standards
provided the required protection for
public welfare, including protection
from PM-related visibility impairment.
The EPA initiated this review in June
2007. Between 2007 and 2011, the EPA
prepared draft and final Integrated
Science Assessments, Risk and
Exposure Assessments, and Policy
Assessments. Multiple drafts of all of
these documents were subject to review
by the public and were peer reviewed
by the EPA’s Clean Air Scientific
Advisory Committee (CASAC). The EPA
proposed revisions to the primary and
secondary PM NAAQS on June 29, 2012
(77 FR 38890). This final rulemaking is
the final step in the review process.
In this rulemaking, the EPA is
revising the suite of standards for PM to
provide requisite protection of public
health and welfare. The EPA is revising
the PSD permitting regulations to
address the changes in the PM NAAQS.
In addition, the EPA is updating the
AQI for PM2.5 and making changes in
the data handling conventions for PM
and ambient air monitoring, reporting,
and network design requirements to
correspond with the changes to the PM
NAAQS.
B. Summary of Major Provisions
With regard to the primary standards
for fine particles, the EPA is revising the
annual PM2.5 standard by lowering the
level from 15.0 to 12.0 mg/m3 so as to
provide increased protection against
health effects associated with long-and
short-term exposures. The EPA is
retaining the level (35 mg/m3) and the
form (98th percentile) of the 24-hour
PM2.5 standard to continue to provide
supplemental protection against health
effects associated with short-term
exposures. This action provides
increased protection for children, older
adults, persons with pre-existing heart
and lung disease, and other at-risk
populations against an array of PM2.5related adverse health effects that
include premature mortality, increased
hospital admissions and emergency
department visits, and development of
chronic respiratory disease. The EPA
also is eliminating spatial averaging
provisions as part of the form of the
annual standard to avoid potential
disproportionate impacts on at-risk
populations.
The final decisions for the primary
annual and 24-hour PM2.5 standards are
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
within the ranges that CASAC advised
the Agency to consider. These decisions
are based on an integrative assessment
of an extensive body of new scientific
evidence, which substantially
strengthens what was known about
PM2.5-related health effects in the last
review, including extended analyses of
key epidemiological studies, and
evidence of health effects observed at
lower ambient PM2.5 concentrations,
including effects in areas that likely met
the current standards. The revised suite
of PM2.5 standards also reflects
consideration of a quantitative risk
assessment that estimates public health
risks likely to remain upon just meeting
the current and various alternative
standards. Based on this information,
the Administrator concludes that the
current primary PM2.5 standards are not
requisite to protect public health with
an adequate margin of safety, as
required by the CAA, and that these
revisions are warranted to provide the
appropriate degree of increased public
health protection.
With regard to the primary standard
for thoracic coarse particles (PM10-2.5),
the EPA is retaining the current 24-hour
PM10 standard, with a level of 150 mg/
m3 and a one-expected exceedance
form, to continue to provide protection
against effects associated with shortterm exposure to PM10-2.5 including
premature mortality and increased
hospital admissions and emergency
department visits. In reaching this
decision, the Administrator concludes
that the available health evidence and
air quality information for PM10-2.5,
taken together with the considerable
uncertainties and limitations associated
with that information, suggests that a
standard is needed to protect against
short-term exposure to all types of
PM10-2.5 and that the degree of public
health protection provided against
short-term exposures to PM10-2.5 does
not need to be increased beyond that
provided by the current PM10 standard.
With regard to the secondary PM
standards, the Administrator is retaining
the current suite of secondary PM
standards, except for a change to the
form of the annual PM2.5 standard.
Specifically, the EPA is retaining the
current secondary 24-hour PM2.5 and
PM10 standards, and is revising only the
form of the secondary annual PM2.5
standard to remove the option for
spatial averaging consistent with this
change to the primary annual PM2.5
standard. This suite of secondary
standards addresses PM-related nonvisibility welfare effects including
ecological effects, effects on materials,
and climate impacts. With respect to
PM-related visibility impairment, the
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
Administrator has identified a target
degree of protection, defined in terms of
a PM2.5 visibility index (based on
speciated PM2.5 mass concentrations
and relative humidity data to calculate
PM2.5 light extinction), a 24-hour
averaging time, and a 90th percentile
form, averaged over 3 years, and a level
of 30 deciviews (dv), which she judges
to be requisite to protect public welfare
with regard to visual air quality (VAQ).
The EPA’s analysis of monitoring data
provides the basis for concluding that
the current secondary 24-hour PM2.5
standard would provide sufficient
protection, and in some areas greater
protection, relative to this target
protection level. Adding a distinct
secondary standard to address visibility
would not affect this protection. Since
sufficient protection from visibility
impairment will be provided for all
areas of the country without adoption of
a distinct secondary standard, and
adoption of a distinct secondary
standard will not change the degree of
over-protection of VAQ provided for
some areas of the country by the
secondary 24-hour PM2.5 standard, the
Administrator judges that adoption of a
distinct secondary standard, in addition
to the current suite of secondary
standards, is not needed to provide
requisite protection for both visibility
and non-visibility related welfare
effects.
The revisions to the PM NAAQS
trigger a process under which states
(and tribes, if they choose) will make
recommendations to the Administrator
regarding designations, identifying areas
of the country that either meet or do not
meet the revised NAAQS. States will
also review, modify and supplement
their existing state implementation
plans (SIPs), as needed. With regard to
these implementation-related activities,
the EPA intends to promulgate a
separate implementation rule on a
schedule that provides timely clarity to
the states, tribes, and other parties
responsible for NAAQS
implementation. The NAAQS revisions
also affect the applicable air permitting
requirement, but cause no significant
change to the transportation conformity
and general conformity processes. The
EPA is revising its PSD regulations to
provide limited grandfathering from the
requirements that result from the
revised PM NAAQS.
On other topics, the EPA is changing
the AQI for PM2.5 to be consistent with
the revised primary PM2.5 NAAQS. The
EPA also is revising the data handling
procedures for PM2.5 consistent with the
revised PM2.5 NAAQS including the
computations necessary for determining
when the standards are met and the
PO 00000
Frm 00005
Fmt 4701
Sfmt 4700
3089
measurement data that are appropriate
for comparison to the standards. With
regard to monitoring-related activities,
the EPA is updating several aspects of
the monitoring regulations and
specifically requiring that a small
number of PM2.5 monitors be relocated
to be collocated with measurements of
other pollutants (e.g., nitrogen dioxide,
carbon monoxide) in the near-road
environment.
C. Costs and Benefits
In setting the NAAQS, the EPA may
not consider the costs of implementing
the standards. This was confirmed by
the United States Supreme Court in
Whitman v. American Trucking
Associations, 531 U.S. 457, 465–472,
475–76 (2001), as noted in section II.A
of this rule. As has traditionally been
done in NAAQS rulemaking, the EPA
has conducted a Regulatory Impact
Analysis (RIA) to provide the public
with information on the potential costs
and benefits of attaining several
alternative PM2.5 standards. In NAAQS
rulemaking, the RIA is done for
informational purposes only, and the
final decisions on the NAAQS in this
rulemaking are not in any way based on
consideration of the information or
analyses in the RIA. The RIA fulfills the
requirements of Executive Orders 13563
and 12866. The summary of the RIA,
which is discussed in more detail below
in section X.A, estimates benefits
ranging from $4,000 million to $9,100
million at a 3 percent discount rate and
$3,600 million to $8,200 million at a 7
percent discount rate in 2020 and costs
ranging from $53 million to $350
million per year at a 7 percent discount
rate.
II. Background
A. Legislative Requirements
Two sections of the CAA govern the
establishment, review and revision of
the NAAQS. Section 108 (42 U.S.C.
7408) directs the Administrator to
identify and list certain air pollutants
and then to issue air quality criteria for
those pollutants. The Administrator is
to list those air pollutants that in her
‘‘judgment, cause or contribute to air
pollution which may reasonably be
anticipated to endanger public health or
welfare;’’ ‘‘the presence of which in the
ambient air results from numerous or
diverse mobile or stationary sources;’’
and ‘‘for which * * * [the
Administrator] plans to issue air quality
criteria * * *’’ Air quality criteria are
intended to ‘‘accurately reflect the latest
scientific knowledge useful in
indicating the kind and extent of all
identifiable effects on public health or
E:\FR\FM\15JAR2.SGM
15JAR2
3090
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
welfare which may be expected from the
presence of [a] pollutant in the ambient
air * * *’’ 42 U.S.C. 7408(b). Section
109 (42 U.S.C. 7409) directs the
Administrator to propose and
promulgate ‘‘primary’’ and ‘‘secondary’’
NAAQS for pollutants for which air
quality criteria are issued. Section
109(b)(1) defines a primary standard as
one ‘‘the attainment and maintenance of
which in the judgment of the
Administrator, based on such criteria
and allowing an adequate margin of
safety, are requisite to protect the public
health.’’ 1 A secondary standard, as
defined in section 109(b)(2), must
‘‘specify a level of air quality the
attainment and maintenance of which,
in the judgment of the Administrator,
based on such criteria, is requisite to
protect the public welfare from any
known or anticipated adverse effects
associated with the presence of [the]
pollutant in the ambient air.’’ 2
The requirement that primary
standards provide an adequate margin
of safety was intended to address
uncertainties associated with
inconclusive scientific and technical
information available at the time of
standard setting. It was also intended to
provide a reasonable degree of
protection against hazards that research
has not yet identified. See Lead
Industries Association v. EPA, 647 F.2d
1130, 1154 (D.C. Cir 1980); American
Petroleum Institute v. Costle, 665 F.2d
1176, 1186 (D.C. Cir. 1981); American
Farm Bureau Federation v. EPA, 559 F.
3d 512, 533 (D.C. Cir. 2009); Association
of Battery Recyclers v. EPA, 604 F. 3d
613, 617–18 (D.C. Cir. 2010). Both kinds
of uncertainties are components of the
risk associated with pollution at levels
below those at which human health
effects can be said to occur with
reasonable scientific certainty. Thus, in
selecting primary standards that provide
an adequate margin of safety, the
Administrator is seeking not only to
prevent pollution levels that have been
demonstrated to be harmful but also to
prevent lower pollutant levels that may
pose an unacceptable risk of harm, even
if the risk is not precisely identified as
to nature or degree. The CAA does not
require the Administrator to establish a
primary NAAQS at a zero-risk level or
at background concentration levels, see
Lead Industries v. EPA, 647 F.2d at 1156
n.51, but rather at a level that reduces
risk sufficiently so as to protect public
health with an adequate margin of
safety.
In addressing the requirement for an
adequate margin of safety, the EPA
considers such factors as the nature and
severity of the health effects involved,
the size of at-risk population(s), and the
kind and degree of the uncertainties that
must be addressed. The selection of any
particular approach to providing an
adequate margin of safety is a policy
choice left specifically to the
Administrator’s judgment. See Lead
Industries Association v. EPA, 647 F.2d
at 1161–62; Whitman v. American
Trucking Associations, 531 U.S. 457,
495 (2001).
In setting standards that are
‘‘requisite’’ to protect public health and
welfare, as provided in section 109(b),
the EPA’s task is to establish standards
that are neither more nor less stringent
than necessary for these purposes. In so
doing, the EPA may not consider the
costs of implementing the standards.
See generally, Whitman v. American
Trucking Associations, 531 U.S. 457,
465–472, 475–76 (2001). Likewise,
‘‘[a]ttainability and technological
feasibility are not relevant
considerations in the promulgation of
national ambient air quality standards.’’
American Petroleum Institute v. Costle,
665 F. 2d at 1185.
Section 109(d)(1) requires that ‘‘not
later than December 31, 1980, and at 5year intervals thereafter, the
Administrator shall complete a
thorough review of the criteria
published under section 108 and the
national ambient air quality standards
* * * and shall make such revisions in
such criteria and standards and
promulgate such new standards as may
be appropriate * * *’’ Section 109(d)(2)
requires that an independent scientific
review committee ‘‘shall complete a
review of the criteria * * * and the
national primary and secondary ambient
air quality standards * * * and shall
recommend to the Administrator any
new * * * standards and revisions of
existing criteria and standards as may be
appropriate. * * *’’ Since the early
1980’s, this independent review
function has been performed by the
CASAC.3
B. Review of the Air Quality Criteria and
Standards for PM
1. Previous PM NAAQS Reviews
The EPA initially established NAAQS
for PM under section 109 of the CAA in
1971. Since then, the Agency has made
a number of changes to these standards
to reflect continually expanding
scientific information, particularly with
respect to the selection of indicator4 and
level. Table 1 provides a summary of the
PM NAAQS that have been promulgated
to date. These decisions are briefly
discussed below.
TABLE 1—SUMMARY OF NATIONAL AMBIENT AIR QUALITY STANDARDS PROMULGATED FOR PM 1971–2006 a
1971—36 FR 8186 April 30,
1971.
Indicator
Averaging
time
Level
TSP ..........
24-hour ....
24-hour ....
260 μg/m3 (primary) ..................
150 μg/m3 ..................................
(secondary) ................................
75 μg/m3 ....................................
(primary) ....................................
150 μg/m3 ..................................
Annual .....
Final rule
50 μg/m3 ....................................
Not to be exceeded more than once per year on
average over a 3-year period.
Annual arithmetic mean, averaged over 3 years.
made materials, animals, wildlife, weather,
visibility and climate, damage to and deterioration
of property, and hazards to transportation, as well
as effects on economic values and on personal
comfort and well-being.’’
3 The CASAC PM Review Panel is comprised of
the seven members of the chartered CASAC,
supplemented by fifteen subject-matter experts
appointed by the Administrator to provide
additional scientific expertise relevant to this
review of the PM NAAQS. Lists of current CASAC
members and review panels are available at: http://
yosemite.epa.gov/sab/sabproduct.nsf/WebCASAC/
CommitteesandMembership?OpenDocument.
Members of the CASAC PM Review Panel are listed
in the CASAC letters providing advice on draft
assessment documents (Samet, 2009a–f, 2012a–d).
4 Particulate matter is the generic term for a broad
class of chemically and physically diverse
substances that exist as discrete particles (liquid
droplets or solids) over a wide range of sizes, such
that the indicator for a PM NAAQS has historically
been defined in terms of particle size ranges.
Annual .....
tkelley on DSK3SPTVN1PROD with
1987—52 FR 24634 July 1,
1987.
PM10 ........
1 The legislative history of section 109 indicates
that a primary standard is to be set at ‘‘the
maximum permissible ambient air level * * *
which will protect the health of any [sensitive]
group of the population,’’ and that for this purpose
‘‘reference should be made to a representative
sample of persons comprising the sensitive group
rather than to a single person in such a group.’’ S.
Rep. No. 91–1196, 91st Cong., 2d Sess. 10 (1970).
2 Welfare effects as defined in section 302(h) (42
U.S.C. 7602(h)) include, but are not limited to,
‘‘effects on soils, water, crops, vegetation, man-
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
PO 00000
Frm 00006
Fmt 4701
Sfmt 4700
Form
Not to be exceeded more than once per year.
Annual average.
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
3091
TABLE 1—SUMMARY OF NATIONAL AMBIENT AIR QUALITY STANDARDS PROMULGATED FOR PM 1971–2006 a—Continued
Level
PM2.5 ........
24-hour ....
65 μg/m3 ....................................
98th percentile, averaged over 3 years.b
15.0 μg/m3 .................................
24-hour ....
150 μg/m3 ..................................
PM2.5 ........
Annual .....
24-hour ....
Annual .....
50 μg/m3 ....................................
35 μg/m3 ....................................
15.0 μg/m3 .................................
PM10 ........
2006—71 FR 61144 October
17, 2006.
Averaging
time
PM10 ........
1997—62 FR 38652 July 18,
1997.
Indicator
Annual .....
Final rule
24-hour ....
150 μg/m3 ..................................
Annual arithmetic mean, averaged over 3
years.c d
Initially promulgated 99th percentile, averaged
over 3 years; when 1997 standards for PM10
were vacated, the form of 1987 standards remained in place (not to be exceeded more
than once per year on average over a 3-year
period).
Annual arithmetic mean, averaged over 3 years.
98th percentile, averaged over 3 years.b
Annual arithmetic mean, averaged over 3
years.c e
Not to be exceeded more than once per year on
average over a 3-year period.
Form
a When
not specified, primary and secondary standards are identical.
level of the 24-hour standard is defined as an integer (zero decimal places) as determined by rounding. For example, a 3-year average
98th percentile concentration of 35.49 μg/m3 would round to 35 μg/m3 and thus meet the 24-hour standard and a 3-year average of 35.50 μg/m3
would round to 36 and, hence, violate the 24-hour standard (40 CFR part 50, appendix N).
c The level of the annual standard is defined to one decimal place (i.e., 15.0 μg/m3) as determined by rounding. For example, a 3-year average
annual mean of 15.04 μg/m3 would round to 15.0 μg/m3 and, thus, meet the annual standard and a 3-year average of 15.05 μg/m3 would round
to 15.1 μg/m3 and, hence, violate the annual standard (40 CFR part 50, appendix N).
d The level of the standard was to be compared to measurements made at sites that represent ‘‘community-wide air quality’’ recording the highest level, or, if specific requirements were satisfied, to average measurements from multiple community-wide air quality monitoring sites (‘‘spatial
averaging’’).
e The EPA tightened the constraints on the spatial averaging criteria by further limiting the conditions under which some areas may average
measurements from multiple community-oriented monitors to determine compliance (See 71 FR 61165 to 61167, October 17, 2006).
tkelley on DSK3SPTVN1PROD with
b The
In 1971, the EPA established NAAQS
for PM based on the original air quality
criteria document (DHEW, 1969; 36 FR
8186, April 30, 1971). The reference
method specified for determining
attainment of the original standards was
the high-volume sampler, which
collects PM up to a nominal size of 25
to 45 mm (referred to as total suspended
particles or TSP). The primary standards
(measured by the indicator TSP) were
260 mg/m3, 24-hour average, not to be
exceeded more than once per year, and
75 mg/m3, annual geometric mean. The
secondary standard was 150 mg/m3, 24hour average, not to be exceeded more
than once per year.
In October 1979, the EPA announced
the first periodic review of the criteria
and NAAQS for PM, and significant
revisions to the original standards were
promulgated in 1987 (52 FR 24634, July
1, 1987). In that decision, the EPA
changed the indicator for PM from TSP
to PM10, the latter including particles
with an aerodynamic diameter less than
or equal to a nominal 10 mm, which
delineates thoracic particles (i.e., that
subset of inhalable particles small
enough to penetrate beyond the larynx
to the thoracic region of the respiratory
tract). The EPA also revised the primary
standards by (1) replacing the 24-hour
TSP standard with a 24-hour PM10
standard of 150 mg/m3 with no more
than one expected exceedance per year
and (2) replacing the annual TSP
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
standard with a PM10 standard of 50 mg/
m3, annual arithmetic mean. The
secondary standard was revised by
replacing it with 24-hour and annual
PM10 standards identical in all respects
to the primary standards. The revisions
also included a new reference method
for the measurement of PM10 in the
ambient air and rules for determining
attainment of the new standards. On
judicial review, the revised standards
were upheld in all respects. Natural
Resources Defense Council v. EPA, 902
F. 2d 962 (D.C. Cir. 1990).
In April 1994, the EPA announced its
plans for the second periodic review of
the criteria and NAAQS for PM, and
promulgated significant revisions to the
NAAQS in 1997 (62 FR 38652, July 18,
1997). Most significantly, the EPA
determined that although the PM
NAAQS should continue to focus on
thoracic particles (PM10), the fine and
coarse fractions of PM10 should be
considered separately. New standards
were added, using PM2.5 as the indicator
for fine particles. The PM10 standards
were retained for the purpose of
regulating the coarse fraction of PM10
(referred to as thoracic coarse particles
or PM10-2.5).5 The EPA established two
new PM2.5 standards: an annual
standard of 15.0 mg/m3, based on the 3year average of annual arithmetic mean
5 See 40 CFR parts 50, 53, and 58 for more
information on reference and equivalent methods
for measuring PM in ambient air.
PO 00000
Frm 00007
Fmt 4701
Sfmt 4700
PM2.5 concentrations from single or
multiple monitors sited to represent
community-wide air quality6 and a 24hour standard of 65 mg/m3, based on the
3-year average of the 98th percentile of
24-hour PM2.5 concentrations at each
population-oriented monitor7 within an
area. Also, the EPA established a new
reference method for the measurement
of PM2.5 in the ambient air and rules for
determining attainment of the new
standards. To continue to address
thoracic coarse particles, the annual
PM10 standard was retained, while the
form, but not the level, of the 24-hour
PM10 standard was revised to be based
on the 99th percentile of 24-hour PM10
concentrations at each monitor in an
area. The EPA revised the secondary
standards by making them identical in
all respects to the primary standards.
Following promulgation of the revised
PM NAAQS in 1997, petitions for
review were filed by a large number of
6 Monitoring stations sited to represent
community-wide air quality would typically be at
the neighborhood or urban-scale; however, where a
population-oriented micro or middle-scale PM2.5
monitoring station represents many such locations
throughout a metropolitan area, these smaller scales
might also be considered to represent communitywide air quality [40 CFR part 58, appendix D,
4.7.1(b)].
7 Population-oriented monitoring (or sites) means
residential areas, commercial areas, recreational
areas, industrial areas where workers from more
than one company are located, and other areas
where a substantial number of people may spend
a significant fraction of their day (40 CFR 58.1).
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
3092
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
parties, addressing a broad range of
issues. In May 1998, a three-judge panel
of the U.S. Court of Appeals for the
District of Columbia Circuit issued an
initial decision that upheld the EPA’s
decision to establish fine particle
standards, holding that ‘‘the growing
empirical evidence demonstrating a
relationship between fine particle
pollution and adverse health effects
amply justifies establishment of new
fine particle standards.’’ American
Trucking Associations v. EPA, 175 F. 3d
1027, 1055–56 (D.C. Cir. 1999),
rehearing granted in part and denied in
part, 195 F. 3d 4 (D.C. Cir. 1999),
affirmed in part and reversed in part,
Whitman v. American Trucking
Associations, 531 U.S. 457 (2001). The
panel also found ‘‘ample support’’ for
the EPA’s decision to regulate coarse
particle pollution, but vacated the 1997
P.M.10 standards, concluding, in part,
that PM10 is a ‘‘poorly matched
indicator for coarse particulate
pollution’’ because it includes fine
particles. Id. at 1053–55. Pursuant to the
court’s decision, the EPA removed the
vacated 1997 P.M.10 standards from the
CFR (69 FR 45592, July 30, 2004) and
deleted the regulatory provision (at 40
CFR 50.6(d)) that controlled the
transition from the pre-existing 1987
P.M.10 standards to the 1997 P.M.10
standards. The pre-existing 1987 P.M.10
standards remained in place (65 FR
80776, December 22, 2000). The court
also upheld the EPA’s determination not
to establish more stringent secondary
standards for fine particles to address
effects on visibility (175 F. 3d at 1027).
More generally, the panel held (over
a strong dissent) that the EPA’s
approach to establishing the level of the
standards in 1997, both for the PM and
for the ozone NAAQS promulgated on
the same day, effected ‘‘an
unconstitutional delegation of
legislative authority.’’ Id. at 1034–40.
Although the panel stated that ‘‘the
factors EPA uses in determining the
degree of public health concern
associated with different levels of ozone
and PM are reasonable,’’ it remanded
the rule to the EPA, stating that when
the EPA considers these factors for
potential non-threshold pollutants
‘‘what EPA lacks is any determinate
criterion for drawing lines’’ to
determine where the standards should
be set. Consistent with the EPA’s longstanding interpretation and D.C. Circuit
precedent, the panel also reaffirmed its
prior holdings that in setting NAAQS,
the EPA is ‘‘not permitted to consider
the cost of implementing those
standards.’’ Id. at 1040–41.
On EPA’s petition for rehearing, the
panel adhered to its position on these
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
points. American Trucking Associations
v. EPA, 195 F. 3d 4 (D.C. Cir. 1999). The
full Court of Appeals denied the EPA’s
request for rehearing en banc, with five
judges dissenting. Id. at 13. Both sides
filed cross appeals on these issues to the
United States Supreme Court, which
granted certiorari. In February 2001, the
Supreme Court issued a unanimous
decision upholding the EPA’s position
on both the constitutional and cost
issues. Whitman v. American Trucking
Associations, 531 U.S. 457, 464, 475–76.
On the constitutional issue, the Court
held that the statutory requirement that
NAAQS be ‘‘requisite’’ to protect public
health with an adequate margin of safety
sufficiently cabined the EPA’s
discretion, affirming the EPA’s approach
of setting standards that are neither
more nor less stringent than necessary.
The Supreme Court remanded the case
to the Court of Appeals for resolution of
any remaining issues that had not been
addressed in that court’s earlier rulings.
Id. at 475–76. In March 2002, the Court
of Appeals rejected all remaining
challenges to the standards, holding
under the statutory standard of review
that the EPA’s PM2.5 standards were
reasonably supported by the
administrative record and were not
‘‘arbitrary and capricious.’’ American
Trucking Association v. EPA, 283 F. 3d
355, 369–72 (D.C. Cir. 2002).
In October 1997, the EPA published
its plans for the next periodic review of
the air quality criteria and NAAQS for
PM (62 FR 55201, October 23, 1997).
After CASAC and public review of
several drafts, the EPA’s National Center
for Environmental Assessment (NCEA)
finalized the Air Quality Criteria
Document for Particulate Matter
(henceforth, AQCD or the ‘‘Criteria
Document’’) in October 2004 (U.S. EPA,
2004) and OAQPS finalized an
assessment document, Particulate
Matter Health Risk Assessment for
Selected Urban Areas (Abt Associates,
2005), and the Review of the National
Ambient Air Quality Standards for
Particulate Matter: Policy Assessment of
Scientific and Technical Information, in
December 2005 (henceforth, ‘‘Staff
Paper,’’ U.S. EPA, 2005). In conjunction
with its review of the Staff Paper,
CASAC provided advice to the
Administrator on revisions to the PM
NAAQS (Henderson, 2005a). In
particular, most CASAC PM Panel
members favored revising the level of
the primary 24-hour PM2.5 standard
within the range of 35 to 30 mg/m3 with
a 98th percentile form, in concert with
revising the level of the primary annual
PM2.5 standard within the range of 14 to
13 mg/m3 (Henderson, 2005a, p.7). For
PO 00000
Frm 00008
Fmt 4701
Sfmt 4700
thoracic coarse particles, the Panel had
reservations in recommending a primary
24-hour PM10-2.5 standard, and agreed
that there was a need for more research
on the health effects of thoracic coarse
particles (Henderson, 2005b). With
regard to secondary standards, most
Panel members strongly supported
establishing a new, distinct secondary
PM2.5 standard to protect urban
visibility (Henderson, 2005a, p. 9).
On January 17, 2006, the EPA
proposed to revise the primary and
secondary NAAQS for PM (71 FR 2620)
and solicited comment on a broad range
of options. Proposed revisions included:
(1) Revising the level of the primary 24hour PM2.5 standard to 35 mg/m3; (2)
revising the form, but not the level, of
the primary annual PM2.5 standard by
tightening the constraints on the use of
spatial averaging; (3) replacing the
primary 24-hour PM10 standard with a
24-hour standard defined in terms of a
new indicator, PM10-2.5, which was
qualified so as to include any ambient
mix of PM10-2.5 dominated by particles
generated by high-density traffic on
paved roads, industrial sources, and
construction sources, and to exclude
any ambient mix of particles dominated
by rural windblown dust and soils and
agricultural and mining sources (71 FR
2667 to 2668), set at a level of 70 mg/
m3 based on the 3-year average of the
98th percentile of 24-hour PM10-2.5
concentrations; (4) revoking the primary
annual PM10 standard; and (5) revising
the secondary standards by making
them identical in all respects to the
proposed suite of primary standards for
fine and coarse particles.8 Subsequent to
the proposal, CASAC provided
additional advice to the EPA in a letter
to the Administrator requesting
reconsideration of CASAC’s
recommendations for both the primary
and secondary PM2.5 standards as well
as the standards for thoracic coarse
particles (Henderson, 2006a).
On October 17, 2006, the EPA
published revisions to the PM NAAQS
to provide increased protection of
public health and welfare (71 FR
61144). With regard to the primary and
secondary standards for fine particles,
the EPA revised the level of the primary
24-hour PM2.5 standard to 35 mg/m3,
retained the level of the primary annual
PM2.5 standard at 15.0 mg/m3, and
8 In recognition of an alternative view expressed
by most members of the CASAC PM Panel, the
Agency also solicited comments on a subdaily (4to 8-hour averaging time) secondary PM2.5 standard
to address visibility impairment, considering
alternative standard levels within a range of 20 to
30 mg/m3 in conjunction with a form within a range
of the 92nd to 98th percentile (71 FR 2685, January
17, 2006).
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
revised the form of the primary annual
PM2.5 standard by adding further
constraints on the optional use of spatial
averaging. The EPA revised the
secondary standards for fine particles by
making them identical in all respects to
the primary standards. With regard to
the primary and secondary standards for
thoracic coarse particles, the EPA
retained the level and form of the 24hour PM10 standard (such that the
standard remained at a level of 150 mg/
m3 with a one-expected exceedance
form and retained the PM10 indicator)
and revoked the annual PM10 standard.
The EPA also established a new Federal
Reference Method (FRM) for the
measurement of PM10-2.5 in the ambient
air (71 FR 61212 to 13). Although the
standards for thoracic coarse particles
were not defined in terms of a PM10-2.5
indicator, the EPA adopted a new FRM
for PM10-2.5 to facilitate consistent
research on PM10-2.5 air quality and
health effects and to promote
commercial development of Federal
Equivalent Methods (FEMs) to support
future reviews of the PM NAAQS (71 FR
61212/2).
Following issuance of the final rule,
CASAC articulated its concern that the
‘‘EPA’s final rule on the NAAQS for PM
does not reflect several important
aspects of the CASAC’s advice’’
(Henderson et al., 2006b, p. 1). With
regard to the primary PM2.5 annual
standard, CASAC expressed serious
concerns regarding the decision to
retain the level of the standard at 15 mg/
m3. Specifically, CASAC stated, ‘‘It is
the CASAC’s consensus scientific
opinion that the decision to retain
without change the annual PM2.5
standard does not provide an ‘adequate
margin of safety * * * requisite to
protect the public health’ (as required
by the Clean Air Act), leaving parts of
the population of this country at
significant risk of adverse health effects
from exposure to fine PM’’ (Henderson
et al., 2006b, p. 2). Furthermore, CASAC
pointed out that its recommendations
‘‘were consistent with the mainstream
scientific advice that EPA received from
virtually every major medical
association and public health
organization that provided their input to
the Agency’’ (Henderson et al., 2006b, p.
2).9 With regard to EPA’s final decision
to retain the 24-hour PM10 standard for
9 CASAC specifically identified input provided
by the American Medical Association, the
American Thoracic Society, the American Lung
Association, the American Academy of Pediatrics,
the American College of Cardiology, the American
Heart Association, the American Cancer Society,
the American Public Health Association, and the
National Association of Local Boards of Health
(Henderson et al., 2006b, p. 2).
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
thoracic coarse particles, CASAC had
mixed views with regard to the decision
to retain the 24-hour standard and the
continued use of PM10 as the indicator
of coarse particles, while also
recognizing the need to have a standard
in place to protect against effects
associated with short-term exposures to
thoracic coarse particles (Henderson et
al., 2006b, p. 2). With regard to the
EPA’s final decision to revise the
secondary PM2.5 standards to be
identical in all respects to the revised
primary PM2.5 standards, CASAC
expressed concerns that its advice to
establish a distinct secondary standard
for fine particles to address visibility
impairment was not followed and
emphasized ‘‘that continuing to rely on
the primary standard to protect against
all PM-related adverse environmental
and welfare effects assures neglect, and
will allow substantial continued
degradation, of visual air quality over
large areas of the country’’ (Henderson
et al, 2006b, p. 2).
2. Litigation Related to the 2006 PM
Standards
Several parties filed petitions for
review following promulgation of the
revised PM NAAQS in 2006. These
petitions addressed the following issues:
(1) Selecting the level of the primary
annual PM2.5 standard; (2) retaining
PM10 as the indicator of a standard for
thoracic coarse particles, retaining the
level and form of the 24-hour PM10
standard, and revoking the PM10 annual
standard; and (3) setting the secondary
PM2.5 standards identical to the primary
standards. On February 24, 2009, the
U.S. Court of Appeals for the District of
Columbia Circuit issued its opinion in
the case American Farm Bureau
Federation v. EPA, 559 F. 3d 512 (D.C.
Cir. 2009). The court remanded the
primary annual PM2.5 NAAQS to the
EPA because the EPA failed to
adequately explain why the standard
provided the requisite protection from
both short- and long-term exposures to
fine particles, including protection for
at-risk populations such as children.
American Farm Bureau Federation v.
EPA, 559 F. 3d 512, 520–27 (D.C. Cir.
2009). With regard to the standards for
PM10, the court upheld the EPA’s
decisions to retain the 24-hour PM10
standard to provide protection from
thoracic coarse particle exposures and
to revoke the annual PM10 standard.
American Farm Bureau Federation v.
EPA, 559 F. 2d at 533–38. With regard
to the secondary PM2.5 standards, the
court remanded the standards to the
EPA because the Agency’s decision was
‘‘unreasonable and contrary to the
requirements of section 109(b)(2)’’ of the
PO 00000
Frm 00009
Fmt 4701
Sfmt 4700
3093
CAA. The court further concluded that
the EPA failed to adequately explain
why setting the secondary PM standards
identical to the primary standards
provided the required protection for
public welfare, including protection
from visibility impairment. American
Farm Bureau Federation v. EPA, 559 F.
2d at 528–32.
The decisions of the court with regard
to these three issues are discussed
further in sections III.A.2, IV.A.2, and
VI.A.2 below. The EPA is responding to
the court’s remands as part of the
current review of the PM NAAQS.
3. Current PM NAAQS Review
The EPA initiated the current review
of the air quality criteria for PM in June
2007 with a general call for information
(72 FR 35462, June 28, 2007). In July
2007, the EPA held two ‘‘kick-off’’
workshops on the primary and
secondary PM NAAQS, respectively (72
FR 34003 to 34004, June 20, 2007).10
These workshops provided an
opportunity for a public discussion of
the key policy-relevant issues around
which the EPA would structure this PM
NAAQS review and the most
meaningful new science that would be
available to inform our understanding of
these issues.
Based in part on the workshop
discussions, the EPA developed a draft
Integrated Review Plan outlining the
schedule, process, and key policyrelevant questions that would guide the
evaluation of the air quality criteria for
PM and the review of the primary and
secondary PM NAAQS (U.S. EPA,
2007a). On November 30, 2007, the EPA
held a consultation with CASAC on the
draft Integrated Review Plan (72 FR
63177, November 8, 2007), which
included the opportunity for public
comment. The final Integrated Review
Plan (U.S. EPA, 2008a) incorporated
comments from CASAC (Henderson,
2008) and the public on the draft plan
as well as input from senior Agency
managers.11 12
10 See workshop materials available at: http://
www.regulations.gov/search/Regs/home.html#home
Docket ID numbers EPA–HQ–OAR–2007–0492–008;
EPA–HQ–OAR–2007–0492–009; EPA–HQ–OAR–
2007–0492–010; and EPA–HQ–OAR–2007–0492–
012.
11 The process followed in this review varies from
the NAAQS review process described in section 1.1
of the Integrated Review Plan (U.S. EPA, 2008a). On
May 21, 2009, Administrator Jackson called for key
changes to the NAAQS review process including
reinstating a policy assessment document that
contains staff analyses of the scientific bases for
alternative policy options for consideration by
senior Agency management prior to rulemaking. In
conjunction with this change, the EPA will no
longer issue a policy assessment in the form of an
advance notice of proposed rulemaking (ANPR) as
E:\FR\FM\15JAR2.SGM
Continued
15JAR2
3094
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
A major element in the process for
reviewing the NAAQS is the
development of an Integrated Science
Assessment. This document provides a
concise evaluation and integration of
the policy-relevant science, including
key science judgments upon which the
risk and exposure assessments build. As
part of the process of preparing the PM
Integrated Science Assessment, NCEA
hosted a peer review workshop in June
2008 on preliminary drafts of key
Integrated Science Assessment chapters
(73 FR 30391, May 27, 2008). CASAC
and the public reviewed the first
external review draft Integrated Science
Assessment (U.S. EPA, 2008b; 73 FR
77686, December 19, 2008) at a meeting
held on April 1 to 2, 2009 (74 FR 2688,
February 19, 2009). Based on CASAC
(Samet, 2009e) and public comments,
NCEA prepared a second draft
Integrated Science Assessment (U.S.
EPA, 2009b; 74 FR 38185, July 31,
2009), which was reviewed by CASAC
and the public at a meeting held on
October 5 and 6, 2009 (74 FR 46586,
September 10, 2009). Based on CASAC
(Samet, 2009f) and public comments,
NCEA prepared the final Integrated
Science Assessment titled Integrated
Science Assessment for Particulate
Matter, December 2009 (U.S. EPA,
2009a; 74 FR 66353, December 15,
2009).
Building upon the information
presented in the PM Integrated Science
Assessment, the EPA prepared Risk and
Exposure Assessments that provide a
concise presentation of the methods,
key results, observations, and related
uncertainties. In developing the Risk
and Exposure Assessments for this PM
NAAQS review, OAQPS released two
planning documents: Particulate Matter
National Ambient Air Quality
Standards: Scope and Methods Plan for
Health Risk and Exposure Assessment
and Particulate Matter National
Ambient Air Quality Standards: Scope
and Methods Plan for Urban Visibility
Impact Assessment (henceforth, Scope
and Methods Plans, U.S. EPA, 2009c,d;
74 FR 11580, March 18, 2009). These
planning documents outlined the scope
and approaches that staff planned to use
in conducting quantitative assessments
as well as key issues that would be
addressed as part of the assessments. In
discussed in the Integrated Review Plan (U.S. EPA,
2008a, p. 3). For more information on the overall
process followed in this review including a
description of the major elements of the process for
reviewing NAAQS see Jackson (2009).
12 All written comments submitted to the Agency
are available in the docket for this PM NAAQS
review (EPA–HQ–OAR–2007–0429). Transcripts of
public meetings and teleconferences held in
conjunction with CASAC’s reviews are also
included in the docket.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
designing and conducting the initial
health risk and visibility impact
assessments, the Agency considered
CASAC comments (Samet 2009a,b) on
the Scope and Methods Plans made
during an April 2009 consultation (74
FR 7688, February 19, 2009) as well as
public comments. CASAC and the
public reviewed two draft assessment
documents, Risk Assessment to Support
the Review of the PM2.5 Primary
National Ambient Air Quality
Standards: External Review Draft,
September 2009 (U.S. EPA, 2009e) and
Particulate Matter Urban-Focused
Visibility Assessment—External Review
Draft, September 2009 (U.S. EPA, 2009f)
at a meeting held on October 5 and 6,
2009 (74 FR 46586, September 10,
2009). Based on CASAC (Samet
2009c,d) and public comments, OAQPS
staff revised these draft documents and
released second draft assessment
documents (U.S. EPA, 2010d,e) in
January and February 2010 (75 FR 4067,
January 26, 2010) for CASAC and public
review at a meeting held on March 10
and 11, 2010 (75 FR 8062, February 23,
2010). Based on CASAC (Samet,
2010a,b) and public comments on the
second draft assessment documents, the
EPA revised these documents and
released final assessment documents
titled Quantitative Health Risk
Assessment for Particulate Matter, June
2010 (henceforth, ‘‘Risk Assessment,’’
U.S. EPA, 2010a) and Particulate Matter
Urban-Focused Visibility Assessment—
Final Document, July 2010 (henceforth,
‘‘Visibility Assessment,’’ U.S. EPA,
2010b) (75 FR 39252, July 8, 2010).
Based on the scientific and technical
information available in this review as
assessed in the Integrated Science
Assessment and Risk and Exposure
Assessments, the EPA staff prepared a
Policy Assessment. The Policy
Assessment is intended to help ‘‘bridge
the gap’’ between the relevant scientific
information and assessments and the
judgments required of the Administrator
in reaching decisions on the NAAQS
(Jackson, 2009, attachment, p. 2).
American Farm Bureau Federation v.
EPA, 559 F. 3d at 521. The Policy
Assessment is not a decision document;
rather it presents the EPA staff
conclusions related to the broadest
range of policy options that could be
supported by the currently available
information. A preliminary draft Policy
Assessment (U.S. EPA, 2009g) was
released in September 2009 for
informational purposes and to facilitate
discussion with CASAC at the October
5 and 6, 2009 meeting on the overall
structure, areas of focus, and level of
detail to be included in the Policy
PO 00000
Frm 00010
Fmt 4701
Sfmt 4700
Assessment. The EPA considered
CASAC’s comments on this preliminary
draft in developing a first draft Policy
Assessment (U.S. EPA, 2010c; 75 FR
4067, January 26, 2010) that built upon
the information presented and assessed
in the final Integrated Science
Assessment and second draft Risk and
Exposure Assessments. The EPA
presented an overview of the first draft
Policy Assessment at a CASAC meeting
on March 10, 2010 (75 FR 8062,
February 23, 2010) and it was discussed
during public CASAC teleconferences
on April 8 and 9, 2010 (75 FR 8062,
February 23, 2010) and May 7, 2010 (75
FR 19971, April 16, 2010).
The EPA developed a second draft
Policy Assessment (U.S. EPA, 2010f; 75
FR 39253, July 8, 2010) based on
CASAC (Samet, 2010c) and public
comments on the first draft Policy
Assessment. CASAC reviewed the
second draft document at a meeting on
July 26 and 27, 2010 (75 FR 32763, June
9, 2010). The EPA staff considered
CASAC (Samet, 2010d) and public
comments on the second draft Policy
Assessment in preparing a final Policy
Assessment titled Policy Assessment for
the Review of the Particulate Matter
National Ambient Air Quality
Standards, April, 2011 (U.S. EPA,
2011a; 76, FR 22665, April 22, 2011).
This document includes final staff
conclusions on the adequacy of the
current PM standards and alternative
standards for consideration.
The schedule for the rulemaking in
this review is subject to a court order in
a lawsuit filed in February 2012 by a
group of plaintiffs who alleged that the
EPA had failed to perform its mandatory
duty, under section 109(d)(1), to
complete a review of the PM NAAQS
within the period provided by statute.
American Lung Association and
National Parks Conservation
Association v. EPA, D.D.C. No. 12–cv–
00243 (consol. with No. 12–cv–00531)
Court orders in that case provide that
the EPA sign a notice of proposed
rulemaking concerning its review of the
PM NAAQS no later than June 14, 2012
and a notice of final rulemaking no later
than December 14, 2012.
On June 14, 2012, the EPA issued its
proposed decision to revise the NAAQS
for PM (77 FR 38890, June 29, 2012)
(henceforth ‘‘proposal’’). In the
proposal, the EPA identified revisions to
the standards, based on the air quality
criteria for PM, and to related data
handling conventions and ambient air
monitoring, reporting, and network
design requirements. The EPA proposed
revisions to the PSD permitting program
with respect to the proposed NAAQS
revisions. The Agency also proposed
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
changes to the AQI for PM2.5, consistent
with the proposed primary PM2.5
standards. The proposal solicited public
comments on alternative primary and
secondary standards and related
matters. The proposal is summarized in
section II.D below.
The EPA held two public hearings to
receive public comment on the
proposed revisions to the PM NAAQS
(77 FR 39205, July 2, 2012). One hearing
took place in Philadelphia, PA on July
17, 2012 and a second hearing took
place in Sacramento, CA on July 19,
2012. At these public hearings, the EPA
heard testimony from 168 individuals
representing themselves or specific
interested organizations.
The EPA received more than 230,000
comments from members of the public
and various interest groups on the
proposed revisions to the PM NAAQS
by the close of the public comment
period on August 31, 2012. Major issues
raised in the public comments are
discussed throughout the preamble of
this final action. A more detailed
summary of all significant comments,
along with the EPA’s responses
(henceforth ‘‘Response to Comments’’)
can be found in the docket for this
rulemaking (Docket No. EPA–HQ–OAR–
2007–0492) (U.S. EPA, 2012a).
In the proposal, the EPA recognized
that there were a number of new
scientific studies on the health effects of
PM that had been published since the
mid-2009 cutoff date for inclusion in the
Integrated Science Assessment.13 As in
the last PM NAAQS review, the EPA
committed to conduct a provisional
review and assessment of any
significant ‘‘new’’ studies published
since the close of the Integrated Science
Assessment, including studies
submitted to the EPA during the public
comment period. The purpose of the
provisional science assessment was to
ensure that the Administrator was fully
aware of the ‘‘new’’ science that has
developed since 2009 before making
final decisions on whether to retain or
revise the current PM NAAQS. The EPA
screened and surveyed the recent health
literature, including studies submitted
during the public comment period, and
13 For ease of reference, these studies will be
referred to as ‘‘new’’ studies or ‘‘new’’ science,
using quotation marks around the word new.
Referring to studies that were published too
recently to have been included in the 2009
Integrated Science Assessment as ‘‘new’’ studies is
intended to clearly differentiate such studies from
those that have been published since the last review
and which are included in the Integrated Science
Assessment (these studies are sometimes referred to
as new (without quotation marks) or more recent
studies, to indicate that they were not included in
the Integrated Science Assessment and thus are
newly available in this review).
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
conducted a provisional assessment
(U.S. EPA, 2012b) that places the results
of those studies of potentially greatest
policy relevance in the context of the
findings of the Integrated Science
Assessment (U.S. EPA, 2009a). This
provisional assessment, including a
summary of the key conclusions, can be
found in the rulemaking docket (EPA–
HQ–OAR–2007–0492).
The provisional assessment found
that the ‘‘new’’ studies expand the
scientific information considered in the
Integrated Science Assessment and
provide important insights on the
relationship between PM exposure and
health effects. The provisional
assessment also found that the ‘‘new’’
studies generally strengthen the
evidence that long- and short-term
exposures to fine particles are
associated with a wide range of health
effects. Some of the ‘‘new’’
epidemiological studies report effects in
areas with lower PM2.5-concentrations
than those in earlier studies considered
in the Integrated Science Assessment.
‘‘New’’ toxicological and
epidemiological studies continue to link
various health effects with a range of
fine particle sources and components.
With regard to thoracic coarse particles,
the provisional assessment recognized
that a limited number of ‘‘new’’ studies
provide evidence of an association with
short-term PM10-2.5 exposures and
increased asthma-related emergency
department visits in children, but
continue to provide no evidence of an
association between long-term PM10-2.5
exposure and mortality. Further, the
provisional assessment found that the
results reported in ‘‘new’’ studies do not
materially change any of the broad
scientific conclusions regarding the
health effects of PM exposure made in
the Integrated Science Assessment.
The EPA believes it was important to
conduct a provisional assessment in this
proceeding, so that the Administrator
would be aware of the science that
developed too recently for inclusion in
the Integrated Science Assessment.
However, it is also important to note
that the EPA’s review of that science to
date has been limited to screening,
surveying, and preparing a provisional
assessment of these studies. Having
performed this limited provisional
assessment, the EPA must decide
whether to consider the ‘‘new’’ studies
in this review and to take such steps as
may be necessary to include them in the
basis for the final decision, or to reserve
such action for the next review of the
PM NAAQS.
As in prior NAAQS reviews, the EPA
is basing its decision in this review on
studies and related information
PO 00000
Frm 00011
Fmt 4701
Sfmt 4700
3095
included in the Integrated Science
Assessment, Risk and Exposure
Assessment, and Policy Assessment,
which have undergone CASAC and
public review. The studies assessed in
the Integrated Science Assessment, and
the integration of the scientific evidence
presented in that document, have
undergone extensive critical review by
the EPA, CASAC, and the public during
the development of the Integrated
Science Assessment. The rigor of that
review makes these studies, and their
integrative assessment, the most reliable
source of scientific information on
which to base decisions on the NAAQS.
NAAQS decisions can have profound
impacts on public health and welfare,
and NAAQS decisions should be based
on studies that have been rigorously
assessed in an integrative manner not
only by the EPA but also by the
statutorily-mandated independent
advisory committee, CASAC, and have
been subject as well to the public review
that accompanies this process. As
described above, the provisional
assessment did not and could not
provide that kind of in-depth critical
review.
This decision is consistent with the
EPA’s practice in prior NAAQS reviews.
Since the 1970 amendments, the EPA
has taken the view that NAAQS
decisions are to be based on scientific
studies and related information that
have been assessed as a part of the
pertinent air quality criteria. See e.g., 36
FR 8186 (April 30, 1971) (the EPA based
original NAAQS for six pollutants on
scientific studies discussed in air
quality criteria documents and limited
consideration of comments to those
concerning validity of scientific basis);
38 FR 25678, 25679–25680 (September
14, 1973) (the EPA revised air quality
criteria for sulfur oxides to provide basis
for reevaluation of secondary NAAQS).
This longstanding interpretation was
strengthened by new legislative
requirements enacted in 1977, which
added section 109(d)(2) of the CAA
concerning CASAC review of air quality
criteria. The EPA has consistently
followed this approach. 52 FR 24634,
24637 (July 1, 1987) (after review by
CASAC, the EPA issued a post-proposal
addendum to the PM Air Quality
Criteria Document, to address certain
new scientific studies not included in
the 1982 Air Quality Criteria
Document); 61 FR 25566, 25568 (May
22, 1996) (after review by CASAC, the
EPA issued a post-proposal supplement
to the 1982 Air Quality Criteria
Document to address certain new health
studies not included in the 1982 Air
Quality Criteria Document or 1986
E:\FR\FM\15JAR2.SGM
15JAR2
3096
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
Addendum). The EPA reaffirmed this
approach in its decision not to revise
the ozone NAAQS in 1993, as well as in
its final decision on the PM NAAQS in
the 1997 and 2006 reviews. 58 FR
13008, 13013 to 13014 (March 9, 1993)
(ozone review); 62 FR 38652, 38662
(July 18, 1997) and 71 FR 61141, 61148
to 61149 (October 17, 2006) (PM
reviews) (The EPA conducted a
provisional assessment but based the
final PM decisions on studies and
related information included in the air
quality criteria that had been reviewed
by CASAC).
As discussed in the EPA’s 1993
decision not to revise the NAAQS for
ozone, ‘new’ studies may sometimes be
of such significance that it is
appropriate to delay a decision on
revision of NAAQS and to supplement
the pertinent air quality criteria so the
‘‘new’’ studies can be taken into account
(58 FR, 13013 to 13014, March 9, 1993).
In this proceeding, the provisional
assessment of recent studies concludes
that, taken in context, the ‘‘new’’
information and findings do not
materially change any of the broad
scientific conclusions regarding the
health effects of PM exposure made in
the Integrated Science Assessment (U.S.
EPA, 2012b). For this reason, reopening
the air quality criteria review would not
be warranted even if there were time to
do so under the court order governing
the schedule for this rulemaking.
Accordingly, the EPA is basing the final
decisions in this review on the studies
and related information included in the
PM air quality criteria that have
undergone CASAC and public review.
The EPA will consider the ‘‘new’’
published studies for purposes of
decision making in the next periodic
review of the PM NAAQS, which will
provide the opportunity to fully assess
them through a more rigorous review
process involving the EPA, CASAC, and
the public.
vehicle and motor vehicle fuel control
program under title II of the Act (CAA
sections 202 to 250) which involves
controls for emissions from mobile
sources and controls for the fuels used
by these sources, and new source
performance standards (NSPS) for
stationary sources under section 111 of
the CAA.
Currently, there are 35 areas in the
U.S. that are designated as
nonattainment for the current annual
PM2.5 standard and 32 areas in the U.S.
that are designated as nonattainment for
the current 24-hour PM2.5 standards.
With the revisions to the PM NAAQS
that are being finalized in this rule, the
EPA will work with the states to
conduct a new area designation process.
Those states with new nonattainment
areas will be required to develop SIPs to
attain the standards. In developing their
attainment plans, states will have to
take into account projected emission
reductions from federal and state rules
that have already been adopted at the
time of plan submittal. A number of
significant emission reduction programs
that will lead to reductions of PM and
its precursors are in place today or are
expected to be in place by the time any
new SIPs will be due. Examples of such
rules include regulations for onroad and
nonroad engines and fuels, the utility
and industrial boilers toxics rules, and
various other programs already adopted
by states to reduce emissions from key
emissions sources. States will then
evaluate the level of additional emission
reductions needed for each
nonattainment area to attain the
standards ‘‘as expeditiously as
practicable’’ and adopt new state
regulations, as appropriate. Section IX
includes additional discussion of
designation and implementation issues
associated with the revised PM NAAQS.
C. Related Control Programs To
Implement PM Standards
States are primarily responsible for
ensuring attainment and maintenance of
NAAQS once the EPA has established
them. Under section 110 of the CAA and
related provisions, states are to submit,
for the EPA’s approval, SIPs that
provide for the attainment and
maintenance of such standards through
control programs directed to sources of
the pollutants involved. The states, in
conjunction with the EPA, also
administer the PSD permitting program
(CAA sections 160 to 169). In addition,
federal programs provide for nationwide
reductions in emissions of PM and other
air pollutants through the federal motor
For reasons discussed in the proposal,
the Administrator proposed to revise the
current primary and secondary PM
standards. With regard to the primary
PM2.5 standards, the Administrator
proposed to revise the level of the
annual PM2.5 standard from 15.0 mg/m3
to a level within a range of 12.0 to 13.0
mg/m3 and to retain the level of the 24hour PM2.5 standard at 35 mg/m3. The
Administrator also proposed to
eliminate spatial averaging provisions as
part of the form of the annual standard
to avoid potential disproportionate
impacts on at-risk populations. The EPA
proposed to revise the AQI for PM2.5,
consistent with the proposed primary
PM2.5 standards.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
D. Summary of Proposed Revisions to
the PM NAAQS
PO 00000
Frm 00012
Fmt 4701
Sfmt 4700
With regard to the primary coarse
particle standard, the EPA proposed to
retain the current 24-hour PM10
standard to continue to provide
protection against effects associated
with short-term exposure to thoracic
coarse particles (i.e., PM10-2.5).
With regard to the secondary PM
standards, the EPA proposed to revise
the suite of secondary PM standards by
adding a distinct standard for PM2.5 to
address PM-related visibility
impairment. The separate secondary
standard was proposed to be defined in
terms of a PM2.5 visibility index, which
would use speciated PM2.5 mass
concentrations and relative humidity
data to calculate PM2.5 light extinction,
translated to the deciview (dv) scale,
similar to the Regional Haze Program; a
24-hour averaging time; a 90th
percentile form averaged over 3 years;
and a level set at one of two options—
either 30 or 28 dv. The EPA also
proposed to retain the current secondary
standards generally to address nonvisibility welfare effects.
The EPA also proposed to revise the
data handling procedures consistent
with the revised primary and secondary
standards for PM2.5 including the
computations necessary for determining
when these standards are met and the
measurement data that are appropriate
for comparison to the standards. With
regard to monitoring-related activities,
the EPA proposed to update several
aspects of the monitoring regulations
and specifically to require that a small
number of PM2.5 monitors be relocated
to be collocated with measurements of
other pollutants (e.g., nitrogen dioxide,
carbon monoxide) in the near-road
environment.
E. Organization and Approach to Final
PM NAAQS Decisions
This action presents the
Administrator’s final decisions on the
review of the current primary and
secondary PM2.5 and PM10 standards.
Consistent with the decisions made by
the EPA in the last review and with the
conclusions in the Integrated Science
Assessment and Policy Assessment, fine
and thoracic coarse particles continue to
be considered as separate subclasses of
PM pollution. Primary standards for fine
particles and for thoracic coarse
particles are addressed in sections III
and IV, respectively. Changes to the AQI
for PM2.5, consistent with the revised
primary PM2.5 standards, are addressed
in section V. Secondary standards for
fine and coarse particles are addressed
in section VI. Related data handling
conventions and exceptional events are
addressed in section VII. Updates to the
monitoring regulations are addressed in
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
section VIII. Implementation activities,
including PSD-related actions, are
addressed in section IX. Section X
addresses applicable statutory and
executive order reviews.
Today’s final decisions addressing
standards for fine and coarse particles
are based on a thorough review in the
Integrated Science Assessment of
scientific information on known and
potential human health and welfare
effects associated with exposure to these
subclasses of PM at levels typically
found in the ambient air. These final
decisions also take into account: (1)
Staff assessments in the Policy
Assessment of the most policy-relevant
information in the Integrated Science
Assessment as well as a quantitative
health risk assessment and urbanfocused visibility assessment based on
that information; (2) CASAC advice and
recommendations, as reflected in its
letters to the Administrator, its
discussions of drafts of the Integrated
Science Assessment, Risk and Exposure
Assessments, and Policy Assessment at
public meetings, and separate written
comments prepared by individual
members of the CASAC PM Review
Panel; (3) public comments received
during the development of these
documents, both in connection with
CASAC meetings and separately; and (4)
extensive public comments received on
the proposed rulemaking.
III. Rationale for Final Decisions on the
Primary PM2.5 Standards
This section presents the
Administrator’s final decision regarding
the need to revise the current primary
PM2.5 standards and, more specifically,
regarding revisions to the level and form
of the existing primary annual PM2.5
standard in conjunction with retaining
the existing primary 24-hour PM2.5
standard. As discussed more fully
below, the rationale for the final
decision is based on a thorough review,
in the Integrated Science Assessment, of
the latest scientific information,
published through mid-2009, on human
health effects associated with long- and
short-term exposures to fine particles in
the ambient air. The final decisions also
take into account: (1) Staff assessments
of the most policy-relevant information
presented and assessed in the Integrated
Science Assessment and staff analyses
of air quality and human risks presented
in the Risk Assessment and the Policy
Assessment, upon which staff
conclusions regarding appropriate
considerations in this review are based;
(2) CASAC advice and
recommendations, as reflected in
discussions of drafts of the Integrated
Science Assessment, Risk Assessment,
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
and Policy Assessment at public
meetings, in separate written comments,
and in CASAC’s letters to the
Administrator; (3) the multiple rounds
of public comments received during the
development of these documents, both
in connection with CASAC meetings
and separately; and (4) extensive public
comments received on the proposal.
In developing this final rule, the
Administrator recognizes that the CAA
requires her to reach a public health
policy judgment as to what standards
would be requisite—neither more nor
less stringent than necessary—to protect
public health with an adequate margin
of safety, based on scientific evidence
and technical assessments that have
inherent uncertainties and limitations.
This judgment requires making
reasoned decisions as to what weight to
place on various types of evidence and
assessments, and on the related
uncertainties and limitations. Thus, in
selecting the final standards, the
Administrator is seeking not only to
prevent fine particle concentrations that
have been demonstrated to be harmful
but also to prevent lower fine particle
concentrations that may pose an
unacceptable risk of harm, even if the
risk is not precisely identified as to
nature or degree.
As discussed below, as well as in
more detail in the proposal, a
substantial amount of new research has
been conducted since the close of the
science assessment in the last review of
the PM2.5 NAAQS (U.S. EPA, 2004),
with important new information coming
from epidemiological studies, in
particular. This body of evidence
includes hundreds of new
epidemiological studies conducted in
many countries around the world. In its
assessment of the evidence judged to be
most relevant to making decisions on
elements of the primary PM2.5
standards, the EPA has placed greater
weight on U.S. and Canadian studies
using PM2.5 measurements, since studies
conducted in other countries may reflect
different demographic and air pollution
characteristics.14
The newly available research studies
as well as the earlier body of scientific
evidence presented and assessed in the
Integrated Science Assessment have
undergone intensive scrutiny through
multiple layers of peer review and
opportunities for public review and
comment. In developing this final rule,
the EPA has drawn upon an integrative
synthesis of the entire body of evidence
14 Nonetheless, the Administrator recognizes the
importance of all studies, including international
studies, in the Integrated Science Assessment’s
considerations of the weight of the evidence that
informs causality determinations.
PO 00000
Frm 00013
Fmt 4701
Sfmt 4700
3097
concerning exposure to ambient fine
particles and a broad range of health
endpoints (U.S. EPA, 2009a, Chapters 2,
4, 5, 6, 7, and 8) focusing on those
health endpoints for which the
Integrated Science Assessment
concludes that there is a causal or likely
causal relationship with long- or shortterm PM2.5 exposures. The EPA has also
considered health endpoints for which
the Integrated Science Assessment
concludes there is evidence suggestive
of a causal relationship with long-term
PM2.5 exposures.
The EPA has also drawn upon a
quantitative risk assessment based upon
the scientific evidence described and
assessed in the Integrated Science
Assessment. These analyses, discussed
in the Risk Assessment (U.S. EPA,
2010a) and Policy Assessment (U.S.
EPA, 2011a, chapter 2), have also
undergone intensive scrutiny through
multiple layers of peer review and
multiple opportunities for public review
and comment.
Although important uncertainties
remain in the qualitative and
quantitative characterizations of health
effects attributable to ambient fine
particles, progress has been made in
addressing these uncertainties in this
review. The EPA’s review of this
information has been extensive and
deliberate. This intensive evaluation of
the scientific evidence and quantitative
assessments has provided a
comprehensive and adequate basis for
regulatory decision making at this time.
This section describes the integrative
synthesis of the evidence and technical
information contained in the Integrated
Science Assessment, the Risk
Assessment, and the Policy Assessment
with regard to the current and
alternative standards. The EPA notes
that the final decision for retaining or
revising the current primary PM2.5
standards is a public health policy
judgment made by the Administrator.
The Administrator’s final decision
draws upon scientific information and
analyses related to health effects and
risks; judgments about uncertainties that
are inherent in the scientific evidence
and analyses; CASAC advice; and
comments received in response to the
proposal.
In presenting the rationale for the
final decisions on the primary PM2.5
standards, this section begins with a
summary of the approaches used in
setting the initial primary PM2.5 NAAQS
in 1997 and in reviewing and revising
those standards in 2006 (section III.A.1).
The DC Circuit Court of Appeals
remand of the primary annual PM2.5
standard in 2009 is discussed in section
III.A.2. Taking into consideration this
E:\FR\FM\15JAR2.SGM
15JAR2
3098
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
history, section III.A.3 describes the
EPA’s general approach used in the
current review for considering the need
to retain or revise the current suite of
fine particle standards, taking into
account public comment on the
proposed approach.
The scientific evidence and
quantitative risk assessment were
presented in sections III.B and III.C of
the proposal, respectively (77 FR 38906
to 38917, June 29, 2012) and are
outlined in sections III.B and III.C
below. Subsequent sections of this
preamble provide a more complete
discussion of the Administrator’s
rationale, in light of key issues raised in
public comments, for concluding that it
is appropriate to revise the suite of
current primary PM2.5 standards
(section III.D), as well as a more
complete discussion of the
Administrator’s rationale for retaining
or revising the specific elements of the
primary PM2.5 standards, namely the
indicator (section III.E.1); averaging time
(section III.E.2); form (section III.E.3);
and level (section III.E.4). A summary of
the final decisions to revise the suite of
primary PM2.5 standards is presented in
section III.F.
A. Background
There are currently two primary PM2.5
standards providing public health
protection from effects associated with
fine particle exposures. The annual
standard is set at a level of 15.0 mg/m3,
based on the 3-year average of annual
arithmetic mean PM2.5 concentrations
from single or multiple monitors sited to
represent community-wide air quality.
The 24-hour standard is set at a level of
35 mg/m3, based on the 3-year average of
the 98th percentile of 24-hour PM2.5
concentrations at each populationoriented monitor within an area.
The past and current approaches for
reviewing the primary PM2.5 standards
described below are all based most
fundamentally on using information
from epidemiological studies to inform
the selection of PM2.5 standards that, in
the Administrator’s judgment, protect
public health with an adequate margin
of safety. Such information can be in the
form of air quality distributions over
which health effect associations have
been observed in scientific studies or in
the form of concentration-response
functions that support quantitative risk
assessment. However, evidence- and
risk-based approaches using information
from epidemiological studies to inform
decisions on PM2.5 standards are
complicated by the recognition that no
population threshold, below which it
can be concluded with confidence that
PM2.5-related effects do not occur, can
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
be discerned from the available
evidence.15 As a result, any general
approach to reaching decisions on what
standards are appropriate necessarily
requires judgments about how to
translate the information available from
the epidemiological studies into a basis
for appropriate standards. This includes
consideration of how to weigh the
uncertainties in the reported
associations across the distributions of
PM2.5 concentrations in the studies and
the uncertainties in quantitative
estimates of risk, in the context of the
entire body of evidence before the
Agency. Such approaches are consistent
with setting standards that are neither
more nor less stringent than necessary,
recognizing that a zero-risk standard is
not required by the CAA.
1. General Approach Used in Previous
Reviews
The general approach used to
translate scientific information into
standards in the previous PM NAAQS
reviews focused on consideration of
alternative standard levels that were
somewhat below the long-term mean
PM2.5 concentrations reported in key
epidemiological studies (U.S. EPA,
2011a, section 2.1.1). This approach
recognized that the strongest evidence
of PM2.5-related associations occurs
where the bulk of the data exists, which
is over a range of concentrations around
the long-term (i.e., annual) mean.
In setting primary PM2.5 annual and
24-hour standards for the first time in
1997, the Agency relied primarily on an
evidence-based approach that focused
on epidemiological evidence, especially
from short-term exposure studies of fine
particles judged to be the strongest
evidence at that time (U.S. EPA, 2011a,
section 2.1.1.1). The EPA selected a
level for the annual standard that was at
or below the long-term mean PM2.5
concentrations in studies providing
evidence of associations with short-term
PM2.5 exposures, placing greatest weight
on those short-term exposure studies
that reported clearly statistically
significant associations with mortality
and morbidity effects. Further
consideration of long-term mean PM2.5
concentrations associated with mortality
and respiratory effects in children did
not provide a basis for establishing a
lower annual standard level. The EPA
did not place much weight on
quantitative risk estimates from the very
15 The term ‘‘evidence-based’’ approach or
consideration generally refers to using the
information in the scientific evidence to inform
judgments on the need to retain or revise the
NAAQS. The term ‘‘risk-based’’ generally refers to
using the quantitative information in the Risk
Assessment to inform such judgments.
PO 00000
Frm 00014
Fmt 4701
Sfmt 4700
limited risk assessment conducted, but
did conclude that the risk assessment
results confirmed the general
conclusions drawn from the
epidemiological evidence that a serious
public health problem was associated
with ambient PM levels allowed under
the then current PM10 standards (62 FR
38665/1, July 18, 1997).
The EPA considered the
epidemiological evidence and data on
air quality relationships to set an annual
PM2.5 standard that was intended to be
the ‘‘generally controlling’’ standard;
i.e., the primary means of lowering both
long- and short-term ambient
concentrations of PM2.5.16 In
conjunction with the annual standard,
the EPA also established a 24-hour
PM2.5 standard to provide supplemental
protection against days with high peak
concentrations, localized ‘‘hotspots,’’
and risks arising from seasonal
emissions that might not be well
controlled by an annual standard (62 FR
38669/3).
In 2006, the EPA used a different
evidence-based approach to assess the
appropriateness of the levels of the 24hour and annual PM2.5 standards (U.S.
EPA, 2011a, section 2.1.1.2). Based on
an expanded body of epidemiological
evidence that was stronger and more
robust than that available in the 1997
review, including additional studies of
both short- and long-term exposures, the
EPA decided that using evidence of
effects associated with periods of
exposure that were most closely
matched to the averaging time of each
standard was the most appropriate
public health policy approach for
evaluating the scientific evidence to
inform selecting the level of each
standard. Thus, the EPA relied upon
evidence from the short-term exposure
studies as the principal basis for
revising the level of the 24-hour PM2.5
standard from 65 to 35 mg/m3 to protect
against effects associated with shortterm exposures. The EPA relied upon
evidence from long-term exposure
16 In so doing, the EPA noted that because an
annual standard would focus control programs on
annual average PM2.5 concentrations, it would not
only control long-term exposure levels, but would
also generally control the overall distribution of 24hour exposure levels, resulting in fewer and lower
24-hour peak concentrations. Alternatively, a 24hour standard that focused controls on peak
concentrations could also result in lower annual
average concentrations. Thus, the EPA recognized
that either standard could provide some degree of
protection from both short- and long-term
exposures, with the other standard serving to
address situations where the daily peaks and
annual averages are not consistently correlated (62
FR 38669, July 18, 1997). In the circumstances
presented in that review, the EPA determined that
it was appropriate to focus on the annual standard
as the standard best suited to control both annual
and daily air quality distributions (62 FR 38670).
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
studies as the principal basis for
retaining the level of the annual PM2.5
standard at 15 mg/m3 to protect against
effects associated with long-term
exposures. This approach essentially
took the view that short-term studies
were not appropriate to inform
decisions relating to the level of the
annual standard, and long-term studies
were not appropriate to inform
decisions relating to the level of the 24hour standard. With respect to
quantitative risk-based considerations,
the EPA determined that the estimates
of risks likely to remain upon
attainment of the 1997 suite of PM2.5
standards were indicative of risks that
could be reasonably judged important
from a public health perspective and,
thus, supported revision of the
standards. However, the EPA judged
that the quantitative risk assessment had
important limitations and did not
provide an appropriate basis for
selecting the levels of the revised
standards in 2006 (71 FR 61174/1–2,
October 17, 2006).
2. Remand of Primary Annual PM2.5
Standard
As noted above in section II.B.2,
several parties filed petitions for review
in the U.S. Court of Appeals for the
District of Columbia Circuit following
promulgation of the revised PM NAAQS
in 2006. These petitions challenged
several aspects of the final rule
including the level of the primary PM2.5
annual standard. The primary 24-hour
PM2.5 standard was not challenged by
any of the litigants and, thus, was not
considered in the court’s review and
decision.
On judicial review, the D.C. Circuit
remanded the primary annual PM2.5
NAAQS to the EPA on grounds that the
Agency failed to adequately explain
why the annual standard provided the
requisite protection from both shortand long-term exposures to fine
particles including protection for at-risk
populations. American Farm Bureau
Federation v. EPA, 559 F. 3d 512 (D.C.
Cir. 2009). With respect to human
health protection from short-term PM2.5
exposures, the court considered the
different approaches used by the EPA in
the 1997 and 2006 p.m. NAAQS
decisions, as summarized in section
III.A.1 above. The court found that the
EPA failed to adequately explain why a
primary 24-hour PM2.5 standard by itself
would provide the protection needed
from short-term exposures and
remanded the primary annual PM2.5
standard to the EPA ‘‘for further
consideration of whether it is set at a
level requisite to protect the public
health while providing an adequate
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
margin of safety from the risk of shortterm exposures to PM2.5.’’ American
Farm Bureau Federation v. EPA, 559 F.
3d at 520–24.
With respect to protection from longterm exposure to fine particles, the court
found that the EPA failed to adequately
explain how the primary annual PM2.5
standard provided an adequate margin
of safety for children and other at-risk
populations. The court found that the
EPA did not provide a reasonable
explanation of why certain morbidity
studies, including a study of children in
Southern California showing lung
damage associated with long-term PM2.5
exposure (Gauderman et al., 2000) and
a multi-city study (24-Cities Study)
evaluating decreased lung function in
children associated with long-term
PM2.5 exposures (Raizenne et al., 1996),
did not warrant a more stringent annual
PM2.5 standard. Id. at 522–23.
Specifically, the court found that:
EPA was unreasonably confident that, even
though it relied solely upon long-term
mortality studies, the revised standard would
provide an adequate margin of safety with
respect to morbidity among children. Notably
absent from the final rule, moreover, is any
indication of how the standard will
adequately reduce risk to the elderly or to
those with certain heart or lung diseases
despite (a) the EPA’s determination in its
proposed rule that those subpopulations are
at greater risk from exposure to fine particles
and (b) the evidence in the record supporting
that determination. Id. at 525.
In addition, the court held that the
EPA had not adequately explained its
decision to base the level of the annual
standard essentially exclusively on the
results of long-term studies and the 24hour standard level essentially
exclusively on the results of short-term
studies. See 559 F. 3d at 522 (‘‘[e]ven if
the long-term studies available today are
useful for setting an annual standard
* * * it is not clear why the EPA no
longer believes it useful to look as well
to short-term studies in order to design
the suite of standards that will most
effectively reduce the risks associated
with short-term exposure’’); see also Id.
at 523–24 (holding that the EPA had not
adequately explained why a standard
based on levels in short-term exposure
studies alone provided appropriate
protection from health effects associated
with short-term PM2.5 exposures given
the stated need to lower the entire air
quality distribution, and not just peak
concentrations, in order to control
against short-term effects).
In remanding the primary annual
PM2.5 standard for reconsideration, the
court did not vacate the standard, Id. at
530, so the standard remains in effect
PO 00000
Frm 00015
Fmt 4701
Sfmt 4700
3099
and is therefore the standard considered
by the EPA in this review.
3. General Approach Used in the Policy
Assessment for the Current Review
This review is based on an assessment
of a much expanded body of scientific
evidence, more extensive air quality
data and analyses, and a more
comprehensive quantitative risk
assessment relative to the information
available in past reviews, as presented
and assessed in the Integrated Science
Assessment and Risk Assessment and
discussed in the Policy Assessment. As
a result, the EPA’s general approach to
reaching conclusions about the
adequacy of the current suite of PM2.5
standards and potential alternative
standards that are appropriate to
consider was broader and more
integrative than in past reviews. Our
general approach also reflected
consideration of the issues raised by the
court in its remand of the primary
annual PM2.5 standard as discussed in
section III.A.2 above, since decisions
made in this review, and the rationales
for those decisions, will comprise the
Agency’s response to the remand.
The EPA’s general approach took into
account both evidence-based and riskbased considerations and the
uncertainties related to both types of
information, as well as advice from
CASAC (Samet, 2010c,d) and public
comments on the first and second draft
Policy Assessments (U.S. EPA, 2010c,f).
In so doing, the EPA staff developed a
final Policy Assessment (U.S. EPA,
2011a) which provided as broad an
array of policy options as was supported
by the available information,
recognizing that the selection of a
specific approach to reaching final
decisions on the primary PM2.5
standards will reflect the judgments of
the Administrator as to what weight to
place on the various approaches and
types of information available in the
current review.
The Policy Assessment concluded it
was most appropriate to consider the
protection against PM2.5-related
mortality and morbidity effects,
associated with both long- and shortterm exposures, afforded by the annual
and 24-hour standards taken together, as
was done in the 1997 review, rather
than to consider each standard
separately, as was done in the 2006
review (U.S. EPA, 2011a, section
2.1.3).17 As the EPA recognized in 1997,
17 By utilizing this approach, the Agency also is
responsive to the remand of the 2006 standard. As
noted in section III.A.2, the D.C. Circuit, in
remanding the 2006 primary annual PM2.5 standard,
concluded that the Administrator had failed to
E:\FR\FM\15JAR2.SGM
Continued
15JAR2
3100
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
there are various ways to combine two
standards to achieve an appropriate
degree of public health protection. The
extent to which these two standards are
interrelated in any given area depends
in large part on the relative levels of the
standards, the peak-to-mean ratios that
characterize air quality patterns in an
area, and whether changes in air quality
designed to meet a given suite of
standards are likely to be of a more
regional or more localized nature.
In considering the combined effect of
annual and 24-hour standards, the
Policy Assessment recognized that
changes in PM2.5 air quality designed to
meet an annual standard would likely
result not only in lower annual average
PM2.5 concentrations but also in fewer
and lower peak 24-hour PM2.5
concentrations. The Policy Assessment
also recognized that changes designed to
meet a 24-hour standard would result
not only in fewer and lower peak 24hour PM2.5 concentrations but also in
lower annual average PM2.5
concentrations. Thus, either standard
could be viewed as providing protection
from effects associated with both shortand long-term exposures, with the other
standard serving to address situations
where the daily peak and annual
average concentrations are not
consistently correlated.
In considering the currently available
evidence, the Policy Assessment
recognized that the short-term exposure
studies were primarily drawn from
epidemiological studies that associated
variations in area-wide health effects
with monitor(s) that measured the
variation in daily PM2.5 concentrations
over the course of several years. The
strength of the associations in these data
was demonstrably in the numerous
‘‘typical’’ days within the air quality
distribution, not in the peak days. See
also 71 FR 61168, October 17, 2006 and
American Farm Bureau Federation v.
EPA, 559 F. 3d at 523, 524 (making the
same point). The quantitative risk
assessments conducted for this and
previous reviews demonstrated the
same point; that is, much, if not most of
the aggregate risk associated with shortterm exposures results from the large
number of days during which the 24hour average concentrations are in the
low-to mid-range, below the peak 24hour concentrations (U.S. EPA, 2011a,
adequately explain why an annual standard was
sufficiently protective in the absence of
consideration of the long-term mean PM2.5
concentrations in short-term exposure studies as
well, and likewise had failed to explain why a 24hour standard was sufficiently protective in the
absence of consideration of the effect of an annual
standard on reducing the overall distribution of 24hour average PM2.5 concentrations. 559 F. 3d at
520–24.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
section 2.2.2; U.S. EPA, 2010a, section
3.1.2.2). In addition, there was no
evidence suggesting that risks associated
with long-term exposures were likely to
be disproportionately driven by peak
24-hour concentrations.18
For these reasons, the Policy
Assessment concluded that strategies
that focused primarily on reducing peak
days were less likely to achieve
reductions in the PM2.5 concentrations
that were most strongly associated with
the observed health effects.
Furthermore, the Policy Assessment
concluded that a policy approach that
focused on reducing peak exposures
would most likely result in more
uneven public health protection across
the U.S. by either providing inadequate
protection in some areas or
overprotecting in other areas (U.S. EPA,
2011a, p. 2–9; U.S. EPA, 2010a, section
5.2.3). This is because, as discussed
above, reductions based on control of
peak days are less likely to control the
bulk of the air quality distribution.
The Policy Assessment concluded
that a policy goal of setting a ‘‘generally
controlling’’ annual standard that will
lower a wide range of ambient 24-hour
PM2.5 concentrations, as opposed to
focusing on control of peak 24-hour
PM2.5 concentrations, was the most
effective and efficient way to reduce
total population risk and so provide
appropriate protection. This approach,
in contrast to one focusing on a
generally controlling 24-hour standard,
would likely reduce aggregate risks
associated with both long- and shortterm exposures with more consistency
and would likely avoid setting national
standards that could result in relatively
uneven protection across the country,
due to setting standards that are either
more or less stringent than necessary in
different geographical areas (U.S. EPA,
2011a, p. 2–9).
The Policy Assessment also
concluded that an annual standard
intended to serve as the primary means
for providing protection from effects
associated with both long- and shortterm PM2.5 exposures cannot be
expected to offer sufficient protection
against the effects of all short-term PM2.5
exposures. As a result, in conjunction
with a generally controlling annual
standard, the Policy Assessment
concluded it was appropriate to
consider setting a 24-hour standard to
provide supplemental protection,
18 In confirmation, a number of studies have
presented analyses excluding higher PM
concentration days and reported a limited effect on
the magnitude of the effect estimates or statistical
significance of the association (e.g., Dominici,
2006b; Schwartz et al., 1996; Pope and Dockery,
1992).
PO 00000
Frm 00016
Fmt 4701
Sfmt 4700
particularly for areas with high peak-tomean ratios possibly associated with
strong local or seasonal sources, or
PM2.5-related effects that may be
associated with shorter-than-daily
exposure periods (U.S. EPA, 2011a, p.
2–10).
The Policy Assessment’s
consideration of the protection afforded
by the current and alternative suites of
standards focused on PM2.5-related
health effects associated with long-term
exposures for which the magnitude of
quantitative estimates of risks to public
health generated in the risk assessment
was appreciably larger in terms of
overall incidence and percent of total
mortality or morbidity effects than for
short-term PM2.5-related effects.
Nonetheless, the EPA also considered
health effects and estimated risks
associated with short-term exposures. In
both cases, the Policy Assessment
placed greatest weight on health effects
that had been judged in the Integrated
Science Assessment to have a causal or
likely causal relationship with PM2.5
exposures, while also considering
health effects judged to be suggestive of
a causal relationship or evidence that
focused on specific at-risk populations.
The Policy Assessment placed relatively
greater weight on statistically significant
associations that yielded relatively more
precise effect estimates and that were
judged to be robust to confounding by
other air pollutants. In the case of shortterm exposure studies, the Policy
Assessment placed greatest weight on
evidence from large multi-city studies,
while also considering associations in
single-city studies.
In translating information from
epidemiological studies into the basis
for reaching staff conclusions on the
adequacy of the current suite of
standards, the Policy Assessment
considered a number of factors. As an
initial matter, the Policy Assessment
considered the extent to which the
currently available evidence and related
uncertainties strengthens or calls into
question conclusions from the last
review regarding associations between
fine particle exposures and health
effects. The Policy Assessment also
considered evidence of health effects in
at-risk populations and the potential
impacts on such populations. Further,
the Policy Assessment explored the
extent to which PM2.5-related health
effects had been observed in areas
where air quality distributions extend to
lower concentrations than previously
reported or in areas that would likely
have met the current suite of standards.
In translating information from
epidemiological studies into the basis
for reaching staff conclusions on
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
standard levels for consideration (U.S.
EPA, 2011a, sections 2.1.3 and 2.3.4),
the Policy Assessment first recognized
the absence of discernible thresholds in
the concentration-response functions
from long- and short-term PM2.5
exposure studies (U.S. EPA, 2011a,
section 2.4.3).19 In the absence of any
discernible thresholds, the Agency’s
general approach for identifying
appropriate standard levels for
consideration involved characterizing
the range of PM2.5 concentrations over
which we have the most confidence in
the associations reported in
epidemiological studies. In so doing, the
Policy Assessment recognized that there
is no single factor or criterion that
comprises the ‘‘correct’’ approach, but
rather there are various approaches that
are reasonable to consider for
characterizing the confidence in the
associations and the limitations and
uncertainties in the evidence.
Identifying the implications of various
approaches for reaching conclusions on
the range of alternative standard levels
that is appropriate to consider can help
inform the final decisions to either
retain or revise the standards. Today’s
final decisions also take into account
public health policy judgments as to the
degree of health protection that is to be
achieved.
In reaching staff conclusions on the
range of annual standard levels that was
appropriate to consider, the Policy
Assessment focused on identifying an
annual standard that provided requisite
protection from effects associated with
both long- and short-term exposures. In
so doing, the Policy Assessment
explored different approaches for
characterizing the range of PM2.5
concentrations over which our
confidence in the nature of the
associations for both long- and shortterm exposures is greatest, as well as the
extent to which our confidence is
reduced at lower PM2.5 concentrations.
First, the Policy Assessment
recognized that the approach that most
directly addressed this issue considered
19 The epidemiological studies evaluated in the
Integrated Science Assessment that examined the
shape of concentration-response relationships and
the potential presence of a threshold focused on
cardiovascular-related hospital admissions and
emergency department visits associated with shortterm PM10 exposures and premature mortality
associated with long-term PM2.5 exposure (U.S.
EPA, 2009a, sections 6.5, 6.2.10.10 and 7.6).
Overall, the Integrated Science Assessment
concluded that the studies evaluated support the
use of a no-threshold, log-linear model but
recognized that ‘‘additional issues such as the
influence of heterogeneity in estimates between
cities, and the effect of seasonal and regional
differences in PM on the concentration-response
relationship still require further investigation’’ (U.S.
EPA, 2009a, section 2.4.3).
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
studies that analyzed confidence
intervals around concentration-response
relationships and in particular, analyses
that averaged across multiple
concentration-response models rather
than considering a single concentrationresponse model.20 The Policy
Assessment explored the extent to
which such analyses had been
published for studies of health effects
associated with long- or short-term
PM2.5 exposures. Such analyses could
potentially be used to characterize a
concentration below which uncertainty
in a concentration-response relationship
substantially increases or is judged to be
indicative of an unacceptable degree of
uncertainty about the existence of a
continuing concentration-response
relationship. The Policy Assessment
concluded that identifying this area of
uncertainty in the concentrationresponse relationship could be used to
inform identification of alternative
standard levels that are appropriate to
consider.
Further, the Policy Assessment
explored other approaches that
considered different statistical metrics
from epidemiological studies. The
Policy Assessment first took into
account the general approach used in
previous PM reviews which focused on
consideration of alternative standard
levels that were somewhat below the
long-term mean PM2.5 concentrations
reported in epidemiological studies
using air quality distributions based on
composite monitor concentrations.21
This approach recognized that the
strongest evidence of PM2.5-related
associations occurs at concentrations
around the long-term (i.e., annual)
mean. In using this approach, the Policy
Assessment placed greatest weight on
those long- and short-term exposure
studies that reported statistically
20 This is distinct from confidence intervals
around concentration-response relationships that
are related to the magnitude of effect estimates
generated at specific PM2.5 concentrations (i.e.,
point-wise confidence intervals) and that are
relevant to the precision of the effect estimate
across the air quality distribution, rather than to our
confidence in the existence of a continuing
concentration-response relationship across the
entire air quality distribution on which a reported
association was based.
21 Using the term ‘‘composite monitor’’ does not
imply that the EPA can identify one monitor that
represents the air quality evaluated in a specific
study area. Rather, the composite monitor
concentration represents the average concentration
across monitors within each area with more than
one monitor included in a given study as typically
reported in epidemiological studies. For multi-city
studies, this metric reflects concentrations averaged
across multiple monitors or from single monitors
within each area and then averaged across study
areas for an overall study mean PM2.5 concentration.
This is consistent with the epidemiological
evidence considered in other NAAQS reviews.
PO 00000
Frm 00017
Fmt 4701
Sfmt 4700
3101
significant associations with mortality
and morbidity effects.
In extending this approach, the Policy
Assessment also considered information
beyond a single statistical metric of
PM2.5 concentrations (i.e., the mean) to
the extent such information was
available. Pursuant to an express
comment from CASAC (Samet 2010d, p.
2), the Policy Assessment utilized
distributional statistics (i.e., statistical
characterization of an entire distribution
of data) to identify the broader range of
PM2.5 concentrations that had the most
influence on the calculation of relative
risk estimates in both long- and shortterm exposure epidemiological studies.
Thus, the Policy Assessment considered
the part of the distribution of PM2.5
concentrations in which the data
analyzed in the study (i.e., air quality
and population-level data, as discussed
below) were most concentrated,
specifically, the range of PM2.5
concentrations around the long-term
mean over which our confidence in the
magnitude and significance of
associations observed in the
epidemiological studies was greatest.
The Policy Assessment then focused on
the lower part of the distribution to
characterize where the data became
appreciably more sparse and, thus,
where our understanding of the
magnitude and significance of the
associations correspondingly became
more uncertain. The Policy Assessment
recognized there was no single
percentile value within a given
distribution that was most appropriate
or ‘‘correct’’ to use to characterize where
our confidence in the associations
becomes appreciably lower. The Policy
Assessment concluded that the range
from the 25th to 10th percentiles is a
reasonable range to consider as a region
where we had appreciably less
confidence in the associations observed
in epidemiological studies.22
In considering distributional statistics
from epidemiological studies, the final
Policy Assessment focused on two types
of population-level metrics that CASAC
advised were most useful to consider in
identifying the PM2.5 concentrations
22 In the PM NAAQS review completed in 2006,
the Staff Paper similarly recognized that the
evidence of an association in any epidemiological
study is ‘‘strongest at and around the long-term
average where the data in the study are most
concentrated. For example, the interquartile range
of long-term average concentrations within a study
[with a lower bound of the 25th percentile] or a
range within one standard deviation around the
study mean, may reasonably be used to characterize
the range over which the evidence of association is
strongest’’ (U.S. EPA, 2005, p. 5–22). A range of one
standard deviation around the mean represents
approximately 68 percent of normally distributed
data, and below the mean falls between the 25th
and 10th percentiles.
E:\FR\FM\15JAR2.SGM
15JAR2
3102
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
most influential in generating the health
effect estimates reported in the
epidemiological studies.23 Consistent
with CASAC advice, the most relevant
information was the distribution of
health events (e.g., deaths,
hospitalizations) occurring within a
study population in relation to the
distribution of PM2.5 concentrations.
However, in recognizing that access to
health event data can be restricted, the
Policy Assessment also considered the
number of study participants within
each study area as an appropriate
surrogate for health event data.
The Policy Assessment recognized
that an approach considering analyses
of confidence intervals around
concentration-response functions was
intrinsically related to an approach that
considered different distributional
statistics. Both of these approaches
could be employed to understand the
broader distribution of PM2.5
concentrations which correspond to the
health events reported in
epidemiological studies. In applying
these approaches, the Policy
Assessment, consistent with CASAC
advice (Samet, 2010d, p. 3), considered
PM2.5 concentrations from long- and
short-term PM2.5 exposure studies using
composite monitor distributions.
In reaching staff conclusions on
alternative standard levels that were
appropriate to consider, the Policy
Assessment also included a broader
consideration of the uncertainties and
limitations of the current scientific
evidence. Most notably, these
uncertainties are related to the
heterogeneity observed in the
epidemiological studies in the eastern
versus western parts of the U.S., the
relative toxicity of PM2.5 components,
and the potential role of co-pollutants
(U.S. EPA, 2011a, pp. 2–25 to 2–26).
The limitations and uncertainties
associated with the currently available
scientific evidence, including the
availability of fewer studies toward the
lower range of alternative annual
standard levels being considered in this
proposal, are summarized in section
III.B below and further discussed in
section III.B.2 of the proposal.
The Policy Assessment recognized
that the level of protection afforded by
the NAAQS relies both on the level and
the form of the standard. The Policy
Assessment concluded that a policy
approach that used data based on
composite monitor distributions to
identify alternative standard levels, and
then compared those levels to
concentrations at maximum monitors to
determine whether an area meets a
given standard, inherently has the
potential to build in some margin of
safety (U.S. EPA, 2011a, p. 2–14).24 This
conclusion was consistent with
CASAC’s comments on the second draft
Policy Assessment, in which CASAC
expressed its preference for focusing on
an approach using composite monitor
distributions ‘‘because of its stability,
and for the additional margin of safety
it provides’’ when ‘‘compared to the
maximum monitor perspective’’ (Samet,
et al., 2010d, pp. 2 to 3).
In reaching staff conclusions on
alternative 24-hour standard levels that
are appropriate to consider for setting a
24-hour standard intended to
supplement the protection afforded by a
generally controlling annual standard,
the Policy Assessment considered
currently available short-term PM2.5
exposure studies. The evidence from
these studies informed our
understanding of the protection afforded
by the suite of standards against effects
associated with short-term exposures. In
considering the short-term exposure
studies, the Policy Assessment
evaluated both the distributions of 24hour PM2.5 concentrations, with a focus
on the 98th percentile concentrations (to
the extent such data were available) to
match the form of the current 24-hour
PM2.5 standard, as well as the long-term
mean PM2.5 concentrations reported in
23 The second draft Policy Assessment focused on
the distributions of ambient PM2.5 concentrations
and associated population data across areas
included in several multi-city studies for which
such data were available in seeking to identify the
most influential range of concentrations (U.S. EPA,
2010f, section 2.3.4.1). In its review of the second
draft Policy Assessment, CASAC advised that it
‘‘would be preferable to have information on the
concentrations that were most influential in
generating the health effect estimates in individual
studies’’ (Samet, 2010d, p.2). Therefore, in the final
Policy Assessment, the EPA considered populationlevel data (i.e., area-specific health event data and
study area population data) along with
corresponding PM2.5 concentrations to generate a
cumulative distribution of the population-level data
relative to long-term mean PM2.5 concentrations to
determine the most influential part of the air quality
distribution (U.S. EPA, 2011a, Figure 2–7 and
associated text).
24 Statistical metrics (e.g., means) based on
composite monitor distributions may be identical to
or below the same statistical metrics based on
maximum monitor distributions. For example, some
areas may have only one monitor, in which case the
composite and maximum monitor distributions will
be identical in those areas. Other areas may have
multiple monitors that may be very close to the
monitor measuring the highest concentrations, in
which case the composite and maximum monitor
distributions could be similar in those areas. As
noted in Hassett-Sipple et al. (2010), for studies
involving a large number of areas, the composite
and maximum concentrations are generally within
5 percent of each other (77 FR 38905, fn. 30). Still
other areas may have multiple monitors that may
be separately impacted by local sources in which
case the composite and maximum monitor
distributions could be quite different (U.S. EPA,
2011a, p. 2–14). See further discussion of this issue
in section III.E.4.c.i below.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
PO 00000
Frm 00018
Fmt 4701
Sfmt 4700
these studies. In addition to considering
the epidemiological evidence, the Policy
Assessment also considered air quality
information based on county-level 24hour and annual design values 25 to
understand the policy implications of
the alternative standard levels
supported by the underlying science. In
particular, the Policy Assessment
considered the extent to which different
combinations of alternative annual and
24-hour standards would support the
policy goal of focusing on a generally
controlling annual standard in
conjunction with a 24-hour standard
that would provide supplemental
protection. In so doing, the Policy
Assessment discussed the roles that
each standard might be expected to play
in the protection afforded by alternative
suites of standards.
Beyond these evidence-based
considerations, the Policy Assessment
also considered the quantitative risk
estimates and the key observations
presented in the Risk Assessment. This
assessment included an evaluation of 15
urban case study areas and estimated
risk associated with a number of health
endpoints associated with long- and
short-term PM2.5 exposures (U.S. EPA,
2010a). As part of the risk-based
considerations, the Policy Assessment
considered estimates of the magnitude
of PM2.5-related risks associated with
recent air quality levels and air quality
simulated to just meet the current and
alternative suites of standards using
alternative simulation approaches. The
Policy Assessment also characterized
the risk reductions, relative to the risks
remaining upon just meeting the current
standards, associated with just meeting
alternative suites of standards. In so
doing, the Policy Assessment
recognized the uncertainties inherent in
such risk estimates, and took such
uncertainties into account by
considering the sensitivity of the ‘‘core’’
risk estimates to alternative assumptions
and methods likely to have substantial
impact on the estimates. In addition, the
Policy Assessment considered
additional analyses characterizing the
representativeness of the urban study
areas within a broader national context
to understand the roles that the annual
and 24-hour standards may play in
affording protection against effects
related to both long- and short-term
PM2.5 exposures.
Based on the approach discussed
above, the Policy Assessment reached
conclusions related to the primary PM2.5
standards that reflected an
25 Design values are the metrics (i.e., statistics)
that are compared to the NAAQS levels to
determine compliance.
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
understanding of both evidence-based
and risk-based considerations to inform
two overarching questions related to: (1)
The adequacy of the current suite of
PM2.5 standards and (2) revisions to the
standards that were appropriate to
consider in this review to protect
against health effects associated with
both long- and short-term exposures to
fine particles. When evaluating the
health protection afforded by the
current or any alternative suites of
standards considered, the Policy
Assessment took into account the four
basic elements of the NAAQS: The
indicator, averaging time, form, and
level.
The general approach for reviewing
the primary PM2.5 standards described
above provided a comprehensive basis
that helped to inform the
Administrator’s judgments in reaching
her proposed and final decisions to
revise the current suite of primary fine
particle NAAQS and in responding to
the remand of the 2006 primary annual
PM2.5 standard.
B. Overview of Health Effects Evidence
This section outlines the key
information presented in section III.B of
the proposal (77 FR 38906 to 38911,
June 29, 2012) and discussed more fully
in the Integrated Science Assessment
(Chapters 2, 4, 5, 6, 7, and 8) and the
Policy Assessment (Chapter 2) related to
health effects associated with fine
particle exposures. Section III.B. of the
proposal discusses available
information on the health effects
associated with exposures to PM2.5,
including the nature of such health
effects (section III.B.1) and associated
limitations and uncertainties (section
III.B.2), at-risk populations (section
III.B.3), and potential PM2.5-related
impacts on public health (section
III.B.4). As was true in the last two
reviews, evidence from epidemiological,
controlled human exposure and animal
toxicological studies played a key role
in the Integrated Science Assessment’s
evaluation of the scientific evidence.
The 2006 PM NAAQS review
concluded that there was ‘‘strong
epidemiological evidence’’ for linking
long-term PM2.5 exposures with
cardiovascular-related and lung cancer
mortality and respiratory-related
morbidity and for linking short-term
PM2.5 exposures with cardiovascularrelated and respiratory-related mortality
and morbidity (U.S. EPA, 2004, p. 9–46;
U.S. EPA, 2005, p. 5–4). Overall, the
evidence from epidemiological,
toxicological, and controlled human
exposure studies supported ‘‘likely
causal associations’’ between PM2.5 and
both mortality and morbidity from
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
3103
(1) In looking across the extensive new
scientific evidence available in this review,
our overall understanding of health effects
associated with fine particle exposures has
been greatly expanded. The currently
available evidence is largely consistent with
evidence available in the last review and
substantially strengthens what is known
about the effects associated with fine particle
exposures.
(2) A number of large multi-city
epidemiological studies have been conducted
throughout the U.S., including extended
analyses of long-term exposure studies that
were important to inform decision-making in
the last review. The body of currently
available scientific evidence has also been
expanded greatly by the publication of a
number of new multi-city, time-series studies
that have used uniform methodologies to
investigate the effects of short-term PM2.5
exposures on public health. This body of
evidence provides a more expansive data
base and considers multiple locations
representing varying regions and seasons that
provide evidence of the influence of different
air pollution mixes on PM2.5-associated
health effects. These studies provide more
precise estimates of the magnitude of effects
associated with short-term PM2.5 exposure
than most smaller-scale single-city studies
that were more commonly available in the
last review. These studies have reported
consistent increases in morbidity and/or
premature mortality related to ambient PM2.5
concentrations, with the strongest evidence
reported for cardiovascular-related effects.
(3) In addition, the findings of new
toxicological and controlled human exposure
studies greatly expand and provide stronger
support for a number of potential biological
mechanisms or pathways for cardiovascular
and respiratory effects associated with longand short-term PM exposures. These studies
provide coherence and biological plausibility
for the effects observed in epidemiological
studies.
(4) Using a more formal framework for
reaching causal determinations than used in
prior reviews,27 the EPA concludes that a
causal relationship exists between both longand short-term exposures to PM2.5 and
premature mortality and cardiovascular
effects and a likely causal relationship exists
between long- and short-term PM2.5
exposures and respiratory effects. Further,
there is evidence suggestive of a causal
relationship between long-term PM2.5
exposures and other health effects, including
developmental and reproductive effects (e.g.,
low birth weight, infant mortality) and
carcinogenic, mutagenic, and genotoxic
effects (e.g., lung cancer mortality).28
(5) The newly available evidence
significantly strengthens the link between
long- and short-term exposure to PM2.5 and
premature mortality, while providing
indications that the magnitude of the PM2.5mortality association with long-term
exposures may be larger than previously
estimated. The strongest evidence comes
from recent studies investigating long-term
exposure to PM2.5 and cardiovascular-related
mortality. The evidence supporting a causal
relationship between long-term PM2.5
exposure and mortality also includes
consideration of new studies that
demonstrated an improvement in community
health following reductions in ambient fine
particles.
(6) Several new studies have examined the
association between cardiovascular effects
and long-term PM2.5 exposures in multi-city
studies conducted in the U.S. and Europe.
While studies were not available in the last
review with regard to long-term exposure and
cardiovascular-related morbidity, recent
studies have provided new evidence linking
long-term exposure to PM2.5 with an array of
cardiovascular effects such as heart attacks,
congestive heart failure, stroke, and
mortality. This evidence is coherent with
studies of short-term exposure to PM2.5 that
have observed associations with a continuum
of effects ranging from subtle changes in
indicators of cardiovascular health to serious
clinical events, such as increased
hospitalizations and emergency department
visits due to cardiovascular disease and
cardiovascular mortality.
(7) Extended analyses of studies available
in the last review as well as new
epidemiological studies conducted in the
U.S. and abroad provide stronger evidence of
respiratory-related morbidity effects
associated with long-term PM2.5 exposure.
The strongest evidence for respiratory-related
26 The term ‘‘likely causal association’’ was used
in the 2004 Criteria Document to summarize the
strength of the available evidence available in the
last review for PM2.5. However, this terminology
was not based on a formal framework for evaluating
evidence for inferring causation. Since the last
review, the EPA has developed a more formal
framework for reaching causal determinations with
standardized language to express evaluation of the
evidence (U.S. EPA, 2009a, section 1.5).
27 The causal framework draws upon the
assessment and integration of evidence from across
epidemiological, controlled human exposure, and
toxicological studies, and the related uncertainties
that ultimately influence our understanding of the
evidence. This framework employs a five-level
hierarchy that classifies the overall weight of
evidence and causality using the following
categorizations: causal relationship, likely to be
causal relationship, suggestive of a causal
relationship, inadequate to infer a causal
relationship, and not likely to be a causal
relationship (U.S. EPA, 2009a, Table 1–3). The
development of the causal framework reflects
considerable input from CASAC and the public,
with CASAC concluding that, ‘‘The five-level
classification of strength of evidence for causal
inference has been systemically applied [for PM];
this approach has provided transparency and a
clear statement of the level of confidence with
regard to causation, and we recommend its
continued use in future ISAs’’ (Samet, 2009f, p. 1).
28 These causal inferences are based not only on
the more expansive epidemiological evidence
available in this review but also reflect
consideration of important progress that has been
made to advance our understanding of a number of
potential biologic modes of action or pathways for
PM-related cardiovascular and respiratory effects
(U.S. EPA, 2009a, chapter 5).
cardiovascular and respiratory diseases,
based on ‘‘an assessment of strength,
robustness, and consistency in results’’
(U.S. EPA, 2004, p. 9–48).26
In this review, based on the expanded
body of evidence, the EPA finds that:
PO 00000
Frm 00019
Fmt 4701
Sfmt 4700
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
3104
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
effects is from studies that evaluated
decrements in lung function growth,
increased respiratory symptoms, and asthma
development. The strongest evidence from
short-term PM2.5 exposure studies has been
observed for increased respiratory-related
emergency department visits and hospital
admissions for chronic obstructive
pulmonary disease (COPD) and respiratory
infections.
(8) The body of scientific evidence is
somewhat expanded from the 2006 review
but is still limited with respect to
associations between long-term PM2.5
exposures and developmental and
reproductive effects as well as cancer,
mutagenic, and genotoxic effects. The
strongest evidence for an association between
PM2.5 and developmental and reproductive
effects comes from epidemiological studies of
low birth weight and infant mortality,
especially due to respiratory causes during
the post-neonatal period (i.e., 1 month–12
months of age). With regard to cancer effects,
‘‘[m]ultiple epidemiologic studies have
shown a consistent positive association
between PM2.5 and lung cancer mortality, but
studies have generally not reported
associations between PM2.5 and lung cancer
incidence’’ (U.S. EPA 2009a p. 2–13).
(9) Efforts to evaluate the relationships
between PM composition and health effects
continue to evolve. While many constituents
of PM2.5 can be linked with differing health
effects, the evidence is not yet sufficient to
allow differentiation of those constituents or
sources that may be more closely related to
specific health outcomes nor to exclude any
individual component or group of
components associated with any source
categories from the fine particle mixture of
concern.
(10) Specific groups within the general
population are at increased risk for
experiencing adverse health effects related to
PM exposures. The currently available
evidence expands our understanding of
previously identified at-risk populations (i.e.,
children, older adults, and individuals with
pre-existing heart and lung disease) and
supports the identification of additional atrisk populations (e.g., persons with lower
socioeconomic status, genetic differences).
Evidence for PM-related effects in these atrisk populations has expanded and is
stronger than previously observed. There is
emerging, though still limited, evidence for
additional potentially at-risk populations,
such as those with diabetes, people who are
obese, pregnant women, and the developing
fetus.
(11) The population potentially affected by
PM2.5 is large. In addition, large subgroups of
the U.S. population have been identified as
at-risk populations. While individual effect
estimates from epidemiological studies may
be small in size, the public health impact of
the mortality and morbidity associations can
be quite large given the extent of exposure.
Taken together, this suggests that exposure to
ambient PM2.5 concentrations can have
substantial public health impacts.
(12) While the currently available scientific
evidence is stronger and more consistent
than in previous reviews, providing a strong
basis for decision making in this review, the
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
EPA recognizes that important uncertainties
and limitations in the health effects evidence
remain. Epidemiological studies evaluating
health effects associated with long- and
short-term PM2.5 exposures have reported
heterogeneity in responses between cities
and geographic regions within the U.S. This
heterogeneity may be attributed, in part, to
differences in the fine particle composition
or related to exposure measurement error,
which can introduce bias and increased
uncertainty in associated health effect
estimates. Variability in the associations
observed across PM2.5 epidemiological
studies may be due in part to exposure error
related to measurement-related issues, the
use of central fixed-site monitors to represent
population exposure to PM2.5, models used
in lieu of or to supplement ambient
measurements, and our limited
understanding of factors that may influence
exposures (e.g., topography, the built
environment, weather, source characteristics,
ventilation usage, personal activity patterns,
photochemistry). In addition, where PM2.5
and other pollutants (e.g., ozone, nitrogen
dioxide, and carbon monoxide) are
correlated, it can be difficult to distinguish
the effects of the various pollutants in the
ambient mixture (i.e., co-pollutant
confounding).29
While uncertainties and limitations
still remain in the available health
effects evidence, the Administrator
judges the currently available scientific
data base to be stronger and more
consistent than in previous reviews
providing a strong basis for decision
making in this review.
C. Overview of Quantitative
Characterization of Health Risks
In addition to a comprehensive
evaluation of the health effects evidence
available in this review, the EPA
conducted an expanded quantitative
risk assessment for selected health
endpoints to provide additional
information and insights to inform
decisions on the primary PM2.5
NAAQS.30 As discussed in section III.C
of the proposal, the approach used to
develop quantitative risk estimates
associated with PM2.5 exposures was
built on the approach used and lessons
learned in the last review and focused
on improving the characterization of the
overall confidence in the risk estimates,
29 A copollutant meets the criteria for potential
confounding in PM-health associations if: (1) It is
a potential risk factor for the health effect under
study; (2) it is correlated with PM; and (3) it does
not act as an intermediate step in the pathway
between PM exposure and the health effect under
study (U.S. EPA, 2004, p. 8–10).
30 The quantitative risk assessment conducted for
this review is more fully described and presented
in the Risk Assessment (U.S. EPA, 2010a) and
summarized in detail in the Policy Assessment
(U.S. EPA, 2011a, sections 2.2.2. and 2.3.4.2). The
scope and methodology for this risk assessment
were developed over the last few years with
considerable input from CASAC and the public as
described in section II.B.3 above.
PO 00000
Frm 00020
Fmt 4701
Sfmt 4700
including related uncertainties, by
incorporating a number of
enhancements, in terms of both the
methods and data used in the analyses.
The goals of this quantitative risk
assessment were largely the same as
those articulated in the risk assessment
conducted for the last review. These
goals included: (1) To provide estimates
of the potential magnitude of premature
mortality and/or selected morbidity
effects in the population associated with
recent ambient levels of PM2.5 and with
simulating just meeting the current and
alternative suites of PM2.5 standards in
15 selected urban study areas,31
including, where data were available,
consideration of impacts on at-risk
populations; (2) to develop a better
understanding of the influence of
various inputs and assumptions on the
risk estimates to more clearly
differentiate among alternative suites of
standards; and (3) to gain insights into
the distribution of risks and patterns of
risk reductions and the variability and
uncertainties in those risk estimates. In
addition, the quantitative risk
assessment included nationwide
estimates of the potential magnitude of
premature mortality associated with
long-term exposure to recent ambient
PM2.5 concentrations to more broadly
characterize this risk on a national scale
and to support the interpretation of the
more detailed risk estimates generated
for selected urban study areas.
The expanded and updated risk
assessment conducted in this review
included estimates of risk for: (1) Allcause, ischemic heart disease-related,
cardiopulmonary-related, and lung
cancer-related mortality associated with
long-term PM2.5 exposure; (2) nonaccidental, cardiovascular-related, and
respiratory-related mortality associated
with short-term PM2.5 exposure; and (3)
cardiovascular-related and respiratoryrelated hospital admissions and asthmarelated emergency department visits
31 The Risk Assessment concluded that these 15
urban study areas were generally representative of
urban areas in the U.S. likely to experience
relatively elevated levels of risk related to ambient
PM2.5 exposure with the potential for better
characterization at the higher end of that
distribution (U.S. EPA, 2011a, p. 2–42; U.S. EPA,
2010a, section 4.4, Figure 4–17). The
representativeness analysis also showed that the 15
urban study areas do not capture areas with the
highest baseline morality risks or the oldest
populations (both of which can result in higher
PM2.5-related mortality estimates). However, some
of the areas with the highest values for these
attributes had relatively low PM2.5 concentrations
(e.g., urban areas in Florida) and, consequently, the
Risk Assessment concluded failure to include these
areas in the set of urban study areas was unlikely
to exclude high PM2.5-risk locations (U.S. EPA,
2010a, section 4.4.1).
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
associated with short-term PM2.5
exposure.32
The Risk Assessment included a core
set of risk estimates supplemented by an
alternative set of risk results generated
using single-factor and multi-factor
sensitivity analyses. The core set of risk
estimates was developed using the
combination of modeling elements and
input data sets identified in the Risk
Assessment as having higher confidence
relative to inputs used in the sensitivity
analyses. The results of the sensitivity
analyses provided information to
evaluate and rank the potential impacts
of key sources of uncertainty on the core
risk estimates. In addition, the
sensitivity analyses represented a set of
reasonable alternatives to the core set of
risk estimates that fell within an overall
set of plausible risk estimates
surrounding the core estimates.
The EPA recognized that there were
many sources of variability and
uncertainty inherent in the inputs to its
quantitative risk assessment.33 The
design of the risk assessment included
a number of elements to address these
issues in order to increase the overall
confidence in the risk estimates
generated for the 15 urban study areas,
including using guidance from the
World Health Organization (WHO,
2008) as a framework for characterizing
uncertainty in the analyses.34
With respect to the sources of
variability, the Risk Assessment
considered those that contributed to
differences in risk across urban study
areas, but did not directly affect the
degree of risk reduction associated with
the simulation of just meeting current or
alternative standard levels (e.g.,
differences in baseline incidence rates,
demographics and population behavior).
The Risk Assessment also focused on
factors that not only introduced
variability into risk estimates across
study areas, but also played an
important role in determining the
magnitude of risk reductions upon
simulation of just meeting current or
alternative standard levels (e.g., peak-tomean ratios of ambient PM2.5
32 The evidence available for these selected health
effect endpoints generally focused on the entire
population, although some information was
available to support analyses that considered
differences in estimated risk for at-risk populations
including older adults and persons with preexisting cardiovascular and respiratory diseases.
33 Variability refers to the heterogeneity of a
variable of interest within a population or across
different populations. Uncertainty refers to the lack
of knowledge regarding the actual values of inputs
to an analysis (U.S. EPA, 2010a, p. 3–63).
34 The extent to which key sources of potential
variability were (or were not) fully captured in the
design of the risk assessment are discussed in
section 3.5.2 of the Risk Assessment (U.S. EPA,
2010a, pp. 3–67 to 3–69).
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
concentrations within individual urban
study areas and the nature of the
rollback approach used to simulate just
meeting the current or alternative
standards). Key sources of potential
variability that were likely to affect
population risks included the following:
(1) Intra-urban variability in ambient
PM2.5 concentrations, including PM2.5
composition; (2) variability in the
patterns of reductions in PM2.5
concentrations associated with different
rollback approaches when simulating
just meeting the current or alternative
standards; (3) co-pollutant exposures;
(4) factors related to demographic and
socioeconomic status; (5) behavioral
differences across urban study areas
(e.g., time spent outdoors); (6) baseline
incidence rates; and (7) longer-term
temporal variability in ambient PM2.5
concentrations reflecting meteorological
trends as well as future changes in the
mix of PM2.5 sources, including changes
in air quality related to future regulatory
actions.
With regard to uncertainties, single
and multi-factor sensitivity analyses
were combined with a qualitative
analysis to assess the impact of potential
sources of uncertainty on the core risk
estimates. Key sources of uncertainty
included: (1) Characterizing intra-urban
population exposure in the context of
epidemiological studies linking PM2.5 to
specific health effects; (2) statistical fit
of the concentration-response functions
for short-term exposure-related health
endpoints; (3) shape of the
concentration-response functions; (4)
specifying the appropriate lag structure
for short-term exposure studies; (5)
transferability of concentration-response
functions from study locations to urban
study area locations for long-term
exposure-related health endpoints; (6)
use of single-city versus multi-city
studies in the derivation of
concentration-response functions; (7)
impact of historical air quality on
estimates of health risk associated with
long-term PM2.5 exposures; and (8)
potential variation in effect estimates
reflecting compositional differences in
PM2.5.
Beyond characterizing uncertainty
and variability, a number of design
elements were included in the risk
assessment to increase the overall
confidence in the risk estimates
generated for the 15 urban study areas
(U.S. EPA, 2011a, pp. 2–38 to 2–41).
These elements included: (1) Use of a
deliberative process for specifying
components of the risk model that
reflects consideration of the latest
research on PM2.5 exposure and risk
(U.S. EPA, 2010a, section 5.1.1); (2)
integration of key sources of variability
PO 00000
Frm 00021
Fmt 4701
Sfmt 4700
3105
into the design as well as the
interpretation of risk estimates (U.S.
EPA, 2010a, section 5.1.2); (3)
assessment of the degree to which the
urban study areas are representative of
areas in the U.S. experiencing higher
PM2.5-related risk (U.S. EPA, 2010a,
section 5.1.3); and (4) identification and
assessment of important sources of
uncertainty and the impact of these
uncertainties on the core risk estimates
(U.S. EPA, 2010a, section 5.1.4).
Further, additional analyses examined
potential bias and overall confidence in
the risk estimates. Greater confidence is
associated with risk estimates based on
simulated annual mean PM2.5
concentrations that are within the
region of the air quality distribution
used in deriving the concentrationresponse functions where the bulk of
the data reside (e.g., within one
standard deviation around the long-term
mean PM2.5 concentration) (U.S. EPA,
2011a, p. 2–38).
Key observations and insights from
the PM2.5 risk assessment, together with
important caveats and limitations, were
discussed in section III.C.3 of the
proposal. In general, in considering the
set of quantitative risk estimates and
related uncertainties and limitations
related to long- and short-term PM2.5
exposure together with consideration of
the health endpoints which could not be
quantified, the Policy Assessment
concluded this information provided
strong evidence that risks estimated to
remain upon simulating just meeting the
current suite of PM2.5 standards are
important from a public health
perspective, both in terms of severity
and magnitude of effects. Patterns of
increasing estimated risk reductions
were generally observed as either the
annual or 24-hour standard level, or
both, were reduced over the ranges
considered in the Risk Assessment.
The magnitude of both long- and
short-term exposure-related risk
estimated to remain upon just meeting
the current suite of standards as well as
alternative standard levels was strongly
associated with the simulated change in
annual mean PM2.5 concentrations.
Although long- and short-term
exposure-related mortality rates have
similar patterns in terms of the subset of
urban study areas experiencing risk
reductions for the current suite of
standard levels, the magnitude of risk
remaining is higher for long-term
exposure-related mortality and
substantially lower for short-term
exposure-related mortality. Short-term
exposure-related morbidity risk
estimates were greater for
cardiovascular-related than respiratoryrelated events and emergency
E:\FR\FM\15JAR2.SGM
15JAR2
3106
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
department visits for asthma-related
events were significant: Furthermore,
most of the aggregate risk associated
with short-term exposures was not
primarily driven by the small number of
days with PM2.5 concentrations in the
upper tail of the air quality distribution,
but rather by the large number of days
with PM2.5 concentrations at and around
the mean of the distribution, that is, the
24-hour average concentrations that are
in the low- to mid-range, well below the
peak 24-hour concentrations (U.S. EPA,
2011a, p. 2–3).
With regard to characterizing
estimates of PM2.5-related risk
associated with simulation of alternative
standards, the Policy Assessment
recognized that greater overall
confidence was associated with
estimates of risk reduction than for
estimates of absolute risk remaining
(U.S. EPA, 2011a, p. 2–94).
Furthermore, the Policy Assessment
recognized that estimates of absolute
risk remaining for each of the alternative
standard levels considered, particularly
in the context of long-term exposurerelated mortality, may be
underestimated.35 In addition, the
Policy Assessment observed that in
considering the overall confidence
associated with the quantitative
analyses, the Risk Assessment
recognized that: (1) Substantial
variability existed in the magnitude of
risk remaining across urban study areas
and (2) in general, higher confidence
was associated with risk estimates based
on PM2.5 concentrations near the mean
PM2.5 concentrations in the underlying
epidemiological studies providing the
concentration-response functions (e.g.,
within one standard deviation of the
mean PM2.5 concentration reported).
Furthermore, although the Risk
Assessment estimated that the
alternative 24-hour standard levels
considered (when controlling) would
result in additional estimated risk
reductions beyond those estimated for
35 Based on the consideration of both the
qualitative and quantitative assessments of
uncertainty, the Risk Assessment concluded that it
is unlikely that the estimated risks are over-stated,
particularly for premature mortality related to longterm PM2.5 exposures. In fact, the Policy
Assessment and the Risk Assessment concluded
that the core risk estimates for this category of
health effects may well be biased low based on
consideration of alternative model specifications
evaluated in the sensitivity analyses (U.S. EPA,
2011a, p. 2–41; U.S. EPA, 2010a, p. 5–16; Figures
4–7 and 4–8). In addition, the Policy Assessment
recognized that the currently available scientific
information included evidence for a broader range
of health endpoints and at-risk populations beyond
those included in the quantitative risk assessment,
including decrements in lung function growth and
respiratory symptoms in children as well as
reproductive and developmental effects (U.S. EPA,
2011a, section 2.2.1).
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
alternative annual standard levels alone,
these additional estimated reductions
were highly variable. Conversely, the
Risk Assessment recognized that
alternative annual standard levels, when
controlling, resulted in more consistent
risk reductions across urban study areas,
thereby potentially providing a more
consistent degree of public health
protection (U.S. EPA, 2010a, p. 5–17).
D. Conclusions on the Adequacy of the
Current Primary PM2.5 Standards
1. Introduction
The initial issue to be addressed in
the current review of the primary PM2.5
standards is whether, in view of the
advances in scientific knowledge and
other information reflected in the
Integrated Science Assessment, the Risk
Assessment, and the Policy Assessment,
the existing standards should be
retained or revised. In considering the
adequacy of the current suite of PM2.5
standards, the Administrator has
considered the large body of evidence
presented and assessed in the Integrated
Science Assessment (U.S. EPA, 2009a),
the quantitative assessment of risks,
staff conclusions and associated
rationales presented in the Policy
Assessment, views expressed by
CASAC, and public comments. The
Administrator has taken into account
both evidence- and risk-based
considerations 36 in developing final
conclusions on the adequacy of the
current primary PM2.5 standards.
a. Evidence- and Risk-based
Considerations in the Policy Assessment
In considering the available
epidemiological evidence in this review,
the Policy Assessment took a broader
approach than was used in the last
review. This approach reflected the
more extensive and stronger body of
evidence available since the last review
on health effects related to both longand short-term exposure to PM2.5. As
discussed in section III.A.3 above, this
broader approach focused on setting the
annual standard as the ‘‘generally
36 Evidence-based considerations include the
assessment of epidemiological, toxicological, and
controlled human exposure studies evaluating longor short-term exposures to PM2.5, with supporting
evidence related to dosimetry and potential
pathways/modes of action, as well as the
integration of evidence across each of these
disciplines, as assessed in the Integrated Science
Assessment (U.S. EPA, 2009a) and focus on the
policy-relevant considerations as discussed in
section III.B above and in the Policy Assessment
(U.S. EPA, 2011a, section 2.2.1). Risk-based
considerations draw from the results of the
quantitative analyses presented in the Risk
Assessment (U.S. EPA, 2010a) and focus on the
policy-relevant considerations as discussed in
section III.C above and in the Policy Assessment
(U.S. EPA, 2011a, section 2.2.2).
PO 00000
Frm 00022
Fmt 4701
Sfmt 4700
controlling’’ standard for lowering both
short- and long-term PM2.5
concentrations and so providing
requisite protection to public health. In
conjunction with such an annual
standard, this approach focused on
setting the 24-hour standard to provide
supplemental protection against days
with high peak PM2.5 concentrations.
In addressing the question whether
the evidence now available in this
review supports consideration of
standards that are more protective than
the current PM2.5 standards, the Policy
Assessment considered whether: (1)
Statistically significant health effects
associations with long- or short-term
exposures to fine particles occur in
areas that would likely have met the
current PM2.5 standards [see American
Trucking Associations, 283 F. 3d at 369,
376 (revision of level of PM NAAQS
justified when health effects are
observed in areas meeting the existing
standard)], and (2) associations with
long-term exposures to fine particles
extend down to lower air quality
concentrations than had previously
been observed. With regard to
associations observed in long-term PM2.5
exposure studies, the Policy Assessment
recognized that extended follow-up
analyses of the ACS and Harvard Six
Cities studies provided consistent and
stronger evidence of an association with
mortality at lower air quality
distributions than had previously been
observed (U.S. EPA, 2011a, pp. 2–31 to
2–32). The original and reanalysis of the
ACS study reported positive and
statistically significant effects associated
with a long-term mean PM2.5
concentration of 18.2 mg/m3 across 50
metropolitan areas for 1979 to 1983
(Pope et al., 1995; Krewski et al.,
2000).37 In extended analyses, positive
and statistically significant effects of
approximately similar magnitude were
associated with declining PM2.5
concentrations, from an aggregate longterm mean in 58 metropolitan areas of
21.2 mg/m3 in the original monitoring
period (1979 to 1983) to 14.0 mg/m3 for
116 metropolitan areas in the most
recent years evaluated (1999–2000),
with an overall average across the two
study periods in 51 metropolitan areas
of 17.7 mg/m3 (Pope et al., 2002;
Krewski et al., 2009). With regard to the
Harvard Six Cities Study, the original
and reanalysis reported positive and
statistically significant effects associated
37 The study periods referred to in the Policy
Assessment (U.S. EPA, 2011a) and in this final rule
reflect the years of air quality data that were
included in the analyses, whereas the study periods
identified in the Integrated Science Assessment
(U.S. EPA, 2009a) reflect the years of health event
data that were included.
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
with a long-term mean PM2.5
concentration of 18.0 mg/m3 for 1980 to
1985 (Dockery et al., 1993; Krewski et
al., 2000). In an extended follow-up of
this study, the aggregate long-term mean
concentration across all years evaluated
was 16.4 mg/m3 for 1980 to 1988 38
(Laden et al., 2006). In an additional
analysis of the extended follow-up of
the Harvard Six Cities study,
investigators reported that the
concentration-response relationship was
linear and ‘‘clearly continuing below the
level’’ of the current annual standard
(U.S. EPA, 2009a, p. 7–92; Schwartz et
al., 2008).
Cohort studies conducted since the
last review provided additional
evidence of mortality associated with air
quality distributions that are generally
lower than those reported in the ACS
and Harvard Six Cities studies, with
effect estimates that were similar or, in
some studies, significantly greater in
magnitude than in the ACS and Harvard
Six Cities studies (see also, section
III.D.1.a of the proposal, 77 FR 38918 to
28919; U.S. EPA, 2011a, pp. 2–32 to 2–
33). The Women’s Health Initiative
(WHI) study reported positive and most
often statistically significant
associations between long-term PM2.5
exposure and cardiovascular-related
mortality as well as morbidity effects,
with much larger relative risk estimates
for mortality than in the ACS and
Harvard Six Cities studies, at an
aggregate long-term mean PM2.5
concentration of 12.9 mg/m3 for 2000
(Miller et al., 2007).39
Using the Medicare cohort, Eftim et
al. (2008) reported somewhat higher
effect estimates than in the ACS and
Harvard Six Cities studies with
aggregate long-term mean
concentrations of 13.6 mg/m3 and 14.1
mg/m3, respectively, for 2000 to 2002.
Zeger et al. (2008) reported associations
between long-term PM2.5 exposure and
mortality for the eastern region of the
U.S. at an aggregated long-term PM2.5
median concentration of 14.0 mg/m3,
although no association was reported for
the western region with an aggregate
long-term PM2.5 median concentration
38 Aggregate mean concentration provided by
study author (personal communication from Dr.
Francine Laden, 2009).
39 The Policy Assessment noted that in
comparison to other long-term exposure studies, the
Miller et al. (2007) study was more limited in that
it was based on only one year of air quality data
(U.S. EPA, 2011a, p. 2–82). The proposal further
noted that the air quality data considered were
extrapolated from that one single year of air quality
data (2000) to the whole study, and that the air
quality data post-dated the years of health events
considered (i.e., 1994 to 1998) (77 FR 38918, fn 62).
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
of 13.1 mg/m3 (U.S. EPA, 2009a, p. 7–
88).40
Premature mortality in children
reported in a national infant mortality
study as well as mortality in a cystic
fibrosis cohort including both children
and adults reported positive but
statistically nonsignificant effects
associated with long-term aggregate
mean concentrations of 14.8 mg/m3 and
13.7 mg/m3, respectively (Woodruff et
al., 2008; Goss et al., 2004).
With respect to respiratory morbidity
effects associated with long-term PM2.5
exposure, the across-city mean of 2week average PM2.5 concentrations
reported in the initial Southern
California Children’s Health Study was
approximately 15.1 mg/m3 (Peters et al.,
1999). These results were found to be
consistent with results of cross-sectional
analyses of the 24-Cities Study (Dockery
et al., 1996; Raizenne et al., 1996),
which reported a long-term cross-city
mean PM2.5 concentration of 14.5 mg/
m3.41 In this review, extended analyses
of the Southern California Children’s
Health Study provide stronger evidence
of PM2.5-related respiratory effects, at
lower air quality concentrations than
had previously been reported, with a
four-year aggregate mean concentration
of 13.8 mg/m3 across the 12 study
communities (McConnell et al., 2003;
Gauderman et al., 2004, U.S. EPA,
2009a, Figure 7–4).
In also considering health effects for
which the Integrated Science
Assessment concluded evidence was
suggestive of a causal relationship, the
Policy Assessment noted a limited
number of birth outcome studies that
reported positive and statistically
significant effects related to aggregate
long-term mean PM2.5 concentrations
down to approximately 12 mg/m3 (U.S.
EPA, 2011a, p. 2–33).
Collectively, the Policy Assessment
concluded that currently available
evidence provided support for
associations between long-term PM2.5
exposure and mortality and morbidity
effects that extend to distributions of
PM2.5 concentrations that are lower than
40 Zeger et al. (2008) also reported positive and
statistically significant effects for the central region,
with an aggregate long-term mean PM2.5
concentration of 10.7 mg/m3. However, in contrast
to the eastern and western risk estimates, the
central risk estimate increased with adjustment for
COPD (used as a proxy for smoking status). Due to
the potential for confounding bias influencing the
risk estimate for the central region, the Policy
Assessment did not focus on the results reported in
the central region to inform the adequacy of the
current suite of standards or alternative annual
standard levels (U.S. EPA, 2011a, p. 2–32).
41 See American Farm Bureau Federation v. EPA,
559 F. 3d at 525 (noting the importance of these
studies, as well as EPA’s failure to properly take
them into account).
PO 00000
Frm 00023
Fmt 4701
Sfmt 4700
3107
those that had previously been
associated with such effects, with
aggregate long-term mean PM2.5
concentrations extending to well below
the level of the current annual standard.
The Policy Assessment also
considered the long-term mean PM2.5
concentrations in short-term exposure
studies in assessing the appropriateness
of the level of the current annual
standard. See American Farm Bureau
Federation v. EPA, 559 F. 3d at 522,
523–24 (remanding 2006 standard
because the EPA had not adequately
explained its choice not to consider
long-term means of short-term exposure
studies in assessing adequacy of
primary annual PM2.5 standard). In light
of the mixed findings reported in singlecity, short-term exposure studies, the
Policy Assessment placed
comparatively greater weight on the
results from multi-city studies in
considering the adequacy of the current
suite of standards (U.S. EPA, 2011a, pp.
2–34 to 2–35).
With regard to associations reported
in short-term PM2.5 exposure studies,
the Policy Assessment recognized that
long-term mean concentrations reported
in new multi-city U.S. and Canadian
studies provided evidence of
associations between short-term PM2.5
exposure and mortality at similar air
quality distributions to those that had
previously been observed in an 8-cities
Canadian study (Burnett and Goldberg,
2003; aggregate long-term mean PM2.5
concentration of 13.3 mg/m3). In a multicity time-series analysis of 112 U.S.
cities, Zanobetti and Schwartz (2009)
reported a positive and statistically
significant association with all-cause,
cardiovascular-related (e.g., heart
attacks, stroke), and respiratory-related
mortality and short-term PM2.5
exposure, in which the aggregate longterm mean PM2.5 concentration was 13.2
mg/m3 (U.S. EPA, 2009a, Figure 6–24).
Furthermore, city-specific effect
estimates indicated the association
between short-term exposure to PM2.5
and total mortality and cardiovascularand respiratory-related mortality was
consistently positive for an
overwhelming majority (99 percent) of
the 112 cities across a wide range of air
quality concentrations (long-term mean
concentrations ranging from 6.6 mg/m3
to 24.7 mg/m3; U.S. EPA, 2009a, Figure
6–24, p. 6–178 to 179). The EPA staff
noted that for all-cause mortality, cityspecific effect estimates were
statistically significant for 55 percent of
the 112 cities, with long-term city-mean
PM2.5 concentrations ranging from 7.8
mg/m3 to 18.7 mg/m3 and 24-hour PM2.5
city-mean 98th percentile
concentrations ranging from 18.4 to 64.9
E:\FR\FM\15JAR2.SGM
15JAR2
3108
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
mg/m3 (personal communication with
Dr. Antonella Zanobetti, 2009).42
With regard to cardiovascular and
respiratory morbidity effects, in the first
analysis of the Medicare cohort
conducted by Dominici et al. (2006a)
across 204 U.S. counties, investigators
reported a statistically significant
association with hospitalizations for
cardiovascular and respiratory diseases
and short-term PM2.5 exposure, in which
the aggregate long-term mean PM2.5
concentration was 13.4 mg/m3.
Furthermore, a sub-analysis restricted to
days with 24-hour average
concentrations of PM2.5 at or below 35
mg/m3 indicated that, in spite of a
reduced statistical power from a smaller
number of study days, statistically
significant associations were still
observed between short-term exposure
to PM2.5 and hospital admissions for
cardiovascular and respiratory diseases
(Dominici, 2006b).43 In an extended
analysis of this cohort, Bell et al. (2008)
reported a positive and statistically
significant increase in cardiovascular
hospitalizations associated with shortterm PM2.5 exposure, in which the
aggregate long-term mean PM2.5
concentration was 12.9 mg/m3. These
results, along with the observation that
approximately 50 percent of the 204
county-specific mean 98th percentile
PM2.5 concentrations in the study
aggregated across all years were below
the 24-hour standard of 35 mg/m3, not
only indicated that effects are occurring
in areas that would meet the current
standards but also suggested that the
overall health effects observed across
the U.S. are not primarily driven by the
higher end of the PM2.5 air quality
distribution (Bell, 2009a, personal
communication from Dr. Michelle Bell
regarding air quality data for Bell et al.,
2008 and Dominici et al., 2006a).
Collectively, the Policy Assessment
concluded that the findings from shortterm PM2.5 exposure studies provided
evidence of PM2.5-associated health
effects occurring in areas that would
likely have met the current suite of
42 Single-city Bayes-adjusted effect estimates for
the 112 cities analyzed in Zanobetti and Schwartz
(2009) were provided by the study authors
(personal communication with Dr. Antonella
Zanobetti, 2009; see also U.S. EPA, 2009a, Figure
6–24).
43 This sub-analysis was not included in the
original publication (Dominici et al., 2006a). The
study authors provided sub-analysis results for the
Administrator’s consideration as a letter to the
docket following publication of the proposed rule
in January 2006 (personal communication with Dr.
Francesca Dominici, 2006b). As noted in section
III.A.3, this study is part of the basis for the
conclusion that there is no evidence suggesting that
risks associated with long-term exposures are likely
to be disproportionately driven by peak 24-hour
concentrations.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
PM2.5 standards (U.S. EPA, 2011a, p. 2–
35). These findings were further
bolstered by evidence of statistically
significant PM2.5-related health effects
occurring in analyses restricted to days
in which 24-hour average PM2.5
concentrations were below 35 mg/m3
(Dominici, 2006b).
In evaluating the currently available
scientific evidence, as summarized in
section III.B of the proposal, the Policy
Assessment first concluded that there
was stronger and more consistent and
coherent support for associations
between long- and short-term PM2.5
exposures and a broad range of health
outcomes than was available in the last
review, providing the basis for fine
particle standards at least as protective
as the current PM2.5 standards (U.S.
EPA, 2011a, p. 2–26). Having reached
this initial conclusion, the Policy
Assessment addressed the question of
whether the available evidence
supported consideration of standards
that were more protective than the
current standards. In so doing, the
Policy Assessment considered whether
there was now evidence that health
effect associations have been observed
in areas that likely met the current suite
of PM2.5 standards. As discussed above,
long- and short-term PM2.5 exposure
studies provided evidence of
associations with mortality and
cardiovascular and respiratory effects
both at lower ambient PM2.5
concentrations than had been observed
in the previous review and at
concentrations allowed by the current
standards (U.S. EPA, 2011a, p. 2–35).
In reviewing this information, the
Policy Assessment recognized that
important limitations and uncertainties
associated with this expanded body of
scientific evidence, as discussed in
section III.B.2 of the proposal, needed to
be carefully considered in determining
the weight to be placed on the body of
studies available in this review. Taking
these limitations and uncertainties into
consideration, the Policy Assessment
concluded that the currently available
evidence clearly calls into question
whether the current suite of primary
PM2.5 standards protects public health
with an adequate margin of safety from
effects associated with long- and shortterm exposures. Furthermore, the Policy
Assessment concluded this evidence
provides strong support for considering
fine particle standards that would afford
increased protection beyond that
afforded by the current standards (U.S.
EPA, 2011a, p. 2–35).
In addition to evidence-based
consideration, the Policy Assessment
also considered the extent to which
health risks estimated to occur upon
PO 00000
Frm 00024
Fmt 4701
Sfmt 4700
simulating just meeting the current
PM2.5 standards may be judged to be
important from a public health
perspective, taking into account key
uncertainties associated with the
quantitative health risk estimates. In so
doing, the Policy Assessment first noted
that the quantitative risk assessment
addresses: (1) The core PM2.5-related
risk estimates; (2) the related
uncertainty and sensitivity analyses,
including additional sets of reasonable
risk estimates generated to supplement
the core analysis; (3) an assessment of
the representativeness of the urban
study areas within a national context; 44
and (4) consideration of patterns in
design values and air quality monitoring
data to inform interpretation of the risk
estimates, as discussed in section III.C
above.
In considering the health risks
estimated to remain upon simulation of
just meeting the current suite of
standards and considering both the
qualitative and quantitative assessment
of uncertainty completed as part of the
assessment, the Policy Assessment
concluded these risks are important
from a public health standpoint and
provided strong support for
consideration of alternative standards
that would provide increased protection
beyond that afforded by the current
PM2.5 (U.S. EPA, 2011a, pp. 2–47 to 2–
48). This conclusion reflected
consideration of both the severity and
the magnitude of the effects. For
example, the Risk Assessment indicated
the possibility that premature deaths
related to ischemic heart disease
associated with long-term PM2.5
exposure alone would likely be on the
order of thousands of deaths per year in
the 15 urban study areas upon
simulating just meeting the current
standards 45 (U.S. EPA, 2011a, pp. 2–46
to 2–47). Moreover, additional risks
were anticipated for premature
mortality related to cardiopulmonary
effects and lung cancer associated with
long-term PM2.5 exposure as well as
mortality and cardiovascular- and
respiratory-related morbidity effects
(e.g., hospital admissions, emergency
department visits) associated with shortterm PM2.5 exposures. Based on the
consideration of both qualitative and
44 Based on analyses of the representativeness of
the 15 urban study areas in the broader national
context, the Policy Assessment concludes that these
study areas are generally representative of urban
areas in the U.S. likely to experience relatively
elevated levels of risk related to ambient PM2.5
exposures (U.S. EPA, 2011a, p. 2–42).
45 Premature mortality for all causes attributed to
PM2.5 exposure was estimated to be on the order of
tens of thousands of deaths per year on a national
scale based on 2005 air quality data (U.S. EPA,
2010a, Appendix G, Table G–1).
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
quantitative assessments of uncertainty
completed as part of the quantitative
risk assessment, the Risk Assessment
concluded that it was unlikely that the
estimated risks are over-stated,
particularly for mortality related to longterm PM2.5 exposure, and may well be
biased low based on consideration of
alternative model specifications
evaluated in the sensitivity analyses
(U.S. EPA, 2010a, p. 5–16; U.S. EPA,
2011a, p. 2–41). Furthermore, the
currently available scientific
information summarized in section III.B
of the proposal provided evidence for a
broader range of health endpoints and
at-risk populations beyond those
included in the quantitative risk
assessment (U.S. EPA, 2011a, p. 2–47).
b. CASAC Advice
The CASAC, based on its review of
drafts of the Integrated Science
Assessment, the Risk Assessment, and
the Policy Assessment, provided an
array of advice both with regard to
interpreting the scientific evidence and
quantitative risk assessment, as well as
with regard to consideration of the
adequacy of the current PM2.5 standards
(Samet, 2009a,b,c,d,e,f; Samet
2010a,b,c,d). With regard to the
adequacy of the current standards,
CASAC concluded that the ‘‘currently
available information clearly calls into
question the adequacy of the current
standards’’ (Samet, 2010d, p. i) and that
the current standards are ‘‘not
protective’’ (Samet, 2010d, p. 1).
Further, in commenting on the first draft
Policy Assessment, CASAC noted:
tkelley on DSK3SPTVN1PROD with
With regard to the integration of evidencebased and risk-based considerations, CASAC
concurs with EPA’s conclusion that the new
data strengthens the evidence available on
associations previously considered in the last
round of the assessment of the PM2.5
standard. CASAC also agrees that there are
significant public health consequences at the
current levels of the standard that justify
consideration of lowering the PM2.5 NAAQS
further (Samet, 2010c, p. 12).
c. Administrator’s Proposed Conclusions
Concerning the Adequacy of the Current
Primary PM2.5 Standards
At the time of the proposal, in
considering the body of scientific
evidence, the Administrator concluded
there was stronger and more consistent
and coherent support for associations
between long- and short-term PM2.5
exposure and a broader range of health
outcomes than was available in the last
review, providing the basis for fine
particle standards at least as protective
as the current PM2.5 standards. In
particular, the Administrator recognized
in section III.D.4 of the proposal that the
Integrated Science Assessment
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
concluded that the results of
epidemiological and experimental
studies form a plausible and coherent
data set that supports a causal
relationship between long- and shortterm PM2.5 exposures and mortality and
cardiovascular effects and a likely
causal relationship between long- and
short-term PM2.5 exposures and
respiratory effects. Furthermore, the
Administrator reflected that effects had
been observed at lower ambient PM2.5
concentrations than what had been
observed in the last review, including at
ambient PM2.5 concentrations in areas
that likely met the current PM2.5
NAAQS. With regard to the results of
the quantitative risk assessment, the
Administrator noted that the Risk
Assessment concluded that the risks
estimated to remain upon simulation of
just meeting the current standards were
important from a public health
standpoint in terms of both the severity
and magnitude of the effects.
At the time of the proposal, in
considering whether the current suite of
PM2.5 standards should be revised to
provide requisite public health
protection, the Administrator carefully
considered the staff conclusions and
rationales presented in the Policy
Assessment, the advice and
recommendations from CASAC, and
public comments to date on this issue.
In so doing, the Administrator placed
primary consideration on the evidence
obtained from the epidemiological
studies and provisionally found the
evidence of serious health effects
reported in long- and short-term
exposure studies conducted in areas
that would have met the current
standards to be compelling, especially
in light of the extent to which such
studies are part of an overall pattern of
positive and frequently statistically
significant associations across a broad
range of studies that collectively
represent a strong and robust body of
evidence.
As discussed in the Integrated Science
Assessment and Policy Assessment, the
Administrator recognized that much
progress has been made since the last
review in addressing some of the key
uncertainties that were important
considerations in establishing the
current suite of PM2.5 standards. For
example, progress made since the last
review provides increased confidence in
the long- and short-term exposure
studies as a basis for considering
whether any revision of the annual
standard is appropriate and increased
confidence in the short-term exposure
studies as a basis for considering
PO 00000
Frm 00025
Fmt 4701
Sfmt 4700
3109
whether any revision of the 24-hour
standard is appropriate.46
Based on her consideration of these
conclusions, as well as consideration of
CASAC’s conclusion that the evidence
and risk assessment clearly called into
question the adequacy of the public
health protection provided by the
current PM2.5 NAAQS and public
comments on the proposal, the
Administrator provisionally concluded
that the current primary PM2.5
standards, taken together, were not
requisite to protect public health with
an adequate margin of safety and that
revision was needed to provide
increased public health protection. The
Administrator provisionally concluded
that the scientific evidence and
information on risk provided strong
support for consideration of alternative
standards that would provide increased
public health protection beyond that
afforded by the current PM2.5 standards.
2. Comments on the Need for Revision
This section addresses general
comments based on relevant facts that
either support or oppose any change to
the current suite of primary PM2.5
standards. Comments on specific longand short-term exposure studies that
relate to consideration of the
appropriate levels of the annual and 24hour standards are addressed in section
III.E.4 below. Many public comments
asserted that the current PM2.5 standards
are insufficient to protect public health
with an adequate margin of safety and
that revisions to the standards are
therefore appropriate, indeed
necessitated.
Among those calling for revisions to
the current standards were the
Children’s Health Protection Advisory
Committee (CHPAC); major medical and
public health groups including the
American Heart Association (AHA),
American Lung Association (ALA),
American Public Health Association
(APHA), American Thoracic Society
(ATS); the Physicians for Social
Responsibility (PSR); major
environmental groups such as the Clean
Air Council, Clean Air Task Force,
Earthjustice, Environmental Defense
Fund (EDF), National Resources Defense
Council (NRDC), and Sierra Club; many
environmental justice organizations as
46 The EPA notes that this increased confidence
in the long- and short-term associations generally
reflects less uncertainty as to the likely causal
nature of such associations, but does not address
directly the question of the extent to which such
associations remain toward the lower end of the
range of ambient PM2.5 concentrations. This
question is central to the Agency’s evaluation of the
relevant evidence to determine appropriate
standards levels, as discussed below in section
III.E.4.
E:\FR\FM\15JAR2.SGM
15JAR2
3110
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
well as medical doctors, academic
researchers, health professionals, and
many private citizens. For example, the
American Heart Association and other
major national public health and
medical organizations stated that, ‘‘[o]ur
organizations are keenly aware of the
public health and medical threats from
particulate matter’’ and called on the
EPA to ‘‘significantly strengthen’’ both
the annual and 24-hour PM2.5 standards
‘‘to help us protect the health of our
patients and our nation’’ (AHA et al.,
2012, pp. 1 and 13). AHA et al. and ALA
et al., as well as a group of more than
350 physicians, environmental health
researchers, and public health and
medical professionals articulated
similar comments on the available
evidence:
tkelley on DSK3SPTVN1PROD with
Ample scientific evidence supports
adopting tighter standards to protect the
health of people who are most susceptible to
the serious health effects of these pollutants.
More than 10,000 peer-reviewed scientific
studies have been published since 1997
when EPA adopted the current annual
standard. These studies validate and extend
earlier epidemiologic research linking both
acute and chronic fine particle pollution with
serious morbidity and mortality. The newer
research has also expanded our
understanding of the range of health
outcomes associated with PM and has
identified adverse respiratory and
cardiovascular health effects at lower
exposure levels than previously reported. As
discussed and interpreted in the EPA’s 2009
Integrated Science Assessment for Particulate
Matter, the new evidence reinforces already
strong existing studies and supports the
conclusion that PM2.5 is causally associated
with numerous adverse health effects in
humans at exposure levels far below the
current standard. Such a conclusion
demands prompt action to protect human
health. (AHA et al., 2012, pp. 1 to 2; ALA et
al., pp. 4 to 5; similar comment submitted by
Rom et al., 2012, p. 1).
All of these medical and public health
commenters stated that the current
PM2.5 standards need to be revised, and
that even more protective standards
than those proposed by the EPA are
needed to adequately protect public
health, particularly for at-risk
populations. Many environmental
justice organizations and individual
commenters also expressed such views.
The National Association of Clean Air
Agencies (NACAA), the Northeast States
for Coordinated Air Use Management
(NESCAUM), and many State and local
air agencies and health departments
who commented on the PM2.5 standards
supported revision of the suite of
current PM2.5 standards, as did five state
attorneys general (Schneiderman et al.,
2012) and the National Tribal Air
Association (NTAA).
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
These commenters based their views
chiefly on the body of evidence and
technical analyses presented and
discussed in the Integrated Science
Assessment, the Risk Assessment, and
the Policy Assessment finding the
available scientific information to be
stronger and more compelling than in
the last review. These commenters
generally placed much weight on
CASAC’s recommendation to revise the
PM2.5 standards to provide increased
public health protection and on the EPA
staff conclusions presented in the final
Policy Assessment.
Some of these commenters
specifically mentioned extended
analyses of seminal long-term exposure
studies—the ACS (Krewski et al., 2009),
Harvard Six Cities (Laden et al., 2006),
and Southern California Children’s
Health (Gauderman et al., 2004) studies.
These commenters also highlighted the
availability of additional long-term
exposure studies in this review,
specifically a study of premature
mortality in older adults (Eftim et al.,
2008) and the WHI study of
cardiovascular morbidity and mortality
effects in women (Miller et al., 2007)
providing stronger evidence of mortality
and morbidity effects associated with
long-term PM2.5 exposures at lower
concentrations than had previously
been observed, including studies of
effects in at-risk populations. For
example, some commenters asserted:
Evidence during the last review showed
clearly that the annual average standard
needed to be much lower than the standard
of 15 mg/m3 that was first set in 1997. The
evidence has only grown since then.
Multiple, multi-city studies over long periods
of time have shown clear evidence of
premature death, cardiovascular and
respiratory harm as well as reproductive and
developmental harm at contemporary
concentrations far below the level of the
current (annual) standard (ALA et al., 2012,
p. 39; AHA et al., 2012, p. 10).
These commenters also highlighted
the availability of a number of shortterm PM2.5 exposure studies as
providing evidence of mortality and
morbidity effects at concentrations
below the level of the current 24-hour
PM2.5 standard. Specifically, these
commenters made note of multi-city
studies of premature mortality
(Zanobetti and Schwartz, 2009) and
increased hospitalizations for
cardiovascular and respiratory-related
effects in older adults (Bell et al., 2008).
These commenters also asserted the
importance of many of the single-city
studies, arguing that these studies
‘‘provide valuable information regarding
impacts on susceptible populations and
on health risk in areas with high peak
PO 00000
Frm 00026
Fmt 4701
Sfmt 4700
to mean concentration ratios’’ (ALA, et
al., 2012, p. 65). Collectively,
considering the multi- and single-city
short-term exposure studies, these
commenters asserted ‘‘the record clearly
supports a more stringent 24-hour
standard of 25 mg/m3 to provide uniform
protection in all regions of the country
particularly from short-term spikes in
pollution and from the sub-daily
exposures that trigger heart attacks and
strokes’’ (ALA et al., 2012, p. 62). A
group of more than 350 physicians,
environmental health researchers, and
public health and medical professionals
argued, ‘‘[s]tudies of short-term
exposure demonstrate that PM2.5 air
pollution increases the risk of hospital
admissions for heart and lung problems
even when you exclude days with
pollution concentrations at or above the
current daily standard of 35 mg/m3.
Daily concentrations must be capped at
lower levels to protect against peak
exposure days that occur due to local
and seasonal sources of emissions’’
(Rom et al., 2012, p. 2).
In addition, many of these
commenters generally concluded that
progress had been made in reducing
many of the uncertainties identified in
the last review, in better understanding
mechanisms by which PM2.5 may be
causing the observed health effects, and
in improving our understanding of atrisk populations. Further, a number of
commenters argued that by making the
standards more protective, the PM2.5
NAAQS would be more consistent with
other existing standards (e.g.,
California’s annual average standard of
12 mg/m3) (CARB, 2012; CA OEHHA,
2012). Other commenters argued that
revising the primary PM2.5 standards
would be more consistent with the
recommendations of the World Health
Organization (WHO) and/or Canada
(e.g., ALA et al., 2012, p. 62; ISEE, 2012,
p. 2; MOE-Ontario, 2012, p. 1).
With regard to the scope of the
literature reviewed for PM2.5-related
health effects, some commenters
asserted that the EPA inappropriately
narrowed the scope of the review by
excluding a number of categories of
relevant studies, specifically related to
studies of diesel pollution and trafficrelated pollution (ALA, et al., 2012, p.
17). These commenters argued that,
based upon the exclusion of these types
of studies, the Integrated Science
Assessment ‘‘came to the erroneous
conclusion that the causal relationship
between PM and cancer is merely
suggestive. This conclusion does not
square with the International Agency
Research on Cancer (IARC) finding that
diesel emissions are a known human
carcinogen nor with the conclusions of
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
the extended analyses of the [Harvard]
Six Cities and ACS cohort studies that
report positive and statistically
significant associations between PM2.5
and lung cancer.’’ Id.
Some of these commenters also noted
the results of the EPA’s quantitative risk
assessment, concluding that it showed
that the risks estimated to remain when
the current standards are met are large
and important from a public health
perspective and warrant increased
protection. For example, ALA et al.,
noted that the Risk Assessment
indicated the quantitative risk analyses
likely underestimated PM2.5-related
mortality (U.S. EPA, 2010a, p. 5–16) and
argued that ‘‘the measurements of risk
should be treated conservatively’’ (ALA,
et al., 2012, p. 73). These commenters
also summarized an expanded analysis
of alternative PM2.5 standard levels that
they argued documented the need for
more protective standards (McCubbin,
2011).
In general, all of these commenters
agreed on the importance of results from
the large body of scientific studies
reviewed in the Integrated Science
Assessment and on the need to revise
the suite of PM2.5 standards as
articulated in the EPA’s proposal, while
generally differing with the EPA’s
proposed judgments about the extent to
which the standards should be revised
based on this evidence, specifically for
providing protection for at-risk
populations.
The EPA generally agrees with these
commenters’ conclusion regarding the
need to revise the current suite of PM2.5
standards. The scientific evidence noted
by these commenters was generally the
same as that assessed in the Integrated
Science Assessment and the Policy
Assessment, and the EPA agrees that
this evidence provides a strong basis for
concluding that the current PM2.5
standards, taken together, are not
requisite to protect public health with
an adequate margin of safety, and they
need to be revised to provide increased
protection. For reasons discussed in
section III.E.4.c below, however, the
EPA disagrees with aspects of these
commenters’ views on the level of
protection that is appropriate.
The EPA disagrees with these
commenters’ views that diesel exhaust
studies were excluded from the
Integrated Science Assessment and were
not considered when making the
causality determination for cancer,
mutagenicity, and genotoxicity. As
discussed in section 7.5 of the
Integrated Science Assessment, diesel
exhaust studies were integrated within
the broader body of scientific evidence
that was considered in reaching the
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
causality determination for these health
endpoints. Additionally, as discussed in
section 1.5.3 of the Integrated Science
Assessment, the evidence from diesel
exhaust studies was also considered as
part of the collective evidence evaluated
when making determinations for other,
noncancer health outcomes (e.g.,
cardiovascular and respiratory
effects).47 Specifically, when evaluating
this evidence, the focus was on
understanding the effects of diesel
exhaust particles.
It is important to recognize that the
Integrated Science Assessment focused
on experimental studies of diesel
exhaust that evaluated exposures that
were relevant to ambient
concentrations, i.e., ‘‘within one or two
orders of magnitude of ambient PM
concentrations’’ (U.S. EPA, 2009a,
section 1.3). The causal determination
for cancer, mutagenicity, and
genotoxicity presented in the Integrated
Science Assessment represents an
integration of experimental and
observational evidence of exposures to
ambient PM concentrations. The EPA
fully considered the findings of studies
that assessed these and other health
effects associated with exposure to
diesel particles in reaching causality
determinations regarding health
outcomes associated with PM2.5
exposures. Furthermore, CASAC
supported the EPA’s change to the
causal determination for cancer and
long-term PM2.5 concentrations from
‘‘inadequate’’ to ‘‘suggestive’’ (Samet,
2009f, p. 2).
With regard to traffic studies, the EPA
disagrees with the commenters’ views
that traffic studies that focused on
exposure indicators such as distance to
roadways should have been included in
the Integrated Science Assessment.
These studies were excluded from
consideration because they did not
measure ambient concentrations of
specific air pollutants, including PM2.5,
but instead were studies evaluating
exposure to the undifferentiated ‘‘traffic
related air pollution’’ mixture (ALA et
al., 2012, p. 17) (U.S. EPA, 2009a,
section 1.3). As a result, these studies do
not add to the collective body of
47 In developing the second draft Integrated
Science Assessment, the EPA reexamined the
controlled human exposure and toxicological
studies of fresh diesel and gasoline exhaust. This
information, in addition to other considerations,
supported a change in the causal determinations for
ultrafine particles. Specifically, in reevaluating the
causal determinations for short-term ultrafine
particle exposures and cardiovascular and
respiratory effects, the EPA changed the
classification from ‘‘inadequate’’ to ‘‘suggestive’’ for
both categories of health outcomes (Vandenberg,
2009, p. 3). CASAC agreed with the EPA’s rationale
for revising these causal determinations (Samet,
2009f, p. 10).
PO 00000
Frm 00027
Fmt 4701
Sfmt 4700
3111
evidence on the relationship between
long- or short-term exposure to ambient
concentrations of PM2.5 and health
effects.
Some of these commenters also
identified ‘‘new’’ studies that were not
included in the Integrated Science
Assessment as providing further support
for the need to revise the primary PM2.5
standards. As discussed in section II.B.3
above, the EPA notes that, as in past
NAAQS reviews, the Agency is basing
the final decisions in this review on the
studies and related information
included in the PM air quality criteria
that have undergone CASAC and public
review and will consider the ‘‘new’’
studies for purposes of decision making
in the next PM NAAQS review.
Nonetheless, in provisionally evaluating
commenters’ arguments (see Response
to Comments document), the EPA notes
that its provisional assessment of ‘‘new’’
science found that such studies did not
materially change the conclusions in the
Integrated Science Assessment (U.S.
EPA, 2012b).
Another group of commenters
opposed revising the current PM2.5
standards. These views were most
extensively presented in comments from
the Utility Air Regulatory Group
(UARG), representing a group of electric
generating companies and organizations
and several national trade associations;
the American Petroleum Institute (API)
representing more than 500 oil and
natural gas companies; the National
Association of Manufacturers (NAM),
the American Chemistry Council (ACC),
the American Fuel & Petroleum
Manufacturers (AFPM), the Alliance of
Automobile Manufacturers (AAM), and
other manufacturing associations; the
Electric Power Research Institute (EPRI);
and the Texas Commission on
Environmental Quality (Texas CEQ).
These commenters generally mentioned
many of the same studies that were
cited by the commenters who supported
revising the standards, as well as other
studies, but highlighted different
aspects of these studies in reaching
substantially different conclusions
about their strength and the extent to
which progress has been made in
reducing uncertainties in the evidence
since the last review. Furthermore, they
asserted that the evidence that has
become available since the last review
does not establish a more certain risk or
a risk of effects that are significantly
different in character to those that
provided a basis for the current
standards, nor does the evidence
demonstrate that the risk to public
health upon attainment of the current
standards would be greater than was
E:\FR\FM\15JAR2.SGM
15JAR2
3112
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
understood when the EPA established
the current standards in 2006.
These commenters generally
expressed the view that the current
standards provide the requisite degree
of public health protection. In
supporting their view, these
commenters generally argued that the
EPA’s conclusions are inconsistent with
the current state of the science and
questioned the underlying scientific
evidence including the causal
determinations reached in the Integrated
Science Assessment. More specifically,
this group of commenters argued that:
(1) The EPA did not apply its framework
for causal determination consistently
across studies or health outcomes and,
in the process, the EPA relied on a
selective group of long- and short-term
exposure studies to reach conclusions
regarding causality; (2) toxicological and
controlled human exposure studies do
not provide supportive evidence that
the health effects observed in
epidemiological studies are biologically
plausible; (3) uncertainties in the
underlying health science are as great or
greater than in 2006; (4) there is no
evidence of greater risk since the last
review to justify tightening the current
annual PM2.5 standard; and (5) ‘‘new’’
studies not included in the Integrated
Science Assessment continue to
increase uncertainty about possible
health risks associated with exposure to
PM2.5. These comments are discussed in
turn below.
(l) Some of these commenters asserted
that the EPA did not apply its
framework for causal determinations
consistently across studies or health
outcomes (e.g., ACC, 2012, Attachment
A, pp. 1 to 2; API, 2012, Attachment 1,
p. 30; NAM et al., 2012, pp. 22 to 25;
Texas CEQ, 2012, pp 2 to 3).48 These
commenters argued that the EPA
downplayed epidemiological studies
with null or inconsistent results,
inappropriately used the Hill criteria
when evaluating the epidemiological
evidence, and used the same study and
the same underlying database to
conclude that there was a causal
association between mortality and
multiple criteria pollutants.
The EPA disagrees with these
commenters’ views. First, the EPA
recognizes that the evaluation of the
scientific evidence and its application of
the causal framework used in the
48 The EPA notes that the same concerns about
the causal determinations presented in the
Integrated Science Assessment were raised in
comments to CASAC on the draft Integrated Science
Assessments (e.g., UARG, 2009; API, 2009; ACC,
2012, Appendix B). CASAC, therefore, had the
opportunity to consider these comments in reaching
consensus conclusions on this issue.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
current PM NAAQS review was the
subject of exhaustive and detailed
review by CASAC and the public. As
summarized in section II.B.3 above,
prior to finalizing the Integrated Science
Assessment, two drafts were released for
CASAC and public review to evaluate
the scientific integrity of the documents.
Evidence related to the substantive
issues raised by CASAC and public
commenters with regard to the content
of the first and second draft Integrated
Science Assessments were discussed at
length during these public CASAC
meetings and considered in developing
the final Integrated Science Assessment.
CASAC supported the development of
the EPA’s causality framework and its
use in the current PM NAAQS review
and concluded:
The five-level classification of strength of
evidence for causal inference has been
systematically applied; this approach has
provided transparency and a clear statement
of the level of confidence with regard to
causation, and we recommend its continued
use in future Integrated Science Assessments
(Samet 2009f, p. 1).
These commenters asserted that
during the application of the causal
framework the EPA inappropriately
relied on a selective group of long- and
short-term exposure studies in reaching
causal inferences (API, 2012, pp 12 to
17; ACC, 2012, Attachment A, pp 1 to
2; NAM et al., 2012, pp. 22 to 25; Texas
CEQ, 2012, pp 2 to 3). Additionally,
these commenters expressed the view
that the EPA focused on a subset of
epidemiological studies that reported
positive and statistically significant
results while ignoring other studies,
especially those that reported no
statistically significant associations,
those that reported potential thresholds,
or those that highlighted uncertainties
and limitations in study design or
results. Furthermore, some of these
commenters argued that
epidemiological studies are
observational in nature and cannot
provide evidence of a causal
association.
The EPA disagrees with these
commenters’ views on assessing the
health effects evidence and on the
conclusions regarding the causality
determinations reached in the Integrated
Science Assessment. In conducting a
comprehensive evaluation of the
evidence in the Integrated Science
Assessment, the EPA recognized the
distinction between the evaluation of
the relative scientific quality of
individual study results and the
evaluation of the pattern of results
within the broader body of scientific
evidence and considered both in
reaching causality determinations. The
PO 00000
Frm 00028
Fmt 4701
Sfmt 4700
more detailed characterizations of
individual studies included an
assessment of the quality of the study
based on specific criteria as described in
the Integrated Science Assessment (U.S.
EPA, 2009a, section 1.5.3).
In developing an integrated
assessment of the health effects
evidence for PM, the EPA emphasized
the importance of examining the pattern
of results across various studies and did
not focus solely on statistical
significance 49 as a criterion of study
strength. This approach is consistent
with views clearly articulated
throughout the epidemiological and
causal inference literature, specifically,
that it is important not to focus on
results of statistical tests to the
exclusion of other information.50 The
concepts underlying the EPA’s approach
to evaluating statistical associations
have been discussed in numerous
publications, including a report by the
U.S. Surgeon General on the health
consequences of smoking (Centers for
Disease Control and Prevention, 2004).
This report cautions against overreliance on statistical significance in
evaluating the overall evidence for an
exposure-response relationship. Criteria
characterized by Hill (1965) also
addressed the value, or lack thereof, of
statistical tests in the determination of
cause:
No formal tests of significance can answer
those [causal] questions. Such tests can, and
should, remind us of the effects the play of
chance can create, and they will instruct us
in the likely magnitude of those effects.
Beyond that, they contribute nothing to the
‘proof’ of our hypothesis (Hill, 1965, p. 299).
The statistical significance of
individual study findings has played an
important role in the EPA’s evaluation
of the study’s results and the EPA has
placed greater emphasis on studies
reporting statistically significant results.
However, in the broader evaluation of
the evidence from many
49 Statistical significance is an indicator of the
precision of a study’s results, which is influenced
by a variety of factors including, but not limited to,
the size of the study, exposure and measurement
error, and statistical model specifications. Studies
typically calculate ‘‘p-values’’ to determine whether
the study results are statistically significant or
whether the study results are likely to occur simply
by chance. In general practice, effects are
considered statistically significant if p values are
less than 0.05.
50 For example, Rothman (1998) stated, ‘‘Many
data analysts appear to remain oblivious to the
qualitative nature of significance testing [and that]
* * * statistical significance is itself only a
dichotomous indicator. As it has only two values,
significant or not significant * * *. Nevertheless, pvalues still confound effect size with study size, the
two components of estimation that we believe need
to be reported separately.’’ As a result, Rothman
recommended that p-values be omitted as long as
point and interval estimates are available.
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
epidemiological studies, and
subsequently during the process of
forming causality determinations in
integrating evidence across
epidemiological, controlled human
exposure, and toxicological studies, the
EPA has emphasized the pattern of
results across epidemiological studies,
and whether the effects observed were
coherent across the scientific disciplines
for drawing conclusions on the
relationship between PM2.5 and different
health outcomes. Thus, the EPA did not
limit its focus or consideration to just
studies that reported positive
associations or where the results were
statistically significant.
In addition, some commenters
asserted that the EPA inappropriately
used the Hill criteria by failing to
consider the limitations of studies with
weak associations, thereby overstating
the consistency of the observed
associations (API, 2012, Attachment 1,
pp. 30 to 35). These commenters argued
that risk estimates greater than 3 to 4
reflect strong associations supportive of
a causal link, while smaller risk
estimates (i.e., 1.5 to 3) are considered
to be weak and require other lines of
evidence to demonstrate causality.
As discussed in section 1.5.3 of the
Integrated Science Assessment, the EPA
thoroughly considered the limitations of
all studies during its evaluation of the
scientific literature (U.S. EPA,, 2009a, p.
1–14). This collective body of evidence,
including known uncertainties and
limitations of the studies evaluated,
were considered during the process of
forming causality determinations as
discussed in chapters 6 and 7 of the
Integrated Science Assessment. For
example, the EPA concluded that ‘‘a
causal relationship exists between shortterm PM2.5 exposure and cardiovascular
effects,’’ however, in reaching this
conclusion, the Agency recognized and
considered limitations of the current
evidence that still requires further
examination (U.S. EPA, 2009a., in
section 6.2.12.1). Therefore, the EPA
disagrees with these commenters’ views
that the Hill criteria were
inappropriately used in that the
limitations of studies were not
considered.
The EPA also disagrees with the
commenters’ assertion that the
magnitude of the association must be
large to support a determination of
causality. As discussed in the Integrated
Science Assessment, the strength of the
observed association is an important
aspect to aid in judging causality and
‘‘while large effects support causality,
modest effects therefore do not preclude
it’’ (U.S. EPA, 2009a, Table 1–2, section
1.5.4). The weight of evidence approach
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
used by the EPA encompasses a
multitude of factors of which the
magnitude of the association is only one
component (U.S. EPA, 2009a, Table 1–
3). An evaluation of the association
across multiple investigators and
locations supports the ‘‘reproducibility
of findings [which] constitutes one of
the strongest arguments for causality’’
(U.S. EPA, 2009a, Table 1–2). Even
though the risk estimates for air
pollution studies may be modest, the
associations are consistent across
hundreds of studies as demonstrated in
the Integrated Science Assessment.
Furthermore, the causality
determinations rely on different lines of
evidence, by integrating evidence across
disciplines, including animal
toxicological studies and controlled
human exposure studies.
Furthermore, as summarized in
section III.B above and discussed more
fully in section III.B.3 of the proposal,
the EPA recognizes that the population
potentially affected by PM2.5 is
considerable, including large subgroups
of the U.S. population that have been
identified as at-risk populations (e.g.,
children, older adults, persons with
underlying cardiovascular or respiratory
disease). While individual effect
estimates from epidemiological studies
may be modest in size, the public health
impact of the mortality and morbidity
associations can be quite large given
that air pollution is ubiquitous. Indeed,
with the large population exposed,
exposure to a pollutant causally
associated at a population level with
mortality and serious illness has
significant public health consequences,
virtually regardless of the relative risk.
Taken together, this information
indicates that exposure to ambient PM2.5
concentrations has substantial public
health impacts.
In addition, these commenters
believed that the EPA downplayed null
or inconsistent findings in numerous
long-term mortality studies with
reported PM2.5 concentrations above
and below the level of the current
annual standard. The EPA disagrees that
studies with null or inconsistent
findings were not accurately presented
and considered in the Integrated
Science Assessment. For example, as
discussed throughout section 7.6 and
depicted in Figures 7–6 and 7–7 of the
Integrated Science Assessment, the EPA
presented the collective evidence from
all studies that examined the association
between long-term PM2.5 exposure and
mortality. Overall, across these studies
there was evidence of consistent
positive associations in different
cohorts. That evidence, in combination
with the biological plausibility provided
PO 00000
Frm 00029
Fmt 4701
Sfmt 4700
3113
by experimental and toxicological
studies evaluated in sections 7.1 and 7.2
of the Integrated Science Assessment,
supported a causal relationship exists
between long-term PM2.5 exposure and
mortality.
Lastly, some of these commenters
argued that in some cases, the EPA used
the same study and the same underlying
database to conclude that there is a
causal association between mortality
and multiple criteria pollutants. These
commenters argued, ‘‘[i]n doing so, EPA
attributes the cause of the mortality
effects observed to whichever criteria
pollutant it is reviewing at the time’’
(API, 2012, pp. 14 to 16).
The EPA strongly disagrees that the
Agency ‘‘attributes the cause of
mortality effects observed to whichever
criteria pollutant it is reviewing at the
time.’’ The EPA consistently recognizes
that other pollutants are also associated
with health outcomes, as is reflected in
the fact that the EPA has established
regulations to limit emissions of
particulate criteria pollutants as well as
other gaseous criteria pollutants.
Epidemiological studies often examine
the association between short- and longterm exposures to multiple air
pollutants and mortality within a
common dataset in an attempt to
identify the air pollutant(s) of the
complex mixture most strongly
associated with mortality. In evaluating
these studies, the EPA employs specific
study selection criteria to identify those
studies most relevant to the review of
the NAAQS. In its assessment of the
health evidence regarding PM2.5, the
EPA has carefully evaluated the
potential for confounding, effect
measure modification, and the role of
PM2.5 as a component of a complex
mixture of air pollutants (U.S. EPA,
2009a, p. 1–9). The EPA used a rigorous
weight of evidence approach to inform
causality that evaluated consistency
across studies within a discipline,
evidence for coherence across
disciplines, and biological plausibility.
Additionally, during this process, the
EPA assessed the limitations of each
study in the context of the collective
body of evidence. It was the collective
evidence, not one individual study that
ultimately determined whether a causal
relationship exists between a pollutant
and health outcome. In the Integrated
Science Assessment, the combination of
epidemiological and experimental
evidence formed the basis for the
Agency concluding for the first time that
a causal relationship exists between
short- or long-term exposure to a criteria
pollutant and mortality (U.S. EPA, 2009,
sections 2.3.1.1 and 2.3.1.2).
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
3114
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
Additionally, while the EPA has
evaluated some of the studies used to
inform the causality determination for
PM in the Integrated Science
Assessments for other criteria air
pollutants, the Agency has done so in
the context of examining the collective
body of evidence for each of the
respective criteria air pollutants. As
such, the body of evidence to inform
causality has varied from pollutant to
pollutant resulting in the association
between each criteria air pollutant and
mortality being classified at a different
level of the five-level hierarchy used to
inform causation (e.g., U.S. EPA, 2008e,
U.S. EPA, 2008f, U.S. EPA, 2010k).
The EPA notes that the final causality
determinations presented in the
Integrated Science Assessment reflected
CASAC’s recommendations on the
second draft Integrated Science
Assessment (Samet, 2009f, pp. 2 to 3).
Specifically, CASAC supported the
EPA’s changes (in the second versus
first draft Integrated Science
Assessment) from ‘‘likely causal’’ to
‘‘causal’’ for long-term exposure to PM2.5
and cardiovascular effects and for
cancer and PM2.5 (from ‘‘inadequate’’ to
‘‘suggestive’’). Id. Furthermore, CASAC
recommended ‘‘upgrading’’ the causal
classification for PM2.5 and total
mortality to ‘‘causal’’ for both the shortand long-term timeframes. Id. With
regard to mortality, the ‘‘EPA carefully
reevaluated the body of evidence,
including the collective evidence for
biological plausibility for mortality
effects, and determined that a causal
relationship exists for short- and longterm exposure to PM2.5 and mortality,
consistent with the CASAC comments’’
(Jackson, 2010).
(2) With regard to toxicological and
controlled human exposure studies,
these commenters argued that the
available evidence does not provide
coherence or biological plausibility for
health effects observed in
epidemiological studies (API, 2012, pp.
21 to 22, Attachment 1, pp. 25 to 29;
AAM, 2012, pp. 15 to 16; Texas CEQ,
2012, p. 3). With regard to the issue of
mechanisms, these commenters noted
that although the EPA recognizes that
new evidence is now available on
potential mechanisms and plausible
biological pathways, the evidence
provided by toxicological and
controlled human exposure studies still
does not resolve all questions about how
PM2.5 at ambient concentrations could
produce the mortality and morbidity
effects observed in epidemiological
studies. More specifically, for example,
some of these commenters argued that:
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
A review of the Integrated Science
Assessment, however, suggests that the
experimental evidence is inconsistent and
not coherent with findings in epidemiology
studies. Specifically, the findings of mild and
reversible effects in most experimental
studies conducted at elevated exposures are
not consistent with the more serious
associations described in epidemiology
studies (e.g., hospital admissions and
mortality). Also, both animal studies and
controlled human exposure studies have
identified no effect levels for acute and
chronic exposure to PM and PM constituents
at concentrations considerably above ambient
levels. EPA should consider the experimental
findings in light of these higher exposure
levels and what the relevance may be for
ambient exposures (API, 2012, Attachment 1,
p. 25).
The EPA notes that in the review
completed in 1997, the Agency
considered the lack of demonstrated
biological mechanisms for the varying
effects observed in epidemiological
studies to be an important caution in its
integrated assessment of the health
evidence upon which the standards
were based (71 FR 61157, October 17,
2006). In the review completed in 2006,
the EPA recognized the findings from
additional research that indicated that
different health responses were linked
with different particle characteristics
and that both individual components
and complex particle mixtures appeared
to be responsible for many biologic
responses relevant to fine particle
exposures. Id. Since that review, there
has been a great deal of research
directed toward advancing our
understanding of biologic mechanisms.
While this research has not resolved all
questions, and further research is
warranted (U.S. EPA, 2011a, section
2.5), it has provided important insights
as discussed in section III.B.1 of the
proposal (77 FR at 38906 to 38909) and
discussed more fully in the Integrated
Science Assessment (U.S. EPA, 2009a,
Chapter 5).
As noted in the proposal,
toxicological studies provide evidence
to support the biological plausibility of
cardiovascular and respiratory effects
associated with long- and short-term PM
exposures observed in epidemiological
studies (77 FR 38906) and provide
supportive mechanistic evidence that
the cardiovascular morbidity effects
observed in long-term exposure
epidemiological studies are coherent
with studies of cardiovascular-related
mortality (77 FR 38907). The Integrated
Science Assessment concluded that the
new evidence available in this review
‘‘greatly expands’’ upon the evidence
available in the last review ‘‘particularly
in providing greater understanding of
the underlying mechanisms for PM2.5
PO 00000
Frm 00030
Fmt 4701
Sfmt 4700
induced cardiovascular and respiratory
effects for both short- and long-term
exposures’’ (U.S. EPA, 2009a, p. 2–17).
The mechanistic evidence now
available, taken together with newly
available epidemiological evidence,
increases the Agency’s confidence that a
causal relationship exists between longand short-term exposure to PM2.5 and
cardiovascular effects and mortality.51
In addition, CASAC supported the
Integrated Science Assessment approach
and characterization of potential
mechanisms or modes of action (Samet,
2009e, pp. 7 to 8; Samet, 2009f, p. 11),
as well as the findings of a causal
relationship at the population level
between exposure to PM2.5 and
mortality and cardiovascular effects
(Samet, 2009f, pp. 2 to 3).52
Additionally, the EPA disagrees with
commenters that the mild and reversible
effects observed in controlled human
exposure studies are inconsistent with
the more serious effects observed in
epidemiological studies. Ethical
considerations regarding the types of
studies that can be performed with
human subjects generally limit the
effects that can be evaluated to those
that are transient, reversible, and of
limited short-term consequence. The
relatively small number of subjects
recruited for controlled exposure
studies should also be expected to have
less variability in health status and risk
factors than occurring in the general
population.53 Consequently, the severity
51 See American Trucking Associations v. EPA,
175 F. 3d 1027, 1055–56 (DC Cir. 1999) reversed in
part and affirmed in part sub nom, Whitman v.
American Trucking Associations, 531 U.S. 457
(2001) holding that the EPA could establish NAAQS
without identifying a biological mechanism (‘‘To
begin with, the statute itself requires no such proof.
The Administrator may regulate air pollutants
‘‘emissions of which, in his judgment, cause or
contribute to air pollution which may reasonably be
anticipated to endanger public health or welfare.’’
(emphasis added by the court). Moreover, this court
has never required the type of explanation
petitioners seek from EPA. In fact, we have
expressly held that EPA’s decision to adopt and set
air quality standards need only be based on
‘reasonable extrapolations from some reliable
evidence’* * *. Indeed, were we to accept
petitioners’ view, EPA (or any agency for that
matter) would be powerless to act whenever it first
recognizes clear trends of mortality or morbidity in
areas dominated by a particular pathogen.’’).
53 For example, the EPA excludes from its
controlled human exposure studies involving
exposure to PM2.5 any individual with a significant
risk factor for experiencing adverse effects from
such exposure. Thus, the EPA excludes a priori the
following categories of persons: those with a history
of angina, cardiac arrhythmias, and ischemic
myocardial infarction or coronary bypass surgery;
those with a cardiac pacemaker; those with
uncontrolled hypertension (greater than 150
systolic and 90 diastolic); those with neurogenetive
diseases; those with a history of bleeding diathesis;
those taking beta-blockers; those using oral
anticoagulants; those who are pregnant, attempting
to become pregnant, or breastfeeding; those who
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
of health effects observed in controlled
human exposure studies evaluating the
effects of PM should be expected to be
less than observed in epidemiologic
studies. Nonetheless, that effects are
observed in relatively healthy
individuals participating in controlled
exposure studies serves as an indicator
that PM is initiating health responses
and that more severe responses may
reasonably be expected in a more
diverse population.
It should also be noted that there is a
small body of toxicological evidence
demonstrating mortality in rodents
exposed to PM (e.g., Killingsworth et al.
1997). Overall it is not surprising that
lethality is not induced in more
toxicological research, as these types of
studies do not readily lend themselves
to this endpoint. Epidemiological
studies have observed associations
between PM and mortality in
communities with populations in the
range of many thousands to millions of
people. Clearly, it is not feasible to
expose hundreds (if not thousands) of
animals to ambient PM (potentially over
many years) in a laboratory setting to
induce enough lethalities to distinguish
between natural deaths and those
attributable to PM. Furthermore, the
heterogeneous human populations
sampled in epidemiological studies are
comprised of individuals with different
physical, genetic, health, and
socioeconomic backgrounds which may
impact the outcome. However, in
toxicological studies, the rodent groups
are typically inbred, such that interindividual variability is minimized.
Thus, if the rodent strain used is quite
robust, PM-induced effects may not be
observed at low exposure
concentrations.
(3) In asserting that the uncertainties
in the underlying health science are as
great or greater than in the last review
and therefore do not support revision to
the standards at this time, commenters
in this group variously discussed a
number of issues related to: (a)
Confounding, (b) heterogeneity in risk
estimates, (c) exposure measurement
error, (d) model specification, (e) the
shape of the concentration-response
have experienced a respiratory infection within four
weeks of exposure; those experiencing eye or
abdominal surgery within six weeks of exposure;
those with active allergies; those with a history of
chronic illnesses such as diabetes, cancer,
rheumatologic diseases, immunodeficiency state,
known cardiovascular disease, or chronic
respiratory diseases; smokers. The EPA
‘‘Application for Independent Review Board
Approval of Human Subjects Research:
Cardiopulmonary Effects of healthy Older GSTM1
Null and Sufficient individuals to Concentrated
Ambient Air Particles (CAPTAIN)’’, Nov. 9, 2011,
p. 9.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
relationship, and (f) understanding the
relative toxicity of components within
the mixture of fine particles. Each of
these issues is addressed below and
some are discussed in more detail in the
Response to Comments document.
In summary, these commenters
concluded that the substantial
uncertainties present in the last review
have not been resolved and/or that the
uncertainty about the possible health
risks associated with PM2.5 exposure has
not diminished. As discussed below, the
EPA believes that the overall
uncertainty about possible health risks
associated with both long- and shortterm PM2.5 exposure has diminished to
an important degree since the last
review. While the EPA agrees that
important uncertainties remain, and that
future research directed toward
addressing these uncertainties is
warranted, the EPA disagrees with
commenters’ views that the remaining
uncertainties in the scientific evidence
are too great to warrant revising the
current PM2.5 NAAQS.
(a) Confounding
Some commenters have criticized the
EPA for not adequately addressing the
issue of confounding in both long- and
short-term exposure studies of mortality
and morbidity. This includes
confounding due to copollutants, as
well as unmeasured confounding.54
With regard to copollutant
confounding, these commenters asserted
that the EPA has not adequately
interpreted the results from studies that
examined the effect of copollutants on
the relationship between long- and
short-term PM2.5 exposures and
mortality and morbidity outcomes.
These commenters contend that the EPA
has inappropriately concluded that
PM2.5-related mortality and morbidity
associations are generally robust to
confounding. The commenters stated
that statistically significant PM2.5
associations in single-pollutant models
in epidemiological studies do not
remain statistically significant in
copollutant models.
54 The Integrated Science Assessment defines
confounding as ‘‘a confusion of effects. Specifically,
the apparent effect of the exposure of interest is
distorted because the effect of an extraneous factor
is mistaken for or mixed with the actual exposure
effect (which may be null) (Rothman and
Greenland, 1998)’’ (U.S. EPA, 2009a, p. 1–16).
Epidemiological analyses attempt to adjust or
control for these characteristics (i.e., potential
confounders) that differ between exposed and nonexposed individuals (U.S. EPA, 2009a, section
1.5.3). Not all risk factors can be controlled for
within a study design/model and are termed
‘‘unmeasured confounders.’’ An unmeasured
confounder is a confounder that has not previously
been measured and therefore is not included in the
study design/model.
PO 00000
Frm 00031
Fmt 4701
Sfmt 4700
3115
The loss of statistical significance or
the reduction in the magnitude of the
effect estimate when a co-pollutant
model is used may be the result of
factors other than confounding. These
changes do not prove either the
existence or absence of confounding.
These impacts must be evaluated in a
broader context that considers the entire
body of evidence. The broader
examination of this issue in the
Integrated Science Assessment included
a focus on evaluating the stability of the
size of the effect estimates in
epidemiological studies conducted by a
number of research groups using singleand copollutant models (U.S. EPA,
2009a, sections 6.2.10.9, 6.3.8.5, and
6.5, Figures 6–5, 6–9, and 6–15). This
examination found that, for most
epidemiological studies, there was little
change in effect estimates based on
single- and copollutant models,
although the Integrated Science
Assessment recognized that in some
cases, the PM2.5 effect estimates were
markedly reduced in size and lost
statistical significance. Additionally, the
EPA notes that these comments do not
adequately reflect the complexities
inherent in assessing the issue of
copollutant confounding. As discussed
in the proposal (77 FR 38907, 38909,
and 38910) and more fully in the
Integrated Science Assessment
(U.S.EPA, 2009a, sections 6.2, 6.3, and
6.5), although copollutant models may
be useful tools for assessing whether
gaseous copollutants may be potential
confounders, such models alone cannot
determine whether copollutants are in
fact confounders. Interpretation of the
results of copollutant models is
complicated by correlations that often
exist among air pollutants, by the fact
that some pollutants play a role in the
atmospheric reactions that form other
pollutants such as secondary fine
particles, and by the statistical power of
the studies in question inherent in the
study methodology. For example, the
every-third or sixth-day sampling
schedule often employed for PM2.5
measurements compared to daily
measurements of gaseous copollutants
drastically reduces the overall sample
size to assess the effect of copollutants
on the PM2.5-morbidity or mortality
relationship, such that the reduced
sample size can lead to less precise
effect estimates (e.g., wider confidence
intervals).
The EPA recognizes that when PM2.5
is correlated with gaseous pollutants it
can be difficult to identify the effect of
individual pollutants in the ambient
mixture (77 FR 38910). However, based
on the available evidence, the EPA
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
3116
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
concludes epidemiological studies
continue to support the conclusion that
PM2.5 associations with mortality and
morbidity outcomes are robust to the
inclusion of gaseous copollutants in
statistical models. The EPA evaluated
the potential confounding effects of
gaseous copollutants and, although it is
recognized that uncertainties and
limitations still remain, the Agency
concluded the collective body of
scientific evidence is ‘‘stronger and
more consistent than in previous
reviews providing a strong basis for
decision making in this review’’ (77 FR
38910/1).
Several commenters offered detailed
comments on the long-term PM2.5
exposure studies arguing that
associations from mortality studies are
subjected to unmeasured confounding
and as a result are not appropriately
characterized as providing evidence of a
causal relationship between long-term
PM2.5 exposure and mortality (e.g.,
UARG, 2012, pp. 10 to 11, Attachment
A, pp. 17 to 23; API, 2012, pp. 13 to 14,
Attachment 1, pp. 11 to 14, Attachment
7, pp. 2–10; ACC, 2012, p. 18 to 21;
AFPM, 2012, p. 8; Texas CEQ, 2012, p.
4). Specifically, commenters cited two
studies (i.e., Janes et al., 2007 and
Greven et al., 2011) that used a new type
of statistical analysis to examine
associations between annual (long-term)
and monthly (sub-chronic) PM2.5
exposure and mortality. The
commenters interpreted the results of
these analyses as evidence of
unmeasured confounding in the longterm PM2.5 exposure-mortality
relationship. These commenters
interpreted these studies as raising
fundamental questions regarding the
EPA’s determination that a causal
relationship exists between long-term
PM2.5 exposure and mortality. In
addition to the commenters mentioned
above, all of the authors of the
publications by Janes et al. (2007) and
Greven et al. (2011) (i.e., Francesca
Dominici, Scott Zeger, Holly Janes, and
Sonja Greven) submitted a joint
comment to the public docket in order
to clarify specific points regarding these
two studies (Dominici et al., 2012).
The first study, Janes et al. (2007), was
evaluated in the Integrated Science
Assessment (U.S. EPA, 2009a, p. 7–88).
The second study, Greven et al. (2011),
an extension of the Janes et al. (2007)
study adding three more years of data,
is a ‘‘new’’ study discussed in the
Provisional Science Assessment (U.S.
EPA, 2012). Both studies used
nationwide Medicare mortality data to
examine the association between
monthly average PM2.5 concentrations
over the preceding 12 months and
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
monthly mortality rates in 113 U.S.
counties and examined whether
community-specific trends in monthly
PM2.5 concentrations and mortality
declined at the same rate as the national
rate. The investigators examined this by
decomposing the association between
PM2.5 and mortality into two
components: (1) National trends,
defined as the association between the
national average trend in monthly PM2.5
concentrations averaged over the
previous 12 months and the national
average trend in monthly mortality
rates, and (2) local trends, defined as
county-specific deviations in monthly
PM2.5 concentrations and monthly
mortality rates from national trends.
The EPA does not question the results
of the national trends analyses
conducted by Janes et al. (2007) and
Greven et al. (2011).55 Both Janes et al.
(2007) and Greven et al. (2011) observed
positive and statistically significant
associations between long-term
exposure to PM2.5 and mortality in their
national analyses. However, Janes et al.
(2007) and Greven et al. (2011)
eliminated all of the spatial variation in
air pollution and mortality in their data
set when estimating the national effect,
focusing instead on both chronic
(yearly) and sub-chronic (monthly)
temporal differences in the data
(Dominici et al. 2012). Janes et al. (2007)
(Table 1) highlighted that over 90
percent of the variance in the data set
used for the analyses conducted by both
Janes et al. (2007) and Greven et al.
(2011) was attributable to spatial
variability, which the authors chose to
discard. As noted above, the focus of the
analyses by Janes et al. (2007) and
Greven et al. (2011) was on two
components: (1) A temporal or time
component, i.e., the ‘‘national’’ trends
analysis, which examined the
association between the national
average trend in monthly PM2.5
concentrations averaged over the
previous 12 months and the national
average trend in monthly mortality rates
and (2) a space-by-time component, i.e.,
the ‘‘local’’ trends analysis, which
examined county-specific deviations in
monthly PM2.5 concentrations and
monthly mortality rates from national
trends. These two components
combined comprised less than 10
percent of the variance in the data set.
The authors included a focus on the
55 In its evaluation of Janes et al. (2007) in the
Integrated Science Assessment, the EPA did not
identify limitations in the statistical methods used
per se (U.S. EPA, 2009a, p. 7–88) and included the
results of the national-scale analyses in that study
in the body of evidence that supported the
determination that there is a causal relationship
between long-term PM2.5 exposure and mortality.
PO 00000
Frm 00032
Fmt 4701
Sfmt 4700
space-by-time component, which
represented approximately 5 percent of
the variance in the data set, in an
attempt to identify, absent confounding,
if PM2.5 was associated with mortality at
this unique exposure window. Thus,
these studies are not directly
comparable to other cohort studies
investigating the relationship between
long-term exposure to PM2.5 and
mortality, which make use of spatial
variability in air pollution and mortality
data.56 This point was highlighted by
the study authors who stated that
‘‘when one considers that this wealth of
information is not accounted for in
[Janes 2007], it is not as surprising that
* * * vastly different estimates of the
PM2.5/mortality relationship [were
observed] than in other studies that do
exploit that variability’’ (Dominici et al.,
2012, p. 2).
The EPA notes that the results of the
local trends analyses conducted by
Janes et al. (2007) and Greven et al.
(2011) are limited by the monthly
timescale used in these analyses. This
view is consistent with comments on
the Janes et al. (2007) study articulated
in Pope and Burnett (2007),57 which
noted that an important limitation of the
local scale analysis conducted by Janes
et al. (2007) and subsequently by
Greven et al. (2011) was the subchronic
exposure window considered in these
analyses. Both studies used annual
average PM2.5 concentrations to
characterize long-term national trends
which was consistent with exposure
windows considered in other studies of
long-term exposure to PM2.5 and
mortality.58 However, the local scale
analyses used monthly average PM2.5
concentrations to characterize countyspecific deviations from national trends
(the local scale). The use of monthly
average data likely does not provide
56 Though not directly comparable, the national
effect estimates for mortality reported by Janes et al.
(2007) and Greven et al. (2011) are coincidentally
similar in magnitude to those previously reported.
It is important to note that previous cohort studies
have focused on identifying spatial differences in
PM2.5 concentrations between cities, while Janes et
al. (2007) and Greven et al. (2011) focus primarily
on temporal differences in PM2.5 concentrations. In
fact, Greven et al. (2011) state ‘‘We do not focus
here on a third type [of statistical approach] used
in cohort studies, measuring the association
between average PM2.5 levels and average ageadjusted mortality rates across cities (purely spatial
or cross-sectional association).’’
57 Some commenters argued that there were flaws
in the criticisms offered by Pope and Burnett (2007)
on the paper by Janes et al. (2007) (UARG, 2012,
Attachment A, pp. 19 to 23). The EPA responds to
each of these specific comments in the Response to
Comments document.
58 As noted above, however, Janes et al. (2007)
and Greven et al. (2011) focused on temporal
variability and other studies of long-term exposure
to PM2.5 and mortality focus on spatial variability.
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
enough exposure contrast to observe
temporal changes in mortality at the
local scale. It also represents a different
exposure window than considered in
the large body of evidence of health
effects related to short-term (from less
than one day to up to several days) and
chronic (one or more years) measures of
PM2.5.
Furthermore, the EPA disagrees with
commenters that studies by Janes et al.
(2007) and Greven et al. (2011) provide
evidence that other studies of long-term
exposure to PM2.5 and mortality are
affected by unmeasured confounding.
As noted above, the design of the
studies conducted by Janes et al. (2007)
and Greven et al. (2011) are
fundamentally different than those used
in other studies of long-term exposure to
PM2.5 and mortality, including the ACS
cohort and the Harvard Six Cities study.
Studies, such as the ACS and Harvard
Six Cities studies, used the spatial
variation between cities to measure the
effect of long-term (annual) exposures to
PM2.5 on mortality risk, and did not
conduct any analyses relying on the
temporal variation in PM2.5. The
opposite is true of the Janes et al. (2007)
and Greven et al. (2011) studies which
first removed the spatial variability in
PM2.5 and then examined the temporal
variation at both the national and local
scale to measure the effects of temporal
differences in PM2.5 on mortality risk.
Janes et al. (2007) and Greven et al.
(2011) focus on changes in PM2.5
concentrations over time and, therefore,
control for confounders would be based
on including variables that vary over
time rather than over space. As a result,
any evidence of potential confounding
of the PM2.5-mortality risk relationship
derived from Janes et al. (2007) and
Greven et al. (2011) cannot be
extrapolated to draw conclusions
related to potential spatial confounding
in studies based on the spatial variation
in PM2.5 concentrations.
As detailed in the Integrated Science
Assessment (U.S. EPA, 2009a, section
7.6), and recognized by the authors of
Janes et al. (2007) and Greven et al.
(2011), the cohort studies that informed
the causality determination for longterm PM2.5 exposure and mortality
‘‘have developed approaches to adjust
for measured and unmeasured
confounders’’ (Dominici et al., 2012, p.
2). These approaches were specifically
designed to adjust for spatial
confounding. The hypothesis that the
authors of Janes et al. (2007) and Greven
et al. (2011) chose to examine was that
differences in the local and national
effects indicated unmeasured temporal
confounding in either the local or
national effect estimate. This hypothesis
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
was specific to these two studies that
examined temporal variability in
exposure to air pollution and did not
include known potential confounders at
either the national or local scale as timevarying covariates in the statistical
model. The authors acknowledged that
the interpretation of either the national
or local estimates needs to occur with
an appreciation of the potential
confounding effects of national and
local scale covariates that were omitted
from the model (Dominici et al., 2012).
It is important to recognize that
because Janes et al. (2007) and Greven
et al. (2011) focused on variations in
PM2.5 over time and not space, the
results from these two studies do not
provide any indication that other
studies of long-term exposure to PM2.5
and mortality exhibit spatial
confounding, or that PM2.5 does not
cause mortality.59 The authors of Janes
et al. (2007) and Greven et al. (2011)
recognized that ‘‘it is entirely possible
that these papers are looking for an
association at a timescale for which no
association truly exists’’ (Dominici et
al., 2012, p. 3). Furthermore, as
highlighted in the Integrated Science
Assessment and discussed by Pope and
Burnett (2007), the conclusions of Janes
et al. (2007) ‘‘are overstated * * *
[T]heir analysis tells us little or nothing
about unmeasured confounding in those
and related studies because the
methodology of Janes et al. largely
excludes the sources of variability that
are exploited in those other studies. By
using monthly mortality counts and
lagged 12-month average pollution
concentrations, the authors eliminate
the opportunity to exploit short-term or
day-to-day variability.’’
In conclusion, the EPA interprets the
results of the analyses conducted by
Janes et al. (2007) and Greven et al.
(2011) as being consistent with prior
knowledge of examining associations
with long-term exposure to PM2.5 at the
national scale using long-term average
PM2.5 concentrations. For the reasons
presented above and discussed in more
detail in the Response to Comments
document, the Agency disagrees with
the commenters’ assumption that the
results of Janes et al. (2007) and Greven
et al. (2011) indicate unmeasured
confounding in the results of other
cohort studies of long-term exposure to
PM2.5 and mortality. Therefore, the EPA
concludes that these studies do not
invalidate the large body of
epidemiological evidence that supports
59 Further, the EPA notes that Janes et al. (2007)
and Greven et al. (2011) provide no information
relevant to examining confounding in studies of
short-term exposure to PM2.5.
PO 00000
Frm 00033
Fmt 4701
Sfmt 4700
3117
the EPA’s determination that a causal
relationship exists between long-term
PM2.5 exposure and mortality.60
(b) Heterogeneity in Risk Estimates
Some commenters argued that the
heterogeneity in risk estimates observed
in multi-city epidemiological studies
and the lack of statistical significance in
many regional or seasonal estimates
highlights a potential bias associated
with combined multi-city
epidemiological study results (e.g., API,
2012, Attachment 1, pp. 15 to 19). These
commenters further argued that more
refined intra-urban exposure estimates
conducted for two of the largest cities
included in the ACS study, Los Angeles
and New York City, based on land-use
regression models and/or kriging
methods (Krewski et al., 2009)
‘‘underscore the importance of
considering city-specific health
estimates, which may account for
heterogeneity in PM2.5 concentrations or
other differences among cities, rather
than relying on pooled nationwide
results from multi-city studies’’ (API,
2012, Attachment 1, p. 17).
With respect to understanding the
nature and magnitude of PM2.5-related
risks, the EPA agrees that
epidemiological studies evaluating
health effects associated with long- and
short-term PM2.5 exposures have
reported heterogeneity in responses
between cities and effect estimates
across geographic regions of the U.S.
(U.S. EPA, 2009a, sections 6.2.12.1,
6.3.8.1, 6.5.2, and 7.6.1; U.S. EPA,
2011a, p. 2–25). For example, when
focusing on short-term PM2.5 exposure,
the Integrated Science Assessment
found that multi-city studies that
examined associations with mortality
and cardiovascular and respiratory
hospital admissions and emergency
department visits demonstrated greater
cardiovascular effects in the eastern
versus the western U.S. (Dominici, et
al., 2006a; Bell et al., 2008; Franklin et
al. (2007, 2008)).
In addition, the Integrated Science
Assessment evaluated studies that
provided some evidence for seasonal
differences in PM2.5 risk estimates,
specifically in the northeast. The
Integrated Science Assessment found
evidence indicating that individuals
may be at greater risk of dying from
higher exposures to PM2.5 in the warmer
months, and at greater risk of PM2.5
associated hospitalization for
60 The EPA notes that the EPA’s conclusion with
regard to interpretation of the results from Janes et
al. (2007) and Greven et al. (2012) is supported by
the study authors’ conclusion that ‘‘[o]ur results do
not invalidate previous epidemiological studies’’
(Dominici, 2012, p. 1 (emphasis original)).
E:\FR\FM\15JAR2.SGM
15JAR2
3118
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
cardiovascular and respiratory diseases
during colder months of the year. The
limited influence of seasonality on PM
risk estimates in other regions of the
U.S. may be due to a number of factors
including varying PM composition by
season, exposure misclassification due
to regional tendencies to spend more or
less time outdoors and air conditioning
usage, and the prevalence of infectious
diseases during the winter months (U.S.
EPA, 2009a, p. 3–182).
Overall, the EPA took note in the
proposal that uncertainties still remain
regarding various factors that contribute
to heterogeneity observed in
epidemiological studies (77 FR 38909/
3). Nonetheless, the EPA recognizes that
this heterogeneity could be attributed, at
least in part, to differences in PM2.5
composition across the U.S., as well as
to exposure differences that vary
regionally such as personal activity
patterns, microenvironmental
characteristics, and the spatial
variability of PM2.5 concentrations in
urban areas (U.S. EPA, 2009a, section
2.3.2; 77 FR 38910).
As recognized in the Policy
Assessment, the current epidemiological
evidence and the limited amount of
city-specific speciated PM2.5 data do not
allow conclusions to be drawn that
specifically differentiate effects of PM2.5
in different locations (U.S. EPA, 2011a,
p. 2–25). Furthermore, the Integrated
Science Assessment concluded ‘‘that
many constituents of PM2.5 can be
linked with multiple health effects, and
the evidence is not yet sufficient to
allow differentiation of those
constituents or sources that are more
closely related to specific health
outcomes’’ (U.S. EPA, 2009a, p. 2–17).
CASAC thoroughly reviewed the EPA’s
presentation of the scientific evidence
indicating heterogeneity in PM2.5 effect
estimates in epidemiological studies
and concurred with the overall
conclusions presented in the Integrated
Science Assessment.
(c) Exposure Measurement Error
Some commenters argued that the
EPA did not adequately consider
exposure measurement error, which
they asserted is an important source of
bias in epidemiological studies that can
bias effect estimates in either direction
(e.g., API, 2012, Attachment 1, pp. 19 to
20).
The EPA agrees that exposure
measurement error is an important
source of uncertainty and that the
variability in risk estimates observed in
multi-city studies could be attributed, in
part, to exposure error due to
measurement-related issues (77 FR
38910). However, the Agency disagrees
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
with the commenters’ assertion that
exposure measurement error was not
adequately considered in this review.
The Integrated Science Assessment
included an extensive discussion that
addresses issues of exposure
measurement error (U.S. EPA, 2009a,
sections 2.3.2 and 3.8.6). Exposure
measurement error may lead to bias in
effect estimates in epidemiological
studies. A number of studies evaluated
in the last review (U.S. EPA, 2004,
section 8.4.5) and in the current review
(U.S. EPA, 2009a, section 3.8.6) have
discussed the direction and magnitude
of bias resulting from specified patterns
of exposure measurement error
(Armstrong 1998; Thomas et al. 1993;
Carroll et al. 1995) and have generally
concluded ‘‘classical’’ (i.e., random,
within-person) exposure measurement
error can bias effect estimates towards
the null. Therefore, consistent with
conclusions reached in the last review,
the Integrated Science Assessment
concluded ‘‘in most circumstances,
exposure error tends to bias a health
effect estimate downward’’ (U.S. EPA,
2009a, sections 2.3.2 and 3.8.6)
(emphasis added). Thus, the EPA has
both considered and accounted for the
possibility of exposure measurement
error, and the possible bias would make
it more difficult to detect true
associations, not less difficult.
(d) Model Specification
Commenters contended that the EPA
did not account for the fact that
‘‘selecting an appropriate statistical
model for epidemiologic studies of air
pollution involves several choices that
involve much ambiguity, scant
biological evidence, and a profound
impact on analytic results, given that
many estimated associations are weak’’
(ACC, 2012, p. 5). For short-term
exposure studies, the EPA recognizes, as
summarized in the HEI review panel
commentary that selecting a level of
control to adjust for time-varying
factors, such as temperature, in timeseries epidemiological studies involves
a trade-off (HEI, 2003). For example, if
the model does not sufficiently adjust
for the relationship between the health
outcome and temperature, some effects
of temperature could be falsely ascribed
to the pollution variable. Conversely, if
an overly aggressive approach is used to
control for temperature, the result
would possibly underestimate the
pollution-related effect and compromise
the ability to detect a small but true
pollution effect (U.S. EPA, 2004, p. 8–
236; HEI, 2003, p. 266). The selection of
approaches to address such variables
depends in part on prior knowledge and
judgments made by the investigators, for
PO 00000
Frm 00034
Fmt 4701
Sfmt 4700
example, about weather patterns in the
study area and expected relationships
between weather and other time-varying
factors and health outcomes considered
in the study. As demonstrated in section
6.5 of the Integrated Science
Assessment, the EPA thoroughly
considered each of these issues and the
overall effect of different model
specifications on the association
between short-term PM2.5 exposure and
mortality. Regardless of the model
employed, consistent positive
associations were observed across
studies that controlled for the potential
confounding effects of time and weather
using different approaches (U.S. EPA
2009a, Figure 6–27). The EPA also
considered the influence of model
specification in the examination of longterm PM2.5 exposure studies. For
example, in section 7.6 of the Integrated
Science Assessment, Figures 7–6 and 7–
7 summarize the collective evidence
that evaluated the association between
long-term PM2.5 exposure and mortality.
Regardless of the model used, these
studies collectively found evidence of
consistent positive associations between
long-term PM2.5 exposure and mortality.
The EPA, therefore, disagrees with
commenters that model specification
was not considered when evaluating the
epidemiological evidence used to form
causality determinations. The EPA
specifically points out that the process
of assessing the scientific quality and
relevance of epidemiological studies
includes examining ‘‘important
methodological issues (e.g., lag or time
period between exposure and effects,
model specifications, thresholds,
mortality displacement) related to
interpretation of the health evidence
(U.S. EPA, 2009, p. 1–9).’’ Consistent
with the conclusions of the 2004 PM Air
Quality Criteria Document, the EPA
recognizes that there is still no clear
consensus at this time as to what
constitutes appropriate control of
weather and temporal trends in shortterm exposure studies, and that no
single statistical modeling approach is
likely to be most appropriate in all cases
(U.S. EPA, 2004, p. 8–238). However,
the EPA believes that the available
evidence interpreted in light of these
remaining uncertainties does provide
increased confidence relative to the last
review in the reported associations
between short- and long-term PM2.5
exposures and mortality and morbidity
effects, alone and in combination with
other pollutants.
(e) Concentration-Response
Relationship
Additionally, commenters questioned
the interpretation of the shape of the
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
concentration-response relationship,
specifically stating that multiple studies
have demonstrated that there is a
threshold in the PM-health effect
relationship and that the log-linear
model is not biologically plausible (API,
2012, Attachment 9; ACC, 2012,
Appendix A, pp. 7 to 8). The EPA
disagrees with this assertion due to the
number of studies evaluated in the
Integrated Science Assessment that
continue to support the use of a nothreshold, log-linear model to most
appropriately represent the PM
concentration-response relationship
(U.S. EPA, 2009a, section 2.4.3). While
recognizing that uncertainties remain,
the EPA believes that our understanding
of this issue for both long- and shortterm exposure studies has advanced
since the last review. As discussed in
the Integrated Science Assessment, both
long- and short-term exposure studies
have employed a variety of statistical
approaches to examine the shape of the
concentration-response function and
whether a threshold exists. While the
EPA recognizes that there likely are
individual biological thresholds for
specific health responses, the Integrated
Science Assessment concluded the
overall evidence from existing
epidemiological studies does not
support the existence of thresholds at
the population level, for effects
associated with either long-term or
short-term PM exposures within the
ranges of air quality observed in these
studies (U.S. EPA, 2009a, section
2.4.3).61 The Integrated Science
Assessment concluded that this
evidence collectively supported the
conclusion that a no-threshold, loglinear model is most appropriate (U.S.
EPA, 2009a, sections 6.2.10.10, 6.5.2.7,
and 7.6.4). CASAC likewise advised that
‘‘[a]lthough there is increasing
uncertainty at lower levels, there is no
evidence of a threshold’’ (Samet, 2010d,
p. ii).
The EPA recognizes that some shortterm exposure studies have examined
the PM2.5 concentration-response
relationship in individual cities or on a
city-to-city basis and observed
heterogeneity in the shape of the
concentration-response curve across
cities. As discussed in (b) above, these
findings are a source of uncertainty that
the EPA agrees requires further
investigation. Nonetheless, the
Integrated Science Assessment
concluded that ‘‘the studies evaluated
61 While epidemiological analyses have not
identified a population threshold in the range of air
quality concentrations evaluated in these studies,
the EPA recognizes that it is possible that such
thresholds exist towards the lower end of these
ranges (or below these ranges).
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
further support the use of a nothreshold, log-linear model, but
additional issues such as the influence
of heterogeneity in estimates between
cities and the effects of seasonal and
regional differences in PM on the
concentration-response-relationship still
require further investigation’’ (U.S. EPA,
2009a, p. 2–25).
(f) Relative Toxicity of PM2.5
Components
Some commenters highlighted
uncertainties in understanding the role
of individual constituents within the
mix of fine particles. These commenters
asserted that a mass-based standard may
not be appropriate due to the growing
body of evidence indicating that certain
PM2.5 components may be more closely
related to specific health outcomes (e.g.,
EC and OC) (EPRI, 2012, p. 2).
With regard to questions about the
role of individual constituents within
the mix of fine particles, as a general
matter, the EPA recognizes that
although new research directed toward
this question has been conducted since
the last review, important questions
remain and the issue remains an
important element in the Agency’s
ongoing research program. At the time
of the last review, the Agency
determined that it was appropriate to
continue to control fine particles as a
group, as opposed to singling out any
particular component or class of fine
particles (71 FR 61162 to 61164, October
17, 2006). This distinction was based
largely on epidemiological evidence of
health effects using various indicators of
fine particles in a large number of areas
that had significant contributions of
differing components or sources of fine
particles, together with some limited
experimental studies that provided
some evidence suggestive of health
effects associated with high
concentrations of numerous fine particle
components.
In this review, as discussed in the
proposal (77 FR 38922 to 38923) and in
section III.E.1 below, while most
epidemiological studies continue to be
indexed by PM2.5 mass, several recent
epidemiological studies included in the
Integrated Science Assessment have
used PM2.5 speciation data to evaluate
health effects associated with fine
particle exposures. In the Integrated
Science Assessment, the EPA
thoroughly evaluated the scientific
evidence that examined the effect of
different PM2.5 components and sources
on a variety of health outcomes (U.S.
EPA, 2009a, section 6.6) and observed
that the available information continues
to suggest that many different chemical
components of fine particles and a
PO 00000
Frm 00035
Fmt 4701
Sfmt 4700
3119
variety of different types of source
categories are all associated with, and
probably contribute to, effects
associated with PM2.5. The Integrated
Science Assessment concluded that the
current body of scientific evidence
indicated that ‘‘many constituents of PM
can be linked with differing health
effects and the evidence is not yet
sufficient to allow differentiation of
those constituents or sources that are
more closely related to specific health
outcomes’’ (U.S. EPA, 2009a, p. 2–26
and 6–212). Furthermore, the Policy
Assessment concluded that the evidence
is not sufficient to support eliminating
any component or group of components
associated with any specific source
categories from the mix of fine particles
included in the PM2.5 indicator (U.S.
EPA, 2009a, p. 2–56). CASAC agreed
that it was reasonable to retain PM2.5 as
an indicator for fine particles in this
review as ‘‘[t]here was insufficient peerreviewed literature to support any other
indicator at this time’’ (Samet, 2010c, p.
12).
This information is relevant to the
Agency’s decision to retain PM2.5 as the
indicator for fine particles as discussed
in section III.E.1 below. The EPA also
believes that it is relevant to the
Agency’s conclusion as to whether
revision of the suite of primary PM2.5
standards is appropriate. While there
remain uncertainties about the role and
relative toxicity of various components
of fine PM, the current evidence
continues to support the view that fine
particles should be addressed as a group
for purposes of public health protection.
In summary, in considering the above
issues related to uncertainties in the
underlying health science, on balance,
the EPA believes that the available
evidence interpreted in light of these
remaining uncertainties does provide
increased confidence relative to the last
review in the reported associations
between long- and short-term PM2.5
exposures and mortality and morbidity
effects, alone and in combination with
other pollutants, and supports stronger
inferences as to the causal nature of the
associations. The EPA also believes that
this increased confidence, when taken
in context of the entire body of available
health effects evidence and in light of
the evidence from epidemiological
studies of associations observed in areas
meeting the current primary PM2.5
standards, specifically in areas meeting
the current primary annual PM2.5
standard, adds support to its conclusion
that the current suite of PM2.5 standards
needs to be revised to provide increased
public health protection.
(4) In asserting that there is no
evidence of greater risk since the 2006
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
3120
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
review to justify lowering the current
annual PM2.5 standard, some
commenters argued that, ‘‘if the current
primary PM2.5 annual standard of 15 mg/
m3 was considered to be adequately
protective of public health in 2006,
given relative risk estimates that EPA
was using at that time, then that
standard would surely still be
adequately protective of the public
health if relative risk estimates remain
at the same level (or lower)’’ (UARG,
2012, Attachment 1, p. 24). These
commenters compared risk coefficients
used for mortality in the EPA’s risk
assessment done in the last review with
those from the Agency’s core risk
assessment done as part of this review,
and they concluded that ‘‘the entire
range of the core relative risk for longterm mortality is lower now than it was
in the prior review’’ (UARG, 2012,
Attachment 1, p. 24). These commenters
used this conclusion as the basis for a
claim that there is no reason to revise
the current annual PM2.5 standard.
The EPA believes that this claim is
fundamentally flawed. In comparing the
scientific understanding of the risk
presented by exposure to PM2.5 between
the last and current reviews, one must
examine not only the quantitative
estimate of risk from those exposures
(e.g., the numbers of premature deaths
or increased hospital admissions at
various concentrations), but also the
degree of confidence that the Agency
has that the observed health effects are
causally linked to PM2.5 exposure at
those concentrations. As documented in
the Integrated Science Assessment and
in the recommendations and
conclusions of CASAC, the EPA
recognizes significant advances in our
understanding of the health effects of
PM2.5, based on evidence that is stronger
than in the last review. As a result of
these advances, the EPA is now more
certain that fine particles, alone or in
combination with other pollutants,
present a significant risk to public
health at concentrations allowed by the
current primary PM2.5 standards. From
this more comprehensive perspective,
since the risks presented by PM2.5 are
more certain, similar or even somewhat
lower relative risk estimates would not
be a basis to conclude that no revision
to the suite of PM2.5 standards is
‘‘requisite’’ to protect public health with
an adequate margin of safety. This also
ignores that the relative risk estimate is
only one factor considered by the
Administrator, e.g. it ignores that
epidemiological studies since the last
review indicate associations between
PM2.5 and mortality and morbidity in
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
areas meeting the current annual
standard.
In any case, the commenters’ reliance
on the flawed 2006 review is misplaced.
As discussed in section III.A.2 above,
the D.C. Circuit remanded
Administrator Johnson’s 2006 decision
to retain the primary annual PM2.5
standard because the Agency failed to
adequately explain why the annual
standard provided the requisite
protection from both short- and longterm exposure to fine particles
including protection for at-risk
populations. The 2006 standard was
also at sharp odds with CASAC advice
and recommendations as to the requisite
level of protection (Henderson,
2006a,b). In other words, the 2006
primary annual PM2.5 standard is not an
appropriate benchmark for comparison.
(5) Some of these commenters also
identified ‘‘new’’ as well as older
studies that had been included in prior
reviews as providing additional
evidence that the causality
determinations presented in the
Integrated Science Assessment did not
consider the totality of the scientific
literature, further supporting their view
that a revision of the PM2.5 is
unwarranted. As discussed in section
II.B.3 above, the EPA notes that, as in
past NAAQS reviews, the Agency is
basing the final decisions in this review
on the studies and related information
included in the Integrated Science
Assessment that have undergone
CASAC and public review, and will
consider newly published studies for
purposes of decisionmaking in the next
PM NAAQS review. In provisionally
evaluating commenters’ arguments (see
Response to Comments document), the
EPA notes that its provisional
assessment of ‘‘new’’ science found that
such studies did not materially change
the conclusions reached in the
Integrated Science Assessment (U.S.
EPA, 2012b).
3. Administrator’s Final Conclusions
Concerning the Adequacy of the Current
Primary PM2.5 Standards
Having carefully considered the
public comments, as discussed above,
the Administrator believes the
fundamental scientific conclusions on
the effects of PM2.5 reached in the
Integrated Science Assessment, and
discussed in the Policy Assessment, are
valid. In considering whether the suite
of primary PM2.5 standards should be
revised, the Administrator places
primary consideration on the evidence
obtained from the epidemiological
studies. The Administrator believes that
this literature, combined with the other
scientific evidence discussed in the
PO 00000
Frm 00036
Fmt 4701
Sfmt 4700
Integrated Science Assessment,
collectively represents a strong and
generally robust body of evidence of
serious health effects associated with
both long- and short-term exposures to
PM2.5. As discussed in the Integrated
Science Assessment and Policy
Assessment, the EPA believes that much
progress has been made since the last
review in reducing some of the major
uncertainties that were important
considerations in establishing the
current suite of PM2.5 standards. In that
context, the Administrator finds the
evidence of serious health effects
reported in exposure studies conducted
in areas with long-term mean
concentrations ranging from
approximately at or above the level of
the annual standard to long-term mean
concentrations significantly below the
level of the annual standard to be
compelling, especially in light of the
extent to which such studies are part of
an overall pattern of positive and
frequently statistically significant
associations across a broad range of
studies. The information in the
quantitative risk assessment lends
support to this conclusion.
There has been extensive critical
review of this body of evidence, the
quantitative risk assessment, and related
uncertainties, including review by
CASAC and the public. The public
comments on the basis for the EPA’s
proposed decision to revise the suite of
primary PM2.5 standards have identified
a number of issues about which
different parties disagree including
issues for which additional research is
warranted. Having weighed all
comments and the advice of CASAC, the
Administrator believes that since the
last review the overall uncertainty about
the public health risks associated with
both long- and short-term exposure to
PM2.5 has been diminished to an
important degree. The remaining
uncertainties in the available evidence
do not diminish confidence in the
associations between exposure to fine
particles and mortality and serious
morbidity effects. Based on her
increased confidence in the association
between exposure to PM2.5 and serious
public health effects, combined with
evidence of such an association in areas
that would meet the current standards,
the Administrator agrees with CASAC
that revision of the current suite of
PM2.5 standards to provide increased
public health protection is necessary.
Based on these considerations, the
Administrator concludes that the
current suite of primary PM2.5 standards
is not sufficient, and thus not requisite,
to protect public health with an
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
adequate margin of safety, and that
revision is needed to increase public
health protection.
It is important to note that this
conclusion, and the reasoning on which
it is based, do not resolve the question
of what specific revisions are
appropriate. That requires looking
specifically at the current 24-hour and
annual PM2.5 standards, including their
indicator, averaging times, forms, and
levels, and evaluating the scientific
evidence and other information relevant
to determining the appropriate revision
of the suite of standards.
tkelley on DSK3SPTVN1PROD with
E. Conclusions on the Elements of the
Primary Fine Particle Standards
1. Indicator
In initially setting standards for fine
particles in 1997, the EPA concluded it
was appropriate to control fine particles
as a group, rather than singling out any
particular component or class of fine
particles. The EPA noted that
community health studies had found
significant associations between various
indicators of fine particles, and that
health effects in a large number of areas
had significant mass contributions of
differing components or sources of fine
particles. In addition, a number of
toxicological and controlled human
exposure studies had reported health
effects associations with high
concentrations of numerous fine particle
components. It was also not possible to
rule out any component within the mix
of fine particles as not contributing to
the fine particle effects found in the
epidemiologic studies (62 FR 38667,
July 18, 1977). In establishing a sizebased indicator in 1977 to distinguish
fine particles from particles in the
coarse mode, the EPA noted that the
available epidemiological studies of fine
particles were based largely on PM2.5
and also considered monitoring
technology that was generally available.
The selection of a 2.5 mm size cut
reflected the regulatory importance of
defining an indicator that would more
completely capture fine particles under
all conditions likely to be encountered
across the U.S., especially when fine
particle concentrations and humidity
are likely to be high, while recognizing
that some small coarse particles would
also be captured by current methods to
monitor PM2.5 (62 FR 38666 to 38668,
July 18, 1997). In the last review, based
on the same considerations, the EPA
again recognized that the available
information supported retaining the
PM2.5 indicator and remained too
limited to support a distinct standard
for any specific PM2.5 component or
group of components associated with
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
any source categories of fine particles
(71 FR 61162 to 61164, October 17,
2006).
In this current review, the same
considerations continue to apply for
selection of an appropriate indicator for
fine particles. As an initial matter, the
Policy Assessment recognizes that the
available epidemiological studies
linking mortality and morbidity effects
with long- and short-term exposures to
fine particles continue to be largely
indexed by PM2.5. For the same reasons
discussed in the last two reviews, the
Policy Assessment concluded that it
was appropriate to consider retaining a
PM2.5 indicator to provide protection
from effects associated with long- and
short-term fine particle exposures (U.S.
EPA, 2011a, p. 2–50).
The Policy Assessment also
considered the expanded body of
evidence available in this review to
consider whether there was sufficient
evidence to support a separate standard
for ultrafine particles 62 or whether there
was sufficient evidence to establish
distinct standards focused on regulating
specific PM2.5 components or a group of
components associated with any source
categories of fine particles (U.S. EPA,
2011a, section 2.3.1).
A number of studies available in this
review have evaluated potential health
effects associated with short-term
exposures to ultrafine particles. As
noted in the Integrated Science
Assessment, the enormous number and
larger, collective surface area of
ultrafine particles are important
considerations for focusing on this
particle size fraction in assessing
potential public health impacts (U.S.
EPA, 2009a, p. 6–83). Per unit mass,
ultrafine particles may have more
opportunity to interact with cell
surfaces due to their greater surface area
and their greater particle number
compared with larger particles (U.S.
EPA, 2009a, p. 5–3). Greater surface area
also increases the potential for soluble
components (e.g., transition metals,
organics) to adsorb to ultrafine particles
and potentially cross cell membranes
and epithelial barriers (U.S. EPA, 2009a,
p. 6–83). In addition, evidence available
in this review suggests that the ability
of particles to enhance allergic
sensitization is associated more strongly
with particle number and surface area
than with particle mass (U.S. EPA,
2009a, p. 6–127).
New evidence, primarily from
controlled human exposure and
62 Ultrafine particles, generally including
particles with a mobility diameter less than or equal
to 0.1 mm, are emitted directly to the atmosphere
or are formed by nucleation of gaseous constituents
in the atmosphere (U.S. EPA, 2009a, p. 3–3).
PO 00000
Frm 00037
Fmt 4701
Sfmt 4700
3121
toxicological studies, expands our
understanding of cardiovascular and
respiratory effects related to short-term
ultrafine particle exposures. However,
the Policy Assessment concluded that
this evidence was still very limited and
largely focused on exposure to diesel
exhaust, for which the Integrated
Science Assessment concluded it was
unclear whether the effects observed are
due to ultrafine particles, larger
particles within the PM2.5 mixture, or
the gaseous components of diesel
exhaust (U.S. EPA, 2009a, p. 2–22). In
addition, the Integrated Science
Assessment noted uncertainties
associated with the controlled human
exposure studies using concentrated
ambient particle systems which have
been shown to modify the composition
of ultrafine particles (U.S. EPA, 2009a,
p. 2–22, see also section 1.5.3).
The Policy Assessment recognized
that there are relatively few
epidemiological studies that have
examined potential cardiovascular and
respiratory effects associated with shortterm exposures to ultrafine particles
(U.S. EPA, 2011a, p. 2–51). These
studies have reported inconsistent and
mixed results (U.S. EPA, 2009a, section
2.3.5).
Collectively, in considering the body
of scientific evidence available in this
review, the Integrated Science
Assessment concluded that the
currently available evidence was
suggestive of a causal relationship
between short-term exposures to
ultrafine particles and cardiovascular
and respiratory effects. Furthermore, the
Integrated Science Assessment
concluded that evidence was inadequate
to infer a causal relationship between
short-term exposure to ultrafine
particles and mortality as well as longterm exposure to ultrafine particles and
all outcomes evaluated (U.S. EPA,
2009a, sections 2.3.5, 6.2.12.3, 6.3.10.3,
6.5.3.3, 7.2.11.3, 7.3.9, 7.4.3.3, 7.5.4.3,
and 7.6.5.3; Table 2–6).
With respect to our understanding of
ambient ultrafine particle
concentrations, at present, there is no
national network of ultrafine particle
samplers; thus, only episodic and/or
site-specific data sets exist (U.S. EPA,
2009a, p. 2–2). Therefore, the Policy
Assessment recognized a national
characterization of concentrations,
temporal and spatial patterns, and
trends was not possible at this time, and
the availability of ambient ultrafine
measurements to support health studies
was extremely limited (U.S. EPA, 2011a,
p. 2–51). In general, measurements of
ultrafine particles are highly dependent
on monitor location and, therefore, more
subject to exposure error than
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
3122
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
accumulation mode particles (U.S. EPA,
2009a, p. 2–22). Furthermore, the
number of ultrafine particles generally
decreases sharply downwind from
sources, as ultrafine particles may grow
into the accumulation mode by
coagulation or condensation (U.S. EPA,
2009a, p. 3–89). Limited studies of
ambient ultrafine particle measurements
have suggested that these particles
exhibit a high degree of spatial and
temporal heterogeneity driven primarily
by differences in nearby source
characteristics (U.S. EPA, 2009a, p. 3–
84). Internal combustion engines and,
therefore, roadways are a notable source
of ultrafine particles, so concentrations
of these particles near roadways are
generally expected to be elevated (U.S.
EPA, 2009a, p. 2–3). Concentrations of
ultrafine particles have been reported to
drop off much more quickly with
distance from roadways than fine
particles (U.S. EPA, 2009a, p. 3–84).
In considering both the currently
available health effects evidence and the
air quality data, the Policy Assessment
concluded that this information was
still too limited to provide support for
consideration of a distinct PM standard
for ultrafine particles (U.S. EPA, 2011a,
p. 2–52).
In addressing the issue of particle
composition, the Integrated Science
Assessment concluded that, ‘‘[f]rom a
mechanistic perspective, it is highly
plausible that the chemical composition
of PM would be a better predictor of
health effects than particle size’’ (U.S.
EPA, 2009a, p. 6–202). Heterogeneity of
ambient concentrations of PM2.5
constituents (e.g., elemental carbon,
organic carbon, sulfates, nitrates)
observed in different geographical
regions as well as regional heterogeneity
in PM2.5-related health effects reported
in a number of epidemiological studies
are consistent with this hypothesis (U.S.
EPA, 2009a, section 6.6).
With respect to the availability of
ambient measurement data for fine
particle components in this review, the
Policy Assessment noted that there were
now more extensive ambient PM2.5
speciation measurement data available
through the Chemical Speciation
Network (CSN) than in previous reviews
(U.S. EPA, 2011a, section 1.3.2 and
Appendix B, section B.1.3). The
Integrated Science Assessment observed
that data from the CSN provided further
evidence of spatial and seasonal
variation in both PM2.5 mass and
composition among cities and
geographic regions (U.S. EPA, 2009a,
pp. 3–50 to 3–60; Figures 3–12 to 3–18;
Figure 3–47). Some of this variation may
be related to regional differences in
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
meteorology, sources, and topography
(U.S. EPA, 2009a, p. 2–3).
The currently available
epidemiological, toxicological, and
controlled human exposure studies
evaluated in the Integrated Science
Assessment on the health effects
associated with ambient PM2.5
constituents and categories of fine
particle sources used a variety of
quantitative methods applied to a broad
set of PM2.5 constituents, rather than
selecting a few constituents a priori
(U.S. EPA, 2009a, p. 2–26).
Epidemiological studies have used
measured ambient PM2.5 speciation
data, including monitoring data from
the CSN, while all of the controlled
human exposure and most of the
toxicological studies have used
concentrated ambient particles and
analyzed the constituents therein (U.S.
EPA, 2009a, p. 6–203).63 The CSN
provides PM2.5 speciation
measurements generally on a one-inthree or one-in-six day sampling
schedule and, thus, does not capture
data every day at most sites.64
The Policy Assessment recognized
that several new multi-city studies
evaluating short-term exposures to fine
particle constituents are now available.
These studies continued to show an
association between mortality and
cardiovascular and/or respiratory
morbidity effects and short-term
exposures to various PM2.5 components
including nickel, vanadium, elemental
carbon, organic carbon, nitrates, and
sulfates (U.S. EPA, 2011a, section 2.3.1;
U.S. EPA, 2009a, sections 6.5.2.5 and
6.6).
Limited evidence is available to
evaluate the health effects associated
with long-term exposures to PM2.5
components (U.S. EPA, 2009a, section
7.6.2). The Policy Assessment noted the
most significant new evidence was
provided by a study that evaluated
multiple PM2.5 components and an
indicator of traffic density in an
63 Most studies considered between 7 to 20
ambient PM2.5 constituents, with elemental carbon,
organic carbon, sulfates, nitrates, and metals most
commonly measured. Many of the studies grouped
the constituents with various factorization or source
apportionment techniques to examine the
relationship between the grouped constituents and
various health effects. However, not all studies
labeled the constituent groupings according to their
presumed source and a small number of controlled
human exposure and toxicological studies did not
use any constituent grouping. These differences
across studies substantially limit any integrative
interpretation of these studies (U.S. EPA, 2009a, p.
6–203).
64 To expand our understanding of the role of
specific PM2.5 components and sources with respect
to the observed health effects, researchers have
expressed a strong interest in having access to PM2.5
speciation measurements collected more frequently
(U.S. EPA, 2011a, p. 2–53, including footnote 47).
PO 00000
Frm 00038
Fmt 4701
Sfmt 4700
assessment of health effects related to
long-term exposure to PM2.5 (Lipfert et
al., 2006a). Using health data from a
cohort of U.S. military veterans and
PM2.5 measurement data from the CSN,
Lipfert et al. (2006a) reported positive
associations between mortality and
long-term exposures to nitrates,
elemental carbon, nickel, and vanadium
as well as traffic density and peak ozone
concentrations (U.S. EPA, 2011a, p. 2–
54; U.S. EPA, 2009a, pp. 7–89 to 7–90).
With respect to source categories of
fine particles potentially associated with
a range of health endpoints, the
Integrated Science Assessment reported
that the currently available evidence
suggests associations between
cardiovascular effects and a number of
specific PM2.5-related source categories,
including oil combustion, wood or
biomass burning, motor vehicle
emissions, and crustal or road dust
sources (U.S. EPA, 2009a, section 6.6;
Table 6–18). In addition, a few studies
have evaluated associations between
PM2.5-related source categories and
mortality. For example, one study
reported an association between
mortality and a PM2.5 coal combustion
factor (Laden et al., 2000), while other
studies linked mortality to a secondary
sulfate long-range transport PM2.5
source (Ito et al., 2006; Mar et al., 2006)
(U.S. EPA, 2009a, section 6.6.2.1). Other
studies have looked at different
components of particulate matter. There
was less consistency in associations
observed between selected sources of
fine particles and respiratory health
endpoints, which may be partially due
to the fact that fewer studies have
evaluated respiratory-related outcomes
and measures. However, there was some
evidence for PM2.5-related associations
with secondary sulfate and decrements
in lung function in asthmatic and
healthy adults (U.S. EPA, 2009a, p. 6–
211; Gong et al., 2005; Lanki et al.,
2006). A couple of studies have
observed an association between
respiratory endpoints in children and
adults with asthma and surrogates for
the crustal/soil/road dust and traffic
sources of PM (U.S. EPA, 2009a, p. 6–
205; Gent et al., 2009; Penttinen et al.,
2006).
Recent studies have shown that
source apportionment methods have the
potential to add useful insights into
which sources and/or PM constituents
may contribute to different health
effects. Of particular interest are several
epidemiological studies that compared
source apportionment methods and
reported consistent results across
research groups (U.S. EPA, 2009a, p. 6–
211; Hopke et al., 2006; Ito et al., 2006;
Mar et al., 2006; Thurston et al., 2005).
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
These studies reported associations
between total mortality and secondary
sulfate in two cities for two different lag
times. The sulfate effect was stronger for
total mortality in Washington, DC and
for cardiovascular-related mortality in
Phoenix (U.S. EPA, 2009a, p. 6–204).
These studies also found some evidence
for associations with mortality and a
number of source categories (e.g.,
biomass/wood combustion, traffic,
copper smelter, coal combustion, sea
salt) at various lag times (U.S. EPA,
2009a, p. 6–204). Sarnat et al. (2008)
compared three different source
apportionment methods and reported
consistent associations between
emergency department visits for
cardiovascular diseases with mobile
sources and biomass combustion as well
as increased respiratory-related
emergency department visits associated
with secondary sulfate (U.S. EPA,
2009a, pp. 6–204 and 6–211).
Collectively, in considering the
currently available evidence for health
effects associated with specific PM2.5
components or groups of components
associated with any source categories of
fine particles as presented in the
Integrated Science Assessment, the
Policy Assessment concluded that
additional information available in this
review continues to provide evidence
that many different constituents of the
fine particle mixture as well as groups
of components associated with specific
source categories of fine particles are
linked to adverse health effects (U.S.
EPA, 2011a, p. 2–55). However, as noted
in the Integrated Science Assessment,
while ‘‘[t]here is some evidence for
trends and patterns that link particular
ambient PM constituents or sources
with specific health outcomes * * *
there is insufficient evidence to
determine whether these patterns are
consistent or robust’’ (U.S. EPA, 2009a,
p. 6–210). Assessing this information,
the Integrated Science Assessment
concluded that ‘‘the evidence is not yet
sufficient to allow differentiation of
those constituents or sources that are
more closely related to specific health
outcomes’’ (U.S. EPA, 2009a, pp. 2–26
and 6–212). Therefore, the Policy
Assessment concluded that the
currently available evidence is not
sufficient to support consideration of a
separate indicator for a specific PM2.5
component or group of components
associated with any source category of
fine particles. Furthermore, the Policy
Assessment concluded that the evidence
is not sufficient to support eliminating
any component or group of components
associated with any source categories of
fine particles from the mix of fine
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
particles included in the PM2.5 indicator
(U.S. EPA, 2011a, p. 2–56).
The CASAC agreed with the EPA staff
conclusions presented in the Policy
Assessment and concluded that it is
appropriate to consider retaining PM2.5
as the indicator for fine particles and
further asserted, ‘‘There [is] insufficient
peer-reviewed literature to support any
other indicator at this time’’ (Samet,
2010c, p. 12). CASAC expressed a strong
desire for the EPA to ‘‘look ahead to
future review cycles and reinvigorate
support for the development of evidence
that might lead to newer indicators that
may correlate better with the health
effects associated with ambient air
concentrations of PM * * *’’ (Samet,
2010c, p 2).
Consistent with the staff conclusions
presented in the Policy Assessment and
CASAC advice, the Administrator
proposed to retain PM2.5 as the indicator
for fine particles. Further, the
Administrator provisionally concluded
that currently available scientific
information does not provide a
sufficient basis for supplementing massbased, primary fine particle standards
with standards using a separate
indicator for ultrafine particles or a
separate indicator for a specific PM2.5
component or group of components
associated with any source categories of
fine particles. In addition, the
Administrator also provisionally
concluded that the currently available
scientific information did not provide a
sufficient basis for eliminating any
individual component or group of
components associated with any source
categories from the mix of fine particles
included in the PM2.5 mass-based
indicator.
The EPA received comparatively few
public comments on issues related to
the indicator for fine particles.65 Some
commenters emphasized the need to
conduct additional research to more
fully understand the effect of specific
PM2.5 components and/or sources on
public health. These commenters
expressed views about the importance
of evaluating health effect associations
with various fine particle components
and types of source categories as a basis
for focusing ongoing and future research
to reduce uncertainties in this area and
for considering whether alternative
indicator(s) may be appropriate to
consider in future PM NAAQS reviews
for standards intended to protect against
the array of health effects that have been
associated with fine particles as indexed
by PM2.5. For example, the PSR
encouraged more research and
65 No public comments were submitted regarding
the use of a different size cut for fine particles.
PO 00000
Frm 00039
Fmt 4701
Sfmt 4700
3123
monitoring related to PM2.5 components
and noted the importance of
components associated with coal
combustion (PSR, 2012, pp. 5 to 6). EPRI
asserted that ‘‘new’’ studies support
focusing on EC and OC and encouraged
the EPA to seriously consider the massbased approach (EPRI, 2012, p. 2).
Likewise, Georgia Mining Association
supported additional monitoring and
research efforts related to PM2.5
composition and specifically
encouraged the evaluation of using
particle number (e.g., particle count)
(GMA, 2012, pp. 2 to 3).
The Administrator agrees with
CASAC as well as these commenters
that the results of additional research
and monitoring efforts will be helpful
for informing future PM NAAQS
reviews. Information from such studies
could also help inform the development
of strategies that emphasize control of
specific types of emission sources so as
to address particles of greatest concern
to public health. However, based upon
the scientific information considered in
the Integrated Science Assessment as
well as the public comments
summarized above, the Administrator
continues to take note there is evidence
that many different constituents of the
fine particle mixture as well as groups
of components associated with specific
sources of fine particles are linked to
adverse health effects. Furthermore, she
recognizes that the evidence is not yet
sufficient to differentiate those
constituents or sources that are most
closely related to specific health
outcomes nor to exclude any PM2.5
components or sources of fine particles
from the mix of particles included in the
PM2.5 indicator.
Having considered the public
comments on this issue, the
Administrator concurs with the Policy
Assessment conclusions and CASAC
recommendations and concludes that it
is appropriate to retain PM2.5 as the
indicator for fine particles.
2. Averaging Time
In 1997, the EPA initially set both an
annual standard, to provide protection
from health effects associated with both
long- and short-term exposures to PM2.5,
and a 24-hour standard to supplement
the protection afforded by the annual
standard (62 FR 38667 to 38668, July,
18, 1997). In the last review, the EPA
retained both annual and 24-hour
averaging times (71 FR 61164, October
17, 2006). These decisions were based,
in part, on evidence of health effects
related to both long-term (from a year to
several years) and short-term (from less
than one day to up to several days)
measures of PM2.5.
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
3124
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
The overwhelming majority of studies
conducted since the last review
continue to utilize annual (or multiyear) and 24-hour averaging times,
reflecting the averaging times of the
current PM2.5 standards. These studies
continue to provide evidence that health
effects are associated with annual and
24-hour averaging times. Therefore, the
Policy Assessment concluded it is
appropriate to retain the current annual
and 24-hour averaging times to provide
protection from effects associated with
both long- and short-term PM2.5
exposures (U.S. EPA, 2011a, p. 2–57).
In considering whether the
information available in this review
supports consideration of different
averaging times for PM2.5 standards
specifically with regard to considering a
standard with an averaging time less
than 24 hours to address health effects
associated with sub-daily PM2.5
exposures, the Policy Assessment noted
there continues to be a growing body of
studies that provide additional evidence
of effects associated with exposure
periods less than 24-hours (U.S. EPA,
2011a, p. 2–57). Relative to information
available in the last review, recent
studies provide additional evidence for
cardiovascular effects associated with
sub-daily (e.g., one to several hours)
exposure to PM, especially effects
related to cardiac ischemia, vasomotor
function, and more subtle changes in
markers of systemic inflammation,
hemostasis, thrombosis and coagulation
(U.S. EPA, 2009a, section 6.2). Because
these studies have used different
indicators (e.g., PM2.5, PM10, PM10-2.5,
ultrafine particles), averaging times (e.g.,
1, 2, and 4 hours), and health outcomes,
it is difficult to draw conclusions about
cardiovascular effects associated
specifically with sub-daily exposures to
PM2.5.
With regard to respiratory effects
associated with sub-daily PM2.5
exposures, the currently available
evidence was much sparser than for
cardiovascular effects and continues to
be very limited. The Integrated Science
Assessment concluded that for several
studies of hospital admissions or
medical visits for respiratory diseases,
the strongest associations were observed
with 24-hour average or longer
exposures, not with less than 24-hour
exposures (U.S. EPA, 2009a, section
6.3).
Collectively, the Policy Assessment
concluded that this information, when
viewed as a whole, is too unclear, with
respect to the indicator, averaging time
and health outcome, to serve as a basis
for consideration of establishing a
primary PM2.5 standard with an
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
averaging time shorter than 24-hours at
this time (U.S. EPA, 2011a, p. 2–57).
With regard to health effects
associated with PM2.5 exposure across
varying seasons in this review, Bell et
al. (2008) reported higher PM2.5 risk
estimates for hospitalization for
cardiovascular and respiratory diseases
in the winter compared to other seasons.
In comparison to the winter season,
smaller statistically significant
associations were also reported between
PM2.5 and cardiovascular morbidity for
spring and autumn, and a positive, but
statistically non-significant association
was observed for the summer months. In
the case of mortality, Zanobetti and
Schwartz (2009) reported a 4-fold higher
effect estimate for PM2.5-associated
mortality for the spring as compared to
the winter. Taken together, these results
provided emerging but limited evidence
that individuals may be at greater risk
of dying from higher exposures to PM2.5
in the warmer months and may be at
greater risk of PM2.5-associated
hospitalization for cardiovascular and
respiratory diseases during colder
months of the year (U.S. EPA, 2011a, p.
2–58).
Overall, the Policy Assessment
observed that there are few studies
presently available to deduce a general
pattern in PM2.5-related risk across
seasons. In addition, these studies
utilized 24-hour exposure periods
within each season to assess the PM2.5associated health effects and do not
provide information on health effects
associated with a season-long exposure
to PM2.5. Due to these limitations in the
currently available evidence, the Policy
Assessment concluded that there was no
basis to consider a seasonal averaging
time separate from a 24-hour averaging
time.
Based on the above considerations,
the Policy Assessment concluded that
the currently available information
provided strong support for
consideration of retaining the current
annual and 24-hour averaging times but
does not provide support for
considering alternative averaging times
(U.S. EPA, 2011a, p. 2–58). In addition,
CASAC considered it appropriate to
retain the current annual and 24-hour
averaging times for the primary PM2.5
standards (Samet, 2010c, pp. 2 to 3). At
the time of the proposal, the
Administrator concurred with the staff
conclusions and CASAC advice and
proposed that the averaging times for
the primary PM2.5 standards should
continue to include annual and 24-hour
averages to protect against health effects
associated with long- and short-term
exposures. Furthermore, the
Administrator provisionally concluded,
PO 00000
Frm 00040
Fmt 4701
Sfmt 4700
consistent with conclusions reached in
the Policy Assessment and by CASAC,
that the currently available information
was too limited to support consideration
of alternative averaging times to
establish a national standard with a
shorter-than 24-hour averaging time or
with a seasonal averaging time.
The EPA received no significant
public comments on the issue of
averaging time for the PM2.5 primary
standards. The Administrator concurs
with recommendations made by CASAC
and the staff conclusions presented in
the Policy Assessment and concludes,
as proposed, that it is appropriate to
retain the current annual and 24-hour
averaging times for the primary PM2.5
standards to protect against health
effects associated with long- and shortterm exposure periods.
3. Form
The ‘‘form’’ of a standard defines the
air quality statistic that is to be
compared to the level of the standard in
determining whether an area attains the
standard. In this review, the EPA
considers whether currently available
information supports retaining or
revising the forms for the annual or 24hour PM2.5 standards.
a. Annual Standard
In 1997, the EPA established the form
of the annual PM2.5 standard as an
annual arithmetic mean, averaged over
3 years, from single or multiple
community-oriented monitors. This
form was intended to represent a
relatively stable measure of air quality
and to characterize longer-term areawide PM2.5 concentrations, in
conjunction with a 24-hour standard
designed to provide adequate protection
against localized peak or seasonal PM2.5
concentrations. The level of the
standard was to be compared to
measurements made at each
community-oriented monitoring site, or,
if specific criteria were met,
measurements from multiple
community-oriented monitoring sites
could be averaged (i.e., spatial
averaging) 66 (62 FR 38671 to 38672,
July 18, 1997). The constraints were
intended to ensure that spatial averaging
would not result in inequities in the
level of protection provided by the
standard (62 FR 38672, July 18, 1997).
This approach was consistent with the
epidemiological studies on which the
PM2.5 standard was primarily based, in
which air quality data were generally
averaged across multiple monitors in an
66 Spatial averaging as part of the form of the
annual PM2.5 standard is unique to this standard
and is not used with other PM standards nor with
other NAAQS.
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
area or were taken from a single monitor
that was selected to represent
community-wide exposures.
In the last review, the EPA tightened
the criteria for use of spatial averaging
to provide increased protection for
vulnerable populations exposed to
PM2.5. This change was based in part on
an analysis of the potential for
disproportionate impacts on potentially
at-risk populations, which found that
the highest concentrations in an area
tend to be measured at monitors located
in areas where the surrounding
population is more likely to have lower
education and income levels and higher
percentages of minority populations (71
FR 61166/2, October 17, 2006; U.S. EPA,
2005, section 5.3.6.1).
In this review, as outlined in section
III.B above and discussed more fully in
section III.B.3 of the proposal, there now
exist more health data such that the
Integrated Science Assessment has
identified persons from lower
socioeconomic strata as an at-risk
population (U.S. EPA, 2009a, section
8.1.7; U.S. EPA, 2011a, section 2.2.1).
Moreover, there now exist more years of
PM2.5 air quality data than were
available in the last review.
Consideration in the Policy Assessment
of the spatial variability across urban
areas that was revealed by this
expanded data base has raised questions
as to whether an annual standard that
allows for spatial averaging, even within
specified constraints as narrowed in
2006 (71 FR 61165 to 61167, October 17,
2006), would provide appropriate
public health protection.
In considering the potential for
disproportionate impacts on at-risk
populations, the Policy Assessment
considered an update of an air quality
analysis conducted for the last review
(U.S. EPA, 2011a, pp. 2–59 to 60;
Schmidt, 2011, Analysis A). This
analysis focused on determining
whether the spatial averaging
provisions, as modified in 2006, could
introduce inequities in protection for atrisk populations exposed to PM2.5.
Specifically, the Policy Assessment
considered whether persons of lower
socioeconomic status, minority groups,
or different age groups (i.e., children or
older adults) are more likely than the
general population to live in areas in
which the monitors recording the
highest air quality values in an area are
located. Data used in this analysis
included demographic parameters
measured at the Census Block or Census
Block Group level, including percent
minority population, percent minority
subgroup population, percent of persons
living below the poverty level, percent
of persons 18 years of age or older, and
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
percent of persons 65 years of age and
older. In each candidate geographic
area, data from the Census Block(s) or
Census Block Group(s) surrounding the
location of the monitoring site (as
delineated by radii buffers of 0.5, 1.0,
2.0, and 3.0 miles) in which the highest
air quality value was monitored were
compared to the average of monitored
values in the area. This analysis looked
beyond areas that would meet the
current spatial averaging criteria and
considered all urban areas (i.e., Core
Based Statistical Areas or CBSAs) with
at least two valid annual design value
monitors (Schmidt, 2011, Analysis A).
Recognizing the limitations of such
cross-sectional analyses, the Policy
Assessment observed that the highest
concentrations in an area tend to be
measured at monitors located in areas
where the surrounding populations are
more likely to live below the poverty
line and to have higher percentage of
minorities (U.S. EPA, 2011a, p. 2–60).
Based upon the analysis described
above, the Policy Assessment concluded
that the existing constraints on spatial
averaging, as modified in 2006, may be
inadequate to avoid substantially greater
exposures in some areas, potentially
resulting in disproportionate impacts on
at-risk populations of persons with
lower SES levels as well as minorities.
Therefore, the Policy Assessment
concluded that it was appropriate to
consider revising the form of the annual
PM2.5 standard such that it did not allow
for the use of spatial averaging across
monitors. In doing so, the level of the
annual PM2.5 standard would be
compared to measurements made at the
monitoring site that represents areawide air quality recording the highest
PM2.5 concentrations 67 (U.S. EPA,
2011a, p. 2–60).
The CASAC agreed with staff
conclusions that it was ‘‘reasonable’’ for
the EPA to eliminate the spatial
averaging provisions (Samet, 2010d, p.
2). Further, in CASAC’s comments on
the first draft Policy Assessment, it
noted, ‘‘Given mounting evidence
showing that persons with lower SES
levels are a susceptible group for PMrelated health risks, CASAC
recommends that the provisions that
allow for spatial averaging across
monitors be eliminated for the reasons
cited in the (first draft) Policy
Assessment’’ (Samet, 2010c, p. 13). In
its review of the second draft Policy
Assessment, CASAC recognized
‘‘although much of the epidemiological
67 As
discussed in section VIII.B.1 below, the EPA
is revising several terms associated with PM2.5
monitor placement. Specifically, the EPA is
revoking the term ‘‘community-oriented’’ and
replacing it with the term ‘‘area-wide’’ monitoring.
PO 00000
Frm 00041
Fmt 4701
Sfmt 4700
3125
research has been conducted using
community-wide averages, several key
studies reference the nearest
measurement site, so that some risk
estimates are not necessarily biased by
the averaging process. Further, the
number of such studies is likely to
expand in the future’’ (Samet, 2010d,
pp. 1 to 2).
Only two areas in the country used
the initial spatial averaging provisions
for demonstrating attainment with the
primary annual PM2.5 standard set in
1997 (70 FR 19847, April 14, 2005; U.S.
EPA, 2006c). Since these provisions
were tightened in 2006, no area has
used spatial averaging to demonstrate
attainment. No areas in the country are
currently using the spatial averaging
provisions to demonstrate attainment
with the current primary annual PM2.5
standard.
In considering the Policy
Assessment’s conclusions based on the
results of the analysis discussed above
and concern over the evidence of
potential disproportionate impacts on
at-risk populations as well as CASAC
advice, the Administrator proposed to
revise the form of the annual PM2.5
standard to eliminate the use of spatial
averaging. Thus, the Administrator
proposed revising the form of the
annual PM2.5 standard to compare the
level of the standard with measurements
from each ‘‘appropriate’’ monitor in an
area 68 with no allowance for spatial
averaging. Thus, for an area with
multiple monitors, the appropriate
reporting monitor with the highest
design value would determine the
attainment status for that area.
Of the commenters noted in section
III.D.2 above who supported a more
stringent annual PM2.5 standard, those
who commented on the form of the
annual PM2.5 standard supported the
EPA’s proposal to eliminate the spatial
averaging provisions. These commenters
contended that the EPA’s analyses of the
potential impacts of spatial averaging,
discussed above and in the proposal (77
FR 38924), demonstrated that the
current form results in uneven public
health protection leading to
disproportionate impacts on at-risk
populations. Specifically, the ALA and
other environmental and public health
commenters contended that ‘‘spatial
averaging allows exposure of people to
unhealthy levels of pollution at specific
locales even within an area meeting the
standard’’ (ALA et al., 2012, p. 23).
68 As discussed in section VIII.B.2.b below, the
EPA concludes that PM2.5 monitoring sites at microand middle-scale locations are comparable to the
annual standard if the monitoring site has been
approved by the Regional Administrator as
representing an area-wide location.
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
3126
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
These commenters particularly focused
on the importance for low-income and
minority populations of eliminating the
spatial averaging provisions. They
concluded that spatial averaging ‘‘is an
environmental justice concern because
poor people are more likely to live near
roads, depots, factories, ports, and other
pollution sources.’’ Id. p. 24.
Other commenters (e.g., AAM, 2012;
Dow, 2012) also supported the
elimination of spatial averaging in order
to ‘‘avoid potential disproportionate
impacts on at-risk populations’’ and to
maximize ‘‘the benefits to public health
of reducing the annual PM2.5 standard.’’
However, these groups expressed
concern that the elimination of spatial
averaging, in combination with the
requirement for near road monitors (as
discussed in section VIII.B.3.b.i of the
proposal), would effectively and
inappropriately increase the stringency
of the annual PM2.5 standard.
This concern was also shared by other
commenters who disagreed with the
elimination of spatial averaging. For
example, the Class of ’85 RRG
emphasized concerns about increasing
the stringency of the standard while
providing few health benefits if spatial
averaging is eliminated, particularly in
combination with the requirement for
near-road monitors. These commenters
contended that ‘‘[b]ecause EPA proposes
to use the readings from the highest
single worst case monitor (rather than
the average of all community area
monitors), and since roadway
monitoring locations will likely be
worst case monitors, the proposed
NAAQS will become more stringent
without targeting the PM2.5 species most
harmful to human health’’ (Class of ’85
RRG, 2012, p. 6).
Several commenters also maintained
that because spatial averaging is
consistent with how air quality data are
considered in the underlying
epidemiological studies, such averaging
should not be eliminated. Specifically,
commenters including NAM et al.,
AFPM, and ACC pointed out that PM2.5
epidemiological studies use spatially
averaged multi-monitor concentrations,
rather than the single highest monitor,
when evaluating health effects.
Therefore, these commenters contended
that allowing spatial averaging would
make the PM2.5 standard more
consistent with the approaches used in
the epidemiological studies upon which
the standard is based. In addition, some
commenters also contended that the
EPA failed to consider whether
modifying, rather than eliminating, the
constraints on spatial averaging would
have been sufficient to protect the
public health. If so, these commenters
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
argued that ‘‘elimination of spatial
averaging would go beyond what is
requisite to protect the public health’’
(NAM et al., 2012, p. 20).
In considering the public comments
on the form of the annual standard, the
EPA recognizes a number of
commenters agreed with the basis for
the EPA’s proposal to eliminate spatial
averaging. While other commenters
expressed disagreement or concern with
the proposed decision to eliminate the
spatial averaging provisions, the Agency
notes that these commenters did not
challenge the analyses or considerations
that provided the fundamental basis for
the Administrator’s proposed decision.
Rather, these commenters generally
raised concerns that eliminating the
option for spatial averaging would
increase the stringency of the standard,
especially in light of additional
monitoring sites in near-road
environments (as discussed in section
VIII.B.3.b.1 below).
The EPA does not agree with the
comment that siting some monitors in
near roadway environments makes the
standard more stringent or
impermissibly more stringent. As
discussed in section VIII.B.3.b.i below,
a significant fraction of the population
lives in proximity to major roads, and
these exposures occur in locations that
represent ambient air. Monitoring in
such areas does not make the standard
more stringent than warranted, but
rather affords the intended protection to
the exposed populations, among them
at-risk populations, exposed to fine
particles in these areas. Thus, in cases
where monitors in near roadway
environments are deemed to be
representative of area-wide air quality
they would be compared to the annual
standard (as discussed more fully in
section VIII below). The 24-hour and
annual NAAQS are designed to protect
the public with an adequate margin of
safety, and this siting provision is fully
consistent with providing the protection
the standard is designed to provide and
does not make the standard more
stringent or more stringent than
necessary.
Monitors that are representative of
area-wide air quality may be compared
to the annual standard. This is
consistent with the use of monitoring
data in the epidemiological studies that
provide the primary basis for
determining the level of the annual
standard. In addition, the EPA notes
that the annual standard is designed to
protect against both long- and shortterm exposures through controlling the
broad distribution of air quality across
PO 00000
Frm 00042
Fmt 4701
Sfmt 4700
an area over time.69 It is fully consistent
with the protection the standard is
designed to provide for near road
monitors to be compared to the annual
standard if the monitor is representative
of area-wide air quality. This does not
make the standard either more stringent
or impermissibly more stringent.
In further considering these
comments, the EPA notes that the
stringency or level of protection
provided by each NAAQS is not based
solely on the form of the standard;
rather, the four elements of the standard
that together serve to define each
standard (i.e., indicator, averaging time,
form, and level) must be considered
collectively in evaluating the protection
afforded by each standard. Therefore,
the EPA considers these comments are
also appropriate to discuss collectively
with other issues related to the
appropriate level for annual standard,
and are discussed below in sections
III.E.4.c–d.
In reaching a final decision on the
form of the annual standard, the
Administrator considers the available
analyses, CASAC advice, and public
comments on form as discussed above.
She also considers related issues in the
public comments on the level of the
annual standard as discussed in section
III.E.4.c below. She notes that even
when the annual PM2.5 standard was
first set in 1997, the spatial averaging
provisions included constraints
intended to ensure that inequities in the
level of protection would not result.
These constraints on spatial averaging
were tightened in the last review, based
on an analysis showing the potential for
spatial averaging to allow higher PM2.5
concentrations in locations where
subgroups within the general
population were potentially
disproportionately exposed and hence,
at disproportionate risk (e.g., low
income and minority communities). The
Administrator notes that in proposing to
eliminate spatial averaging altogether in
this review, she has relied on further
analyses in the current review (Schmidt,
2011, Analysis A). As discussed above
and in the proposal (77 FR 38924), these
analyses showed that the current
constraints on spatial averaging may be
inadequate in some areas to avoid
substantially greater exposures for
people living near monitors recording
the highest PM2.5 concentrations. Such
exposures could result in
69 This is in contrast to the 24-hour standard
which is designed to provide supplemental
protection, addressing peak exposures that might
not otherwise be addressed by the annual standard.
Consistent with this, monitors are not required to
be representative of area-wide air quality to be
compared to the 24-hour standard.
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
disproportionate impacts to at-risk
populations, including low-income
populations as well as minority groups.
On this basis, the Administrator
concludes that public health would not
be protected with an adequate margin of
safety in all locations, as required by
law, if disproportionately higher
exposure concentrations in at-risk
populations such as low income
communities as well as minority
communities were averaged together
with lower concentrations measured at
other sites in a large urban area. See
ALA v. EPA, 134 F. 3d 388, 389 (D.C.
Cir., 1998) (‘‘this court has held that
‘NAAQS must protect not only average
healthy individuals, but also sensitive
citizens such as children,’ and ‘if a
pollutant adversely affects the health of
these sensitive individuals, EPA must
strengthen the entire national
standard’’’) and Coalition of Battery
Recyclers Association v. EPA, 604 F 3d.
613, 617 (D.C. Cir., 2010) (‘‘Petitioners’
assertion that the revised lead NAAQS
is overprotective because it is more
stringent than necessary to protect the
entire population of young U.S. children
ignores that the Clean Air Act allows
protection of sensitive
subpopulations.’’) In reaching this
conclusion, the Administrator further
notes that her concern over possible
disproportionate PM2.5-related health
impacts in at-risk populations extends
to populations living near important
sources of PM2.5, including the large
populations that live near major
roadways.70
In light of all of the above
considerations, including consideration
of available analyses, CASAC advice,
and public comments, the
Administrator concludes that the
current form of the annual PM2.5
standard should be revised to eliminate
spatial averaging provisions. Thus, the
level of the revised annual PM2.5
standard established with this rule will
be compared with measurements from
each appropriate monitor in an area,
with no allowance for spatial averaging.
The Administrator’s conclusions with
regard to the appropriate level of the
annual PM2.5 standard to set in
conjunction with this form are
discussed below in section III.E.4.d.
b. 24-Hour Standard
In 1997, the EPA established the form
of the 24-hour PM2.5 standard as the
98th percentile of 24-hour
concentrations at each populationoriented monitor within an area,
70 Section VIII.B.3.b.i below discusses public
comments specifically related to the proposed
requirement for near-road monitors.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
averaged over three years (62 FR at
38671 to 38674, July 18, 1997). The
Agency selected the 98th percentile as
an appropriate balance between
adequately limiting the occurrence of
peak concentrations and providing
increased stability which, when
averaged over 3 years, facilitated
effective health protection through the
development of more stable
implementation programs. By basing the
form of the standard on concentrations
measured at population-oriented
monitoring sites, the EPA intended to
provide protection for people residing
in or near localized areas of elevated
concentrations. In the last review, in
conjunction with lowering the level of
the 24-hour standard, the EPA retained
this form based in part on a comparison
with the 99th percentile form.71
In revisiting the stability of a 98th
versus 99th percentile form for a 24hour standard intended to provide
supplemental protection for a generally
controlling annual standard, an analysis
presented in the Policy Assessment
considered air quality data reported in
2000 to 2008 to update our
understanding of the ratio between
peak-to-mean PM2.5 concentrations.
This analysis provided evidence that the
98th percentile value was a more stable
metric than the 99th percentile (U.S.
EPA, 2011a, Figure 2–2, p. 2–62).
At the time of the proposal, the
Agency recognized that the selection of
the appropriate form of the 24-hour
standard includes maintaining adequate
protection against peak 24-hour
concentrations while also providing a
stable target for risk management
programs, which serves to provide for
the most effective public health
protection in the long run.72 As in
previous reviews, the EPA recognized
that a concentration-based form,
compared to an exceedance-based form,
was more reflective of the health risks
posed by elevated pollutant
concentrations because such a form
gives proportionally greater weight to
days when concentrations are well
above the level of the standard than to
71 In reaching this final decision, the EPA
recognized a technical problem associated with a
potential bias in the method used to calculate the
98th percentile concentration for this form. The
EPA adjusted the sampling frequency requirement
in order to reduce this bias. Accordingly, the
Agency modified the final monitoring requirements
such that areas that are within 5 percent of the
standards are required to increase the sampling
frequency to every day (71 FR 61164 to 61165,
October 17, 2006).
72 See ATA III, 283 F.3d at 374–376 which
concludes that it is legitimate for the EPA to
consider overall stability of the standard and its
resulting promotion of overall effectiveness of
NAAQS control programs in setting a standard that
is requisite to protect the public health.
PO 00000
Frm 00043
Fmt 4701
Sfmt 4700
3127
days when the concentrations are just
above the level of the standard. Further,
the Agency provisionally concluded
that a concentration-based form, when
averaged over three years, provided an
appropriate balance between limiting
peak pollutant concentrations and
providing a stable regulatory target, thus
facilitating the development of more
stable implementation programs.
In considering the information
provided in the Policy Assessment and
recognizing that the degree of public
health protection likely to be afforded
by a standard is a result of the
combination of the form and the level of
the standard, the Administrator
proposed to retain the 98th percentile
form of the 24-hour standard. The
Administrator provisionally concluded
that the 98th percentile form represents
an appropriate balance between
adequately limiting the occurrence of
peak concentrations and providing
increased stability relative to an
alternative 99th percentile form.
Few public commenters commented
specifically on the form of the 24-hour
standard. None of the public
commenters raised objections to
continuing the use of a concentrationbased form for the 24-hour standard.
Many of the individuals and groups
who supported a more stringent 24-hour
PM2.5 standard noted in section III.D.2
above, however, recommended a more
restrictive concentration-based
percentile form, specifically a 99th
percentile form. The limited number of
these commenters who provided a
specific rationale for this
recommendation generally expressed
their concern that the 98th percentile
form could allow too many days where
concentrations exceeded the level of the
standard, and thus fail to adequately
protect public health. Other public
commenters representing state and local
air agencies and industry groups
generally supported retaining the
current 98th percentile form. In most
cases, these groups expressed the
overall view that the current 24-hour
PM2.5 standard, including the form of
the current standard, should be
retained.
The EPA notes that the viewpoints
represented in this review are similar to
comments submitted in the last review
and through various NAAQS reviews.
The EPA recognizes that the selection of
the appropriate form includes
maintaining adequate protection against
peak 24-hour values while also
providing a stable target for risk
management programs, which serves to
provide for the most effective public
E:\FR\FM\15JAR2.SGM
15JAR2
3128
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
health protection in the long run.73
Nothing in the commenters’ views has
provided a reason to change the
Administrator’s previous conclusion
regarding the appropriate balance
represented in the proposed form of the
24-hour PM2.5 standard. Therefore, the
Administrator concurs with staff
conclusions presented in the Policy
Assessment and CASAC
recommendations and concludes that it
is appropriate to retain the 98th
percentile form for the 24-hour PM2.5
standard.
4. Level
In the last review, the EPA selected
levels for the annual and the 24-hour
PM2.5 standards using evidence of
effects associated with periods of
exposure that were most closely
matched to the averaging time of each
standard. Thus, as discussed in section
III.A.1, the EPA relied upon evidence
from long-term exposure studies as the
principal basis for selecting the level of
the annual PM2.5 standard that would
protect against effects associated with
long-term exposures. The EPA relied
upon evidence from the short-term
exposure studies as the principal basis
for selecting the level of the 24-hour
PM2.5 standard that would protect
against effects associated with shortterm exposures. As summarized in
section III.A.2 above, the 2006 decision
to retain the level of the annual PM2.5
standard at 15 mg/m3 74 was challenged
and on judicial review, the DC Circuit
remanded the primary annual PM2.5
standard to the EPA, finding that EPA’s
explanation for its approach to setting
the level of the annual standard was
inadequate.
tkelley on DSK3SPTVN1PROD with
a. General Approach for Considering
Standard Levels
Building upon the lessons learned in
the previous PM NAAQS reviews, in
considering alternative standard levels
supported by the currently available
scientific information, the Policy
Assessment used an approach that
73 As just noted above, it is legitimate for the EPA
to consider promotion of overall effectiveness of
risk management programs designed to attain the
NAAQS, including their overall stability, in setting
a standard that is requisite to protect the public
health. The context for the court’s discussion in
ATA III is identical to that here; whether to adopt
a 98th percentile form for a 24-hour standard
intended to provide supplemental protection for a
generally controlling annual standard.
74 Throughout this section, the annual standard
levels are denoted as integer values for simplicity,
although, as noted above in section II.B.1, Table 1,
the annual standard level is defined to one decimal
place, such that the current annual standard level
is 15.0 mg/m3. Alternative annual standard levels
discussed in this section are similarly defined to
one decimal place.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
integrated evidence-based and riskbased considerations, took into account
CASAC advice, and considered the
issues raised by the court in remanding
the primary annual PM2.5 standard.
Following the general approach
outlined in section III.A.3 above, for the
reasons discussed below, the Policy
Assessment concluded it was
appropriate to consider the protection
afforded by the annual and 24-hour
standards taken together against
mortality and morbidity effects
associated with both long- and shortterm PM2.5 exposures. This was
consistent with the approach taken in
the review completed in 1997 rather
than considering each standard
separately, as was done in the review
completed in 2006.
Beyond looking directly at the
relevant epidemiologic evidence, the
Policy Assessment considered the
extent to which specific alternative
PM2.5 standard levels were likely to
reduce the nature and magnitude of
both long-term exposure-related
mortality risk and short-term exposurerelated mortality and morbidity risk
(U.S. EPA, 2011a, section 2.3.4.2;
U.S.EPA, 2010a, section 4.2.2). As noted
in section III.C above, patterns of
increasing estimated risk reductions
were generally observed as either the
annual or 24-hour standard, or both,
were reduced below the level of the
current standards (U.S. 2011a, Figures
2–11 and 2–12; U.S. EPA, 2010a,
sections 4.2.2, 5.2.2, and 5.2.3).
Based on the quantitative risk
assessment, the Policy Assessment
observed, as discussed in section III.A.3,
that analyses conducted for this and
previous reviews demonstrated that
much, if not most, of the aggregate risk
associated with short-term exposures
results from the large number of days
during which the 24-hour average
concentrations are in the low-to midrange, below the peak 24-hour
concentrations (U.S. EPA, 2011a, p. 2–
9). Furthermore, as discussed in section
III.C above and in section III.C.3 of the
proposal, the Risk Assessment observed
that alternative annual standard levels,
when controlling, resulted in more
consistent risk reductions across urban
study areas, thereby potentially
providing a more consistent degree of
public health protection (U.S. EPA,
2010a, pp. 5–15 to 5–16). In contrast,
the Risk Assessment noted that the
results of simulating alternative suites of
PM2.5 standards including different
combinations of alternative annual and
24-hour standard levels suggested that
an alternative 24-hour standard level
can produce additional estimated risk
reductions beyond that provided by an
PO 00000
Frm 00044
Fmt 4701
Sfmt 4700
alternative annual standard alone.
However, the degree of estimated risk
reduction provided by alternative 24hour standard levels was highly
variable, in part due to the choice of
rollback approached used (U.S. EPA,
2010a, p. 5–17).
Based on its review of the second
draft Policy Assessment, CASAC agreed
with the EPA staff’s general approach
for translating the available
epidemiological evidence, risk
information, and air quality information
into the basis for reaching conclusions
on alternative standards for
consideration. Furthermore, CASAC
agreed ‘‘that it is appropriate to return
to the strategy used in 1997 that
considers the annual and the short-term
standards together, with the annual
standard as the controlling standard,
and the short-term standard
supplementing the protection afforded
by the annual standard’’ and ‘‘considers
it appropriate to place the greatest
emphasis’’ on health effects judged to
have evidence supportive of a causal or
likely causal relationship as presented
in the Integrated Science Assessment
(Samet, 2010d, p. 1).
Therefore, the Policy Assessment
concluded, consistent with specific
CASAC advice, that it was appropriate
to set a ‘‘generally controlling’’ annual
standard that will lower a wide range of
ambient 24-hour concentrations. The
Policy Assessment concluded this
approach would likely reduce aggregate
risks associated with both long- and
short-term exposures with more
consistency than a generally controlling
24-hour standard and would be the most
effective and efficient way to reduce
total PM2.5-related population risk and
so provide appropriate protection. The
staff believed this approach, in contrast
to one focusing on a generally
controlling 24-hour standard, would
likely reduce aggregate risks associated
with both long- and short-term
exposures with more consistency and
would likely avoid setting national
standards that could result in relatively
uneven protection across the country
due to setting standards that were either
more or less stringent than necessary in
different geographical areas.
The Policy Assessment recognized
that an annual standard intended to
serve as the primary means for
providing protection against effects
associated with both long- and shortterm PM2.5 exposures cannot be
expected to offer an adequate margin of
safety against the effects of all shortterm PM2.5 exposures. As a result, in
conjunction with a generally controlling
annual standard, the Policy Assessment
concluded it was appropriate to
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
consider setting a 24-hour standard to
provide supplemental protection,
particularly for areas with high peak-tomean ratios possibly associated with
strong local or seasonal sources, or
PM2.5-related effects that may be
associated with shorter-than-daily
exposure periods.
At the time of the proposal, the
Administrator agreed with the approach
discussed in the Policy Assessment as
summarized in section III.A.3 above,
and supported by CASAC, of
considering the protection afforded by
the annual and 24-hour standards taken
together for mortality and morbidity
effects associated with both long- and
short-term exposures to PM2.5.
Furthermore, based on the evidence and
quantitative risk assessment, the
Administrator provisionally concluded
it was appropriate to set a ‘‘generally
controlling’’ annual standard that will
lower a wide range of ambient 24-hour
concentrations, with a 24-hour standard
focused on providing supplemental
protection, particularly for areas with
high peak-to-mean ratios possibly
associated with strong local or seasonal
sources, or PM2.5-related effects that
may be associated with shorter-than
daily exposure periods. The
Administrator provisionally concluded
this approach would likely reduce
aggregate risks associated with both
long- and short-term exposures more
consistently than a generally controlling
24-hour standard and would be the most
effective and efficient way to reduce
total PM2–5-related population risk.
The Administrator is mindful that
considering what standards are requisite
to protect public health with an
adequate margin of safety requires
public health policy judgments that
neither overstate nor understate the
strength and limitations of the evidence
or the appropriate inferences to be
drawn from the evidence. At the time of
the proposal, in considering how to
translate the available information into
appropriate standard levels, the
Administrator weighed the available
scientific information and associated
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
uncertainties and limitations. For the
purpose of determining what standard
levels were appropriate to propose, the
Administrator recognized, as did the
EPA staff in the Policy Assessment, that
there was no single factor or criterion
that comprised the ‘‘correct’’ approach
to weighing the various types of
available evidence and information, but
rather there were various approaches
that were appropriate to consider. The
Administrator further recognized that
different evaluations of the evidence
and other information before the
Administrator could reflect placing
different weight on the relative strengths
and limitations of the scientific
information, and different judgments
could be made as to how such
information should appropriately be
used in making public health policy
decisions on standard levels. This
recognition led the Administrator to
consider various approaches to
weighing the evidence so as to identify
appropriate standard levels to propose.
In so doing, the Administrator
encouraged extensive public comment
on alternative approaches to weighing
the evidence and other information so
as to inform her public health policy
judgments before reaching final
decisions on appropriate standard
levels.
b. Proposed Decisions on Standard
Levels
i. Consideration of the Alternative
Standard Levels in the Policy
Assessment
In recognizing the absence of a
discernible population threshold below
which effects would not occur, the
Policy Assessment’s general approach
for identifying alternative annual
standard levels that were appropriate to
consider focused on characterizing the
part of the distribution of PM2.5
concentrations in which we had the
most confidence in the associations
reported in the epidemiological studies
and conversely where our confidence in
the association became appreciably
lower. The most direct approach to
PO 00000
Frm 00045
Fmt 4701
Sfmt 4700
3129
address this issue, consistent with
CASAC advice (Samet, 2010c, p. 10),
was to consider epidemiological studies
reporting confidence intervals around
concentration-response relationships
(U.S. EPA, 2011a, p. 2–63). Based on a
thorough search of the available
evidence, the Policy Assessment
identified only one study (Schwartz et
al., 2008) that conducted a multi-model
analysis to characterize confidence
intervals around the estimated
concentration-response relationship.
The Policy Assessment concluded that
this single relevant analysis was too
limited to serve as the principal basis
for identifying alternative standard
levels in this review (U.S. EPA, 2011a,
p. 2–70).
The Policy Assessment explored other
approaches to characterize the part of
the distributions of long-term mean
PM2.5 concentrations that were most
influential in generating health effect
estimates in long- and short-term
epidemiological studies, and placed
greatest weight on those studies that
reported positive and statistically
significant associations (U.S. EPA,
2011a, p. 2–63). First, as discussed in
section III.A.3 above, the Policy
Assessment considered the statistical
metric used in previous reviews. This
approach recognized the EPA’s views
that the strongest evidence of
associations occurs at concentrations
around the long-term mean
concentration. Thus, in earlier reviews,
the EPA focused on identifying standard
levels that were somewhat below the
long-term mean concentrations reported
in PM2.5 epidemiological studies. The
long-term mean concentrations
represented air quality data typically
used in epidemiological analyses and
provided a direct link between PM2.5
concentrations and the observed health
effects. Further, these data were
available for all long- and short-term
exposure studies analyzed and,
therefore, represented the data set
available for the broadest set of
epidemiological studies.
E:\FR\FM\15JAR2.SGM
15JAR2
3130
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
However, consistent with CASAC’s
comments on the second draft Policy
Assessment 75 (Samet, 2010d, p. 2), in
preparing the final Policy Assessment,
the EPA staff explored ways to take into
account additional information from
epidemiological studies, when available
(Rajan et al., 2011). These analyses
focused on evaluating different
statistical metrics, beyond the long-term
mean concentration, to characterize the
part of the distribution of PM2.5
concentrations in which staff continued
to have confidence in the associations
observed in epidemiological studies and
below which there was a comparative
lack of data such that the staff’s
confidence in the relationship was
appreciably less. This would also be the
part of the distribution of PM2.5
concentrations which had the most
influence on generating the health effect
estimates reported in epidemiological
studies. As discussed in section III.A.3
above, the Policy Assessment
recognized there was no one percentile
value within a given distribution that
was the most appropriate or ‘‘correct’’
way to characterize where our
confidence in the associations becomes
appreciably lower. The Policy
Assessment concluded that focusing on
concentrations within the lower quartile
of a distribution, such as the range from
the 25th to the 10th percentile, was
reasonable to consider as a region
within which we begin to have
appreciably less confidence in the
associations observed in
epidemiological studies.76 In the EPA
tkelley on DSK3SPTVN1PROD with
75 While CASAC expressed the view that it would
be most desirable to have information on
concentration-response relationships, they
recognized that it would also be ‘‘preferable to have
information on the concentrations that were most
influential in generating the health effect estimates
in individual studies’’ (Samet, 2010d, p. 2).
76 In the last review, staff believed it was
appropriate to consider a level for an annual PM2.5
standard that was somewhat below the averages of
the long-term concentrations across the cities in
each of the key long-term exposures studies,
recognizing that the evidence of an association in
any such study was strongest at and around the
long-term average where the data in the study are
most concentrated. For example, the interquartile
range of long-term average concentrations within a
study and a range within one standard deviation
around the study mean were considered reasonable
approaches for characterizing the range over which
the evidence of association is strongest (U.S. EPA,
2005, pp. 5–22 to 5–23). In this review, the Policy
Assessment noted the interrelatedness of the
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
staff’s view, considering lower PM2.5
concentrations, down to the lowest
concentration observed in a study,
would be a highly uncertain basis for
selecting alternative standard levels
(U.S. EPA, 2009a, p. 2–71).
As outlined in section III.A.3 above,
the Policy Assessment recognized that
there were two types of population-level
information to consider in identifying
the range of PM2.5 concentrations which
have the most influence on generating
the health effect estimates reported in
epidemiological studies. The most
relevant information to consider was the
number of health events (e.g., deaths,
hospitalizations) occurring within a
study population in relation to the
distribution of PM2.5 concentrations
likely experienced by study
participants. However, in recognizing
that access to health event data may be
restricted, and consistent with advice
from CASAC (Samet 2010d, p. 2), EPA
staff also considered the number of
participants within each study area, in
relation to the distribution of PM2.5
concentrations (i.e., study population
data), as a surrogate for health event
data.
In applying this approach, the Policy
Assessment focused on identifying the
part of the distribution of PM2.5
concentrations which had the most
influence on generating health effect
estimates in epidemiological studies, as
discussed in section III.A.3 above. As
discussed below, in working with study
investigators, the EPA staff was able to
obtain health event data for three large
multi-city studies (Krewski et al., 2009;
Zanobetti and Schwartz, 2009; Bell et
al., 2008) and population data for the
same three studies and one additional
long-term exposure study (Miller et al.,
2007), as documented in a staff
memorandum (Rajan et al., 2011).77 For
the three studies for which both health
event and study population data were
distributional statistics and a range of one standard
deviation around the mean which contains
approximately 68 percent of normally distributed
data, in that one standard deviation below the mean
falls between the 25th and 10th percentiles (U.S.
EPA, 2011a, p. 2–71).
77 The distributional statistical analysis of
population-level data built upon an earlier analysis
that evaluated the distributions of air quality and
associated population data for three long-term
exposure studies and three short-term exposure
studies (Schmidt et al., 2010, Analysis 2).
PO 00000
Frm 00046
Fmt 4701
Sfmt 4700
available, the EPA staff analyzed the
reliability of using study population
data as a surrogate for health event data.
Based on these analyses, the EPA staff
recognized that the 10th and 25th
percentiles of the health event and
study population distributions are
nearly identical and concluded that the
distribution of population data can be a
useful surrogate for event data,
providing support for consideration of
the study population data for Miller et
al. (2007), for which health event data
were not available (Rajan et al., 2011,
Analysis 1 and Analysis 2, in particular,
Table 1 and Figures 1 and 2).
With regard to the long-term mean
PM2.5 concentrations which are relevant
to the first approach, Figures 1 through
3 (U.S. EPA, 2011a, Figures 2–4, 2–5, 2–
6, and 2–8) summarize data available for
multi-city, long- and short-term
exposure studies that evaluated
endpoints classified in the Integrated
Science Assessment as having evidence
of a causal or likely causal relationship
or evidence suggestive of a causal
relationship, showing the studies with
long-term mean PM2.5 concentrations
below 17 mg/m3.78 As discussed in more
detail in section III.E.4.b of the proposal,
Figures 1 and 3 summarize the health
outcomes evaluated, relative risk
estimates, air quality data, and
geographic scope for long- and shortterm exposure studies, respectively, that
evaluated mortality (evidence of a
causal relationship); cardiovascular
effects (evidence of a causal
relationship); and respiratory effects
(evidence of a likely causal relationship)
in the general population, as well as in
older adults, an at-risk population.
Figure 2 provides this same summary
information for long-term exposure
studies that evaluated respiratory effects
(evidence of a likely causal relationship)
in children, an at-risk population, as
well as developmental effects (evidence
suggestive of a causal relationship).
78 Additional studies presented and assessed in
the Integrated Science Assessment report effects at
higher long-term mean PM2.5 concentrations (e.g.,
U.S. EPA, 2009a, Figures 2–1, 2–2, 7–6, and 7–7).
79 The long-term mean PM
2.5 concentrations
reported by the study authors for the Miller et al.
(2007) and Lipfert et al. (2006a) studies are
discussed more fully in the Response to Comments
document (U.S. EPA, 2012a).
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
VerDate Mar<15>2010
StudJ
Cite
.~
YursofAir
QuaII1y
Data
Air Qualilv Data 'u~
Endpoint
Effect Estimate !t6% CD
Author Rtported DatI
Meani-;S·
RqI
Jkt 229001
GennI~
,
~
PO 00000
WHI
Frm 00047
CystIc FIbrosis
Milet at at (2007)
GeIss etaL (2004)"
36UScilie&
...
~
2000
AIIevD
IncidentMl
RevascuIa!izati
SbnIIe.
,
,
.
•
•
.
12:9"
102
2000
~
I
I
Fmt 4701
~ et~. (2(M)9)
11~IJSMSM
1999-2000
MorIaIily-iiD
MorWIy-CPD
·
Sfmt 4725
~ etaL (2IlOO)
tli!99-2001
1'.btaIIy4 cause
131
9.5
·
I•
I
I
·
,
•
, •
14.0
11.0
.-,,
.*
.5.8-22
I
14.3
11.3
•
,~
5.0-1
~cause
E:\FR\FM\15JAR2.SGM
H~ !,aden etal. (200&)
~
~tdIi!esI:}
1979"1_
,
I
MorIaIty-CV
~
16.•
10.8
•
I•
I
10-22
,
,
:
,
II!
,
,
~caooer
OfderA.dt*
MCAPS-wutem US Ztgeret at (2008)
Mecllcare-ACS
Ellin et at (2008)
15JAR2
MCAP~US
Zeger et aI. (2OOtl)
MedIcare .sea
E1II'il et at (2001)
62US 00UIIIies
2.000-2005
MortaII;y4 cause
13.1d
.
10.+185
51USMSM
2.000-2002
MortaII;y4 cause
13.8
10B
tto.25.1
421 US QOI.IIlies
BOOGIes
•
•
i
11.8-15.9
(lOR)
t.bfaIity-lung caooer
VA
•
I
~cause
Acs.ReanaJp1s II
•
•
:.
3.4-28.3
CSVD
~
•
•
I
(lOR}
2.000-2005
MutaIy4 cause
14.00
-
2.000-2002
MoItIIy-aI cause
14.1
11.0
I
12.3-15.3
9.6-19.1
Source: U.S. EPA, 20lla, Figure 2-4
.
i
•
. .......
,
os
"Median (IQR: In!erq\IIa.tilutlhge);
tkelley on DSK3SPTVN1PROD with
3132
VerDate Mar<15>2010
Jkt 229001
Children
PO 00000
Cite
Geographic
Area
Years of Air QuaJity
Data
Endpoint
Belletal.
(2007)
Study
GT,MA
199&-2002
Low Birth Weight
Air Quality Data (pgIm3)
Mean
Mean1SD
11.9"
Effect Estimate (95% el)
10.3
Range
I
I
I
Frm 00048
I
I
•
I
IUGR -1 nd !rimester
r---
IUGR -2M trimester
I
I
Fmt 4701
Uuetal.
(2007)
3Canadian cities
1.985-1999
12.2
-
I
I
Sfmt 4725
IUGR - Jrdtrimester
r--I
Pal1
:-
0.3-15
I
I
(J.B
1
1.2
1.4
1.6
1.B
2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
20:39 Jan 14, 2013
Figure 2. Summary of Effect Estimates (per 10 Jlglm3) and Air Quality Distributions for Multi-City, Long-term PM2.5 Exposure
Studies of Children
tkelley on DSK3SPTVN1PROD with
Geographic
Area
Study/Cite
Years of
AirQualily
Data
1';-
General Population
Jkt 229001
Burnett at aI. (2004)
12 Carman Cities 1981-1999
NonaccidenIaI
m(II'I~"dy
12.8
-
-
,
38.0
Frm 00049
Fmt 4701
112 US coonties
1999-2005
N~
13.2-
8 Garman Cities 1986-1986
Nonaooidenlal
moIWrty
13.3
3.91
.
1979-1988
N~
14.7·
·
9-23
(lOR)
.
2000-2005
NonacckIenIaI
lI'ICfIaIiIy
14.80
· 9.9-27.'"
43.0
N~
15.6-
-
•
38.9"
45.8
Halvard Six~r" and Mason
Sfmt 4700
Franldfn et al. (2008)
Franldfn et at (2007)
6USciIies
(Nodheast/
MKMesI)
25 US
oomllU1ilies
ool'~
1991-2002
10.30 6.6-24.7
8.8-23.9
34.3
------
-
OlderAduIIsfCIIiIdre.
MCAPSIBeII et aI. (2008)
202 US counties
CVOHA
1999-2005
12.9- 102-
RespHA
4-20
f--.
f--o---
•
GHFHA
-
Dysrhythmia HA
204 US counties
1999-2002
13.•
CBVDHA
10,50
4-23
34.8
PVDHA
15JAR2
•
•
COPDHA
-
-
---
- ---_ ...
O' Connor (2008)
_-_
.. _----------------_._---------
-
- -- ---
7USCities
1998-2001
RfIHA
Wheeze/Cough
---- -
---- -- -------
•
-
342
IHOHA
MCAPSJDominici etal. 2006
-_ .. _--
14.0
·
-
-------------
39.0OwU
oEahl11ed from deta provided by study author or publi!lhed study
loQIiml11ed from coefficient of varielion reported in original wdy by Burnett lit .1. (2000)
E1fect Estimate 195~ ell
Air QualitY Data (ulll'm!)
A.uthor Reported Data
Mean
Range ~
Endpoint
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
20:39 Jan 14, 2013
With regard to consideration of
additional information from
VerDate Mar<15>2010
Figure 3. Summary of Effect Estimates (per 10 Jlg/m3) and Air Quality Distributions for Multi-City, Short-term PM2•5 Exposure
Studies of the General Population and Older Adults
3134
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
corresponding with the 25th to 10th
percentiles of health event or study
population data from the four multi-city
studies, for which distributional
statistics are available 80 (U.S. EPA,
2011a, Figure 2–7; Rajan et al., 2011,
Table 1). By considering this approach,
one could focus on the range of PM2.5
concentrations below the long-term
mean ambient concentrations over
which we continue to have confidence
in the associations observed in
epidemiological studies (e.g., above the
25th percentile) where commensurate
public health protection could be
obtained for PM2.5-related effects and,
conversely, identify the range in the
distribution below which our
confidence in the associations is
appreciably less, to identify alternative
annual standard levels.
The mean PM2.5 concentrations
associated with the studies summarized
in Figures 1, 2, and 3 and with the
tkelley on DSK3SPTVN1PROD with
80 The EPA staff obtained health event data (e.g.,
number of deaths, hospitalizations) occurring in a
study population for three multi-city studies
(Krewski et al., 2009; Zanobetti and Schwartz, 2009;
Bell et al., 2008) and study population data were
obtained for the same three studies and one
additional study (Miller et al., 2007) (U.S. EPA,
2011a, p. 2–71). If health event or study population
data were available for additional studies, the EPA
could employ distributional statistics to identify the
broader range of PM2.5 concentrations that were
most influential in generating health effect
estimates in those studies.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
distributional statistics analyses (Rajan
et al., 2011) are based on concentrations
averaged across ambient monitors
within each area included in a given
study and then averaged across study
areas to calculate an overall study mean
concentration, as discussed above.
Figure 4, discussed in more detail in
section III.E.4.a of the proposal,
summarizes statistical metrics for those
key studies 81 included in Figures 1, 2,
and 3 that provide evidence of positive
and generally statistically significant
PM2.5-related effects, which are relevant
to the two approaches for translating
epidemiological evidence into potential
standard levels as discussed above. The
81 Long- and short-term exposure studies
considered ‘‘key’’ studies for consideration are
summarized in Figure 4 and include those studies
observing effects for which the evidence supported
a causal or likely causal association. This figure
represents the subset of multi-city studies included
in Figures 1 through 3 that provided evidence of
positive and generally statistically significant
effects associated in whole or in part with more
recent air quality data, generally representing health
effects associated with lower PM2.5 concentrations
than had previously been considered in the last
review. The EPA notes that many of these studies
evaluated multiple health endpoints, and not all of
the effects evaluated provided evidence of positive
and statistically significant effects. For purposes of
informing the Administrator’s decision on the
appropriate standard levels, the Agency considers
the full body of scientific evidence and focuses on
those aspects of the key studies that provided
evidence of positive and generally statistically
significant effects.
PO 00000
Frm 00050
Fmt 4701
Sfmt 4700
top of Figure 4 includes information for
long-term exposure studies evaluating
health outcomes classified as having
evidence of a causal or likely causal
relationship with PM2.5 exposures (longterm mean PM2.5 concentrations
indicated by diamond symbols). The
middle of Figure 4 includes information
for short-term exposure studies
evaluating health outcomes classified as
having evidence of a causal or likely
causal relationship with PM2.5
exposures (long-term mean PM2.5
concentrations indicated by triangle
symbols). The bottom of Figure 4
includes information for long-term
exposures studies evaluating health
outcomes classified as having evidence
suggestive of a causal relationship
(long-term mean PM2.5 concentrations
indicated by square symbols). Figure 4
also summarizes the range of PM2.5
concentrations corresponding with the
25th (indicated by solid circles) to 10th
(indicated by open circles) percentiles
of the health event or study population
data from the four multi-city studies
(highlighted in bold text) for which
distributional statistics are available.
82 The long-term mean PM
2.5 concentrations
reported by the study authors for the Miller et al.
(2007) and Lipfert et al. (2006a) studies are
discussed more fully in the Response to Comments
document (U.S. EPA, 2012a).
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
Causal / likely Causa! - Long-Term Exposure Studies
Miller et al., 2007 (WHI, 36 cities)
-
""'
4
Eltim
I.
SUggestive· Long-Term Exposure Sludies
IJI.t
•
•
••
•
••
•
..
.
Laden "I 81.. 2006 (Harvard Six CiIies)
FllInkIin 2010
Figure 4. Translating Epidemiological Evidence from Multi-City Exposure Studies into an Annual PM2.5
Standard82
tkelley on DSK3SPTVN1PROD with
3136
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
the weight placed on different aspects of
the evidence and inherent uncertainties,
consideration of different alternative
standard levels could be supported.
Given the currently available
evidence discussed in more detail in
section III.E.4.b of the proposal and
considering the various approaches
discussed above, the Policy Assessment
concluded it was appropriate to focus
on an annual standard level within a
range of about 12 to 11 mg/m3 (U.S. EPA,
2011a, pp. 2–82, 2–101, and 2–106). As
illustrated in Figure 4, the Policy
Assessment recognized that a standard
level of 12 mg/m3, at the upper end of
this range, was somewhat below the
long-term mean PM2.5 concentrations
reported in all the multi-city, long- and
short-term exposure studies that
provided evidence of positive and
statistically significant associations with
health effects classified as having
evidence of a causal or likely causal
relationship, including premature
mortality and hospitalizations and
emergency department visits for
cardiovascular and respiratory effects as
well as respiratory effects in children.
Further, a level of 12 mg/m3 would
reflect consideration of additional
population-level information from such
epidemiological studies in that it
generally corresponded with
approximately the 25th percentile of the
available distributions of health events
data in the studies for which
population-level information was
available. In addition, a level of 12 mg/
m3 would reflect some consideration of
studies that provided more limited
evidence of reproductive and
developmental effects, which were
suggestive of a causal relationship, in
that it was about at the same level as the
lowest long-term mean PM2.5
concentrations reported in such studies
(see Figure 4).
Alternatively the Policy Assessment
recognized that an annual standard level
of 11 mg/m3, at the lower end of this
range, was well below the lowest longterm mean PM2.5 concentrations
reported in all multi-city long- and
short-term exposure studies that provide
evidence of positive and statistically
significant associations with health
effects classified as having evidence of
a causal or likely causal relationship. A
level of 11 mg/m3 would reflect placing
more weight on the distributions of
health event and population data, in
that this level was within the range of
PM2.5 concentrations corresponding to
the 25th and 10th percentiles of all the
available distributions of such data. In
addition, a level of 11 mg/m3 was
somewhat below the lowest long-term
mean PM2.5 concentrations reported in
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
reproductive and developmental effects
studies that are suggestive of a causal
relationship. Thus, a level of 11 mg/m3
would reflect an approach to translating
the available evidence that places
relatively more emphasis on margin of
safety considerations and less certain
causal relationships than would a
standard set at a higher level. Such a
policy approach would tend to weigh
uncertainties in the evidence in such a
way as to avoid potentially
underestimating PM2.5-related risks to
public health. Further, recognizing the
uncertainties inherent in identifying any
particular point at which our confidence
in reported associations becomes
appreciably less, the Policy Assessment
concluded that the available evidence
did not provide a sufficient basis to
consider alternative annual standard
levels below 11 mg/m3 (U.S. EPA, 2011a,
p. 2–81).
The Policy Assessment also
considered the extent to which the
available evidence provided a basis for
considering alternative annual standard
levels above 12 mg/m3. As discussed
below, the Policy Assessment
concluded that it could be reasonable to
consider a standard level up to 13 mg/
m3 based on a policy approach that
weighed uncertainties in the evidence
in such a way as to avoid potentially
overestimating PM2.5-related risks to
public health, especially to the extent
that primary emphasis was placed on
long-term exposure studies as a basis for
an annual standard level. A level of 13
mg/m3 was somewhat below the longterm mean PM2.5 concentrations
reported in all but one of the long-term
exposure studies providing evidence of
positive and statistically significant
associations with PM2.5-related health
effects classified as having a causal or
likely causal relationship. As shown in
Figure 4, the one long-term exposure
study with a long-term mean PM2.5
concentration just below 13 mg/m3 was
the Miller et al., (2007) study. However,
as noted in section III.D.1.a of the
proposal and discussed in more detail
in the Response to Comments
document, the Policy Assessment
observed that in comparison to other
long-term exposure studies, the Miller et
al. study was more limited in that it was
based on only one year of air quality
data and the one year was after the
health outcomes were reported (U.S.
EPA, 2011a, pp. 2–81 to 2–82). Thus, to
the extent that less weight was placed
on the Miller et al. study than on other
long-term exposure studies with more
robust air quality data, a level of 13 mg/
m3 could be considered as being
protective of long-term exposure related
PO 00000
Frm 00052
Fmt 4701
Sfmt 4700
effects classified as having a causal or
likely causal relationship. In also
considering short-term exposure
studies, however, the Policy Assessment
noted that a level of 13 mg/m3 was below
the long-term mean PM2.5
concentrations reported in most but not
all such studies. In particular, two
studies—Burnett et al. (2004) and Bell et
al. (2008)—reported long-term mean
PM2.5 concentrations of 12.8 and 12.9
mg/m3, respectively. In considering
these studies, the Policy Assessment
found no basis to conclude that these
two studies were any more limited or
uncertain than the other short-term
exposure studies shown in Figures 3
and 4 (U.S. EPA, 2011a, p. 2–82). On
this basis, as discussed below, the
Policy Assessment concluded that
consideration of an annual standard
level of 13 mg/m3 would have
implications for the degree of protection
that would need to be provided by the
24-hour standard, in order that the suite
of PM2.5 standards, taken together,
would provide appropriate protection
from effects on public health related to
short-term exposure to PM2.5 (U.S. EPA,
2011a, p. 2–82).
The Policy Assessment also noted that
a standard level of 13 mg/m3 would
reflect a judgment that the uncertainties
in the epidemiological evidence as
summarized in section III.B above and
discussed in more detail in section
III.B.2 of the proposal, including
uncertainties related to the
heterogeneity observed in the
epidemiological studies in the eastern
versus western parts of the U.S., the
relative toxicity of PM2.5 components,
and the potential role of co-pollutants,
are too great to warrant placing any
weight on the distributions of health
event and population data that extend
down below the long-term mean
concentrations into the lower quartile of
the data. This level would also reflect a
judgment that the evidence from
reproductive and developmental effects
studies that is suggestive of a causal
relationship was too uncertain to
support consideration of any lower
level.
Beyond evidence-based
considerations, the Policy Assessment
also considered the extent to which the
quantitative risk assessment supported
consideration of these alternative
standard levels or provided support for
lower levels. In considering simulations
of just meeting alternative annual
standard levels within the range of 13 to
11 mg/m3 (in conjunction with the
current 24-hour standard level of 35 mg/
m3), the Policy Assessment concluded
that important public health
improvements are associated with risk
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
reductions estimated for standard levels
of 13 and 12 mg/m3 and noted that the
level of 11 mg/m3 was not included in
the quantitative risk assessment. The
Policy Assessment noted that the overall
confidence in the quantitative risk
estimates varied for the different
alternative standard levels evaluated
and was stronger for the higher levels
and substantially lower for the lowest
level evaluated (i.e., 10 mg/m3). Based
on the above considerations, the Policy
Assessment concluded that the
quantitative risk assessment provided
support for considering alternative
annual standard levels within a range of
13 to 11 mg/m3, but did not provide
strong support for considering lower
alternative standard levels (U.S. EPA,
2011a, pp. 2–102 to 2–103).
Taken together, the Policy Assessment
concluded that consideration of
alternative annual standard levels in the
range of 13 to 11 mg/m3 may be
appropriate. Furthermore, the Policy
Assessment concluded that the
currently available evidence most
strongly supported consideration of an
alternative annual standard level in the
range of 12 to 11 mg/m3 (U.S. EPA,
2011a, p. 2–82). The Policy Assessment
concluded that an alternative level
within the range of 12 to 11 mg/m3
would more fully take into
consideration the available information
from all long- and short-term PM2.5
exposure studies, including studies of
at-risk populations, than would a higher
level. This range also reflected placing
weight on information from studies that
helped to characterize the range of PM2.5
concentrations over which we continue
to have confidence in the associations
observed in epidemiological studies, as
well as the extent to which our
confidence in the associations was
appreciably less at lower
concentrations.
As recognized in sections III.A.3 and
III.E.4.a above, an annual standard
intended to serve as the primary means
for providing protection from effects
associated with both long- and shortterm PM2.5 exposures is not expected to
provide appropriate protection against
the effects of all short-term PM2.5
exposures (unless established at a level
so low as to undoubtedly provide more
protection than necessary for long-term
exposures). Of particular concern are
areas with high peak-to-mean ratios
possibly associated with strong local or
seasonal sources, or PM2.5-related effects
that may be associated with shorterthan-daily exposure periods. As a result,
the Policy Assessment concluded that it
was appropriate to consider alternative
24-hour PM2.5 standard levels that
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
would supplement the protection
provided by an annual standard.
As outlined in section III.A.3 above,
the Policy Assessment considered the
available evidence from short-term
PM2.5 exposure studies, as well as the
uncertainties and limitations in that
evidence, to assess the degree to which
alternative annual and 24-hour PM2.5
standards can be expected to reduce the
estimated risks attributed to short-term
fine particle exposures. In considering
the available epidemiological evidence,
the Policy Assessment took into account
information from multi-city studies as
well as single-city studies. The Policy
Assessment considered the distributions
of 24-hour PM2.5 concentrations
reported in short-term exposure studies,
focusing on the 98th percentile
concentrations to match the form of the
24-hour standard as discussed in section
III.E.3.b above. In recognizing that the
annual and 24-hour standards work
together to provide protection from
effects associated with short-term PM2.5
exposures, the Policy Assessment also
considered information on the long-term
mean PM2.5 concentrations from these
studies.
In addition to considering the
epidemiological evidence, the Policy
Assessment considered air quality
information, specifically peak-to-mean
ratios using county-level 24-hour and
annual design values, to characterize air
quality patterns in areas possibly
associated with strong local or seasonal
sources. These patterns helped in
understanding the extent to which
different combinations of annual and
24-hour standards would be consistent
with the policy goal of setting a
generally controlling annual standard
with a 24-hour standard that provides
supplemental protection especially for
areas with high peak-to-mean ratios
(U.S. EPA, 2011a, p. 2–14).
In considering the information
provided by the short-term exposure
studies, the Policy Assessment
recognized that to the extent these
studies were conducted in areas that
likely did not meet one or both of the
current standards, such studies did not
help inform the characterization of the
potential public health improvements of
alternative standards set at lower levels.
Therefore, in considering the short-term
exposure studies to inform staff
conclusions regarding levels of the 24hour standard that are appropriate to
consider, the Policy Assessment placed
greatest weight on studies conducted in
areas that likely met both the current
annual and 24-hour standards.
With regard to multi-city studies that
evaluated effects associated with shortterm PM2.5 exposures, as summarized in
PO 00000
Frm 00053
Fmt 4701
Sfmt 4700
3137
Figure 3 above and discussed in more
detail in section III.E.4.c of the proposal,
the Policy Assessment noted that, to the
extent air quality distributions were
reduced to reflect just meeting the
current 24-hour standard, additional
protection would be anticipated for the
effects observed in the three multi-city
studies with 98th percentile values
greater than 35 mg/m3 (Burnett et al.,
2004; Burnett and Goldberg, 2003;
Franklin et al., 2008). In the three
additional studies with 98th percentile
values below 35 mg/m3, specifically 98th
percentile concentrations of 34.2, 34.3,
and 34.8 mg/m3, the Policy Assessment
noted that these studies reported longterm mean PM2.5 concentrations of 12.9,
13.2, and 13.4 mg/m3, respectively (Bell
et al., 2008; Zanobetti and Schwartz,
2009; Dominici et al., 2006a). To the
extent that consideration was given to
revising the level of the annual
standard, as discussed in section
III.E.4.b of the proposal, the Policy
Assessment recognized that potential
changes associated with meeting such
an alternative annual standard would
result in lowering risks associated with
both long- and short-term PM2.5
exposures. Consequently, in considering
a 24-hour standard that would operate
in conjunction with an annual standard
to provide appropriate public health
protection, the Policy Assessment noted
that to the extent that the level of the
annual standard was revised to within
a range of 13 to 11 mg/m3, in particular
in the range of 12 to 11 mg/m3,
additional protection would be
provided for the long-term effects
observed in these multi-city studies
(U.S. EPA, 2011a, p. 2–84).
Based on this information, the Policy
Assessment concluded that the multicity, short-term exposure studies
generally provided support for retaining
the 24-hour standard level at 35 mg/m3
so long as the standard is in conjunction
with an annual standard level revised to
within a range of 12 to 11 mg/m3 (U.S.
EPA, 2011a, p. 2–84). Alternatively, in
conjunction with an annual standard
level of 13 mg/m3, the Policy Assessment
concluded that the multi-city studies
provided limited support for revising
the 24-hour standard level somewhat
below 35 mg/m3, such as down to 30 mg/
m3, based on one study (Bell et al.,
2008) that reported positive and
statistically significant effects with an
overall 98th percentile value below the
level of the current 24-hour standard
and an overall long-term mean
concentration slightly less than 13 mg/
m3 (Figure 3; U.S. EPA, 2011a, p. 2–84).
In reaching staff conclusions
regarding alternative 24-hour standard
levels that were appropriate to consider,
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
3138
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
the Policy Assessment also took into
account relevant information from
single-city studies that evaluated effects
associated with short-term PM2.5
exposures. The Policy Assessment
recognized that these studies may
provide additional insights regarding
impacts on at-risk populations and/or
on areas with isolated peak
concentrations.
As discussed in more detail in section
III.E.4.c of the proposal, although a
number of single-city studies reported
effects at appreciably lower PM2.5
concentrations than multi-city shortterm exposure studies, the uncertainties
and limitations associated with the
single-city studies were considerably
greater than those associated with the
multi-city studies and, thus, the Policy
Assessment concluded there was less
confidence in using these studies as a
basis for setting the level of a standard.
Therefore, the Policy Assessment
concluded that the multi-city short-term
exposure studies provided the strongest
evidence to inform decisions on the
level of the 24-hour standard, and the
single-city studies did not warrant
consideration of 24-hour standard levels
different from those supported by the
multi-city studies (U.S. EPA, 2011a, p.
2–88).
In addition to considering the
epidemiological evidence, the Policy
Assessment took into account air quality
information based on county-level 24hour and annual design values to
understand the public health
implications of the alternative standard
levels supported by the currently
available scientific evidence, as
discussed in this section. Consistent
with the general approach discussed in
section III.A.3 above, the Policy
Assessment considered the extent to
which different combinations of
alternative annual and 24-hour standard
levels based on the evidence would
support the policy goal of lowering
annual and 24-hour air quality
distributions by using the annual
standard to be the ‘‘generally
controlling’’ standard in conjunction
with setting the 24-hour standard to
provide supplemental protection (U.S.
EPA, 2011a, pp 2–88 to 2–91, Figure 2–
10).
Using information on the relationship
of the 24-hour and annual design
values, the Policy Assessment examined
the implications of three alternative
suites of PM2.5 standards identified as
appropriate to consider based on the
currently available scientific evidence,
as discussed above. The Policy
Assessment concluded that an
alternative suite of PM2.5 standards that
would include an annual standard level
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
of 11 or 12 mg/m3 and a 24-hour
standard with a level of 35 mg/m3 (i.e.,
11/35 or 12/35) would result in the
annual standard being the generally
controlling standard in most areas
although the 24-hour standard would
continue to be the generally controlling
standard in the Northwest (U.S. EPA,
2011a, pp. 2–89 to 2–91 and Figure 2–
10). These Northwest counties generally
represented areas where the annual
mean PM2.5 concentrations have
historically been low but where
relatively high 24-hour concentrations
occur, often related to seasonal wood
smoke emissions. Alternatively,
combining an alternative annual
standard of 13 mg/m3 with a 24-hour
standard of 30 mg/m3 would result in
many more areas across the country in
which the 24-hour standard would
likely become the controlling standard
(the standard driving air quality
distributions lower) than if an
alternative annual standard of 12 or 11
mg/m3 were paired with the current
level of the 24-hour standard (i.e., 35 mg/
m3).
The Policy Assessment concluded
that consideration of retaining the 24hour standard level at 35 mg/m3 would
reflect placing greatest weight on
evidence from multi-city studies that
reported positive and statistically
significant associations with health
effects classified as having a causal or
likely causal relationship. In
conjunction with lowering the annual
standard level, especially within a range
of 12 to 11 mg/m3, this alternative
recognized additional public health
protection against effects associated
with short-term PM2.5 exposures which
would be provided by lowering the
annual standard such that revision to
the 24-hour standard would not be
warranted (U.S. EPA, 2011a, p. 2–91).
Beyond evidence-based
considerations, the Policy Assessment
also considered the extent to which the
quantitative risk assessment supported
consideration of retaining the current
24-hour standard level or provided
support for lower standard levels. In
considering simulations of just meeting
the current 24-hour standard level of 35
mg/m3 or alternative levels of 30 or 25
mg/m3 (in conjunction with alternative
annual standard levels within a range of
13 to 11 mg/m3), the Policy Assessment
noted that the overall confidence in the
quantitative risk estimates varied for the
different standard levels evaluated and
was stronger for the higher levels and
substantially lower for the lowest level
evaluated (i.e., 25 mg/m3). Based on this
information, the Policy Assessment
concluded that the quantitative risk
assessment provided support for
PO 00000
Frm 00054
Fmt 4701
Sfmt 4700
considering a 24-hour standard level of
35 or 30 mg/m3 (in conjunction with an
alternative standard level within a range
of 13 to 11 mg/m3) but did not provide
strong support for considering lower
alternative 24-hour standard levels (U.S.
EPA, 2011a, pp. 2–102 to 2–103).
Taken together, the Policy Assessment
concluded that while it was appropriate
to consider an alternative 24-hour
standard level within a range of 35 to 30
mg/m3, the currently available evidence
most strongly supported consideration
for retaining the current 24-hour
standard level at 35 mg/m3 in
conjunction with lowering the level of
the annual standard within a range of 12
to 11 mg/m3 (U.S. EPA, 2011a, p. 2–92).
ii. CASAC Advice
Based on its review of the second
draft Policy Assessment, CASAC agreed
with the general approach for
translating the available epidemiological
evidence, risk information, and air
quality information into the basis for
reaching conclusions on alternative
standards for consideration.
Furthermore, CASAC agreed ‘‘that it is
appropriate to return to the strategy
used in 1997 that considers the annual
and the short-term standards together,
with the annual standard as the
controlling standard, and the short-term
standard supplementing the protection
afforded by the annual standard’’ and
‘‘considers it appropriate to place the
greatest emphasis’’ on health effects
judged to have evidence supportive of a
causal or likely causal relationship as
presented in the Integrated Science
Assessment (Samet, 2010d, p. 1).
CASAC concluded that the range of
levels presented in the second draft
Policy Assessment (i.e., alternative
annual standard levels within a range of
13 to 11 mg/m3 and alternative 24-hour
standard levels within a range of 35 to
30 mg/m3) ‘‘are supported by the
epidemiological and toxicological
evidence, as well as by the risk and air
quality information compiled’’ in the
Integrated Science Assessment, Risk
Assessment, and second draft Policy
Assessment. CASAC further noted that
‘‘[a]lthough there is increasing
uncertainty at lower levels, there is no
evidence of a threshold (i.e., a level
below which there is no risk for adverse
health effects)’’ (Samet, 2010d, p. ii).
Although CASAC supported the
alternative standard level ranges
presented in the second draft Policy
Assessment, it did not express support
for any specific levels or combinations
of standards. Rather, CASAC
encouraged the EPA to develop a clearer
rationale in the final Policy Assessment
for staff conclusions regarding annual
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
and 24-hour standards that were
appropriate to consider, including
consideration of the combination of
these standards supported by the
available information (Samet, 2010d, p.
ii). Specifically, in commenting on a
distributional statistical analysis of air
quality and associated population data
presented in the second draft Policy
Assessment, CASAC encouraged staff to
focus on information related to the
concentrations that were most
influential in generating the health
effect estimates in individual studies to
inform alternative standard levels.
CASAC urged that the EPA redo that
analysis using health event or study
population data (Samet, 2010d, p. 2).
CASAC also commented that the
approach presented in the second draft
Policy Assessment to identify
alternative 24-hour standard levels
which focused on peak-to-mean ratios
was not relevant for informing the
actual level (Samet 2010d, p. 4).
Further, they expressed the concern that
the combinations of annual and 24-hour
standard levels discussed in the second
draft Policy Assessment (i.e., in the
range of 13 to 11 mg/m3 for the annual
standard, in conjunction with retaining
the current 24-hour PM2.5 standard level
of 35 mg/m3; alternatively, revising the
level of the 24-hour standard to 30 mg/
m3 in conjunction with an annual
standard level of 11 mg/m3) ‘‘may not be
adequately inclusive’’ and ‘‘[i]t was not
clear why, for example a daily standard
of 30 mg/m3 should only be considered
in combination with an annual level of
11 mg/m3’’ (Samet, 2010d, p. ii). CASAC
encouraged the EPA to more clearly
explain its rationale for identifying the
24-hour/annual combinations that are
appropriate for consideration (Samet
2010d, p. ii).
In considering CASAC’s advice as
well as public comment on the second
draft Policy Assessment, the EPA staff
conducted additional analyses and
modified their conclusions regarding
alternative standard levels that were
appropriate to consider. The staff
conclusions in the final Policy
Assessment (U.S. EPA, 2011a, section
2.3.4.4) differed somewhat from the
alternative standard levels discussed in
the second draft Policy Assessment
(U.S. EPA, 2010f, section 2.3.4.3), upon
which CASAC based its advice. Changes
made in the final Policy Assessment
were primarily focused on improving
and clarifying the approach for
translating the epidemiological evidence
into a basis for staff conclusions on the
broadest range of alternative standard
levels supported by the available
scientific information and more clearly
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
articulating the rationale for the staff’s
conclusions (Wegman, 2011, pp. 1 to 2).
Consistent with CASAC’s advice to
consider more information from
epidemiological studies, as discussed in
section III.E.4.b.1 above, the EPA
analyzed additional population-level
data obtained from several study
authors (Rajan et al., 2011). In
transmitting the final Policy Assessment
to CASAC, the Agency notified CASAC
that the final staff conclusions reflected
consideration of CASAC’s advice and
that those staff conclusions were based,
in part, on the specific distributional
analysis that CASAC had urged the EPA
to conduct (Wegman, 2011, p.2). Thus,
CASAC had an opportunity to comment
on the final Policy Assessment, but
chose not to provide any additional
comments or advice after receiving it.
iii. Administrator’s Proposed Decisions
on the Primary PM2.5 Standard Levels
In reaching her conclusions regarding
appropriate alternative standard levels
to consider, the Administrator
considered the epidemiological and
other scientific evidence, estimates of
risk reductions associated with just
meeting alternative annual and/or 24hour standards, air quality analyses,
related limitations and uncertainties,
staff conclusions as presented in the
Policy Assessment, and the advice of
CASAC. As an initial matter, the
Administrator agreed with the general
approach discussed in the Policy
Assessment as summarized in sections
III.A.3 and III.E.4.a above, and
supported by CASAC, of considering the
protection afforded by the annual and
24-hour standards taken together for
mortality and morbidity effects
associated with both long- and shortterm exposures to PM2.5 (77 FR 38939).
Furthermore, based on the evidence and
quantitative risk assessment, the
Administrator provisionally concluded
it is appropriate to set a ‘‘generally
controlling’’ annual standard that will
lower a wide range of ambient 24-hour
concentrations, with a 24-hour standard
focused on providing supplemental
protection, particularly for areas with
high peak-to-mean ratios possibly
associated with strong local or seasonal
sources, or PM2.5-related effects that
may be associated with shorter-than
daily exposure periods. The
Administrator provisionally concluded
this approach would likely reduce
aggregate risks associated with both
long- and short-term exposures more
consistently than a generally controlling
24-hour standard and would be the most
effective and efficient way to reduce
total PM2.5-related population risk. Id.
PO 00000
Frm 00055
Fmt 4701
Sfmt 4700
3139
In reaching decisions on alternative
standard levels to propose, the
Administrator judged that it was most
appropriate to examine where the
evidence of associations observed in the
epidemiological studies was strongest
and, conversely, where she had
appreciably less confidence in the
associations observed in the
epidemiological studies. Based on the
characterization and assessment of the
epidemiological and other studies
presented and assessed in the Integrated
Science Assessment and the Policy
Assessment, the Administrator
recognized the substantial increase in
the number and diversity of studies
available in this review including
extended analyses of the seminal
studies of long-term PM2.5 exposures
(i.e., ACS and Harvard Six Cities
studies) as well as important new longterm exposure studies (as summarized
in Figures 1 and 2). Collectively, the
Administrator noted that these studies,
along with evidence available in the last
review, provided consistent and
stronger evidence of an association with
premature mortality, with the strongest
evidence related to cardiovascularrelated mortality, at lower ambient
concentrations than previously
observed. The Administrator also
recognized the availability of stronger
evidence of morbidity effects associated
with long-term PM2.5 exposures,
including evidence of cardiovascular
effects from the WHI study and
respiratory effects, including decreased
lung function growth, from the extended
analyses for the Southern California
Children’s Health Study. Furthermore,
the Administrator recognized new U.S.
multi-city studies that greatly expanded
and reinforced our understanding of
mortality and morbidity effects
associated with short-term PM2.5
exposures, providing stronger evidence
of associations at ambient
concentrations similar to those
previously observed (as summarized in
Figure 3). Id. at 38939–40.
The newly available scientific
evidence built upon the previous
scientific data base to provide evidence
of generally robust associations and to
provide a basis for greater confidence in
the reported associations than in the last
review. The Administrator recognized
that the weight of evidence, as evaluated
in the Integrated Science Assessment,
was strongest for health endpoints
classified as having evidence of a causal
relationship. These relationships
included those between long- and shortterm PM2.5 exposures and mortality and
cardiovascular effects. She recognized
that the weight of evidence was also
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
3140
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
strong for health endpoints classified as
having evidence of a likely causal
relationship, which included those
between long- and short-term PM2.5
exposures and respiratory effects. In
addition, the Administrator made note
of the much more limited evidence for
health endpoints classified as having
evidence suggestive of a causal
relationship, including developmental,
reproductive and carcinogenic effects.
Id. at 38940.
Based on information discussed and
presented in the Integrated Science
Assessment, the Administrator
recognized that health effects may occur
over the full range of concentrations
observed in the long- and short-term
epidemiological studies and that no
discernible threshold for any effects can
be identified based on the currently
available evidence (U.S. EPA, 2009a,
section 2.4.3). She also recognized, in
taking note of CASAC advice and the
distributional statistics analysis
discussed in section III.E.4.b.i above and
in the Policy Assessment, that there was
significantly greater confidence in
observed associations over certain parts
of the air quality distributions in the
studies, and conversely, that there was
significantly diminished confidence in
ascribing effects to concentrations
toward the lower part of the
distributions.
Consistent with the general approach
summarized in section III.A.3 above,
and supported by CASAC as discussed
in section III.E.4.a above, the
Administrator generally agreed that it
was appropriate to consider a level for
an annual standard that was somewhat
below the long-term mean PM2.5
concentrations reported in long- and
short-term exposure studies. In
recognizing that the evidence of an
association in any such study was
strongest at and around the long-term
average where the data in the study are
most concentrated, she understood that
this approach did not provide a bright
line for reaching decisions about
appropriate standard levels. The
Administrator noted that long-term
mean PM2.5 concentrations were
available for each study considered and,
therefore, represented the most robust
data set to inform her decisions on
appropriate annual standard levels. She
also noted that the overall study mean
PM2.5 concentrations were generally
calculated based on monitored
concentrations averaged across monitors
in each study area with multiple
monitors, referred to as a composite
monitor concentration, in contrast to the
highest concentration monitored in each
study area, referred to as a maximum
monitor concentration, which are used
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
to determine whether an area meets a
given standard. In considering such
long-term mean concentrations, the
Administrator understood that it was
appropriate to consider the weight of
evidence for the health endpoints
evaluated in such studies in giving
weight to this information. Id.
Based on the information summarized
in Figure 4 above and presented in more
detail in the Policy Assessment (U.S.
EPA, 2011a, chapter 2) for effects
classified in the Integrated Science
Assessment as having a causal or likely
causal relationship with PM2.5
exposures, the Administrator observed
an overall pattern of statistically
significant associations reported in
studies of long-term PM2.5 exposures
with long-term mean concentrations
ranging from somewhat above the
current standard level of 15 mg/m3 down
to the lowest mean concentration in
such studies of 12.9 mg/m3 (in Miller et
al., 2007).83 She observed a similar
pattern of statistically significant
associations in studies of short-term
PM2.5 exposures with long-term mean
concentrations ranging from around 15
mg/m3 down to 12.8 mg/m3 (in Burnett
et al., 2004). With regard to effects
classified as providing evidence
suggestive of a causal relationship, the
Administrator observed a small number
of long-term exposure studies related to
developmental and reproductive effects
that reported statistically significant
associations with overall study mean
PM2.5 concentrations down to 11.9 mg/
m3 (in Bell et al., 2007).84 Id.
The Administrator also considered
additional information from
epidemiological studies, consistent with
CASAC advice, to take into account the
broader distribution of PM2.5
concentrations and the degree of
confidence in the observed associations
over the broader air quality distribution.
In considering this additional
83 The EPA notes that the Miller et al., (2007)
study provides strong evidence of cardiovascular
related effects associated with long-term PM2.5
exposures. At the time of the proposal, the EPA
recognized the limited nature of the air quality data
considered in this study (77 FR 38918, fn. 62). The
EPA has reviewed those limitations, in conjunction
with consideration of public comments received on
the proposal as discussed in section III.E.4.c, in
conjunction with reaching a final decision on the
level of the annual standard.
84 With respect to suggestive evidence related to
cancer, mutagenic, and genotoxic effects, the PM2.5
concentrations reported in studies generally
included ambient concentrations that are equal to
or greater than ambient concentrations observed in
studies that reported mortality and cardiovascular
and respiratory effects (U.S. EPA, 2009a, section
7.5), such that in selecting alternative standard
levels that provide protection from mortality and
cardiovascular and respiratory effects, it is
reasonable to anticipate that protection will also be
provided for carcinogenic effects.
PO 00000
Frm 00056
Fmt 4701
Sfmt 4700
information, she understood that the
Policy Assessment presented
information on the 25th and 10th
percentiles of the distributions of PM2.5
concentrations available from four
multi-city studies to provide a general
frame of reference as to the part of the
distribution in which the data become
appreciably more sparse and, thus,
where her confidence in the
associations observed in
epidemiological studies would become
appreciably less.
As summarized in Figure 4 above, the
Administrator took note of additional
population-level data that were
available for four studies (Krewski et al.,
2009; Miller et al., 2007; Bell et al.,
2008; Zanobetti and Schwartz, 2009),
each of which reported statistically
significant associations with health
endpoints classified as having evidence
of a causal relationship. In considering
the long-term PM2.5 concentrations
associated with the 25th percentile
values of the population-level data for
these four studies, she observed that
these values ranged from somewhat
above to somewhat below 12 mg/m3. The
Administrator recognized that these
studies include some of the strongest
evidence available within the overall
body of scientific evidence and noted
that three of these studies (Krewski et
al., 2009; Bell et al., 2008; Zanobetti and
Schwartz, 2009) were used as the basis
for concentration-response functions
used in the quantitative risk assessment
(U.S. EPA, 2010a, section 3.3.3).
In considering this information, the
Administrator noted that CASAC
advised that information about the longterm PM2.5 concentrations that were
most influential in generating the health
effect estimates in epidemiological
studies can help to inform selection of
an appropriate annual standard level.
However, the Administrator also
recognized that additional populationlevel data were available for only these
four studies and, therefore, she believed
that these studies comprised a more
limited data set than one based on longterm mean PM2.5 concentrations for
which data were available for all studies
considered, as discussed above.
The Administrator recognized, as
summarized in section III.B above, that
important uncertainties remain in the
evidence and information considered in
this review of the primary fine particle
standards. These uncertainties are
generally related to understanding the
relative toxicity of the different
components in the fine particle mixture,
the role of PM2.5 in the complex ambient
mixture, exposure measurement errors
inherent in epidemiological studies
based on concentrations measured at
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
fixed monitor sites, and the nature,
magnitude, and confidence in estimated
risks related to increasingly lower
ambient PM2.5 concentrations.
Furthermore, the Administrator noted
that epidemiological studies have
reported heterogeneity in responses
both within and between cities and
geographic regions across the U.S. She
recognized that this heterogeneity may
be attributed, in part, to differences in
fine particle composition in different
regions and cities. The Administrator
also recognized that there are additional
limitations associated with evidence for
reproductive and developmental effects,
identified as being suggestive of a causal
relationship with long-term PM2.5
exposures, including: the limited
number of studies evaluating such
effects; uncertainties related to
identifying the relevant exposure time
periods of concern; and limited
toxicological evidence providing little
information on the mode of action(s) or
biological plausibility for an association
between long-term PM2.5 exposures and
adverse birth outcomes. Id. at 38941.
The Administrator was mindful that
considering what standards were
requisite to protect public health with
an adequate margin of safety required
public health policy judgments that
neither overstated nor understated the
strength and limitations of the evidence
or the appropriate inferences to be
drawn from the evidence. In considering
how to translate the available
information into appropriate standard
levels, the Administrator weighed the
available scientific information and
associated uncertainties and limitations.
For the purpose of determining what
standard levels were appropriate to
propose, the Administrator recognized,
as did EPA staff in the Policy
Assessment, that there was no single
factor or criterion that comprised the
sole ‘‘correct’’ approach to weighing the
various types of available evidence and
information, but rather there were
various approaches that are appropriate
to consider. The Administrator further
recognized that different evaluations of
the evidence and other information
before the Administrator could reflect
placing different weight on the relative
strengths and limitations of the
scientific information, and different
judgments could be made as to how
such information should appropriately
be used in making public health policy
decisions on standard levels. This
recognition led the Administrator to
consider various approaches to
weighing the evidence so as to identify
appropriate standard levels to propose.
In so doing, the Administrator
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
encouraged extensive public comment
on alternative approaches to weighing
the evidence and other information so
as to inform her public health policy
judgments before reaching final
decisions on appropriate standard
levels.
In considering the available
information, the Administrator noted
the advice of CASAC that the currently
available scientific information,
including epidemiological and
toxicological evidence as well as risk
and air quality information, provided
support for considering an annual
standard level within a range of 13 to 11
mg/m3 and a 24-hour standard level
within a range of 35 to 30 mg/m3. In
addition, the Administrator recognized
that the Policy Assessment concluded
that the available evidence and riskbased information support
consideration of annual standard levels
in the range of 13 to 11 mg/m3, and that
the Policy Assessment also concluded
that the evidence most strongly
supported consideration of an annual
standard level in the range of 12 to 11
mg/m3. In considering how the annual
and 24-hour standards work together to
provide appropriate public health
protection, the Administrator observed
that CASAC did not express support for
any specific levels or combinations of
standards within these ranges. Nor did
CASAC choose to comment on
additional information and analyses
presented in the final Policy Assessment
prepared in response to CASAC’s
recommendations on the second draft
Policy Assessment (Wegman, 2011).
In considering the extent to which the
currently available evidence and
information provided support for
specific standard levels within the
ranges identified by CASAC and the
Policy Assessment as appropriate for
consideration, the Administrator
initially considered standard levels
within the range of 13 to 11 mg/m3 for
the annual standard. In so doing, the
Administrator first considered the longterm mean PM2.5 concentrations
reported in studies of effects classified
as having evidence of a causal or likely
causal relationship, as summarized in
Figure 4 above and discussed more
broadly above. She noted that a level at
the upper end of this range would be
below most but not all the overall study
mean concentrations from the multi-city
studies of long- and short-term
exposures, whereas somewhat lower
levels within this range would be below
all such overall study mean
concentrations. In considering the
appropriate weight to place on this
information, the Administrator again
noted that the evidence of an
PO 00000
Frm 00057
Fmt 4701
Sfmt 4700
3141
association in any such study was
strongest at and around the long-term
average where the data in the study are
most concentrated, and that long-term
mean PM2.5 concentrations were
available for each study considered and,
therefore, represented the most robust
data set to inform her decisions on
appropriate annual standard levels.
Further, she was mindful that this
approach did not provide a bright line
for reaching decisions about appropriate
standard levels. Id.
In considering the long-term mean
PM2.5 concentrations reported in studies
of effects classified as having evidence
suggestive of a causal relationship, as
summarized in Figure 4 for reproductive
and developmental effects, the
Administrator noted that a level at the
upper end of this range would be below
the overall study mean concentration in
one of the three studies, while levels in
the mid- to lower part of this range
would be below the overall study mean
concentrations in two or three of these
studies. In considering the appropriate
weight to place on this information, the
Administrator noted the very limited
nature of this evidence of such effects
and the additional uncertainties in these
epidemiological studies relative to the
studies that provide evidence of causal
or likely causal relationships.
The Administrator also considered
the distributional analyses of
population-level information that were
available from four of the
epidemiological studies that provide
evidence of effects identified as having
a causal relationship with long- or shortterm PM2.5 concentrations for annual
standard levels within the same range of
13 to 11 mg/m3. In so doing, the
Administrator first noted that a level in
the mid-part of this range generally
corresponds with approximately the
25th percentile of the distributions of
health events data available in three of
these studies. The Administrator also
noted that standard levels toward the
upper part of this range would reflect
placing substantially less weight on this
information, whereas standard levels
toward the lower part of this range
would reflect placing substantially more
weight on this information. In
considering this information, the
Administrator noted that there was no
bright line that delineates the part of the
distribution of PM2.5 concentrations
within which the data become
appreciably more sparse and, thus,
where her confidence in the
associations observed in
epidemiological studies became
appreciably less.
In considering mean PM2.5
concentrations and distributional
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
3142
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
analyses from the various sets of
epidemiological studies noted above,
the Administrator was mindful, as noted
above, that such studies typically report
concentrations based on composite
monitor distributions, in which
concentrations may be averaged across
multiple ambient monitors that may be
present within each area included in a
given study. Thus, a policy approach
that used data based on composite
monitors to identify potential
alternative standard levels would
inherently build in a margin of safety of
some degree relative to an alternative
standard level based on measurements
at the monitor within an area that
records the highest concentration, or the
maximum monitor, since once a
standard was set, concentrations at
appropriate maximum monitors within
an area were generally used to
determine whether an area meets a
given standard.
The Administrator also recognized
that judgments about the appropriate
weight to place on any of the factors
discussed above should reflect
consideration not only of the relative
strength of the evidence but also on the
important uncertainties that remained
in the evidence and information being
considered in this review. The
Administrator noted that the extent to
which these uncertainties influenced
judgments about appropriate annual
standard levels within the range of 13 to
11 mg/m3 would likely be greater for
standard levels in the lower part of this
range which would necessarily be based
on fewer available studies than would
higher levels within this range.
Based on the above considerations,
the Administrator concluded that it was
appropriate to propose to set a level for
the primary annual PM2.5 standard
within the range of 12 to 13 mg/m3. The
Administrator provisionally concluded
that a standard set within this range
would reflect alternative approaches to
appropriately placing the most weight
on the strongest available evidence,
while placing less weight on much more
limited evidence and on more uncertain
analyses of information available from a
relatively small number of studies.
Further, she provisionally concluded
that a standard level within this range
would reflect alternative approaches to
appropriately providing an adequate
margin of safety for the populations at
risk for the serious health effects
classified as having evidence of a causal
or likely causal relationship, depending
in part on the emphasis placed on
margin of safety considerations. The
Administrator recognized that setting an
annual standard level at the lower end
of this range would reflect an approach
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
that placed more emphasis on the entire
body of the evidence, including the
analysis of the distribution of air quality
concentrations most influential in
generating health effect estimates in the
studies, and on margin of safety
considerations, than would setting a
level at the upper end of the range.
Conversely, an approach that would
support a level at the upper end of this
range would generally support a view
that the uncertainties remaining in the
evidence are such that the evidence
does not warrant setting a lower annual
standard level. Id. at 38942.
At the time of the proposal, while the
Administrator recognized that CASAC
advised, and the Policy Assessment
concluded, that the available scientific
information provided support for
considering a range that extended down
to 11 mg/m3, she concluded that
proposing such an extended range
would reflect a public health policy
approach that placed more weight on
relatively limited evidence and more
uncertain information and analyses than
she considered appropriate at this time.
Nonetheless, the Administrator solicited
comment on a level down to 11 mg/m3
as well as on approaches for translating
scientific evidence and rationales that
would support such a level. Such an
approach might reflect a view that the
uncertainties associated with the
available scientific information warrant
a highly precautionary public health
policy response that would incorporate
a large margin of safety.
The Administrator recognized that
potential air quality changes associated
with meeting an annual standard set at
a level within the range of 12 to 13 mg/
m3 will result in lowering risks
associated with both long- and shortterm PM2.5 exposures. However, the
Administrator recognized that such an
annual standard intended to serve as the
primary means for providing protection
from effects associated with both longand short-term PM2.5 exposures would
not by itself be expected to offer
requisite protection with an adequate
margin of safety against the effects of all
short-term PM2.5 exposures. As a result,
in conjunction with proposing an
annual standard level in the range of 12
to 13 mg/m3, the Administrator
provisionally concluded that it was
appropriate to continue to provide
supplemental protection by means of a
24-hour standard set at the appropriate
level, particularly for areas with high
peak-to-mean ratios possibly associated
with strong local or seasonal sources, or
for PM2.5-related effects that may be
associated with shorter-than-daily
exposure periods.
PO 00000
Frm 00058
Fmt 4701
Sfmt 4700
Based on the approach discussed in
section III.A.3 above, at the time of the
proposal the Administrator relied upon
evidence from the short-term exposure
studies as the principal basis for
selecting the level of the 24-hour
standard. In considering these studies as
a basis for the level of a 24-hour
standard, and having selected a 98th
percentile form for the standard, the
Administrator agreed with the focus in
the Policy Assessment of looking at the
98th percentile values, as well as at the
long-term mean PM2.5 concentrations in
these studies.
In considering the information
provided by the short-term exposure
studies, the Administrator recognized
that to the extent these studies were
conducted in areas that likely did not
meet one or both of the current
standards, such studies did not help
inform the characterization of the
potential public health improvements of
alternative standards set at lower levels.
By reducing the PM2.5 concentrations in
such areas to just meet the current
standards, the Administrator anticipated
that additional public health protection
would occur. Therefore, the
Administrator focused on studies that
reported positive and statistically
significant associations in areas that
would likely have met both the current
24-hour and annual standards. She also
considered whether or not these studies
were conducted in areas that would
likely have met an annual standard level
of 12 to 13 mg/m3 to inform her decision
regarding an appropriate 24-hour
standard level. As discussed in section
III.E.4.a, consistent with the Policy
Assessment, the Administrator
concluded that multi-city, short-term
exposure studies provided the strongest
data set for informing her decisions on
appropriate 24-hour standard levels.
The Administrator viewed the singlecity, short-term exposure studies as a
much more limited data set providing
mixed results and, therefore, she had
less confidence in using those studies as
a basis for setting the level of a 24-hour
standard. With regard to the limited
number of single-city studies that
reported positive and statistically
significant associations for a range of
health endpoints related to short-term
PM2.5 concentrations in areas that would
likely have met the current suite of
PM2.5 standards, the Administrator
recognized that many of those studies
had significant limitations (e.g., limited
statistical power, limited exposure data)
or equivocal results (mixed results
within the same study area) that made
them unsuitable to form the basis for
setting the level of a 24-hour standard.
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
With regard to multi-city studies that
evaluated effects associated with shortterm PM2.5 exposures, the Administrator
observed an overall pattern of positive
and statistically significant associations
in studies with 98th percentile values
averaged across study areas in the range
of 45.8 to 34.2 mg/m3 (Burnett et al.,
2004; Zanobetti and Schwartz, 2009;
Bell et al., 2008; Dominici et al., 2006a,
Burnett and Goldberg, 2003; Franklin et
al., 2008). The Administrator noted that,
to the extent air quality distributions
were reduced to reflect just meeting the
current 24-hour standard, additional
protection would be anticipated for the
effects observed in the three multi-city
studies with 98th percentile values
greater than 35 mg/m3 (Burnett et al.,
2004; Burnett and Goldberg, 2003;
Franklin et al., 2008). In the three
additional studies with 98th percentile
values below 35 mg/m3, specifically 98th
percentile concentrations of 34.2, 34.3,
and 34.8 mg/m3, the Administrator noted
that these studies reported long-term
mean PM2.5 concentrations of 12.9, 13.2,
and 13.4 mg/m3, respectively (Bell et al.,
2008; Zanobetti and Schwartz, 2009;
Dominici et al., 2006a).
In proposing to revise the level of the
annual standard to within the range of
12 to 13 mg/m3, as discussed above, the
Administrator recognized that
additional protection would be
provided for the short-term effects
observed in these multi-city studies in
conjunction with an annual standard
level of 12 mg/m3, and in two of these
three studies in conjunction with an
annual standard level of 13 mg/m3. She
noted that the study-wide mean
concentrations were based on averaging
across monitors within study areas and
that compliance with the standard
would be based on concentrations
measured at the monitor reporting the
highest concentration within each area.
The Administrator believed it would be
reasonable to conclude that revision to
the 24-hour standard would not be
appropriate in conjunction with an
annual standard within this range.
Based on the above considerations
related to the epidemiological evidence,
the Administrator provisionally
concluded that it was appropriate to
retain the level of the 24-hour standard
at 35 mg/m3, in conjunction with a
revised annual standard level in the
proposed range of 12 to 13 mg/m3.
In addition to considering the
epidemiological evidence, the
Administrator also took into account air
quality information based on countylevel 24-hour and annual design values
to understand the public health
implications of retaining the 24-hour
standard level at 35 mg/m3 in
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
conjunction with an annual standard
level within the proposed range of 12 to
13 mg/m3. She considered whether these
suites of standards would meet a public
health policy goal which included
setting the annual standard to be the
‘‘generally controlling’’ standard in
conjunction with setting the 24-hour
standard to provide supplemental
protection to the extent that additional
protection is warranted. As discussed
above, the Administrator provisionally
concluded that this approach was the
most effective and efficient way to
reduce total population risk associated
with both long- and short-term PM2.5
exposures, resulting in more uniform
protection across the U.S. than the
alternative of setting the 24-hour
standard to be the controlling standard.
In considering the air quality
information, the Administrator first
recognized that there was no annual
standard within the proposed range of
levels, when combined with a 24-hour
standard at the proposed level of 35 mg/
m3, for which the annual standard
would be the generally controlling
standard in all areas of the country. She
further observed that such a suite of
PM2.5 standards with an annual
standard level of 12 mg/m3 would result
in the annual standard as the generally
controlling standard in most regions
across the country, except for certain
areas in the Northwest, where the
annual mean PM2.5 concentrations have
historically been low but where
relatively high 24-hour concentrations
occur, often related to seasonal wood
smoke emissions (U.S. EPA, 2011a, pp.
2–89 to 2–91, Figure 2–10). Although
not explicitly delineated on Figure 2–10
in the Policy Assessment, an annual
standard of 13 mg/m3 would be
somewhat less likely to be the generally
controlling standard in some regions of
the U.S. outside the Northwest in
conjunction with a 24-hour standard
level of 35 mg/m3.
Taking the above considerations into
account, the Administrator proposed to
revise the level of the primary annual
PM2.5 standard from 15.0 mg/m3 to
within the range of 12.0 to 13.0 mg/m3
and to retain the 24-hour standard level
at 35 mg/m3. In the Administrator’s
judgment, such a suite of primary PM2.5
standards and the rationale supporting
such levels could reasonably be judged
to reflect alternative approaches to the
appropriate consideration of the
strength of the available evidence and
other information and their associated
uncertainties and the advice of CASAC.
The Administrator recognized that the
final suite of standards selected from
within the proposed range of annual
standard levels, or the broader range of
PO 00000
Frm 00059
Fmt 4701
Sfmt 4700
3143
annual standard levels on which public
comment was solicited, must be clearly
responsive to the issues raised by the
DC Circuit’s remand of the 2006 primary
annual PM2.5 standard. Furthermore, at
the time of the proposal, she recognized
that the final suite of standards will
reflect her ultimate judgment in the
final rulemaking as to the suite of
primary PM2.5 standards that would be
requisite to protect the public health
with an adequate margin of safety from
effects associated with fine particle
exposures. The final judgment to be
made by the Administrator will
appropriately consider the requirement
for a standard that is neither more nor
less stringent than necessary and will
recognize that the CAA does not require
that primary standards be set at a zerorisk level, but rather at a level that
reduces risk sufficiently so as to protect
public health with an adequate margin
of safety.
At the time of the proposal, having
reached her provisional judgment to
propose revising the annual standard
level from 15.0 to within a range of 12.0
to 13.0 mg/m3 and to propose retaining
the 24-hour standard level at 35 mg/m3,
the Administrator solicited public
comment on this range of levels and on
approaches to considering the available
evidence and information that would
support the choice of levels within this
range. The Administrator also solicited
public comment on alternative annual
standard levels down to 11 mg/m3 and
on the combination of annual and 24hour standards that commenters may
believe is appropriate, along with the
approaches and rationales used to
support such levels. In addition, given
the importance the evidence from
epidemiologic studies played in
considering the appropriate annual and
24-hour levels, the Administrator
solicited public comment on issues
related to translating epidemiological
evidence into standards, including
approaches for addressing the
uncertainties and limitations associated
with this evidence.
c. Comments on Standard Levels
This section addresses comments that
relate to consideration of the
appropriate levels of the primary annual
and 24-hour PM2.5 standards, including
comments on the general approach used
by the EPA to translate the available
scientific information into standard
levels and how specific PM2.5 exposure
studies should be considered as a basis
for the standard levels. These comments
on standard levels expand upon the
more general comments that either
supported or opposed any change to the
current suite of primary PM2.5
E:\FR\FM\15JAR2.SGM
15JAR2
3144
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
standards, which are addressed above in
section III.D.2.85 As explained there, one
group of commenters generally opposed
any change to the current primary PM2.5
standards and more specifically
disagreed with the basis for the EPA’s
proposal to revise the annual standard
level. Another group of commenters
supported revising the current suite of
primary PM2.5 standards to provide
increased public health protection.
Some commenters in this second group
argued that both the annual and 24-hour
standard levels should be lowered while
other commenters in this group agreed
with the EPA’s proposal to retain the
level of the 24-hour standard in
conjunction with revising the level of
the annual standard. While generally
supporting the EPA’s proposal to lower
the level of the annual standard, many
commenters in this group disagreed that
a level within the EPA’s proposed range
was adequately protective and
supported a level of 11 mg/m3 or below.
tkelley on DSK3SPTVN1PROD with
i. Annual Standard Level
The group of commenters opposed to
any change to the current suite of
primary PM2.5 standards generally
raised questions regarding the
underlying scientific evidence,
including the causal determinations
reached in the Integrated Science
Assessment, and focused strongly on the
uncertainties they saw in the scientific
evidence as a basis for their conclusion
that no changes to the current standard
levels were warranted. In commenting
on the proposed standard levels, these
commenters typically relied on the
arguments summarized and addressed
above in section III.D.2 as to why they
believed it was inappropriate for the
EPA to make any revisions to the suite
of primary PM2.5 standards. That is, they
asserted that the EPA’s causal
determinations were not adequately
supported by the underlying scientific
information; the biological plausibility
of health effects observed in
epidemiological studies has not been
demonstrated in controlled human
exposure and toxicological studies;
uncertainties in the underlying health
science are as great or greater than in
2006; there is no evidence of greater risk
since the last review to justify tightening
the current annual PM2.5 standard; and
‘‘new’’ studies not included in the
Integrated Science Assessment continue
to increase uncertainty about possible
health risks associated with exposure to
PM2.5.
85 Specific comments on the forms of the annual
and 24-hour standards are addressed in section
III.E.3.a and III.E.3.b, respectively.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
With regard to the level of the annual
standard, these commenters strongly
disagreed with the Agency’s proposed
decision to revise the level to within a
range of 12 to 13 mg/m3 and argued that
the current standard level of 15 mg/m3
should be retained. For example, UARG,
API, and other commenters in this
group raised a number of issues that
they asserted called into question the
EPA’s interpretation of the
epidemiological evidence to support
revising the annual standard level.
These commenters raised specific
questions related to the general
approach used by the EPA to translate
the air quality and other information
from specific epidemiological studies
into standard levels, including: (1) The
EPA’s approach for using composite
monitor air quality distributions
reported in epidemiological studies to
select a standard level that would be
compared to measurements at the
monitor recording the highest value in
an area to determine compliance with
the standard; (2) the appropriate
exposure period for effects observed in
long-term exposure mortality studies;
and (3) the use of the EPA’s analysis of
distributions of underlying populationlevel data (i.e., health event and study
population data) for those
epidemiological studies for which such
information was available. These
commenters also raised questions
regarding the EPA’s consideration of
specific scientific evidence as a basis for
setting a standard level, including: (4)
evidence of respiratory morbidity effects
in long-term exposure studies and (5)
more limited evidence of health effects
which have been categorized in the
Integrated Science Assessment as
suggestive of a causal relationship (i.e.,
developmental and reproductive
outcomes). These comments are
discussed in turn below.
(1) Some commenters in this group
argued that one reason why they believe
there is no basis for setting a standard
level below 15 mg/m3 is that the air
quality metric from epidemiological
studies that the EPA relied on in the
proposal is not the same metric that will
be compared to the level of the standard
to determine compliance with the
standard. That is, commenters noted
that the long-term mean PM2.5
concentrations that the EPA considered,
shown in Figure 4 above, are composite
monitor mean concentrations (i.e.,
concentrations averaged across multiple
monitors within areas with more than
one monitor), whereas the PM2.5
concentrations that will be compared to
the level of the standard are maximum
monitor concentrations (i.e., the
PO 00000
Frm 00060
Fmt 4701
Sfmt 4700
concentration measured by the monitor
within an area reporting the highest
concentration). This comment was
presented most specifically in UARG’s
comments (UARG, 2012, Attachment 1,
pp. 2 to 6), which raised two
overarching issues as discussed below.
First, the commenter noted that the
EPA’s approach of considering
composite monitor mean PM2.5
concentrations in selecting a standard
level, and then comparing the maximum
monitor mean PM2.5 concentration in
each area to the standard level when the
standard is implemented, was
characterized in the proposal as
inherently having the potential to build
in a margin of safety (UARG, 2012,
Attachment 1, p. 4, citing 77 FR 38905).
The commenter asserted that the
Administrator is ignoring this
distinction between composite and
maximum monitor concentrations, and
that this approach creates an
unwarranted case for lowering the
standard level, since in the commenter’s
view, it would result in a margin of
safety that would be arbitrary, not based
on evidence, and unquantified (UARG,
2012, Attachment 1, p. 4). In support of
this view, the commenter asserted that
there is a significant difference between
composite monitor mean PM2.5
concentrations and maximum monitor
mean PM2.5 concentrations. The
commenter asserted that the maximum
monitor value will always be higher
than the composite monitor value
(except in areas that contain only a
single monitor), such that when an area
just attains the NAAQS, that area’s
composite monitor long-term mean
PM2.5 concentration will be lower than
the level of the standard (UARG, 2012,
Attachment 1, p. 3).
Second, the commenter asserted that
a more ‘‘reasoned and consistent
approach would be to decide on a mean
composite monitor PM2.5 level that
should be achieved and then identify
the maximum monitor level that would
result in that composite value’’ (UARG,
2012, Attachment 1, p. 4). The
commenter conducted an analysis of
maximum monitor versus composite
monitor annual mean PM2.5
concentrations using monitoring data 86
from 2006 to 2008 and presented results
averaged across areas within two groups
(i.e., those with design values 87 above
the current standard level and those
with design values just below the
86 The commenter indicated that this analysis was
based on monitoring data for every core based
statistical area (CBSA) in the EPA’s Air Quality
System (AQS) database.
87 The design value is the air quality statistic that
is compared to the level of the NAAQS to determine
the attainment status of a given area.
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
current standard level) to illustrate their
suggested alternative approach. The
commenter interpreted this analysis as
showing that the composite monitor
long-term mean PM2.5 concentrations
from the subset of the epidemiological
studies shown in Figure 4 (of the
proposal and above) that the commenter
considered to be an appropriate focus
for this analysis would be achieved
across the U.S. if the current annual
NAAQS of 15 mg/m3 is retained and
attained. The commenter considered the
subset of epidemiological studies that
included only long-term exposures
studies of effects for which the evidence
is categorized as causal or likely causal,
but did not consider short-term
exposure studies. On this basis, the
commenter asserted that attaining the
current annual PM2.5 standard would
result in composite monitor long-term
mean concentrations in all areas that
would be generally within or below the
range of the composite monitor longterm mean concentrations from such
studies and, as a result, there is no
reason to lower the level of the current
annual NAAQS.
In considering the first issue related to
the EPA’s approach, the EPA notes that
in proposing to revise both the form and
level of the annual standard, the
Administrator clearly took into account
the distinction between the composite
monitor long-term mean PM2.5
concentrations from the epidemiological
studies, considered as a basis for
selecting an annual standard level, and
maximum monitor long-term mean
PM2.5 concentrations. In deciding to
focus on the composite monitor longterm mean concentrations in selecting
the standard level, and on the maximum
monitor concentrations in selecting the
form of the standard (i.e., consistent
with proposing to eliminate the option
for spatial averaging across monitors
within an area when implementing the
standard 88), the Administrator
reasonably considered the distinction
between these metrics in a manner that
was consistent with advice from CASAC
(Samet et al., 2010d, pp. 2 to 3).
As noted above in section III.A.3, the
EPA recognizes that a statistical metric
(e.g., the mean of a distribution) based
on maximum monitor concentrations
may be identical to or above the same
statistical metric based on composite
monitor concentrations. More
specifically, many areas have only one
monitor, in which case the composite
and maximum monitor concentrations
are identical. Based on the most recent
data from the EPA’s AQS from 2009 to
2011 in the 331 CBSAs in which valid
88 As
discussed above in section III.E.3.a.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
PM2.5 data are available, as discussed in
Frank (2012a, Table 5), there were 208
such areas (with design values ranging
up to about 15 mg/m3). Frank (2012a)
also observed that other areas have
multiple monitors with composite and
maximum monitor mean PM2.5
concentrations that were the same or
relatively close, with 57 areas in which
the maximum monitor mean
concentration was no more than 0.5 mg/
m3 higher than the composite monitor
mean concentration and 56 areas in
which the difference was between 0.6
and 2 mg/m3. Further, there were only a
few other areas in which the maximum
monitor mean concentration was
appreciably higher than the composite
monitor mean concentration, such as
areas in which some monitors may be
separately impacted by local sources.
There were only 10 such areas in the
country in which the maximum monitor
mean concentration was between 2 to 6
mg/m3 higher than the composite
monitor concentration (Frank, 2012a,
Table 4).89 Thus, the EPA does not agree
that there is a significant difference
between composite monitor mean PM2.5
concentrations and maximum monitor
mean PM2.5 concentrations in the large
majority of areas across the country.
In proposing to revise the form of the
annual PM2.5 standard, as discussed
above in section III.E.3.a, the EPA noted
that when an annual PM2.5 standard was
first set in 1997, the form of the
standard included the option for
averaging across measurements at
appropriate monitoring sites within an
area, generally consistent with the
composite monitor approach used in
epidemiological studies, with some
constraints intended to ensure that
spatial averaging would not result in
inequities in the level of protection for
communities within large metropolitan
areas. In the last review the EPA
tightened the constraints on spatial
averaging, and in this review has
eliminated the option altogether, on the
basis of analyses in each review that
showed that such constraints may be
inadequate to avoid substantially greater
exposures for people living in locations
around the monitors recording the
highest PM2.5 concentrations in some
areas, potentially resulting in
disproportionate impacts on at-risk
populations of persons with lower SES
levels as well as minorities. In light of
these analyses, and consistent with the
Administrator’s decision to revise the
89 The average difference between the maximum
and composite design value among the 123 CBSAs
with two or more monitors is 0.8 mg/m3 and the
median difference is 0.6 mg/m3. The 25th and 75th
percentiles are 0.3 and 1.0 mg/m3, respectively
(Frank, 2012a, p. 4).
PO 00000
Frm 00061
Fmt 4701
Sfmt 4700
3145
form of the annual PM2.5 standard by
eliminating the option for spatial
averaging, the EPA continues to
conclude that a standard level based on
consideration of long-term mean
concentrations from composite
monitors, and applied at each monitor
within an area including the monitor
measuring the highest concentration, is
the appropriate approach to use in
setting a standard that will protect
public health, including the health of atrisk populations, with an adequate
margin of safety, as required by the
CAA.
The EPA acknowledges that at
proposal, the Agency characterized the
approach of using maximum monitor
concentrations to determine compliance
with the standard, while selecting the
standard level based on consideration of
composite monitor concentrations, as
one that inherently had the potential to
build in a margin of safety (77 FR
38905), and CASAC reiterated that view
in supporting the EPA’s approach
(Samet, 2010d, p. 3). Nonetheless, in
light of the discussion above, the EPA
more specifically recognizes that this
approach does not build in any margin
of safety in the large number of areas
across the country with only one
monitor. Further, based on the analyses
done to inform consideration of the
form of the standard (Schmidt, 2011,
Analysis A), the EPA concludes that this
approach does not provide a margin of
safety for the at-risk populations that
live around the monitor measuring the
highest concentration, such as in those
few areas in which the maximum
monitor concentration is appreciably
higher than the composite monitor
concentration. Rather, this approach
properly treats those at-risk populations
the same way it does the broader
populations that live in areas with only
one monitor, by providing the same
degree of protection for those at-risk
populations that would otherwise be
disproportionately impacted as it does
for the broader populations in other
areas, While the EPA recognizes that
this approach can result in some
additional margin of safety for the
subset of areas with multiple monitors
in which at-risk populations may not be
disproportionately represented in areas
around the maximum monitor, which
may be the case in areas with relatively
small differences between the maximum
and composite monitor concentrations,
the EPA notes that this margin would be
relatively small in such areas.
Based on the above considerations,
the EPA does not agree that the
Agency’s approach of using maximum
monitor concentrations to determine
compliance with the standard, while
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
3146
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
selecting the standard level based on
consideration of composite monitor
concentrations creates an unwarranted
case for lowering the standard level
based on a margin of safety that would
be arbitrary, not based on evidence, or
lack quantification. The EPA recognizes
that setting a standard to protect public
health, including the health of at-risk
populations, with an adequate margin of
safety, depends upon selecting a
standard level sufficiently below where
the EPA has found the strongest
evidence of health effects so as to
provide such protection, and that the
EPA’s approach regarding consideration
of composite and maximum monitor
concentrations is intended to, and does,
serve to address this requirement as part
of and not separate from the selection of
an appropriate standard level based on
the health effects evidence.
In considering the second issue
related to the commenter’s suggested
alternative approach, the EPA strongly
disagrees with the commenter’s view
that a more ‘‘reasoned and consistent
approach would be to decide on a mean
composite monitor PM2.5 level that
should be achieved and then identify
the maximum monitor level that would
result in that composite value’’ (UARG,
2012, Attachment 1, p. 4). As discussed
above, the EPA notes that for areas with
only one monitor, or with multiple
monitors that measure concentrations
that are very close in magnitude, the
maximum monitor level that would
limit the composite monitor PM2.5 level
to be no greater than the level that
should be achieved to protect public
health with an adequate margin of
safety, would essentially be the same as
that composite monitor level. Further,
as discussed above, even for areas in
which the maximum monitor
concentration is appreciably higher than
other monitor concentrations within the
same area, public health would not be
protected with an adequate margin of
safety if the disproportionately higher
exposures of at-risk, susceptible
populations around the monitor
measuring the highest concentration
were in essence averaged away with
measurements from monitors in other
locations within large urban areas.
Further, the commenter’s suggested
approach would be based on annual
average PM2.5 concentrations that have
been measured over some past time
period. Such an approach would reflect
the air quality that existed in the past,
but it would not necessarily provide
appropriate constraints on the range of
concentrations that would be allowed
by such a standard in the future, when
relationships between maximum and
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
composite monitor concentrations in
areas across the country may be
different. For these reasons, the EPA
fundamentally rejects the commenter’s
suggested approach because in the
EPA’s view it would not protect public
health, including providing protection
for at-risk populations, with an adequate
margin of safety in areas across the
country.
More specifically, in further
considering the commenter’s analysis of
design values based on maximum
versus composite monitor annual mean
PM2.5 concentrations using monitoring
data from 2006 to 2008 which they
assert supports retaining the current
standard level of 15 mg/m3, the EPA
finds flaws with the numerical results
and the scope of the analysis, as well as
flaws in the commenter’s translation of
the analysis results into the basis for
selecting an annual standard level.
In considering the commenter’s
analysis, the EPA notes that the analysis
compared maximum versus composite
monitor annual mean PM2.5
concentrations, averaged over 3 years,
for two groups of areas: (1) Areas with
design values that exceed the current
annual standard level (i.e., greater than
15.0 mg/m3) and (2) areas with design
values that are just attaining the current
annual standard (i.e., between 14.5 and
15.0 mg/m3).90 The commenter indicated
that they used the full body of PM2.5
monitoring data from the EPA’s AQS
database (UARG, 2012, Attachment 1, p.
4), In attempting to reproduce the
commenter’s results, the EPA repeated
the calculations using only valid air
quality data (i.e., data that meet data
completeness and monitor siting
criteria) from the AQS database for the
same time period (Frank, 2012a).91
Based on this corrected analysis, the
EPA finds that the composite monitor
concentrations averaged across the areas
within each group are somewhat higher
than those calculated by the commenter,
and the average differences between the
maximum and composite monitor
90 For the first group of areas (which included 33
areas), this analysis calculated an average across the
areas of maximum monitor annual mean PM2.5
concentrations, averaged over 3 years, of 17.2 mg/
m3 compared to an average of composite monitor
concentrations of 14.3 mg/m3. For the second group
of areas (which included 11 areas), this analysis
calculated an average across the areas of maximum
monitor annual mean concentrations, averaged over
3 years, of 14.8 mg/m3 compared to an average of
composite monitor concentrations of 13.6 mg/m3
(UARG, 2012, Attachment 1, Table 1).
91 The EPA notes that the Frank (2012a) analysis
is similar to an earlier EPA staff analysis (HassettSipple et al., 2010), which used air quality data
from EPA’s AQS database to compare maximum
versus composite monitor long-term mean PM2.5
concentrations across the study areas in six selected
multi-city epidemiological studies.
PO 00000
Frm 00062
Fmt 4701
Sfmt 4700
concentrations are somewhat smaller
(Frank, 2012a, Table 3).92 Notably, the
difference between the maximum and
composite monitor average
concentrations for the second group of
areas is substantially reduced in the
corrected analysis, such that the
difference (averaged across the 10 areas
with valid data in the second group) is
approximately 0.5 mg/m3, not 1.2 mg/m3
as in the commenter’s analysis. In
addition, the commenter’s analysis
compared the average of the composite
monitors to the average of the maximum
monitors for each subset of areas. This
comparison of averages across all the
areas in each subset masks the fact that
the large majority of areas across the
country have only one monitor, with the
composite monitor and maximum
monitor values the same for such areas,
and many other areas have a maximum
monitor value that is close to the
composite monitor value. As discussed
above, these circumstances have a major
impact on the protection that would be
achieved by the approach suggested by
the commenter.
With regard to the scope of the
commenter’s analysis, the EPA finds
that by limiting the scope to a small
subset of areas with design values above
or just below the current annual
standard level of 15 mg/m3, the analysis
ignores the large number of areas across
the country with lower design values
that are relevant to consider in light of
the epidemiological evidence of serious
health effects at lower concentrations,
well below the level of the current
standard.
In translating the analysis results into
the basis for selecting an annual
standard level, the commenter’s
translation is premised on the view that
the ‘‘natural focal point’’ for setting an
annual PM2.5 standard level should be
somewhere within the range of the longterm mean PM2.5 concentrations from
the subset of epidemiological studies
that included only long-term exposure
studies of effects for which the evidence
is categorized as causal or likely causal,
but not for effects categorized as
suggestive of causality, nor did it
92 The EPA’s analysis was intended to repeat the
commenter’s analysis, but using only valid air
quality data (from 2006 to 2008). For the first group
of areas (which included 21 areas with valid data),
the EPA’s analysis calculated an average across the
areas of maximum monitor annual mean
concentrations, averaged of 3 years, of 16.8 mg/m3
compared to an average of composite monitor
concentrations of 14.8 mg/m3. For the second group
of areas (which included 10 areas with valid data),
the EPA’s analysis calculated an average across the
areas of maximum monitor annual mean
concentrations, averaged over 3 years, of 14.8 mg/
m3 compared to an average of composite monitor
concentrations of 14.2 mg/m3 (Frank, 2012a, Table
3).
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
include short-term exposure studies
(which are included in Figure 4 of the
proposal notice and above). Such a view
is not consistent with setting a standard
that would provide sufficient protection
from the serious health effects reported
even in the limited subset of studies
considered by the commenter, including
protecting public health with an
adequate margin of safety. As discussed
below, the EPA does not agree with the
commenter’s view as to the appropriate
focal point for selecting the level of an
annual PM2.5 standard, or with the
limited set of studies considered by the
commenter as a basis for selecting the
level of the annual PM2.5 standard.
Regarding an appropriate focal point
for selecting the level of the annual
standard, as discussed in the proposal
and as advised by CASAC, the EPA has
focused on PM2.5 concentrations
somewhat below the lowest long-term
mean concentrations from each of the
key studies of both long- and short-term
exposures of effects for which the
evidence is causal or likely causal, as
considered by the EPA (i.e., the first two
sets of studies shown in Figure 4). If the
level of the annual standard was set just
somewhere within the range of the longterm mean concentrations from the
various long-term exposure studies,
then one or more of the studies would
have a long-term mean concentration
below the selected level of the standard.
Absent some reason to ignore or
discount these studies, which the
commenter does not provide (and of
which the EPA is unaware), setting such
a standard would allow that level of air
quality, where the evidence of health
effects is strongest, and its associated
risk of PM2.5-related mortality and/or
morbidity effects to continue. Selecting
such a standard level could not be
considered sufficient to protect the
public health with an adequate margin
of safety.
Further, focusing on just the longterm mean PM2.5 concentrations in the
key epidemiological studies—even the
lowest long-term mean concentration
from the set of key studies—is not
appropriate. Concentrations at and
around the long-term mean
concentrations represent the part of the
air quality distribution where the data
in any given study are most
concentrated and, thus, where the
confidence in the magnitude and
significance of an association in such
study is strongest. However, the
evidence of an association with adverse
health effects in the studies is not
limited to the PM2.5 concentrations just
at and around the long-term mean, but
rather extends more broadly to a lower
part of the distribution, recognizing that
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
no discernible population-level
threshold for any such effects can be
identified based on the available
evidence. This broader region of the
distribution of PM2.5 concentrations
should be considered to the extent
relevant information is available,
recognizing that the degree of
confidence in the association identified
in a study would become lower as one
moves below concentrations at and
around the long-term mean
concentration in any given study. The
commenter’s approach ignores this
fundamental consideration.
Regarding the set of studies that is
appropriate to inform the selection of
the level of the annual PM2.5 standard,
the EPA finds that limiting
consideration only to the long-term
exposure studies, as this commenter
suggests, would be tantamount to
ignoring the short-term exposure
studies,93 which provide some of the
strongest evidence from the entire body
of epidemiological studies. Thus,
selecting an annual standard level using
the limited set of studies suggested by
the commenter would fail to provide a
degree of protection that would be
sufficient to protect public health with
an adequate margin of safety.
For all the reasons discussed above,
the EPA finds the commenter’s concerns
with the EPA’s approach to considering
composite and maximum monitor PM2.5
concentrations in selecting the level of
the annual PM2.5 standard to be without
merit. Further, the EPA finds no support
in the commenter’s analysis for their
suggested alternative approach.
(2) With respect to the appropriate
exposure period for mortality effects
observed in long-term exposure studies,
some commenters in this group
generally expressed views consistent
with comments from UARG that argued
that these studies ‘‘are most likely
detecting health risk from earlier, higher
PM2.5 levels and misattributing those
risks to more recent, lower PM2.5 levels’’
93 The commenter suggests that the EPA should
not place significant reliance on the long-term mean
concentrations from short-term exposure studies
because ‘‘[T]he short-term studies did not use the
annual average of PM2.5 to develop their
associations; they used the daily 24-hour averages
of PM2.5. Thus, short-term studies do not provide
a natural indicator for the appropriate level of an
annual standard * * *.’’ (UARG, 2012, Attachment
1, p. 3). The EPA finds this argument unpersuasive.
Quite simply, effects were observed in these studies
with an air quality distribution that can
meaningfully be characterized by these long-term
mean concentrations. Indeed, in remanding the
2006 standard, the D.C. Circuit discussed at length
the interrelationship of the long- and short-term
standards and studies, and remanded the 2006
standard to the EPA, in part, for ignoring those
relationships without adequate explanation.
American Farm Bureau Federation v. EPA. 559 F.
3d at 522–24.
PO 00000
Frm 00063
Fmt 4701
Sfmt 4700
3147
(UARG, 2012, Attachment 1, p 7).
Further, this commenter asserted that
‘‘there is no knowledge or evidence
indicating whether premature deaths are
the result of PM2.5 exposures in the most
recent year; or due to physical damages
incurred from PM2.5 exposures much
earlier in life (with the impact on
lifespan only emerging later in life); or
due to total accumulated PM2.5 exposure
over many years.’’ Id. In addition, the
commenter asserted that the long-term
exposure studies of mortality are central
to the EPA’s basis for proposing to set
a lower annual standard level, since
most of the estimated benefits
associated with a lower annual PM2.5
standard are based on reductions in
mortality related to long-term exposures
to PM2.5.
As an initial matter, the EPA has
recognized the challenge in
distinguishing between PM2.5-associated
effects due to past and recent long-term
exposures, and in identifying the
relevant latency period for long-term
exposure to PM and resultant health
effects (U.S. EPA, 2009a, section 7.6.4;
77 FR 38941/1). While the EPA has
acknowledged that there remain
important uncertainties related to
characterizing the most relevant
exposure periods in long-term exposure
studies, the assertion that there is ‘‘no
knowledge or evidence’’ that helps to
inform this issue is not correct, as
discussed below.
Both in the last review and in the
current review, the EPA has assessed
studies that used different air quality
periods for estimating long-term
exposure and tested associations with
mortality for the different exposure
periods (U.S. EPA, 2004, section 8.2.3.5;
U.S. EPA 2009a, section 7.6.4). In this
review, the Integrated Science
Assessment discussed studies available
since the last review that have assessed
the relationship between long-term
exposure to PM2.5 and mortality to
explore the issue of the latency period
between exposure to PM2.5 and death
(U.S. EPA, 2009a, section 7.6.4).
Notably, in a recent analysis of the
extended Harvard Six Cities Study,
Schwartz et al. (2008) used model
averaging (i.e., multiple models were
averaged and weighted by probability of
accuracy) to assess exposure periods
prospectively (77 FR 38907/1–2). The
exposure periods were estimated across
a range of unconstrained distributed lag
models (i.e., same year, one year prior,
two years prior to death). In comparing
lags, the authors reported that the effects
of changes in exposure to PM2.5 on
mortality were strongest within a 2-year
period prior to death (U.S. EPA, 2009a,
p. 7–92, Figure 7–9). Similarly, a large
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
3148
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
multi-city study of the elderly found
that the mortality risk associated with
long-term exposure to PM10 reported
cumulative effects that extended over
the years that deaths were observed in
the study population (i.e., the follow-up
period) and for the 3-year period prior
to death (Zanobetti et al., 2008).
Further, in a study of two locations
that experienced an abrupt decline in
PM2.5 concentrations (i.e., Utah Steel
¨¨
Strike, coal ban in Ireland), Roosli et al.
(2005) reported that approximately 75
percent of health benefits were observed
in the first 5 years (U.S. EPA, 2009a,
Table 7–9). Schwartz et al. (2008) and
Puett et al. (2008) found, in a
comparison of exposure periods ranging
from 1 month to 48 months prior to
death, that exposure to PM10 24 months
prior to death exhibited the strongest
association, and the weakest association
was reported for exposure in the time
period of 1 month prior to death.
Overall, the EPA notes that the
available evidence for determining the
exposure period that is causally related
to the mortality effects of long-term
PM2.5 exposures, as discussed above,
cannot specifically disentangle the
effects observed in long-term exposure
studies associated with more recent air
quality measurements from effects that
may have been associated with earlier,
and most likely higher, PM2.5 exposures.
While the evidence suggests that a
latency period of up to five years would
account for the majority of deaths, it
does not provide a basis for concluding
that it is solely recent PM2.5
concentrations that account for the
mortality risk observed in such studies.
Nonetheless, the more recent air quality
data does well at explaining the
relationships observed between longterm exposures to PM2.5 and mortality,
with the strongest association observed
in the two years prior to death. Further,
the EPA recognizes that there is no
discernible population-level threshold
below which effects would not occur,
such that it is reasonable to consider
that health effects may occur over the
full range of concentrations observed in
the epidemiological studies, including
the lower concentrations in the latter
years.
In light of this evidence and these
considerations, the EPA concludes that
it is appropriate to consider air quality
concentrations that are generally
contemporaneous with the collection of
health event data (i.e., collected over the
same time period) as being causally
associated with at least some proportion
of the deaths assessed in a long-term
exposure study. This would include
long-term mean PM2.5 concentrations
from most of the key long-term exposure
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
studies of effects with causal or likely
causal evidence shown in Figure 4
above, which reported long-term mean
PM2.5 concentrations ranging from 13.6
mg/m3 to 14.3 mg/m3. These studies
include studies of mortality by Eftim et
al. (2008), which separately analyzed
the ACS and Harvard Six City sites,
Zeger et al. (2008), and Lipfert et al.
(2006a), as well as studies of morbidity
endpoints by Goss et al. (2004),
McConnell et al. (2003) and Gauderman
et al. (2004), and Dockery et al. (1996)
and Razienne et al. (1996). The EPA
acknowledges that uncertainty in the
relevant exposure period is most notable
in two other long-term exposure studies
of mortality. The Miller et al. (2007)
reported a long-term mean PM2.5
concentration for a 1-year exposure
period that post-dated the follow-up
period in which health event data were
collected by two years. Also, the
Krewski et al. (2009) study reported a
long-term mean PM2.5 concentration for
an exposure period that included only
the last two years of the 18-year followup period. Based on these
considerations, the EPA does not now
consider it appropriate to put weight on
the reported long-term mean
concentrations from these two studies
for the purpose of translating the
information from the long-term
mortality studies into a basis for
selecting the level of the annual PM2.5
standard.94
In addition, the EPA acknowledges
that exposure periods that extend at
least a couple years prior to the followup period in which health event data
were collected would likely more fully
capture the PM-related deaths in such
studies. To explore how much higher
the long-term mean PM2.5
concentrations would likely have been
had air quality data prior to the followup years of the studies been included,
the EPA conducted a sensitivity analysis
of long-term mean PM2.5 concentrations
(Schmidt, 2012a) particularly
considering studies that only included
deaths from a relatively recent followup period. As examples of such studies,
this analysis considered the Eftim et al.
(2008) study of mortality in the ACS
sites and the Harvard Six Cities sites, as
well as sites in the eastern region in the
Zeger et al. (2008) study. Using data
from the EPA’s AQS database, the
analysis added the two years of air
quality data just prior to the follow-up
94 Nonetheless, the EPA notes that the Krewski et
al. (2009) and Miller et al. (2007) studies provide
strong evidence of mortality and cardiovascularrelated effects associated with long-term PM2.5
exposures to inform causality determinations
reached in the Integrated Science Assessment (U.S.
EPA, 2009a, sections 7.2.11 and 7.6).
PO 00000
Frm 00064
Fmt 4701
Sfmt 4700
period in each study, which was 2000
to 2002 in Eftim et al. (2008) and 2000
to 2005 in Zeger et al. (2008). The
analysis then calculated the extended
long-term mean PM2.5 concentration for
each study. As discussed in Schmidt
(2012a), in each case the long-term
mean PM2.5 concentration averaged over
the extended exposure period was less
than 0.4 mg/m3 higher than the longterm mean PM2.5 concentration averaged
over the follow-up period. The EPA
finds it reasonable to conclude that such
a relatively small difference in longterm mean PM2.5 concentrations would
likely apply for other long-term
exposure studies that used similarly
recent follow-up periods as well (e.g.,
Goss et al., 2004; Lipfert et al., 2006a).
Based on the above considerations,
the EPA concludes that it is appropriate
to consider the available air quality
information from the long-term
exposure studies, while taking into
account the uncertainties in the relevant
long-term exposure periods in weighing
the information from these studies. The
EPA recognizes that considering such
information in selecting an appropriate
annual standard level has the potential
to build in some margin of safety. The
EPA further concludes that it is
appropriate to consider the air quality
information from the set of long-term
exposure studies discussed above in the
context of the broader array of
epidemiological studies that inform the
EPA’s consideration of the level of the
annual PM2.5 standard.
The EPA also notes that while the
long-term exposure studies are an
important component of the
epidemiological evidence that informs
the Agency’s consideration of the level
of the annual standard, they do not
provide the only relevant information,
nor are they the set of studies for which
the relevant long-term mean PM2.5
concentrations are the lowest. As
discussed in the proposal, the EPA also
considers the long-term mean PM2.5
concentrations from the short-term
mortality and morbidity studies as
providing important information in
considering the level of the annual
standard. As discussed above, a large
proportion of the aggregate risk
associated with short-term exposures
results from the large number of days
during which the 24-hour average
concentrations are in the low- to midrange of the concentrations observed in
the studies. Thus, setting the level of the
annual standard based on long-term
mean concentrations, as well as the
distribution of concentrations below the
mean, in the short-term exposure
studies is the most effective and
efficient way to reduce total PM2.5-
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
related risk from the broad array of
mortality and morbidity effects
associated with short-term exposures.
Further, the EPA notes that the
relevant exposure period for the shortterm exposure studies is the period
contemporaneous with the collection of
health event data, and that this exposure
period is not subject to the uncertainties
discussed above related to the long-term
exposure studies. Recognizing that the
long-term mean PM2.5 concentrations
from several of the multi-city short-term
exposure studies shown in Figure 4 are
below the long-term mean PM2.5
concentrations from the long-term
exposure studies (with the exception of
Miller et al., 2007).95 It is reasonable
that in selecting the level of the annual
standard primary consideration should
be given to the information from this set
of short-term exposure studies. There is
no reasonable basis to discount the longterm mean concentrations of the shortterm exposure studies for purposes of
setting the level of the annual standard.
Thus, the commenter is incorrect in
asserting that the long-term exposure
studies, not the short-term exposure
studies, would be central in the
Administrator’s decision on the level of
the annual standard. The standard is
ultimately intended to protect not just
against the single type of effect that
contributes the most to quantitative
estimates of risk to public health, but
rather to the broad array of effects,
including mortality and morbidity
effects from long- and short-term
exposures across the range of at-risk
populations impacted by PM2.5-related
effects.
(3) With regard to the EPA’s analysis
of distributions of underlying
population-level data (i.e., health event
and study population data) and
corresponding air quality data from each
study area in certain key multi-city
epidemiological studies (Rajan et al.,
2011), some commenters in this group
raised a number of issues related to this
analysis (API, 2012, Attachment 1 pp. 5
to 6; McClellan, 2012, pp.2 to 4). Some
commenters noted the limited number
of studies for which health event and
study population data were available,
and questioned whether these
distributions would apply to other
studies. Commenters expressed
concerns that this analysis had not been
formally reviewed by CASAC and was
not published in the peer-review
literature. Based on such concerns,
95 As
noted above, the EPA is not placing weight
on the reported long-term mean concentrations
from the Miller et al. (2007) study for the purpose
of translating the information from the long-term
mortality studies into a basis for selecting the level
of the annual PM2.5 standard.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
some commenters asserted that the EPA
should not consider this information as
a basis for selecting a standard level.
As an initial matter, as discussed in
section III.E.4.b above, the EPA agrees
with CASAC’s advice that it is
appropriate to consider additional data
beyond the mean PM2.5 concentrations
in key multi-city studies to help inform
selection of the level of the annual PM2.5
standard. As both the EPA and CASAC
recognize, in the absence of a
discernible threshold, health effects may
occur over the full range of
concentrations observed in the
epidemiological studies. Nonetheless,
the EPA recognizes that confidence in
the magnitude and significance of an
association is highest at and around the
long-term mean PM2.5 concentrations
reported in the studies and the degree
of confidence becomes lower at lower
concentrations within any given study.
Following CASAC’s advice (Samet,
2010d, p.2), the EPA used additional
population-level and air quality data
made available by study authors to
conduct an analysis of the distributions
of such data, to help inform
consideration of how the degree of
confidence in the magnitude and
significance of observed associations
varies across the range of long-term
mean PM2.5 concentrations in study
areas within key multi-city
epidemiological studies. In the EPA’s
view, such consideration is important in
selecting a level for an annual standard
that will protect public health with an
adequate margin of safety.
With regard to the number of multicity studies for which an analysis of the
distributions of population-level data
across the study areas and the
corresponding annual mean PM2.5
concentrations was done, the EPA noted
at proposal that data for such an
analysis were made available from study
authors for four studies, including two
long-term exposure studies and two
short-term exposure studies.96 The EPA
recognized that access to health event
data can be restricted due to
confidentiality issues, such that it is not
reasonable to expect that such
information could be made available
from all studies. In considering the
information from these four studies, the
EPA has further taken into
consideration uncertainties discussed in
response to the above comment related
to the appropriate exposure period for
96 Health event data and study population data
were available from two short-term exposure
studies (Bell et al. 2008; Zanobetti and Schwartz,
2009) and one long-term exposure study (Krewski
et al., 2009). Only study population data were
available from another long-term exposure study
(Miller et al., 2007).
PO 00000
Frm 00065
Fmt 4701
Sfmt 4700
3149
long-term exposure studies. Based on
these considerations, as noted above,
the EPA concludes that such
uncertainties are an important factor in
evaluating the usefulness of the air
quality information from the two longterm exposure studies in this analysis
(Krewski et al., 2009; Miller et al., 2007)
and that it would not be appropriate to
place weight on the distributional
analysis of health event and air quality
data from these two studies specifically
for the purpose of translating the
information from the long-term
mortality studies into a basis for
selecting the level of the annual PM2.5
standard. Such uncertainties are not
relevant to the short-term exposure
studies, and thus, the Agency focuses on
the two short-term exposure studies in
this analysis (Bell et al., 2008; Zanobetti
and Schwartz, (2009).
In focusing on these two short-term
exposure studies, the EPA first notes
that these studies are key multi-city
studies that reported positive and
statistically significant associations
between mortality and cardiovascularrelated hospital admissions across a
large number of areas throughout the
U.S. (112 U.S. cities in Zanobetti and
Schwartz, 2009; 202 U.S. counties in
Bell et al., 2008) using relatively recent
air quality and health event data (i.e.,
1999 through 2005 in both studies). The
EPA considers this to be a modest but
important data set to use for this
distributional analysis to help inform
consideration of how much below the
long-term mean PM2.5 concentrations in
key multi-city long- and short-term
exposure studies the annual PM2.5
standard level should be set. While the
EPA acknowledges that having such
data available from more studies would
have been useful, the Agency finds the
information from this limited set of
studies to be an important consideration
in selecting an annual standard level,
consistent with CASAC advice to
consider such information.
In considering the results of this
distributional analysis, as discussed
more fully in the Response to Comments
document, the EPA considers PM2.5
concentrations between the 25th and
10th percentiles of the distribution of
health events to be a reasonable range
for providing a general frame of
reference for that part of the distribution
in which confidence in the magnitude
and significance of the association may
be appreciably lower than confidence at
and around the long-term mean
concentration. For the two short-term
exposure studies included in this
analysis, the EPA notes that the PM2.5
concentrations corresponding to the
25th percentiles of the distributions of
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
3150
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
health events were 12.5 mg/m3 and 11.5
mg/m3, respectively, for Zanobetti and
Schwartz (2009) and for Bell et al.
(2008), with the 10th percentiles being
lower by approximately 2 mg/m3 in each
study (Rajan et al., 2011, Table 1). In
considering this information, the EPA
recognizes, however, that there is no
clear dividing line or single percentile
within a given distribution (including
both above and below the 25th
percentile) provided by the scientific
evidence that is most appropriate or
‘correct’ to use to characterize where the
degree of confidence in the associations
warrants setting the annual standard
level. The decision as to the appropriate
standard level below the long-term
mean concentrations of the key studies
is largely a public health policy
judgment to be made by the
Administrator, taking into account all of
the evidence and its related
uncertainties, as discussed in section
III.E.4.d below.
In response to concerns that this
analysis was not reviewed by CASAC
nor published in the peer-reviewed
literature, the EPA notes that this
analysis was conducted to directly
respond to advice from CASAC, as
discussed in section III.E.4.b.i above, in
conjunction with their review of the
Policy Assessment. The EPA notes that
the same type of distributional analysis
was presented in the second draft Policy
Assessment based on air quality data, as
well as population-weighted air quality
data, rather than health event or study
population data. In considering that
distributional information, CASAC
urged that the EPA redo the analysis
using health event or study population
data, which is exactly what the EPA did
and presented in the final Policy
Assessment. The EPA provided CASAC
with the final Policy Assessment and
communicated how the final staff
conclusions reflected consideration of
its advice and that those staff
conclusions were based in part on the
specific distributional analysis that
CASAC had urged the EPA to conduct
(Wegman, 2011, Attachment p. 2).
CASAC did not choose to provide any
additional comments or advice after
receiving the final Policy Assessment.
The EPA considers this distributional
analysis to be the product of the peer
review conducted by CASAC of the
Policy Assessment, and thus does not
agree with commenters’ characterization
that the analysis lacked appropriate peer
review. The EPA’s final analysis was
based on the comments provided by
CASAC, the peer review committee
established pursuant to the CAA, on the
draft analysis, such that the final
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
analysis stems directly from CASAC’s
advice and the EPA’s response to its
comments.
Based on the above considerations,
the EPA continues to conclude that its
analysis of distributions of health event
and air quality data from two key multicity epidemiological studies provides
important information related to
understanding the associations between
health events observed in each city (e.g.,
deaths, hospitalizations) and the
corresponding long-term mean PM2.5
concentrations observed in the studies.
While recognizing that this is a
relatively modest data set, the EPA
further concludes that such information
can appropriately help to inform the
selection of the level of an annual
standard that will protect public health
with an adequate margin of safety from
these types of health effects which are
causally related to long- and short-term
exposures to PM2.5.
(4) Some commenters in this group
asserted there were limitations in the
long-term exposure studies of
morbidity, including studies evaluating
respiratory effects in children. For
example, one commenter (UARG, 2012,
p. 12, Attachment 1, pp. 14 to 16)
asserted there were serious limitations
in the long-term exposure studies of
respiratory morbidity in each of the
studies considered by the EPA
(including McConnell et al., 2003;
Gauderman et al., 2004; Dockery et al.,
1996; Raizenne et al., 1996; and Goss et
al., 2004) and argued that this evidence
provides only a ‘‘weak association’’ with
PM2.5 exposures. This commenter
asserted that many of these long-term
exposure studies evaluating respiratory
effects were considered at the time the
EPA reaffirmed the current annual
standard level of 15 mg/m3 in 2006, that
the Administrator in the last review
determined that the information they
provided ‘‘was too limited to serve as
the basis for setting a level of a national
standard,’’ and that they should be
given little weight in setting the level of
the annual standard in this review
(UARG, 2012, Attachment 1, p. 14).
More specifically, this commenter
asserted that the McConnell et al. (2003)
and Gauderman et al. (2004) studies
reported mixed results for associations
with PM2.5 and stronger associations
with NO2 (API, 2012, Attachment 1, pp.
14 to 15). Similarly, this commenter
argued that the Dockery et al. (1996) and
Raizenne et al. (1996) studies showed
stronger associations with acidity than
with fine particles (measured as PM2.1).
Id. pp. 15 to 16. With regard to the
cystic fibrosis study, this commenter
noted that the association between
pulmonary exacerbations and PM2.5 in
PO 00000
Frm 00066
Fmt 4701
Sfmt 4700
this study was no longer statistically
significant when the model adjusted for
each individual’s baseline lung
function. The commenters referred to
the data on lung function as an
‘‘important explanatory variable,’’ and
suggested that the EPA should rely on
results from the model that included
individual baseline lung function
information. Id. p. 16. For the reasons
discussed below and in more detail in
the Response to Comments document,
the EPA disagrees with the commenters’
interpretation of these studies.
As an initial matter, the EPA notes
that three of these studies (McConnell et
al., 2003; Dockery et al., 1996; Raizenne
et al., 1996) as well as the initial studies
from the Southern California Children’s
Health Study (Peters et al., 1999;
McConnell et al., 1999; Gauderman et
al., 2000, 2002; Avol et al., 2001) were
discussed and considered in the 2004
Air Quality Criteria Document (U.S.
EPA, 2004) and, thus, considered within
the air quality criteria supporting the
EPA’s final decisions in the review
completed in 2006. Two additional
studies (Gauderman et al., 2004; Goss et
al., 2004) were discussed and
considered in the provisional science
assessment conducted for the last
review (U.S. EPA, 2006a). The EPA
concluded that ‘‘new’’ studies
considered in the provisional
assessment completed in 2006 did not
materially change any of the broad
scientific conclusions regarding the
health effects of PM exposure made in
the Criteria Document (71 FR 61148 to
61149, October 17, 2006). All of these
studies were considered in the
Integrated Science Assessment that
informs the current review (U.S. EPA,
2009a).
With regard to the Southern California
Children’s Health Study, extended
analyses considered in the Integrated
Science Assessment provided evidence
that clinically important deficits in lung
function 97 associated with long-term
exposure to PM2.5 persist into early
adulthood (U.S. EPA, 2009a, p. 7–27;
Gauderman et al., 2004). These effects
remained positive in copollutant
models.98 Additional analyses of the
97 Clinical significance was defined as an FEV
1
below 80 percent of the predicted value, a criterion
commonly used in clinical settings to identify
persons at increased risk for adverse respiratory
conditions (U.S. EPA, 2009a, p. 7–29 to 7–30). The
primary NAAQS for sulfur dioxide (SO2) also
included this interpretation for FEV1 (75 FR 35525,
June 22, 2010).
98 Gauderman et al. (2004) clearly stated
throughout their analysis that NO2 was one
component of a highly correlated mixture that
contains PM2.5. Gauderman et al. (2004) did not
present the results from copollutants models but
stated ‘‘two-pollutant models for any pair of
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
Southern California Children’s Health
Study cohort reported an association
between long-term PM2.5 exposure and
bronchitic symptoms (U.S. EPA, 2009a,
p. 7–23 to 7–24; McConnell et al., 2003,
long-term mean concentration of 13.8
mg/m3) that remained positive in copollutant models, with the PM2.5 effect
estimates increasing in magnitude in
some models and decreasing in others,
and a strong modifying effect of PM2.5
on the association between lung
function and asthma incidence (U.S.
EPA, 2009a, 7–24; Islam et al., 2007).
The outcomes observed in the more
recent reports from the Southern
California Children’s Health Study,
including evaluation of a broader range
of endpoints and longer follow-up
periods, were larger in magnitude and
more precise than reported in the initial
version of the study. Supporting these
results were new longitudinal cohort
studies conducted by other researchers
in varying locations using different
methods (U.S. EPA, 2009a, section
7.3.9.1). The EPA, therefore, disagrees
with the commenters that the studies by
McConnell et al. (2003) and Gauderman
et al. (2004) are flawed and should not
be used in the PM NAAQS review
process.
The 24-City study 99 by Dockery et al.
(1996) (long-term mean concentration of
14.5 mg/m3) was considered in the
current as well as two previous reviews
(U.S. EPA, 2009a; U.S. EPA, 2004; U.S.
EPA, 1996). This study observed that
PM, specifically ‘‘particle strong
acidity’’ and sulfate particles (indicators
of fine particles), were associated with
reports of bronchitis in the previous
year. Similarly, the magnitude of the
associations between bronchitis and
PM10 and PM2.1 were similar to those for
acidic aerosols and sulfate particles,
though the confidence intervals for the
PM10 and PM2.1 associations were
slightly wider and the associations were
not statistically significant. Acid
aerosols, sulfate, and fine particles are
formed in secondary reactions of the
emissions from incomplete combustion
and these pollutants have similar
regional and temporal distributions. As
noted by the study authors, ‘‘the strong
correlations of several pollutants in this
study, especially particle strong acidity
with sulfate (r=0.90) and PM2.1 (r=0.82),
make it difficult to distinguish the agent
pollutants did not provide a significantly better fit
to the data than the corresponding single-pollutant
models.’’
99 The 24-City study conducted by Dockery et al.
(1996) included 18 sites in the U.S. and 6 sites in
Canada. The Raizenne et al. (1996) study
considered 22 of these 24 study areas. Athens, OH
and South Brunswick, NJ were not included in this
study.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
of interest’’ (Dockery et al., 1996, p.
505). Overall, Dockery et al. (1996) (and,
similarly, Raizenne et al., 1996)
observed similar associations between
respiratory health effects and acid
aerosols, sulfate, PM10 and PM2.1
concentrations. The commenters noted
that the associations with particle
acidity were sensitive to the inclusion of
the six Canadian sites. The EPA notes
that none of these Canadian cities were
in the ‘‘sulfate belt’’ where particle
strong acidity was highest. Thus, the
change in the effect estimate when the
six Canadian cities were excluded from
the analysis is likely due to the lower
prevalence of bronchitis and the lower
concentrations of acid aerosols in these
cities, and not due to some difference in
susceptibility to bronchitis between the
U.S. and Canadian populations that is
not due to air pollution, as suggested by
the commenters (UARG, 2012,
Attachment 1, p. 15). In fact, contrary to
the statements made by the commenters,
the authors did not observe any
subgroups that appeared to be markedly
more susceptible to the risk of
bronchitis.
The Goss et al. (2004) study
considered a U.S. cohort of cystic
fibrosis patients and provided evidence
of association between long-term PM2.5
exposures and exacerbations of
respiratory symptoms resulting in
hospital admissions or use of home
intravenous antibiotics (U.S. EPA,
2009a, p. 7–25; long-term mean
concentration of 13.7 mg/m3). The
commenters noted that the association
between pulmonary exacerbations and
PM2.5 in this study was no longer
statistically significant when the model
adjusted for each individual’s baseline
lung function. The commenters referred
to the data on lung function as an
‘‘important explanatory variable,’’ and
suggested that the EPA should rely on
results from the model that included
individual baseline lung function
information. The EPA disagrees with the
commenters’ interpretation of this
study. The Agency concludes it is
unlikely that lung function is a potential
confounder or an important explanatory
variable in this study. In fact, the
authors noted that ‘‘it is more likely that
lung function decline may be intimately
associated with chronic exposure to air
pollutants and may be part of the causal
pathway in worsening prognosis in CF
[cystic fibrosis]; in support of this
explanation, we found both crosssectional and longitudinal strong
inverse relationships between FEV1 and
PM levels’’ (Goss et al., 2004, p. 819).
The EPA notes that adjusting for a
variable that is on the causal pathway
PO 00000
Frm 00067
Fmt 4701
Sfmt 4700
3151
can lead to overadjustment bias, which
is likely to attenuate the association
(Schisterman et al. 2009); this is likely
what was observed by the authors.
Thus, the EPA continues to believe it is
appropriate to focus on the results
reported in Goss et al. (2004) that did
not include individual baseline lung
function in the model.
In addition, the EPA disagrees with
commenters’ reliance solely on
statistical significance when
interpreting the study results from
individual study results and the
collective evidence across studies. As
discussed in section III.D.2 above,
statistical significance of individual
study findings has played an important
role in the EPA’s evaluation of the
study’s results and the EPA has placed
greater emphasis on studies reporting
statistically significant results. However,
in the broader evaluation of the
evidence from many epidemiological
studies, and subsequently during the
process of forming causality
determinations in the Integrated Science
Assessment by integrating evidence
from across epidemiological, controlled
human exposure, and toxicological
studies, the EPA has emphasized the
pattern of results across epidemiological
studies and whether the effects observed
were coherent across the scientific
disciplines for drawing conclusions on
the relationship between PM2.5 and
different health outcomes.
As noted in section III.B.1.a of the
proposal, with regard to respiratory
effects, the Integrated Science
Assessment concluded that extended
analyses of studies available in the last
review as well as new epidemiological
studies conducted in the U.S. and
abroad provided stronger evidence of
respiratory-related morbidity associated
with long-term PM2.5 exposure (77 FR
38918). The strongest evidence for
respiratory-related effects available in
this review was from epidemiological
studies that evaluated decrements in
lung function growth in children and
increased respiratory symptoms and
disease incidence in adults (U.S. EPA,
2009a, sections 2.3.1.2, 7.3.1.1, and
7.3.2.1).
In considering the collective evidence
from epidemiological, toxicological, and
controlled human exposure studies,
including the studies discussed above,
the EPA recognizes that the Integrated
Science Assessment concluded that a
causal relationship is likely to exist
between long-term PM2.5 exposures and
respiratory effects (U.S. EPA, 2009a, p.
2–12, pp. 7–42 to 7–43). CASAC
concurred with this causality
determination (Samet, 2009f, p.9).
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
3152
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
The commenter’s assertion that the
EPA should adhere to its assessment of
these studies as it did in the review
completed in 2006 is significantly
mistaken. Most obviously, the EPA’s
final decision in the last review was
held to be deficient by the DC Circuit in
remanding the 2006 primary annual
PM2.5 standard. As discussed in section
III.A.2 above, the DC Circuit specifically
held that the EPA did not provide a
reasonable explanation of why certain
morbidity studies, including an earlier
study from the Southern California
Children’s Health Study (Gauderman et
al., 2000, long-term mean PM2.5
concentration approximately 15 mg/m3)
and the 24-Cities Study (Raizenne et al.,
1996, long-term mean concentrations
approximately 14.5 mg/m3) did not
warrant a more stringent annual PM2.5
standard when the long-term mean
PM2.5 concentrations reported in those
studies were at or lower than the level
of the annual standard. American Farm
Bureau Federation v. EPA. 559 F. 3d at
525. Indeed, the court found that,
viewed together, the Gauderman et al.
(2000) and Raizenne et al., (1996)
studies ‘‘are related and together
indicate a significant public health risk
* * * On this record, therefore, it
appears the EPA too hastily discounted
the Gauderman and 24-Cities studies as
lacking in significance.’’ Id.
In this review, the EPA recognizes a
significant amount of evidence beyond
these two studies that expands our
understanding of respiratory effects
associated with long-term PM2.5
exposures. This body of scientific
evidence includes an extended and new
analyses from the Southern California
Children’s Health Study (Gauderman et
al., 2004; Islam et al., 2007; Stanojevic
et al., 2008) as well as additional studies
that examined these health effects (Kim
et al., 2004; Goss et al., 2004). Thus,
even more so than in the last review, the
evidence indicates a ‘‘significant public
health risk’’ to children from long-term
PM2.5 exposures at concentrations below
the level of the current annual standard.
A standard that does not reflect
appropriate consideration of this
evidence would not be requisite to
protect public health with an adequate
margin of safety.
(5) With regard to the use of studies
of health effects for which the EPA finds
the evidence to be ‘‘suggestive’’ of a
causal relationship, some commenters
argued that such studies ‘‘do not merit
any weight in the setting of the annual
NAAQS’’ (e.g., UARG, 2012, Appendix
1, p. 3).
The EPA disagrees with the
commenter’s view that studies of health
effects for which the evidence is
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
suggestive of a causal relationship,
rather than studies of health effects for
which the evidence supports a causal or
likely causal relationship, merit no
weight at all in setting the NAAQS. To
place no weight at all on such evidence
would in essence treat such evidence as
though it had been categorized as ‘‘not
likely to be a causal relationship.’’ To do
so would ignore the important
distinctions in the nature of the
evidence supporting these different
causality determinations in the
Integrated Science Assessment. It would
also ignore the CAA requirement that
primary standards are to be set to
provide protection with an adequate
margin of safety, including providing
protection for at-risk populations. Thus,
ignoring this information in making
decisions on the appropriate standard
level would not be appropriate.100
Nonetheless, in considering studies of
health effects for which the evidence is
suggestive of a causal relationship, the
EPA does believe that it is appropriate
to place less weight on such studies
than on studies of health effects for
which there is evidence of a causal or
likely causal relationship.
A second group of commenters
supported revising the suite of primary
PM2.5 standards to provide increased
public health protection. These
commenters found the available
scientific information and technical
analyses to be stronger and more
compelling than in the last review.
These commenters generally placed
substantial weight on CASAC advice
and on the EPA staff analyses presented
in the final Policy Assessment, which
concluded that the evidence most
strongly supported an annual standard
level within a range of 11 to 12 mg/m3
(U.S. EPA, 2011a, p. 2–206). While some
of these commenters felt that the level
should be set within the proposed range
(12 to 13 mg/m3), most of these
commenters advocated a level of 11 mg/
m3.101 For example, ALA et al.,
asserted:
The EPA’s proposed PM2.5 standards,
while a step in the right direction are
insufficient to protect public health,
including the health of susceptible
100 As discussed in section II.A above, the
requirement that primary standards provide an
adequate margin of safety was intended to address
uncertainties associated with inconclusive
scientific and technical information available at the
time of standard setting. I was also intended to
provide a reasonable degree of protection against
hazards that research has not yet identified. This
certainly encompasses consideration of effects for
which there is evidence suggestive of a causal
relationship.
101 As discussed in section III.E.4.c.ii, many of
these commenters also supported lowering the level
of the primary 24-hour PM2.5 standard.
PO 00000
Frm 00068
Fmt 4701
Sfmt 4700
populations, with an adequate margin of
safety as required by the Clean Air Act
* * *we will discuss the enormous gap in
public health protection afforded by an
annual standard of 13 mg/m3, at the upper
end of the proposed range, compared to the
more protective 11 mg/m3, as advocated by
our organizations (ALA et al., 2012, p. 6).
In general, these commenters
expressed the view that given the
strength of the available scientific
evidence, the serious nature of the
health effects associated with PM2.5
exposures, the large size of the at-risk
populations, the risks associated with
long- and short-term PM2.5 exposures,
and the important uncertainties
inherently present in the evidence, the
EPA should follow a highly
precautionary policy response by
selecting an annual standard level that
incorporates a large margin of safety.
More specifically, these commenters
offered a range of comments related to
the general approach used by the EPA
to select standard levels, including: (1)
The EPA’s approach for setting a
generally controlling annual standard;
(2) the importance of the greatly
expanded and stronger overall scientific
data base; (3) consideration of the
distributional statistical analysis
conducted by the EPA and other
approaches for translating the air quality
information from specific
epidemiological studies into standard
levels; and (4) the significance of the
PM2.5-related public health impacts,
especially potential impacts on at-risk
populations, including children, in
reaching judgments on setting standards
that provide protection with an
adequate margin of safety. These
comments are discussed in turn below.
(1) Some of these commenters
disagreed with the EPA’s approach for
setting a ‘‘generally controlling’’ annual
standard in conjunction with a 24-hour
standard providing supplemental
protection particularly for areas with
high peak-to-mean ratios. These
commenters argued this approach
would lead to ‘‘regional inequities’’ as
demonstrated in the EPA’s analyses
contained in Appendix C of the Policy
Assessment (ALA et al., pp. 26 to 27).
Specifically, these commenters argued:
There is no basis in the Clean Air Act for
such a determination. The Clean Air Act
requires only that the NAAQS achieve public
health protection with an adequate margin of
safety. It is well-documented that both longand short-term exposures to PM2.5 have
serious and sometimes irreversible health
impacts. There is no health protection reason
to argue that one standard should be
‘‘controlling’’ as a matter of policy without
regard to the health consequences of such a
policy. To adopt such a policy ignores the
obligation to provide equal protection under
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
the law to all Americans because it would
result in uneven protection from air pollution
in different localities and regions of the
country (ALA et al., 2012, p. 26).
The EPA believes these commenters
misunderstood the basis for the EPA’s
policy goal of setting a ‘‘generally
controlling’’ annual standard. This
approach relates exclusively to setting
standards that will provide requisite
protection against effects associated
with both long- and short-term PM2.5
exposures. It does so by lowering the
overall air quality distributions across
an area, recognizing that changes in
PM2.5 air quality designed to meet an
annual standard would likely result not
only in lower annual mean PM2.5
concentrations but also in fewer and
lower peak 24-hour PM2.5
concentrations. As discussed in section
III.A.3 in the proposal and above, the
EPA recognizes that there are various
ways to combine the two primary PM2.5
standards to achieve an appropriate
degree of public health protection.
Furthermore, the extent to which these
two standards are interrelated in any
given area depends in large part on the
relative levels of the standards, the
peak-to-mean ratios that characterize air
quality patterns in an area, and whether
changes in air quality designed to meet
a given suite of standards are likely to
be of a more regional or more localized
nature.
In focusing on an approach of setting
a generally controlling annual standard,
the EPA’s intent is in fact to avoid the
potential ‘‘regional inequities’’ that are
of concern to the commenters. The EPA
judges that the most appropriate way to
set standards that provide more
consistent public health protection is by
using the approach of setting a generally
controlling annual standard. This
judgment builds upon information
presented in the Policy Assessment as
discussed in section III.A.3 above. More
specifically, the Policy Assessment
recognized that the short-term exposure
studies primarily evaluated daily
variations in health effects with
monitor(s) that measured the variation
in daily PM2.5 concentrations over the
course of several years. The strength of
the associations observed in these
epidemiological studies was
demonstrably in the numerous ‘‘typical’’
days within the air quality distribution,
not in the peak days (U.S. EPA, 2011a,
p. 2–9). In addition, the quantitative risk
assessments conducted for this and
previous reviews demonstrated the
same point, that is, much, if not most,
of the aggregate risk associated with
short-term PM2.5 exposures results from
the large number of days during which
the 24-hour average concentrations are
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
in the low-to mid-range, below the peak
24-hour concentrations (U.S. EPA,
2011a, section 2.2.2; U.S. EPA, 2010a,
section 3.1.2.2). In addition, there was
no evidence suggesting that risks
associated with long-term exposures
were likely to be disproportionately
driven by peak 24-hour
concentrations.102
For these reasons, the Policy
Assessment concluded that strategies
that focused primarily on reducing peak
days were less likely to achieve
reductions in the PM2.5 concentrations
that were most strongly associated with
the observed health effects.
Furthermore, the Policy Assessment
concluded that an approach that
focused on reducing peak exposures
would most likely result in more
uneven public health protection across
the U.S. by either providing inadequate
protection in some areas or
overprotecting in other areas (U.S. EPA,
2011a, p. 2–9; U.S. EPA, 2010a, section
5.2.3). This is because reductions based
on control of peak days are less likely
to control the bulk of the air quality
distribution.
As a result, the EPA believes an
approach that focuses on a generally
controlling annual standard would
likely reduce aggregate risks associated
with both long- and short-term
exposures more consistently than a
generally controlling 24-hour standard
and, therefore, would be the most
effective and efficient way to reduce
total PM2.5-related population risk. The
CASAC agreed with this approach and
considered it was ‘‘appropriate to return
to the strategy used in 1997 that
considers the annual and the short-term
standards together, with the annual
standard as the controlling standard,
and the short-term standard
supplementing the protection afforded
by the annual standard’’ (Samet, 2010d,
p. 1). For the reasons discussed above,
the EPA disagrees with the comments
that this approach will result in the
concerns raised by the commenters;
rather the EPA concludes that this
approach will help to address these
concerns.
(2) Many of these commenters
asserted that the currently available
scientific information is greatly
expanded and stronger compared to the
last review. Some of these commenters
highlighted the availability of multiple,
multi-city long- and short-term exposure
102 In confirmation, a number of studies have
presented analyses excluding higher PM
concentration days and reported a limited effect on
the magnitude of the effect estimates or statistical
significance of the association (e.g., Dominici,
2006b; Schwartz et al., 1996; Pope and Dockery,
1992).
PO 00000
Frm 00069
Fmt 4701
Sfmt 4700
3153
studies providing ‘‘repeated, consistent
evidence of effects below the current
annual standard level’’ (ALA et al.,
2012, pp. 39 to 49) and, more
specifically, ‘‘significant evidence of
harm with strong confidence well below
EPA’s proposed annual standard range
of 12–13 mg/m3’’ (AHA et al., 2012, pp.
10 to 12).
The EPA recognizes that in setting
standards that are requisite to protect
public health with an adequate margin
of safety, the Administrator must weigh
the various types of available scientific
information in reaching public health
policy judgments that neither overstate
nor understate the strength and
limitations of this information or the
appropriate inferences to be drawn from
the available science.
In general, the EPA agrees with these
commenters’ views that the currently
available scientific evidence is stronger
‘‘because of its breadth and the
substantiation of previously observed
health effects’’ (77 FR 38906/2) and
provides ‘‘greater confidence in the
reported associations than in the last
review’’ (77 FR 38940/1). The EPA also
agrees with the commenters’ position
that it is appropriate to consider the
regions within the broader air quality
distributions where we have the
strongest confidence in the associations
reported in epidemiological studies in
setting the level of the annual standard.
However, as discussed in section
III.E.4.d below, in weighing the
available evidence and technical
analyses, as well as the associated
uncertainties and limitations in that
information, the EPA disagrees with the
commenters’ views regarding the extent
to which the available scientific
information provides support for
considering an annual standard level
below the proposed range (i.e., below 12
to 13 mg/m3). In particular, the EPA
disagrees with the degree to which these
commenters place more weight on the
relatively more uncertain evidence that
is suggestive of a causal relationship
(e.g., low birth weight). Consistent with
CASAC advice (Samet, 2010d, p. 1), the
Agency concludes it is appropriate and
reasonable to place the greatest
emphasis on health effects for which the
Integrated Science Assessment
concluded there is evidence of a causal
or likely causal relationship and to
place less weight on the health effects
that provide evidence that is only
suggestive of a causal relationship.
(3) With regard to using the air quality
information from epidemiological
studies to inform decisions on standard
levels, commenters in this group
generally supported the EPA’s efforts to
explore different statistical metrics from
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
3154
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
epidemiological studies to inform the
Administrator’s decisions. These
commenters argued that by considering
different analytic measures—either
concentrations one standard deviation
below the long-term means reported in
the epidemiological studies or the EPA’s
distributional statistical analysis of
population-level data that extends the
approach used in previous PM NAAQS
reviews to consider information beyond
a single statistical metric—‘‘the annual
standard must be significantly lower
than EPA has proposed’’ (ALA et al.,
2012, pp. 50 to 61). Furthermore, with
regard to characterizing the PM2.5 air
quality at which associations have been
observed, some of these commenters
highlighted CASAC’s recommendation
that ‘‘[f]urther consideration should be
given to using the 10th percentile as a
level for assessing various scenarios of
levels for the PM NAAQS’’ (Samet,
2010c, p. 11) (ALA et al., 2012, p. 55).
Other commenters urged that the EPA
extend the distributional analysis to
include additional studies. For example,
CHPAC urged the EPA to also conduct
distributional analysis for children’s
health studies to better inform standards
that would protect both children and
adults from adverse health outcomes
(CHPAC, 2012, p. 3).
The EPA agrees with these
commenters’ views that it is appropriate
to take into account different statistical
metrics from epidemiological studies to
inform the decisions on standard levels
that are appropriate to consider in
setting a standard that will protect
public health with an adequate margin
of safety. In the development of the
Policy Assessment, the EPA staff
explored various approaches for using
information from epidemiological
studies in setting the standards. The
general approach used in the final
Policy Assessment, discussed in
sections III.A.3 and III.E.4.a above,
reflects consideration of CASAC advice
(Samet, 2010c, d) and public comments
on multiple drafts of the Policy
Assessment.
With regard to using the distributional
statistical analysis to characterize the
confidence in the associations, the EPA
emphasizes that there is no clear
dividing line provided by the scientific
evidence, and that choosing how far
below the long-term mean
concentrations from the epidemiological
studies is appropriate to identify a
standard level that will provide
protection for the public health with an
adequate margin of safety is largely a
public health policy judgment. The EPA
considers the region from approximately
the 25th to 10th percentiles to be a
reasonable range for providing a general
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
frame of reference as to the part of the
distribution over which our confidence
in the magnitude and significance of the
associations observed in
epidemiological studies is appreciably
lower. Based on these considerations,
the EPA concludes that it is not
appropriate to place as much confidence
in the magnitude and significance of the
associations over the lower percentiles
of the distributions in each study as at
and around the long-term mean
concentrations. Thus, the EPA disagrees
with the commenters’ views that this
analysis compels placing more
emphasis on the lower part of this range
in selecting a level for an annual
standard that will protect public health
with an adequate margin of safety. The
EPA recognizes that this information
comes primarily from two short-term
exposure studies, a relatively modest
data set. In light of the limited nature of
this information, and in recognition of
more general uncertainties inherent in
the epidemiological evidence, the
Administrator deems it reasonable not
to place more emphasis on
concentrations in the lower part of this
range, as discussed below in section
III.E.4.d.
With regard to the scope of the
distributional statistical analysis, the
EPA requested additional populationlevel data from the study authors for a
group of six multi-city studies for which
previous air quality analyses had been
conducted (Hassett-Sipple et al., 2010;
Schmidt et al., 2010, Analysis 2). These
six studies were originally selected
because they considered multiple
locations representing varying
geographic regions across multiple
years. Thus, these studies provided
evidence on the influence of different
particle mixtures on health effects
associated with long- and short-term
PM2.5 exposures. In addition, these
multi-city studies considered relatively
more recent health events and air
quality conditions (1999 to 2005). As
discussed in section III.E.4.b.i above, the
EPA received and analyzed populationlevel data for four of the six studies
(Rajan et al., 2011). Three of these four
studies (Krewski et al., 2009; Bell et al.,
2008; Zanobetti and Schwartz, 2009)
served as the basis for the
concentration-response functions used
to develop the core risk estimates (U.S.
EPA, 2010a, section 3.3.3). While, the
EPA agrees that it would be useful to
have such data from more studies, the
Agency believes that the additional data
that was requested and received from
study authors provide useful
information to help inform the
PO 00000
Frm 00070
Fmt 4701
Sfmt 4700
Administrator’s selection of the annual
standard level.
(4) Many commenters in this group
highlighted PM2.5-related impacts on atrisk populations, including potential
impacts on children, older adults,
persons with pre-existing heart and lung
disease, and low-income populations, to
support their views that the annual
standard should be revised to a level of
11 mg/m3 or lower (CHPAC, 2012; AHA
et al., 2012; ALA, 2012, pp. 29 to 38;
Rom et al., 2012; Air Alliance Houston,
et al., 2012). These commenters urged
the EPA to adopt a policy approach that
placed less weight on the remaining
uncertainties and limitations in the
evidence and placed more emphasis on
margin of safety considerations,
including providing protection against
effects for which there is more limited
scientific evidence. For example,
CHPAC urged the EPA ‘‘to place the
same weight on studies examining
impacts on children’s health as that of
adult studies. * * * The fact that there
may be stronger evidence from adult
studies does not mean that standards
based on adult studies will be protective
for children and consequently will meet
the standard requisite to protect public
health with an adequate margin of
safety’’ (CHPAC, 2012 p. 3).
Furthermore, with regard to the EPA’s
approach for weighing uncertainties,
some of these commenters stated that
‘‘we find no justification in the
preamble for an annual standard level as
high as 13 mg/m3, other than the vague
assertion that uncertainties increase at
lower concentrations. Further, the final
proposal completely failed to address
the Policy Assessment
recommendations that if 13 mg/m3 was
proposed, the 24-hour standard should
be strengthened as well’’ (ALA et al., p.
7).
The EPA has carefully evaluated and
considered evidence of effects in at-risk
populations. With regard to effects
classified as having evidence of a causal
or likely causal relationship with longor short-term PM2.5 exposures (i.e.,
premature mortality, cardiovascular
effects, and respiratory effects), the
Agency takes note that it considered the
full range of studies evaluating these
effects, including studies of at-risk
populations, to inform its review of the
primary PM2.5 standards. Specific multicity studies summarized in Figures 1, 2,
and 3 above highlight evidence of
effects observed in two different
lifestages—children and older adults—
that have been identified as at-risk
populations. Thus, the EPA places as
much weight on studies that explored
effects in children for which the
evidence is causal or likely causal in
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
nature as on studies of such effects in
adults, including older adults. As
discussed above in responses to
commenters supporting the retention of
the current standards, in setting the
standard, the EPA has focused on
considering PM2.5 concentrations
somewhat below the lowest long-term
mean concentrations from each of the
key studies of both long- and short-term
exposures of effects for which the
evidence supports a causal or likely
causal relationship (i.e., the first two
sets of studies shown in Figure 4).
Absent some reason to ignore or
discount these studies, which the
commenter does not provide (and of
which the EPA is unaware), the EPA
considers the available evidence of
effects in children as well as other atrisk populations.
With respect to the EPA’s
consideration of more limited studies
providing evidence suggestive of a
causal relationship (e.g., developmental
and reproductive effects), as noted
above in responding to comments from
the first group of commenters, the
Agency agrees that it is important to
place some weight on this body of
evidence in setting standards that
provide protection for at-risk
populations, as required by the CAA.
However, the Agency does not agree
that the same weight must be placed on
this information as on the body of
scientific information for which there is
evidence of a causal or likely causal
relationship. To do so would ignore the
difference in the breadth and strength of
the evidence supporting the different
causality determinations reached in the
Integrated Science Assessment.
With regard to weighing the
uncertainties and limitations remaining
in the evidence and technical analyses,
as discussed in section II.A above, the
EPA recognizes that in setting a primary
NAAQS that provides an adequate
margin of safety, the Administrator must
consider a number of factors including
the nature and severity of the health
effects involved, the size of sensitive
population(s) at risk, and the kind and
degree of the uncertainties that remain.
As discussed in section III.E.4.d below,
the Agency agrees with these
commenters that, in weighing the
available evidence and technical
analyses including the uncertainties and
limitations in this scientific
information, there is no justification for
setting a primary PM2.5 annual standard
level as high as 13 mg/m3.
Finally, some commenters in both
groups also identified ‘‘new’’ studies
that were not included in the Integrated
Science Assessment as providing further
support for their views on the level of
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
the annual standard. As discussed in
section II.B.3 above, the EPA completed
a provisional review and assessment of
‘‘new’’ studies published since the close
of the Integrated Science Assessment,
including ‘‘new’’ studies submitted by
commenters (U.S. EPA, 2012b). The
provisional assessment found that the
‘‘new’’ studies expand the scientific
information considered in the Integrated
Science Assessment and provide
important insights on the relationship
between PM2.5 exposure and health
effects of PM (U.S. EPA, 2012b).
However, the EPA notes that the
provisional assessment found that the
‘‘new’’ science did not materially
change the conclusions reached in the
Integrated Science Assessment. The
EPA notes that, as in past NAAQS
reviews, the Agency is basing the final
decisions in this review on the studies
and related information included in the
Integrated Science Assessment that have
undergone CASAC and public review,
and will consider newly published
studies for purposes of decision making
in the next PM NAAQS review.
ii. 24-Hour Standard Level
With respect to the level of the 24hour standard, the EPA received
comments on the proposal from two
distinct groups of commenters. One
group that included virtually all
commenters representing industry
associations, businesses, and many
States agreed with the Agency’s
proposed decision to retain the level of
the 24-hour PM2.5 standard. The other
group of commenters included many
medical groups, numerous physicians
and academic researchers, many public
health organizations, some State and
local agencies, five State Attorneys
General, and a large number of
individual commenters. These
commenters disagreed with the
Agency’s proposed decision and argued
that EPA should lower the level of the
24-hour standard to 30 or 25 mg/m3.
Comments from these groups on the
level of the 24-hour PM2.5 standard are
addressed below and in the Response to
Comments Document.
As noted above, of the public
commenters who addressed the level of
the 24-hour PM2.5 standard, all industry
commenters and most State and local
commenters supported the proposed
decision to retain the current level of 35
mg/m3. In many cases, these groups
agreed with the rationale supporting the
Administrator’s proposed decision to
retain the current 24-hour PM2.5
standard, including her emphasis on the
annual standard as the generally
controlling standard with the 24-hour
standard providing supplementary
PO 00000
Frm 00071
Fmt 4701
Sfmt 4700
3155
protection, and her conclusion that
multi-city, short-term exposure studies
provide the strongest data set for
informing decisions on the appropriate
24-hour standard level. Many of these
commenters agreed with the
Administrator’s view that the singlecity, short-term studies provided a
much more limited data set (e.g., limited
statistical power, limited exposure data)
and more equivocal results (e.g., mixed
results within the same study area),
making them an unsuitable basis for
setting the level of the 24-hour standard.
While these commenters agreed with
the EPA’s proposed decision to retain
the current 24-hour PM2.5 standard,
some did not agree with the EPA’s
approach to considering the evidence
from short-term multi-city studies. For
example, a commenter representing
UARG pointed out that the 98th
percentile concentrations reported in
the proposal for multi-city studies
reflect the averages of 98th percentile
concentrations across the cities
included in those studies (UARG, 2012;
Attachment 1; p. 25). This commenter
contended that such averaged 98th
percentile PM2.5 concentrations do not
provide information that can
appropriately inform a decision on the
adequacy of the public health protection
provided by the current or alternative
24-hour standards.
While the EPA agrees that there is
uncertainty in linking effects reported in
multi-city studies to specific air quality
concentrations (U.S. EPA, 2011a,
section 2.3.4.1), the EPA disagrees with
this commenter’s view that such
uncertainty precludes the use of
averaged 98th percentile PM2.5
concentrations to inform a decision on
the appropriateness of the protection
provided by the 24-hour PM2.5 standard.
In particular, the EPA notes that
averaged 98th percentile concentrations
do provide information on the extent to
which study cities contributing to
reported associations would likely have
met or violated the current 24-hour
PM2.5 standard during the study period.
As evidence of this, the EPA notes the
three multi-city studies specifically
highlighted by this commenter as
having averaged 98th percentile 24-hour
PM2.5 concentrations below 35 mg/m3
(Dominici et al., 2006a; Bell et al., 2008;
Zanobetti and Schwartz, 2009). Based
on the 98th percentiles of 24-hour PM2.5
concentrations in the individual cities
evaluated in these studies, the EPA
notes that the majority of these study
cities would likely have met the current
standard during the study periods
(Hassett-Sipple et al., 2010). Therefore,
regardless of whether the averaged 98th
percentile concentrations or the 98th
E:\FR\FM\15JAR2.SGM
15JAR2
3156
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
percentile concentrations in each city
are considered, these studies provide
evidence for associations between shortterm PM2.5 and mortality or morbidity
across a large number of U.S. cities, the
majority of which would likely have
met the current 24-hour PM2.5 standard
during study periods. In their review of
the PM Policy Assessment, CASAC
endorsed the conclusions drawn from
analyses of averaged 98th percentile 24hour PM2.5 concentrations, and the EPA
continues to conclude that this type of
information can appropriately inform
the Administrator’s decision on the
current 24-hour PM2.5 standard.103
Another group of commenters argued
that the 24-hour standard level should
be lowered. Many of these commenters
supported setting the level of the 24hour PM2.5 standard at either 25 or 30
mg/m3. In support of their position, the
ALA et. al., AHA et al., five state
Attorneys General, and a number of
additional groups pointed to 98th
percentile PM2.5 concentrations in
locations of multi-city and single-city
epidemiological studies. For example,
the ALA and others pointed to multicity studies by Dominici et al. (2006a),
Zanobetti and Schwartz (2009), Burnett
et al. (2000), and Bell et al. (2008) as
providing evidence for associations with
mortality and morbidity in study
locations with averaged (i.e., averaged
across cities) 98th percentile 24-hour
PM2.5 concentrations below 35 mg/m3.
These commenters also pointed to
several single-city and panel studies
reporting associations between shortterm PM2.5 and mortality or morbidity in
locations with relatively low 24-hour
PM2.5 concentrations. Because some of
these multi- and single-city studies have
reported associations with health effects
in locations with 98th percentile PM2.5
concentrations below 35 mg/m3,
commenters maintained that the current
24-hour PM2.5 standard (i.e., with its
level of 35 mg/m3) does not provide an
appropriate degree of protection in all
areas.
In further support of their position
that the level of the current 24-hour
standard should be lowered, these
commenters pointed out the variability
across the U.S. in ratios of 24-hour to
103 This is not to say that the EPA’s decision on
whether to revise the 24-hour PM2.5 standard
should be based on or only be informed by
considerations of whether studies reported
associations with mortality or morbidity in areas
with averaged 98th percentile PM2.5 concentrations
less than 35 mg/m3. As discussed below, in
reaching a decision in this final notice on the most
appropriate approach to strengthen the suite of
PM2.5 standards, the Administrator considers the
degree of public health protection provided by the
combination of the annual and 24-hour standards
together.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
annual PM2.5 concentrations. They
standard with its level of 12 mg/m3,
noted that some locations, including
additional protection would be
parts of the northwestern U.S.,
anticipated against the effects reported
experience relatively low annual PM2.5
in these short-term, multi-city studies.
concentrations but can experience
Put another way, to attain an annual
relatively high 24-hour concentrations
standard with a level below the longterm means in the locations of these
at certain times of the year. In order to
short-term studies (as EPA is adopting
provide protection against effects
associated with short-term PM2.5
here), the overall air quality
exposures, especially in locations with
distributions in the majority of study
high ratios of 24-hour to annual PM2.5
cities will necessarily be reduced,
concentrations, these commenters
resulting in lower daily PM2.5 ambient
advocated setting a lower level for the
concentrations. We therefore expect that
24-hour standard.
the revised annual standard will result
The EPA agrees with these
in 98th percentile PM2.5 concentrations
commenters that it is appropriate to
in these cities that are lower than those
maintain a 24-hour PM2.5 standard in
measured in the studies, and that the
order to supplement the protection
overall distributions of PM2.5
provided by the revised annual
concentrations will be lower than those
standard, particularly in locations with
reported to be associated with health
relatively high ratios of 24-hour to
effects. Thus, even for effects reported
annual PM2.5 concentrations. However,
in multi-city studies with averaged 98th
in highlighting 98th percentile PM2.5
percentile concentrations below 35 mg/
concentrations in study locations
m3, additional protection from the risks
without also considering the impact of
associated with short-term exposures is
a revised annual standard on short-term anticipated from the revised annual
concentrations, these commenters
standard, without revising the 24-hour
ignore the fact that many areas would be standard, because long-term average
expected to experience decreasing short- PM2.5 concentrations in multi-city study
and long-term PM2.5 concentrations in
locations were above the level of the
response to a revised annual standard.
revised annual standard (i.e., 12 mg/
In considering the specific multi-city
m3).105 As discussed above, reducing
studies highlighted by public
the annual standard is the most efficient
commenters who advocated a more
way to reduce the risks from short-term
stringent 24-hour standard, the EPA
exposures identified in these studies, as
notes that such studies have reported
the bulk of the risk comes from the large
consistently positive and statistically
number of days across the bulk of the
significant associations with short-term
air quality distribution, not the
PM2.5 exposures in locations with
relatively small number of days with
averaged 98th percentile PM2.5
peak concentrations.
concentrations ranging from 45.8 to 34.2
In considering the single-city studies
mg/m3 and long-term mean PM2.5
highlighted by public commenters who
concentrations ranging from 13.4 to 12.9 advocated a more stringent 24-hour
(Burnett and Goldberg, 2003; Burnett et
standard, the EPA first notes that,
al., 2004; Dominici et al., 2006a; Bell et
overall, these single-city studies
al., 2008; Franklin et al., 2008; Zanobetti reported mixed results. Specifically,
104 The EPA notes
and Schwartz, 2009).
some studies reported positive and
that to the extent air quality
statistically significant associations with
distributions are reduced to meet the
PM2.5, some studies reported positive
current 24-hour standard with its level
but non-significant associations, and
3 and/or the revised annual
of 35 mg/m
several studies reported negative
associations or a mix of positive and
104 Commenters also highlighted associations
negative associations with PM2.5. In
with short-term PM2.5 concentrations reported in
light of these inconsistent results, the
sub-analyses restricted to days with 24-hour
concentrations at or below 35 mg/m3 (Dominici,
proposal noted that the overall body of
2006b). These sub-analyses were not included in
evidence from single-city studies is
the original publication by Dominici et al. (2006a).
mixed, particularly in locations with
Authors provided results of sub-analyses for the
Administrator’s consideration in a letter to the
98th percentiles of 24-hour
docket following publication of the proposed rule
concentrations below 35 mg/m3.
in January 2006 (personal communication with Dr.
Therefore, although some single-city
Francesca Dominici, 2006b). As noted in section
III.A.3, these sub-analyses are part of the basis for
the conclusion that there is no evidence suggesting
that risks associated with long-term exposures are
likely to be disproportionately driven by peak 24hour concentrations. Because the sub-analyses did
not present long-term average PM2.5 concentrations,
it is not clear whether they reflected PM2.5 air
quality that would have been allowed by the
revised annual PM2.5 standard being established in
this rule.
PO 00000
Frm 00072
Fmt 4701
Sfmt 4700
105 It is also the case that additional protection is
anticipated in locations with 98th percentile 24hour PM2.5 concentrations above 35 mg/m3, even if
long-term concentrations are below 12 mg/m3. As
noted in the proposal and in the Policy Assessment
(U.S. EPA, 2011a, Figure 2–10), parts of the
northwestern U.S. are more likely than other parts
of the country to violate the 24-hour standard and
meet the revised annual standard.
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
studies reported effects at appreciably
lower PM2.5 concentrations than shortterm multi-city studies, the
uncertainties and limitations associated
with the single-city studies were noted
to be greater. In light of these greater
uncertainties and limitations, the
Administrator concluded in the
proposal that she had less confidence in
using these studies as a basis for setting
the level of the standard (77 FR 38943).
Given the considerations and
conclusions noted above, in the
proposal the Administrator concluded
that the short-term multi-city studies
provide the strongest evidence to inform
decisions on the level of the 24-hour
standard. Further, she viewed singlecity, short-term exposure studies as a
much more limited data set providing
mixed results, and she had less
confidence in using these studies as a
basis for setting the level of a 24-hour
standard (77 FR 38942). In highlighting
specific single-city studies, public
health, environmental, and State and
local commenters appear to have
selectively focused on studies reporting
associations with PM2.5 and to have
overlooked studies that reported more
equivocal results (e.g., Ostro et al., 2003;
Rabinovitch et al., 2004; Slaughter et al.,
2005; Villeneuve et al., 2006) (U.S. EPA,
2011, Figure 2–9). As such, these
commenters have not presented new
information that causes the EPA to
reconsider its decision to emphasize
multi-city studies over single-city
studies when identifying the
appropriate level of the 24-hour PM2.5
standard.
In further considering the single-city
studies highlighted by public
commenters, the EPA notes that some
commenters advocating for a lower level
for the 24-hour PM2.5 standard also
discussed short-term studies that have
been published since the close of the
Integrated Science Assessment. These
recent studies were conducted in single
cities or in small panels of volunteers.
As in prior NAAQS reviews and as
discussed above in more detail (section
II.B.3), the EPA is basing its decisions in
this review on studies and related
information assessed in the Integrated
Science Assessment. The studies
assessed in the Integrated Science
Assessment, and the conclusions based
on those studies, have undergone
extensive critical review by the EPA,
CASAC, and the public. The rigor of
that review makes the studies assessed
in the Integrated Science Assessment,
and the conclusions based on those
studies, the most reliable source of
scientific information on which to base
decisions on the NAAQS.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
3157
However, as discussed above (section
II.B.3), the EPA recognizes that ‘‘new
studies’’ may sometimes be of such
significance that it is appropriate to
delay a decision on revision of a
NAAQS and to supplement the
pertinent air quality criteria so the
studies can be taken into account. In the
present case, the EPA’s provisional
consideration of ‘‘new studies’’
concludes that, taken in context, the
‘‘new’’ information and findings do not
materially change any of the broad
scientific conclusions made in the air
quality criteria regarding the health
effects of PM2.5 (U.S. EPA, 2012b).
For this reason, reopening the air
quality criteria review would not be
warranted, even if there were time to do
so under the court order governing the
schedule for completing this review.
Accordingly, the EPA is basing its final
decisions in this review on the studies
and related information included in the
PM Integrated Science Assessment (i.e.,
the air quality criteria) that has
undergone CASAC and public review.
The EPA will consider the ‘‘new
studies’’ in the next periodic review of
the PM NAAQS, which will provide an
opportunity to fully assess these studies
through a more rigorous review process
involving the EPA, CASAC, and the
public.
Some public health, medical, and
environmental commenters also
criticized the EPA’s interpretation of
PM2.5 risk results. These commenters
presented risk estimates for
combinations of annual and 24-hour
standards using more recent air quality
data than that used in the EPA’s Risk
Assessment (U.S. EPA, 2010a). Based on
these additional risk analyses, the ALA
and other commenters contended that
public health benefits could continue to
increase as annual and 24-hour standard
levels decrease below 13 mg/m3 and 35
mg/m3, respectively.
The EPA agrees with commenters that
important public health benefits are
expected as a result of revising the level
of the annual standard to 12 mg/m3, as
is done in this rule, rather than 13 mg/
m3. The Agency also acknowledges that
estimated PM2.5-associated health risks
continue to decrease with annual
standard levels below 12 mg/m3 and/or
with 24-hour standard levels below 35
mg/m3. However, the EPA disagrees with
the commenters’ views regarding the
extent to which risk estimates support
setting standard levels below 12 mg/m3
(annual standard) and 35 mg/m3 (24hour standard).106
d. Administrator’s Final Conclusions on
the Primary PM2.5 Standard Levels
In reaching her conclusions regarding
appropriate standard levels, the
Administrator has considered the
epidemiological and other scientific
evidence, estimates of risk reductions
associated with just meeting alternative
annual and/or 24-hour standards, air
quality analyses, related limitations and
uncertainties, the advice of CASAC, and
extensive public comments on the
proposal. After careful consideration of
all of these, the Administrator has
decided to revise the level of the
primary annual PM2.5 standard from
15.0 mg/m3 to 12.0 mg/m3 and to retain
the level of the primary 24-hour
standard at 35 mg/m3.
As an initial matter, the Administrator
agrees with the approach supported by
CASAC and discussed in the Policy
Assessment as summarized in sections
III.A.3 and III.E.4.a above, of
considering the annual and 24-hour
standards together in determining the
protection afforded against mortality
and morbidity effects associated with
both long- and short-term exposures to
PM2.5. This approach is consistent with
the approach taken in the review
106 This section focuses on the 24-hour standard.
Section III.E.4.c.i above also discusses these
commenters’ recommendations within the context
of the annual PM2.5 standard.
PO 00000
Frm 00073
Fmt 4701
Sfmt 4700
The CAA charges the Administrator
with setting NAAQS that are ‘‘requisite’’
(i.e., neither more nor less stringent than
necessary) to protect public health with
an adequate margin of safety. In setting
such standards the Administrator must
weigh the available scientific evidence
and information, including associated
uncertainties and limitations. As
described above, in reaching her
proposed decisions on the PM2.5
standards that would provide
‘‘requisite’’ protection, the
Administrator carefully considered the
available scientific evidence and risk
information, making public health
policy judgments that, in her view,
neither overstated nor understated the
strengths and limitations of that
evidence and information. In contrast,
as discussed more fully above, public
health, medical, and environmental
commenters who recommended levels
below 35 mg/m3 for the 24-hour PM2.5
standard have not provided new
information or analyses to suggest that
such standard levels are appropriate,
given the uncertainties and limitations
in the available health evidence,
particularly uncertainties in studies
conducted in locations with 98th
percentile 24-hour PM2.5 concentrations
below 35 mg/m3 and long-term average
concentrations below 12 mg/m3.
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
3158
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
completed in 1997, in contrast to the
approach used in the review completed
in 2006 where each standard was
considered independently of the other
(i.e., only data from long-term exposure
studies were used to inform the level of
the annual standard and only data from
short-term exposure studies were used
to inform the level of the 24-hour
standard).107
Based on the evidence and
quantitative risk assessment, the
Administrator concludes that it is
appropriate to set an annual standard
that is generally controlling, which will
lower the broad distribution of 24-hour
average concentrations in an area as
well as the annual average
concentration, so as to provide
protection from both long- and shortterm PM2.5 exposures. In conjunction
with this, it is appropriate to set a 24hour standard focused on providing
supplemental protection, particularly
for areas with high peak-to-mean ratios
of 24-hour concentrations, possibly
associated with strong local or seasonal
sources, and for PM2.5-related effects
that may be associated with shorter-than
daily exposure periods. The
Administrator concludes this approach
will reduce aggregate risks associated
with both long- and short-term
exposures more consistently than a
generally controlling 24-hour standard
and is the most effective and efficient
way to reduce total PM2.5-related
population risk and to protect public
health with an adequate margin of
safety.
In selecting the level of the annual
PM2.5 standard, based on the
characterization and assessment of the
epidemiological and other studies
presented and assessed in the Integrated
Science Assessment and the Policy
Assessment, the Administrator
recognizes the substantial increase in
the number and diversity of studies
available in this review. This expanded
body of evidence includes extended
analyses of the seminal studies of longterm PM2.5 exposures (i.e., ACS and
Harvard Six Cities studies) as well as
important new long-term exposure
studies (as summarized in Figures 1 and
2). Collectively, the Administrator notes
that these studies, along with evidence
available in the last review, provide
consistent and stronger evidence than
previously observed of an association
between long-term PM2.5 exposures and
premature mortality in areas with lower
long-term ambient concentrations than
previously observed, with the strongest
evidence related to cardiovascularrelated mortality. The Administrator
107 See
71 FR 61148 and 61168, October 17, 2006.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
also recognizes the availability of
stronger evidence of morbidity effects
associated with long-term PM2.5
exposures, including evidence of
respiratory effects such as decreased
lung function growth, from the extended
analyses for the Southern California
Children’s Health Study and evidence of
cardiovascular effects from the WHI
study. Furthermore, the Administrator
recognizes new U.S. multi-city studies
that greatly expand and reinforce our
understanding of mortality and
morbidity effects associated with shortterm PM2.5 exposures, providing
stronger evidence of associations in
areas with ambient concentrations
similar to those previously observed in
short-term exposure studies considered
in the previous review (as summarized
in Figure 3).
The Administrator recognizes the
strength of the scientific evidence for
evaluating health effects associated with
fine particles, noting that the newly
available scientific evidence builds
upon the previous scientific data base to
provide evidence of generally robust
associations and a basis for greater
confidence in the reported associations
than in the last review. She notes the
conclusion of the Integrated Science
Assessment that this body of evidence
supports a causal relationship between
long- and short-term PM2.5 exposures
and mortality and cardiovascular effects
and a likely causal relationship between
long- and short-term PM2.5 exposures
and respiratory effects. In addition, the
Administrator notes additional, but
more limited evidence, for a broader
range of health endpoints including
evidence suggestive of a causal
relationship for developmental and
reproductive effects as well as for
carcinogenic effects.
Based on information discussed and
presented in the Integrated Science
Assessment, the Administrator
recognizes that health effects may occur
over the full range of concentrations
observed in the epidemiological studies
of both long-term and short-term
exposures, since no discernible
population-level threshold for any such
effects can be identified based on the
currently available evidence (U.S. EPA,
2009a, section 2.4.3). To inform her
decisions on an appropriate level for the
annual standard that will protect public
health with an adequate margin of
safety, in the absence of any discernible
population-level thresholds, the
Administrator judges that it is
appropriate to consider the relative
degree of confidence in the magnitude
and significance of the associations
observed in epidemiological studies
across the range of long-term PM2.5
PO 00000
Frm 00074
Fmt 4701
Sfmt 4700
concentrations in such studies. Further,
she recognizes, in taking note of CASAC
advice and the distributional statistics
analysis discussed in the Policy
Assessment and in section III.E.4.a
above, that there is significantly greater
confidence in the magnitude and
significance of observed associations for
the part of the air quality distribution
corresponding to where the bulk of the
health events evaluated in each study
have been observed, generally at and
around the long-term mean
concentrations. Conversely, she also
recognizes that there is significantly
diminished confidence in the
magnitude and significance of observed
associations in the lower part of the air
quality distribution corresponding to
where a relatively small proportion of
the health events were observed.
Further, the Administrator recognizes
that the long-term mean concentrations,
or any other specific point in the air
quality distribution of each study, do
not represent a ‘‘bright line’’ at and
above which effects have been observed
and below which effects have not been
observed.
In considering the long-term mean
concentrations reported in
epidemiological studies, the
Administrator recognizes that in
selecting a level of the annual standard
that will protect public health with an
adequate margin of safety, it is not
sufficient to focus on a concentration
generally somewhere within the range
of long-term mean concentrations from
the key long-term and short-term
exposure studies that reported lower
concentrations than had been observed
in earlier reviews. These key studies
provide information for various types of
serious health endpoints (including
mortality and morbidity effects),
different study populations (which may
include at-risk populations such as
children and older adults), and different
air quality distributions that are specific
to each study. A level somewhere
within the range of long-term mean
concentrations of the full set of key
studies would be higher than the longterm mean of at least one of the studies
being considered and therefore would
not provide a sufficient degree of
protection against the health effects
observed in that study. Absent some
reasoned basis to place less weight on
the evidence in the epidemiological
study with the lowest long-term mean
concentration among these key studies,
this approach would not be consistent
with the requirement to set a standard
that will protect public health with an
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
adequate margin of safety.108 Thus, the
Administrator recognizes it is important
to protect against the serious effects
observed in each of these studies so as
to protect public health with an
adequate margin of safety. In so doing,
she looks to identify the study with the
lowest long-term mean concentration
within the full set of key studies to help
inform her decision of the appropriate
standard level which will provide
protection for the broad array of health
outcomes observed in all of the studies,
including effects observed in at-risk
populations.
Further, consistent with the general
approach summarized in section
III.E.4.a above and supported by CASAC
as discussed in section III.E.4.b.ii above,
the Administrator recognizes that it is
appropriate to consider a level for an
annual standard that is not just at but
rather is somewhat below the long-term
mean PM2.5 concentrations reported in
each of the key long- and short-term
exposure studies. In so doing, she
focuses especially on multi-city studies
that evaluated health endpoints for
which the associations are causal or
likely causal (i.e., mortality and
cardiovascular and respiratory effects
associated with both long- and shortterm PM2.5 exposures). As discussed
above, the importance of considering a
level somewhat below the lowest longterm mean concentrations in this set of
key studies is to establish a standard
that would be protective against the
observed effects in all of the studies,
and that takes into account the relative
degree of confidence in the magnitude
and significance of observed
associations across the air quality
distributions in these studies.
The Administrator recognizes that
there is no clear way to identify how
much below the long-term mean
concentrations of key studies to set a
standard that would provide requisite
protection with an adequate margin of
safety. She therefore must use her
judgment to weigh the available
scientific and technical information,
and associated uncertainties, to reach a
final decision on the appropriate
standard level. In considering the
information in Figures 1–4 for effects
classified as having evidence of a causal
or likely causal relationship with longor short-term PM2.5 exposures, she
observes a cluster of short-term
exposure studies with long-term mean
concentrations within a range of 13.4
mg/m3 down to 12.8 mg/m3 (Dominici et
al., 2006a; Burnett and Goldberg, 2003;
Zanobetti and Schwartz, 2009; Bell et
108 See American Farm Bureau Federation v.
EPA, 559 F. 3d 512, 525–26 (D.C. Cir. 2009).
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
al., 2008; Burnett et al., 2004). She also
observes a cluster of long-term exposure
studies with long-term mean
concentrations within a range of 14.5
mg/m3 to 13.6 mg/m3 (Dockery et al.,
1996; Lipfert et al., 2006a; Zeger et al.,
2008; McConnell et al., 2003; Goss et al.,
2004; Eftim et al., 2008). For the reasons
discussed in response to public
comments in section III.E.4.c above, the
Administrator is less influenced by the
long-term mean PM2.5 concentrations
from the Miller et al. (2007) and
Krewski et al. (2009) studies with
reported long-term mean PM2.5
concentrations of 12.9 and 14.0 mg/m3,
respectively. In each case, the most
relevant exposure periods would likely
have had higher mean PM2.5
concentrations than those reported in
the studies.109 Thus, the Administrator
considers the long-term mean PM2.5
concentrations from these two studies to
be a highly uncertain basis for informing
her selection of the annual standard
level.110
To help guide her judgment of the
appropriate level below the long-term
mean concentrations in the
epidemiological studies at which to set
the standard, the Administrator
considered additional information from
epidemiological studies concerning the
broader distribution of PM2.5
concentrations which correspond to the
health events observed in these studies
(e.g., deaths, hospitalizations). The
Administrator observes that the
development and use of this
information in considering standard
levels is consistent with CASAC’s
advice, as discussed in section
III.E.4.b.ii above, to focus on
understanding the concentrations that
were most influential in generating the
health effect estimates in individual
studies (Samet, 2010d, p. 2).
In considering this additional
population-level information, the
Administrator recognizes that, in
general, the confidence in the
magnitude and significance of an
association identified in a study is
strongest at and around the long-term
mean concentration for the air quality
109 In
the case of Miller et al. (2007), the mean
concentration is based on a single year of air quality
data which post-dated by two years the period for
which the health events data were collected. In the
case of Krewski et al. (2009), the air quality data
were based on the last two years of the 18-year
period for which the health event data were
collected.
110 Nonetheless, as noted above, the EPA notes
that the Krewski et al. (2009) and Miller et al.
(2007) studies provide strong evidence of mortality
and cardiovascular-related effects associated with
long-term PM2.5 exposures to inform causality
determinations reached in the Integrated Science
Assessment (U.S. EPA, 2009a, sections 7.2.11 and
7.6).
PO 00000
Frm 00075
Fmt 4701
Sfmt 4700
3159
distribution, as this represents the part
of the distribution in which the data in
any given study are generally most
concentrated. She also recognizes that
the degree of confidence decreases as
one moves towards the lower part of the
distribution. Consistent with the
approach used in the Policy
Assessment, the Administrator believes
that the range from approximately the
25th to 10th percentiles is a reasonable
range for providing a general frame of
reference as to the part of the
distribution in which her confidence in
the associations observed in
epidemiological studies is appreciably
lower. However, as noted above, it is
important to emphasize that there is no
clear dividing line or single percentile
within a given distribution provided by
the scientific evidence that is most
appropriate or ‘correct’ to use to
characterize where the degree of
confidence in the associations warrants
setting the annual standard level. The
decision of the appropriate standard
level below the long-term mean
concentrations of the key studies, which
in conjunction with the other elements
of the standard would protect public
health with an adequate margin of
safety, is largely a public health policy
judgment, taking into account all of the
evidence and its related uncertainties.
As discussed in section III.E.4.b, the
Administrator takes note of additional
population-level data that were made
available to the EPA by study
authors.111 In considering this
information, the Administrator
particularly focuses on the analysis of
the distributions of the health event data
for each area within these studies and
the corresponding air quality data for
the two short-term exposure studies
(Zanobetti and Schwartz, 2009; Bell et
al., 2008). These short-term exposure
studies evaluate the relationship
between daily changes (one or more
days) in PM2.5 concentrations and daily
changes in health events (e.g., deaths,
hospitalizations), such that the air
quality concentrations that comprise the
most relevant exposure periods in these
111 As summarized in section III.E.4.a,
population-level data were provided to the EPA for
four studies. These four studies represent some of
the strongest evidence showing associations
between health effects and PM2.5 within the overall
body of scientific evidence and include three
studies (Krewski et al., 2009; Bell et al., 2008; and
Zanobetti and Schwartz, 2009) that were used as the
basis for concentration-response functions in the
quantitative risk assessment (U.S. EPA, 2010a,
section 3.3.3). The Administrator recognizes that
the additional population-level data available for
these four multi-city studies represents a more
limited data set compared to the set of long-term
mean PM2.5 concentrations which were available in
the published literature for all studies considered
in the Integrated Science Assessment.
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
3160
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
studies are contemporaneous with the
health event data. In addition, these
studies considered more recent air
quality data, representing generally
lower PM2.5 concentrations, in a large
number of study areas across the U.S.
Thus, such studies provide the most
useful evidence for an analysis
evaluating the distribution of health
event data and the corresponding longterm mean PM2.5 concentrations across
the areas included in each multi-city
study.
The Administrator also considered
the additional population-level data that
were made available to EPA for two
long-term exposure studies (Krewski et
al., 2009; Miller et al., 2007). She
recognizes that in long-term exposure
studies investigators follow a specific
group of study participants (i.e., cohort)
over time and across urban study areas,
and evaluate how PM2.5 concentrations
averaged over a period of years are
associated with specific health
endpoints (e.g., deaths) across cities. As
discussed in response to public
comments in section III.E.4.c,
disentangling the effects observed in
long-term exposure studies associated
with more recent air quality
measurements from effects that may
have been associated with earlier, and
most likely higher, PM2.5 exposures
introduces some uncertainty with regard
to understanding the appropriate
exposure window associated with the
observed effects. This is in contrast to
the short-term exposure studies where
the relevant exposure period is
contemporaneous to the period for
which the health data were collected. In
light of these considerations, as noted
above, the Administrator considers the
analysis of air quality concentrations
that correspond to the distribution of
population-level data in these two
studies to be a highly uncertain basis for
informing her selection of the annual
standard level.
Based on the above considerations,
the Administrator views the additional
population-level data for the two shortterm exposure studies as appropriate to
help inform her judgment of how much
below the long-term mean
concentrations to set the level of the
annual standard. The Administrator
notes that the long-term mean PM2.5
concentrations corresponding with
study areas contributing to the 25th
percentiles of the distribution of deaths
and cardiovascular-related
hospitalizations in these two short-term
exposure studies were 12.5 mg/m3 and
11.5 mg/m3, respectively, for Zanobetti
and Schwartz (2009) and for Bell et al.
(2008), with the 10th percentiles being
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
lower by approximately 2 mg/m3 in each
study.
The Administrator recognizes, as
summarized in section III.B above and
discussed more fully in section III.B.2 of
the proposal, that important
uncertainties remain in the evidence
and information considered in this
review of the primary fine particle
standards. These uncertainties are
generally related to understanding the
relative toxicity of the different
components in the fine particle mixture,
the role of PM2.5 in the complex ambient
mixture, exposure measurement errors,
and the nature and magnitude of
estimated risks related to increasingly
lower ambient PM2.5 concentrations.
Furthermore, the Administrator notes
that epidemiological studies have
reported heterogeneity in responses
both within and between cities and
geographic regions across the U.S. She
recognizes that this heterogeneity may
be attributed, in part, to differences in
fine particle composition in different
regions and cities.112
With regard to evidence for
reproductive and developmental effects
identified as being suggestive of a causal
relationship with long-term PM2.5
exposures, the Administrator recognizes
that there are a number of limitations
associated with this body of evidence
including: the limited number of studies
evaluating such effects; uncertainties
related to identifying the relevant
exposure time periods of concern; and
limited toxicological evidence providing
little information on the mode of
action(s) or biological plausibility for an
association between long-term PM2.5
exposures and adverse birth outcomes.
Nonetheless, the Administrator believes
that this more limited body of evidence
provides some support for considering
that serious effects may be occurring in
a susceptible population at
concentrations lower than those
associated with effects classified as
having a causal or likely causal
relationship with long-term PM2.5
exposures (i.e., mortality,
cardiovascular, and respiratory effects).
Overall, the Administrator believes
that the available evidence interpreted
in light of the remaining uncertainties,
as summarized above and discussed
more fully in the Integrated Science
112 Nonetheless, as explained in section III.E.1,
the currently available evidence is not sufficient to
support replacing or supplementing the PM2.5
indicator with any other indicator defined in terms
of a specific fine particle component or group of
components associated with any source categories
of fine particles. Furthermore, the evidence is not
sufficient to support eliminating any component or
group of components associated with any source
categories of fine particles from the mix of fine
particles included in the PM2.5 indicator.
PO 00000
Frm 00076
Fmt 4701
Sfmt 4700
Assessment and the Policy Assessment,
provides increased confidence relative
to information available in the last
review and provides a strong basis for
informing her final decisions in the
current review. The Administrator is
mindful that considering what
standards are requisite to protect public
health with an adequate margin of safety
requires public health policy judgments
that neither overstate nor understate the
strength and limitations of the evidence
or the appropriate inferences to be
drawn from the evidence. In considering
how to translate the available
information into appropriate standard
levels, the Administrator weighs the
available scientific information and
associated uncertainties and limitations.
For the purpose of determining what
annual standard level is appropriate the
Administrator recognizes that there is
no single factor or criterion that
comprises the ‘‘correct’’ approach to
weighing the various types of available
evidence and information.
In considering this information, the
Administrator notes the advice of
CASAC that ‘‘there are significant
public health consequences at the
current levels of the standards that
justify consideration of lowering the
PM2.5 NAAQS further’’ (Samet, 2010c, p.
12). In addition, she recognizes that
CASAC concluded, ‘‘although there is
increasing uncertainty at lower levels,
there is no evidence of a threshold (i.e.,
a level below which there is no risk for
adverse effects)’’ (Samet, 2010d, p.ii)
and that the final decisions on standard
levels must reflect a judgment of the
available scientific information with
respect to her interpretation of the
CAA’s requirement to set primary
standards that provide requisite
protection to public health with an
adequate margin of safety (Samet,
2010d, p. 4). The Administrator
recognizes CASAC’s advice that the
currently available scientific
information provided support for
considering an annual standard level
within a range of 13 to 11 mg/m3 and a
24-hour standard level within a range of
35 to 30 mg/m3. In considering how the
annual and 24-hour standards work
together to provide appropriate public
health protection, the Administrator
observes that CASAC did not express
support for any specific levels or
combinations of standards within these
ranges. She also notes that CASAC
encouraged the EPA staff to consider
additional data from epidemiological
studies to help quantify the
characterization of the PM2.5
concentrations that were most
influential in generating the health
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
effect estimates in these studies (Samet,
2010d, p. 2).
In response to CASAC’s advice, the
Administrator recognizes that the EPA
staff acquired additional data from
authors of key epidemiological studies
and analyzed these data to characterize
the distribution of PM2.5 concentrations
in relation to health events data to better
understand the degree of confidence in
the associations observed in the studies
as discussed above. The Administrator
recognizes that the final Policy
Assessment included consideration of
these additional analyses in reaching
final staff conclusions with regard to the
broadest range of alternative standard
levels supported by the science. She
takes note that the final Policy
Assessment concluded that while
alternative standard levels within the
range of 13 to 11 mg/m3 were
appropriate to consider, the evidence
most strongly supported consideration
of an annual standard level in the range
of 12 to 11 mg/m3. The Administrator is
aware that, in transmitting the final
Policy Assessment to CASAC, the
Agency notified CASAC that the final
staff conclusions reflected consideration
of CASAC’s advice and that those staff
conclusions were based, in part, on the
specific distributional analysis that
CASAC had urged the EPA to conduct
(Wegman, 2011). Thus, CASAC had an
opportunity to comment on the final
Policy Assessment, but chose not to
provide any additional comments or
advice after receiving it.
In selecting the annual standard level,
the Administrator has considered many
factors including the nature and severity
of the health effects involved, the
strength of the overall body of scientific
evidence as considered in reaching
causality determinations, the size of the
at-risk populations, and the estimated
public health impacts. She has also
considered the kind and degree of the
uncertainties that remain in the
available scientific information. She
recognizes that the association between
PM2.5 and serious health effects is well
established, including at concentrations
below those allowed by the current
standard. Further, she recognizes the
CAA requirement that requires primary
standards to provide an adequate
margin of safety was intended to
address uncertainties associated with
inconclusive scientific and technical
information as well as to provide a
reasonable degree of protection against
hazards that research has not yet
identified. In considering the currently
available evidence, as summarized and
discussed more broadly above, the
information on risk, CASAC advice, the
conclusions of the Policy Assessment,
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
and public comments on the proposal,
the Administrator strongly believes that
a lower annual standard level is needed
to protect public health with an
adequate margin of safety.
In reaching her final decision on the
appropriate annual standard level to set,
the Administrator is mindful that the
CAA does not require that primary
standards be set at a zero-risk level, but
rather at a level that reduces risk
sufficiently so as to protect public
health, including the health of at-risk
populations, with an adequate margin of
safety. On balance, the Administrator
concludes that an annual standard level
of 12 mg/m3 would be requisite to
protect the public health with an
adequate margin of safety from effects
associated with long- and short-term
PM2.5 exposures, while still recognizing
that uncertainties remain in the
scientific information.
In the Administrator’s judgment, an
annual standard of 12 mg/m3
appropriately reflects placing greatest
weight on evidence of effects for which
the Integrated Science Assessment
determined there is a causal or likely
causal relationship with long- and shortterm PM2.5 exposures. An annual
standard level of 12 mg/m3 is below the
long-term mean PM2.5 concentrations
reported in each of the key multi-city,
long- and short-term exposures studies
providing evidence of an array of
serious health effects (e.g., premature
mortality, increased hospitalization for
cardiovascular and respiratory effects).
As noted above, the importance of
considering a level somewhat below the
lowest long-term mean concentration in
the full set of studies considered is to
set a standard that would provide
appropriate protection against the
observed effects in all such studies.
In reaching her decision, the
Administrator has taken into account
that at and around the mean PM2.5
concentration in any given study
represents a part of the air quality
distribution in which the health event
data in that study are generally most
concentrated. Furthermore, in
identifying an appropriate annual
standard level below the long-term
mean concentrations, she recognizes
that there is no evidence to support the
existence of any discernible threshold,
and, therefore, she has a high degree of
confidence that the observed effects are
associated with concentrations not just
at but extending somewhat below the
long-term mean concentration. To
further inform her judgment in setting
the annual standard level so as to
protect public health with an adequate
margin of safety, the Administrator has
placed weight on additional population-
PO 00000
Frm 00077
Fmt 4701
Sfmt 4700
3161
level information available from a
subset of these epidemiological studies,
consistent with CASAC advice. In
particular, she has drawn from two
short-term exposure studies, which
provide the most relevant information
for evaluating the distribution of health
events and corresponding long-term
PM2.5 concentrations. As explained
above, this helps inform her judgment
as to the degree of confidence in the
observed associations in the
epidemiological studies. In this regard,
the Administrator generally judges the
region around the 25th percentile as a
reasonable part of the distribution to
help guide her decision on the
appropriate standard level. Since this
evidence comes primarily from two
studies, a relatively modest data set, the
Administrator deems it reasonable not
to draw further inferences from air
quality and health event data in the
lower part of the distribution for the
purpose of setting a standard level. The
Administrator notes that the long-term
mean PM2.5 concentrations around the
25th percentile of the distributions of
deaths and cardiovascular-related
hospitalizations were approximately
around 12 mg/m3 in these two studies.
The Administrator views this
information as helpful in guiding her
determination as to where her
confidence in the magnitude and
significance of the associations is
reduced to such a degree that a standard
set at a lower level would not be
warranted to provide requisite
protection that is neither more nor less
than needed to provide an adequate
margin of safety.
The Administrator also recognizes
that a level of 12 mg/m3 places some
weight on studies which provide
evidence of reproductive and
developmental effects (e.g., infant
mortality, low birth weight). These
studies were identified in the Integrated
Science Assessment as having evidence
suggestive of a causal relationship with
long-term PM2.5 concentrations. A level
of 12 mg/m3 is approximately the same
level as the lowest long-term mean
concentration reported in such studies
(Figures 2 and 4; 11.9 mg/m3 for Bell et
al., 2007).113 While the Administrator
113 With respect to cancer, mutagenic, and
genotoxic effects, the Administrator observes that
the PM2.5 concentrations reported in studies
evaluating these effects generally included ambient
concentrations that are equal to or greater than
ambient concentrations observed in studies that
reported mortality and cardiovascular and
respiratory effects (U.S. EPA, 2009a, section 7.5).
Therefore, the Administrator concludes that in
selecting alternative standard levels that provide
protection from mortality and cardiovascular and
respiratory effects, it is reasonable to anticipate that
E:\FR\FM\15JAR2.SGM
Continued
15JAR2
tkelley on DSK3SPTVN1PROD with
3162
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
acknowledges that this evidence is
limited, she believes it is appropriate to
place some weight on these studies in
order to set a standard that provides
protection with an adequate margin of
safety, including providing protection
for at-risk populations, as required by
the CAA. Due to the limited nature of
this evidence, she has determined it is
not necessary to set a standard below
the lowest long-term mean
concentration in these studies.
In reflecting on extensive public
comments received on the proposal as
discussed in section III.E.4.c above, the
Administrator recognizes that some
commenters have offered different
evaluations of the evidence and other
information available in this review and
would make different judgments about
the weight to place on the relative
strengths and limitations of the
scientific information and about how
such information could be used in
making public health policy decisions
on the annual standard level. One group
of such commenters who supported a
higher annual standard level (e.g., above
13 mg/m3) would place greater weight on
the remaining uncertainties in the
evidence as a basis for supporting a
higher standard level than the
Administrator judges to be appropriate.
Such an approach is based on these
commenters’ judgment that the
uncertainties remaining in the evidence
are too great to warrant setting an
annual standard below the current level.
The Administrator does not agree.
As an initial matter, an annual
standard level of 13 mg/m3 or higher
would be above the long-term mean
concentrations reported in two wellconducted, multi-city short-term
exposure studies reporting positive and
statistically significant associations of
serious effects (Burnett et al., 2004 and
Bell et al., 2008). These important
studies are fully consistent with the
pattern of evidence presented by the
large body of evidence in this review.
As the Administrator recognized in the
proposal, and as advised by CASAC, the
appropriate focus for selecting the level
of the annual PM2.5 standard is on
concentrations somewhat below the
lowest long-term mean concentrations
from the set of key studies of both longterm and short-term PM2.5 exposures
considered by the EPA (i.e., as shown in
Figure 4). Thus, a standard level set at
13 mg/m3 or higher would clearly not
provide protection for the effects
observed in the full set epidemiological
studies and, therefore, this standard
protection will also be provided for carcinogenic
effects.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
level could not be judged to be requisite
with an adequate margin of safety.114
In addition, as noted above, in
recognizing that there is no evidence to
support the existence of a discernible
threshold below which an effect would
not occur, the Administrator is mindful
that effects occur around and below the
long-term mean concentrations reported
in both the short-term and long-term the
epidemiological studies. A standard
level of 13 mg/m3 or higher would not
appropriately take into account
evidence from the two well-conducted,
multi-city, short-term exposure studies
reporting serious effects with long-term
mean concentrations below 13 mg/m3
noted above (Burnett et al, 2004; Bell et
al., 2008). Such a standard level would
also not appropriately take into account
additional population-level data from a
limited number of epidemiological
studies. This approach would ignore
CASAC’s advice to consider such
information in order to better
understand the concentrations over
which there is a high degree of
confidence regarding the magnitude and
significance of the associations observed
in individual epidemiological studies
and where there is appreciably less
confidence.
Furthermore, a standard level of 13
mg/m3 or higher would not
appropriately take into account the
more limited evidence of effects in some
at-risk populations (e.g., low birth
weight). In the Administrator’s view, a
standard set at this level would not
provide protection with an adequate
margin of safety, including providing
protection for at-risk populations. The
Administrator is mindful that the CAA
requirement that primary standards
provide an adequate margin of safety,
discussed in section II.A above, was
intended to address uncertainties
associated with inconclusive scientific
and technical information available at
the time of standard setting as well as
to provide a reasonable degree of
protection against hazards that research
has not yet identified.
In light of the entire body of evidence
as discussed above, the Administrator
judges that an annual standard level set
114 The Administrator is mindful that, in
reviewing the 2006 final PM NAAQS decisions, the
D.C. Circuit Court of Appeals concluded that the
EPA failed to adequately explain why that annual
standard provided requisite protection from effects
associated with both long- and short-term exposures
or from morbidity effects in children and other atrisk populations when long-term means of
important short-term studies were below the level
the Administrator selected for the annual standard.
See American Farm Bureau v. EPA. 559 F. 3d 512,
524–26. There is no reasonable basis to discount
these two studies for purposes of setting the level
of the annual standard.
PO 00000
Frm 00078
Fmt 4701
Sfmt 4700
above 12 mg/m3 would not be sufficient
to protect public health with an
adequate margin of safety from the
serious health effects associated with
long- and short-term exposure to PM2.5.
The Administrator also recognizes
that a second group of commenters
supported a lower annual standard level
(e.g., no higher than 11 mg/m3). Such a
standard level would reflect placing
essentially as much weight on the
relatively more limited data providing
evidence suggestive of a causal
relationship for effects observed in some
at-risk populations (e.g., low birth
weight) as on more certain evidence of
effects classified as having a causal or
likely causal relationship with PM2.5
exposures. In the Administrator’s view,
while it is important to place some
weight on such suggestive evidence, it
would not be appropriate to place as
much weight on it as the commenters
would do.
An annual standard level of 11 mg/m3
would also reflect these commenters’
judgment that it is appropriate to focus
on a lower part of the distributions of
health event data from the small number
of epidemiological studies for which
this information was made available
than the Administrator believes is
warranted. In the Administrator’s view,
using this type of information to set a
standard level of 11 mg/m3 or below
would assume too high a degree of
confidence in the magnitude and
significance of the associations observed
in the lower part of the distributions of
health events observed in these studies.
Given the uncertainties in the evidence
and the limited set of studies for which
the EPA has information on the
distribution of health event data and
corresponding air quality data, the
Administrator believes it is not
appropriate to focus on the lower part
of the distributions of health events
data.
On balance, the Administrator finds
that the available evidence interpreted
in light of the remaining uncertainties
does not justify a standard level set
below 12 mg/m3 as necessary to protect
public health with an adequate margin
of safety.
After carefully considering the above
considerations and the public comments
summarized in section III.E.4.c above,
the Administrator has decided to set the
level of the primary annual PM2.5
standard at 12 mg/m3. In her judgment,
a standard set at this level provides the
requisite degree of public health
protection, including the health of atrisk populations, with an adequate
margin of safety and is neither more nor
less stringent than necessary for this
purpose.
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
As discussed above, the
Administrator concludes that an
approach that focuses on setting a
generally controlling annual standard is
the most effective and efficient way to
reduce total population risk associated
with both long- and short-term PM2.5
exposures. Such an approach would
result in more uniform protection across
the U.S. than the alternative of setting
the levels of the 24-hour and annual
standard such that the 24-hour standard
would generally be the controlling
standard in areas across the country (see
section III.A.3).
The Administrator recognizes that
potential air quality changes associated
with meeting an annual standard level
of 12.mg/m3 will result in lowering risks
associated with both long- and shortterm PM2.5 exposures by lowering the
overall air quality distribution.
However, the Administrator recognizes
that such an annual standard alone
would not be expected to offer sufficient
protection with an adequate margin of
safety against the effects of short-term
PM2.5 exposures in all parts of the
country. As a result, in conjunction with
an annual standard level of 12 mg/m3,
the Administrator concludes that it is
appropriate to continue to provide
supplemental protection by means of a
24-hour standard set at the appropriate
level, particularly for areas with high
peak-to-mean ratios possibly associated
with strong local or seasonal sources
and for areas with PM2.5-related effects
that may be associated with shorterthan-daily exposure periods.
In selecting the level of a 24-hour
standard meant to provide such
supplemental protection, the
Administrator relies upon evidence and
air quality information from key shortterm exposure studies. In considering
these studies, the Administrator notes
that to the extent air quality
distributions in the study areas
considered are reduced to meet the
current 24-hour standard (at a level of
35 mg/m3) or to meet the revised annual
standard discussed above (at a level of
12 mg/m3), additional protection would
be anticipated against the effects
observed in these studies. In light of
this, when selecting the appropriate
level for the 24-hour standard, the
Administrator considers both the 98th
percentiles of 24-hour PM2.5
concentrations and the long-term mean
PM2.5 concentrations in the locations of
the short-term exposure studies. She
notes that such consideration of both
short- and long-term PM2.5
concentrations can inform her decision
on the extent to which a given 24-hour
standard, in combination with the
revised annual standard established in
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
this rule, would provide protection
against the health effects reported in
short-term studies.
As discussed in section III.E.4.a
above, the Administrator concludes that
multi-city short-term exposure studies
provide the strongest data set for
informing her decisions on appropriate
24-hour standard levels. With regard to
the limited number of single-city studies
that reported positive and statistically
significant associations for a range of
health endpoints related to short-term
PM2.5 concentrations in areas that would
likely have met the current suite of
PM2.5 standards, the Administrator
recognizes that many of these studies
had significant limitations (e.g., limited
statistical power, limited exposure data)
or equivocal results (mixed results
within the same study area) that make
them unsuitable to form the basis for
setting the level of a 24-hour standard.
With regard to multi-city studies that
evaluated effects associated with shortterm PM2.5 exposures, the Administrator
observes an overall pattern of positive
and statistically significant associations
in studies with 98th percentile 24-hour
values averaged across study areas
within the range of 45.8 to 34.2 mg/m3
(Burnett et al., 2004; Zanobetti and
Schwartz, 2009; Bell et al., 2008;
Dominici et al., 2006a, Burnett and
Goldberg, 2003; Franklin et al., 2008).
The Administrator notes that, to the
extent air quality distributions are
reduced to reflect just meeting the
current 24-hour standard, additional
protection would be provided for the
effects observed in the three multi-city
studies with 98th percentile values
greater than 35 mg/m3 (Burnett et al.,
2004; Burnett and Goldberg, 2003;
Franklin et al., 2008). In the three
additional multi-city studies with 98th
percentile values below 35 mg/m3,
specifically 98th percentile
concentrations of 34.2, 34.3, and 34.8
mg/m3, the Administrator notes that
these studies reported long-term mean
PM2.5 concentrations of 12.9, 13.2, and
13.4 mg/m3, respectively (Bell et al.,
2008; Zanobetti and Schwartz, 2009;
Dominici et al., 2006a). In revising the
level of the annual standard to 12 mg/
m3, as discussed above, the
Administrator recognizes that additional
protection would be provided for the
short-term effects observed in these
multi-city studies such that revision to
the 24-hour standard would not be
warranted. That is, by lowering the level
of the annual standard to 12 mg/m3, the
98th percentile of the distribution
would be lowered as well such that
additional protection from effects
associated with short-term exposures
would be afforded. Therefore, the
PO 00000
Frm 00079
Fmt 4701
Sfmt 4700
3163
epidemiological evidence supports a
conclusion that it is appropriate to
retain the level of the 24-hour standard
at 35 mg/m3, in conjunction with a
revised annual standard level of 12 mg/
m3.
In addition to considering the
epidemiological evidence, the
Administrator also has taken into
account air quality information based on
county-level 24-hour and annual design
values to understand the implications of
revising the annual standard level from
15 to 12 mg/m3 in conjunction with
retaining the 24-hour standard level at
35 mg/m3. She has considered this
information to evaluate the public
health protection provided by the two
standards in combination and to
evaluate the most appropriate means of
developing a suite of standards
providing requisite public health
protection with an adequate margin of
safety.
In considering the air quality
information, the Administrator observes
that a suite of PM2.5 standards that
includes an annual standard level of 12
mg/m3 and a 24-hour standard level of
35 mg/m3 would result in the annual
standard as the generally controlling
standard in most regions across the
country, except for certain areas in the
Northwest, where the annual mean
PM2.5 concentrations have historically
been low but where relatively high 24hour concentrations occur, often related
to seasonal wood smoke emissions (U.S.
EPA, 2011a, pp. 2–89 to 2–91, Figure 2–
10). In fact, these are the type of areas
for which the supplemental protection
afforded by the 24-hour standard is
intended, such that the two standards
together provide the requisite degree of
protection. The Administrator
concludes the current 24-hour standard
at a level of 35 mg/m3, in conjunction
with a revised annual standard level of
12 mg/m3, will provide appropriate
protection from effects observed in
studies in such areas in which the longterm mean concentrations were below
12 mg/m3 and the 98th percentile 24hour concentrations were above 35 mg/
m3 (e.g., areas in the Northwest U.S.).
After carefully taking the public
comments and above considerations
into account, the Administrator has
decided to retain the current level of the
primary PM2.5 24-hour standard at 35
mg/m3 in conjunction with revising the
annual standard level from 15.0 mg/m3
to 12.0 mg/m3.115 In the Administrator’s
115 As noted in section II.B.1, Table 1 and section
III.E.4.a above, the annual standard level is defined
to one decimal place. Throughout this section, the
annual standard levels discussed have been
E:\FR\FM\15JAR2.SGM
Continued
15JAR2
3164
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
judgment, this suite of primary PM2.5
standards and the rationale supporting
these levels appropriately reflects
consideration of the strength of the
available evidence and other
information and its associated
uncertainties as well as the advice of
CASAC and consideration of public
comments. In the Administrator’s
judgment, this suite of primary PM2.5
standards is sufficient but not more
protective than necessary to protect the
public health, including at-risk
populations, with an adequate margin of
safety from effects associated with longand short-term exposures to fine
particles. This suite of standards will
provide significant protection from
serious health effects including
premature mortality and cardiovascular
and respiratory morbidity effects that
are causally or likely causally related to
long- and short-term PM2.5 exposures.
These standards will also provide an
appropriate degree of protection against
other health effects for which there is
more limited evidence of effects and
causality, such as reproductive and
developmental effects. This judgment by
the Administrator appropriately
considers the requirement for a standard
that is requisite to protect public health
but is neither more nor less stringent
than necessary.116
tkelley on DSK3SPTVN1PROD with
D. Administrator’s Final Decisions on
Primary PM2.5 Standards
For the reasons discussed above, and
taking into account the information and
assessments presented in the Integrated
Science Assessment, Risk Assessment,
and Policy Assessment, the advice and
recommendations of CASAC, and public
comments to date, the Administrator
revises the current suite of primary
PM2.5 standards. Specifically, the
Administrator revises: (1) The level of
the primary annual PM2.5 standard to
12.0 mg/m3 and (2) the form of the
primary annual PM2.5 standard to one
based on the highest appropriate areawide monitor in an area, with no option
for spatial averaging. In conjunction
with revising the primary annual PM2.5
standard to provide protection from
effects associated with long- and shortterm PM2.5 exposures, the Administrator
retains the level of 35 mg/m3 and the
98th percentile form of the primary 24hour PM2.5 standard to continue to
provide supplemental protection for
areas with high peak PM2.5
concentrations. The Administrator is
denoted as integer values (e.g., 12 mg/m3) for
simplicity.
116 The Administrator also judges that this suite
of standards addresses the issues raised by the D.C.
Circuit’s remand of the 2006 primary annual PM2.5
standard by appropriately revising that standard.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
not revising the current PM2.5 indicator
or the annual and 24-hour averaging
times for the primary PM2.5 standards.
The Administrator concludes that this
suite of standards would be requisite to
protect public health with an adequate
margin of safety against health effects
potentially associated with long- and
short-term PM2.5 exposures.
IV. Rationale for Final Decision on
Primary PM10 Standard
This section presents the rationale for
the Administrator’s final decision to
retain the current 24-hour primary PM10
standard in order to continue to provide
public health protection against shortterm exposures to inhalable particles in
the size range of 2.5 to 10 mm (i.e.,
PM10-2.5 or thoracic coarse particles).
These are particles capable of reaching
the most sensitive areas of the lung,
including the trachea, bronchi, and deep
lungs. The current standard uses PM10
as the indicator for thoracic coarse
particles, and thus is referred to as a
PM10 standard.117
As discussed more fully in the
proposal and below, this rationale is
based on a thorough review of the latest
scientific evidence, published through
mid-2009 and assessed in the Integrated
Science Assessment (U.S. EPA, 2009a),
evaluating human health effects
associated with long- and short-term
exposures to thoracic coarse particles.
The Administrator’s final decision also
takes into account: (1) The EPA staff
analyses of air quality information and
health evidence and staff conclusions
regarding the current and potential
alternative standards, as presented in
the Policy Assessment for the PM
NAAQS (U.S. EPA, 2011a); (2) CASAC
advice and recommendations, as
reflected in discussions at public
meetings of drafts of the Integrated
Science Assessment and Policy
Assessment, and in CASAC’s letters to
the Administrator; (3) the multiple
rounds of public comments received
during the development of the
Integrated Science Assessment and
Policy Assessment, both in connection
with CASAC meetings and separately;
and (4) public comments (including
testimony at the public hearings)
received on the proposal.
In presenting the rationale for the
final decision to retain the current
primary PM10 standard, this section
discusses the EPA’s past reviews of the
PM NAAQS and the general approach
taken to review the current standard
117 Throughout this section of the preamble, we
are using the terms ‘‘thoracic coarse particles’’,
‘‘inhalable coarse particles’’, and ‘‘PM10-2.5’’
synonymously.
PO 00000
Frm 00080
Fmt 4701
Sfmt 4700
(section IV.A), the health effects
associated with exposures to ambient
PM10-2.5 (section IV.B), the consideration
of the current and potential alternative
standards in the Policy Assessment
(section IV.C), CASAC
recommendations regarding the current
and potential alternative standards
(section IV.D), the Administrator’s
proposed decision to retain the current
primary PM10 standard (section IV.E),
public comments received in response
to the Administrator’s proposed
decision (section IV.F), and the
Administrator’s final decision to retain
the current primary PM10 standard
(section IV.G).
A. Background
The following sections discuss
previous reviews of the PM NAAQS
(section IV.A.1), the litigation of the
EPA’s 2006 decision on the PM10
standards (section IV.A.2), and the
general approach taken to review the
primary PM10 standard in the current
review (section IV.A.3).
1. Previous Reviews of the PM NAAQS
a. Reviews Completed in 1987 and 1997
The PM NAAQS have always
included some type of a primary
standard to protect against effects
associated with exposures to thoracic
coarse particles. In 1987, when the EPA
first revised the PM NAAQS, the EPA
changed the indicator for PM from TSP
to focus on inhalable particles, those
which can penetrate into the trachea,
bronchi, and deep lungs (52 FR 24634,
July 1, 1987). In that review, the EPA
changed the PM indicator to PM10 based
on evidence that the risk of adverse
health effects associated with particles
with a nominal mean aerodynamic
diameter less than or equal to 10 mm
was significantly greater than risks
associated with larger particles (52 FR
24639, July 1, 1987).
In the 1997 review, in conjunction
with establishing new fine particle (i.e.,
PM2.5) standards (discussed above in
sections II.B.1 and III.A.1), the EPA
concluded that continued protection
was warranted against potential effects
associated with thoracic coarse particles
in the size range of 2.5 to 10 mm. This
conclusion was based on particle
dosimetry, toxicological information,
and on limited epidemiological
evidence from studies that measured
PM10 in areas where the coarse fraction
was likely to dominate PM10 mass (62
FR 38677, July 18, 1997). The EPA
concluded there that a PM10 standard
could provide requisite protection
against effects associated with particles
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
in the size range of 2.5 to 10 mm.118
Although the EPA considered a more
narrowly defined indicator for thoracic
coarse particles in that review (i.e.,
PM10-2.5), the EPA concluded that it was
more appropriate, based on existing
evidence, to continue to use PM10 as the
indicator. This decision was based, in
part, on the recognition that the only
studies of clear quantitative relevance to
health effects most likely associated
with thoracic coarse particles used
PM10. These were two studies
conducted in areas where the coarse
fraction was the dominant fraction of
PM10, and which substantially exceeded
the 24-hour PM10 standard (62 FR
38679). In addition, there were only
very limited ambient air quality data
then available specifically for PM10-2.5,
in contrast to the extensive monitoring
network already in place for PM10.
Therefore, the EPA considered it more
administratively feasible to use PM10 as
an indicator. The EPA also stated that
the PM10 standards would work in
conjunction with the PM2.5 standards by
regulating the portion of particulate
pollution not regulated by the then
newly adopted PM2.5 standards.
In May 1998, a three-judge panel of
the U.S. Court of Appeals for the District
of Columbia Circuit found ‘‘ample
support’’ for the EPA’s decision to
regulate coarse particle pollution, but
vacated the 1997 PM10 standards,
concluding that the EPA had failed to
adequately explain its choice of PM10 as
the indicator for thoracic coarse
particles American Trucking
Associations v. EPA, 175 F. 3d 1027,
1054–56 (D.C. Cir. 1999). In particular,
the court held that the EPA had not
explained the use of an indicator under
which the allowable level of coarse
particles varied according to the amount
of PM2.5 present, and which, moreover,
potentially double regulated PM2.5. The
court also rejected considerations of
administrative feasibility as justification
for use of PM10 as the indicator for
thoracic coarse PM, since NAAQS (and
their elements) are to be based
exclusively on health and welfare
considerations. Id. at 1054. Pursuant to
the court’s decision, the EPA removed
the vacated 1997 PM10 standards from
the CFR (69 FR 45592, July 30, 2004)
and deleted the regulatory provision (at
40 CFR 50.6(d)) that controlled the
transition from the pre-existing 1987
PM10 standards to the 1997 PM10
standards (65 FR 80776, December 22,
2000). The pre-existing 1987 PM10
118 With regard to the 24-hour PM
10 standard, the
EPA retained the indicator, averaging time, and
level (150 mg/m3), but revised the form (i.e., from
one-expected-exceedance to the 99th percentile).
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
standards thus remained in place. Id. at
80777.
b. Review Completed in 2006
In the review of the PM NAAQS that
concluded in 2006, the EPA considered
the growing, but still limited, body of
evidence supporting associations
between health effects and thoracic
coarse particles measured as PM10-2.5.119
The new studies available in the 2006
review included epidemiological
studies that reported associations with
health effects using direct
measurements of PM10-2.5, as well as
dosimetric and toxicological studies. In
considering this growing body of
PM10-2.5 evidence, as well as evidence
from studies that measured PM10 in
locations where the majority of PM10
was in the PM10-2.5 fraction (U.S. EPA,
2005, section 5.4.1), staff concluded that
the level of protection afforded by the
existing 1987 PM10 standard remained
appropriate (U.S. EPA, 2005, p. 5–67)
but recommended that the indicator for
the standard be revised. Specifically,
staff recommended replacing the PM10
indicator with an indicator of urban
thoracic coarse particles in the size
range of 10–2.5 mm (U.S. EPA, 2005, pp.
5–70 to 5–71). The agency proposed to
retain a standard for a subset of thoracic
coarse particles, proposing a qualified
PM10-2.5 indicator to focus on the mix of
thoracic coarse particles generally
present in urban environments. More
specifically, the proposed revised
thoracic coarse particle standard would
have applied only to an ambient mix of
PM10-2.5 dominated by resuspended dust
from high-density traffic on paved roads
and/or by industrial and construction
sources. The proposed revised standard
would not have applied to any ambient
mix of PM10-2.5 dominated by rural
windblown dust and soils. In addition,
agricultural sources, mining sources,
and other similar sources of crustal
material would not have been subject to
control in meeting the standard (71 FR
2667 to 2668, January 17, 2006).
The Agency received a large number
of comments overwhelmingly and
persuasively opposed to the proposed
qualified PM10-2.5 indicator (71 FR
61188 to 61197, October 17, 2006). After
careful consideration of the scientific
evidence and the recommendations
contained in the 2005 Staff Paper, the
advice and recommendations from
119 The PM Staff Paper (U.S. EPA, 2005) also
presented results of a quantitative assessment of
health risks for PM10-2.5. However, staff concluded
that the nature and magnitude of the uncertainties
and concerns associated with this risk assessment
weighed against its use as a basis for recommending
specific levels for a thoracic coarse particle
standard (U.S. EPA, 2005, p. 5–69).
PO 00000
Frm 00081
Fmt 4701
Sfmt 4700
3165
CASAC, and the public comments
received regarding the appropriate
indicator for coarse particles, and after
extensive evaluation of the alternatives
available to the Agency, the
Administrator decided it would not be
appropriate to adopt the proposed
qualified PM10-2.5 indicator, or any
qualified indicator. Underlying this
determination was the Administrator’s
decision that it was requisite to provide
protection from exposure to all thoracic
coarse PM, regardless of its origin. The
Administrator thus rejected arguments
that there are no health effects from
community-level exposures to coarse
PM in non-urban areas (71 FR 61189).
The EPA concluded that dosimetric,
toxicological, occupational and
epidemiological evidence supported
retention of a primary standard for
short-term exposures that included all
thoracic coarse particles (i.e., particles
of both urban and non-urban origin),
consistent with the Act’s requirement
that primary NAAQS must be requisite
to protect the public health and provide
an adequate margin of safety. At the
same time, the Agency concluded that
the standard should target protection
toward urban areas, where the evidence
of health effects from exposure to
PM10-2.5 was strongest (71 FR at 61193,
61197). The proposed indicator was not
suitable for that purpose. Not only did
it inappropriately provide no protection
at all to many areas, but it failed to
identify many areas where the ambient
particle mix was dominated by coarse
particles contaminated with urban/
industrial types of coarse particles for
which evidence of health effects was
strongest (71 FR 61193).
The Agency ultimately concluded that
the existing indicator, PM10, was most
consistent with the evidence. Although
PM10 includes both coarse and fine PM,
the Agency concluded that it remained
an appropriate indicator for thoracic
coarse particles because, as discussed in
the PM Staff Paper (U.S. EPA, 2005, p.
2–54, Figures 2–23 and 2–24), fine
particle levels are generally higher in
urban areas and, therefore, a PM10
standard set at a single unvarying level
will generally result in lower allowable
concentrations of thoracic coarse
particles in urban areas than in nonurban areas (71 FR 61195–96). The EPA
considered this to be an appropriate
targeting of protection given that the
strongest evidence for effects associated
with thoracic coarse particles came from
epidemiological studies conducted in
urban areas and that elevated fine
particle concentrations in urban areas
could result in increased contamination
of coarse fraction particles by PM2.5,
E:\FR\FM\15JAR2.SGM
15JAR2
3166
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
potentially increasing the toxicity of
thoracic coarse particles in urban areas
(id.). Given the evidence that the
existing (i.e., 1987) PM10 standard was
established at a level and form which
afforded requisite protection with an
adequate margin of safety, the Agency
retained the level and form of the 24hour PM10 standard.120
The Agency also revoked the annual
PM10 standard, in light of the
conclusion in the PM Criteria Document
(U.S. EPA, 2004, p. 9–79) that the
available evidence does not suggest an
association with long-term exposure to
PM10-2.5 and the conclusion in the Staff
Paper (U.S. EPA, 2005, p. 5–61) that
there is no quantitative evidence that
directly supports retention of an annual
standard. This decision was consistent
with CASAC advice and
recommendations (Henderson, 2005a,b).
In the same rulemaking, the EPA also
included a new FRM for the
measurement of PM10-2.5 in the ambient
air (71 FR 61212 to 61213, October 17,
2006). Although the standard for
thoracic coarse particles does not use a
PM10-2.5 indicator, the new FRM for
PM10-2.5 was established to provide a
basis for approving FEMs and to
promote the gathering of scientific data
to support future reviews of the PM
NAAQS (71 FR 61202/3, October 17,
2006).121
tkelley on DSK3SPTVN1PROD with
2. Litigation Related to the 2006 Primary
PM10 Standards
A number of groups filed suit in
response to the final decisions made in
the 2006 review. See American Farm
Bureau Federation v. EPA, 559 F. 3d
512 (D.C. Cir. 2009). Among the
petitions for review were challenges
from industry groups on the decision to
retain the PM10 indicator and the level
of the PM10 standard and from
environmental and public health groups
on the decision to revoke the annual
PM10 standard. The court upheld both
the decision to retain the 24-hour PM10
standard and the decision to revoke the
annual standard.
120 Thus, the standard is met when a 24-hour
average PM10 concentration of 150 mg/m3 is not
exceeded more than one day per year, on average
over a three-year period. As noted above, the 1987
PM10 standard was not adopted solely to control
thoracic coarse particles. However, when reviewing
this standard in the 2006 review, EPA determined
that the level and form of the standard being
reviewed (i.e., the 1987 PM10 standard) provided
requisite protection with an adequate margin of
safety from short-term exposures to thoracic coarse
particles.
121 As noted below, however, with this rule the
EPA is revoking the requirement for PM10-2.5
speciation at NCore monitoring sites due to
technical issues related to the development of
appropriate monitoring methods (section VIII.B.3.c).
The requirement for PM10-2.5 mass measurements at
NCore sites is being retained.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
First, the court upheld the EPA’s
decision for a standard to encompass all
thoracic coarse PM, both of urban and
non-urban origin. The court rejected
arguments that the evidence showed
there are no risks from exposure to nonurban coarse PM. The court further
found that the EPA had a reasonable
basis not to set separate standards for
urban and non-urban coarse PM, namely
the inability to reasonably define what
ambient mixes would be included under
either ‘urban’ or ‘non-urban;’ and the
evidence in the record that supported
the EPA’s appropriately cautious
decision to provide ‘‘some protection
from exposure to thoracic coarse
particles * * * in all areas.’’ 559 F. 3d
at 532–33. Specifically, the court stated,
Although the evidence of danger from
coarse PM is, as EPA recognizes,
‘‘inconclusive,’’ (71 FR 61193, October 17,
2006), the agency need not wait for
conclusive findings before regulating a
pollutant it reasonably believes may pose a
significant risk to public health. The
evidence in the record supports the EPA’s
cautious decision that ‘‘some protection from
exposure to thoracic coarse particles is
warranted in all areas.’’ Id. As the court has
consistently reaffirmed, the CAA permits the
Administrator to ‘‘err on the side of caution’’
in setting NAAQS. 559 F. 3d at 533.
The court also upheld the EPA’s
decision to retain the level of the
standard at 150 mg/m3 and to use PM10
as the indicator for thoracic coarse
particles. In upholding the level of the
standard, the court referred to the
conclusion in the Staff Paper that there
is ‘‘little basis for concluding that the
degree of protection afforded by the
current PM10 standards in urban areas is
greater than warranted, since potential
mortality effects have been associated
with air quality levels not allowed by
the current 24-hour standard, but have
not been associated with air quality
levels that would generally meet that
standard, and morbidity effects have
been associated with air quality levels
that exceeded the current 24-hour
standard only a few times.’’ 559 F. 3d
at 534. The court also rejected
arguments that a PM10 standard
established at an unvarying level will
result in arbitrarily varying levels of
protection given that the level of coarse
PM would vary based on the amount of
fine PM present. The court agreed that
the variation in allowable coarse PM
was in accord with the strength of the
evidence: Typically less coarse PM
would be allowed in urban areas (where
levels of fine PM are typically higher),
in accord with the strongest evidence of
health effects from coarse particles. 559
F. 3d at 535–36. In addition, such
regulation would not impermissibly
PO 00000
Frm 00082
Fmt 4701
Sfmt 4700
double regulate fine particles, since any
additional control of fine particles
(beyond that afforded by the primary
PM2.5 standard) would be for a different
purpose: To prevent contamination of
coarse particles by fine particles. 559 F.
3d at 535, 536. These same explanations
justified the choice of PM10 as an
indicator and provided the reasoned
explanation for that choice lacking in
the record for the 1997 standard. 559 F.
3d at 536.
With regard to the challenge from
environmental and public health
groups, the court upheld the EPA’s
decision to revoke the annual PM10
standard. The court rejected the
argument that the EPA is required by
law to have an annual PM10 standard,
holding that section 109(d)(1) of the Act
allows the EPA to revoke a standard no
longer warranted by the current
scientific understanding. 559 F. 3d at
538. The court further held that the
EPA’s decision to revoke the annual
standard was supported by the science:
The EPA reasonably decided that an
annual coarse PM standard is not necessary
because, as the Criteria Document and the
Staff Paper make clear, the latest scientific
data do not indicate that long-term exposure
to coarse particles poses a health risk. The
CASAC also agreed that an annual coarse PM
standard is unnecessary. 559 F. 3d at 538–39.
3. General Approach Used in the
Current Review
The approach taken to considering the
existing and potential alternative
primary PM10 standards in the current
review builds upon the approaches used
in previous PM NAAQS reviews. This
approach is based most fundamentally
on using information from
epidemiological studies and air quality
analyses to inform the identification of
a range of policy options for
consideration by the Administrator. The
Administrator considers the
appropriateness of the current and
potential alternative standards, taking
into account the four elements of the
NAAQS: Indicator, averaging time,
form, and level.
Evidence-based approaches to using
information from epidemiological
studies to inform decisions on PM
standards are complicated by the
recognition that no population
threshold, below which it can be
concluded with confidence that PMrelated effects do not occur, can be
discerned from the available evidence
(U.S. EPA, 2009a, sections 2.4.3 and
6.5.2.7).122 As a result, any approach to
122 Studies that have characterized the
concentration-response relationships for PM
exposures have evaluated PM10, which includes
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
reaching decisions on what standards
are appropriate requires judgments
about how to translate the information
available from the epidemiological
studies into a basis for appropriate
standards, which includes consideration
of how to weigh the uncertainties in
reported associations across the
distributions of PM concentrations in
the studies. The approach taken to
informing these decisions in the current
review recognizes that the available
health effects evidence reflects a
continuum consisting of ambient levels
at which scientists generally agree that
health effects are likely to occur through
lower levels at which the likelihood and
magnitude of the response become
increasingly uncertain. Such an
approach is consistent with setting
standards that are neither more nor less
stringent than necessary, recognizing
that a zero-risk standard is not required
by the CAA.
Because the purpose of the PM10
standard is to protect against exposures
to PM10-2.5, it is most appropriate to
focus on PM10-2.5 health studies when
considering the degree of public health
protection provided by the current PM10
standard. Compared to health studies of
PM10, studies that evaluate associations
with PM10-2.5 provide clearer evidence
for health effects following exposures to
thoracic coarse particles. In contrast, it
is difficult to interpret PM10 studies
within the context of a standard meant
to protect against exposures to PM10-2.5
because PM10 is comprised of both fine
and coarse particles, even in locations
with the highest concentrations of
PM10-2.5 (U.S. EPA, 2011a, Figure 3–4).
Therefore, the extent to which PM10
effect estimates reflect associations with
PM10-2.5 versus PM2.5 can be highly
uncertain. In light of this uncertainty, it
is preferable to consider PM10-2.5 studies
when such studies are available. Given
the availability in this review of a
number of studies that evaluated
associations with PM10-2.5, and given
that the Integrated Science Assessment
weight-of-evidence conclusions for
thoracic coarse particles were based on
studies of PM10-2.5, in this review the
EPA focuses primarily on studies that
have specifically evaluated PM10-2.5.123
As discussed in more detail in the
Risk Assessment (U.S. EPA, 2010a,
Appendix H), the EPA did not conduct
a quantitative assessment of health risks
associated with PM10-2.5. The Risk
both coarse and fine particles, and PM2.5 (U.S. EPA,
2009a, sections 2.4.3 and 6.5.2.7).
123 It should also be noted that CASAC endorsed
the approach adopted in the Integrated Science
Assessment, which draws weight-of-evidence
conclusions for PM2.5 and PM10-2.5, but not for PM10
(Samet, 2009f).
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
Assessment concluded that limitations
in the monitoring network and in the
health studies that rely on that
monitoring network, which would be
the basis for estimating PM10-2.5 health
risks, would introduce significant
uncertainty into a PM10-2.5 risk
assessment such that the risk estimates
generated would be of limited value in
informing review of the standard.
Therefore, it was judged that a
quantitative assessment of PM10-2.5 risks
is not supportable at this time (U.S.
EPA, 2010a, p. 2-6). This decision does
not indicate that health effects are not
associated with exposure to thoracic
coarse particles. Rather, as noted above,
it reflects the conclusion that limitations
in the available health studies and air
quality information would introduce
significant uncertainty into a
quantitative assessment of PM10-2.5 risks
such that the risk estimates generated
would be of limited value in informing
review of the standard.
B. Health Effects Related to Exposure to
Thoracic Coarse Particles
This section briefly outlines the key
information presented in section IV.B of
the proposal (77 FR 38947 to 38951,
June 29, 2012), and discussed more fully
in the Integrated Science Assessment
(U.S. EPA, 2009a, Chapters 2, 4, 5, 6, 7,
and 8) and the Policy Assessment (U.S.
EPA, 2011a, Chapter 3), related to health
effects associated with thoracic coarse
particle exposures. In looking across the
new scientific evidence available in this
review, our overall understanding of
health effects associated with thoracic
coarse particle exposures has been
expanded, though important
uncertainties remain. Some highlights of
the key policy-relevant scientific
evidence available in this review
include the following:
(1) A number of multi-city and single-city
epidemiological studies have evaluated
associations between short-term PM10-2.5 and
mortality, cardiovascular effects (e.g.,
including hospital admissions and
emergency department visits), and/or
respiratory effects. Despite differences in the
approaches used to estimate ambient PM10-2.5
concentrations, the majority of these studies
have reported positive, though often not
statistically significant, associations with
short-term PM10-2.5 concentrations. Most
PM10-2.5 effect estimates remained positive in
co-pollutant models that included either
gaseous or particulate co-pollutants. In U.S.
study locations likely to have met the current
PM10 standard during the study period, a few
PM10-2.5 effect estimates were statistically
significant and remained so in co-pollutant
models.124
124 The statistical significance of effect estimates
provides important information on their statistical
precision. However, when a group of studies report
PO 00000
Frm 00083
Fmt 4701
Sfmt 4700
3167
(2) A small number of controlled human
exposure studies have reported alterations in
heart rate variability or increased pulmonary
inflammation following short-term exposure
to PM10-2.5, providing some support for the
associations reported in epidemiological
studies. Toxicological studies that have
examined the effects of PM10-2.5 have used
intratracheal instillation and, because these
studies do not directly mirror any real-world
mode of exposure, they provide only limited
evidence for the biological plausibility of
PM10-2.5-induced effects.
(3) Using a more formal framework for
reaching causal determinations than used in
previous reviews, the Integrated Science
Assessment concluded that the existing
evidence is ‘‘suggestive’’ of a causal
relationship between short-term PM10-2.5
exposures and mortality, cardiovascular
effects, and respiratory effects (U.S. EPA,
2009a, section 2.3.3).125 In contrast, the
Integrated Science Assessment concluded
that available evidence is ‘‘inadequate’’ to
infer a causal relationship between long-term
PM10-2.5 exposures and various health effects.
(4) There are several at-risk populations
that may be especially susceptible or
vulnerable to PM-related effects, including
effects associated with exposures to coarse
particles. These groups include those with
preexisting heart and lung diseases, specific
genetic differences, and lower socioeconomic
status as well as the lifestages of childhood
and older adulthood. Evidence for PMrelated effects in these at-risk populations
has expanded and is stronger than previously
observed. There is emerging, though still
limited, evidence for additional potentially
at-risk populations, such as those with
diabetes, people who are obese, pregnant
women, and the developing fetus.
(5) The Integrated Science Assessment
concludes that currently available evidence
is insufficient to draw distinctions in particle
toxicity based on composition and notes that
recent studies have reported that PM (both
PM2.5 and PM10-2.5) from a variety of sources,
effect estimates that are similar in direction and
magnitude, such a pattern of results warrants
consideration of those studies even if not all
reported statistically significant associations in
single- or co-pollutant models (section III.D.2,
above). In considering the PM10-2.5 epidemiologic
studies below, the Administrator considers both the
pattern of results across studies and the statistical
significance of those results.
125 The causal framework draws upon the
assessment and integration of evidence from across
epidemiological, controlled human exposure, and
toxicological studies, and the related uncertainties
that ultimately influence our understanding of the
evidence. This framework employs a five-level
hierarchy that classifies the overall weight-ofevidence using the following categorizations:
Causal relationship, likely to be causal relationship,
suggestive of a causal relationship, inadequate to
infer a causal relationship, and not likely to be a
causal relationship (U.S. EPA, 2009a, Table 1–3). In
the case of a ‘‘suggestive’’ determination, ‘‘the
evidence is suggestive of a causal relationship with
relevant pollutant exposures, but is limited because
chance, bias and confounding cannot be ruled out.
For example, at least one high-quality
epidemiologic study shows an association with a
given health outcome but the results of other
studies are inconsistent’’ (U.S. EPA, 2009a, Table 1–
3).
E:\FR\FM\15JAR2.SGM
15JAR2
3168
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
including sources likely to be present in
urban and non-urban locations, is associated
with adverse health effects.
tkelley on DSK3SPTVN1PROD with
Although new PM10-2.5 scientific
studies have become available since the
last review and have expanded our
understanding of the association
between PM10-2.5 and adverse health
effects (see above and U.S. EPA, 2009a,
Chapter 6), important uncertainties
remain. These uncertainties, and their
implications for interpreting the
scientific evidence, include the
following:
(1) The potential for confounding by cooccurring pollutants, especially PM2.5, has
been addressed with co-pollutant models in
only a relatively small number of PM10-2.5
epidemiological studies (U.S. EPA, 2009a,
section 2.3.3). This is a particularly
important limitation given the relatively
small body of experimental evidence (i.e.,
controlled human exposure and animal
toxicological studies) available to support the
associations between PM10-2.5 and adverse
health effects. The net impact of such
limitations is to increase uncertainty in
characterizations of the extent to which
PM10-2.5 itself, rather than one or more cooccurring pollutants, is responsible for the
mortality and morbidity effects reported in
epidemiological studies.
(2) There is greater spatial variability in
PM10-2.5 concentrations than PM2.5
concentrations, resulting in increased
exposure error for PM10-2.5 (U.S. EPA, 2009a,
p. 2–8). Available measurements do not
provide sufficient information to adequately
characterize the spatial distribution of
PM10-2.5 concentrations (U.S. EPA, 2009a,
section 3.5.1.1). The net effect of these
uncertainties on PM10-2.5 epidemiological
studies is to bias the results of such studies
toward the null hypothesis. That is, as noted
in the Integrated Science Assessment, these
limitations in estimates of ambient PM10-2.5
concentrations ‘‘would tend to increase
uncertainty and make it more difficult to
detect effects of PM10-2.5 in epidemiologic
studies’’ (U.S. EPA, 2009a, p. 2–21).
(3) Only a relatively small number of
PM10-2.5 monitoring sites are currently
operating and such sites have been in
operation for a relatively short period of time,
limiting the spatial and temporal coverage for
routine measurement of PM10-2.5
concentrations. Given these limitations in
routine monitoring, epidemiological studies
have employed different approaches for
estimating PM10-2.5 concentrations. Given the
relatively small number of PM10-2.5
monitoring sites, the relatively large spatial
variability in ambient PM10-2.5 concentrations
(see above), the use of different approaches
to estimating ambient PM10-2.5 concentrations
across epidemiological studies, and the
limitations inherent in such estimates, the
distributions of thoracic coarse particle
concentrations over which reported health
outcomes occur remain highly uncertain
(U.S. EPA, 2009a, sections 2.2.3, 2.3.3, 2.3.4,
and 3.5.1.1).
(4) There is relatively little information on
the chemical and biological composition of
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
PM10-2.5 and the effects associated with the
various components (U.S. EPA, 2009a,
section 2.3.4). Without more information on
the chemical speciation of PM10-2.5, the
apparent variability in associations with
health effects across locations is difficult to
characterize (U.S. EPA, 2009a, section
6.5.2.3).
(5) One of the implications of the
uncertainties and limitations discussed above
is that the Risk Assessment concluded it
would not be appropriate to conduct a
quantitative assessment of health risks
associated with PM10-2.5. The lack of a
quantitative PM10-2.5 risk assessment in the
current review adds to the uncertainty in any
conclusions about the extent to which
revision of the current PM10 standard would
be expected to improve the protection of
public health, beyond the protection
provided by the current standard.126
C. Consideration of the Current and
Potential Alternative Standards in the
Policy Assessment
The following sections discuss the
Policy Assessment’s consideration of
the current and potential alternative
standards to protect against exposures to
thoracic coarse particles (U.S. EPA,
2011a, chapter 3). Section IV.C.1
discusses the consideration of the
current standard while section IV.C.2
discusses the consideration of potential
alternative standards in terms of the
basic elements of a standard: Indicator,
averaging time, form, and level.
1. Consideration of the Current Standard
in the Policy Assessment
As discussed above the 24-hour PM10
standard is meant to protect the public
health against exposures to thoracic
coarse particles (i.e., PM10-2.5). In
considering the adequacy of the current
PM10 standard, the Policy Assessment
considered the health effects evidence
linking short-term PM10-2.5 exposures
with mortality and morbidity (U.S. EPA,
2009a, chapters 2 and 6), the ambient
PM10 concentrations in PM10-2.5 study
locations (U.S. EPA, 2011a, section
3.2.1), the uncertainties and limitations
associated with this health evidence
(U.S. EPA, 2011a, section 3.2.1), and the
consideration of these uncertainties and
limitations as part of the weight of
evidence conclusions in the Integrated
Science Assessment (U.S. EPA, 2009a).
In considering the health evidence, air
quality information, and associated
uncertainties as they relate to the
current PM10 standard, the Policy
Assessment noted that a decision on the
adequacy of the public health protection
126 As noted above, the EPA’s decision not to
conduct a quantitative risk assessment reflects
uncertainty regarding the value of such an
assessment, but does not indicate that health effects
are not associated with exposure to thoracic coarse
particles.
PO 00000
Frm 00084
Fmt 4701
Sfmt 4700
provided by that standard is a public
health policy judgment in which the
Administrator weighs the evidence and
information, as well as its uncertainties.
Therefore, depending on the emphasis
placed on different aspects of the
evidence, information, and
uncertainties, consideration of different
conclusions on the adequacy of the
current standard could be supported.
For example, the Policy Assessment
noted that one approach to considering
the evidence, information, and its
associated uncertainties would be to
place emphasis on the following (U.S.
EPA, 2011a, section 3.2.3):
(1) While most of PM10-2.5 effect estimates
reported for mortality and morbidity were
positive, many were not statistically
significant, even in single-pollutant models.
This includes effect estimates reported in
study locations with PM10 concentrations
above those allowed by the current 24-hour
PM10 standard.
(2) The number of epidemiological studies
that have employed co-pollutant models to
address the potential for confounding,
particularly by PM2.5, remains limited.
Therefore, the extent to which PM10-2.5 itself,
rather than one or more co-pollutants,
contributes to reported health effects remains
uncertain.
(3) Only a limited number of experimental
studies provide support for the associations
reported in epidemiological studies, resulting
in further uncertainty regarding the
plausibility of a causal link between PM10-2.5
and mortality and morbidity.
(4) Limitations in PM10-2.5 monitoring and
the different approaches used to estimate
PM10-2.5 concentrations across
epidemiological studies result in uncertainty
as to the ambient PM10-2.5 concentrations at
which the reported effects occur.
(5) The chemical and biological
composition of PM10-2.5, and the effects
associated with the various components,
remains uncertain. Without more information
on the chemical speciation of PM10-2.5, the
apparent variability in associations across
locations is difficult to interpret.
(6) In considering the available evidence
and its associated uncertainties, the
Integrated Science Assessment concluded
that the evidence is ‘‘suggestive’’ of a causal
relationship between short-term PM10-2.5
exposures and mortality, cardiovascular
effects, and respiratory effects. These weightof-evidence conclusions contrast with those
for the relationships between PM2.5
exposures and adverse health effects, which
were judged in the Integrated Science
Assessment to be either ‘‘causal’’ or ‘‘likely
causal’’ for mortality, cardiovascular effects,
and respiratory effects.
The Policy Assessment concluded
that, to the extent a decision on the
adequacy of the current 24-hour PM10
standard were to place emphasis on the
considerations noted above, it could be
judged that, although it remains
appropriate to maintain a standard to
protect against short-term exposures to
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
thoracic coarse particles, the available
evidence suggests that the current 24hour PM10 standard appropriately
protects public health and provides an
adequate margin of safety against effects
that have been associated with PM10-2.5
exposures. Although such an approach
to considering the adequacy of the
current standard would recognize the
positive, and in some cases statistically
significant, associations between all
types of PM10-2.5 and mortality and
morbidity, it would place relatively
greater emphasis on the limitations and
uncertainties noted above, which tend
to complicate the interpretation of that
evidence.
In addition, the Policy Assessment
noted the judgment that, given the
uncertainties and limitations in the
PM10-2.5 health evidence and air quality
information, it would not have been
appropriate to conduct a quantitative
assessment of health risks associated
with PM10-2.5 (U.S. EPA, 2011a, p. 3–6;
U.S. EPA, 2010a, pp. 2–6 to 2–7,
Appendix H). As discussed above, the
lack of a quantitative PM10-2.5 risk
assessment adds to the uncertainty
associated with any characterization of
potential public health improvements
that would be realized with a revised
standard.
The Policy Assessment also noted an
alternative approach to considering the
evidence and its uncertainties would
place emphasis on the following (U.S.
EPA, 2011a, section 3.2.3):
(1) Several multi-city epidemiological
studies conducted in the U.S., Canada, and
Europe, as well as a number of single-city
studies, have reported generally positive, and
in some cases statistically significant,
associations between short-term PM10-2.5
concentrations and adverse health endpoints
including mortality and cardiovascularrelated and respiratory-related hospital
admissions and emergency department visits.
(2) Both single-city and multi-city analyses,
using different approaches to estimate
ambient PM10-2.5 concentrations, have
reported positive PM10-2.5 effect estimates in
locations that would likely have met the
current 24-hour PM10 standard. In a few
cases, these PM10-2.5 effect estimates were
statistically significant.
(3) While limited in number, studies that
have evaluated co-pollutant models have
generally reported that PM10-2.5 effect
estimates remain positive, and in a few cases
statistically significant, when these models
include gaseous pollutants or fine particles.
(4) Support for the plausibility of the
associations reported in epidemiological
studies is provided by a small number of
controlled human exposure studies reporting
that short-term (i.e., 2-hour) exposures to
PM10-2.5 decrease heart rate variability and
increase markers of pulmonary inflammation.
This approach to considering the
health evidence, air quality information,
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
and the associated uncertainties would
place substantial weight on the
generally positive PM10-2.5 effect
estimates that have been reported for
mortality and morbidity, even those
effect estimates that are not statistically
significant. The Policy Assessment
concluded that this could be judged
appropriate given that consistent results
have been reported across multiple
studies using different approaches to
estimate ambient PM10-2.5
concentrations and that exposure
measurement error, which is likely to be
larger for PM10-2.5 than for PM2.5, tends
to bias the results of epidemiological
studies toward the null hypothesis,
making it less likely that associations
will be detected. Such an approach
would place less weight on the
uncertainties and limitations in the
evidence that resulted in the Integrated
Science Assessment conclusions that
the evidence is only suggestive of a
causal relationship.
Given all of the above, the Policy
Assessment concluded that it would be
appropriate to consider either retaining
or revising the current 24-hour PM10
standard, depending on the approach
taken to considering the available
evidence, air quality information, and
the uncertainties and limitations
associated with that evidence and
information (U.S. EPA, 2011a, section
3.2.3).
2. Consideration of Potential Alternative
Standards in the Policy Assessment
Given the conclusion that it would be
appropriate to consider either retaining
or revising the current PM10 standard,
the Policy Assessment also considered
what potential alternative standards, if
any, could be supported by the available
scientific evidence in order to increase
public health protection against
exposures to PM10-2.5. The Policy
Assessment considered such potential
alternative standards defined in terms of
the elements of a standard (i.e.,
indicator, averaging time, form, and
level). Key conclusions from the Policy
Assessment regarding indicator,
averaging time, and form included the
following:
(1) A PM10 indicator would continue to
appropriately target protection against
thoracic coarse particle exposures to those
locations where the evidence is strongest for
associations with adverse health effects (i.e.,
urban areas).
(2) The available evidence supports the
importance of maintaining a standard that
protects against short-term exposures to all
thoracic coarse particles. Given that the
majority of this evidence is based on 24-hour
average thoracic coarse particle
concentrations, consideration of a 24-hour
averaging time remains appropriate.
PO 00000
Frm 00085
Fmt 4701
Sfmt 4700
3169
(3) Given the limited body of evidence
supporting PM10-2.5-related effects following
long-term exposures, which resulted in the
Integrated Science Assessment conclusion
that the available evidence is ‘‘inadequate’’ to
infer a causal relationship between long-term
PM10-2.5 exposures and a variety of health
effects, consideration of an annual thoracic
coarse particle standard is not supported at
this time.
(4) To the extent it is judged appropriate
to revise the current 24-hour PM10 standard,
it would be appropriate to consider revising
the form to the 3-year average of the 98th
percentile of the annual distribution of 24hour PM10 concentrations.
In considering the available evidence
and air quality information within the
context of identifying potential
alternative standard levels for
consideration (assuming a decision were
made that it is appropriate to amend the
standard), the Policy Assessment first
noted that a standard level as high as
about 85 mg/m3, for a 24-hour PM10
standard with a 98th percentile form,
could be supported. Based on
considering air quality concentrations in
study locations, the Policy Assessment
noted that such a standard level would
be expected to maintain PM10 and
PM10-2.5 concentrations below those
present in U.S. locations of single-city
studies where PM10-2.5 effect estimates
have been reported to be positive and
statistically significant and below those
present in some locations where singlecity studies reported PM10-2.5 effect
estimates that were positive, but not
statistically significant. These include
some locations likely to have met the
current PM10 standard during the study
periods (U.S. EPA, 2011a, section 3.3.4).
The Policy Assessment also noted
that, based on analysis of the number of
people living in counties that could
violate the current and potential
alternative PM10 standards, a 24-hour
PM10 standard with a 98th percentile
form and a level between 75 and 80 mg/
m3 would provide a level of public
health protection that is generally
equivalent, across the U.S., to that
provided by the current standard. Given
this, the Policy Assessment concluded
that it would be appropriate to consider
standard levels in the range of
approximately 75 to 80 mg/m3 (with a
98th percentile form), to the extent
population counts were emphasized in
comparing the public health protection
provided by the current and potential
alternative standards and to the extent
it was judged appropriate to set a
revised standard providing at least the
level of public health protection that is
provided by the current standard, based
on such population counts (U.S. EPA,
2011a, section 3.3.4).
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
3170
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
The Policy Assessment also
concluded that alternative approaches
to considering the evidence could lead
to consideration of standard levels
below 75 mg/m3 for a standard with a
98th percentile form. For example, a
number of single-city epidemiological
studies have reported positive, though
not statistically significant, PM10-2.5
effect estimates in locations with 98th
percentile PM10 concentrations below
75 mg/m3. Given that exposure error is
particularly important for PM10-2.5
epidemiological studies and can bias the
results of these studies toward the null
hypothesis (see section IV.B above), the
Policy Assessment noted that it could be
judged appropriate to place more weight
on positive associations reported in
these epidemiological studies, even
when those associations are not
statistically significant. In addition, the
Policy Assessment noted that multi-city
averages of 98th percentile PM10
concentrations in the locations
evaluated by U.S. multi-city studies of
thoracic coarse particles (Zanobetti and
Schwartz, 2009; Peng et al., 2008) were
near or below 75 ppb. Despite
uncertainties in the extent to which
effects reported in multi-city studies are
associated with the short-term air
quality in any particular location, the
Policy Assessment noted that emphasis
could be placed on these multi-city
averaged concentrations. The Policy
Assessment concluded that, to the
extent more weight is placed on singlecity studies reporting positive, but not
statistically significant, PM10-2.5 effect
estimates and on multi-city studies, it
could be appropriate to consider
standard levels as low as 65 mg/m3 with
a 98th percentile form (U.S. EPA, 2011a,
section 3.3.4).
In considering potential alternative
standard levels below 65 mg/m3, the
Policy Assessment noted that the overall
body of PM10-2.5 health evidence is
relatively uncertain, with somewhat
stronger support in U.S. studies for
associations with PM10-2.5 in locations
with 98th percentile PM10
concentrations above 85 mg/m3 than in
locations with 98th percentile PM10
concentrations below 65 mg/m3. In light
of the limitations in the evidence for a
relationship between PM10-2.5 and
adverse health effects in locations with
relatively low PM10 concentrations,
along with the overall uncertainties in
the body of PM10-2.5 health evidence as
described above and in the Integrated
Science Assessment, the Policy
Assessment concluded that
consideration of standard levels below
65 mg/m3 was not appropriate (U.S.
EPA, 2011a, section 3.3.4).
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
D. CASAC Advice
Following their review of the first and
second draft Policy Assessments,
CASAC provided advice and
recommendations regarding the current
and potential alternative standards for
thoracic coarse particles (Samet,
2010c,d). With regard to the existing
PM10 standard, CASAC concluded that
‘‘the current data, while limited, is
sufficient to call into question the level
of protection afforded the American
people by the current standard’’ (Samet,
2010d, p. 7). In drawing this conclusion,
CASAC noted the positive associations
in multi-city and single-city studies,
including in locations with PM10
concentrations below those allowed by
the current standard. In addition,
CASAC gave ‘‘significant weight to
studies that have generally reported that
PM10-2.5 effect estimates remain positive
when evaluated in co-pollutant models’’
and concluded that ‘‘controlled human
exposure PM10-2.5 studies showing
decreases in heart rate variability and
increases in markers of pulmonary
inflammation are deemed adequate to
support the plausibility of the
associations reported in epidemiologic
studies’’ (Samet, 2010d, p. 7).127 Given
all of the above conclusions CASAC
recommended that ‘‘the primary
standard for PM10 should be revised’’
(Samet, 2010d, p. ii and p. 7). In
discussing potential revisions, while
CASAC noted that the scientific
evidence supports adoption of a
standard at least as stringent as the
current standard, they recommended
revising the current standard in order to
increase public health protection. In
considering potential alternative
standards, CASAC drew conclusions
and made recommendations in terms of
the major elements of a standard:
indicator, averaging time, form, and
level.
The CASAC agreed with the EPA
staff’s conclusions that the available
evidence supports consideration in the
current review of retaining the current
PM10 indicator and the current 24-hour
averaging time (Samet, 2010c, Samet,
2010d). Specifically, with regard to
indicator, CASAC concluded that
‘‘[w]hile it would be preferable to use an
indicator that reflects the coarse PM
directly linked to health risks (PM10-2.5),
CASAC recognizes that there is not yet
sufficient data to permit a change in the
indicator from PM10 to one that directly
127 Nonetheless, CASAC endorsed the Integrated
Science Assessment weight of evidence conclusions
for PM10-2.5 (i.e., that the evidence is only
‘‘suggestive’’ of a causal relationship between shortterm exposures and mortality, respiratory effects,
and cardiovascular effects) (Samet, 2009e; Samet,
2009f).
PO 00000
Frm 00086
Fmt 4701
Sfmt 4700
measures thoracic coarse particles’’
(Samet, 2010d, p. ii). In addition,
CASAC ‘‘vigorously recommends the
implementation of plans for the
deployment of a network of PM10-2.5
sampling systems so that future
epidemiological studies will be able to
more thoroughly explore the use of
PM10-2.5 as a more appropriate indicator
for thoracic coarse particles’’ (Samet,
2010d, p. 7).
The CASAC also agreed that the
evidence supports consideration of a
potential alternative form. Specifically,
CASAC ‘‘felt strongly that it is
appropriate to change the statistical
form of the PM10 standard to a 98th
percentile’’ (Samet, 2010d, p.7). In
reaching this conclusion, CASAC noted
that ‘‘[p]ublished work has shown that
the percentile form has greater power to
identify non-attainment and a smaller
probability of misclassification relative
to the expected exceedance form of the
standard’’ (Samet, 2010d. p. 7).
With regard to standard level, in
conjunction with a 98th percentile form,
CASAC concluded that ‘‘alternative
standard levels of 85 and 65 mg/m3
(based on consideration of 98th
percentile PM10 concentration) could be
justified’’ (Samet, 2010d, p.8). However,
in considering the evidence and
uncertainties, CASAC recommended a
standard level from the lower part of the
range discussed in the Policy
Assessment, recommending a level
‘‘somewhere in the range of 75 to 65 mg/
m3’’ (Samet, 2010d, p. ii).
In making this recommendation,
CASAC noted that the number of people
living in counties with air quality not
meeting the current standard is
approximately equal to the number
living in counties that would not meet
a 98th percentile standard with a level
between 75 and 80 mg/m3. CASAC used
this information as the basis for their
conclusion that a 98th percentile
standard between 75 and 80 mg/m3
would be ‘‘comparable to the degree of
protection afforded to the current PM10
standard’’ (Samet, 2010d, p. ii). Given
this conclusion regarding the
comparability of the current and
potential alternative standards, as well
as their conclusion on the public health
protection provided by the current
standard (i.e., that available evidence is
sufficient to call it into question),
CASAC recommended a level within a
range of 75 to 65 mg/m3 in order to
increase public health protection,
relative to that provided by the current
standard (Samet 2010d, p. ii).
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
E. Administrator’s Proposed
Conclusions Concerning the Adequacy
of the Current Primary PM10 Standard
In considering the evidence and
information as they relate to the
adequacy of the current 24-hour PM10
standard, the Administrator first noted
in the proposal that this standard is
meant to protect the public health
against effects associated with shortterm exposures to PM10-2.5. In the last
review, it was judged appropriate to
maintain such a standard given the
‘‘growing body of evidence suggesting
causal associations between short-term
exposure to thoracic coarse particles
and morbidity effects, such as
respiratory symptoms and hospital
admissions for respiratory diseases, and
possibly mortality’’ (71 FR 61185,
October 17, 2006). Given the continued
expansion in the body of scientific
evidence linking short-term PM10-2.5 to
health outcomes such as premature
death and hospital visits, discussed in
detail in the Integrated Science
Assessment (U.S. EPA, 2009a, Chapter
6) and summarized in the proposal, the
Administrator provisionally concluded
that the available evidence continued to
support the appropriateness of
maintaining a standard to protect the
public health against effects associated
with short-term (e.g., 24-hour)
exposures to all PM10-2.5. In drawing
provisional conclusions in the proposal
as to whether the current PM10 standard
remains requisite (i.e., neither more nor
less stringent than necessary) to protect
public health with an adequate margin
of safety against such exposures, the
Administrator considered the following:
tkelley on DSK3SPTVN1PROD with
(1) The extent to which it is appropriate to
maintain a standard that provides some
measure of protection against all PM10-2.5,
regardless of composition or source of origin;
(2) The extent to which it is appropriate to
retain a PM10 indicator for a standard meant
to protect against exposures to ambient
PM10-2.5; and
(3) The extent to which the current PM10
standard provides an appropriate degree of
public health protection.
With regard to the first point, the
proposal noted the conclusion from the
last review that dosimetric,
toxicological, occupational, and
epidemiological evidence supported
retention of a primary standard to
provide some measure of protection
against short-term exposures to all
thoracic coarse particles, regardless of
their source of origin or location,
consistent with the Act’s requirement
that primary NAAQS provide requisite
protection with an adequate margin of
safety (71 FR 61197). In that review, the
EPA concluded that PM from a number
of source types, including motor vehicle
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
emissions, coal combustion, oil burning,
and vegetative burning, are associated
with health effects (U.S. EPA, 2004).
This information formed part of the
basis for the D.C. Circuit’s holding that
it was appropriate for the thoracic
coarse particle standard to provide
‘‘some protection from exposure to
thoracic coarse particles * * * in all
areas’’ (American Farm Bureau
Federation v. EPA, 559 F. 3d at 532–33).
In considering this issue in the
proposal, the Administrator judged that
the expanded body of scientific
evidence in this review provides even
more support for a standard that
protects against exposures to all thoracic
coarse particles, regardless of their
location or source of origin. Specifically,
the Administrator noted that
epidemiological studies have reported
positive associations between PM10-2.5
and mortality or morbidity in a large
number of cities across North America,
Europe, and Asia, encompassing a
variety of environments where PM10-2.5
sources and composition are expected to
vary widely. See 77 FR 38959. In
considering this evidence, the Integrated
Science Assessment concluded that
‘‘many constituents of PM can be linked
with differing health effects’’ (U.S. EPA,
2009a, p. 2–26). While PM10-2.5 in most
of these study areas is of largely urban
origin, the Administrator noted that
some recent studies have also linked
mortality and morbidity with relatively
high ambient concentrations of thoracic
coarse particles of non-urban crustal
origin. In considering these studies, she
noted the Integrated Science
Assessment’s conclusion that ‘‘PM (both
PM2.5 and PM10-2.5) from crustal, soil or
road dust sources or PM tracers linked
to these sources are associated with
cardiovascular effects’’ (U.S. EPA,
2009a, p. 2–26).
In light of this body of available
evidence reporting PM10-2.5-associated
health effects across different locations
with a variety of sources, as well as the
Integrated Science Assessment’s
conclusions regarding the links between
adverse health effects and PM sources
and composition, the Administrator
provisionally concluded in the proposal
that it is appropriate to maintain a
standard that provides some measure of
protection against exposures to all
thoracic coarse particles, regardless of
their location, source of origin, or
composition (77 FR 38959–60).
With regard to the second point, in
considering the appropriateness of a
PM10 indicator for a standard meant to
provide such public health protection,
the Administrator noted that the
rationale used in the last review to
support the unqualified PM10 indicator
PO 00000
Frm 00087
Fmt 4701
Sfmt 4700
3171
(see above) remains relevant in the
current review. Specifically, as an initial
consideration, she noted that PM10 mass
includes both coarse PM (PM10-2.5) and
fine PM (PM2.5). As a result, the
concentration of PM10-2.5 allowed by a
PM10 standard set at a single level
declines as the concentration of PM2.5
increases. At the same time, the
Administrator noted that PM2.5
concentrations tend to be higher in
urban areas than in rural areas (U.S.
EPA, 2005, p. 2–54, and Figures 2–23
and 2–24) and, therefore, a PM10
standard will generally allow lower
PM10-2.5 concentrations in urban areas
than in rural areas. 77 FR 38960.
In considering the appropriateness of
this variation in allowable PM10-2.5
concentrations, the Administrator
considered the relative strength of the
evidence for health effects associated
with PM10-2.5 of urban origin versus nonurban origin. She specifically noted
that, as described above and similar to
the scientific evidence available in the
last review, the large majority of the
available evidence for thoracic coarse
particle health effects comes from
studies conducted in locations with
sources more typical of urban and
industrial areas than of rural areas.
Although as just noted, associations
with adverse health effects have been
reported in some study locations where
PM10-2.5 is largely non-urban in origin
(i.e., in dust storm studies), particle
concentrations in these study areas are
typically much higher than reported in
study locations where the PM10-2.5 is of
urban origin. Therefore, the
Administrator noted that the strongest
evidence for a link between PM10-2.5 and
adverse health impacts, particularly for
such a link at relatively low particle
concentrations, comes from studies
where exposure is to PM10-2.5 of urban
or industrial origin. 77 FR 38960.
The Administrator also noted that
chemical constituents present at higher
levels in urban or industrial areas,
including byproducts of incomplete
combustion (e.g. polycyclic aromatic
hydrocarbons) emitted as PM2.5 from
motor vehicles as well as metals and
other contaminants emitted from
anthropogenic sources, can contaminate
PM10-2.5 (U.S. EPA, 2004, p. 8–344; 71
FR 2665). While the Administrator
acknowledged the uncertainty
expressed in the Integrated Science
Assessment regarding the extent to
which, based on available evidence,
particle composition can be linked to
health outcomes, she also considered
the possibility that PM10-2.5
contaminants typical of urban or
industrial areas could increase the
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
3172
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
toxicity of thoracic coarse particles in
urban locations (77 FR 38960).
Given that the large majority of the
evidence for PM10-2.5 toxicity,
particularly at relatively low particle
concentrations, comes from study
locations where thoracic coarse particles
are of urban origin, and given the
possibility that PM10-2.5 contaminants in
urban areas could increase particle
toxicity, the Administrator provisionally
concluded in the proposal that it
remains appropriate to maintain a
standard that targets public health
protection to urban locations.
Specifically, she concluded at proposal
that it is appropriate to maintain a
standard that allows lower ambient
concentrations of PM10-2.5 in urban
areas, where the evidence is strongest
that thoracic coarse particles are linked
to mortality and morbidity, and higher
concentrations in non-urban areas,
where the public health concerns are
less certain. Id.
Given all of the above considerations
and conclusions, the Administrator
judged that the available evidence
supported retaining a PM10 indicator for
a standard that is meant to protect
against exposure to thoracic coarse
particles. In reaching this initial
judgment, she noted that, to the extent
a PM10 indicator results in lower
allowable concentrations of thoracic
coarse particles in some areas compared
to others, lower concentrations will be
allowed in those locations (i.e., urban or
industrial areas) where the science has
shown the strongest evidence of adverse
health effects associated with exposure
to thoracic coarse particles and where
we have the most concern regarding
PM10-2.5 toxicity. Therefore, the
Administrator provisionally concluded
that the varying amounts of coarse
particles that are allowed in urban vs.
non-urban areas under the 24-hour PM10
standard, based on the varying levels of
PM2.5 present, appropriately reflect the
differences in the strength of evidence
regarding coarse particle effects in urban
and non-urban areas (77 FR 38960).
In reaching this provisional
conclusion, the Administrator also
noted that, in their review of the second
draft Policy Assessment, CASAC
concluded that ‘‘[w]hile it would be
preferable to use an indicator that
reflects the coarse PM directly linked to
health risks (PM10-2.5), CASAC
recognizes that there is not yet sufficient
data to permit a change in the indicator
from PM10 to one that directly measures
thoracic coarse particles’’ (Samet,
2010d, p. ii). In addition, CASAC
‘‘vigorously recommends the
implementation of plans for the
deployment of a network of PM10-2.5
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
sampling systems so that future
epidemiological studies will be able to
more thoroughly explore the use of
PM10-2.5 as a more appropriate indicator
for thoracic coarse particles’’ (Samet,
2010d, p. 7). Given this
recommendation, the Administrator
further judged that, although current
evidence is not sufficient to identify a
standard based on an alternative
indicator that would be requisite to
protect public health with an adequate
margin of safety across the United
States, consideration of alternative
indicators (e.g., PM10-2.5) in future
reviews is desirable and could be
informed by additional research, as
described in the Policy Assessment
(U.S. EPA, 2011a, section 3.5).
With regard to the third point, in
evaluating the degree of public health
protection provided by the current PM10
standard, the Administrator noted that
the Policy Assessment discussed two
different approaches to considering the
scientific evidence and air quality
information (U.S. EPA, 2011a, section
3.2.3). These different approaches,
which are described above (section
IV.C.1), lead to different conclusions
regarding the appropriateness of the
degree of public health protection
provided by the current PM10 standard.
The Administrator further noted that the
primary difference between the two
approaches lies in the extent to which
weight is placed on the following (U.S.
EPA, 2011a, section 3.2.3):
(1) The PM10-2.5 weight-of-evidence
classifications presented in the Integrated
Science Assessment concluding that the
existing evidence is suggestive of a causal
relationship between short-term PM10-2.5
exposures and mortality, cardiovascular
effects, and respiratory effects (a
classification supported by CASAC);
(2) Individual PM10-2.5 epidemiological
studies reporting associations in locations
that meet the current PM10 standard,
including associations that are not
statistically significant;
(3) The limited number of PM10-2.5
epidemiological studies that have evaluated
co-pollutant models;
(4) The limited number of PM10-2.5
controlled human exposure studies;
(5) Uncertainties in the PM10-2.5 air quality
concentrations reported in epidemiological
studies, given limitations in PM10-2.5
monitoring data and the different approaches
used across studies to estimate ambient
PM10-2.5 concentrations; and
(6) Uncertainties and limitations in the
evidence that tend to call into question the
presence of a causal relationship between
PM10-2.5 exposures and mortality/morbidity.
In evaluating the different possible
approaches to considering the public
health protection provided by the
current PM10 standard, the
Administrator first noted that when the
PO 00000
Frm 00088
Fmt 4701
Sfmt 4700
available PM10-2.5 scientific evidence
and its associated uncertainties are
considered, the Integrated Science
Assessment concluded that the evidence
is suggestive of a causal relationship
between short-term PM10-2.5 exposures
and mortality, cardiovascular effects,
and respiratory effects. As discussed in
section IV.B.1 above and in more detail
in the Integrated Science Assessment
(U.S. EPA, 2009a, section 1.5), a
suggestive determination is made when
the ‘‘[e]vidence is suggestive of a causal
relationship with relevant pollutant
exposures, but is limited because
chance, bias and confounding cannot be
ruled out.’’ In contrast, the
Administrator noted that she proposed
to strengthen the annual fine particle
standard based on a body of scientific
evidence judged sufficient to conclude
that a causal relationship exists (i.e.,
mortality, cardiovascular effects) or is
likely to exist (i.e., respiratory effects)
(section III.B). 77 FR 38961. The
suggestive judgment for PM10-2.5 reflects
the greater degree of uncertainty
associated with this body of evidence,
as discussed above (sections IV.B and
IV.C) and summarized below.
In the proposal (77 FR 38961), the
Administrator noted that the important
uncertainties and limitations associated
with the scientific evidence and air
quality information raise questions as to
whether public health benefits would be
achieved by revising the existing PM10
standard. Such uncertainties and
limitations include the following:
(1) While PM10-2.5 effect estimates reported
for mortality and morbidity were generally
positive, most were not statistically
significant, even in single-pollutant models.
This includes effect estimates reported in
some study locations with PM10
concentrations above those allowed by the
current 24-hour PM10 standard.
(2) The number of epidemiological studies
that have employed co-pollutant models to
address the potential for confounding,
particularly by PM2.5, remains limited.
Therefore, the extent to which PM10-2.5 itself,
rather than one or more co-pollutants,
contributes to reported health effects is less
certain.
(3) Only a limited number of experimental
studies (i.e., controlled human exposure and
animal toxicological) provide support for the
associations reported in epidemiological
studies, resulting in further uncertainty
regarding the plausibility of the associations
between PM10-2.5 and mortality and morbidity
reported in epidemiological studies.
(4) Limitations in PM10-2.5 monitoring data
and the different approaches used by
epidemiological study researchers to estimate
PM10-2.5 concentrations across
epidemiological studies result in uncertainty
in the ambient PM10-2.5 concentrations at
which the reported effects occur, increasing
uncertainty in estimates of the extent to
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
which changes in ambient PM10-2.5
concentrations would likely impact public
health.
(5) The lack of a quantitative PM10-2.5 risk
assessment further contributes to uncertainty
regarding the extent to which any revisions
to the current PM10 standard would be
expected to improve the protection of public
health, beyond the protection provided by
the current standard (see section III.B.5
above).
(6) The chemical and biological
composition of PM10-2.5, and the effects
associated with the various components,
remains uncertain. Without more information
on the chemical speciation of PM10-2.5, the
apparent variability in associations across
locations is difficult to interpret.
In considering these uncertainties and
limitations, the Administrator noted in
particular the considerable degree of
uncertainty in the extent to which
health effects reported in
epidemiological studies are due to
PM10-2.5 itself, as opposed to one or
more co-occurring pollutants. As
discussed above, this uncertainty
reflects the fact that there are a
relatively small number of PM10-2.5
studies that have utilized co-pollutant
models, particularly co-pollutant
models that have included PM2.5, and a
very limited body of controlled human
exposure evidence supporting the
biological plausibility of a causal
relationship between PM10-2.5 and
mortality and morbidity at ambient
concentrations. The Administrator
noted that these important limitations in
the overall body of health evidence
introduce uncertainty into the
interpretation of individual
epidemiological studies, particularly
those studies reporting associations
with PM10-2.5 that are not statistically
significant. Given this, the
Administrator reached the provisional
conclusion in the proposal that it is
appropriate to place relatively little
weight on epidemiological studies
reporting associations with PM10-2.5 that
are not statistically significant in singlepollutant and/or co-pollutant models.
Id.
With regard to this provisional
conclusion, the Administrator noted
that, for single-city mortality studies
conducted in the United States where
ambient PM10 concentration data were
available for comparison to the current
standard, positive and statistically
significant PM10-2.5 effect estimates were
only reported in study locations that
would likely have violated the current
PM10 standard during the study period
(U.S. EPA, 2011a, Figure 3–2). In U.S.
study locations that would likely have
met the current standard, PM10-2.5 effect
estimates for mortality were positive,
but not statistically significant (U.S.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
EPA, 2011a, Figure 3–2). In considering
U.S. study loc‘ations where single-city
morbidity studies were conducted, and
which would likely have met the
current PM10 standard during the study
period, the Administrator noted that
PM10-2.5 effect estimates were both
positive and negative, with most not
statistically significant (U.S. EPA,
2011a, Figure 3–3).
In addition, in considering single-city
analyses for the locations evaluated in a
large U.S. multi-city mortality study
(Zanobetti and Schwartz, 2009), the
Administrator noted that associations in
most of the study locations were not
statistically significant and that this was
the only study to estimate ambient
PM10-2.5 concentrations as the difference
between county-wide PM10 and PM2.5
mass. As discussed in the Policy
Assessment and in the proposal, it is not
clear how computed PM10-2.5
measurements, such as those used by
Zanobetti and Schwartz (2009), compare
with the PM10-2.5 concentrations
obtained in other studies either by
direct measurement or by calculating
the difference using co-located samplers
(U.S. EPA, 2009a, section 6.5.2.3). For
these reasons, in the proposal the
Administrator noted that ‘‘there is
considerable uncertainty in interpreting
the associations in these single-city
analyses’’ (77 FR 38961–62).
The Administrator acknowledged that
an approach to considering the available
scientific evidence and air quality
information that emphasizes the above
considerations differs from the approach
taken by CASAC. Specifically, in its
review of the draft Policy Assessment
CASAC placed a substantial amount of
weight on individual studies,
particularly those reporting positive
health effects associations for PM10-2.5 in
locations that met the current PM10
standard during the study period. In
emphasizing these studies, as well as
the limited number of supporting
studies that have evaluated co-pollutant
models and the small number of
supporting experimental studies,
CASAC concluded that ‘‘the current
data, while limited, is sufficient to call
into question the level of protection
afforded the American people by the
current standard’’ (Samet, 2010d, p. 7)
and recommended revising the current
PM10 standard (Samet, 2010d).
The Administrator carefully
considered CASAC’s advice and
recommendations. She noted that in
making its recommendation on the
current PM10 standard, CASAC did not
discuss its approach to considering the
important uncertainties and limitations
in the health evidence, and did not
discuss how these uncertainties and
PO 00000
Frm 00089
Fmt 4701
Sfmt 4700
3173
limitations were reflected in its
recommendation. Nor did CASAC
discuss uncertainties in the reported
concentrations of PM10-2.5 in the
epidemiological studies, or how
reported concentrations in the various
studies relate to one another when
differing measurement methodologies
are used. As discussed above, such
uncertainties and limitations
contributed to the conclusions in the
Integrated Science Assessment that the
PM10-2.5 evidence is only suggestive of a
causal relationship, a conclusion that
CASAC endorsed (Samet, 2009e,f).
Given the importance of these
uncertainties and limitations to the
interpretation of the evidence, as
reflected in the weight of evidence
conclusions in the Integrated Science
Assessment and as discussed above, the
Administrator judged it appropriate to
consider and account for them when
drawing conclusions about the potential
implications of individual PM10-2.5
health studies for the current standard.
In light of the above approach to
considering the scientific evidence, air
quality information, and associated
uncertainties, the Administrator reached
the following provisional conclusions in
the proposal:
(1) When viewed as a whole the available
evidence and information suggests that the
degree of public health protection provided
against short-term exposures to PM10-2.5 does
not need to be increased beyond that
provided by the current PM10 standard. This
provisional conclusion noted the important
uncertainties and limitations associated with
the overall body of health evidence and air
quality information for PM10-2.5, as discussed
above and as reflected in the Integrated
Science Assessment weight-of-evidence
conclusions; that PM10-2.5 effect estimates for
the most serious health effect, mortality, were
not statistically significant in U.S. locations
that met the current PM10 standard and
where coarse particle concentrations were
either directly measured or estimated based
on co-located samplers; and that PM10-2.5
effect estimates for morbidity endpoints were
both positive and negative in locations that
met the current standard, with most not
statistically significant.
(2) The degree of public health protection
provided by the current standard is not
greater than warranted. This provisional
conclusion noted that positive and
statistically significant associations with
mortality were reported in single-city U.S.
study locations likely to have violated the
current PM10 standard.128
128 There are similarities with the conclusions
drawn by the Administrator in the last review.
There, the Administrator concluded that there was
no basis for concluding that the degree of protection
afforded by the current PM10 standards in urban
areas is greater than warranted, since potential
mortality effects have been associated with air
quality levels not allowed by the current 24-hour
E:\FR\FM\15JAR2.SGM
Continued
15JAR2
3174
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
In reaching these provisional
conclusions, the Administrator noted
that the Policy Assessment also
discussed the potential for a revised
PM10 standard (i.e., with a revised form
and level) to be ‘‘generally equivalent’’
to the current standard, but to better
target public health protection to
locations where there is greater concern
regarding PM10-2.5-associated health
effects (U.S. EPA, 2011a, sections 3.3.3
and 3.3.4). In considering such a
potential revised standard, the Policy
Assessment discussed the large amount
of variability in PM10 air quality
correlations across monitoring locations
and over time (U.S. EPA, 2011a, Figure
3–7) and the regional variability in the
relative degree of public health
protection that could be provided by the
current and potential alternative
standards (U.S. EPA, 2011a, Table 3–2).
In light of this variability, the
Administrator noted the Policy
Assessment conclusion that no single
revised PM10 standard (i.e., with a
revised form and level) would provide
public health protection equivalent to
that provided by the current standard,
consistently over time and across
locations (U.S. EPA, 2011a, section
3.3.4). That is, a revised standard, even
one that is meant to be ‘‘generally
equivalent’’ to the current PM10
standard, could increase protection in
some locations while decreasing
protection in others (77 FR 38962).
In considering the appropriateness of
revising the current PM10 standard in
this way, the Administrator noted the
following:
tkelley on DSK3SPTVN1PROD with
(1) Positive PM10-2.5 effect estimates for
mortality were not statistically significant in
U.S. locations that met the current PM10
standard and where coarse particle
concentrations were either directly measured
or estimated based on co-located samplers,
while positive and statistically significant
associations with mortality were reported in
locations likely to have violated the current
PM10 standard.
(2) Effect estimates for morbidity endpoints
in locations that met the current standard
were both positive and negative, with most
not statistically significant.
(3) Important uncertainties and limitations
associated with the overall body of health
evidence and air quality information for
standard, but have not been associated with air
quality levels that would generally meet that
standard, and morbidity effects have been
associated with air quality levels that exceeded the
current 24-hour standard only a few times (71 FR
61202). In addition, the Administrator concluded
that there was a high degree of uncertainty in the
relevant population exposures implied by the
morbidity studies suggesting that there is little basis
for concluding that a greater degree of protection is
warranted. Id. The D.C. Circuit in American Farm
Bureau Federation v EPA explicitly endorsed this
reasoning. 559 F. 3d at 534.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
PM10-2.5, as discussed above and as reflected
in the Integrated Science Assessment weightof-evidence conclusions, call into question
the extent to which the type of quantified
and refined targeting of public health
protection envisioned under a revised
standard could be reliably accomplished.
Given all of the above considerations,
the Administrator noted that there is a
large amount of uncertainty in the
extent to which public health would be
improved by changing the locations to
which the PM10 standard targets
protection. Therefore, she reached the
provisional conclusion that the current
PM10 standard should not be revised in
order to change that targeting of
protection.
In considering all of the above,
including the scientific evidence, the air
quality information, the associated
uncertainties, and CASAC’s advice, the
Administrator reached the provisional
conclusion that the current 24-hour
PM10 standard is requisite (i.e., neither
more protective nor less protective than
necessary) to protect public health with
an adequate margin of safety against
effects that have been associated with
PM10-2.5. In light of this provisional
conclusion, the Administrator proposed
to retain the current PM10 standard in
order to protect against health effects
associated with short-term exposures to
PM10-2.5 (77 FR 38963).
The Administrator recognized that her
proposed conclusions and decision to
retain the current PM10 standard
differed from CASAC’s
recommendations, stemming from the
differences in how the Administrator
and CASAC considered and accounted
for the evidence and its limitations and
uncertainties. In light of CASAC’s views
and recommendation to revise the
current PM10 standard, the
Administrator welcomed the public’s
views on these different approaches to
considering and accounting for the
evidence and its limitations and
uncertainties, as well as on the
appropriateness of revising the primary
PM10 standard, including revising the
form and level of the standard. In doing
so, the Administrator solicited comment
on all aspects of the proposed decision,
including her rationale for reaching the
provisional conclusion that the current
PM10 standard is requisite to protect
public health with an adequate margin
of safety and the provisional conclusion
that it is not appropriate to revise the
current PM10 standard by setting a
‘‘generally equivalent’’ standard with
the goal of better targeting public health
protection.
PO 00000
Frm 00090
Fmt 4701
Sfmt 4700
F. Public Comments on the
Administrator’s Proposed Decision To
Retain the Primary PM10 Standard
This section discusses the major
public comments received on the
Administrator’s proposed decision to
retain the primary PM10 standard.
Additional comments are addressed in
the Response to Comments Document
(U.S. EPA, 2012a).
Many public commenters agreed with
the Administrator’s proposed decision
to retain the current 24-hour primary
PM10 standard. Among those expressing
a position on this proposed decision,
industry groups and most State and
Local commenters endorsed the
Administrator’s proposed rationale for
retaining the current primary PM10
standard, including her consideration of
the available scientific evidence and
associated uncertainties and her
consideration of CASAC
recommendations.
Although industry commenters
generally agreed with the
Administrator’s proposed decision to
retain the current primary PM10
standard, some also contended that the
current standard is ‘‘excessively
precautionary’’ (NMA and NCBA, 2012,
p. 4) and a few expressed support for a
less stringent standard for coarse
particles that are comprised largely of
crustal material. For example, the
Coarse Particulate Matter Coalition
(CPMC) (2012) and several other
industry commenters recommended that
the final decision allow application of a
98th percentile form for the current
standard (i.e. with its level of 150 mg/
m3) in cases where coarse particles
consist primarily of crustal material.
Such an approach would allow more
yearly exceedances of the existing
standard level than are allowed with the
current one-expected-exceedance form.
These industry commenters contended
that a 98th percentile form applied in
this way would provide appropriate
regulatory relief for areas where the
evidence for coarse particle-related
health effects is relatively uncertain.
In reaching her conclusion that the
current primary PM10 standard is
requisite to protect public health with
an adequate margin of safety, the
Administrator considered the degree of
public health protection provided by the
current standard as a whole, including
all elements of that standard (i.e.,
indicator, averaging time, form, level).
As discussed above and in the following
section, this conclusion reflects the
Administrator’s judgments that (1) the
current standard appropriately provides
some measure of protection against
exposures to all thoracic coarse
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
particles, regardless of their location,
source of origin, or composition and (2)
the current standard appropriately
allows lower ambient concentrations of
PM10-2.5 in urban areas, where the
evidence is strongest that thoracic
coarse particles are linked to mortality
and morbidity, and higher
concentrations in non-urban areas,
where the public health concerns are
less certain.
Because the considerations that led to
these judgments, and to the conclusion
that the current primary PM10 standard
is requisite to protect public health, took
into account the degree of public health
protection provided by the standard as
a whole, it would not be appropriate to
consider revising one element of the
standard (e.g., the form, as suggested by
commenters in this case) without
considering the extent to which the
other elements of the standard should
also be revised. The change in form
requested by industry commenters,
without also lowering the level of the
standard, would markedly reduce the
public health protection provided
against exposures to thoracic coarse
particles.129 However, industry
commenters have not presented new
evidence or analyses to support their
conclusion that an appropriate degree of
public health protection could be
achieved by allowing the use of an
alternative form (i.e., 98th percentile)
for some coarse particles, while
retaining the other elements of the
current standard. Nor have these
commenters presented new evidence or
analyses challenging the basis for the
conclusion in the proposal that the
varying amounts of coarse particles
allowed in urban versus non-urban
areas under the current 24-hour PM10
standard, based on the varying levels of
PM2.5 present, appropriately reflect the
differences in the strength of evidence
regarding coarse particle effects in urban
and non-urban areas. In light of this,
EPA does not believe that a reduction in
public health protection, such as that
129 Based on regression analyses presented in the
PA (U.S. EPA, 2011a, Figures 3–7 and 3–8), PM10
one-expected-exceedance concentration-equivalent
design values were between approximately 175 and
300 mg/m3 at monitoring locations recording 3-year
averages of 98th percentile 24-hour PM10
concentrations around 150 mg/m3 (i.e., the level of
the current standard). This suggests that, depending
on the location, a 24-hour PM10 standard with a
98th percentile form in conjunction with the
current level (i.e., as recommended by these
commenters) could be ‘‘generally equivalent’’ to a
24-hour PM10 standard with a one-expectedexceedance form and a level as high as
approximately 300 mg/m3. Based on this analysis, a
24-hour PM10 standard with a 98th percentile form
and a level of 150 mg/m3 would be markedly less
health protective than the current standard.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
requested by industry commenters, is
warranted.
In further considering these
comments, it is to be remembered that
epidemiologic studies have not
demonstrated that coarse particles of
non-urban origin do not cause health
effects, and commenters have not
provided additional evidence on this
point. While there are fewer studies of
non-urban coarse particles than of urban
coarse particles, several studies have
reported positive and statistically
significant associations between coarse
particles of crustal, non-urban origin
and mortality or morbidity (Ostro et al.,
2003; Bell et al., 2008; Chan et al., 2008;
Middleton et al., 2008; Perez et al.,
2008). These studies formed part of the
basis for the PM Integrated Science
Assessment conclusion that ‘‘recent
studies have suggested that PM (both
PM2.5 and PM10-2.5) from crustal, soil or
road dust sources or PM tracers linked
to these sources are associated with
cardiovascular effects’’ (U.S. EPA,
2009a, p. 2–26). Moreover, crustal
coarse particles may be contaminated
with toxic trace elements and other
components from previously deposited
fine PM from ubiquitous sources such as
mobile source engine exhaust, as well as
by toxic metals from smelters or other
industrial activities, animal waste, or
pesticides (U.S. EPA, 2004, p. 8–344). In
the proposal, the Administrator
acknowledged the potential for this type
of contamination to increase the toxicity
of coarse particles of crustal, non-urban
origin (77 FR 38960; see also 71 FR
61190).
In suggesting a change in the form of
the current standard, industry
commenters also did not address the
manifold difficulties noted above, and
in the last review, associated with
developing an indicator that could
reliably identify ambient mixes
dominated by particular types of
sources of coarse particles. See above
and 71 FR 61193. Yet such an indicator
would be a prerequisite of the type of
standard these commenters request.
For all of the reasons discussed above,
the EPA does not agree with industry
commenters who recommended
allowing the application of a 98th
percentile form for the current standard
in cases where coarse particles consist
primarily of crustal material.
Some industry commenters
contended that the uncertainties and
limitations that precluded a quantitative
risk assessment also preclude revising
the PM10 standard. Although the EPA
agrees that there are important
uncertainties and limitations in the
extent to which the quantitative
relationships between ambient PM10-2.5
PO 00000
Frm 00091
Fmt 4701
Sfmt 4700
3175
and health outcomes can be
characterized in risk models, the
Agency does not agree that such
limitations alone preclude the option of
revising a NAAQS. As noted above, the
lack of a quantitative PM10-2.5 risk
assessment in the current review adds
uncertainty to conclusions about the
extent to which revision of the current
PM10 standard would be expected to
improve the protection of public health,
beyond the protection provided by the
current standard. However, the EPA
does not agree that such uncertainties
necessarily preclude revision of a
NAAQS. Indeed, with respect to
thoracic coarse particles, the DC Circuit
noted that ‘‘[a]lthough the evidence of
danger from coarse PM is, as the EPA
recognizes, ‘inconclusive’, the agency
need not wait for conclusive findings
before regulating a pollutant it
reasonably believes may pose a
significant risk to public health.’’ 559 F.
3d at 533. Thus, the Administrator’s
conclusion that the current 24-hour
PM10 standard provides requisite
protection of public health relies on her
consideration of the broad body of
evidence, rather than solely on the
uncertainties that led to the decision not
to conduct a quantitative assessment of
PM10-2.5 health risks.
Commenters representing a number of
environmental groups and medical
organizations disagreed with the
Administrator’s proposal to retain the
current primary PM10 standard. These
commenters generally requested that the
EPA revise the PM10 standard to
increase public health protection,
consistent with the recommendations
from CASAC.
As discussed above and in the
proposal, in reaching provisional
conclusions in the proposal regarding
the current standard, the Administrator
carefully considered CASAC’s advice
and recommendations. She specifically
noted that in making its
recommendation on the current PM10
standard, CASAC did not discuss its
approach to considering the important
uncertainties and limitations in the
health evidence, and did not discuss
how these uncertainties and limitations
were reflected in its recommendations.
Such uncertainties and limitations
contributed to the conclusions in the
Integrated Science Assessment that the
PM10-2.5 evidence is only suggestive of a
causal relationship, a conclusion that
CASAC endorsed (Samet, 2009e,f).
These commenters also did not address
the important uncertainties in the
epidemiologic studies on which their
comments are based. Given the
importance of these uncertainties and
limitations to the interpretation of the
E:\FR\FM\15JAR2.SGM
15JAR2
3176
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
evidence, as reflected in the weight of
evidence conclusions in the Integrated
Science Assessment and as discussed in
the proposal, the Administrator judges
that it is appropriate to consider and
account for them when drawing
conclusions about the implications of
individual PM10-2.5 health studies for the
current standard. Commenters have not
provided new information that would
change the Administrator’s views on the
evidence and uncertainties.
In recommending that the PM10
standard be revised, some commenters
supported their conclusions by
referencing studies that evaluated PM10,
rather than PM10-2.5. These commenters
contended that ‘‘[t]he most relevant
studies to the setting of a PM10 standard
are the thousands of studies that have
reported adverse effects associated with
PM10 pollution’’ (ALA et al., 2012).
As discussed in the Policy
Assessment, the proposal, and above,
since the establishment of the primary
PM2.5 standards, the purpose of the
primary PM10 standard has been to
protect against health effects associated
with exposures to PM10-2.5. PM10 is the
indicator, not the target pollutant. With
regard to the appropriateness of
considering PM10 health studies for the
purpose of reaching conclusions on a
standard meant to protect against
exposures to PM10-2.5, the proposal
noted that PM10 includes both fine and
coarse particles, even in locations with
the highest concentrations of PM10-2.5.
Therefore, the extent to which PM10
effect estimates reflect associations with
PM10-2.5 versus PM2.5 can be highly
uncertain and it is often unclear how
PM10 health studies should be
interpreted when considering a standard
meant to protect against exposures to
PM10-2.5. Given this uncertainty and the
availability of a number of PM10-2.5
health studies in this review, the
Integrated Science Assessment
considered PM10-2.5 studies, but not
PM10 studies, when drawing weight-ofevidence conclusions regarding the
coarse fraction.130 In light of the
uncertainty in ascribing PM10-related
health effects to the coarse or fine
fractions, indicating that the best
evidence for effects associated with
exposures to PM10-2.5 comes from
studies evaluating PM10-2.5 itself, and
130 Although EPA relied in the 1997 review on
evidence from PM10 studies, EPA did so out of
necessity (i.e., there were as yet no reliable studies
measuring PM10-2.5). In the 2006 review, EPA placed
primary reliance on epidemiologic studies
measuring or estimating PM10-2.5, although there
were comparatively few such studies. In this
review, a larger body of PM10-2.5 studies are
available. EPA regards these studies as the evidence
to be given principal weight in reviewing the
adequacy of the PM10 standard.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
given CASAC’s support for the approach
adopted in the Integrated Science
Assessment, which draws weight-ofevidence conclusions for PM2.5 and
PM10-2.5 but not for PM10 (Samet, 2009f),
the EPA continues to conclude that it is
appropriate to focus on PM10-2.5 health
studies when considering the degree of
public health protection provided by the
current primary PM10 standard, a
standard intended exclusively to
provide protection against exposures to
PM10-2.5.
G. Administrator’s Final Decision on the
Primary PM10 Standard
In reaching a final decision on the
primary PM10 standard, the
Administrator takes into account the
available scientific evidence, and the
assessment of that evidence, in the
Integrated Science Assessment; the
analyses and staff conclusions presented
in the Policy Assessment; the advice
and recommendations of CASAC; and
public comments on the proposal. In
particular, as in the proposal, the
Administrator places emphasis on her
consideration of the following issues:
(1) The extent to which it is appropriate to
maintain a standard that provides some
measure of protection against all PM10-2.5,
regardless of composition or source of origin;
(2) The extent to which it is appropriate to
retain a PM10 indicator for a standard meant
to protect against exposures to ambient
PM10-2.5; and
(3) The extent to which the current PM10
standard provides an appropriate degree of
public health protection.
Each of these issues is discussed
below.
With regard to the first issue, as in the
proposal the Administrator judges that
the expanded body of scientific
evidence available in this review
provides ample support for a standard
that protects against exposures to all
thoracic coarse particles, regardless of
their location or source of origin. There
was already ample evidence for this
position in the previous review,131 and
that evidence has since increased.
Specifically, the Administrator notes
that epidemiological studies have
reported positive associations between
PM10-2.5 and mortality or morbidity in a
large number of cities across North
America, Europe, and Asia,
encompassing a variety of environments
where PM10-2.5 sources and composition
are expected to vary widely. In
considering this evidence, the Integrated
Science Assessment concludes that
‘‘many constituents of PM can be linked
with differing health effects’’ (U.S. EPA,
131 The
D.C. Circuit agreed. See 559 F. 3d at 532–
33.
PO 00000
Frm 00092
Fmt 4701
Sfmt 4700
2009a, p. 2–26). Although PM10-2.5 in
most of these study areas is of largely
urban origin, the Administrator notes
that some recent studies have also
linked mortality and morbidity with
relatively high ambient concentrations
of particles of non-urban crustal origin.
In considering these studies, she notes
the Integrated Science Assessment’s
conclusion that ‘‘PM (both PM2.5 and
PM10-2.5) from crustal, soil or road dust
sources or PM tracers linked to these
sources are associated with
cardiovascular effects’’ (U.S. EPA,
2009a, p. 2–26). The Administrator
likewise notes CASAC’s emphatic
advice that a standard remains needed
for all types of thoracic coarse PM.132 In
light of this body of available evidence
reporting PM10-2.5-associated health
effects across different locations with a
variety of sources, the Integrated
Science Assessment’s conclusions
regarding the links between adverse
health effects and PM sources and
composition, and CASAC’s advice, the
Administrator concludes in the current
review that it is appropriate to maintain
a standard that provides some measure
of protection against exposures to all
thoracic coarse particles, regardless of
their location, source of origin, or
composition.
With regard to the second issue, in
considering the appropriateness of a
PM10 indicator for a standard meant to
provide such public health protection,
the Administrator notes that the
rationale used in the last review to
support the unqualified PM10 indicator
remains relevant in the current review.
Specifically, as an initial consideration,
she notes that PM10 mass includes both
coarse PM (PM10-2.5) and fine PM
(PM2.5). As a result, the concentration of
PM10-2.5 allowed by a PM10 standard set
at a single level declines as the
concentration of PM2.5 increases. At the
same time, the Administrator notes that
PM2.5 concentrations tend to be higher
in urban areas than rural areas (U.S.
EPA, 2005, p. 2–54, and Figures 2–23
and 2–24) and, therefore, a PM10
standard will generally allow lower
PM10-2.5 concentrations in urban areas
than in rural areas.
In considering the appropriateness of
this variation in allowable PM10-2.5
concentrations, the Administrator
considers the relative strength of the
evidence for health effects associated
with PM10-2.5 of urban origin versus nonurban origin. She specifically notes that,
as discussed in the proposal, the large
majority of the available evidence for
132 Indeed, CASAC recommended making the
standard for all types of thoracic coarse PM more
stringent (Samet, 2010d).
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
thoracic coarse particle health effects
comes from studies conducted in
locations with sources more typical of
urban and industrial areas than rural
areas. While associations with adverse
health effects have been reported in
some study locations where PM10-2.5 is
largely non-urban in origin (i.e., in dust
storm studies), particle concentrations
in these study areas are typically much
higher than reported in study locations
where the PM is of urban origin.
Therefore, the Administrator notes that
the strongest evidence for a link
between PM10-2.5 and adverse health
impacts, particularly for such a link at
relatively low particle concentrations,
comes from studies of urban or
industrial PM10-2.5.
The Administrator also notes that
chemical constituents present at higher
levels in urban or industrial areas,
including byproducts of incomplete
combustion (e.g. polycyclic aromatic
hydrocarbons) emitted as PM2.5 from
motor vehicles as well as metals and
other contaminants emitted from
anthropogenic sources, can contaminate
PM10-2.5 (U.S. EPA, 2004, p. 8–344; 71
FR 2665, January 17, 2006). While the
Administrator acknowledges the
uncertainty expressed in the Integrated
Science Assessment regarding the extent
to which particle composition can be
linked to health outcomes based on
available evidence, she also considers
the possibility that PM10-2.5
contaminants typical of urban or
industrial areas could increase the
toxicity of thoracic coarse particles in
urban locations.
Given that the large majority of the
evidence for PM10-2.5 toxicity,
particularly at relatively low particle
concentrations, comes from study
locations where thoracic coarse particles
are of urban origin, and given the
possibility that PM10-2.5 contaminants in
urban areas could increase particle
toxicity, the Administrator concludes
that it remains appropriate to maintain
a standard that provides some
protection in all areas but targets public
health protection to urban locations.
Specifically, she concludes that it is
appropriate to maintain a standard that
allows lower ambient concentrations of
PM10-2.5 in urban areas, where the
evidence is strongest that thoracic
coarse particles are linked to mortality
and morbidity, and higher
concentrations in non-urban areas,
where the public health concerns are
less certain.
Given all of the above considerations
and conclusions, the Administrator
judges that the available evidence
supports retaining a PM10 indicator for
a standard that is meant to protect
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
against exposures to thoracic coarse
particles. In reaching this judgment, she
notes that, to the extent a PM10 indicator
results in lower allowable
concentrations of thoracic coarse
particles in some areas compared to
others, lower concentrations will be
allowed in those locations (i.e., urban or
industrial areas) where the science has
shown the strongest evidence of adverse
health effects associated with exposure
to thoracic coarse particles and where
we have the most concern regarding
PM10-2.5 toxicity. Therefore, the
Administrator concludes that the
varying amounts of coarse particles that
are allowed in urban vs. non-urban
areas under the 24-hour PM10 standard,
based on the varying levels of PM2.5
present, appropriately reflect the
differences in the strength of evidence
regarding coarse particle effects in urban
and non-urban areas.133 134
In reaching this conclusion, the
Administrator also notes that, in their
review of the second draft Policy
Assessment, CASAC concluded that
‘‘[w]hile it would be preferable to use an
indicator that reflects the coarse PM
directly linked to health risks (PM10-2.5),
CASAC recognizes that there is not yet
sufficient data to permit a change in the
indicator from PM10 to one that directly
measures thoracic coarse particles’’
(Samet, 2010d, p. ii). Thus, consistent
the considerations presented above and
with CASAC advice, the Administrator
concludes that it is appropriate to retain
PM10 as the indicator for thoracic coarse
particles.135
133 As discussed in the proposal, the
Administrator recognizes that this relationship is
qualitative. That is, the varying coarse particle
concentrations allowed under the PM10 standard do
not precisely correspond to the variable toxicity of
thoracic coarse particles in different areas (insofar
as that variability is understood). Although
currently available information does not allow any
more precise adjustment for relative toxicity, the
Administrator believes the standard will generally
ensure that the coarse particle levels allowed will
be lower in urban areas and higher in non-urban
areas. Addressing this qualitative relationship, the
DC Circuit held that ‘‘[i]t is true that the EPA relies
on a qualitative analysis to describe the protection
the coarse PM NAAQS will provide. But the fact
that the EPA’s analysis is qualitative rather than
quantitative does not undermine its validity as an
acceptable rationale for the EPA’s decision.’’ 559 F.
3d at 535.
134 The D.C. Circuit agreed with similar
conclusions in the last review and held that this
rationale reasonably supported use of an
unqualified PM10 indicator for thoracic coarse
particles. American Farm Bureau Federation v.
EPA, 559 F. 3d at 535–36.
135 In addition, CASAC ‘‘vigorously recommends
the implementation of plans for the deployment of
a network of PM10-2.5 sampling systems so that
future epidemiological studies will be able to more
thoroughly explore the use of PM10-2.5 as a more
appropriate indicator for thoracic coarse particles’’
(Samet, 2010d, p. 7). Consideration of alternative
indicators (e.g., PM10-2.5) in future reviews could be
PO 00000
Frm 00093
Fmt 4701
Sfmt 4700
3177
With regard to the third issue, in
evaluating the degree of public health
protection provided by the current PM10
standard, the Administrator first notes
that when the available PM10-2.5
scientific evidence and its associated
uncertainties were considered, the
Integrated Science Assessment
concluded that the evidence is
suggestive of a causal relationship
between short-term PM10-2.5 exposures
and mortality, cardiovascular effects,
and respiratory effects. As discussed
above and in more detail in the
Integrated Science Assessment (U.S.
EPA, 2009a, section 1.5), a suggestive
determination is made when the
‘‘[e]vidence is suggestive of a causal
relationship with relevant pollutant
exposures, but is limited because
chance, bias and confounding cannot be
ruled out.’’ In contrast, the
Administrator notes that she is
strengthening the annual fine particle
standard based on a body of scientific
evidence judged sufficient to conclude
that a causal relationship exists (i.e.,
mortality, cardiovascular effects) or is
likely to exist (i.e., respiratory effects).
The suggestive judgment for PM10-2.5
reflects the greater degree of uncertainty
associated with this body of evidence,
as discussed above and in more detail
in the proposal, and as summarized
below.
The Administrator notes that the
important uncertainties and limitations
associated with the scientific evidence
and air quality information raise
questions as to whether public health
benefits would be achieved by revising
the existing PM10 standard. Such
uncertainties and limitations include
the following:
(1) While PM10-2.5 effect estimates reported
for mortality and morbidity were generally
positive, most were not statistically
significant, even in single-pollutant models.
This includes effect estimates reported in
some study locations with PM10
concentrations above those allowed by the
current 24-hour PM10 standard.
(2) The number of epidemiological studies
that have employed co-pollutant models to
address the potential for confounding,
particularly by PM2.5, remains limited.
Therefore, the extent to which PM10-2.5 itself,
rather than one or more co-pollutants,
contributes to reported health effects remains
uncertain.
(3) Only a limited number of experimental
studies provide support for the associations
reported in epidemiological studies, resulting
in further uncertainty regarding the
plausibility of the associations between
PM10-2.5 and mortality and morbidity
reported in epidemiological studies.
informed by additional research, as described in the
Policy Assessment (U.S. EPA, 2011a, section 3.5).
E:\FR\FM\15JAR2.SGM
15JAR2
3178
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
(4) Limitations in PM10-2.5 monitoring data
and the different approaches used to estimate
PM10-2.5 concentrations across
epidemiological studies result in uncertainty
in the ambient PM10-2.5 concentrations at
which the reported effects occur, increasing
uncertainty in estimates of the extent to
which changes in ambient PM10-2.5
concentrations would likely impact public
health.
(5) The lack of a quantitative PM10-2.5 risk
assessment further contributes to uncertainty
regarding the extent to which any revisions
to the current PM10 standard would be
expected to improve the protection of public
health, beyond the protection provided by
the current standard (see section III.B.5
above).
(6) The chemical and biological
composition of PM10-2.5, and the effects
associated with the various components,
remains uncertain. Without more information
on the chemical speciation of PM10-2.5, the
apparent variability in associations across
locations is difficult to characterize.
tkelley on DSK3SPTVN1PROD with
In considering these uncertainties and
limitations, the Administrator notes in
particular the considerable degree of
uncertainty in the extent to which
health effects reported in
epidemiological studies are due to
PM10-2.5 itself, as opposed to one or
more co-occurring pollutants. As
discussed above, this uncertainty
reflects the fact that there are a
relatively small number of PM10-2.5
studies that have evaluated co-pollutant
models, particularly co-pollutant
models that have included PM2.5, and a
very limited body of controlled human
exposure evidence supporting the
plausibility of a causal relationship
between PM10-2.5 and mortality and
morbidity at ambient concentrations.
The Administrator notes that these
important limitations in the overall
body of health evidence introduce
uncertainty into the interpretation of
individual epidemiological studies,
particularly those studies reporting
associations with PM10-2.5 that are not
statistically significant. Given this, the
Administrator reaches the conclusion
that it is appropriate to place relatively
little weight on epidemiological studies
reporting associations with PM10-2.5 that
are not statistically significant in singlepollutant and/or co-pollutant models.136
136 The Administrator acknowledges that this
approach to interpreting the evidence differs in
emphasis from the approach she has adopted for the
evidence relating to PM2.5. As discussed above in
section III.E.4, for fine particles the Administrator
has considered not only whether study results are
statistically significant (or remain so after
application of co-pollutant models), but she also
places emphasis on the overall pattern of results
across the epidemiological literature. This includes
giving some credence to studies that reported
statistically non-significant associations. This
difference in emphasis stems from the much
stronger overall body of evidence available for fine
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
With regard to this conclusion, the
Administrator notes that, for single-city
mortality studies conducted in the
United States where ambient PM10
concentration data were available for
comparison to the current standard,
positive and statistically significant
PM10-2.5 effect estimates were only
reported in study locations that would
likely have violated the current PM10
standard during the study period (U.S.
EPA, 2011a, Figure 3–2). In U.S. study
locations that would likely have met the
current standard, PM10-2.5 effect
estimates for mortality were positive,
but not statistically significant (U.S.
EPA, 2011a, Figure 3–2). In considering
U.S. study locations where single-city
morbidity studies were conducted, and
which would likely have met the
current PM10 standard during the study
period, the Administrator notes that
PM10-2.5 effect estimates were both
positive and negative, with most not
statistically significant (U.S. EPA,
2011a, Figure 3–3).
In addition, in considering single-city
analyses for the locations evaluated in a
large U.S. multi-city mortality study
(Zanobetti and Schwartz, 2009), the
Administrator notes that associations in
most of the study locations were not
statistically significant and that this was
the only study to estimate ambient
PM10-2.5 concentrations as the difference
between county-wide PM10 and PM2.5
mass. As discussed in the proposal, the
Administrator notes that it is not clear
how computed PM10-2.5 measurements,
such as those used by Zanobetti and
Schwartz (2009), compare with the
PM10-2.5 concentrations obtained in
other studies either by direct
measurement by calculating the
difference using co-located samplers
(U.S. EPA, 2009a, section 6.5.2.3). For
these reasons, as in the proposal, the
Administrator notes that there is
considerable uncertainty in interpreting
the associations, and especially the
concentrations at which such
particles, compared to coarse particles. As
discussed above, when the available PM2.5 scientific
evidence and its associated uncertainties were
considered, the Integrated Science Assessment
concluded that the evidence was sufficient to
conclude that causal relationships exist with
mortality and cardiovascular effects, and that a
causal relationship is likely to exist with respiratory
effects. In contrast, the Integrated Science
Assessment concluded that the evidence is
suggestive of a causal relationship between shortterm PM10-2.5 exposures and mortality,
cardiovascular effects, and respiratory effects. A
suggestive determination is made when the
‘‘[e]vidence is suggestive of a causal relationship
with relevant pollutant exposures, but is limited
because chance, bias and confounding cannot be
ruled out’’ (U.S. EPA, 2009a, section 1.5). The
suggestive judgment for PM10-2.5 reflects the greater
degree of uncertainty associated with this body of
evidence.
PO 00000
Frm 00094
Fmt 4701
Sfmt 4700
associations may have occurred, in
these single-city analyses.
The Administrator acknowledges that
an approach to considering the available
scientific evidence and air quality
information that emphasizes the above
considerations differs from the approach
taken by CASAC. Specifically, CASAC
placed a substantial amount of weight
on individual studies, particularly those
reporting positive health effects
associations in locations that met the
current PM10 standard during the study
period. In emphasizing these studies, as
well as the limited number of
supporting studies that have evaluated
co-pollutant models and the small
number of supporting experimental
studies, CASAC concluded that ‘‘the
current data, while limited, is sufficient
to call into question the level of
protection afforded the American
people by the current standard’’ (Samet,
2010d, p. 7) and recommended revising
the current PM10 standard (Samet,
2010d).
The Administrator has carefully
considered CASAC’s advice and
recommendations. She notes that in
making its recommendation on the
current PM10 standard, CASAC did not
discuss its approach to considering the
important uncertainties and limitations
in the health evidence, and did not
discuss how these uncertainties and
limitations are reflected in its
recommendation. As discussed above,
such uncertainties and limitations
contributed to the conclusions in the
Integrated Science Assessment that the
PM10-2.5 evidence is only suggestive of a
causal relationship, a conclusion that
CASAC endorsed (Samet, 2009e,f).
Given the importance of these
uncertainties and limitations to the
interpretation of the evidence, as
reflected in the weight of evidence
conclusions in the Integrated Science
Assessment and as discussed above, the
Administrator judges that it is
appropriate to consider and account for
them when drawing conclusions about
the potential implications of individual
PM10-2.5 health studies for the current
standard.
In light of the above approach to
considering the scientific evidence, air
quality information, and associated
uncertainties, the Administrator reaches
the following conclusions:
(1) When viewed as a whole the available
evidence and information suggests that the
degree of public health protection provided
against short-term exposures to PM10-2.5
should be maintained but does not need to
be increased beyond that provided by the
current PM10 standard. This conclusion
emphasizes the important uncertainties and
limitations associated with the overall body
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
of health evidence and air quality
information for PM10-2.5, as discussed above
and as reflected in the Integrated Science
Assessment weight-of-evidence conclusions;
that PM10-2.5 effect estimates for the most
serious health effect, mortality, were not
statistically significant in U.S. locations that
met the current PM10 standard and where
coarse particle concentrations were either
directly measured or estimated based on colocated samplers; and that PM10-2.5 effect
estimates for morbidity endpoints were both
positive and negative in locations that met
the current standard, with most not
statistically significant.137
(2) The degree of public health protection
provided by the current standard is not
greater than warranted. This conclusion
notes that positive and statistically
significant associations with mortality were
reported in single-city U.S. study locations
likely to have violated the current PM10
standard.138
tkelley on DSK3SPTVN1PROD with
In reaching these conclusions, the
Administrator notes that the Policy
Assessment also discussed the potential
for a revised PM10 standard (i.e., with a
revised form and level) to be ‘‘generally
equivalent’’ to the current standard, but
to better target public health protection
to locations where there is greater
concern regarding PM10-2.5-associated
health effects (U.S. EPA, 2011a, sections
3.3.3 and 3.3.4).139 In considering such
137 This is not to say that the EPA could not adopt
or revise a standard for a pollutant for which the
evidence is suggestive of a causal relationship.
Indeed, with respect to thoracic coarse particles
itself, the DC Circuit noted that ‘‘[a]lthough the
evidence of danger from coarse PM is, as the EPA
recognizes, ‘inconclusive’, the agency need not wait
for conclusive findings before regulating a pollutant
it reasonably believes may pose a significant risk to
public health.’’ American Farm Bureau Federation
v EPA 559 F. 3d at 533. As explained in the text
above, it is the Administrator’s judgment that
significant uncertainties presented by the evidence
and information before her in this review, both as
to causality and as to concentrations at which
effects may be occurring, best support a decision to
retain rather than revise the current primary 24hour PM10 standard.
138 There are similarities with the conclusions
drawn by the Administrator in the last review.
There, the Administrator concluded that there was
no basis for concluding that the degree of protection
afforded by the current PM10 standards in urban
areas is greater than warranted, since potential
mortality effects have been associated with air
quality levels not allowed by the current 24-hour
standard, but have not been associated with air
quality levels that would generally meet that
standard, and morbidity effects have been
associated with air quality levels that exceeded the
current 24-hour standard only a few times. 71 FR
61202. In addition, the Administrator concluded
that there was a high degree of uncertainty in the
relevant population exposures implied by the
morbidity studies suggesting that there is little basis
for concluding that a greater degree of protection is
warranted. Id. The D.C. Circuit in American Farm
Bureau Federation v EPA explicitly endorsed this
reasoning. 559 F. 3d at 534.
139 As discussed in detail above (section IV.C.2.d)
and in the Policy Assessment (U.S. EPA, 2011a,
sections 3.3.3 and 3.3.4), a revised standard that is
generally equivalent to the current PM10 standard
could provide a degree of public health protection
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
a potential revised standard, the Policy
Assessment discusses the large amount
of variability in PM10 air quality
correlations across monitoring locations
and over time (U.S. EPA, 2011a, Figure
3–7) and the regional variability in the
relative degree of public health
protection that could be provided by the
current and potential alternative
standards (U.S. EPA, 2011a, Table 3–2).
In light of this variability, the
Administrator notes the Policy
Assessment conclusion that no single
revised PM10 standard (i.e., with a
revised form and level) would provide
public health protection equivalent to
that provided by the current standard,
consistently over time and across
locations (U.S. EPA, 2011a, section
3.3.4). That is, a revised standard, even
one that is meant to be ‘‘generally
equivalent’’ to the current PM10
standard, could increase protection in
some locations while decreasing
protection in other locations.
In considering the appropriateness of
revising the current PM10 standard in
this way, the Administrator notes the
following:
(1) As discussed above, positive PM10-2.5
effect estimates for mortality were not
statistically significant in U.S. locations that
met the current PM10 standard and where
coarse particle concentrations were either
directly measured or estimated based on colocated samplers, while positive and
statistically significant associations with
mortality were reported in locations likely to
have violated the current PM10 standard.
(2) Also as discussed above, effect
estimates for morbidity endpoints in
locations that met the current standard were
both positive and negative, with most not
statistically significant.
(3) Important uncertainties and limitations
associated with the overall body of health
evidence and air quality information for
PM10-2.5, as discussed above and as reflected
in the Integrated Science Assessment weightof-evidence conclusions, call into question
the extent to which the type of quantified
and refined targeting of public health
protection envisioned under a revised
standard could be reliably accomplished.
Given all of the above considerations,
the Administrator notes that there is a
large amount of uncertainty in the
extent to which public health would be
improved by changing the locations to
which the PM10 standard targets
protection. Therefore, she reaches the
conclusion that the current PM10
standard should not be revised in order
to change that targeting of protection.
In considering all of the above,
including the scientific evidence, the air
quality information, the associated
uncertainties, CASAC’s advice, and
public comments received on the
proposed rule, the Administrator
reaches the conclusion in the current
review that the existing 24-hour PM10
standard, with its one-expected
exceedance form and a level of 150 mg/
m3, is requisite (i.e., neither more
protective nor less protective than
necessary) to protect public health with
an adequate margin of safety against
effects that have been associated with
PM10-2.5. In light of this conclusion, with
this rule the Administrator retains the
current PM10 standard.
V. Communication of Public Health
Information
Sections 319(a)(1) and (3) of the CAA
require the EPA to establish a uniform
air quality index for reporting of air
quality. These sections specifically
direct the Administrator to ‘‘promulgate
regulations establishing an air quality
monitoring system throughout the
United States which utilizes uniform air
quality monitoring criteria and
methodology and measures such air
quality according to a uniform air
quality index’’ and ‘‘provides for daily
analysis and reporting of air quality
based upon such uniform air quality
index * * *’’ In 1979, the EPA
established requirements for index
reporting (44 FR 27598, May 10, 1979).
The requirement for State and local
agencies to report the AQI appears in 40
CFR 58.50, and the specific
requirements (e.g., what to report, how
to report, reporting frequency,
calculations) are in appendix G to 40
CFR part 58.
Information on the public health
implications of ambient concentrations
of criteria pollutants is currently made
available primarily by AQI reporting
through EPA’s AIRNow Web site.140 The
current AQI has been in use since its
inception in 1999.141 It provides
accurate, timely, and easily
understandable information about daily
levels of pollution (40 CFR 58.50). The
AQI establishes a nationally uniform
system of indexing pollution levels for
ozone, carbon monoxide, nitrogen
140 See
that is similar to the degree of protection provided
by the current standard, across the United States as
a whole. However, compared to the current PM10
standard, such a generally equivalent standard
would change the degree of public health protection
provided in some specific areas, providing
increased protection in some locations and
decreased protection in other locations.
PO 00000
Frm 00095
Fmt 4701
Sfmt 4700
3179
http://www.airnow.gov/.
1976, the EPA established a nationally
uniform air quality index, then called the Pollutant
Standard Index (PSI), for use by State and local
agencies on a voluntary basis (41 FR 37660,
September 7, 1976). In August 1999, the EPA
adopted revisions to this air quality index (64 FR
42530, August 4, 1999) and renamed the index the
AQI.
141 In
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
3180
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
dioxide, PM, and sulfur dioxide. The
AQI is also recognized internationally as
a proven tool to effectively
communicate air quality information to
the public.
The AQI converts pollutant
concentrations in a community’s air to
a number on a scale from 0 to 500.
Reported AQI values enable the public
to know whether air pollution levels in
a particular location are characterized as
good (0–50), moderate (51–100),
unhealthy for sensitive groups (101–
150), unhealthy (151–200), very
unhealthy (201–300), or hazardous
(301–500). The AQI index value of 100
typically corresponds to the level of the
short-term (e.g., daily or hourly
standard) NAAQS for each pollutant.
Below an index value of 100, an
intermediate value of 50 was defined
either as the level of the annual
standard if an annual standard has been
established (e.g., PM2.5, nitrogen
dioxide), or as a concentration equal to
one-half the value of the short-term
standard used to define an index value
of 100 (e.g., carbon monoxide). An AQI
value greater than 100 means that a
pollutant is in one of the unhealthy
categories (i.e., unhealthy for sensitive
groups, unhealthy, very unhealthy, or
hazardous) on a given day. An AQI
value at or below 100 means that a
pollutant concentration is in one of the
satisfactory categories (i.e., moderate or
good). The underlying health
information that supports the NAAQS
review also supports the selection of the
AQI ‘‘breakpoints’’—the ambient
concentrations that delineate the
various AQI categories for each
pollutant.
Historically, state and local agencies
have primarily used the AQI to provide
general information to the public about
air quality and its relationship to public
health. For more than a decade, many
states and local agencies, as well as the
EPA and other Federal agencies, have
been developing new and innovative
programs and initiatives to provide
more information to the public in a
more timely way. These initiatives,
including air quality forecasting, realtime data reporting through the AirNow
Web site, and state and local air quality
action day programs, can serve to
provide useful, up-to-date, and timely
information to the public about air
pollution and its effects. Such
information will help individuals take
actions to avoid or to reduce exposures
to ambient pollution at levels of concern
to them. Thus, these programs have
significantly broadened the ways in
which state and local agencies can meet
the nationally uniform AQI reporting
requirements and contribute to state and
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
local efforts to provide community
health protection.
With respect to an AQI value of 50,
the historical approach is to set it at the
same level of the annual primary
standard, if there is one. This is
consistent with the previous AQI subindex for PM2.5, in which the AQI value
of 50 was set at 15 mg/m3 in 1999,
consistent with the level of the annual
PM2.5 standard at that time. In
recognition of the proposed change to
the annual PM2.5 standard summarized
in section III.F of the proposal, the EPA
proposed a conforming change to the
PM2.5 sub-index of the AQI to be
consistent with the proposed change to
the annual standard. As discussed
below, no state or local agencies, or
their organizations (e.g., NACAA), that
commented on the proposed changes to
the AQI disagreed with our proposed
approach. Based on these comments, the
EPA continues to see no basis for
deviating from this approach in this
review. Thus, the EPA is taking final
action to set an AQI value of 50 at 12.0
mg/m3, 24-hour average, consistent with
the final decision on the annual PM2.5
standard level (section III.F).
With respect to an AQI value of 100,
which is the basis for advisories to
individuals in sensitive groups, in the
proposal we described two general
approaches that could be used to select
the associated PM2.5 level. By far the
most common approach, which has
been used with all of the other subindices, is to set an AQI value of 100 at
the same level as the short-term
standard. In the proposal, the EPA
recognized that some state and local air
quality agencies have expressed a strong
preference that the Agency set an AQI
value of 100 equal to any short-term
standard (77 FR 38964). These agencies
typically express the view that this
linkage is useful for the purpose of
communicating with the public about
the standard, as well as providing
consistent messages about the health
impacts associated with daily air
quality. The EPA proposed to use this
approach to set the AQI value of 100 at
35 mg/m3, 24-hour average, consistent
with the proposed decision to retain the
current 24-hour PM2.5 standard. Id.
An alternative approach discussed in
the proposal (77 FR 38964), was to
directly evaluate the health effects
evidence to select the level for an AQI
value of 100. This was the approach
used in the 1999 rulemaking to set the
AQI value of 100 at a level of 40 mg/m3,
24-hour average,142 when the 24-hour
standard level was 65 mg/m3. This
alternative approach was used in the
case of the PM2.5 sub-index, because the
annual and 24-hour PM2.5 standards set
in 1997 were designed to work together,
and the intended degree of health
protection against short-term risks was
not defined by the 24-hour standard
alone, but rather by the combination of
the two standards working in concert.
Indeed, at that time, the 24-hour
standard was set to provide
supplemental protection relative to the
principal protection provided by the
annual standard. In the proposal, the
EPA solicited comment on this
alternative approach in recognition that,
as proposed, the 24-hour PM2.5 standard
is intended to continue to provide
supplemental protection against effects
associated with short-term exposures of
PM2.5 by working in conjunction with
the annual standard to reduce 24-hour
exposures to PM2.5. The EPA recognized
that in the past, some state and local air
quality agencies have expressed support
for this alternative approach. Using this
alternative approach could have
resulted in consideration of a lower
level for an AQI value of 100, based on
the discussion of the health information
pertaining to the level of the 24-hour
standard in section III.E.4 of the
proposal. The EPA encouraged state and
local air quality agencies to comment on
both the approach and the level at
which to set an AQI value of 100
together with any supporting rationale.
Of the state or local agencies, or their
organizations (e.g., NACAA), that
commented on the proposed changes to
the AQI, only one organization,
NESCAUM, expressed some support for
this approach. In its comments,
NESCAUM expressed support for a 24hour standard set at 30 mg/m3, 24-hour
average. NESCAUM also expressed the
view that EPA should carefully consider
how to set the breakpoint for an AQI
value of 100. NESCAUM expressed the
view that if the EPA were to keep the
24-hour PM2.5 standard at 35 mg/m3, the
annual standard would be controlling,
and a 24-hour breakpoint at that level
(35 mg/m3) would not be very effective
for the purposes of public health
messaging. However, other agencies,
such as Georgia Department of Natural
Resources (Georgia DNR), expressed the
view that linkage between the shortterm standard and the AQI of 100 is
useful for the purpose of
communicating with the public about
the standard as well as providing
consistent messages about the health
142 Currently, we are cautioning members of
sensitive groups at the AQI value of 100 at 35 mg/
m3, 24-hour average, consistent with more recent
guidance from the EPA with regard to the
development of State emergency episode
contingency plans (Harnett, 2009, Attachment B).
PO 00000
Frm 00096
Fmt 4701
Sfmt 4700
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
impacts associated with the daily air
quality. Based on these comments, the
EPA sees no basis for deviating from the
approach proposed in this review. Thus,
the EPA is taking final action to set an
AQI value of 100 at 35 mg/m3, 24-hour
average, consistent with the final
decision on the 24-hour PM2.5 standard
level (section III.F).
With respect to an AQI value of 150,
this level is based upon the same health
effects information that informs the
selection of the level of the 24-hour
standard and the AQI value of 100. The
AQI value of 150 was set in the 1999
rulemaking at a level of 65 mg/m3, 24hour average. In considering what level
to propose for an AQI value of 150, we
stated the view that the health effects
evidence indicates that the level of 55
mg/m3, 24-hour average, is appropriate
to use 143 in conjunction with an AQI
value of 100 set at the level of 35 mg/
m3. The Agency’s approach to selecting
the levels at which to set the AQI values
of 100 and 150 inherently recognizes
that the epidemiological evidence upon
which these decisions are based
provides no evidence of discernible
thresholds, below which effects do not
occur in either sensitive groups or in the
general population, at which to set these
two breakpoints. Therefore, the EPA
concluded the use of a proportional
adjustment would be appropriate.
Commenters did not comment on this
proposed approach to revising the AQI
value of 150; thus, the EPA is taking
final action to set an AQI value of 150
at 55 mg/m3, 24-hour average.
Based on the air quality and health
considerations discussed in section V of
the proposal, the EPA concluded that it
was appropriate to propose to retain the
current level of 500 mg/m3, 24-hour
average, for the AQI value of 500. In
addition, the EPA solicited comment on
alternative levels and approaches to
setting a level for the AQI value of 500,
as well as supporting information and
rationales for such alternative levels.
The EPA also solicited any additional
information, data, research or analyses
that may be useful to inform a final
decision on the appropriate level to set
the AQI value of 500. Receiving no
information with which to inform
alternative approaches to setting an AQI
value of 500, the EPA is taking final
action to retain the current level of 500
mg/m3, 24-hour average, for the AQI
value of 500.
For the intermediate breakpoints in
the AQI between the values of 150 and
500, the EPA proposed PM2.5
concentrations that generally reflected a
3181
linear relationship between increasing
index values and increasing PM2.5
values (77 FR 38965). The available
scientific evidence of health effects
related to population exposures to PM2.5
concentrations between the level of the
24-hour standard and an AQI value of
500 suggested a continuum of effects in
this range, with increasing PM2.5
concentrations being associated with
increasingly larger numbers of people
likely to experience such effects. The
generally linear relationship between
AQI values and PM2.5 concentrations in
this range is consistent with the health
evidence. This also is consistent with
the Agency’s practice of setting
breakpoints in symmetrical fashion
where health effects information does
not suggest particular levels.
Table 2 below summarizes the
finalized breakpoints for the PM2.5 subindex.144 Table 2 shows the
intermediate breakpoints for AQI values
of 200, 300 and 400 based on a linear
interpolation between the proposed
levels for AQI values of 150 and 500. If
a different level were to be set for an
AQI value of 150 or 500, intermediate
levels would be calculated based on a
linear relationship between the selected
levels for AQI values of 150 and 500.
TABLE 2—BREAKPOINTS FOR PM2.5 SUB-INDEX
AQI category
Index values
tkelley on DSK3SPTVN1PROD with
Good ..................................................................................................................................................
Moderate ............................................................................................................................................
Unhealthy for Sensitive Groups .........................................................................................................
Unhealthy ...........................................................................................................................................
Very Unhealthy ..................................................................................................................................
Hazardous ..........................................................................................................................................
0–50
51–100
101–150
151–200
201–300
301–400
401–500
Proposed breakpoints
(μg/m3, 24-hour
average)
0.0–(12.0)
(12.1)–35.4
35.5–55.4
55.5–150.4
150.5–250.4
250.5–350.4
350.5–500.4
In retaining the 500 level for the AQI
as described above, we note that the
EPA is not establishing a Significant
Harm Level (SHL) for PM2.5. The SHL is
an important part of air pollution
Emergency Episode Plans, which are
required for certain areas by CAA
section 110(a)(2)(G) and associated
regulations at 40 CFR 51.150, under the
Prevention of Air Pollution Emergency
Episodes program. The Agency believes
that air quality responses established
through an Emergency Episode Plan
should be developed through a
collaborative process working with State
and Tribal air quality, forestry and
agricultural agencies, Federal land
management agencies, private land
managers and the public. Therefore, if
in future rulemaking the EPA proposes
revisions to the Prevention of Air
Pollution Emergency Episodes program,
the proposal will include a SHL for
PM2.5 that is developed in collaboration
with these organizations. As discussed
in the 1999 Air Quality Index Reporting
Rule (64 FR 42530), if a future
rulemaking results in a SHL that is
different from the 500 value of the AQI
for PM2.5, the AQI will be revised
accordingly.
The EPA also received more general
comments on AQI reporting, comments
that did not pertain to setting specific
breakpoints. One set of commenters
(e.g., API and UARG), expressed the
view that changes to the AQI are not
appropriate. They noted that air quality
is getting better, and in fact is better
than when EPA established the AQI.
These commenters stated that the
proposed changes to the annual
standard and the AQI would mean that
the public would hear less often that air
quality is good, and thereby would
receive apparently inconsistent or
misleading messages that air quality is
143 We note that this level is consistent with the
level recommended in the more recent EPA
guidance (Harnett, 2009, Attachment B), which is
in use by many State and local agencies.
144 As discussed in section VII.C below, the EPA
is also updating the data handling procedures for
reporting the AQI and corresponding updates for
other AQI-sub-indices presented in Table 2 of
appendix G of 40 CFR part 58.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
PO 00000
Frm 00097
Fmt 4701
Sfmt 4700
E:\FR\FM\15JAR2.SGM
15JAR2
3182
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
worse. The AQI has been revised several
times in conjunction with revisions to
the standards. State and local air quality
agencies and organizations are
proficient at communicating with the
public about the reasons for changes to
the AQI. Therefore, the EPA strongly
disagrees with these commenters that
the public will receive inconsistent or
misleading messages. Recognizing the
importance of the AQI as a
communication tool that allows the
public to take exposure reduction
measures when air quality may pose
health risks, the EPA agrees with state
and local air quality agencies and
organizations that favored revising the
AQI at the same time as the primary
standard.
A few state and local air quality
agencies and organizations
recommended against using nearroadway PM2.5 monitors for AQI
reporting. In support of this comment,
they expressed the following views, that
near-roadway monitors are sourceoriented, represent micro-scale
conditions, and the agencies don’t have
experience using them for AQI
reporting. The EPA disagrees with the
comment in that these monitors will be
sited at existing near-road stations sited
to be representative of area-wide PM2.5
concentrations indicative of general
population exposure. Accordingly, data
from these near-road monitors should be
included in the AQI since they provide
information about PM2.5 levels that
millions of people, who work, live and
go to school near busy roadways, are
exposed to. The stations are
representative of somewhat elevated
concentrations in near-road
environments, but since these stations
represent many such locations
throughout a metropolitan area, they are
appropriate for characterizing exposure
in typical portions of major urban areas.
The EPA is committed to helping air
quality agencies develop appropriate
ways to report PM2.5 levels from these
monitors using the AQI.
VI. Rationale for Final Decisions on the
Secondary PM Standards
This section presents the
Administrator’s final decisions
regarding the need to revise the current
suite of secondary PM2.5 and PM10
standards to address visibility
impairment and other welfare effects
considered in this review. Specifically,
this section describes the
Administrator’s final decision to retain
the current suite of secondary PM
standards to address PM-related
visibility impairment as well as other
PM-related welfare effects, including
ecological effects, effects on materials,
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
and climate impacts. This suite of
standards includes an annual PM2.5
standard of 15 mg/m3, a 24-hour PM2.5
standard of 35 mg/m3, and a 24-hour
PM10 standard of 150 mg/m3. The
Administrator is revising only the form
of the secondary annual PM2.5 standard
to remove the option for spatial
averaging consistent with this change to
the primary annual PM2.5 standard.
Contrary to what was proposed, the
Administrator has decided not to
establish a distinct standard to address
PM-related visibility impairment. The
rationale for this decision is presented
below.
The Administrator’s final decisions
on the secondary standards are based on
a thorough review of the latest scientific
information published through mid2009 on welfare effects associated with
fine and coarse particles in the ambient
air, as presented in the Integrated
Science Assessment. The final decisions
also take into account: (1) Staff
assessments of the most policy-relevant
information presented and assessed in
the Integrated Science Assessment and
staff analyses of air quality and visibility
effects presented in the Visibility
Assessment and the Policy Assessment,
upon which staff conclusions regarding
appropriate considerations in this
review are based; (2) CASAC advice and
recommendations, as reflected in
discussions of drafts of the Integrated
Science Assessment, Visibility
Assessment, and Policy Assessment at
public meetings, in separate written
comments, and in CASAC’s letters to
the Administrator; (3) the multiple
rounds of public comments received
during the development of these
documents, both in connection with
CASAC meetings and separately; and (4)
public comments received on the
proposal.
In particular, this section presents
background information on the EPA’s
previous and current reviews of the
secondary PM standards (section VI.A),
a summary of the proposed decisions
regarding the secondary PM standards
(section VI.B), a discussion of
significant public comments received on
those proposed decisions (section VI.C),
and the Administrator’s final decisions
on the secondary PM standards (section
VI.D).
A. Background
The current suite of secondary PM
standards is identical to the suite of
primary PM standards set in 2006,
including 24-hour and annual PM2.5
standards and a 24-hour PM10 standard.
The current secondary PM2.5 standards
are intended to provide protection from
PM-related visibility impairment,
PO 00000
Frm 00098
Fmt 4701
Sfmt 4700
whereas the entire suite of secondary
PM standards is intended to provide
protection from other PM-related effects
on public welfare, including effects on
sensitive ecosystems, materials damage
and soiling, and climatic and radiative
processes.
The approach used for reviewing the
current suite of secondary PM standards
built upon and broadened the
approaches used in previous PM
NAAQS reviews. The following
discussion focuses particularly on the
current secondary PM2.5 standards
related to visibility impairment and
provides a summary of the approaches
used to review and establish secondary
PM2.5 standards in the last two reviews
(section VI.A.1); judicial review of the
2006 standards that resulted in the
remand of the secondary annual and 24hour PM2.5 NAAQS to the EPA (section
VI.A.2); and the approach used in this
review for evaluating the secondary
PM2.5 standards (section VI.A.3).
1. Approaches Used in Previous
Reviews
The original secondary PM2.5
standards were established in 1997, and
a revision to the 24-hour standard was
made in 2006. The approaches used in
making final decisions on secondary
standards in those reviews, as well as
the current review, utilized different
ways to consider the underlying body of
scientific evidence. They also reflected
an evolution in EPA’s understanding of
the nature of the effect on public welfare
from PM-related visibility impairment,
from an approach that focused only on
Federal Class I area visibility impacts to
a more multifaceted approach that also
considered PM-related impacts on
visibility in non-Federal Class I areas,
such as in urban areas. This evolution
occurred in conjunction with the
expansion of available PM data and
information from visibility-related
studies of public perception, valuation,
and personal comfort and well-being.
In 1997, the EPA revised the PM
NAAQS in part by establishing new
identical primary and secondary PM2.5
standards. In revising the secondary
standards, the EPA recognized that PM
produces adverse effects on visibility
and that impairment of visibility was
being experienced throughout the U.S.,
in multi-state regions, urban areas, and
remote mandatory Federal Class I areas
alike. However, in considering an
appropriate level for a secondary
standard to address adverse effects of
PM2.5 on visibility, the EPA concluded
that the determination of a single
national level was complicated by
important regional differences
influenced by factors such as
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
background and current levels of PM2.5,
composition of PM2.5, and average
relative humidity. Variations in these
factors across regions could thus result
in situations where attaining an
appropriately protective concentration
of fine particles in one region might or
might not provide adequate protection
in a different region. The EPA also
determined that there was insufficient
information at that time to establish a
level for a national secondary standard
that would represent a threshold above
which visibility conditions would
always be adverse and below which
visibility conditions would always be
acceptable.
Based on an assessment of the
potential visibility improvements that
would result from reaching attainment
with the new primary standards for
PM2.5, the EPA concluded that
attainment of the annual and 24-hour
PM2.5 primary standards would lead to
visibility improvements in the eastern
U.S. at both urban and regional scales,
but little or no change in the western
U.S., except in and near certain urban
areas.
The EPA also considered the potential
effectiveness of a regional haze program,
required by sections 169A and 169B of
the CAA 145 to address those effects of
PM on visibility that would not be
addressed through attainment of the
primary PM2.5 standards. The regional
haze program would be designed to
address the widespread, regionally
uniform type of haze caused by a
multitude of sources. The structure and
requirements of sections 169A and 169B
of the CAA provide for visibility
protection programs that can be more
responsive to the factors contributing to
regional differences in visibility than
can programs addressing the kinds of
nationally applicable secondary NAAQS
considered in the 1997 review. The
regional haze visibility goal is more
protective than a secondary NAAQS
since the goal is to eliminate any
anthropogenic impairment rather than
to provide a level of protection from
visibility impairment that is requisite to
protect the public welfare. Thus, an
important factor considered in the 1997
review was whether a regional haze
program, in conjunction with secondary
standards set identical to the suite of
PM2.5 primary standards, would provide
145 In 1977, Congress established as a national
goal ‘‘the prevention of any future, and the
remedying of any existing, impairment of visibility
in mandatory Federal Class I areas which
impairment results from manmade air pollution,’’
section 169A(a)(1) of the CAA. The EPA is required
by section 169A(a)(4) of the CAA to promulgate
regulations to ensure that ‘‘reasonable progress’’ is
achieved toward meeting the national goal.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
appropriate protection for visibility in
non-Federal Class I areas. The EPA
concluded that the two programs and
associated control strategies should
provide such protection due to the
regional approaches needed to manage
emissions of pollutants that impair
visibility in many of these areas.
For these reasons, in 1997 the EPA
concluded that a national regional haze
program, combined with a nationally
applicable level of protection achieved
through secondary PM2.5 standards set
identical to the primary PM2.5 standards,
would be more effective for addressing
regional variations in the adverse effects
of PM2.5 on visibility than would be
national secondary standards for PM
with levels lower than the primary
PM2.5 standards. The EPA further
recognized that people living in certain
urban areas may place a high value on
unique scenic resources in or near these
areas and as a result might experience
visibility problems attributable to
sources that would not necessarily be
addressed by the combined effects of a
regional haze program and PM2.5
secondary standards. The EPA
concluded that in such cases, state or
local regulatory approaches, such as
past action in Colorado to establish a
local visibility standard for the City of
Denver, would be more appropriate and
effective in addressing these special
situations because of the localized and
unique characteristics of the problems
involved. Visibility in an urban area
located near a mandatory Federal Class
I area could also be improved through
state implementation of the then-current
visibility regulations, by which
emission limitations can be imposed on
a source or group of sources found to be
contributing to ‘‘reasonably
attributable’’ impairment in the
mandatory Federal Class I area.
Based on these considerations, in
1997 the EPA set secondary PM2.5
standards identical to the primary PM2.5
standards, that would work in
conjunction with the Regional Haze
Program to be established under
sections 169A and 169B of the CAA, as
the most appropriate and effective
means of addressing the public welfare
effects associated with visibility
impairment. Together, the two programs
and associated control strategies were
expected to provide appropriate
protection against PM-related visibility
impairment and enable all regions of the
country to make reasonable progress
toward the national visibility goal.
In 2006, the EPA revised the suite of
secondary PM2.5 standards to address
visibility impairment by making the
suite of secondary standards identical to
the revised suite of primary PM2.5
PO 00000
Frm 00099
Fmt 4701
Sfmt 4700
3183
standards. The EPA’s decision regarding
the need to revise the suite of secondary
PM2.5 standards reflected a number of
new developments that had occurred
and sources of information that had
become available following the 1997
review. First, the EPA promulgated a
Regional Haze Program in 1999 (65 FR
35713, July 1, 1999) which required
states to establish goals for improving
visibility in Federal Class I areas and to
adopt control strategies to achieve these
goals. Second, extensive new
information from visibility and fine
particle monitoring networks had
become available, allowing for updated
characterizations of visibility trends and
PM concentrations in urban areas, as
well as Federal Class I areas. These new
data allowed the EPA to better
characterize visibility impairment in
urban areas and the relationship
between visibility and PM2.5
concentrations. Finally, additional
studies in the U.S. and abroad provided
the basis for the establishment of
standards and programs to address
specific visibility concerns in a number
of local areas. These studies (Denver,
Phoenix, and British Columbia) utilized
photographic representations of
visibility impairment and produced
reasonably consistent results in terms of
the visual ranges found to be generally
acceptable by study participants. The
EPA considered the information
generated by these studies useful in
characterizing the nature of particleinduced haze and for informing
judgments about the acceptability of
various levels of visual air quality in
urban areas across the U.S. Based
largely on this information, the
Administrator concluded that it was
appropriate to revise the secondary
PM2.5 standards to provide increased
protection from visibility impairment
principally in urban areas, in
conjunction with the regional haze
program for protection of visual air
quality in Federal Class I areas.
In so doing, the Administrator
recognized that PM-related visibility
impairment is principally related to fine
particle concentrations and that
perception of visibility impairment is
most directly related to short-term,
nearly instantaneous levels of visual air
quality. Thus, in considering whether
the then-current suite of secondary
standards would provide the
appropriate degree of protection, he
concluded that it was appropriate to
focus on just the 24-hour secondary
PM2.5 standard to provide requisite
protection.
The Administrator then considered
whether PM2.5 mass remained the
appropriate indicator for a secondary
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
3184
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
standard to protect visibility, primarily
in urban areas. The Administrator noted
that PM-related visibility impairment is
principally related to fine particle
levels. Hygroscopic components of fine
particles, in particular sulfates and
nitrates, contribute disproportionately
to visibility impairment under high
humidity conditions. Particles in the
coarse mode generally contribute only
marginally to visibility impairment in
urban areas. With the substantial
addition to the air quality and visibility
data made possible by the national
urban PM2.5 monitoring networks, an
analysis conducted for the 2006 review
found that, in urban areas, visibility
levels showed far less difference
between eastern and western regions on
a 24-hour or shorter time basis than
implied by the largely non-urban data
available in the 1997 review. In
analyzing how well PM2.5
concentrations correlated with visibility
in urban locations across the U.S., the
2005 Staff Paper concluded that clear
correlations existed between 24-hour
average PM2.5 concentrations and
calculated (i.e., reconstructed) light
extinction, which is directly related to
visual range (U.S. EPA, 2005, p. 7–6).
These correlations were similar in the
eastern and western regions of the U.S.
These correlations were less influenced
by relative humidity and more
consistent across regions when PM2.5
concentrations were averaged over
shorter, daylight time periods (e.g., 4 to
8 hours) when relative humidity in
eastern urban areas was generally lower
and thus more similar to relative
humidity in western urban areas. The
2005 Staff Paper noted that a standard
set at any specific PM2.5 concentration
would necessarily result in visual
ranges that vary somewhat in urban
areas across the country, reflecting the
variability in the correlations between
PM2.5 concentrations and light
extinction. The 2005 Staff Paper
concluded that it was appropriate to use
PM2.5 as an indicator for standards to
address visibility impairment in urban
areas, especially when the indicator is
defined for a relatively short period
(e.g., 4 to 8 hours) of daylight hours
(U.S. EPA, 2005, p. 7–6). Based on their
review of the Staff Paper, most CASAC
Panel members also endorsed such a
PM2.5 indicator for a secondary standard
to address visibility impairment
(Henderson, 2005a, p. 9). Based on the
above considerations, the Administrator
concluded that PM2.5 should be retained
as the indicator for fine particles as part
of a secondary standard to address
visibility protection, in conjunction
with averaging times from 4 to 24 hours.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
In considering what level of
protection against PM-related visibility
impairment would be appropriate, the
Administrator took into account the
results of the public perception and
attitude surveys regarding the
acceptability of various degrees of
visibility impairment in the U.S. and
Canada, state and local visibility
standards within the U.S., and visual
inspection of photographic
representations of several urban areas
across the U.S. In the Administrator’s
judgment, these sources provided useful
but still quite limited information on the
range of levels appropriate for
consideration in setting a national
visibility standard primarily for urban
areas, given the generally subjective
nature of the public welfare effect
involved. Based on photographic
representations of varying levels of
visual air quality, public perception
studies, and local and state visibility
standards, the 2005 Staff Paper had
concluded that 30 to 20 mg/m3 PM2.5
represented a reasonable range for a
national visibility standard primarily for
urban areas, based on a sub-daily
averaging time (U.S. EPA, 2005, p. 7–
13). The upper end of this range was
below the levels at which illustrative
scenic views are significantly obscured,
and the lower end was around the level
at which visual air quality generally
appeared to be good based on
observation of the illustrative views.
This concentration range generally
corresponded to median visual ranges in
urban areas within regions across the
U.S. of approximately 25 to 35 km, a
range that was bounded above by the
visual range targets selected in specific
areas where state or local agencies
placed particular emphasis on
protecting visual air quality. In
considering a reasonable range of forms
for a PM2.5 standard within this range of
levels, the 2005 Staff Paper had
concluded that a concentration-based
percentile form was appropriate, and
that the upper end of the range of
concentration percentiles for
consideration should be consistent with
the 98th percentile used for the primary
standard and that the lower end of the
range should be the 92nd percentile,
which represented the mean of the
distribution of the 20 percent most
impaired days, as targeted in the
regional haze program (U.S. EPA, 2005
pp. 7–11 to 7–13). While recognizing
that it was difficult to select any specific
level and form based on then-currently
available information (Henderson,
2005a, p. 9), the CASAC Panel was
generally in agreement with the ranges
PO 00000
Frm 00100
Fmt 4701
Sfmt 4700
of levels and forms presented in the
2005 Staff Paper.
The Administrator also considered
the level of protection that would be
afforded by the proposed suite of
primary PM2.5 standards (71 FR 2681,
January 17, 2006), on the basis that
although significantly more information
was available than in the 1997 review
concerning the relationship between
fine PM levels and visibility across the
country, there was still little available
information for use in making the
relatively subjective value judgment
needed in selecting the appropriate
degree of protection to be afforded by
such a standard. In so doing, the
Administrator compared the extent to
which the proposed suite of primary
standards would require areas across the
country to improve visual air quality
with the extent of increased protection
likely to be afforded by a standard based
on a sub-daily averaging time. Based on
such an analysis, the Administrator
observed that the predicted percent of
counties with monitors not likely to
meet the proposed suite of primary
PM2.5 standards was actually somewhat
greater than the predicted percent of
counties with monitors not likely to
meet a sub-daily secondary standard
with an averaging time of 4 daylight
hours, a level toward the upper end of
the range recommended in the 2005
Staff Paper, and a form within the
recommended range. Based on this
comparison, the Administrator
tentatively concluded that revising the
secondary 24-hour PM2.5 standard to be
identical to the proposed revised
primary PM2.5 standard (and retaining
the then-current annual secondary PM2.5
standard) was a reasonable policy
approach to addressing visibility
protection primarily in urban areas. In
proposing this approach, the
Administrator also solicited comment
on a sub-daily (4- to 8-hour averaging
time) secondary PM2.5 standard (71 FR
2675 to 2781, January 17, 2006).
In commenting on the proposed
decision, the CASAC requested that a
sub-daily standard to protect visibility
‘‘be favorably reconsidered’’
(Henderson, 2006a, p.6). The CASAC
noted three cautions regarding the
proposed reliance on a secondary PM2.5
standard identical to the proposed 24hour primary PM2.5 standard: (1) PM2.5
mass measurement is a better indicator
of visibility impairment during daylight
hours, when relative humidity is
generally low; the sub-daily standard
more clearly matches the nature of
visibility impairment, whose adverse
effects are most evident during the
daylight hours; using a 24-hour PM2.5
standard as a proxy introduces error and
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
uncertainty in protecting visibility; and
sub-daily standards are used for other
NAAQS and should be the focus for
visibility; (2) CASAC and its monitoring
subcommittees had repeatedly
commended EPA’s initiatives promoting
the introduction of continuous and
near-continuous PM monitoring and
recognized that an expanded
deployment of continuous PM2.5
monitors would be consistent with
setting a sub-daily standard to protect
visibility; and (3) the analysis showing
a similarity between percentages of
counties not likely to meet what the
CASAC Panel considered to be a lenient
4- to 8-hour secondary standard and a
secondary standard identical to the
proposed 24-hour primary standard was
a numerical coincidence that was not
indicative of any fundamental
relationship between visibility and
health. The CASAC Panel further stated
that ‘‘visual air quality is substantially
impaired at PM2.5 concentrations of 35
mg/m3’’ and that ‘‘[i]t is not reasonable
to have the visibility standard tied to the
health standard, which may change in
ways that make it even less appropriate
for visibility concerns’’ (Henderson,
2006a, pp. 5 to 6).
In reaching a final decision, the
Administrator focused on the relative
protection provided by the proposed
primary standards based on the abovementioned similarities in percentages of
counties meeting alternative standards
and on the limitations in the
information available concerning
studies of public perception and
attitudes regarding the acceptability of
various degrees of visibility impairment
in urban areas, as well as on the
subjective nature of the judgment
required. In so doing, the Administrator
concluded that caution was warranted
in establishing a distinct secondary
standard for visibility impairment and
that the available information did not
warrant adopting a secondary standard
that would provide either more or less
protection against visibility impairment
in urban areas than would be provided
by secondary standards set equal to the
proposed primary PM2.5 standards.
2. Remand of 2006 Secondary PM2.5
Standards
As noted above in section II.B.2
above, several parties filed petitions for
review challenging EPA’s decision to set
the secondary NAAQS for fine PM
identical to the primary NAAQS. On
judicial review, the D.C. Circuit
remanded to the EPA for
reconsideration the secondary NAAQS
for fine PM because the Agency’s
decision was unreasonable and contrary
to the requirements of section 109(b)(2).
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
American Farm Bureau Federation v.
EPA, 559 F. 3d 512 (D.C. Cir., 2009).
The petitioners argued that the EPA’s
decision lacked a reasoned basis. First,
they asserted that the EPA never
determined what level of visibility was
‘‘requisite to protect the public welfare.’’
They argued that the EPA unreasonably
rejected the target level of protection
recommended by its staff, while failing
to provide a target level of its own. The
court agreed, stating that ‘‘the EPA’s
failure to identify such a level when
deciding where to set the level of air
quality required by the revised
secondary fine PM NAAQS is contrary
to the statute and therefore unlawful.
Furthermore, the failure to set any target
level of visibility protection deprived
the EPA’s decision-making of a reasoned
basis.’’ 559 F. 3d at 530.
Second, the petitioners challenged
EPA’s method of comparing the
protection expected from potential
standards. They contended that the EPA
relied on a meaningless numerical
comparison, ignored the effect of
humidity on the usefulness of a
standard using a daily averaging time,
and unreasonably concluded that the
primary standards would achieve a level
of visibility roughly equivalent to the
level the EPA staff and CASAC deemed
‘‘requisite to protect the public welfare.’’
The court found that the EPA’s
equivalency analysis based on the
percentages of counties exceeding
alternative standards ‘‘failed on its own
terms.’’ The same table showing the
percentages of counties exceeding
alternative secondary standards, used
for comparison to the percentages of
counties exceeding alternative primary
standards to show equivalency, also
included six other alternative secondary
standards within the recommended
CASAC range that would be more
‘‘protective’’ under EPA’s definition
than the adopted primary standards.
Two-thirds of the potential secondary
standards within the CASAC’s
recommended range would be
substantially more protective than the
adopted primary standards. The court
found that the EPA failed to explain
why it looked only at one of the few
potential secondary standards that
would be less protective, and only
slightly less so, than the primary
standards. More fundamentally,
however, the court found that the EPA’s
equivalency analysis based on
percentages of counties demonstrated
nothing about the relative protection
offered by the different standards, and
that the tables offered no valid
information about the relative visibility
protection provided by the standards.
559 F. 3d at 530–31.
PO 00000
Frm 00101
Fmt 4701
Sfmt 4700
3185
Finally, the Staff Paper had made
clear that a visibility standard using
PM2.5 mass as the indicator in
conjunction with a daily averaging time
would be confounded by regional
differences in humidity. The court
noted that the EPA acknowledged this
problem, yet did not address this issue
in concluding that the primary
standards would be sufficiently
protective of visibility. 559 F. 3d at 530.
Therefore, the court granted the petition
for review and remanded for
reconsideration the secondary PM2.5
NAAQS.
3. General Approach Used in the Policy
Assessment for the Current Review
The approach used in this review
broadened the general approaches used
in the last two PM NAAQS reviews by
utilizing, to the extent available,
enhanced tools, methods, and data to
more comprehensively characterize
visibility impacts. As such, the EPA
took into account considerations based
on both the scientific evidence
(‘‘evidence-based’’) and a quantitative
analysis of PM-related impacts on
visibility (‘‘impact-based’’) to inform
conclusions related to the adequacy of
the current secondary PM2.5 standards
and alternative standards that were
appropriate for consideration in this
review. As in past reviews, the EPA also
considered that the secondary NAAQS
should address PM-related visibility
impairment in conjunction with the
Regional Haze Program, such that the
secondary NAAQS would focus on
protection from visibility impairment
principally in urban areas in
conjunction with the Regional Haze
Program that is focused on improving
visibility in Federal Class I areas. The
EPA again recognized that such an
approach remains the most appropriate
and effective means of addressing the
public welfare effects associated with
visibility impairment in areas across the
country.
The Policy Assessment drew from the
qualitative evaluation of all studies
discussed in the Integrated Science
Assessment (U.S. EPA, 2009a).
Specifically, the Policy Assessment
considered the extensive new air quality
and source apportionment information
available from the regional planning
organizations, long-standing evidence of
PM effects on visibility, and limited
public preference study information
from four urban areas (U.S. EPA, 2009a,
chapter 9), as well as the integration of
evidence across disciplines (U.S. EPA,
2009a, chapter 2). In addition, limited
information that had become available
regarding the characterization of public
preferences in urban areas provided
E:\FR\FM\15JAR2.SGM
15JAR2
3186
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
some new perspectives on the
usefulness of this information in
informing the selection of target levels
of urban visibility protection. On these
bases, the Policy Assessment again
focused assessments on visibility
conditions in urban areas.
The conclusions in the Policy
Assessment reflected EPA staff’s
understanding of both evidence-based
and impact-based considerations to
inform two overarching questions
related to (1) the adequacy of the current
suite of PM2.5 standards and (2) what
potential alternative standards, if any,
should be considered in this review to
provide appropriate protection from
PM-related visibility impairment. In
addressing these broad questions, the
discussions in the Policy Assessment
were organized around a series of more
specific questions reflecting different
aspects of each overarching question
(U.S. EPA, 2011a, Figure 4–1). When
evaluating the visibility protection
afforded by the current or any
alternative standards considered, the
Policy Assessment took into account the
four basic elements of the NAAQS:
indicator, averaging time, level, and
form.
tkelley on DSK3SPTVN1PROD with
B. Proposed Decisions on Secondary PM
Standards
At the time of proposal, the
Administrator proposed to revise the
suite of secondary PM standards by
adding a distinct standard for PM2.5 to
address PM-related visibility
impairment, focused primarily on
visibility in urban areas. This proposed
standard was to be defined in terms of
a PM2.5 visibility index, which would
use measured PM2.5 mass concentration,
in combination with speciation and
relative humidity data, to calculate
PM2.5 light extinction, translated into
the deciview (dv) scale; a 24-hour
averaging time; a 90th percentile form,
averaged over 3 years; and a level of 28–
30 dv. To address other non-visibility
welfare effects, the Administrator
proposed to retain the current suite of
secondary PM standards generally,
while revising only the form of the
secondary annual PM2.5 standard to
remove the option for spatial averaging
consistent with this proposed change to
the primary annual PM2.5 standard. Each
of these proposed decisions is described
in more detail in the proposal and
below.
1. PM-Related Visibility Impairment
As discussed in Section VI.B of the
proposal, the Administrator’s proposed
decision regarding a distinct secondary
standard to provide protection from
visibility impairment reflected careful
VerDate Mar<15>2010
21:22 Jan 14, 2013
Jkt 229001
consideration of the following: (1) The
latest scientific information on visibility
effects associated with PM as described
in the Integrated Science Assessment
(U.S. EPA, 2009a); (2) insights gained
from assessments of correlations
between ambient PM2.5 and visibility
impairment prepared by EPA staff in the
Visibility Assessment (U.S. EPA,
2010b); and (3) specific conclusions
regarding the need for revisions to the
current standards (i.e., indicator,
averaging time, form, and level) that,
taken together, would be requisite to
protect the public welfare from adverse
effects on visual air quality. This section
summarizes key information from the
proposal regarding the nature of
visibility impairment, including the
relationship between ambient PM and
visibility, temporal variations in light
extinction, periods during the day of
interest for assessing visibility
conditions, and exposure durations of
interest (section VI.B.1.a); limited public
perceptions and attitudes about
visibility impairment and the impacts of
visibility impairment on public welfare
(section VI.B.1.b); CASAC advice
regarding the need for, and design of,
secondary standards to protect visibility
(section VI.B.1.c); and the
Administrator’s proposed conclusions
regarding setting a distinct standard to
address visibility impairment (section
VI.B.1.d).
a. Nature of PM-Related Visibility
Impairment
As noted at the time of proposal, the
fundamental science characterizing the
contribution of PM, especially fine
particles, to visibility impairment is
well understood. This science provides
the basis for the Integrated Science
Assessment designation of the
relationship between PM and visibility
impairment as causal. New research
available in this review, discussed in
chapter 9 of the Integrated Science
Assessment, continues to support and
refine EPA’s understanding of the effect
of PM on visibility and the source
contributions to that effect in rural and
remote locations. This research provides
new insights regarding the regional
source contributions to urban visibility
impairment and better characterization
of the increment in PM concentrations
and visibility impairment that occur in
many cities (i.e., the urban excess)
relative to conditions in the surrounding
rural areas (i.e., regional background).
Ongoing urban PM2.5 speciated and
aggregated mass monitoring has
produced new information that has
allowed for updated characterization of
current visibility levels in urban areas.
PO 00000
Frm 00102
Fmt 4701
Sfmt 4700
i. Relationship Between Ambient PM
and Visibility
Visibility impairment is caused by the
scattering and absorption of light by
suspended particles and gases in the
atmosphere. When PM is present in the
air, its contribution to light extinction
typically greatly exceeds that of gases.
The combined effect of light scattering
and absorption by both particles and
gases is characterized as light
extinction, i.e., the fraction of light that
is scattered or absorbed in the
atmosphere. Light extinction can be
quantified by a light extinction
coefficient with units of 1/distance,
which is often expressed as 1/(1 million
meters) or inverse megameters
(abbreviated Mm–1) or in terms of an
alternative scale known as the deciview
scale, defined by the following
equation: 146
Deciview (dv) = 10 ln (bext/ 10 Mm-1)
The deciview scale is frequently used in
the scientific literature on visibility, as
well as in the Regional Haze Program.
In particular, the deciview scale is used
in the public perception studies that
were considered in the past and current
reviews to inform judgments about an
appropriate degree of protection to be
provided by a secondary NAAQS.
The amount of light extinction
contributed by PM depends on the
particle concentration as well as on the
particle size distribution and
composition and also on the relative
humidity. As described in detail in
section VI.B.1.a of the proposal,
visibility scientists have developed an
algorithm, known as the IMPROVE
algorithm,147 to estimate light extinction
using routinely monitored fine particle
(PM2.5) speciation and coarse particle
mass (PM10-2.5) data, as well as data on
relative humidity. There is both an
original and a revised version of the
IMPROVE algorithm (Pitchford et al.,
2007). The revised version was
developed to address observed biases in
the predictions using the original
algorithm under very low and very high
146 As used in the Regional Haze Program, the
term bext refers to light extinction due to PM2.5,
PM10-2.5, and ‘‘clean’’ atmospheric gases. In the
Policy Assessment, in focusing on light extinction
due to PM2.5, the deciview values include only the
effects of PM2.5 and the gases. The ‘‘Rayleigh’’ term
associated with clean atmospheric gases is
represented by the constant value of 10 Mm¥1.
Omission of the Rayleigh term would create the
possibility of negative deciview values when the
PM2.5 concentration is very low.
147 The algorithm is referred to as the IMPROVE
algorithm because it was developed specifically to
use the aerosol monitoring data generated at
network sites and with equipment specifically
designed to support the IMPROVE program and was
evaluated using IMPROVE optical measurements at
the subset of sites that make those measurements
(Malm et al., 1994).
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
light extinction conditions.148 These
IMPROVE algorithms are routinely used
to calculate light extinction levels on a
24-hour basis in Federal Class I areas
under the Regional Haze Program.
In either version of the IMPROVE
algorithm, the concentration of each of
the major aerosol components is
multiplied by a dry extinction efficiency
value and, for the hygroscopic
components (i.e., ammoniated sulfate
and ammonium nitrate), also multiplied
by an additional factor to account for
the water growth to estimate these
components’ contribution to light
extinction. Summing the contribution of
each component gives the estimate of
total light extinction per unit distance
denoted as the light extinction
coefficient (bext), as shown below for the
original IMPROVE algorithm.
bext ≈ 3 × f(RH) × [Sulfate]
+ 3 × f(RH) x [Nitrate]
+ 4 × [Organic Mass]
+ 10 × [Elemental Carbon]
+ 1 × [Fine Soil]
+ 0.6 × [Coarse Mass]
+ 10
Light extinction (bext) is in units of
Mm-1, the mass concentrations of the
components indicated in brackets are in
units of mg/m3, and f(RH) is the unitless
water growth term that depends on
relative humidity. The final term of 10
Mm-1 is known as the Rayleigh
scattering term and accounts for light
scattering by the natural gases in
unpolluted air. Despite the simplicity of
this algorithm, it performs reasonably
well and permits the contributions to
light extinction from each of the major
components (including the water
associated with the sulfate and nitrate
compounds) to be separately
approximated. Inspection of the PM
component-specific terms in the simple
original IMPROVE algorithm shows that
most of the PM2.5 components
contribute 5 times or more light
extinction than a similar concentration
of PM10-2.5.
The f(RH) term in the original
algorithm reflects the increase in light
scattering caused by particulate sulfate
and nitrate under conditions of high
relative humidity. Particles with
hygroscopic components (e.g.,
particulate sulfate and nitrate)
contribute more light extinction at
higher relative humidity than at lower
relative humidity because they change
size in the atmosphere in response to
ambient relative humidity conditions.
For relative humidity below 40 percent
148 These biases were detected by comparing light
extinction estimates generated from the IMPROVE
algorithm to direct optical measurements in a
number of rural Federal Class I areas.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
the f(RH) value is 1, but it increases to
2 at approximately 66 percent, 3 at
approximately 83 percent, 4 at
approximately 90 percent, 5 at
approximately 93 percent, and 6 at
approximately 95 percent relative
humidity. The result is that both
particulate sulfate and nitrate are more
efficient per unit mass in light
extinction than any other aerosol
component for relative humidity above
approximately 85 percent where their
total light extinction efficiency exceeds
the 10 m2/g associated with elemental
carbon (EC). PM containing elemental or
black carbon (BC) absorbs light as well
as scattering it, making it the component
with the greatest light extinction
contributions per unit of mass
concentration, except for the
hygroscopic components under these
high relative humidity conditions.149
As noted above, subsequent to the
development of the original IMPROVE
algorithm, an alternative algorithm
(variously referred to as the ‘‘revised
algorithm’’ or the ‘‘new algorithm’’ in
the literature) was developed. The
revised IMPROVE algorithm is different
from the original algorithm in several
important ways. First, the revised
algorithm employs a more complex
split-component mass extinction
efficiency to correct biases believed to
be related to particle size
distributions.150 Specifically, the
revised algorithm incorporates terms to
account for particles representing the
different dry extinction and water
uptake from two size modes of sulfate,
nitrate and organic mass.151 Second, the
149 The IMPROVE algorithm does not explicitly
separate the light-scattering and light-absorbing
effects of elemental carbon.
150 In either version of the IMPROVE algorithm,
the concentration of each of the major aerosol
components is multiplied by a dry extinction
efficiency value and, for the hygroscopic
components (i.e., ammoniated sulfate and
ammonium nitrate), also multiplied by an
additional factor to account for the water growth to
estimate these components’ contribution to light
extinction. Both the dry extinction efficiency and
water growth terms have been developed by a
combination of empirical assessment and
theoretical calculation using typical particle size
distributions associated with each of the major
aerosol components.
151 The relative contributions of sulfate, nitrate,
and organic mass concentrations to visibility
impairment with the revised algorithm are different
than with the original algorithm due to the
combination of the dry extinction coefficient and
f(RH) functions for derived concentrations of small
and large particles. The apportionment of the total
fine particle concentration of each of the three PM2.5
components into the concentrations of the small
and large size fractions was empirically developed
for remote areas. The fraction of the fine particle
component that is in the large mode is estimated
by dividing the total concentration of the
component by 20 mg/m3. If the total concentration
of a component exceeds 20 mg/m3, all of it is
assumed to be in the large mode.
PO 00000
Frm 00103
Fmt 4701
Sfmt 4700
3187
revised algorithm uses a different
multiplier for organic carbon for
purposes of estimating organic
carbonaceous material to better
represent aged aerosol found in remote
areas.152 In addition, the revised
algorithm includes a term for
hygroscopic sea salt that can be
important for remote coastal areas, and
site-specific Rayleigh light scattering
terms in place of a universal Rayleigh
light scattering value. As noted in
section VI.B.1.a of the proposal, the
revised IMPROVE algorithm can yield
higher estimates of current light
extinction levels in urban areas on days
with relatively poor visibility as
compared to the original algorithm
(Pitchford, 2010). This difference is
primarily attributable to the splitcomponent mass extinction efficiency
treatment in the revised algorithm. This
revised algorithm was evaluated at 21
remote locations and is generally used
by RPOs and States for implementation
of the Regional Haze Rule.
ii. Temporal Variations of Light
Extinction
Particulate matter concentrations and
light extinction in urban environments
vary from hour to hour throughout the
24-hour day due to a combination of
diurnal changes in meteorological
conditions and systematic changes in
emissions activity (e.g., rush hour
traffic). Various factors combine to make
early morning the most likely time for
peak urban light extinction; although
the net effects of the systematic urbanand larger-scale variations mean that
peak daytime PM light extinction levels
can occur any time of day, in many
areas they occur most often in early
morning hours (U.S. EPA, 2010b,
sections 3.4.2 and 3.4.3; Figures 3–9, 3–
10, and 3–12). This temporal pattern in
urban areas contrasts with the general
lack of a strong diurnal pattern in PM
concentrations and light extinction in
most Federal Class I areas, reflective of
a relative lack of local sources as
compared to urban areas. The use in the
Regional Haze Program of 24-hour
average concentrations in the IMPROVE
algorithm is consistent with this general
lack of a strong diurnal pattern in
Federal Class I areas.
iii. Periods During the Day of Interest for
Assessment of Visibility
As noted in sections VI.B.1.b and
VI.B.1.c of the proposal, daytime
visibility has dominated the attention of
152 The revised IMPROVE algorithm uses a
multiplier of 1.8 for rural areas instead of 1.4 as
used in the original algorithm for the mean ratio of
organic mass to organic carbon.
E:\FR\FM\15JAR2.SGM
15JAR2
3188
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
those who have studied the visibility
effects of air pollution, particularly in
urban areas. The EPA recognizes,
however, that physically PM light
extinction behaves the same at night as
during the day and can contribute to
nighttime visibility effects by enhancing
the scattering of anthropogenic light,
contributing to the ‘‘skyglow’’ within
and over populated areas, adding to the
total sky brightness, and contributing to
the reduction in contrast of stars against
the background. However, little research
has been conducted on nighttime
visibility, and the state of the science is
not comparable to that associated with
daytime visibility impairment,
particularly in terms of the impact on
human welfare. The Policy Assessment
notes that the science is not available at
this time to support adequate
characterization specifically of
nighttime PM light extinction
conditions and the related effects on
public welfare (U.S. EPA, 2011a, p. 4–
18). Therefore the EPA has focused its
assessments of PM visibility impacts in
urban areas on daylight hours during
this review.
iv. Exposure Durations of Interest
As noted in section VI.B.1.d of the
proposal, the roles that exposure
duration and variations in visual air
quality within any given exposure
period play in determining the
acceptability or unacceptability of a
given level of visual air quality have not
been investigated via preference studies.
In the preference studies available for
this review, subjects were simply asked
to rate the acceptability or
unacceptability of each image of a hazeobscured scene, without being provided
any suggestion of assumed duration or
of assumed conditions before or after
the occurrence of the scene presented.
Preference and/or valuation studies
show that atmospheric visibility
conditions can be quickly assessed and
preferences determined. The EPA is
unaware of any studies that characterize
the extent to which different frequencies
and durations of exposure to visibility
conditions contribute to the degree of
public welfare impact that occurs.
The Policy Assessment considered a
variety of circumstances that are
commonly expected to occur in
evaluating the potential impact of
visibility impairment on the public
welfare based on available information
(U.S. EPA, 2011a, pp. 4–19 to 4–20). In
some circumstances, such as infrequent
visits to scenic vistas in natural or urban
environments, people are motivated
specifically to take the opportunity to
view a valued scene and are likely to do
so for many minutes to hours to
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
appreciate various aspects of the vista
they choose to view. However, the
public has many more opportunities to
notice visibility conditions on a daily
basis in settings associated with
performing daily routines (e.g., during
commutes and while working,
exercising, or recreating outdoors). As
noted in the Policy Assessment,
information regarding the fraction of the
public that has only one or a few
opportunities to experience visibility
during the day, or on the role the
duration of the observed visibility
conditions has on wellbeing effects
associated with those visibility
conditions, is not available (U.S. EPA,
2011a, p. 4–20). However, it is possible
that people with limited opportunities
to experience visibility conditions on a
daily basis would receive the entire
impact of the day’s visual air quality
based on the visibility conditions that
occur during the short time period when
they can see it. Since this group could
be affected on the basis of observing
visual air quality conditions for periods
as short as one hour or less, and because
during each daylight hour there are
some people outdoors, commuting, or
near windows, the Policy Assessment
judged that it would be appropriate to
use the maximum hourly value of PM
light extinction during daylight hours
for each day for purposes of evaluating
the adequacy of the current suite of
secondary standards. Other observers
may have access to visibility conditions
throughout the day. For this group, it
might be that an hour with poor or
‘‘unacceptable’’ visibility can be offset
by one or more other hours with clearer
conditions. Therefore, the proposal
acknowledged that it might also be
appropriate to consider a multi-hour
daylight exposure period.
v. Periods of Fog and Rain
As discussed in section VI.C of the
proposal, the EPA also recognized that
it is appropriate to give special
treatment to periods of fog and rain
when considering whether current PM2.5
standards adequately protect public
welfare from PM-related visibility
impairment. Visibility impairment
occurs during periods with fog or
precipitation irrespective of the
presence or absence of PM. Therefore, it
is logical that periods with naturally
impaired visibility due to fog or
precipitation should not be treated as
having PM-impaired visibility. There
are multiple ways to adjust visibility
data to reduce the effects of fog and
precipitation. In the Visibility
Assessment, following the advice of
CASAC, the EPA evaluated the effect of
excluding daylight hours for which
PO 00000
Frm 00104
Fmt 4701
Sfmt 4700
relative humidity was greater than 90
percent from analyses in order to avoid
precipitation and fog confounding
estimates of PM visibility impairment.
For the 15 urban areas included in the
Visibility Assessment, the EPA found
that a 90 percent relative humidity
cutoff criterion was effective in that on
average less than 6 percent of the
daylight hours were removed from
consideration, yet those hours had on
average ten times the likelihood of rain,
six times the likelihood of snow/sleet,
and 34 times the likelihood of fog
compared with hours with 90 percent or
lower relative humidity. In the Regional
Haze program, the EPA utilizes monthly
average relative humidity values based
on 10 years of climatological data to
reduce the effect of fog and
precipitation. This approach focuses on
longer-term averages for each
monitoring site and thereby eliminates
the effect of very high humidity
conditions on visibility at those
locations.
b. Public Perception of Visibility
Impairment
As described in section VI.B.2 of the
proposal, there are two main types of
studies that evaluate the public
perception of urban visibility
impairment: urban visibility preference
studies and urban visibility valuation
studies. As noted in the Integrated
Science Assessment, ‘‘[b]oth types of
studies are designed to evaluate
individuals’ desire (or demand) for good
visual air quality (VAQ) where they live,
using different metrics to evaluate
demand. Urban visibility preference
studies examine individuals’ demand by
investigating what amount of visibility
degradation is unacceptable while
economic studies examine demand by
investigating how much one would be
willing to pay to improve visibility’’
(U.S. EPA, 2009a, p. 9–66). Because of
the limited number of new studies on
urban visibility valuation, the Integrated
Science Assessment cites to the
discussion in the 2004 Criteria
Document of the various methods one
can use to determine the economic
valuation of changes in visibility, which
include hedonic valuation, contingent
valuation and contingent choice, and
travel cost.
Contingent valuation studies are a
type of stated preference study that
measures the strength of preferences
and expresses that preference in dollar
values. Contingent valuation studies
often include payment vehicles that
require respondents to consider
implementation costs and their ability
to pay for visibility improvements in
their responses. This study design
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
aspect is critical because the EPA
cannot consider implementations costs
in setting either primary or secondary
NAAQS. Therefore in considering the
information available to help inform the
standard-setting process, the EPA has
focused on the public perception
studies that do not embed consideration
of implementation costs. Nonetheless,
the EPA recognizes that valuation
studies do provide additional evidence
that the public is experiencing losses in
welfare due to visibility impairment.153
The public perception studies are
described in detail below.
In order to identify levels of visibility
impairment appropriate for
consideration in setting secondary PM
NAAQS to protect the public welfare,
the Visibility Assessment
comprehensively examined information
that was available in this review
regarding people’s stated preferences
regarding acceptable and unacceptable
visual air quality.
Light extinction is an atmospheric
property that by itself does not directly
translate into a public welfare effect.
Instead, light extinction becomes
meaningful in the context of the impact
of differences in visibility on the human
observer. This has been studied in terms
of the acceptability or unacceptability
expressed for the visibility impact of a
given level of light extinction by a
human observer. The perception of the
visibility impact of a given level of light
extinction occurs in conjunction with
the associated characteristics and
lighting conditions of the viewed
scene.154 Thus, a given level of light
extinction may be perceived differently
by observers looking at different scenes
153 In the regulatory impact analysis (RIA)
accompanying this rulemaking, the EPA describes
a revised approach to estimate urban residential
visibility benefits that applies the results of several
contingent valuation studies. The EPA is unable to
apply the public perception studies to estimate
benefits because they do not provide sufficient
information on which to develop monetized
benefits estimates. Specifically, the public
perception studies do not provide preferences
expressed in dollar values, even though they do
provide additional evidence that the benefits
associated with improving residential visibility are
not zero. As previously noted in this preamble, the
RIA is done for informational purposes only, and
the proposed decisions on the NAAQS in this
rulemaking are not in any way based on
consideration of the information or analyses in the
RIA.
154 By ‘‘characteristics of the scene’’ the EPA
means the distance(s) between the viewer and the
object(s) of interest, the shapes and colors of the
objects, the contrast between objects and the sky or
other background, and the inherent interest of the
objects to the viewer. Distance is particularly
important because at a given value of light
extinction, which is a property of air at a given
point(s) in space, more light is actually absorbed
and scattered when light passes through more air
between the object and the viewer.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
or the same scene with different lighting
characteristics. Likewise, different
observers looking at the same scene
with the same lighting may have
different preferences regarding the
associated visual air quality. When
scene and lighting characteristics are
held constant, the perceived appearance
of a scene (i.e., how well the scenic
features can be seen and the amount of
visible haze) depends only on changes
in light extinction. This has been
demonstrated using the WinHaze model
(Molenar et al., 1994) that uses image
processing technology to apply userspecified changes in light extinction
values to the same base photograph with
set scene and lighting characteristics.
Much of what is known about the
acceptability of levels of visibility
comes from survey studies in which
participants were asked questions about
their preference or the value they place
on various visibility levels as displayed
to them in scenic photographs and/or
WinHaze images with a range of known
light extinction levels. The Visibility
Assessment (U.S. EPA, 2010b, chapter
2) reviewed the limited number of urban
visibility preference studies currently
available (i.e., four studies) to assess the
light extinction levels judged by the
participant to have acceptable visibility
for those particular scenes.
The reanalysis of urban preference
studies conducted in the Visibility
Assessment for this review included
three completed western urban visibility
preference survey studies plus a pair of
smaller focus studies designed to
explore and further develop urban
visibility survey instruments. The three
western studies included one in Denver,
Colorado (Ely et al., 1991), one in the
lower Fraser River valley near
Vancouver, British Columbia (BC),
Canada (Pryor, 1996), and one in
Phoenix, Arizona (BBC Research &
Consulting, 2003). A pilot focus group
study was also conducted for
Washington, DC (Abt Associates Inc.,
2001). In response to an EPA request for
public comment on the Scope and
Methods Plan (74 FR 11580, March 18,
2009), comments were received (Smith,
2009) about the results of a new focus
group study of scenes from Washington,
DC, that had been conducted on subjects
from both Houston, Texas, and
Washington, DC, using scenes, methods
and approaches similar to the method
and approach employed in the EPA
pilot study (Smith and Howell, 2009).
When taken together, these studies from
the four different urban areas included
a total of 852 individuals, with each
individual responding to a series of
questions while viewing a set of images
PO 00000
Frm 00105
Fmt 4701
Sfmt 4700
3189
of various urban visual air quality
conditions.
The approaches used in the four
studies were similar and were all
derived from the method first developed
for the Denver urban visibility study. In
particular, the studies all used a similar
group interview type of survey to
investigate the level of visibility
impairment that participants described
as ‘‘acceptable.’’ In each preference
study, participants were initially given
a set of ‘‘warm up’’ exercises to
familiarize them with how the scene in
the photograph or image appears under
different VAQ conditions. The
participants next were shown 25
randomly ordered photographs (images),
and asked to rate each one based on a
scale of 1 (poor) to 7 (excellent). They
were then shown the same photographs
or images again, in the same order, and
asked to judge whether each of the
photographs (images) would violate
what they would consider to be an
appropriate urban visibility standard
(i.e. whether the level of impairment
was ‘‘acceptable’’ or ‘‘unacceptable’’).
The term ‘‘acceptable’’ was not defined,
so that each person’s response was
based on his/her own values and
preferences for VAQ. However, when
answering this question, participants
were instructed to consider the
following three factors: (1) The standard
would be for their own urban area, not
a pristine national park area where the
standards might be stricter; (2) The level
of an urban visibility standard violation
should be set at a VAQ level considered
to be unreasonable, objectionable, and
unacceptable visually; and (3)
Judgments of standards violations
should be based on visibility only, not
on health effects. While the results
differed among the four urban areas,
results from a rating exercise show that
within each preference study,
individual survey participants
consistently distinguish between photos
or images representing different levels
of light extinction, and that more
participants rate as acceptable images
representing lower levels of light
extinction than they do images
representing higher levels.
Given the similarities in the
approaches used, the EPA staff
concluded that it was reasonable to
compare the results to identify overall
trends in the study findings and to
conclude that this comparison can
usefully inform the selection of a range
of levels for use in further analyses.
However, the staff also noted that
variations in the specific materials and
methods used in each study introduce
uncertainties that should also be
considered when interpreting the results
E:\FR\FM\15JAR2.SGM
15JAR2
3190
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
graphical summary of the results of the
studies in the four cities and draws on
results previously presented in Figures
2–3, 2–5, 2–7, and 2–11 of chapter 2 in
the Visibility Assessment. Figure 5 also
contains lines at 20 dv and 30 dv that
generally identify a range where the 50
percent acceptance criteria occur across
all four of the urban preference studies
(U.S. EPA, 2011a, p. 4–24). Out of the
114 data points shown in Figure 5, only
one photograph (or image) with a visual
air quality below 20 dv was rated as
acceptable by less than 50 percent of the
participants who rated that
photograph.155 Similarly, only one
image with a visual air quality above 30
dv was rated acceptable by more than 50
percent of the participants who viewed
it.156
analysis using a logit model of the
greater than 19,000 ratings of haze
images as acceptable or unacceptable.
The model results can be used to
estimate the visual air quality in terms
of dv values where the estimated
response functions cross the 50 percent
acceptability level, as well as any
alternative criteria levels. Selected
examples of these are shown in Table 4–
155 Only 47 percent of the British Columbia
participants rated a 19.2 dv photograph as
acceptable.
156 In the 2001 Washington, DC study, a 30.9 dv
image was used as a repeated slide. The first time
it was shown 56 percent of the participants rated
it as acceptable, but only 11 percent rated it as
acceptable the second time it was shown. The same
visual air quality level was rated as acceptable by
4 percent of the participants in the 2009 study (Test
1). All three points are shown in Figure 5.
157 Top scale shows light extinction in inverse
megameter units; bottom scale in deciviews. Logit
analysis estimated response functions are shown as
the color-coded curved lines for each of the four
urban areas.
158 At present, data is only available for four
urban areas, as presented in Figure 5 and discussed
throughout this section. Additional research could
help inform whether the range identified by
combining the results of the studies depicted in
Figure 5 is more broadly representative.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
PO 00000
Frm 00106
Fmt 4701
Sfmt 4700
E:\FR\FM\15JAR2.SGM
15JAR2
ER15JA13.004
photograph as ‘‘acceptable.’’ Ely et al.
(1991) introduced a ‘‘50% acceptability’’
criterion analysis of the Denver
preference study results. The 50 percent
acceptability criterion is designed to
identify the visual air quality level
(defined in terms of deciviews or light
extinction) that best divides the
photographs into two groups: Those
with a visual air quality rated as
acceptable by the majority of the
participants, and those rated not
acceptable by the majority of
participants. The Visibility Assessment
adopted this criterion as a useful index
for comparison between studies. The
results of each analysis were then
combined graphically to allow for visual
comparison. This information was then
carried forward into the Policy
Assessment. Figure 5 presents the
As Figure 5 above shows, each urban
area has a separate and unique response
curve that appears to indicate that it is
distinct from the others.158 These curves
are the result of a logistical regression
tkelley on DSK3SPTVN1PROD with
of these comparisons. Key differences
between the studies include the
following: (1) Scene characteristics; (2)
image presentation methods (e.g.,
projected slides of actual photos,
projected images generated using
WinHaze (a significant technical
advance in the method of presenting
visual air quality conditions), or use of
a computer monitor screen; (3) number
of participants in each study; (4)
participant representativeness of the
general population of the relevant
metropolitan area; and (5) specific
wording used to frame the questions
used in the group interview process.
In the Visibility Assessment, each
study was evaluated separately and
figures developed to display the
percentage of participants that rated the
visual air quality depicted in each
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
1 of the Policy Assessment (U.S. EPA,
2011a; U.S. EPA, 2010b, Table 2–4).
This table shows that the logit model
results also support the upper and lower
ends of the range of 50th percentile
acceptability values (e.g., near 20 dv for
Denver and near 30 dv for Washington,
DC) already identified in Figure 5.
Based on the composite results and
the effective range of 50th percentile
acceptability across the four urban
preference studies shown in Figure 5
and Table 4–1 of the Policy Assessment,
benchmark levels of (total) light
extinction were selected in a range from
20 dv to 30 dv (75 to 200 Mm¥1) 159 for
the purpose of provisionally assessing
whether visibility conditions would be
considered acceptable (i.e., less than the
low end of the range), unacceptable (i.e.,
greater than the high end of the range),
or potentially acceptable (within the
range) based on the very limited public
preference information. A midpoint of
25 dv (120 Mm¥1) was also selected for
use in the assessment. This level is also
very near to the 50th percentile criterion
value from the Phoenix study (i.e., 24.2
dv), which is by far the best of the four
studies in terms of the fit of the data to
the response curve and the
representativeness of study participants.
Based on the currently available
information, the Policy Assessment
concluded that the use of 25 dv to
represent the middle of the distribution
of results seemed well supported (U.S.
EPA, 2011a, p. 4–25).
These three benchmark values
provide a low, middle, and high set of
light extinction conditions that are used
to provisionally define daylight hours
with urban haze conditions that have
been judged unacceptable by at least 50
percent of the participants in one or
more of these preference studies. As
discussed above, PM light extinction is
taken to be (total) light extinction minus
the Rayleigh scatter,160 such that the
low, middle, and high levels correspond
to PM light extinction levels of about 65
Mm¥1, 110 Mm¥1, and 190 Mm¥1. In
the Visibility Assessment, these three
159 These values were rounded from 74 Mm¥1
and 201 Mm¥1 to avoid an implication of greater
precision than is warranted. Note that the middle
value of 25 dv when converted to light extinction
is 122 Mm¥1 is rounded to 120 Mm¥1 for the same
reason. Assessments conducted for the Visibility
Assessment and the first and second drafts of the
Policy Assessment used the unrounded values. The
Policy Assessment considered the results of
assessment using unrounded values to be
sufficiently representative of what would result if
the rounded values were used that it was
unnecessary to redo the assessments. That is why
some tables and figures in the Policy Assessment
reflected the unrounded values.
160 Rayleigh scatter is light scattering by
atmospheric gases which is on average about 10
Mm¥1.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
light extinction levels were called
Candidate Protection Levels (CPLs).
This term was also used in the Policy
Assessment and in the proposal notice.
It is important to note, however, that the
degree of protection provided by a
secondary NAAQS is not determined
solely by any one component of the
standard but by all the components (i.e.,
indicator, averaging time, form, and
level) being applied together. Therefore,
the Policy Assessment noted that the
term CPL is meant only to indicate
target levels of visibility within a range
that the EPA staff felt appropriate for
consideration that could, in conjunction
with other elements of the standard,
including indicator, averaging time, and
form, potentially provide an appropriate
degree of visibility protection.
In characterizing the Policy
Assessment’s confidence in each CPL
and across the range, a number of issues
were considered (U.S. EPA, 2011a, p. 4–
26). Looking first at the two studies that
define the upper and lower bounds of
the range, the Policy Assessment
considered whether they represent a
true regional distinction in preferences
for urban visibility conditions between
western and eastern U.S. There was
little information available to help
evaluate the possibility of a regional
distinction especially given that there
have been preference studies in only
one eastern urban area. Smith and
Howell (2009) found little difference in
preference response to Washington, DC,
haze photographs between the study
participants from Washington, DC, and
those from Houston, Texas.161 This
provides some limited evidence that the
value judgment of the public in different
areas of the country may not be an
important factor in explaining the
differences in these study results.
In further considering what factors
could explain the observed differences
in preferences across the four urban
areas, the Policy Assessment noted that
the urban scenes used in each study had
different characteristics (U.S. EPA,
2011a, p. 4–26). For example, each of
the western urban visibility preference
study scenes included mountains in the
background while the single eastern
urban study did not. It is also true that
each of the western scenes included
objects at greater distances from the
camera location than in the eastern
161 The
first preference study using WinHaze
images of a scenic vista from Washington, DC was
conducted in 2001 using subjects who were
residents of Washington, DC. More recently, Smith
and Howell (2009) interviewed additional subjects
using the same images and interview procedure.
The additional subjects included some residents of
the Washington, DC area and some residents of the
Houston, Texas area.
PO 00000
Frm 00107
Fmt 4701
Sfmt 4700
3191
study. There is no question that objects
at a greater distance have a greater
sensitivity to perceived visibility
changes as light extinction is changed
compared to otherwise similar scenes
with objects at a shorter range. This
alone might explain the difference
between the results of the eastern study
and those from the western urban
studies. Having scenes with the object of
greatest intrinsic value nearer and hence
less sensitive in the eastern urban area
compared with more distant objects of
greatest intrinsic value in the western
urban areas could further explain the
difference in preference results.
Another question considered was
whether the high CPL value that is
based on the eastern preference results
is likely to be generally representative of
urban areas that do not have associated
mountains or other valued objects
visible in the distant background. Such
areas would include the middle of the
country, many areas in the eastern U.S.,
and possibly some areas in the western
U.S. as well.162 Based on the currently
available information, the Policy
Assessment concluded that the high end
of the CPL range (30 dv) is an
appropriate level to consider (U.S. EPA,
2011a, p. 4–27).
With respect to the low end of the
range, the Policy Assessment considered
factors that might further refine its
understanding of the robustness of this
level. The Policy Assessment concluded
that additional urban preference studies,
especially with a greater variety in types
of scenes, could help evaluate whether
the lower CPL value of 20 dv is
generally supportable (U.S. EPA, 2011a,
p. 4–27). Further, the reason for the
noisiness in data points around the
curves apparent in both the Denver and
British Columbia results compared to
the smoother curve fit of Phoenix study
results could be explored. One possible
explanation discussed in the Policy
Assessment is that these older studies
use photographs taken at different times
of day and on different days to capture
the range of light extinction levels
needed for the preference studies. In
contrast, the use of WinHaze in the
Phoenix (and Washington, DC) study
reduced variations that affect scene
appearance preference rating and
avoided the uncertainty inherent in
using ambient measurements to
162 In order to examine this issue, an effort would
have to be made to see if scenes in such areas could
be found that would be generally comparable to the
western scenes (e.g., scenes that contain valued
scenic elements at more sensitive distances than
that used in the eastern study). This is only one of
a family of issues concerning how exposure to
urban scenes of varying sensitivity affects public
perception for which no preference study
information is currently available.
E:\FR\FM\15JAR2.SGM
15JAR2
3192
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
represent sight path-averaged light
extinction values. Reducing these
sources of noisiness and uncertainty in
the results of future studies of sensitive
urban scenes could provide more
confidence in the selection of a low CPL
value.
Based on the above considerations,
and recognizing the limitations in the
currently available information, the
Policy Assessment concluded that it is
reasonable to consider a range of CPL
values including a high value of 30 dv,
a mid-range value of 25 dv, and a low
value of 20 dv (U.S. EPA, 2011a, p. 4–
27). Based on its review of the second
draft Policy Assessment, CASAC also
supported this set of CPLs for
consideration by the EPA in this review.
CASAC noted that these CPL values
were based on all available visibility
preference data and that they bound the
study results as represented by the 50
percent acceptability criteria. While
recommending that further visibility
preference studies be conducted to
reduce remaining uncertainties,163
CASAC concluded that this range of
levels was ‘‘adequately supported by the
evidence presented’’ (Samet, 2010d, p.
iii).
c. Summary of Proposed Conclusions
tkelley on DSK3SPTVN1PROD with
i. Adequacy of the Current Standards for
PM-Related Visibility Impairment
At the time of proposal, the
Administrator provisionally concluded
that the current suite of secondary PM
standards is not sufficiently protective
of visual air quality, and that
consideration should be given to an
alternative secondary standard that
would provide additional protection
against PM-related visibility
impairment, with a focus primarily in
urban areas. This proposed conclusion
was based on the information presented
in the proposal with regard to the nature
of PM-related visibility impairment, the
results of public perception surveys on
the acceptability of varying degrees of
visibility impairment in urban areas,
analyses of the number of days that are
estimated to exceed a range of candidate
protection levels under conditions
simulated to just meet the current
standards, and the advice of CASAC.
This section summarizes key points
from section VI.C of the proposal
163 ‘‘CASAC has also identified needs for the next
review cycle in terms of further research on a
number of topics related to urban visibility; * * *.
In particular, there is a need for the Agency to
conduct additional urban visibility preference
studies over a broad range of urban areas and
viewing conditions, to further evaluate and refine
the range of visibility levels considered to be
acceptable in the current assessment.’’ (Samet,
2010a)
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
regarding visibility under current
conditions, the degree of protection
afforded by the current standards, and
CASAC’s advice regarding the adequacy
of the current standards.
As discussed in section VI.C.1 of the
proposal, to evaluate visibility under
current conditions the Visibility
Assessment and Policy Assessment
estimated PM-related light extinction164
levels for 15 urban areas165 in the
United States. Consistent with the
emphasis in this review on the hourly
or multi-hour time periods that might
reasonably characterize the visibility
effects experienced by various segments
of the population, these analyses
focused on using maximum 1-hour and
4-hour values of PM light extinction
during daylight hours for purposes of
evaluating the degree of visibility
impairment. Hourly average PM-related
light extinction was analyzed in terms
of both PM10 and PM2.5 light extinction.
For reasons discussed above, hours with
relative humidity greater than 90
percent were excluded from
consideration. Recent visibility
conditions in these urban areas were
then compared to the CPLs identified
above. The Visibility Assessment, which
focused on PM10 light extinction in 14
of the 15 urban areas during the 2005 to
2007 time period,166 found that all 14
areas had daily maximum hourly PM10
light extinction values estimated to
exceed even the highest CPL some of the
days. Except for the two Texas areas and
the non-California western urban areas,
all of the other urban areas were
estimated to have maximum hourly
PM10 concentrations that exceeded the
high CPL on about 20 percent to over 60
percent of the days. All 14 of the urban
164 PM-related light extinction is used here to
refer to the light extinction caused by PM regardless
of particle size; PM10 light extinction refers to the
contribution by particles sampled through an inlet
with a particle size 50 percent cutpoint of 10 mm
diameter; and PM2.5 light extinction refers to the
contribution by particles sampled through an inlet
with a particle size 50 percent cutpoint of 2.5 mm
diameter.
165 The 15 urban areas are Tacoma, Fresno, Los
Angeles, Phoenix, Salt Lake City, Dallas, Houston,
St. Louis, Birmingham, Atlanta, Detroit, Pittsburgh,
Baltimore, Philadelphia, and New York.
166 Comments on the second draft Visibility
Assessment from those familiar with the monitoring
sites in St. Louis indicated that the site selected to
provide continuous PM10 monitoring, although less
than a mile from the site of the PM2.5 data, was not
representative of the urban area and resulted in
unrealistically large PM10-2.5 values. The EPA staff
considered these comments credible and set aside
the St. Louis assessment results for PM10 light
extinction. Thus, results and statements in the
Policy Assessment regarding PM10 light extinction
applied to only the other 14 areas. However, results
regarding PM2.5 light extinction in most cases
applied to all 15 study areas because the St. Louis
estimates for PM2.5 light extinction were not
affected by the PM10 monitoring issue.
PO 00000
Frm 00108
Fmt 4701
Sfmt 4700
areas were estimated to have maximum
hourly PM10 concentrations that
exceeded the low CPL on about 40
percent to over 90 percent of the days.
In general, areas in the East and in
California tend to have a higher
frequency of hourly visibility conditions
estimated to be above the high CPL
compared with those in the western
U.S.
The Policy Assessment repeated the
Visibility Assessment-type modeling
based on PM2.5 light extinction and data
from the more recent 2007 to 2009 time
period for the same 15 study areas
(including St. Louis). While the
estimates of the percentage of daily
maximum hourly PM2.5 light extinction
values exceeding the CPLs were
somewhat lower than for PM10 light
extinction, the patterns of these
estimates across the study areas was
found to be similar. More specifically,
except for the two Texas and the nonCalifornia western urban areas, all of the
other urban areas were estimated to
have maximum hourly PM2.5
concentrations that exceeded the high
CPL on about 10 percent up to about 50
percent of the days based on PM2.5 light
extinction, while all 15 areas were
estimated to have maximum hourly
PM2.5 concentrations that exceeded the
low CPL on over 10 percent to over 90
percent of the days.
To evaluate how PM-related visibility
would be affected by just meeting the
current suite of PM2.5 secondary
standards, the Policy Assessment
applied the proportional rollback
approach described in section VI.C.2 of
the proposal to all the PM2.5 monitoring
sites in each study area.167 After
adjusting for composition, the Policy
Assessment applied the original
IMPROVE algorithm to calculate the
PM10 light extinction, using ‘‘rolled
back’’ PM2.5 component concentrations,
the current conditions PM10-2.5
concentration for the day and hour, and
relative humidity for the day and hour.
In these analyses, the Policy
Assessment estimated both PM2.5 and
PM10 light extinction in terms of both
daily maximum 1-hour average values
and multi-hour (i.e., 4-hour) average
values for daylight hours. Figure 4–7
and Table 4–6 of the Policy Assessment
displayed the results of the rollback
procedures as a box and whisker plot of
daily maximum daylight 1-hour PM2.5
light extinction and the percentage of
daily maximum hourly PM2.5 light
extinction values estimated to exceed
the CPLs when just meeting the current
167 Phoenix and Salt Lake City met the current
PM2.5 NAAQS under current conditions and
required no reduction.
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
suite of PM2.5 secondary standards for
all 15 areas considered in the Visibility
Assessment (including St. Louis)
(excluding hours with relative humidity
greater than 90 percent). These displays
showed that the daily maximum 1-hour
average PM2.5 light extinction values in
all of the study areas other than the
three western non-California areas were
estimated to exceed the high CPL on
about 8 percent up to over 30 percent
of the days and to exceed the middle
CPL on about 30 percent up to about 70
percent of the days, while all areas
except Phoenix were estimated to have
daily maximum 1-hour average PM2.5
light extinction values that exceeded the
low CPL on over 15 percent to about 90
percent of the days. Figure 4–8 and
Table 4–7 of the Policy Assessment
present results based on daily maximum
4-hour average values. These displays
show that the daily maximum 4-hour
average PM2.5 light extinction values in
all of the study areas other than the
three western non-California areas and
the two areas in Texas were estimated
to exceed the high CPL on about 4
percent up to over 15 percent of the
days and to exceed the middle CPL on
about 15 percent up to about 45 percent
of the days, while all areas except
Phoenix were estimated to have daily
maximum 4-hour average PM2.5 light
extinction values that exceeded the low
CPL on over 10 percent to about 75
percent of the days. A similar set of
figures and tables were developed in
terms of PM10 light extinction (U.S.
EPA, 2011a, Figures 4–5 and 4–6, Tables
4–4 and 4–5).
Taking the results of these analyses
focusing on 1-hour and 4-hour
maximum light extinction values into
account, the Policy Assessment
concluded that the available
information in this review clearly called
into question the adequacy of the
current suite of PM2.5 standards in the
context of public welfare protection
from visibility impairment, primarily in
urban areas, and supported
consideration of alternative standards to
provide appropriate protection (U.S.
EPA, 2011a, p. 4–39). This conclusion
was based in part on the large
percentage of days, in many urban areas,
that were estimated to have maximum
1-hour or 4-hour light extinction values
that exceed the range of CPLs identified
for consideration under simulations of
conditions that would just meet the
current suite of PM2.5 secondary
standards. In particular, for air quality
that was simulated to just meet the
current PM2.5 standards, greater than 10
percent of the days were estimated to
have peak light extinction values that
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
exceed the highest, least protective CPL
of 30 dv in terms of PM2.5 light
extinction for 9 of the 15 urban areas,
based on 1-hour average values, and
would thus likely fail to meet a 90th
percentile-based standard at that level.
For these areas, the percent of days
estimated to have maximum 1-hour
values that exceed the highest CPL
ranged from over 10 percent to over 30
percent. Similarly, when the middle
CPL of 25 dv was considered, greater
than 30 percent up to approximately 70
percent of the days were estimated to
have peak light extinction that exceeded
that CPL in terms of PM2.5 light
extinction, for 11 of the 15 urban areas,
based on 1-hour average values. Based
on a 4-hour averaging time, 5 of the
areas were estimated to have at least 10
percent of the days with peak light
extinction exceeding the highest CPL in
terms of PM2.5 light extinction, and 8 of
the areas were estimated to have at least
30 percent of the days with peak light
extinction exceeding the middle CPL in
terms of PM2.5 light extinction. For the
lowest CPL of 20 dv, the percentages of
days with 4-hour maximum light
extinction estimated to exceed that CPL
are even higher for all cases considered.
Based on all of the above, the Policy
Assessment concluded that PM light
extinction estimated to be associated
with just meeting the current suite of
PM2.5 secondary standards in many
areas across the country exceeded levels
and percentages of days that could
reasonably be considered to be
important from a public welfare
perspective (U.S. EPA, 2011a, p. 4–40).
Further, the Policy Assessment
concluded that use of the current
indicator of PM2.5 mass, in conjunction
with the current 24-hour and annual
averaging times, is clearly called into
question for a national standard
intended to protect public welfare from
PM-related visibility impairment (U.S.
EPA, 2011a, p. 4–40). This is because
such a standard is inherently variable in
the degree of protection provided
because of regional differences in
relative humidity and species
composition of PM2.5, which are critical
factors in the relationship between the
mix of fine particles in the ambient air
and the associated impairment of
visibility. The Policy Assessment noted
that this concern was one of the
important elements in the court’s
decision to remand the PM2.5 secondary
standards set in 2006 to the Agency.
Thus, in addition to concluding that
the available information clearly calls
into question the adequacy of the
protection against PM-related visibility
impairment afforded by the current
suite of PM2.5 standards, the Policy
PO 00000
Frm 00109
Fmt 4701
Sfmt 4700
3193
Assessment also concluded that it
clearly calls into question the
appropriateness of each of the current
standard elements: indicator, averaging
time, form, and level (U.S. EPA, 2011a,
p. 4–40).
After reviewing the information and
analysis in the second draft Policy
Assessment, CASAC concluded that the
‘‘currently available information clearly
calls into question the adequacy of the
current standards and that consideration
should be given to revising the suite of
standards to provide increased public
welfare protection’’ (Samet, 2010d, p.
iii). CASAC noted that the detailed
estimates of hourly PM light extinction
associated with just meeting the current
standards ‘‘clearly demonstrate that
current standards do not protect against
levels of visual air quality which have
been judged to be unacceptable in all of
the available urban visibility preference
studies.’’ Further, CASAC stated, with
respect to the current suite of secondary
PM2.5 standards, that ‘‘[T]he levels are
too high, the averaging times are too
long, and the PM2.5 mass indicator could
be improved to correspond more closely
to the light scattering and absorption
properties of suspended particles in the
ambient air’’ (Samet, 2010d, p. 9).
After considering the available
evidence and the advice of CASAC, the
Administrator concluded at the time of
proposal that such information did
provide an appropriate basis to inform
a conclusion as to whether the current
standards afford adequate protection
against PM-related visibility impairment
in urban areas. The Administrator took
into account the information discussed
above with regard to the nature of PMrelated visibility impairment, the results
of public perception surveys on the
acceptability of varying degrees of
visibility impairment in urban areas,
analyses of the number of days on
which peak 1-hour or 4-hour light
extinction values are estimated to
exceed a range of candidate protection
levels under conditions simulated to
just meet the current standards, and the
advice of CASAC. She noted the clear
causal relationship between PM in the
ambient air and impairment of
visibility, the evidence from the
visibility preference studies, and the
rationale for determining a range of
candidate protection levels based on
those studies. She also noted the
relatively large number of days when
maximum 1-hour or 4-hour light
extinction values were estimated to
exceed the three candidate protection
levels, including the highest level of 30
dv, under the current standards. While
recognizing the limitations in the
available information on public
E:\FR\FM\15JAR2.SGM
15JAR2
3194
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
perceptions of the acceptability of
varying degree of visibility impairment
and the information on the number of
days estimated to exceed the CPLs, she
concluded that such information
provided an appropriate basis to inform
a conclusion as to whether the current
standards provide adequate protection
against PM-related visibility impairment
in urban areas. Based on these
considerations, and placing great
importance on the advice of CASAC, the
Administrator provisionally concluded
that the current standards are not
sufficiently protective of visual air
quality, and that consideration should
be given to an alternative secondary
standard that would provide additional
protection against PM-related visibility
impairment, with a focus primarily in
urban areas.
Having reached this conclusion, the
Administrator also stated at the time of
proposal that the current indicator of
PM2.5 mass, in conjunction with the
current 24-hour and annual averaging
times, is not well suited for a national
standard intended to protect public
welfare from PM-related visibility
impairment. As noted in the proposal,
the current standards do not incorporate
information on the concentrations of
various species within the mix of
ambient particles, nor do they
incorporate information on relative
humidity, both of which play a central
role in determining the relationship
between the mix of PM in the ambient
air and impairment of visibility. Such
considerations were reflected both in
CASAC’s advice to set a distinct
secondary standard that would more
directly reflect the relationship between
ambient PM and visibility impairment
and in the court’s remand of the current
secondary PM2.5 standards. Based on the
above considerations, at the time of
proposal the Administrator
provisionally concluded that the current
secondary PM2.5 standards, taken
together, are neither sufficiently
protective nor suitably structured to
provide an appropriate degree of public
welfare protection from PM-related
visibility impairment, primarily in
urban areas. This led the EPA to
consider alternative standards by
looking at each of the elements of the
standards—indicator, averaging time,
form, and level—as discussed below.
ii. Indicator
At the time of proposal, the EPA
considered three alternative indicators
for a PM2.5 standard designed to protect
against visibility impairment: The
current PM2.5 mass indicator; directly
measured PM2.5 light extinction; and
calculated PM2.5 light extinction.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
Directly measured PM2.5 light extinction
is a measurement (or combination of
measurements) of the light absorption
and scattering caused by PM2.5 under
ambient conditions. Calculated PM2.5
light extinction uses the IMPROVE
algorithm to calculate PM2.5 light
extinction using measured PM2.5 mass,
speciated PM2.5 mass, and measured
relative humidity. The Policy
Assessment evaluated each of these
alternatives, finally concluding that
consideration should be given to
establishing a new calculated PM2.5 light
extinction indicator (U.S. EPA, 2011a, p.
4–51).
As discussed in section VI.D.1 of the
proposal, the Policy Assessment
concluded that consideration of the use
of either directly measured PM2.5 light
extinction or calculated PM2.5 light
extinction as an indicator is justified
because light extinction is a physically
meaningful measure of the characteristic
of ambient PM2.5 that is most relevant
and directly related to PM-related
visibility effects (U.S. EPA, 2011a, p. 4–
41). Further, as noted above, PM2.5 is the
component of PM responsible for most
of the visibility impairment in most
urban areas. In these areas, the
contribution of PM10-2.5 is a minor
contributor to visibility impairment
most of the time. The Policy Assessment
also indicated that the available
evidence demonstrated a strong
correspondence between calculated
PM2.5 light extinction and PM-related
visibility impairment, as well as the
significant degree of variability in
visibility protection across the U.S.
allowed by a PM2.5 mass indicator. The
Policy Assessment recognized that
while in the future it would be
appropriate to consider a direct
measurement of PM2.5 light extinction it
was not an appropriate option in this
review because a suitable specification
of the equipment and associated
performance verification procedures
cannot be developed in the time frame
for this review.
(a) PM2.5 Mass
In terms of utilizing a PM2.5 mass
indicator, the proposal noted that PM2.5
mass monitoring methods are in
widespread use, including the FRM
involving the collection of periodic
(usually 1-day-in-6 or 1-day-in-3) 24hour filter samples. However, these
routine monitoring activities do not
include measurement of the full water
content of the ambient PM2.5 that
contributes, often significantly, to
visibility impacts. Further, the PM2.5
mass concentration monitors do not
provide information on the composition
of the ambient PM2.5, which plays a
PO 00000
Frm 00110
Fmt 4701
Sfmt 4700
central role in the relationship between
PM-related visibility impairment and
ambient PM2.5 mass concentrations.
Additional analyses discussed in the
proposal that looked at the contribution
of PM2.5 to total PM-related light
extinction (defined in terms of hourly
PM10 calculated light extinction)
indicate that there is a poor correlation
between hourly PM10 light extinction
and hourly PM2.5 mass principally due
to the impact of the water content of the
particles on light extinction, which
depends on both the composition of the
PM2.5 and the ambient relative
humidity. Both composition and
especially relative humidity vary during
a single day, as well as from day-to-day,
at any site and time of year. Also, there
are systematic regional and seasonal
differences in the distribution of
ambient humidity and PM2.5
composition conditions that make it
impossible to select a PM2.5
concentration that generally would
correspond to the same PM-related light
extinction levels across all areas of the
nation. Analyses discussed in the
proposal quantify the projected uneven
protection that would result from the
use of 1-hour average PM2.5 mass as the
indicator.
(b) Directly Measured PM2.5 Light
Extinction
PM light extinction has a nearly oneto-one relationship to light extinction,
unlike PM2.5 mass concentration. As
explained above, PM2.5 is the
component responsible for the large
majority of PM light extinction in most
places and times. PM2.5 light extinction
can be directly measured using several
instrumental methods, some of which
have been used for decades to routinely
monitor the two components of PM2.5
light extinction (light scattering and
absorption) or to jointly measure both as
total light extinction (from which
Rayleigh scattering is subtracted to get
PM2.5 light extinction). As noted at the
time of proposal, there are a number of
advantages to direct measurements of
light extinction for use in a secondary
standard relative to estimates of PM2.5
light extinction calculated using PM2.5
mass and speciation data. These include
greater accuracy of direct measurements
with shorter averaging times and overall
greater simplicity when compared to the
need for measurements of multiple
parameters to calculate PM light
extinction.
In evaluating whether direct
measurement of PM2.5 or PM10 light
extinction is appropriate to consider in
the context of this PM NAAQS review,
the EPA solicited comment from the
Ambient Air Monitoring and Methods
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
Subcommittee (AAMMS) of CASAC.
The CASAC AAMMS recommended
that consideration of direct
measurement should be limited to PM2.5
light extinction, and that although
instruments suitable for this purpose are
commercially available at present,
research is expected to produce even
better instruments in the near term. The
CASAC AAMMS advised against
choosing any currently available
commercial instrument, or even a
general measurement approach, as an
FRM because to do so could discourage
development of other potentially
superior approaches. Instead, the
CASAC AAMMS recommended that the
EPA develop performance-based
approval criteria for direct measurement
methods in order to put all approaches
on a level playing field.
At the present time, the EPA has not
undertaken to develop and test such
performance-base approval criteria. The
EPA anticipates that if an effort were
begun it would take at least several
years before such criteria would be
ready for regulatory use. Thus, the
Policy Assessment concluded that while
in the future it would be appropriate to
consider a direct measurement of PM2.5
light extinction, or the sum of separate
measurements of light scattering and
light absorption, as the indicator for the
secondary PM2.5 standard, this is not an
appropriate option in this review
because a suitable specification of the
equipment or appropriate performancebased verification procedures cannot be
developed in the time frame for this
review (U.S. EPA, 2011a, p. 4–51, –52).
tkelley on DSK3SPTVN1PROD with
(c) Calculated PM2.5 Light Extinction
For the reasons discussed above, the
Policy Assessment concluded that a
calculated PM2.5 light extinction
indicator would be the preferred
approach. PM2.5 light extinction can be
calculated from PM2.5 mass, combined
with speciated PM2.5 mass concentration
data plus relative humidity data, as is
presently routinely done on a 24-hour
average basis under the Regional Haze
Program using data from the rural
IMPROVE monitoring network. This
same calculation procedure, using a 24hour average basis, could be used for a
NAAQS focused on protecting against
PM-related visibility impairment
primarily in urban areas. This approach
would use the type of data that is
routinely collected from the urban
CSN 168 in combination with monthly
168 About 200 sites in the CSN routinely measure
24-hour average PM2.5 chemical components using
filter-based samplers and chemical analysis in a
laboratory, on either a 1-day-in-3 or 1-day-in-6
schedule (U.S. EPA, 2011a, Appendix B, section
B.1.3).
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
average relative humidity data based on
long-term climatological means as used
in the Regional Haze Program (U.S.
EPA, 2011a, Appendix G, section G.2).
The proposal discussed the complex
approach utilized in the Visibility
Assessment for calculating hourly PM2.5
light extinction 169 and discussed
various simplified approaches for
calculating these hourly values that
were analyzed in the Policy Assessment.
The Policy Assessment concluded that
each of these simplified approaches
provided reasonably good estimates of
PM2.5 light extinction and each would
be appropriate to consider as the
indicator for a distinct hourly or multihour secondary standard (U.S. EPA,
2011a, p. 4–48). The proposal also
recognized that the Policy Assessment
identified a number of variations on
these simplified approaches that it
would be appropriate to consider,
including:
(1) The use of the split-component mass
extinction efficiency approach from the
revised IMPROVE algorithm170
(2) The use of more refined value(s) for the
organic carbon multiplier 171
(3) The use of the reconstructed 24-hour
PM2.5 mass (i.e., the sum of the five PM2.5
components from speciated monitoring) as a
normalization value for the hourly
measurements from the PM2.5 instrument as
a way of better reflecting ambient nitrate
concentrations
(4) The use of historical monthly or
seasonal, or regional, speciation averages
Overall, the analyses conducted for
the Visibility Assessment and Policy
Assessment indicated that the use of a
calculated PM2.5 light extinction
indicator would provide a much higher
degree of uniformity in terms of the
degree of protection from visibility
impairment across the country than a
PM2.5 mass indicator, because a
169 As noted at the time of proposal, the sheer size
of the ambient air quality, meteorological, and
chemical transport modeling data files involved
with the Visibility Assessment approach would
make it very difficult for state agencies or any
interested party to consistently apply such an
approach on a routine basis for the purpose of
implementing a national standard defined in terms
of the Visibility Assessment approach.
170 If the revised IMPROVE algorithm were used
to define the calculated PM2.5 mass-based indicator,
it would not be possible to algebraically reduce the
revised algorithm to a two-factor version as
described above and in Appendix F of the Policy
Assessment for the simplified approaches. Instead,
five component fractions would be determined from
each day of speciated sampling, and then either
applied to hourly measurements of PM2.5 mass on
the same day or averaged across a month and then
applied to measurements of PM2.5 mass on each day
of the month.
171 An organic carbon (OC)-to-organic mass (OM)
multiplier of 1.6 was used for the assessment,
which was found to produce a value of OM
comparable to the one derived with the original,
albeit more complex, Visibility Assessment method.
PO 00000
Frm 00111
Fmt 4701
Sfmt 4700
3195
calculated PM2.5 light extinction
indicator would directly incorporate the
effects of humidity and PM2.5
composition differences between
various regions. Further, the proposal
noted that the Policy Assessment
concluded that consideration could be
given to defining a calculated PM2.5
light extinction indicator on either a 24hour or a sub-daily basis (U.S. EPA,
2011a, p. 4–52). However, the Policy
Assessment noted that approval of
continuous FEM monitors has been
based only on 24-hour average, not
hourly, PM2.5 mass. In addition, there
are mixed results of data quality
assessments on a 24-hour basis for these
monitors, as well as the near absence of
performance data for sub-daily
averaging periods. Thus, while it is
possible to utilize data from PM2.5
continuous FEMs on a 1-hour or multihour (e.g., 4-hour) basis, these factors
increase the uncertainty of utilizing
continuous methods to support 1-hour
or 4-hour PM2.5 mass measurements as
an input to the light extinction
calculation. Therefore, as noted at the
time of proposal, until issues regarding
the comparability of 24-hour PM2.5 mass
values derived from continuous FEMs
and filter-based FRMs 172 are resolved,
there is reason to be cautious about
relying on a calculation procedure that
uses hourly PM2.5 mass values reported
by continuous FEMs in combination
with speciated PM2.5 mass values from
24-hour filter-based samplers.
(d) CASAC Advice
In reviewing the second draft Policy
Assessment, CASAC stated that it
‘‘overwhelmingly * * * would prefer
the direct measurement of light
extinction,’’ recognizing it as the
property of the atmosphere that most
directly relates to visibility effects
(Samet, 2010d, p. iii). CASAC noted that
‘‘[I]t has the advantage of relating
directly to the demonstrated harmful
welfare effect of ambient PM on human
visual perception.’’ However, CASAC
also concluded that the calculated PM2.5
light extinction indicator ‘‘appears to be
a reasonable approach for estimating
hourly light extinction’’ (Samet, 2010d,
p. 11). Further, based on CASAC’s
understanding of the time that would be
required to develop an FRM for this
indicator, CASAC agreed with the staff
preference presented in the second draft
Policy Assessment for a calculated PM2.5
light extinction indicator. CASAC noted
that ‘‘[I]ts reliance on procedures that
172 Filter-based FRMs are designed to adequately
quantify the amount of PM2.5 collected over 24hours. They cannot be presumed to be appropriate
for quantifying average concentrations over 1-hour
or 4-hour periods.
E:\FR\FM\15JAR2.SGM
15JAR2
3196
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
have already been implemented in the
CSN and routinely collected continuous
PM2.5 data suggest that it could be
implemented much sooner than a
directly measured indicator’’ (Samet,
2010d, p. iii).173
tkelley on DSK3SPTVN1PROD with
(e) Administrator’s Proposed
Conclusions on Indicator
At the time of proposal, while
agreeing with CASAC that a directly
measured PM light extinction indicator
would provide the most direct link
between PM in the ambient air and PMrelated light extinction, the
Administrator provisionally concluded
that this was not an appropriate option
in this review because a suitable
specification of currently available
equipment or performance-based
verification procedures cannot be
developed in the time frame of this
review. Taking all of the above
considerations and CASAC advice into
account, the Administrator
provisionally concluded that a new
calculated PM2.5 light extinction
indicator, similar to that used in the
Regional Haze Program (i.e., using an
IMPROVE algorithm as translated into
the deciview scale), was the appropriate
indicator to replace the current PM2.5
mass indicator. Such an indicator,
referred to as a PM2.5 visibility index,
would appropriately reflect the
relationship between ambient PM and
PM-related light extinction, based on
the analyses discussed in the proposal
and incorporation of factors based on
measured PM2.5 speciation
concentrations and relative humidity
data. In addition, selection of this type
of indicator would address, in part, the
issues raised in the court’s remand of
the 2006 p.m.2.5 standards. The
Administrator also noted that such a
PM2.5 visibility index would afford a
relatively high degree of uniformity of
visual air quality protection in areas
across the country by virtue of directly
incorporating the effects of differences
in PM2.5 composition and relative
humidity across the country.
Based on these above considerations,
the Administrator proposed to set a
distinct secondary standard for PM2.5
defined in terms of a PM2.5 visibility
index (i.e., a calculated PM2.5 light
extinction indicator, translated into the
deciview scale) to protect against PMrelated visibility impairment primarily
in urban areas. The Administrator
proposed that such an index be based
173 In commenting on the second draft Policy
Assessment, CASAC did not have an opportunity to
review the assessment of continuous PM2.5 FEMs
compared to collocated FRMs (Hanley and Reff,
2011) as presented and discussed in the final Policy
Assessment (U.S. EPA, 2011a, p. 4–50).
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
on the original IMPROVE algorithm in
conjunction with monthly average
relative humidity data based on longterm climatological means as used in
the Regional Haze Program. The EPA
solicited comment on all aspects of the
proposed indicator, especially:
(1) The proposed use of a PM2.5 visibility
index rather than a PM10 visibility index
which would include an additional term for
coarse particles;
(2) Using the revised IMPROVE algorithm
rather than the original IMPROVE algorithm;
(3) The use of alternative values for the
organic carbon multiplier in conjunction
with either the original or revised IMPROVE
algorithm;
(4) The use of historical monthly, seasonal,
or regional speciation averages;
(5) Alternative approaches to determining
relative humidity; and
(6) Simplified approaches to generating
hourly PM2.5 light extinction values for
purposes of calculating an hourly or multihour indicator.
iii. Averaging Times
In this review, as discussed in section
VI.D.2 of the proposal, consideration of
appropriate averaging times for use in
conjunction with a PM2.5 visibility
index was informed by information
related to the nature of PM visibility
effects and the nature of inputs to the
calculation of PM2.5 light extinction, as
discussed above. The EPA considered
both sub-daily (1- and 4-hour averaging
times) and 24-hour averaging times. In
considering sub-daily averaging times,
the EPA has also considered what
diurnal periods and ambient relative
humidity conditions would be
appropriate to consider in conjunction
with such an averaging time.
As an initial matter, the Policy
Assessment considered sub-daily
averaging times. Taking into account
what is known from available studies
concerning how quickly people
experience and judge visibility
conditions, the possibility that some
fraction of the public experiences
infrequent or short periods of exposure
to ambient visibility conditions, and the
typical rate of change of the pathaveraged PM light extinction over urban
areas, the initial analyses conducted as
part of the Visibility Assessment
focused on a 1-hour averaging time. In
its review of the first draft Policy
Assessment, CASAC agreed that a 1hour averaging time would be
appropriate to consider, noting that PM
effects on visibility can vary widely and
rapidly over the course of a day and
such changes are almost instantaneously
perceptible to human observers (Samet,
2010c, p. 19). The Policy Assessment
noted that this view related specifically
to a standard defined in terms of a
PO 00000
Frm 00112
Fmt 4701
Sfmt 4700
directly measured PM light extinction
indicator, in that CASAC also noted that
a 1-hour averaging time is well within
the instrument response times of the
various currently available and
developing optical monitoring methods.
However, CASAC also advised that if
a PM2.5 mass indicator were to be used,
it would be appropriate to consider
‘‘somewhat longer averaging times—2 to
4 hours—to assure a more stable
instrumental response’’ (Samet, 2010c,
p. 19). In considering this advice, the
Policy Assessment concluded that since
a calculated PM2.5 light extinction
indicator relies in part on measured
PM2.5 mass, it would be appropriate to
consider a multi-hour averaging time on
the order of a few hours (e.g. 4-hours).
A multi-hour averaging time might
reasonably characterize the visibility
effects experienced by the segment of
the population who have access to
visibility conditions often or
continuously throughout the day. For
this segment of the population, it may
be that their perception of visual air
quality reflects some degree of offsetting
an hour with poor visual air quality
with one or more hours of clearer visual
conditions. Further, the Policy
Assessment recognized that a multihour averaging time would have the
effect of averaging away peak hourly
visibility impairment, which can change
significantly from one hour to the next
(U.S. EPA, 2011a, p. 4–53; U.S. EPA,
2010b, Figure 3–12).
In considering either 1-hour or multihour averaging times, the Policy
Assessment recognized that no data are
available with regard to how the
duration and variation of time a person
spends outdoors during the daytime
impacts his or her judgment of the
acceptability of different degrees of
visibility impairment. As a
consequence, it is not clear to what
degree, if at all, the protection levels
found to be acceptable in the public
preference studies would change for a
multi-hour averaging time as compared
to a 1-hour averaging time. Thus, the
Policy Assessment concluded that it is
appropriate to consider a 1-hour or
multi-hour (e.g., 4-hour) averaging time
as the basis for a sub-daily standard
defined in terms of a calculated PM2.5
light extinction indicator (U.S. EPA,
2011a, p. 4–53).
In addition, as discussed above, some
data quality uncertainties have been
observed with regard to hourly data
collected by FEMs. Specifically, as part
of the review of data from all
continuous FEM PM2.5 instruments
operating at state/local monitoring sites,
the Policy Assessment noted that the
occurrence of questionable outliers in 1-
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
hour data submitted to AQS from
continuous FEM PM2.5 instruments had
been observed at some of these sites
(Evangelista, 2011). Some of these
outliers were questionable simply by
virtue of their extreme magnitude, as
high as 985 mg/m3, whereas other values
were questionable because they were
isolated to single hours with much
lower values before and after, a pattern
that is much less plausible than if the
high concentrations were more
sustained.174 The Policy Assessment
noted that any current data quality
problems might be resolved in the
normal course of monitoring program
evolution as operators become more
adept at instrument operation and
maintenance and data validation or by
improving the approval criteria and
testing requirements for continuous
instruments. Regardless, the Policy
Assessment noted that multi-hour
averaging of FEM data could serve to
reduce the effects of such outliers
relative to the use of a 1-hour averaging
time.
The Policy Assessment noted that
there are significant reasons to consider
using PM2.5 light extinction calculated
on a 24-hour basis to reduce the various
data quality concerns described above
with respect to relying on continuous
PM2.5 monitoring data. However, the
Policy Assessment recognized that 24
hours is far longer than the hourly or
multi-hour time periods that might
reasonably characterize the visibility
effects experienced by various segments
of the population, including both those
who do and do not have access to
visibility conditions often or
continuously throughout the day. Thus,
the Policy Assessment concluded that
the appropriateness of considering a 24hour averaging time would depend
upon the extent to which PM-related
light extinction calculated on a 24-hour
average basis would be a reasonable and
appropriate surrogate for PM-related
light extinction calculated on a subdaily basis.
To examine this relationship, the EPA
conducted comparative analyses of 24hour and 4-hour averaging times in
conjunction with a calculated PM2.5
indicator. For these analyses, 4-hour
average PM2.5 light extinction was
calculated based on using the Visibility
174 Similarly questionable hourly data were not
observed in the 2005 to 2007 continuous PM2.5 data
used in the Visibility Assessment, all of which
came from early-generation continuous instruments
that had not been approved as FEMs. However, only
15 sites and instruments were involved in the
Visibility Assessment analyses, versus about 180
currently operating FEM instruments submitting
data to AQS. Therefore, there were more
opportunities for very infrequent measurement
errors to be observed in the larger FEM data set.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
Assessment approach. The 24-hour
average PM2.5 light extinction was
calculated using the original IMPROVE
algorithm and long-term relative
humidity conditions to calculate PM2.5
light extinction. Based on these
analyses,175 which are presented and
discussed in Appendix G of the Policy
Assessment, scatter plots comparing 24hour and 4-hour calculated PM2.5 light
extinction were constructed for each of
the 15 cities included in the Visibility
Assessment and for all 15 cities pooled
together (U.S. EPA, 2011a, Figures G–4
and G–5). Though there was some
scatter around the regression line for
each city because the calculated 4-hour
light extinction values included dayspecific and hour-specific influences
that are not captured by the simpler 24hour approach, these analyses generally
showed good correlation between 24hour and 4-hour average PM2.5 light
extinction, as evidenced by reasonably
high city-specific and pooled R2 values,
generally in the range of over 0.6 to over
0.8.176 This suggested that PM2.5 light
extinction calculated on a 24-hour basis
is a reasonable and appropriate
surrogate to PM2.5 light extinction
calculated on a sub-daily basis.
Taking the above considerations and
CASAC’s advice into account, the Policy
Assessment concluded that it would be
appropriate to consider a 24-hour
averaging time, in conjunction with a
calculated PM2.5 light extinction
indicator and an appropriately specified
standard level, as discussed below. By
using site-specific daily data on PM2.5
composition and site-specific long-term
relative humidity conditions, this 24hour average indicator would provide
more consistent protection from PM2.5related visibility impairment than
would a secondary PM2.5 NAAQS based
only on 24-hour or annual average PM2.5
mass. In particular, this approach would
account for the systematic difference in
humidity conditions between most
eastern states and most western states.
The Policy Assessment also concluded
that it would also be appropriate to
consider a multi-hour, sub-daily
averaging time, for example a period of
4 hours, in conjunction with a
calculated PM2.5 light extinction
indicator and with further consideration
of the data quality issues discussed
above. Such an averaging time, to the
extent that data quality issues can be
appropriately addressed, would be more
175 These analyses are also based on the use of a
90th percentile form, averaged over 3 years, as
discussed below in section VI.D.3 and in section
4.3.3 of the Policy Assessment (U.S. EPA, 2011a).
176 The EPA staff noted that the R2 value (0.44)
for Houston was notably lower than for the other
cities.
PO 00000
Frm 00113
Fmt 4701
Sfmt 4700
3197
directly related to the short-term nature
of the perception of visibility
impairment, short-term variability in
PM-related visual air quality, and the
short-term nature (hourly to multiple
hours) of relevant exposure periods for
segments of the viewing public. Such an
averaging time would still result in an
indicator that is less sensitive than a 1hour averaging time to short-term
instrument variability with respect to
PM2.5 mass measurement. In
conjunction with consideration of a
multi-hour, sub-daily averaging time,
the Policy Assessment concluded that
consideration should be given to
including daylight hours only and to
applying a relative humidity screen of
approximately 90 percent to remove
hours in which fog or precipitation is
much more likely to contribute to the
observed visibility impairment (U.S.
EPA, 2011a, p. 4–58). Recognizing that
a 1-hour averaging time would be even
more sensitive to data quality issues,
including short-term variability in
hourly data from currently available
continuous monitoring methods, the
Policy Assessment concluded that it
would not be appropriate to consider a
1-hour averaging time in conjunction
with a calculated PM2.5 light extinction
indicator in this review (U.S. EPA,
2011a, p. 4–58).
As noted above, in its review of the
first draft Policy Assessment, CASAC
concluded that PM effects on visibility
can vary widely and rapidly over the
course of a day and such changes are
almost instantaneously perceptible to
human observers (Samet, 2010c, p. 19).
Based in part on this consideration,
CASAC agreed that a 1-hour averaging
time would be appropriate to consider
in conjunction with a directly measured
PM light extinction indicator, noting
that a 1-hour averaging time is well
within the instrument response times of
the various currently available and
developing optical monitoring methods.
At that time, CASAC also advised that
if a PM2.5 mass indicator were to be
used, it would be appropriate to
consider ‘‘somewhat longer averaging
times—2- to 4-hours—to assure a more
stable instrumental response’’ (Samet,
2010c, p. 19). Thus, CASAC’s advice on
averaging times that would be
appropriate for consideration was
predicated in part on the capabilities of
monitoring methods that were available
for the alternative indicators discussed
in the draft Policy Assessment.
CASAC’s views on a multi-hour
averaging time would also apply to the
calculated PM2.5 light extinction
indicator since hourly PM2.5 mass
measurements are also required for this
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
3198
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
indicator when calculated on a subdaily basis.
It is important to note that at the time
it provided advice on suitable averaging
times, CASAC did not have the benefit
of EPA’s subsequent assessment of the
data quality issues associated with the
use of continuous FEMs as the basis for
hourly PM2.5 mass measurements.
Furthermore, since CASAC only
commented on the first and second
drafts of the Policy Assessment, neither
of which included discussion of a
calculated PM2.5 indicator based on a
24-hour averaging time, CASAC did not
have a basis to offer advice regarding a
24-hour averaging time. In addition, the
24-hour averaging time is not based on
consideration of 24-hours as a relevant
exposure period, but rather as a
surrogate for a sub-daily period of 4
hours, which is consistent with
CASAC’s advice concerning an
averaging time associated with the use
of a PM2.5 mass indicator.
Taking into account the information
discussed above with regard to analyses
and conclusions presented in the final
Policy Assessment the Administrator
recognized that hourly or sub-daily,
multi-hour averaging times, within
daylight hours and excluding hours
with relative humidity above
approximately 90 percent, are more
directly related than a 24-hour averaging
time to the short-term nature of the
perception of PM-related visibility
impairment and the relevant exposure
periods for segments of the viewing
public. On the other hand, she
recognized that data quality
uncertainties have recently been
associated with currently available
instruments that would be used to
provide the hourly PM2.5 mass
measurements that would be needed in
conjunction with an averaging time
shorter than 24-hours. As a result, while
the Administrator recognized the
desirability of a sub-daily averaging
time, she had strong reservations about
proposing to set a standard at this time
in terms of a sub-daily averaging time.
In considering the information and
analyses related to consideration of a
24-hour averaging time, the
Administrator recognized that the
Policy Assessment concluded that PM2.5
light extinction calculated on a 24-hour
averaging basis is a reasonable and
appropriate surrogate for sub-daily
PM2.5 light extinction calculated on a 4hour average basis. In light of this
finding and the views of CASAC based
on its reviews of the first and second
drafts of the Policy Assessment, the
Administrator proposed to set a distinct
secondary standard with a 24-hour
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
averaging time in conjunction with a
PM2.5 visibility index.
iv. Form
As discussed in section VI.D.3 of the
proposal, the ‘‘form’’ of a standard
defines the air quality statistic that is to
be compared to the level of the standard
in determining whether the standard is
achieved. The form of the current 24hour PM2.5 NAAQS is such that the
level of the standard is compared to the
3-year average of the annual 98th
percentile value of the measured
indicator. The purpose in averaging for
three years is to provide stability from
the occasional effects of inter-annual
meteorological variability that can result
in unusually high pollution levels for a
particular year. The use of a multi-year
percentile form, among other things,
makes the standard less subject to the
possibility of transient violations caused
by statistically unusual indicator values,
thereby providing more stability to the
air quality management process that
may enhance the practical effectiveness
of efforts to implement the NAAQS.
Also, a percentile form can be used to
take into account the number of times
an exposure might occur as part of the
judgment on protectiveness in setting a
NAAQS. For all of these reasons, the
Policy Assessment concluded it would
be appropriate to consider defining the
form of a distinct secondary standard in
terms of a 3-year average of a specified
percentile air quality statistic (U.S. EPA,
2011a, p. 4–58).
The urban visibility preference
studies that provided results leading to
the range of CPLs being considered in
this review offer no information that
addresses the frequency of time that
visibility levels should be below those
values. Given this lack of information,
and recognizing that the nature of the
public welfare effect is one of aesthetics
and/or feelings of well-being, the Policy
Assessment concluded that it would not
be appropriate to consider eliminating
all exposures above the level of the
standard and that allowing some
number of hours/days with reduced
visibility can reasonably be considered
(U.S. EPA, 2011a, p. 4–59). In the
Visibility Assessment, 90th, 95th, and
98th percentile forms were assessed for
alternative PM light extinction
standards (U.S. EPA, 2010b, section
4.3.3). In considering these alternative
percentiles, the Policy Assessment
noted that the Regional Haze Program
targets the 20 percent most impaired
days for improvements in visual air
quality in Federal Class I areas. If
improvement in the 20 percent most
impaired days were similarly judged to
be appropriate for protecting visual air
PO 00000
Frm 00114
Fmt 4701
Sfmt 4700
quality in urban areas, a percentile well
above the 80th percentile would be
appropriate to increase the likelihood
that all days in this range would be
improved by control strategies intended
to attain the standard. A focus on
improving the 20 percent most impaired
days suggests that the 90th percentile,
which represents the median of the
distribution of the 20 percent worst
days, would be an appropriate form to
consider. Strategies that are
implemented so that 90 percent of days
have visual air quality that is at or
below the level of the standard would
reasonably be expected to lead to
improvements in visual air quality for
the 20 percent most impaired days.
Higher percentile values within the
range assessed could have the effect of
limiting the occurrence of days with
peak PM-related light extinction in
urban areas to a greater degree. In
considering the limited information
available from the public preference
studies, the Policy Assessment found no
basis to conclude that it would be
appropriate to consider limiting the
occurrence of days with peak PMrelated light extinction in urban areas to
a greater degree.
Another aspect of the form discussed
in the proposal for a sub-daily averaging
time was whether to include all daylight
hours or only the maximum daily
daylight hour(s). The maximum daily
daylight 1-hour or multi-hour form
would be most directly protective of the
welfare of people who have limited,
infrequent or intermittent exposure to
visibility during the day (e.g., during
commutes), but spend most of their time
without an outdoor view. For such
people a view of poor visibility during
their morning commute may represent
their perception of the day’s visibility
conditions until the next time they
venture outside during daylight, which
may be hours later or perhaps the next
day. Other people have exposure to
visibility conditions throughout the day.
For those people, it might be more
appropriate to include every daylight
hour in assessing compliance with a
standard, since it is more likely that
each daylight hour could affect their
welfare.
The Policy Assessment did not have
information regarding the fraction of the
public that has only one or a few
opportunities to experience visibility
during the day, nor did it have
information on the role the duration of
the observed visibility conditions has on
wellbeing effects associated with those
visibility conditions. However, it is
logical to conclude that people with
limited opportunities to experience
visibility conditions on a daily basis
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
would experience the entire impact
associated with visibility based on their
short-term exposure. The impact of
visibility for those who have access to
visibility conditions often or
continuously during the day may be
based on varying conditions throughout
the day.
In light of these considerations, the
analyses conducted as part of the
Visibility Assessment analyses included
both the maximum daily hour and the
all daylight hours forms. The Policy
Assessment noted that there is a close
correspondence between the level of
protection afforded for all 15 urban
areas by a maximum daily daylight 1hour approach using the 90th percentile
form and an all daylight hours approach
combined with the 98th percentile form
(U.S. EPA, 2010b, section 4.1.4). This
suggested that reductions in visibility
impairment required to meet either form
of the standard would provide
protection to both fractions of the public
(i.e., those with limited opportunities
and those with greater opportunities to
view PM-related visibility conditions).
CASAC generally supported
consideration of both types of forms
without expressing a preference based
on its review of information presented
in the second draft Policy Assessment
(Samet, 2010d, p. 11).
In conjunction with a calculated PM2.5
light extinction indicator and alternative
24-hour or sub-daily (e.g., 4-hour)
averaging times, based on the above
considerations, and given the lack of
information on and the high degree of
uncertainty over the impact on public
welfare of the number of days with
visibility impairment over a year, the
Policy Assessment concluded that it
would be appropriate to give primary
consideration to a 90th percentile form,
averaged over three years (U.S. EPA,
2011a, p. 4–60). Further, in the case of
a multi-hour, sub-daily alternative
standard, the Policy Assessment
concluded that it would be appropriate
to give primary consideration to a form
based on the maximum daily multi-hour
period in conjunction with the 90th
percentile form (U.S. EPA, 2011a, p. 4–
60). This sub-daily form would be
expected to provide appropriate
protection for various segments of the
population, including those with
limited opportunities during a day and
those with more extended opportunities
over the daylight hours to experience
PM-related visual air quality.
Though CASAC did not provide
advice as to a specific form that would
be appropriate, it took note of the
alternative forms considered in that
document and encouraged further
analyses in the final Policy Assessment
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
that might help to clarify a basis for
selecting from within the range of forms
identified. In considering the available
information and the conclusions in the
final Policy Assessment in light of
CASAC’s comments, at the time of
proposal the Administrator concluded
that a 90th percentile form, averaged
over 3 years, is appropriate, and
proposed such a form in conjunction
with a PM2.5 visibility index and a 24hour averaging time.
3199
extinction standard, it would be
appropriate to consider whether some
adjustment to these CPLs is warranted
since these preference studies cannot be
directly interpreted as applying to a 24hour exposure period (as noted above
and in Policy Assessment section 4.3.1).
Considerations related to such
adjustments are more specifically
discussed below.
In considering alternative levels for a
sub-daily standard based directly on the
four preference study results, the Policy
v. Level
Assessment noted that the individual
As discussed in section VI.D.4 of the
low and high CPLs are in fact generally
proposal, in considering appropriate
reflective of the results from the Denver
levels for a 24-hour standard defined in
and Washington, DC studies
terms of a PM2.5 visibility index and an
respectively, and the middle CPL is very
90th percentile form, averaged over 3
near to the 50th percentile criteria result
years, the Policy Assessment took into
from the Phoenix study, which was by
account the evidence- and impact-based far the best of the studies, providing
somewhat more support for the middle
considerations discussed above, with a
focus on the results of public perception CPL.
In considering the results from the
and attitude surveys related to the
four visibility preference studies, the
acceptability of various levels of visual
Policy Assessment recognized that
air quality and on the important
currently available studies are limited in
limitations in the design and scope of
that they were conducted in only four
such available studies. The Policy
areas, three in the U.S. and one in
Assessment considered a variety of
Canada. Further, the Policy Assessment
approaches for identifying appropriate
recognized that available studies
levels for such a standard, including
provide no information on how the
utilizing both adjusted and unadjusted
duration and variation of time a person
CPLs derived from the visibility
spends outdoors during the daytime
preference studies.
may impact their judgment of the
The Policy Assessment interpreted
acceptability of different degrees of
the results from the visibility
visibility impairment. As such, there is
preferences studies conducted in four
a relatively high degree of uncertainty
urban areas to define a range of low,
associated with using the results of
middle, and high CPLs for a sub-daily
these studies to inform consideration of
standard (e.g., 1- to 4-hour averaging
a national standard for any specific
time) of 20, 25, and 30 dv, which are
averaging time. Nonetheless, the Policy
approximately equivalent to PM2.5 light
Assessment concluded, as did CASAC,
extinction of values of 65, 110, and 190
Mm¥1. The CASAC generally supported that these studies are appropriate to use
for this purpose (U.S. EPA, 2011a, p. 4–
this approach, noting that the ‘‘EPA
61).
staff’s approach for translating and
Using approaches described in section
presenting the technical evidence and
assessment results is logically conceived VI.C.4 of the proposal, the Policy
Assessment explored various
and clearly presented. The 20–30
deciview range of levels chosen by EPA approaches to adjusting the CPLs
derived from the preference studies to
staff as ‘Candidate Protection Levels’ is
inform alternative levels for a 24-hour
adequately supported by the evidence
presented’’ (Samet, 2010d, p. 11).177 The standard. These various approaches,
based on analyses of 2007–2009 data
Policy Assessment also recognized that
from the 15 urban areas assessed in the
to define a range of alternative levels
Visibility Assessment, focused on
that would be appropriate to consider
estimating CPLs for a 24-hour standard
for a 24-hour calculated PM2.5 light
that would provide generally equivalent
protection as that provided by a 4-hour
177 In 2009, the DC Circuit remanded the
standard with CPLs of 20, 25, and 30 dv.
secondary PM2.5 standards to the EPA in part
because the Agency failed to identify a target level
In conducting these analyses, staff
of protection, even though EPA staff and CASAC
initially expected that the values of 24had identified a range of target levels of protection
hour average PM2.5 light extinction and
that were appropriate for consideration. The court
daily maximum daylight 4-hour average
determined that the Agency’s failure to identify a
target level of protection as part of its final decision
PM2.5 light extinction would differ on
was contrary to the statute and therefore unlawful,
any given day, with the shorter term
and that it deprived EPA’s decision-making of a
peak value generally being larger. This
reasoned basis. See 559F. 3d at 528–31; see also
would mean that, in concept, the level
section VI.A.2 above and the Policy Assessment,
section 4.1.2.
of a 24-hour standard should include a
PO 00000
Frm 00115
Fmt 4701
Sfmt 4700
E:\FR\FM\15JAR2.SGM
15JAR2
3200
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
downward adjustment compared to the
level of a 4-hour standard to provide
generally equivalent protection. As
discussed more fully in section G.5 of
Appendix G and summarized below,
this initial expectation was not found to
be the case across the range of CPLs
considered. In fact, as shown in Tables
G–7 and G–8 of Appendix G and in the
corrected version of Table G–6 found in
Frank et al. (2012b),178 in considering
estimates aggregated or averaged over all
15 cities as well as the range of cityspecific estimates for the various
approaches considered, these analyses
indicated that the generally equivalent
24-hour levels ranged from somewhat
below the 4-hour level to just above the
4-hour level for each of the CPLs.179 In
all cases, the range of city-specific
estimates of generally equivalent 24hour levels included the 4-hour level for
each of the CPLs of 20, 25, and 30 dv.
As noted in the proposal, looking more
broadly at these results could support
consideration of using the same CPL for
a 24-hour standard as for a 4-hour
standard, recognizing that there is no
one approach that can most closely
identify a generally equivalent 24-hour
standard level in each urban area for
each CPL. The use of such an
unadjusted CPL for a 24-hour standard
would place more emphasis on the
relatively high degree of spatial and
temporal variability in relative humidity
and fine particle composition observed
in urban areas across the country, so as
to reduce the potential of setting a 24hour standard level that would require
more than the intended degree of
protection in some areas.
In considering the appropriate level of
a secondary standard focused on
178 Note that the city-specific ranges shown in
Table G–6, Appendix G of the Policy Assessment
are incorrectly stated for Approaches C and E.
Drawing from the more detailed and correct results
for Approaches C and E presented in Tables G–7
and G–8, respectively, the city-specific ranges in
Table G–6 for Approach C should be 17–21 dv for
the CPL of 20 dv; 21–25 dv for the CPL of 25 dv;
and 24–30 dv for the CPL of 30 dv; the city-specific
ranges in Table G–6 for Approach E should be 17–
21 dv for the CPL of 20 dv; 21–26 dv for the CPL
of 25 dv; and 25–31 dv for the CPL of 30 dv. In
the EPA’s reanalysis comparing 4- vs. 24-hour
values, Frank et al. (2012b) recreated Table G–6
using the correct values from Tables G–7 and G–8.
179 As discussed in more detail in Appendix G of
the Policy Assessment, some days have higher
values for 24-hour average light extinction than for
daily maximum 4-hour daylight light extinction,
and consequently an adjusted ‘‘equivalent’’ 24-hour
CPL can be greater than the original 4-hour CPL.
This can happen for two reasons. First, the use of
monthly average historical RH data will lead to
cases in which the f(RH) values used for the
calculation of 24-hour average light extinction are
higher than all or some of the four hourly values
of f(RH) used to determine daily maximum 4-hour
daylight light extinction on the same day. Second,
PM2.5 concentrations may be greater during nondaylight periods than during daylight hours.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
protection from PM-related urban
visibility impairment based on either a
24-hour or a multi-hour, sub-daily (e.g.,
4-hour) averaging time, the EPA has
been mindful of the important
limitations in the available evidence
from public preference studies. These
uncertainties and limitations are due in
part to the small number of stated
preference studies available for this
review; the relatively small number of
study participants and the extent to
which the study participants may not be
representative of the broader study area
population in some of the studies; and
the variations in the specific materials
and methods used in each study such as
scene characteristics, the range of VAQ
levels presented to study participants,
image presentation methods and
specific wording used to frame the
questions used in the group interviews.
In addition the EPA has noted that the
scenic vistas available on a daily basis
in many urban areas across the country
generally may not have the inherent
visual interest or the distance between
viewer and object of greatest intrinsic
value as in the Denver and Phoenix
preference studies, and that there is the
possibility that there could be regional
differences in individual preferences for
VAQ.
It is also important to note that as in
past reviews, the EPA is considering a
national visibility standard in
conjunction with the Regional Haze
Program as a means of achieving
appropriate levels of protection against
PM-related visibility impairment in
urban, non-urban, and Federal Class I
areas across the country. The EPA
recognizes that programs implemented
to meet a national standard focused
primarily on the visibility problems in
urban areas can be expected to improve
visual air quality in surrounding nonurban areas as well, as would programs
now being developed to address the
requirements of the Regional Haze
Program established for protection of
visual air quality in Federal Class I
areas. The EPA also believes that the
development of local programs, such as
those in Denver and Phoenix, can
continue to be an effective and
appropriate approach to provide
additional protection, beyond that
afforded by a national standard, for
unique scenic resources in and around
certain urban areas that are particularly
highly valued by people living in those
areas.
The Policy Assessment concluded
that it is appropriate to give primary
consideration to alternative standard
levels toward the upper end of the
ranges identified above for 24-hour and
sub-daily standards, respectively (U.S.
PO 00000
Frm 00116
Fmt 4701
Sfmt 4700
EPA, 2011a, p. 4–63). Thus, the Policy
Assessment concluded it is appropriate
to consider the following alternative
levels: A level of 28 dv or somewhat
below, down to 25 dv, for a standard
defined in terms of a calculated PM2.5
light extinction indicator, a 90th
percentile form, and a 24-hour averaging
time; and a standard level of 30 dv or
somewhat below, down to 25 dv, for a
similar standard but with a 4-hour
averaging time (U.S. EPA, 2011a, p. 4–
63). The Policy Assessment judged that
such standards would provide
appropriate protection against PMrelated visibility impairment primarily
in urban areas. The Policy Assessment
noted that CASAC generally supported
consideration of the 20–30 dv range as
CPLs and, more specifically, that
support for consideration of the upper
part of the range of the CPLs derived
from the public preference studies was
expressed by some CASAC Panel
members during the public meeting on
the second draft Policy Assessment. The
Policy Assessment concluded that such
a standard would be appropriate in
conjunction with the Regional Haze
Program to achieve appropriate levels of
protection against PM-related visibility
impairment in areas across the country
(U.S. EPA, 2011a, p. 4–63).
Based on the considerations discussed
above and in section VI.D.4 of the
proposal, and taking into account the
advice of CASAC, at the time of
proposal the Administrator concluded
that it would be appropriate to establish
a target level of protection—for a
standard defined in terms of a PM2.5
visibility index; a 90th percentile form
averaged over 3 years; and a 24-hour
averaging time—equivalent to the
protection afforded by such a sub-daily
(i.e., 4-hour) standard at a level of 30 dv,
which is the upper end of the range of
CPLs identified in the Policy
Assessment and generally supported by
CASAC. More specifically, the
Administrator provisionally concluded
that a 24-hour level of either 30 dv or
28 dv could be construed as providing
such a degree of protection, and that
either level was supported by the
available information and was generally
consistent with the advice of CASAC.
Thus, the EPA proposed two options for
the level of a new 24-hour standard
(defined in terms of a PM2.5 visibility
index and a 90th percentile form,
averaged over 3 years) to provide
appropriate protection from PM-related
visibility impairment: Either 30 dv or 28
dv. As noted in the proposal, the option
of setting such a 24-hour standard at a
level of 30 dv would reflect recognition
that there is considerable spatial and
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
temporal variability in the key factors
that determine the value of the PM2.5
visibility index in any given urban area,
such that there is a relatively high
degree of uncertainty as to the most
appropriate approach to use in selecting
a 24-hour standard level that would be
generally equivalent to a specific 4-hour
standard level. Selecting a 24-hour
standard level of 30 dv would reflect a
judgment that such substantial degrees
of variability and uncertainty should be
reflected in a higher standard level than
would be appropriate if the underlying
information were more consistent and
certain. Alternatively, the option of
setting such a 24-hour standard at a
level of 28 dv would reflect placing
more weight on statistical analyses of
aggregated data from across the study
cities and not placing as much emphasis
on the city-to-city variability as a basis
for determining an appropriate degree of
protection on a national scale.
The information available for the
Administrator to consider when setting
the secondary PM standard raises a
number of uncertainties. While CASAC
supported moving forward with a new
standard on the basis of the available
information, CASAC also recognized
these uncertainties, referencing the
discussion of key uncertainties and
areas for future research in the second
draft of the Policy Assessment. In
discussing areas of future research,
CASAC stated that: ‘‘The range of 50%
acceptability values discussed as
possible standards are based on just four
studies (Figure 4–2), which, given the
large spread in values, provide only
limited confidence that the benchmark
candidate protection levels cover the
appropriate range of preference values.
Studies using a range of urban scenes
(including, but not limited to, iconic
scenes—‘‘valued scenic elements’’ such
as those in the Washington, DC study),
should also be considered’’ (Samet,
2010d, p. 12). The EPA solicited
comment on how the Administrator
should weigh those uncertainties as
well as any additional comments and
information to inform her consideration
of these uncertainties.
In addition, the EPA solicited
comment on a number of other issues
related to the level of the standard,
including:
(1) Both of the proposed levels and the
various approaches to identifying generally
equivalent levels upon which the alternative
proposed levels are based.
(2) A broader range of levels down to 25
dv in conjunction with a 24-hour averaging
time.
(3) A range of alternative levels from 30 to
25 dv in conjunction with a sub-daily (e.g.,
4-hour) averaging time.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
(4) The strengths and limitations associated
with the public preference studies and the
use of these studies to inform the selection
of a range of levels that could be used to
provide an appropriate degree of public
welfare protection when combined with the
other elements of the standard (i.e. indicator,
form and averaging time).
(5) Specific aspects of the public
preference studies, including the extent to
which the 50 percent acceptability criterion
is an appropriate basis for establishing target
protection levels in the context of
establishing a distinct secondary NAAQS to
address PM-related visibility impairment in
urban areas; how the variability among
preference studies in the extent to which
study participants may be representative of
the broader study area population should be
weighed in the context of considering these
studies in reaching proposed conclusions on
a distinct secondary NAAQS; and the extent
to which the ranges of VAQ levels presented
to participants in each of the studies may
have influenced study results and on how
this aspect of the study designs should
appropriately be weighed in the context of
considering these studies in the context of
this review.
vi. Administrator’s Proposed
Conclusions Regarding PM Standards
To Protect Visibility
At the time of proposal, based on the
considerations described above, the
Administrator proposed to revise the
suite of secondary PM standards by
adding a distinct standard for PM2.5 to
address PM-related visibility
impairment, focused primarily on
visibility in urban areas. This proposed
visibility standard was to be defined in
terms of a PM2.5 visibility index, which
would use measured PM2.5 mass,
combined with PM2.5 speciation data
and relative humidity data, to calculate
PM2.5 light extinction, translated into
the deciview (dv) scale; a 24-hour
averaging time; a 90th percentile form,
averaged over 3 years; and a level of 28–
30 dv.
vii. Related Technical Analysis
At the time of proposal, the EPA
conducted a two-pronged technical
analysis of the relationships between
the proposed PM2.5 visibility index
standard and the current 24-hour PM2.5
mass-based standard (Kelly, et al.,
2012a). This analysis was designed to
provide technical information to inform
key issues related to implementing a
distinct secondary standard for visibility
as proposed. Specifically, the EPA
recognized that significant technical
issues were likely to arise for new or
modified emissions sources conducting
air quality analyses for purposes of
demonstrating that they would not
cause or contribute to a violation of the
visibility standard under the Prevention
of Significant Deterioration (PSD)
PO 00000
Frm 00117
Fmt 4701
Sfmt 4700
3201
program. Such a demonstration for the
proposed secondary PM2.5 visibility
index standard could require each PSD
applicant to predict, via air quality
modeling, the increase in visibility
impairment, in terms of the proposed
PM2.5 visibility index, that would result
from the proposed source’s emissions in
conjunction with an assessment of
existing air quality (visibility
impairment) conditions in terms of the
proposed PM2.5 visibility index. The
EPA noted that if this demonstration
were to be attempted using the six-step
procedure that the EPA proposed to use
for calculating PM2.5 visibility index
design values from monitored air
concentrations of PM2.5 components,
significant technical issues with the
modeling procedures could arise.
To address these technical issues, the
EPA sought to explore whether sources
that met the requirements pertaining to
the 24-hour mass-based standard of 35
mg/m3 would also meet the requirements
pertaining to the proposed visibility
index standard. As described in Kelly et
al. (2012a), the first prong of the
analysis addressed aspects of a PSD
significant impact analysis by
evaluating whether an individual
source’s impact resulting in a small
increase in the ambient PM2.5
concentration would produce a
comparably small increase in visibility
impairment. This analysis included
estimates of PM2.5 speciation profiles
based on direct PM2.5 emission profiles
for a broad range of source categories
and for theoretical upper and lower
bound scenarios.
The second prong of the analysis
addressed aspects of a PSD cumulative
impact analysis by exploring the
relationship between the three-year
design values for the existing 24-hour
PM2.5 standard and coincident design
values for the proposed PM2.5 visibility
index standard based on recent air
quality data. This aspect of the analysis
indicated that increases in 24-hour
PM2.5 design values generally
correspond to increases in visibility
index design values, and vice-versa. The
analysis further explored the
appropriateness of using a
demonstration that a source does not
cause or contribute to a violation of the
24-hour PM2.5 standard as a surrogate
for a demonstration that a source does
not cause or contribute to a violation of
the proposed secondary PM2.5 visibility
index standard. This analysis was based
on 2008 to 2010 air quality data, and
compared the proposed level of 35 mg/
m3 for the 24-hour PM2.5 standard and
for illustrative purposes an alternative
standard level of 12 mg/m3 for the
annual PM2.5 standard with the
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
3202
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
proposed levels of 28 or 30 dv for the
secondary PM2.5 visibility index
standard with a 24-hour averaging time
and a 90th percentile form. The results
indicated that all (for the 30 dv level) or
nearly all (for the 28 dv level) areas in
attainment of the 24-hour PM2.5
standard would also have been in
attainment of the proposed secondary
PM2.5 visibility index standard.
Based on this technical analysis, the
EPA proposed that there is sufficient
evidence that a demonstration that a
source does not cause or contribute to
a violation of the mass-based 24-hour
PM2.5 standard serves as a suitable
surrogate for demonstrating that a
source does not cause or contribute to
a violation of the proposed secondary
24-hour PM2.5 visibility index standard
under the PSD program. As such, the
EPA proposed to conclude that many or
all sources undergoing PSD review for
PM2.5 could rely upon their analysis for
demonstrating that they do not cause or
contribute to a violation of the massbased 24-hour PM2.5 standard to also
show that they do not cause or
contribute to a violation of the proposed
secondary PM2.5 visibility index
standard, if a distinct visibility standard
were finalized.
Although this proposed ‘‘surrogacy
policy’’ was designed to address an
implementation-related issue, the
second prong of the technical analysis
addresses the broader technical question
of the relationship between the existing
24-hour PM2.5 standard and the
proposed PM2.5 visibility index standard
in terms of the degree of protection
likely to be afforded by each standard.
Specifically, the analysis indicated that
depending on the level of the proposed
PM2.5 visibility index standard, the
existing 24-hour PM2.5 mass-based
standard would be as protective or in
some areas more protective of visibility
than a distinct secondary standard set
within the range of levels proposed.
Commenters on the proposed PM2.5
visibility index explored the
implications of this analysis at length,
as discussed further below in section
VI.C.1.f. For this reason, the analysis is
described in some detail here.
Kelly et al. (2012a) noted that the
relationship between design values for
the 24-hour PM2.5 standard and the
proposed secondary visibility index
standard is not obvious a priori because
of differences in design value
calculations for the standards. However,
closer examination of this relationship
indicated that increases or decreases in
24-hour PM2.5 design values correspond,
respectively, to increases or decreases in
visibility index values. Specifically,
based on measurements from 102 sites
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
with complete data from 2008–2010,
Kelly et al. (2012a) found linear
correlations between the 24-hour PM2.5
design values and the visibility index
design values with r2 values ranging
from 0.65 to 0.98 across these sites, with
an average r2 value of 0.75 across all
U.S. sites. Moreover, the data indicated
that no design value existed where the
visibility index design value exceeded
30 dv, but the 24-hour PM2.5 standard
level of 35 mg/m3 was attained.
Visibility index design values for certain
sites in the Industrial Midwest were
shown to exceed 28 dv despite the fact
that the 24-hour PM2.5 design values for
these sites were below 35 mg/m3. This
was attributed to the combination of
high nitrate and sulfate fractions,
substantial RH adjustment factors, and
PM2.5 distribution characteristics that
led to relatively high visibility index
design values for a given 24-hour PM2.5
design value for counties in the
Industrial Midwest.180 Kelly et al.
(2012a) concluded that the ‘‘overall,
design values based on 2008–2010 data
suggest that counties that attain 24-hour
PM2.5 NAAQS level of 35 mg/m3 would
attain the proposed secondary PM2.5
visibility index NAAQS level of 30 dv
and generally attain the level of 28 dv’’
(pp. 17–18). In addition, the Kelly et al.
analysis indicated that at sites that
violated both the 24-hour PM2.5 level
and the proposed visibility index 30 dv
level, the proposed level of 30 dv would
likely be attained if PM2.5
concentrations were reduced such that
the 24-hour PM2.5 level of 35 mg/m3 was
attained (Kelly et al., 2012a, p.15).181 A
key implication of this analysis,
therefore, was that within the range of
levels proposed by the EPA for a
visibility index standard (28–30 dv), the
24-hour PM2.5 standard of 35 mg/m3
would be controlling in almost all (at 28
dv) or all (at 30 dv) instances.
2. Other (Non-Visibility) PM-related
Welfare Effects
In the 2006 review, the EPA
concluded that there was insufficient
information to consider a distinct
secondary standard based on PM-related
impacts to ecosystems, materials
180 Kelly et al. (2012a) also noted that ‘‘Regional
reductions in sulfate PM2.5 due to emission controls
planned as part of national rules as well as emission
reductions associated with potential annual
standard violations are expected to improve
visibility in this region’’ (p. 17).
181 The analysis also showed that attaining the 24hour PM2.5 standard level of 35 mg/m3 would result
in achieving a lower PM2.5 visibility index level in
certain areas of the country, largely western areas,
than would be achieved in other areas of the
country. This is due to differences in the
composition of ambient PM2.5 and the lower relative
humidity in those areas.
PO 00000
Frm 00118
Fmt 4701
Sfmt 4700
damage and soiling, and climatic and
radiative processes (71 FR 61144,
October 17, 2006). Specifically, there
was a lack of evidence linking various
non-visibility welfare effects to specific
levels of ambient PM. In that review, to
provide a level of protection for these
welfare-related effects, the secondary
standards were set equal to the revised
primary standards to directionally
improve the level of protection afforded
vegetation, ecosystems, and materials
(71 FR 61210, October 17, 2006).
This section briefly outlines key
conclusions discussed more fully in
section VI.E of the proposal regarding
the non-visibility welfare effects of PM.
These conclusions relate to the climate,
ecological (including effects on plants,
soil and nutrient cycling, wildlife and
water) and materials damage effects of
PM. For all of these effects, the Policy
Assessment concluded that there is
insufficient information at this time to
revise the current suite of secondary
standards. It is important to note that
the Policy Assessment explicitly
excluded discussion of the effects
associated with deposited particulate
matter components of NOX and SOx and
their transformation products which are
addressed fully in the joint review of the
secondary NO2 and SO2 NAAQS.
a. Evidence of Other Welfare Effects
Related to PM
With regard to the role of PM in
climate, the proposal noted that there is
considerable ongoing research focused
on understanding aerosol contributions
to changes in global mean temperature
and precipitation patterns. The
Integrated Science Assessment
concluded ‘‘that a causal relationship
exists between PM and effects on
climate, including both direct effects on
radiative forcing and indirect effects
that involve cloud feedbacks that
influence precipitation formation and
cloud lifetimes’’ (U.S. EPA, 2009a,
section 9.3.10). These effects are
discussed in more detail in section
VI.E.1 of the proposal, which provides
information on the major aerosol
components of interest for climate
processes, including black carbon (BC),
organic carbon (OC), sulfates, nitrates,
and mineral dusts, and the nature,
magnitude, and direction (e.g., cooling
vs. warming) of various aerosol impacts
on climate.182 The Policy Assessment
concluded that aerosols alter climate
processes directly through radiative
forcing and by indirect effects on cloud
brightness, changes in precipitation, and
182 Atmospheric PM is referred to as aerosols in
the remainder of this section to be consistent with
the Integrated Science Assessment.
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
possible changes in cloud lifetimes (U.S.
EPA, 2011a, p. 5–10). Further, the
Policy Assessment noted that the major
aerosol components that contribute to
climate processes (i.e. BC, OC, sulfate,
nitrate and mineral dusts) vary in their
reflectivity, forcing efficiencies and
even in the direction of climate forcing,
though there is an overall net climate
cooling associated with aerosols in the
global atmosphere (U.S. EPA, 2009a,
section 9.2.10). The Policy Assessment
concluded that the current mass-based
PM2.5 and PM10 secondary standards
were not an appropriate or effective
means of focusing protection against
PM-associated climate effects due to
these differences in components (U.S.
EPA, 2011a, p. 5–11). In addition, in
light of the significant uncertainties in
current scientific information and the
lack of sufficient data, the Policy
Assessment concluded it is not
currently feasible to conduct a
quantitative analysis for the purpose of
informing revisions of the current
secondary PM standards based on
climate (U.S. EPA, 2011a, p. 5–11).
Overall the Policy Assessment
concluded that there is insufficient
information at this time to base a
national ambient standard on climate
impacts associated with current ambient
concentrations of PM or its constituents
(U.S. EPA, 2011a, p. 5–11, –12).183
With regard to ecological effects, the
proposal noted that several ecosystem
components (e.g., plants, soils and
nutrient cycling, wildlife and water) are
impacted by PM air pollution, which
may alter the services provided by
affected ecosystems. Ecological effects
include both direct effects due to
deposition (e.g., wet, dry or occult) to
vegetation surfaces and indirect effects
occurring via deposition to ecosystem
soils or surface waters where the
deposited constituents of PM then
interact with biological organisms.
Some of the ecological effects
considered in this review include direct
effects to metabolic processes of plant
foliage; contribution to total metal
loading resulting in alteration of soil
biogeochemistry and microbiology, and
plant and animal growth and
reproduction; and contribution to total
organics loading resulting in
bioaccumulation and biomagnification
across trophic levels. Section VI.E.2 of
the proposal summarizes key findings
related to:
(1) Impacts on plants and the ecosystem
services they provide due to deposition of
PM to vegetative surfaces, which alters the
183 This conclusion would apply for both the
secondary (welfare-based) and the primary (healthbased) standards.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
radiation received by the plant, and uptake
of deposited PM components by plants from
soil or foliage, which can lead to stress and
decreased photosynthesis;
(2) Impacts on ecosystem support services
such as nutrient cycling, products such as
crops and the regulation of flooding and
water quality;
(3) Impacts on wildlife, especially due to
biomagnification of heavy metals (especially
Hg) up the food chain and bioconcentration
of POPs and PBDEs; and
(4) Impacts of deposited PM, especially
metals and organics, on the ecosystem
services provided by water bodies, including
primary production, provision of fresh water,
regulation of climate and floods, recreational
fishing and water purification.
3203
local, regional and/or global sources of
deposited PM components and their
concurrent effects on ecological receptors.
The proposal noted that the Integrated
Science Assessment had concluded that
ecological evidence is sufficient to
conclude that a causal relationship is
likely to exist between deposition of PM
and a variety of effects on individual
organisms and ecosystems (U.S. EPA,
2009a, sections 2.5.3 and 9.4.7), and
also noted that vegetation and other
ecosystem components are affected
more by particulate chemistry than size
fraction. However, the proposal also
pointed to the Integrated Science
Assessment conclusion that it is
generally difficult to characterize the
nature and magnitude of effects and to
quantify relationships between ambient
concentrations of PM and ecosystem
response due to significant data gaps
and uncertainties as well as
considerable variability that exists in
the components of PM and their various
ecological effects. There are few studies
that link ambient PM concentrations to
observed effect. Most direct ecosystem
effects associated with particulate
pollution occur in severely polluted
areas near industrial point sources
(quarries, cement kilns, metal smelting)
(U.S. EPA, 2009a, sections 9.4.3 and
9.4.5.7).
Based on the evidence available at
this time, the proposal noted the
following key conclusions in the Policy
Assessment:
The proposal noted that the Policy
Assessment had concluded that the
currently available information is
insufficient for purposes of assessing the
adequacy of the protection for
ecosystems afforded by the current suite
of PM secondary standards or
establishing a distinct national standard
for ambient PM based on ecosystem
effects of particulates not addressed in
the NOX/SOX secondary review (e.g.,
metals, organics) (U.S. EPA, 2011a, p. 5–
24). Furthermore, the Policy Assessment
had concluded that in the absence of
information providing a basis for
specific standards in terms of particle
composition, the observations continue
to support retaining an appropriate
degree of control on both fine and
coarse particles to help address effects
to ecosystems and ecosystem
components associated with PM (U.S.
EPA, 2011a, p. 5–24).
With regard to materials damage, the
proposal discussed effects associated
with deposition of PM, including both
physical damage (materials damage
effects) and impaired aesthetic qualities
(soiling effects). As with the other
categories of welfare effects discussed
above, the Integrated Science
Assessment concluded that evidence is
sufficient to support a causal
relationship between PM and effects on
materials (U.S. EPA, 2009a, sections
2.5.4 and 9.5.4). The deposition of PM
can physically affect materials, adding
to the effects of natural weathering
processes, by potentially promoting or
accelerating the corrosion of metals, by
degrading paints and by deteriorating
building materials such as stone,
concrete and marble (U.S. EPA, 2009a,
section 9.5). In addition, the deposition
of ambient PM can reduce the aesthetic
appeal of buildings and objects through
soiling. The Policy Assessment made
the following observations:
(1) A number of significant environmental
effects that either have already occurred or
are currently occurring are linked to
deposition of chemical constituents found in
ambient PM.
(2) Ecosystem services can be adversely
impacted by PM in the environment,
including supporting, provisioning,
regulating and cultural services.
(3) The lack of sufficient information to
relate specific ambient concentrations of
particulate metals and organics to a degree of
impairment of a specific ecological endpoint
hinders the identification of a range of
appropriate indicators, levels, forms and
averaging times of a distinct secondary
standard to protect against associated effects.
(4) Data from regionally-based ecological
studies can be used to establish probable
(1) Materials damage and soiling that occur
through natural weathering processes are
enhanced by exposure to atmospheric
pollutants, most notably sulfur dioxide and
particulate sulfates.
(2) While ambient particles play a role in
the corrosion of metals and in the weathering
of materials, no quantitative relationships
between ambient particle concentrations and
rates of damage have been established.
(3) While soiling associated with fine and
course particles can result in increased
cleaning frequency and repainting of
surfaces, no quantitative relationships
between particle characteristics and the
frequency of cleaning or repainting have been
established.
(4) Limited new data on the role of
microbial colonizers in biodeterioration
PO 00000
Frm 00119
Fmt 4701
Sfmt 4700
E:\FR\FM\15JAR2.SGM
15JAR2
3204
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
processes and contributions of black crust to
soiling are not sufficient for quantitative
analysis.
(5) While several studies in the PM
Integrated Science Assessment and NOX/SOX
Integrated Science Assessment suggest that
particles can promote corrosion of metals
there remains insufficient evidence to relate
corrosive effects to specific particulate levels
or to establish a quantitative relationship
between ambient PM and metal degradation.
With respect to damage to calcareous stone,
numerous studies suggest that wet or dry
deposition of particles and dry deposition of
gypsum particles can enhance natural
weathering processes.
tkelley on DSK3SPTVN1PROD with
The Policy Assessment concluded
that none of the new evidence in this
review called into question the
adequacy of the current standards for
protecting against material damage
effects, that such effects could play no
quantitative role in determining
whether revisions to the secondary PM
NAAQS are appropriate at this time,
and that observations continue to
support retaining an appropriate degree
of control on both fine and coarse
particles to help address materials
damage and soiling associated with PM
(U.S. EPA, 2011a, p. 5–29).
b. CASAC Advice
In advising the EPA regarding the
non-visibility welfare effects, CASAC
stated that it ‘‘concurs with the Policy
Assessment’s conclusions that while
these effects are important, and should
be the focus of future research efforts,
there is not currently a strong technical
basis to support revisions of the current
standards to protect against these other
welfare effects’’ (Samet, 2010c). More
specifically, with regard to climate
impacts, CASAC concluded that while
there is insufficient information on
which to base a national standard, the
causal relationship is established and
the risk of impacts is high, so further
research on a regional basis is urgently
needed (Samet, 2010c, p. 5). CASAC
also noted that reducing certain aerosol
components could lead to increased
radiative forcing and regional climate
warming while having a beneficial effect
on PM-related visibility. As a
consequence, CASAC noted that a
secondary standard directed toward
reducing PM-related visibility
impairment has the potential to be
accompanied by regional warming if
light scattering aerosols are
preferentially targeted.
With regard to ecological effects,
CASAC concluded that the published
literature is insufficient to support a
national standard for PM effects on
ecosystem services (Samet, 2010c, p.23).
CASAC noted that the best-established
effects are related to particles containing
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
nitrogen and sulfur, which are being
considered in the EPA’s ongoing review
of the secondary NAAQS for NOX/SOX.
With regard to PM-related effects on
materials, CASAC concluded that the
published literature, including literature
published since the last review, is
insufficient either to call into question
the current level of the standard or to
support any specific national standard
for PM effects on materials (Samet,
2010c, p.23). Nonetheless, with regard
to both types of effects, CASAC noted
the importance of maintaining an
appropriate degree of control of both
fine and coarse particles to address such
effects, even in the current absence of
sufficient information to develop a
standard.
c. Summary of Proposed Decisions
Regarding Other Welfare Effects
Based on the above considerations
and the advice of CASAC, at the time of
proposal the Administrator
provisionally concluded that it would
not be appropriate to establish any
distinct secondary PM standards to
address other non-visibility PM-related
welfare effects, including ecological
effects, effects on materials, and climate
impacts. Nonetheless, the Administrator
concurred with the conclusions of the
Policy Assessment and CASAC advice
that it is important to maintain an
appropriate degree of control of both
fine and coarse particles to address such
effects. Noting that there is an absence
of information that would support any
different standards, the Administrator
proposed generally to retain the current
suite of secondary PM standards 184 to
address non-visibility welfare effects.
Specifically, the Administrator
proposed to retain all aspects of the
current secondary 24-hour PM2.5 and
PM10 standards. With regard to the
secondary annual PM2.5 standard, the
Administrator proposed to retain the
level of the current standard and to
revise the form of the standard by
removing the option for spatial
averaging consistent with this change to
the primary annual PM2.5 standard.
C. Public Comments on Proposed
Decisions Regarding Secondary PM
Standards
The EPA received a large number of
comments on its proposed decisions
with regard to secondary PM standards,
with the large majority of those
comments focusing on the proposal to
set a distinct standard to protect against
184 As summarized in section VI.A and Table 1
above, the current suite of secondary PM standards
includes annual and 24-hour PM2.5 standards and
a 24-hour PM10 standard.
PO 00000
Frm 00120
Fmt 4701
Sfmt 4700
visibility impairment, discussed below
in section VI.C.1. Very few commenters
addressed the proposal to retain the
existing secondary standards for nonvisibility welfare effects, discussed
below in section VI.C.2. As discussed in
section VI.D. below, the Administrator
has decided to retain the current suite
of secondary PM standards generally,
while revising only the form of the
secondary annual PM2.5 standard to
remove the option for spatial averaging
consistent with this change to the
primary annual PM2.5 standard. The
Administrator has also decided,
contrary to what was proposed, not to
establish a distinct secondary standard
to address PM-related visibility
impairment. This section discusses
EPA’s responses to the comments EPA
received on its proposal, and the
rationale behind the Administrator’s
final decisions is discussed in section
VI.D. below.
1. Comments on Proposed Secondary
Standard for Visibility Protection
a. Overview of Comments
Among those commenting on the
proposal to set a distinct secondary
PM2.5 visibility index standard, a large
majority of commenters, including more
than 25 state and local agencies;
regional organizations such as NACAA,
NESCAUM, and WESTAR; and industry
commenters, such as ACC, API, BP,
EPRI, NCBA, NEDA–CAP, NMA,
NSSGA, and UARG, opposed setting a
distinct secondary standard for visibility
at this time. Many commenters in this
group expressed the view that such a
standard was not needed, primarily on
the basis that adequate protection was
provided by the existing 24-hour
secondary PM2.5 standard. Some of these
commenters also expressed legal
concerns with the nature of the
proposed standard. Other commenters
in this group supported a distinct
secondary standard for visibility in
concept, but expressed the view that it
was premature to set such a standard
pending collection of additional
visibility preference study data and the
resolution of a number of key technical
issues. Support for setting such a
distinct secondary standard for visibility
at this time came from a second group
of commenters, including the
Department of the Interior (National
Park Service), several states, the MidAtlantic/Northeast Visibility Union
(MANE–VU), the National Tribal Air
Association (NTAA), environmental
organizations such as the Appalachian
Mountain Club, National Parks
Conservation Association, Earthjustice
(AMC, et al.) and the League of Women
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
Voters of Texas. These commenters
argued that the existing secondary
standards are not sufficiently protective
of visual air quality, and that a distinct
secondary standard similar to the
proposed visibility index standard is
both necessary and appropriate to
ensure adequate protection of visibility.
Commenters in both groups expressed
concerns about various aspects of the
proposed distinct secondary standard,
including the indicator, averaging time,
level, and form. In addition, a large
number of commenters, including
commenters from both groups,
expressed concern and/or confusion
over the relationship between the
Regional Haze Program and the
proposed distinct secondary standard
for visibility, raising issues such as
analytical differences in methods
between the programs, monitoring
issues, and other implementation
challenges.
A discussion of the significant
comments outlined above, including
EPA’s responses to the comments, is
presented here, with more detailed
discussion in the Response to
Comments document. Comments
relating to the specific elements of the
proposed standard—indicator, averaging
time, form and level—are discussed in
sections VI.C.1.b-e, respectively.
Comments related to the need for a
distinct secondary standard at this time
are discussed in section VI.C.f. Legal
issues raised by commenters opposed to
setting a secondary standard based on
the proposed visibility index are
discussed in section VI.C.g. Finally,
comments related to the relationship
between a distinct secondary standard
and the Regional Haze Program are
discussed in section VI.C.h.185 While
the EPA concludes in section VI.D
below to retain the current suite of
secondary PM2.5 standards, the
appropriateness of the protection that
would be provided by the proposed
PM2.5 visibility index standard, and the
relationship between this degree of
protection and that provided by the
current secondary 24-hour secondary
PM2.5 standard, are key elements in the
Administrator’s decision, and are
discussed below.
tkelley on DSK3SPTVN1PROD with
b. Indicator
Numerous commenters, both those
supporting a distinct secondary
standard and those opposed to setting
185 Comments pertaining to implementation
issues, which the Administrator may not consider
in making decisions about setting national ambient
air quality standards, are discussed in the Response
to Comments document, as are comments regarding
monitoring issues related to the proposed distinct
visibility index standard.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
such a standard, expressed views on the
suitability of utilizing a PM2.5 calculated
light extinction indicator for the
standard as proposed. While these
groups of commenters differed in terms
of their views on the appropriateness of
using calculated PM2.5 light extinction
as the basis for the indicator rather than
relying on direct measurements of PM2.5
light extinction, commenters from both
groups expressed concern over specific
elements of the proposed method of
calculating PM2.5 light extinction. In
particular, commenters expressed
differing views on which IMPROVE
algorithm should be utilized; whether it
is appropriate to exclude coarse
particles from the indicator; and
whether the proposed protocols for
incorporating data on relative humidity
and PM2.5 species are appropriate.186
i. Comments on Calculated vs. Directly
Measured Light Extinction
The majority of commenters in both
groups noted the uncertainties
associated with relying on a calculated
light extinction indicator and stated a
preference for utilizing direct light
extinction measurements. However,
recognizing the limitations on applying
direct measurements at present,
commenters supporting the proposal to
set a distinct standard argued that
relying on ‘‘calculated light extinction is
a reasonable first approach’’ (DOI, p. 2).
These commenters pointed to the advice
of CASAC, which had acknowledged
that it was not possible for the EPA to
develop an FRM for direct measurement
of light extinction within the time frame
of this review and had concluded that
relying on a calculated PM2.5 light
extinction indicator represented a
reasonable approach that could be
implemented sooner than a directly
measured indicator. These commenters
generally supported the proposal to
adopt a calculated PM2.5 light extinction
indicator, at least as an interim
approach.
Commenters opposed to setting a
distinct standard generally argued that it
was inappropriate to rely on a
calculated light extinction indicator
rather than direct measurements. Some
of these commenters argued that the
proposed calculated light extinction
indictor is ill suited for a bright line
standard because the method uses
average humidity and a reconstructed
visibility measurement calculated from
PM2.5 speciation filter analysis, rather
than measuring what is actually
186 Some commenters expressed concern about
the omission of other contributors to visibility
impairment from the visibility index, as discussed
in the Response to Comments document.
PO 00000
Frm 00121
Fmt 4701
Sfmt 4700
3205
observed by individuals. A number of
commenters advocated postponing
setting a distinct standard until an
approach based on direct light
extinction measurements can be
adopted. Many of these commenters
stated that relying on direct light
extinction measurements would enable
a standard to be based on a shorter
averaging time, either 1-hour or subdaily (4 to 6 hours), consistent with the
more instantaneous nature of
perceptions of visual air quality and the
advice of CASAC in this review.
The EPA generally agrees with
commenters that an indicator based on
directly measured light extinction
would provide the most direct link
between PM in the ambient air and PMrelated light extinction. However, as
noted at the time of proposal and in
accordance with the advice of CASAC,
the EPA has concluded that this is not
an appropriate option in this review
because a suitable specification of
currently available equipment or
performance-based verification
procedures could not be developed in
the time frame of this review. Moreover,
CASAC concluded that relying on a
calculated PM2.5 light extinction
indicator based on PM2.5 chemical
speciation and relative humidity data
represented a reasonable approach. The
inputs that are necessary include
measurements that are available through
existing monitoring networks and
approved protocols. Thus, the EPA
remains confident that the available
evidence demonstrates that a strong
correspondence exists between
calculated PM2.5 light extinction and
PM-related visibility impairment.
Furthermore, CASAC agreed, noting that
the proposed calculated PM2.5 light
extinction indicator based on the
original IMPROVE algorithm ‘‘appears
to be a reasonable approach for
estimating hourly light extinction’’
(Samet, 2010d, p. 11) and ‘‘its reliance
on procedures that have already been
implemented in the CSN and routinely
collected continuous PM2.5 data suggest
that it could be implemented much
sooner than a directly measured
indicator’’ (Samet, 2010d, p. iii). Thus it
would not be appropriate to postpone
setting a distinct secondary standard
until an approach based on direct light
extinction measurements could be
adopted.
ii. Comments on Specific Aspects of
Calculated Light Extinction Indicator
Some commenters, even those
supporting the adoption of a calculated
light extinction indicator, also
expressed concern over specific aspects
of the proposed indicator. First, a
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
3206
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
number of commenters expressed
concern over the proposal to use the
original IMPROVE algorithm as the
basis for the calculated light extinction
indicator. These commenters noted that
the original IMPROVE algorithm has
been shown to have consistent biases at
both low and high levels of light
extinction. In particular, these
commenters expressed concern with the
algorithm’s bias at higher levels of light
extinction, which they pointed out were
the conditions that might be
encountered on hazier days in urban
areas.
Some commenters supported use of
the revised IMPROVE algorithm. These
commenters noted that the revised
equation has been through a peer review
which confirmed that it is based on the
best science and corrects the biases
inherent in the original algorithm.
Commenters also noted that this revised
algorithm has been widely incorporated
into Regional Haze plans, and urged the
EPA to use this same equation in the
visibility index for the sake of
consistency: ‘‘EPA approved this
approach for regional haze and does not
dispute its greater accuracy. Therefore,
a national secondary ambient air quality
standard based on criteria that
accurately reflect the latest scientific
knowledge logically should not revert to
the original IMPROVE algorithm’’
(Oklahoma DEQ, p. 2). Other
commenters noted that both the original
and the revised IMPROVE algorithms
were designed in support of the
Regional Haze Program which is
focused on largely rural Class I areas,
and that neither algorithm is necessarily
suitable for urban areas. Noting that the
EPA has not thoroughly evaluated the
applicability of either IMPROVE
algorithm in urban areas, these
commenters urged additional research
to evaluate the suitability of either
algorithm (or an alternative approach) in
urban areas.
Second, a number of commenters
argued that exclusion of coarse PM from
the calculated light extinction indicator
was inappropriate. These commenters
noted that coarse particulate matter is
an important contributor to visibility
impairment in many areas, particularly
in the western U.S., and that the levels
of ‘‘acceptable’’ visual air quality
derived from the visibility preference
studies reflected total light extinction
due to the full mix of particles
(including coarse PM) in ambient air. A
few commenters noted that due to the
exclusion of coarse particles, a
‘‘deciview’’ calculated for purposes of
the proposed PM2.5 visibility index is
inconsistent with the unit as
conventionally defined under the
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
Regional Haze Program. Other
commenters, however, supported the
proposal to exclude coarse PM from the
calculated light extinction indicator,
noting the important role that PM2.5
plays in urban visibility and arguing it
would be more difficult to control the
contribution of coarse particle sources
such as wind-blown dust to urban
visibility impairment.
Third, some commenters questioned
why the EPA was proposing to rely on
monthly average relative humidity
(f(RH)) values when hourly humidity
data are widely available, particularly in
urban areas. One commenter argued that
the EPA’s proposed approach involves
‘‘guessing relative humidity’’ rather than
relying on accurate, readily available
measurements (Oklahoma DEQ, p. 1).
The commenter stated that since relative
humidity is highly variable and weather
dependent, the proposed approach
‘‘effectively undermines the capacity of
the prescribed monitoring regime to
identify periods when PM2.5 adversely
affects visibility.’’ Other commenters
supported this view, noting that relative
humidity can vary substantially even
within a 24-hour period, and that light
extinction can be very sensitive to these
changes. These commenters
recommended that hourly or daily
humidity measurements should be
utilized in place of the proposed
monthly average f(RH) values.
Some commenters also recommended
that the EPA should utilize a 90 percent
relative humidity screen rather than 95
percent cap for purposes of eliminating
periods in which visibility impairment
is due to rain or fog. These commenters
claimed that under a 95 percent cap,
both the average f(RH) values and the
PM2.5 visibility index values could be
inflated in locations frequently affected
by fog and/or precipitation. These
commenters preferred the approach of
excluding hours with relative humidity
above 90 percent on the grounds that
this approach would eliminate foggy/
rainy hours irrespective of the frequency
of occurrence.
The EPA does not agree with
commenters who advocated using the
revised IMPROVE algorithm. Both the
original and the revised IMPROVE
algorithms have been evaluated by
comparing the calculated estimates of
light extinction with coincident optical
measurements. As discussed above in
section VI.B.1.a.i, the revised algorithm
was developed to address observed
biases in the predictions using the
original algorithm under very low and
very high light extinction conditions,
with further modifications and
additions to better account for
differences in particle composition and
PO 00000
Frm 00122
Fmt 4701
Sfmt 4700
aging in remote areas.187 However, the
EPA does not believe that these same
modifications and additions would
necessarily be appropriate for
calculating light extinction in urban
areas. Instead, the EPA considers the
original algorithm to be suitable for
purposes of calculating urban lightextinction, although some adjustments
may be appropriate for urban
environments as well. The reasons why
the original algorithm is suited to urban
environments are discussed further
below, along with adjustments that the
EPA believes are likely appropriate
based on the current (limited) state of
knowledge.
First, the EPA considers that the
multiplier of 1.8 used to convert OC to
OM in the revised IMPROVE algorithm
is too high for urban environments. The
EPA is aware that there has been
considerable debate within the research
community about the appropriate
multiplier to use to best represent urban
environments. As discussed in
Appendix F of the Policy Assessment
(U.S. EPA, 2011a), the EPA used the
SANDWICH mass closure approach
(Frank, 2006) in the Urban Focused
Visibility Assessment (U.S. EPA, 2010b)
for purposes of calculating maximum
daylight hourly PM2.5 light extinction
and evaluated which multiplier would
produce 24-hour results most similar to
the SANDWICH approach using 24-hour
PM2.5 organic carbon derived from the
new Chemical Speciation Network
(CSN) carbon monitoring protocol
established in 2007.188 Analyses
presented in Appendix F of the Policy
Assessment indicate that a multiplier of
1.6 is most appropriate for purposes of
comparing the hourly PM2.5 light
extinction with calculated 24-hour
extinction (see Appendix F, section F.6
for a full explanation). The EPA also
considers this higher multiplier to be a
better approach for urban CSN
monitoring sites where the new
measurements of organic carbon tend to
be lower than those produced by the
older NIOSH-type monitoring protocol
187 Specifically, the revised IMPROVE algorithm
incorporates additional terms to account for
particles representing the different dry extinction
and water uptake (f(RH)) from two size modes of
sulfate, nitrate and organic mass, as well as adding
a term for hygroscopic sea salt. There are also
adjustments for the calculation of OM as 1.8*OC
compared to 1.4*OC in the original algorithm to
better account for the more aged PM organic
components found in remote areas.
188 Starting in 2007, the CSN adopted the
IMPROVE monitoring protocol for the measurement
of organic and elemental carbon using the
IMPROVE analytical method and an IMPROVE-like
sampler. The transition was completed in 2009.
(See ‘‘Modification of Carbon Procedures in the
Speciation Network,’’ http://www.epa.gov/ttn/
amtic/files/ambient/pm25/spec/faqcarbon.pdf.)
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
(Malm, 2011). A multiplier of 1.6 is now
used to calculate OM from OC
measurements at CSN sites.
At the time of proposal, the EPA
proposed to use the original IMPROVE
algorithm with its 1.4 multiplier for
converting OC to OM, but requested
comment on whether this value was
appropriate. Comments received by the
Agency generally indicate that the OCto-OM multiplier of 1.4 used in the
original IMPROVE algorithm is too low
for urban areas. Based on the analyses
presented in Appendix F of the Policy
Assessment, the EPA agrees with these
commenters. However, the EPA also
believes that it would be inappropriate
to use a multiplier as high as 1.8 to
convert OC to OM in urban areas. As
noted by commenters, the organic mass
contribution to visibility impairment
can be large, and generally OM is
significantly larger in urban areas
compared to surrounding rural areas.189
Because a large portion of the organic
component of urban PM results from
nearby emissions sources, the total OM
mass is generally closer to the measured
OC from which it is derived. This means
it is appropriate to use a smaller
multiplier to convert OC to OM in urban
areas as compared to the value of 1.8
used in the revised algorithm, which is
tailored to remote areas. The CASAC
noted that urban OM includes fresh
emissions and the EPA concluded in the
Visibility Assessment that ‘‘the original
version is considered more
representative of urban situations when
emissions are still fresh rather than aged
as at remote IMPROVE sites’’ (U.S. EPA,
2010b, p. 3–19). Although the revised
algorithm represents the best science of
estimating extinction in remote areas
with its aged aerosol, the commenters
did not address how the EPA should
modify the revised algorithm to best
represent the more complex and
different urban aerosol, particularly for
OM. In light of all of these
considerations, in particular the
analyses the EPA conducted for
Appendix F of the Policy Assessment
and the fact that the monitoring method
for organic carbon has recently changed
in the CSN network, the EPA judges that
a multiplier of 1.6 for urban areas would
be most appropriate for purposes of
calculating PM2.5 light extinction in
urban areas.190 In formulating this
189 The difference between higher PM
2.5 mass in
urban areas compared to surrounding regions,
known as the urban excess, is largely attributed to
organic mass (U.S. EPA, 2004b).
190 The implications of this shift to a 1.6
multiplier for OC in urban areas for decisions about
averaging time, level, and need for a distinct
secondary standard are discussed further below in
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
judgment, the EPA recognizes that
neither the original nor the revised
IMPROVE algorithm has been tested for
suitability in urban areas and that
additional research is necessary to
reduce the uncertainties about the most
appropriate value for the OC to OM
multiplier in urban environments. With
regard to other changes between the
original and revised IMPROVE
algorithms, the EPA also does not
believe that it would be appropriate to
include a term for hygroscopic sea salt
for urban light extinction, or to
differentiate between different size
modes of sulfate, nitrate, and organic
mass as empirically defined by the
revised IMPROVE algorithm. Unlike in
some remote coastal locations, sea salt
is not major contributor to light
extinction in urban areas. Moreover,
urban sources of salt include sanding of
roads during the winter and those reentrained particles are mostly in the
coarse size range.
Like in remote areas, small and large
size modes of sulfate, nitrate and
organic mass would exist in the urban
environment. However, the
apportionment of the total fine particle
concentration of each of the three PM2.5
components into the concentrations of
the small and large size fractions would
likely need a different approach than
that used for remote areas. This is
because of the closer proximity of urban
sources to their emissions. This is a
particular concern not only for organic
mass, which as explained previously
has a large contribution from nearby
urban emission sources, but also for
PM2.5 nitrate whose concentrations are
also higher in urban areas compared to
the surrounding regions. Thus, a higher
portion of the total urban concentration
may be in the small mode compared to
remote areas and thus a different
apportionment algorithm would be
needed.
Finally, the EPA does not consider it
necessary to employ site-specific
Rayleigh light scattering terms in place
of a universal Rayleigh light scattering
value for purposes of calculating light
extinction in urban areas for purposes of
calculating the 90th percentile values.
The site-specific Rayleigh value is most
important to accurately estimate
extinction on the best visibility days
which is an essential metric for the
regional haze program.
For all of these reasons, the EPA
considers the original IMPROVE
algorithm better suited to the task of
calculating urban light extinction than
the revised IMPROVE algorithm.
sections VI.C.1.c, VI.C.1.e, and VI.C.1.f,
respectively.
PO 00000
Frm 00123
Fmt 4701
Sfmt 4700
3207
However, the EPA does consider it
appropriate to make certain adjustments
to the original algorithm for purposes of
calculating urban light extinction. As
discussed above, the EPA believes it is
appropriate to use a 1.6 multiplier to
convert OC to OM in urban areas. In
addition, the EPA believes it is
appropriate to exclude the term for
coarse particles from the equation. The
EPA does not agree with commenters
who suggested that coarse particles
should be included in the calculated
light extinction indicator. As noted in
the proposal, PM2.5 is the component of
PM responsible for most of the visibility
impairment in most urban areas.
Currently available data suggest that
PM10-2.5 is a minor contributor to
visibility impairment most of the time,
although at some locations (U.S. EPA,
2010b, Figure 3–13 for Phoenix) PM10-2.5
can be a major contributor to urban
visibility effects. While it is reasonable
to assume that other urban areas in the
desert southwestern region of the
country may have conditions similar to
the conditions shown for Phoenix, in
fact few urban areas conduct continuous
PM10-2.5 monitoring. This significantly
increases the difficulty of assessing the
role of coarse particles in urban
visibility impairment. For example,
among the 15 urban areas assessed in
this review, only four areas had
collocated continuous PM10 data
allowing calculation of hourly PM10-2.5
data for 2005 to 2007. In addition,
PM10-2.5 is generally less homogenous in
urban areas than PM2.5 in that coarse
particle concentrations exhibit greater
temporal variability and a steeper
gradient across urban areas than fine
particles (U.S. EPA, 2009a, p. 3–72).
This makes it more challenging to select
sites that would adequately represent
urban visibility conditions. Thus, while
it would be possible to include a
PM10-2.5 light extinction term in a
calculated light extinction indicator, as
was done in the Visibility Assessment,
there is insufficient information
available at this time to assess the
impact and effectiveness of such a
refinement in providing public welfare
protection in areas across the country
(U.S. EPA, 2011a, pp. 4–41 to 4–42).
Therefore, the EPA concludes that it is
not appropriate to set a standard based
on a calculated light extinction
indicator that includes coarse particles
at this time, and the calculated indicator
should be based on PM2.5 light
extinction.
With regard to the suggestion by some
commenters that the calculated light
extinction indicator should be
calculated using hourly humidity data,
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
3208
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
the EPA disagrees that concurrent
humidity measurements should be used.
The use of longer-term averages for each
monitoring site adequately captures the
seasonal variability of relative humidity
and its effects of visibility impairment,
and this approach focuses more on the
underlying aerosol contributions to
visibility impairment and less on the
day-to-day variations in humidity. This
provides a more stable indicator for
comparison to the NAAQS and one that
is more directly related to the
underlying emissions that contribute to
visibility impairment.
With regard to the comments
advocating the use of a 90 percent
humidity screen as opposed to a 95
percent humidity cap, the EPA believes
that relying on monthly average relative
humidity values based on 10 years of
climatological data appropriately
reduces the effect of fog and
precipitation. Although the approach of
using a 95 percent humidity cap, as in
the Regional Haze Program, includes
some hours with relative humidity
between 90–95 percent, the general
approach of using a longer-term average
for each monitoring site effectively
eliminates the effect of very high
humidity conditions on visibility at
those locations.
Therefore, taking all of the above
considerations and CASAC advice into
account, the EPA continues to conclude
that a calculated PM2.5 light extinction
indicator, similar to that used in the
Regional Haze Program (i.e., using an
IMPROVE algorithm as translated into
the deciview scale), would be the most
appropriate indicator to replace the
current PM2.5 mass indicator for a
distinct secondary standard. Moreover,
the EPA continues to conclude that this
calculated indicator should based on the
original IMPROVE algorithm, adjusted
to use a 1.6 OC multiplier and exclude
the term for coarse particles, in
conjunction with monthly average
relative humidity data (i.e., f(RH)
values) based on long-term
climatological means as used in the
Regional Haze Program. A PM2.5
visibility index defined in this way
would appropriately reflect the
relationship between ambient PM and
PM-related light extinction, based on
the analyses discussed in the proposal
and reflecting the aerosol and relative
humidity contributions to visibility
impairment by incorporation of factors
based on measured PM2.5 speciation
concentrations and climatological
average relative humidity data. In
addition, this type of indicator would
address, in part, the issues raised in the
court’s remand of the 2006 PM2.5
standards. Such a PM2.5 visibility index
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
would afford a relatively high degree of
uniformity of visual air quality
protection in areas across the country by
virtue of directly incorporating the
effects of differences in PM2.5
composition and relative humidity
across the country.
c. Averaging Time
Few commenters specifically
addressed the issue of averaging time.
Those who did generally expressed the
view that an hourly or sub-daily
averaging time would be the most
appropriate approach, as supported by
CASAC and the EPA’s own analyses in
this review. These comments were
generally consistent with the emphasis
among all commenters on the
desirability of adopting a directly
measured light extinction indicator that
could be measured on an hourly or subdaily time scale. Some commenters
noted that a standard based on a 4–6
hour averaging time would better
capture peak daily light extinction
while allowing stable signal quality;
others urged EPA to adopt a 1-hour
averaging time in conjunction with
direct measurements. Commenters
pointed to significant limitations
associated with using a 24-hour
averaging time, including the
uncertainties in translating hourly or
sub-daily visibility index values into 24hour equivalent values. Some
commenters criticized the analysis
presented in the Policy Assessment
comparing the 24-hour calculated light
extinction values to the maximum
daylight 4-hour calculated light
extinction values. These commenters
stated that the scatter plots and
regressions presented in the Policy
Assessment indicate there is
considerable variation in the 24-hour vs.
4-hour relationship, and interpreted this
to mean that 24-hour light extinction
values are a poor surrogate for 4-hour
values. For example, several industry
commenters cited an analysis which
noted that the correlation coefficient
between the 24-hour and 4-hour values
was as low as r2 = 0.42 in Houston, and
stated that the EPA was being overly
‘‘optimistic’’ in concluding that cityspecific and pooled r2 values in the
range of 0.6 to 0.8 showed good
correlation (UARG, Attachment 2, p.
27).
In addition, some commenters
expressed concern over potential bias
and greater uncertainty introduced by
the inclusion of nighttime hours, noting
that because relative humidity tends to
be higher at night, inclusion of these
hours could cause areas to ‘‘record
NAAQS exceedances that have no
corresponding visibility impairment
PO 00000
Frm 00124
Fmt 4701
Sfmt 4700
value’’ (UARG, p. 36). Commenters also
emphasized the poor fit of a 24-hour
averaging time with the near
instantaneous judgments about visibility
impairment reflected in the visibility
preference studies. Commenters also
noted that there is greater hourly
variation in PM concentrations and
resulting visibility conditions in urban
areas than in Class I areas; thus, while
the Regional Haze Program uses 24-hour
IMPROVE data, the commenters stated
that a shorter averaging time is needed
for an urban-focused PM2.5 visibility
standard. Some commenters objected to
a 24-hour averaging time as
unsupported by the record in this
review: ‘‘Because the science the
Administrator relies on for the other
elements of the proposed visibility
standard is tied to short-term exposures
to visibility impairment, the EPA has no
basis for promulgating a standard that
uses a 24-hour averaging time’’ (API, p.
43). These commenters claimed that
while the EPA may not have the
information or infrastructure in place to
allow the Agency to set a standard based
on a 1-hour or other sub-daily averaging
time, this does not justify moving to a
24-hour averaging time.
Among commenters supporting the
proposed distinct secondary standard
for visibility, many commenters
recognized the limitations on
monitoring methods and currently
available data that led to the EPA’s
proposal to adopt a standard based on
a 24-hour averaging time. Most of these
commenters acknowledged that the lack
of reliable hourly speciation data means
that a 24-hour averaging time is the only
workable approach for a standard based
on calculated light extinction.
Commenters advocating a distinct
secondary standard for visibility
therefore generally supported the
proposal to adopt a 24-hour averaging
time, at least as an interim approach
until a directly measured light
extinction indicator could be adopted in
the future. This approach was also
supported by a few industry
commenters who noted that since a
visibility index standard would be
based on data from the IMPROVE and
CSN monitors, which operate on a 24hour basis with 1-in-3 (or 1-in-6) day
sampling, ‘‘it is imperative that EPA
retain a 24-hour averaging time if a
secondary visibility standard is
promulgated’’ (API, Attachment 2, p. 9).
In response to comments supporting a
1-hour or sub-daily (4- to 6- hour)
averaging time in conjunction with a
direct light extinction measurements,
the EPA notes that, as discussed above
in the response to comments on
indicator, the Agency has concluded
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
that a directly measured light extinction
indicator is not an appropriate option in
this review, independent of the decision
on averaging time. Having reached the
conclusion that a calculated PM2.5 light
extinction indicator would be most
appropriate, the EPA has next
considered what averaging time would
be most desirable for such an indicator.
As noted in the proposal, the EPA has
recognized that hourly or sub-daily (4to 6-hour) averaging times, within
daylight hours and excluding hours
with high relative humidity, are more
directly related than a 24-hour averaging
time to the short-term nature of the
perception of PM-related visibility
impairment and the relevant exposure
periods for segments of the viewing
public. Thus, the Agency agrees with
commenters’ general point that, as a
starting premise, a sub-daily averaging
time would generally be preferable.
However, as noted at the time of
proposal and discussed above in section
VI.B.1.c, important data quality
uncertainties have recently been
identified in association with currently
available instruments that would be
used to provide the hourly PM2.5 mass
measurements that would be needed in
conjunction with an averaging time
shorter than 24 hours. As a result, at this
time the Agency has strong technical
reservations about a secondary standard
that would be defined in terms of a subdaily averaging time. The data quality
issues which have been identified,
including short-term variability in
hourly data from currently available
continuous monitoring methods,
effectively preclude adoption of a 1hour averaging time in this review,
given the sensitivity of a 1-hour
averaging time to these data quality
limitations. Even with regard to multihour averaging times, the EPA continues
to conclude that the data quality
concerns preclude adoption of a subdaily averaging time.
Moreover, analyses conducted for the
Policy Assessment indicate that PM2.5
light extinction calculated on a 24-hour
average basis would be a reasonable and
appropriate surrogate for PM2.5 light
extinction calculated on a 4-hour basis.
The scatter plots comparing 24-hour and
4-hour calculated PM2.5 light extinction
in the Policy Assessment (U.S. EPA,
2011a, Figures G–4 and G–5) do show
some scatter around the regression line
for each city. This was to be expected,
since the calculated 4-hour light
extinction includes day-specific and
hour-specific influences that are not
captured by the simpler 24-hour
approach. Overall, however, in the
EPA’s view, both the city-specific and
pooled 15-city 24-hour vs. 4-hour
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
comparisons show strong correlation
between the two averaging times.
Moreover, the 90th percentile design
values calculated for 4-hour vs. 24-hour
light extinction are much more closely
correlated than are the values for
individual days in particular urban
areas calculated using these two
approaches. Thus, while the EPA agrees
with commenters who pointed out the
relatively low correlation between 4and 24-hour values in cities such as
Houston, the Agency points out that the
correlations of 90th percentile values
are much higher, particularly when one
considers the average values across
urban areas. In general, the 90th
percentile values line up better and
demonstrate closer to a one-to-one
relationship.
The EPA has conducted a reanalysis
(Frank et al., 2012b) of the relationships
between estimated 24-hour and 4-hour
visibility impairment based on the
variety of metrics discussed in
Appendix G of the Policy Assessment
that further supports this finding. The
reanalysis more appropriately
considered the uncertainty of the
calculated 4-hour values. It also
considered the effect of changing the OC
to OM multiplier used in urban areas
with the new CSN monitoring protocol
from 1.4 to 1.6. The revised analysis
shows that the 24-hour values are
generally closer to the 4-hour values
than originally estimated.
Since conclusions in the proposal
about the relationship between 4-hour
and 24-hour values were drawn not just
on the basis of the city-specific results
but also on the more robust 90th
percentile values, the EPA disagrees
with commenters who state that the
Agency was overly optimistic in
considering 24-hour values an
appropriate surrogate for 4-hour values.
Also, it is appropriate to focus on the
90th percentile design value comparison
since the design values would
determine attainment status and the
degree of improvement in air quality
that could be expected in areas
instituting controls to meet the NAAQS.
Therefore the EPA does not agree with
commenters who state that a 24-hour
averaging time cannot serve as an
appropriate surrogate for sub-daily
periods of visibility impairment. On the
contrary, the EPA continues to
conclude, on the basis of this analysis,
that PM2.5 light extinction calculated on
a 24-hour basis is a reasonable and
appropriate surrogate for sub-daily
PM2.5 light extinction calculated on a 4hour basis.
The EPA recognizes that the effect of
adopting a 24-hour averaging time may
be to smooth out some of the hour-by-
PO 00000
Frm 00125
Fmt 4701
Sfmt 4700
3209
hour variability in visibility index
values. (Indeed, this is true if we
compare a 4-hour averaging time to a 1hour averaging time as well.) Hourspecific influences which would be
evident if an hourly or sub-daily
averaging time were to be used will be
masked to some extent when those
hours are averaged together with other
hours. This means, in part, that a 24hour averaging time may effectively
reduce peak values by means of
averaging them together with other
hours, which may have lower values.
However, given the well documented
variability in hourly visibility
conditions, especially in urban areas, as
noted by commenters, it is reasonable to
assume that in some cases peak hours
may be significantly influenced by
atypical conditions, making it
appropriate to adopt an averaging time
that is sufficiently long to ensure that
hour-specific influences are balanced
against more typical conditions. Perhaps
even more important is the concern that
many peak hourly measurements may
be significantly influenced by atypical
instrument performance; this reinforces
the conclusion that it is appropriate to
adopt a longer averaging time, to ensure
that hour-specific uncertainties are
balanced against more robust
measurements.
Thus, in agreement with commenters
who supported a daily averaging time,
the EPA concludes that a 24-hour
averaging time would be appropriate for
a distinct secondary standard based on
a calculated PM2.5 light extinction
indicator.
d. Form
The EPA received very few comments
with regard to the proposal to adopt a
90th percentile form, averaged over 3years, in conjunction with a PM2.5
visibility index and a 24-hour averaging
time. One commenter stated that it was
inappropriate to use a 90th percentile
form, noting that this would result in
the exclusion of a minimum of 36 days
of data annually. The commenter
expressed particular concern that this
proposed approach, in combination
with a 24-hour standard based on an
unadjusted CPL, would not capture the
worst visibility impairment and that this
would undermine ‘‘the intent of setting
a meaningful secondary visibility
standard’’ (AMC, et al., p. 2). Another
commenter argued that the EPA had
provided no scientific basis for why the
90th percentile form was suitable, and
claimed that the Agency was making ‘‘a
somewhat arbitrary judgment that
people’s welfare would be affected only
if adverse urban visibility were to occur
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
3210
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
more than 10 percent of the time’’ (API,
Attachment 2, p. 4).
On other hand, a few commenters
who appeared to generally support the
proposal to use a 90th percentile form
advocated averaging the 90th percentile
values over longer time periods, arguing
that averaging over only 3 years would
not provide a stable assessment of visual
air quality in the West because this time
period is insufficient to properly
account for western drought and fire
cycles. These commenters pointed to
the approach in the Regional Haze
Program of averaging visibility
impairment over 5 years, and noted that
even within this longer time period data
can be significantly influenced by high
emissions during significant fire years.
The EPA disagrees with all of these
comments. With regard to the comment
opposing the 90th percentile form as
inappropriately excluding the worst
visibility days, the EPA notes that there
is a significant lack of information on,
and a high degree of uncertainty
regarding, the impact on public welfare
of the number of days with visibility
impairment over the course of a year.
For example, the visibility preference
studies used to derive the range of CPLs
considered in this review offered no
information regarding the frequency of
time that visibility levels should be
below those values. Based on this
limitation, the EPA concluded in the
Policy Assessment that it would not be
appropriate to consider eliminating all
exposures above the level of the
standard and that it was reasonable to
consider allowing some number of days
with reduced visibility. Recognizing
that the Regional Haze Program focuses
attention on the 20 percent worst
visibility days (i.e., those at or above the
80th percentile of visibility
impairment), the EPA continues to
believe, as noted in the proposal, that a
percentile well above the 80th
percentile would be appropriate to
increase the likelihood that all days in
this range would be improved by
control strategies intended to help areas
attain the standard. Focusing on the
90th percentile, which represents the
median of the distribution of the 20
percent worst visibility days, could be
reasonably expected to lead to
improvements in visual air quality on
the 20 percent most impaired days.
Thus, the EPA has made a reasoned
judgment based on a full consideration
of the upper end of the distribution of
visibility impairment conditions and
continues to conclude that it is
appropriate to focus on the 90th
percentile of visibility impairment
values.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
With regard to comments requesting
the EPA adopt a longer multi-year
averaging period for the 90th percentile
values, the EPA disagrees that it would
be appropriate to average the 90th
percentile values over periods longer
than 3 years. The EPA recognizes that a
multi-year percentile form offers greater
stability to the air quality management
process by reducing the possibility that
statistically unusual indicator values
will lead to transient violations of the
standard. Utilizing a 3-year average form
provides stability from the occasional
effects of inter-annual meteorological
variability that can result in unusually
high pollution levels for a particular
year. The Agency has adopted this
approach in other NAAQS, including
the current secondary 24-hour PM2.5
NAAQS, which has a 98th percentile
form averaged over 3 years. However,
adopting a multi-year averaging period
longer than 3 years would increase the
number of days with visibility
impairment above the target level of
protection and would therefore reduce
the protectiveness of the standard.
Based on this the EPA does not believe
it would be appropriate to average 90th
percentile values over a period as long
as five years. Therefore, the EPA
continues to conclude that a 90th
percentile form, averaged over 3 years,
would be appropriate, in conjunction
with a calculated PM2.5 light extinction
indicator and a 24-hour averaging time.
e. Level
With regard to level, commenters
focused on two main themes. First, a
large number of commenters addressed
the information available from the
public preference studies with regard to
the acceptability of various levels of
visual air quality. These comments,
which are discussed in subsection
VI.C.1.e.i below, address the EPA’s use
of visibility preference studies as the
basis for the selection of a range of
appropriate levels for the Administrator
to consider. Many commenters
challenged the use of these studies as
the basis for setting a distinct secondary
standard, arguing that limitations in
these studies rendered them an
unsuitable and insufficient basis on
which to establish such a standard.
Second, commenters expressed different
views as to what level(s) of a distinct
secondary standard would be
appropriate, if the EPA were to set such
a standard. These comments reflected
consideration of the results of the public
preference studies as well as analyses
conducted in the Visibility Assessment
and the Policy Assessment, as discussed
in the proposal. Comments addressing
the appropriateness of specific levels are
PO 00000
Frm 00126
Fmt 4701
Sfmt 4700
discussed in subsection VI.C.1.e.ii
below.
i. Comments on Visibility Preference
Studies
A majority of commenters expressed
the view that the existing preference
studies provide an insufficient basis for
selection by the Administrator of an
appropriate level of public welfare
visibility protection for a national
standard. These commenters
highlighted a number of limitations and
uncertainties (enumerated below)
associated with these studies as support
for this view. In contrast, other
commenters felt that despite certain
limitations, these studies do provide a
sufficient basis on which the
Administrator can select an appropriate
level of a standard to provide national
public welfare visibility protection. The
remainder of this section organizes and
discusses these comments under four
broad topic areas, including: (a)
Limitations and uncertainties associated
with the visibility preference studies; (b)
preference study methods and design;
(c) use of preference study results for
determining adversity; (d) the
appropriateness of using regionally
varying preference study results to
select a single level for a national
standard.
(a) Preference Study Limitations and
Uncertainties
A large and diverse number of
limitations and uncertainties associated
with the visibility preference studies
have been identified and discussed in
the public comments. Many of these
same limitations and uncertainties were
also identified and discussed by the
EPA in the various documents
developed throughout this review. The
most important and fundamental
limitations and uncertainties will be
discussed here in the preamble, while
more specific, unique or detailed
comments will be addressed in the
Response to Comments document.
The primary or most frequent
limitation cited by many commenters
relates to the small number of
preference studies that are available in
this review. In particular, some
commenters note that these preference
studies cover just four locations, only
three of which occur in the U.S., that
the two studies conducted in
Washington, DC were pilot studies, not
full preference studies, and/or that three
of the preference studies were
conducted in the West, while only one
was conducted in the East, providing
only limited geographic coverage.
Typically, these same commenters also
pointed out that taken together, these
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
limited studies only included a total of
852 participants, which they claimed
was too small a sample size and
unrepresentative nationally. These
commenters thus concluded that there
is insufficient information, both
geographically and demographically,
upon which to select a national level of
a visibility index for purposes of
visibility protection.
In contrast, several commenters stated
support for using the preference studies,
concluding they provide an adequate
basis, in spite of their limited nature. In
particular, AMC et al. state:
tkelley on DSK3SPTVN1PROD with
We believe that these studies provide
sufficient results to inform setting a national
visibility standard. While the number of
studies is small, they do incorporate spatial
variation and, in the case of Denver and
Phoenix, varied populations* * *. EPA
should have confidence, rather than
uncertainty, in the fact that these studies
used different methods and respondents and
yield a range of 20–24 dv, with one outlier
of 29. (AMC, et al., pp. 6–7)
Regarding the first group of
commenters, the EPA notes that it is
well aware of the limited nature of the
information, which it has described in
great detail in the Integrated Science
Assessment, Visibility Assessment, and
Policy Assessment, as well as in section
VI.B.2 of the proposed rule (77 FR
38973). The EPA further notes, however,
that limited information does not
preclude the Administrator from making
judgments based on the best available
science, taking into account the existing
uncertainties and limitations associated
with that available science. Thus, in
reaching judgments based on the
science, the Administrator appropriately
weighs the associated uncertainties. The
CASAC supported this view and
concluded that the available
information provided a sufficient basis
on which the Administrator could form
a judgment about requisite PM-related
public welfare visibility protection.
Specifically, CASAC stated ‘‘[t]he 20–30
deciview range of levels chosen by EPA
staff as ‘Candidate Protection Levels’ is
adequately supported by the evidence
presented’’ (Samet, 2010b, p. iii). As
discussed in the proposed rule (77 FR
38990), the Administrator recognized
and explicitly took into account the
uncertainties and limitations in the
science in determining an appropriate
degree of protection when she proposed
a level at the upper end of the
recommended range. As discussed
below, the Administrator continues to
be mindful of these uncertainties and
limitations in reaching her final
determination regarding what
constitutes an appropriate degree of
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
protection with respect to PM-related
visibility impairment.
With respect to the comments of AMC
et al., the EPA agrees that these studies
provide a sufficient basis to inform the
Administrator’s judgments regarding an
appropriate level of protection from PMrelated visibility impairment, but she
recognizes that these studies, which are
the only studies before her, are a limited
source of information. However, the
EPA does not agree that the Washington,
DC, results represent an outlier, and
thus the EPA believes these results are
appropriately included in the range
identified for the Administrator to
consider.
Some commenters made the point
that the EPA relied on much of this
same evidence to reach the conclusion
in 2006 that the information was too
limited to allow selection of a national
standard. For example, API stated:
[T]he bulk of the VAQ preference studies
were available during the previous PM
NAAQS review and were considered by the
Agency in its establishment of the 2006 p.m.
secondary NAAQS * * *. The Proposed Rule
does not mention this fact and does not
explain why many of these same studies now
compel EPA to propose this new secondary
NAAQS * * *. The Proposed Rule notes in
passing that, since the last review of the PM
NAAQS, ‘limited information that has
become available regarding the
characterization of public preferences in
urban areas has provided some new
perspectives on the usefulness of this
information in informing the selection of
target levels of urban visibility protection.’ 77
Fed. Reg. at 38969/2. It is a serious oversight
that the Proposed Rule makes no attempt to
explain what that information is or how it
affects the interpretation of the VAQ
preference studies. This ‘limited information’
is an apparent reference to information
provided by Dr. Anne Smith. (API, p. 37)
The EPA disagrees with these
commenters. First, the EPA disagrees
that it failed to distinguish between
studies that were available in the
previous review and the current review.
The discussion in section VI.A.1 of the
proposal specifically identifies the
studies from Denver, Phoenix and
British Columbia (77 FR 38967/2) as
being considered in the last review. The
EPA further disagrees with the
implication that it is being circumspect
about identifying the ‘‘limited
information that has become available
regarding the characterization of public
preferences in urban areas.’’ Beginning
in section VI.A.3 of the proposed rule
(77 FR 38969), the EPA was clear about
what information, both preexisting and
new, it relied upon in this review to
inform its views and provide the basis
for its proposal. In section VI.B.2, the
EPA elaborates on the specific
PO 00000
Frm 00127
Fmt 4701
Sfmt 4700
3211
information, tools, methods and data
which are considered in relation to the
public preference studies, including the
new information available since the last
review.
As noted above and in the proposal,
in addition to the substantial PM urban
air quality information and analyses
new to this review, there are three other
sources of information that have
specifically ‘‘provided some new
perspectives on the usefulness of’’ the
preference studies ‘‘in informing the
selection of target levels of urban
visibility protection’’ (77 FR 38969).
They include: (1) Results from
additional urban visibility preference
study experiments conducted for
Washington, DC by Smith and Howell
(2009) which added to the preference
data for that location and shed light on
the role of location in preference
responses; (2) a review and reanalysis
(Stratus Consulting, 2009) of the urban
visibility public preference studies from
the four urban areas, including the
newly available Smith and Howell
(2009) experiments which examined the
similarities and differences between the
studies and evaluated the potential
significance of those differences on the
study results; and (3) additional
analyses, including most importantly a
logit analysis (Deck and Lawson, 2010,
as discussed in Chapter 2 and Appendix
J of the Visibility Assessment), which
was requested and reviewed by CASAC,
which showed that each city’s responses
represented unique and statistically
different curves. Taken together, these
sources contributed to the EPA’s current
knowledge and understanding of each
survey study’s results, the
appropriateness of comparing each
study’s results to the others, and the key
uncertainties relevant to data
interpretation. In addition, in the last
review the decision to not adopt a
distinct secondary standard was
remanded as contrary to law and failing
to provide a reasoned explanation for
the decision. As such it is not
appropriate for purposes of comparison
with the Administrator’s judgment and
reasoning in this review.
(b) Preference Study Methods and
Design
In addition to the limitations and
uncertainties noted above, many
comments also asserted the
methodologies used in the preference
studies are fundamentally flawed. Many
commenters cited some of the same
issues that have already been identified
by the EPA as sources of uncertainty
and potential factors in producing the
statistically different study results (see
section VI.B.1.b above). As noted above,
E:\FR\FM\15JAR2.SGM
15JAR2
3212
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
the EPA is well aware of the issues
raised regarding the adequacy of the
preference studies to serve as a basis for
a secondary NAAQS (see 77 FR 38975)
and solicited comment on how these
uncertainties should be considered (see
77 FR 38990). Most of these same
commenters also pointed to an
assessment of the preference studies
methodology provided by Smith and
Howell (2009) as the basis for their
views, as indicated by the following
comments:
tkelley on DSK3SPTVN1PROD with
Smith and Howell (2009) show that VAQ
preference study outcomes are malleable and
depend entirely on the design of the study.
Accordingly, such studies do not identify any
meaningful threshold of acceptable visibility
conditions. Despite Smith and Howell’s
conclusions, EPA continues to assert that the
VAQ preference studies can be used to
identify minimally acceptable visibility
conditions even though the Agency has never
provided any valid scientific basis for
discounting the Smith and Howell (2009)
results. (API, p. 38)
Well-controlled preference studies
discussed by Anne Smith of Charles River
Associates at the March 2010 CASAC
meeting demonstrated that the judgment of
panel members was affected by the order in
which photographs were presented and
tendency to identify the middle of the range
of visibility degredation as a threshold of
acceptability. This points to a potential flaw
in these studies and that artifacts caused by
these tendencies may have influenced study
results. Dismissing these inherent flaws in
the existing preference studies and then
using these studies to set a secondary
NAAQS is arbitrary and capricious. (API,
Attachment 2, p. 12)
EPA also fails to acknowledge that the only
study conducted since the last review rebuts
the validity of the VAQ preference studies
previously conducted. (UARG, Attachment 2,
p. 28)
As is explained in a more detailed
discussion in the Response to
Comments document, the EPA disagrees
that the study conducted by Smith and
Howell (2009) supports the conclusion
that the preference study methodologies
were fundamentally flawed; however,
the EPA notes that their experiments do
identify areas where additional research
would be useful to further inform our
limited understanding of public
preferences in urban areas. The EPA
views the Smith and Howell
experiments as increasing the EPA’s
knowledge and understanding of the
findings of the 2001 Washington, DC
focus group pilot study (Abt, 2001) in
several important ways, although this
information still remains limited
overall. Specifically, the Smith and
Howell results suggest: (1) The 2001
results, while based on a small sample
size of 9, were consistent with results
from a larger sample of the general
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
Washington, DC population; (2) an
individual’s preferences for visibility in
one location may not depend on
whether they live in that location; and
(3) presentation method (i.e., changing
from slide projection to computer
monitor) did not appear to affect the
reported preferences.
(c) Preference Study Results and
Adversity
A number of comments were received
regarding the EPA’s use of preference
study results to make the determination
that adverse PM2.5-related visibility
effects on the public welfare are
occurring. In this context, several
commenters questioned whether the
EPA had made the case that
unacceptable levels of visual air quality
based on preference study results alone
can be equated with an adverse public
welfare effect. These commenters
suggested that unless preference study
information is linked to personal
comfort and well-being or other
associated welfare effects, it cannot form
the basis of a determination of adversity.
For example, Kennecott Utah Copper
LLC stated that:
Thus, EPA seemingly was building the
foundation for a determination of what
constitutes an adverse effect on visibility in
the context of public welfare. However * * *
EPA subsequently veered toward an
oversimplified focus on public acceptance of
visibility conditions * * *. EPA’s discussion
of visibility in the Policy Assessment and its
proposed rule in the Federal Register focuses
entirely on ‘‘acceptable’’ and ‘‘unacceptable’’
visual air quality and make no mention of an
‘‘adverse effect’’ in the context of visibility.
EPA’s reliance on only 3 urban preference
studies represents a paucity of data and a
wholesale abandonment of any effort to seek
a scientifically measurable adverse effect.
(Kennecott Utah Copper LLC, p. 26)
In response, the EPA first notes that
the definition of effects on welfare
included in section 302(h) of the CAA
identifies both visibility and the broader
category of effects on personal comfort
and well-being as effects on welfare. In
setting a secondary standard to address
visibility impairment, the EPA
considers the effect on the public from
impairment of visibility as a separate
and distinct welfare effect in its own
right. The EPA is not required to
translate this into terms of personal
comfort and well-being, as visibility
impairment is designated explicitly by
Congress as an effect on welfare. While
there may be a large degree of overlap
among these different welfare effects,
the EPA properly focuses on evaluating
all of the information before the Agency
on the effect visibility impairment has
on the public, whether or not this
impairment would also be categorized
PO 00000
Frm 00128
Fmt 4701
Sfmt 4700
as having an adverse effect on personal
comfort and well-being. It is in the
context of all of this information that the
EPA makes the judgment as to the
appropriate degree of protection from
known and anticipated adverse effects
on the public from visibility
impairment. The EPA recognizes that
there is uncertainty about the degree of
adversity to the public welfare
associated with PM-related visibility
impairment. However a secondary
standard is designed to provide
protection from ‘‘known or anticipated’’
adverse effects, and a bright line
determination of adversity is not
required in judging the requisite degree
of protection under section 109(b)(2).
Furthermore, the EPA disagrees that it
has abandoned its consideration of
visibility-related impacts on the welfare
effect of personal comfort and wellbeing, as is made clear in the following
quote:
Research has demonstrated that people are
emotionally affected by low visual air
quality, that perception of pollution is
correlated with stress, annoyance, and
symptoms of depression, and that visual air
quality is deeply intertwined with a ‘‘sense
of place,’’ affecting people’s sense of the
desirability of a neighborhood (U.S. EPA,
2009a, section 9.2.4). Though it is not known
to what extent these emotional effects are
linked to different periods of exposure to
poor visual air quality, providing additional
protection against short-term exposures to
levels of visual air quality considered
unacceptable by subjects in the context of the
preference studies would be expected to
provide some degree of protection against the
risk of loss in the public’s ‘‘sense of wellbeing.’’ (77 FR 38973/1, emphasis added)
The approach taken to address such
qualitative, but policy-relevant,
information in this review is the same
as in other NAAQS reviews. The review
is initiated with a comprehensive
assessment of all possible public health
and welfare effects associated with PM
in the Integrated Science Assessment.
Then policy-relevant effects for which
there is sufficient quantitative
information to allow a determination of
the change in risks associated with
incremental changes in air quality are
assessed (in this review, in the Visibility
Assessment) and used to provide a
quantitative basis to inform the
selection of an appropriate range of
levels for further consideration in the
Policy Assessment. In the Policy
Assessment, the EPA considers all
important policy-relevant evidence and
information, both quantitative and
qualitative, in making recommendations
regarding the range of policy options
appropriate for the Administrator to
consider. It is in the context of all of this
information that the Administrator
E:\FR\FM\15JAR2.SGM
15JAR2
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
makes her final judgment as to the
appropriate degree of protection from
known and anticipated adverse effects
on the public from visibility
impairment.
Another issue raised in the comments
regarding adversity is the EPA’s
decision to use the 50 percent
acceptability criterion from the public
preference studies in determining
candidate protection levels of visibility
impairment for the selection of a
national level of visibility protection.
For example, AMC et al. recommended
‘‘a 75% acceptability criterion as a target
that is in line with protecting the
broader public from the negative effects
of visibility impairment’’ (AMC, et al.,
p. 9).
In the Visibility Assessment, the EPA
noted that the use of the 50 percent
acceptance level for urban visibility was
first presented in Ely et al. (1991) (U.S.
EPA, 2010b, p. 2–5). Ely discussed the
use of the 50 percent acceptability
criterion as a reasonable basis for setting
an urban visibility standard.
tkelley on DSK3SPTVN1PROD with
The standard was determined based on a
50% acceptability criterion, that is, the
standard was set at the level of extinction
that would divide the slides into two groups:
those judged acceptable and those judged
unacceptable by a majority of the people in
the study. The criterion is politically
reasonable because it defines the point where
a majority of the study participants begin to
judge slides as representing unacceptable
visibility. It is also consistent with
psychological scaling theory which indicates
that a ‘‘true score’’ exceeds a standard when
more than 50% of the ‘‘observed scores’’
exceed that standard. (Ely et al., 1991, p. 11)
As Ely described, the 50 percent
acceptability criterion and the
preference study conducted by Ely were
used as the basis for setting the level of
the Denver Visibility Standard in 1990.
That same criterion was judged
appropriate and selected for use in the
Phoenix preference study (BBC
research, 2003) and as the basis for
setting the level of the Phoenix
Visibility Standard in 2003. Most
recently, the 50 percent acceptability
criterion has been recommended by the
British Columbia Visibility Coordinating
Committee as the basis for the visibility
standard currently under consideration
by British Columbia, Canada.
Furthermore, CASAC supported this
approach, while recognizing the
uncertainty associated with this issue.
Specifically, CASAC agreed that ‘‘the
50th percentile for the acceptability
criteria is logical, given the noted
similarities in methodologies employed
in the 4 study areas. * * * In terms of
choosing a specific percentile from the
preference studies, we note that there
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
may not be a ‘‘preferred’’ one, but in
assessing preference studies to propose
a PM secondary NAAQS, the 50th
percentile is sufficient, as it is the basis
for existing visibility indexes used in
the Denver/Colorado Front Range and
Phoenix metropolitan areas’’ (Samet,
2009c, pp. 8–9). Therefore, after
considering the information that served
as the original basis for its selection as
described in Ely et al., 1991, and given
its acceptance and use in existing
visibility programs, the EPA continues
to conclude, consistent with the advice
of CASAC, that it is reasonable to use
the 50 percent acceptability criterion in
determining target levels of protection
from visibility impairment.
(d) Appropriateness of using
regionally varying preference study
results to select a single level for a
national standard.
A number of commenters raised
concerns regarding the bases for and
implications of the differences observed
in the preference study results,
concluding that these results were due
to regionally varying factors and thus
could not be used to set a national
standard. For example, some
commenters asserted that because the
confidence intervals around the four 50
percent acceptability levels do not
overlap at all, and because there are
variations in preference study designs
and inherent differences in the visual
setting among cities and panels, the four
preference curves and their associated
50 percent dv values are city-specific
and statistically different. The
commenters concluded, therefore, that it
was inappropriate to aggregate the 50th
percentile dv values from multiple
studies and that they should instead be
evaluated individually.
Other commenters expressed the
related view that the preference study
results cannot be used to set a national
standard for visibility impairment
because the results show that visibility
preferences vary regionally. For
example, API stated that:
The ‘one-size-fits-all’ approach * * * is
not viable because it does not account for
regional and city-specific factors that have
been made evident in the disparity of
preference study data * * *. It is well
known, for example, that the level of light
extinction to which people in different areas
of the country are accustomed, as well as the
urban setting, are the primary factors that
affect a person’s visual perception of an
urban vista. Thus, the degree to which
extinction threshold can be related to human
welfare is inevitably regionally-dependent.
(API, Attachment 2, p. 4)
Some of these commenters argued that
because acceptable visual air quality is
regionally dependent, it would be more
PO 00000
Frm 00129
Fmt 4701
Sfmt 4700
3213
appropriate to develop distinct visibility
standards at the state or local level.
Others pointed out that areas which lack
‘‘important visibility vistas’’ might not
need standards at all, since flat areas
without significant terrain have a
limited maximum visual range (NEDA/
CAP, p. 3).
Other commenters stated that due to
regionally varying factors, such as
relative humidity, it is not possible to
select a single level for a national
standard to protect visibility across the
United States. In particular, these
commenters pointed to differences
between Eastern and Western areas,
arguing that a single national standard
could not offer the appropriate degree of
protection in locations with distinct
characteristics. For example:
[T]he proposed method falls short because
it is not temporally or geographically
representative enough to have any meaning
* * *. The uncertainty evidenced in these
studies and the non-uniformity between the
western and eastern vistas makes it
impossible at this time to set an acceptable
light extinction value that would
appropriately address visibility concerns in
non-Class I areas. (New York DOH/DEC, pp.
5–6)
The EPA agrees that the preference
curves and the 50 percent dv levels are
separate and distinct data points
representing four different VAQ
preference curves for four unique urban
scenes. However, the EPA does not
consider the fact that the four curves are
distinct as a weakness of the approach
or a reason that the results cannot be
compared. In addition, the EPA does not
agree that the study results necessarily
support a conclusion that preferences
are regionally dependent. In particular,
the EPA notes that the results of Smith
and Howell (2009) which show that
participants in Houston and
Washington, DC did not have
significantly different views on
acceptable air quality in Washington,
DC, provide limited support for the
conclusion that people’s preferences
differ less because of where they live
and more because of the scene they are
viewing.
On the other hand, the existing
literature indicates that people’s
preferences for VAQ depend in large
part on the characteristics and
sensitivity of the scene being viewed.
The EPA understands there is a wide
variety or range of urban scenes within
the United States. These sensitive urban
scenes include those with natural vistas
such as the Colorado Rocky Mountains
as well as those with iconic man-made
urban structures like the Washington
Monument. The EPA believes that the
scenes presented in the four urban areas
E:\FR\FM\15JAR2.SGM
15JAR2
3214
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
include important types of sensitive
valued urban scenes and therefore,
when considered together, can inform
the selection of a level of acceptable
urban VAQ at the national scale, taking
into account the variation across the
country evidenced in the studies. This
is discussed further in the next section,
below.
The EPA does agree with commenters
that there are regionally varying factors
that are important to take into account
when setting a national standard for
visibility protection. Section VI.A above
regarding the history of the secondary
PM NAAQS review discusses the
evolution of the EPA’s understanding
regarding the regional differences in PM
concentrations, relative humidity and
other factors. As a result, the current
review has gone to great lengths to
address these factors, leading to the
EPA’s proposal to use the IMPROVE
algorithm to calculate light extinction in
order to take into account the varying
effects of relative humidity and
speciated PM. While this approach does
not result in a uniform level of ambient
PM2.5, it does ensure a nationally
uniform level of visibility protection.
The EPA refers the reader to other
sections of the final rule, including
sections VI.B.1.a, VI.B.1.c, VI.C.1.b and
VI.C.1.f, and the Response to Comments
document for a more detailed response
as to how it is taking these variables into
account.
ii. Specific Comments on Level
The EPA received relatively few
comments endorsing a specific level for
a distinct secondary standard for
visibility. In general, commenters who
opposed setting a distinct secondary
standard at this time did not address the
question of what level would be
appropriate if the EPA were to set a
distinct secondary standard for
visibility; similarly, commenters who
supported adopting a distinct secondary
standard at this time generally did not
recommend a specific level. However, a
few commenters did provide comments
in support of a specific level or range of
levels, with some commenters
advocating standards at the upper end
of the range of proposed levels (i.e., 30
dv), while others supported levels
below the lower end of the proposed
range (i.e., below 28 dv).
As discussed above, a large number of
commenters argued that the currently
available data are insufficient to
determine what constitutes a standard
that would be neither more nor less
protective than necessary and that no
standard should be set at this time.
These commenters pointed to the
limitations and uncertainties in the
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
preference studies discussed above as
the basis for this claim. These
commenters pointed to significant
variation in the results of the preference
studies in support of their arguments
that the studies should not be used to
derive a level for a distinct secondary
standard for visibility. For example, one
consultant cited by several industry
commenters argued that the proposed
level of 28 or 30 dv did not reflect the
substantial difference in visibility
preferences between the East and the
West reflected in the preference studies
(UARG, Attachment 2, p. 11), and that
it did not reflect the full range of
preferences (i.e., potential 50 percent
acceptability levels) likely to exist
nationwide (UARG, Attachment 2, p.
19). This commenter further objected to
the EPA’s proposal for a level of 28 or
30 dv on the grounds that the EPA had
inaccurately adjusted 4-hour values into
24-hour values. Based on his analysis,
the consultant concluded that ‘‘a range
of adjusted values from 28 to 32 dv is
needed’’ to account for the majority of
the spread between the 4-hour vs. 24hour equivalent values at the upper end
of the distribution of values.
A number of commenters questioned
whether the proposed range of levels
was appropriate. One industry
commenter claimed that the EPA had
not explicitly justified why a standard
within the proposed range was
requisite, stating that ‘‘EPA makes no
attempt to explain how the proposed
level of the standard is neither lower
nor higher than necessary to protect
public welfare’’ (NSSGA, p. 15). Arizona
DEQ noted that since the proposed
calculated light extinction indicator
excluded coarse particles and Rayleigh
scattering, the proposed levels of 28 or
30 dv were inconsistent with the
visibility preference studies, which
considered total light extinction. Noting
these perceived problems with the
proposed range of levels, a few
commenters noted that if the EPA were
to set a distinct secondary standard, the
level should be set no lower than 30 dv,
‘‘to account for inconsistent value
judgments, a great deal of spatial and
temporal variability, and a very high
level of uncertainty’’ (Texas CEQ, p. 7).
In contrast, some commenters
supporting the EPA’s proposal for a
distinct secondary standard for visibility
stated that the proposed range of levels
from 28–30 dv was insufficiently
protective based on a 24-hour averaging
time, and recommended a lower level
for the visibility index standard. These
commenters expressed the view that the
proposed levels of 28 or 30 dv
represented neither adequate surrogates
for equivalent 4-hour values, as the EPA
PO 00000
Frm 00130
Fmt 4701
Sfmt 4700
claimed, nor sufficiently protective
levels based on recent air quality data.
Several commenters stated that the
EPA’s own analyses suggested that a
standard set at a level of 28 or 30 dv was
insufficiently protective based on a 24hour averaging time. One commenter
emphasized that the Policy Assessment
had indicated a level between 25–28 dv
was appropriate for a standard
calculated on a 24-hour average, and
encouraged the EPA to adopt a standard
level of 25 dv. Several environmental
groups provided comments stating that
a 24-hour average would underestimate
a 4-hour value by 13–42 percent and
certain areas of the country—
particularly the Northeast—would be
affected disproportionately. These
commenters suggested that a 24-hour
PM2.5 visibility index standard should
be set at a level of 18.6–20 dv. The
Department of the Interior pointed to
recent air quality data indicating that
visibility on the 20% worst days in
several large metropolitan areas,
including Birmingham, Fresno, New
York City, Phoenix, and Washington,
DC was below 29 dv. While noting that
these calculations were based on
IMPROVE calculations which include
contributions from coarse PM mass, DOI
expressed the view that the proposed
level of 28 to 30 dv would not provide
adequate visibility protection compared
to the current 24-hour PM2.5 standard of
35 mg/m3 and recommended that the
standard be set at a level of 25 dv
consistent with the results of the
Phoenix visibility preference study.
In contrast, the states of Arizona and
Colorado submitted comments arguing
that the visibility preference studies
conducted in Phoenix and Denver,
respectively, were designed to address a
specific local problem and that the
results of these studies were not an
appropriate basis for selecting the level
of a national standard. For example,
Arizona DEQ noted:
The cited studies were conducted
considering total light extinction; including
extinction resulting from particulate matter
and Rayleigh scattering. Visibility
impairment due to coarse particulate matter
can be an important contributor in Arizona,
specifically in the Phoenix area where
ongoing measurements have been made.
Therefore, ADEQ believes that the proposed
levels of the secondary visibility standard are
inconsistent with applicable urban studies.
(Arizona DEQ, p. 2)
Similarly, the Colorado Department of
Public Health and the Environment
noted that the Denver visibility standard
was designed to address ‘‘brown
clouds’’, i.e., strong inversions that
occur in the Denver metropolitan area,
and that this standard ‘‘is based on a
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
specific view of Denver’’ associated
with particular sight paths and direct
measurement methods. The commenter
stated that this standard ‘‘is applicable
only to this location,’’ and that these
limitations make it potentially
unsuitable for application as ‘‘a national
secondary standard, particularly a
proposed standard that does not use a
direct measurement method’’ (Colorado
DPHE, p. 2).
While acknowledging the
uncertainties and limitations associated
with the visibility preference studies as
discussed above, the EPA continues to
conclude, as did CASAC, that the
preference studies are appropriate to use
as the basis for selecting a target level
of protection from visibility impairment.
However, the EPA agrees with
commenters who emphasize the high
degree of variability in visibility
conditions and the potential variability
in visibility preferences across different
parts of the country. In light of the
associated uncertainty, as noted in the
proposal, the Administrator judged it
appropriate to establish a target level of
protection equivalent to the upper end
of the range of Candidate Protection
Levels (CPLs) identified in the Policy
Assessment and generally supported by
CASAC. Thus, the EPA proposed to set
a 24-hour visibility index standard that
would provide protection equivalent to
the protection afforded by a 4-hour
standard set at a level of 30 dv. In light
of the comments received on the
proposal, in particular comments
emphasizing the uncertainty and
variability in the results of the public
preference studies, the EPA continues to
conclude that this approach is
warranted, and that it is appropriate to
set a target level of protection equivalent
to the protection that would be afforded
by a 4-hour, 30 dv visibility index
standard.
Moreover, the EPA disagrees with
commenters who argued that the EPA’s
approach for translating 4-hour CPLs
into equivalent 24-hour values was
inappropriate. In adjusting 4-hour
values for purposes of defining an
appropriate level for a 24-hour standard,
the EPA noted at the time of proposal
that there were multiple approaches for
estimating generally equivalent levels
on a city-specific or national basis.
While expressing the view that it was
appropriate to consider the two
approaches with the highest r2 values
(Approaches A and B in Appendix G of
the Policy Assessment),191 which used
191 In particular, EPA staff expressed a preference
for Approach B in the Policy Assessment. However,
in light of the additional information provided by
the other approaches explored in Appendix G of the
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
regressions of 90th percentile light
extinction values, the EPA determined it
would also be appropriate to consider
the city-specific estimates resulting from
Approaches C and E which showed
greater variability than the aggregated
estimates. Approaches C and E
generated a range of city-specific
estimates of generally equivalent 24hour levels that encompassed the range
of levels considered appropriate for 4hour CPLs, including the CPL of 30 dv
at the upper end of that range. This
information provided support for using
the same CPL for a 24-hour standard as
for a 4-hour standard, since no single
approach could generate an equivalent
24-hour standard level in each urban
area for each CPL. The EPA continues
to conclude, as it did at the time of
proposal, that using an unadjusted 4hour CPL for purposes of establishing a
target level of protection for a 24-hour
standard is appropriate because this
approach places more emphasis on the
relatively high degree of spatial and
temporal variability in relative humidity
and fine particle composition observed
in urban areas across the country,
consistent with EPA’s reanalysis
discussed below.
The EPA has conducted a reanalysis
(Frank et al., 2012b) of the relationships
between estimated 24-hour and 4-hour
visibility impairment based on the
variety of metrics discussed in
Appendix G of the Policy Assessment.
The reanalysis has more appropriately
considered the uncertainty of the
calculated 4-hour values. The revised
analysis shows that the 24-hour
equivalent level is generally closer to
the 4-hour value at the upper end of the
range of CPLs than originally estimated,
as can be seen in the results for
Approaches B, C, and D.192 For
example, the reanalysis indicates that
Approach B yields an adjusted 24-hour
CPL of 29 dv193 as generally being
equivalent to a 4-hour CPL of 30 dv,
while Approach C yields a 24-hour
equivalent CPL of 29 dv averaged across
cities and a range of city-specific values
Policy Assessment and the reanalysis in Frank, et
al. (2012b), the EPA judges it more appropriate to
consider the range of values resulting from all five
analytical approaches for purposes of informing
decisions about the equivalent level of a 24-hour
standard.
192 Approach E as presented in the Policy
Assessment is based on the median values for each
city; these results are not affected by the regression
analyses. Therefore, Approach E was not included
in the reanalysis, and the results remain unchanged
from those reported in the corrected Table G–6 as
reported in Frank, et al., 2012b.
193 In Appendix G of the Policy Assessment, a 24hour adjusted CPL of 28 dv was estimated to be
equivalent to a 4-hour value of 30 dv under
Approach B (annual 90th percentile values
regression).
PO 00000
Frm 00131
Fmt 4701
Sfmt 4700
3215
from 25–36 dv.194 195 Not only are the
90th percentile and pooled average
values closer to the 4-hour CPL of 30 dv,
the range of city-specific results shows
a wider spread that clearly encompasses
the unadjusted 4-hour value of 30 dv
near the midpoint of the city-specific
range. This provides support for
concluding that the EPA’s approach to
translating of 4-hour CPLs into
equivalent 24-hour values was
appropriate, and that it is appropriate to
use unadjusted 4-hour values for
purposes of selecting a level for a
standard based on a 24-hour averaging
time.196
Moreover, the EPA disagrees with
commenters who argue that the
currently available evidence is sufficient
to justify establishing a target level of
protection at 25 dv or below. The EPA
recognizes that 25 dv represents the
middle of the range of 50 percent
acceptability levels from the 4 cities
studied, and represents the 50 percent
acceptability level from the Phoenix
study, which the Agency has
acknowledged as the best of the four
studies in terms of having the least
noise in the preference study results and
the most representative selection of
participants. The EPA also notes the
caveats discussed in the proposal
regarding whether it would be
appropriate to interpret results from the
western studies as generally
representative of a broader range of
scenic vistas in urban areas across the
country. The Policy Assessment noted
significant differences in the
194 In Appendix G of the Policy Assessment,
under Approach C (all-days city-specific
regression), a 24-hour adjusted CPL of 27 dv was
estimated to be equivalent to a 4-hour CPL of 30 dv
when averaged across cities, while city-specific
values were estimated to range from 24–30 dv.
195 In the reanalysis, Approach D (all days pooled
regression) generated results of 28 dv for the 24hour CPL equivalent to a 4-hour value of 30 dv as
compared to a value of 27 dv in the original
analysis described in Appendix G.
196 The analysis in Appendix G of the Policy
Assessment used the 4-hour light extinction value
treated as the independent (x-axis) variable in an
ordinary least squares regression. The EPA now
concludes that this regression approach was not the
most appropriate approach because that variable
has error and in fact may be more uncertain than
the calculated 24-hour extinction values. The Frank
et al. (2012b) reanalysis uses an orthogonal
regression instead of ordinary least squares
regression and results in slopes closer to the 1:1 line
for all the results, particularly for Dallas, TX.
Furthermore, consistent with the EPA’s conclusion
that a higher multiplier for converting OC to OM
would be appropriate (see section VI.C.1.b.ii above),
the reanalysis substitutes a 1.6 multiplier for
converting OC to OM in the calculation of 24-hour
values instead of the value of 1.4 that was used in
calculating 24-hour values for Appendix G. The
higher multiplier is more consistent with the
SANDWICH approach used to calculate the 4-hour
values found in Appendix G. See Frank et al.
(2012b) for a more detailed explanation.
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
3216
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
characteristics of the urban scenes used
in each study, with western urban
visibility preference study scenes
including mountains in the background
and objects at greater distances, while
scenes in the eastern study did not.
Since objects at a greater distance have
a greater sensitivity to perceived
visibility changes as light extinction
changes compared to otherwise similar
scenes with objects at a shorter range,
this likely explains part of the difference
between the results of the eastern study
and results of the western studies. In the
proposal, the EPA noted that the scenic
vistas available on a daily basis in many
urban areas across the country generally
do not have the inherent visual interest
or the distance between viewer and
object of greatest intrinsic value as in
the Denver and Phoenix preference
studies. Also, the Agency takes note of
the caution expressed by Colorado and
Arizona about using the results of the
Denver and Phoenix preference studies,
which were aimed at addressing specific
local visibility problems, to inform the
choice of level for a national standard.
Therefore, the Agency considers it
reasonable to conclude, especially in
light of the significant uncertainties,
that it is appropriate to place less weight
on the western preference results and
that the high CPL value (30 dv) that is
based on the eastern preference results
is likely to be more representative of
urban areas that do not have associated
mountains or other valued objects
visible in the distant background. These
areas would include the middle of the
country and many areas in the eastern
U.S., as well as some western areas. As
a result, the EPA concludes that it is
more appropriate to establish a target
level of protection at the upper end of
the range of 24-hour CPLs considered,
recognizing that no one level will be
‘‘correct’’ for every urban area in the
country.
In considering the upper end of this
range, the EPA must identify a target
level of protection that is considered
requisite to protect public welfare from
a national perspective, recognizing that
the same target level would apply in all
locations. Making this judgment
requires a balancing of the risks to the
public welfare and the substantial
uncertainties surrounding appropriate
levels of visibility protection. As
acknowledged in the proposal, the EPA
recognizes that setting a target level of
protection for a 24-hour standard at 30
dv would reflect a judgment that the
current substantial degrees of variability
and uncertainty inherent in the public
preference studies should be reflected in
a higher target protection level than
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
would be appropriate if the underlying
information were more consistent and
certain. Also, a 24-hour visibility index
at a level of 30 dv would reflect
recognition that there is considerable
spatial and temporal variability in the
key factors that determine the value of
the PM2.5 visibility index in any given
urban area, such that there is a relatively
high degree of uncertainty as to the most
appropriate approach to use in selecting
a 24-hour standard level that would be
generally equivalent to a specific 4-hour
standard level. In light of these
uncertainties, the EPA continues to
believe that it is appropriate to establish
a target level of protection for visual air
quality of 30 dv, averaged over 24hours, with a form as discussed above.
In reaching this conclusion, the EPA
notes that any national ambient air
quality standard for visibility would be
designed to work in conjunction with
the Regional Haze Program as a means
of achieving appropriate levels of
protection against PM-related visibility
impairment in all areas of the country,
including urban, non-urban, and
Federal Class I areas. While the Regional
Haze Program is focused on improving
visibility in Federal Class I areas and a
secondary visibility index NAAQS
would focus on protecting visual air
quality principally in urban areas, both
programs could be expected to provide
benefits in surrounding areas. In
addition, the development of local
programs, such as those in Denver and
Phoenix, can continue to be an effective
and appropriate approach to provide
additional protection, beyond that
afforded by a national standard, for
unique scenic resources in and around
certain urban areas that are particularly
highly valued by people living in those
areas. With regard to comments from the
Department of Interior noting that many
large metropolitan areas have 24-hour
IMPROVE values below 30 dv on the
worst 20 percent of days already, the
EPA notes that the purpose of
establishing NAAQS is to ensure
adequate protection of public welfare
everywhere, not to mandate continuous
improvements in areas that may already
be relatively clean. In fact, the evidence
from the IMPROVE program that many
urban areas have total 24-hour PMrelated light extinction below 29 dv on
the 20 percent worst visibility days
suggests that many areas have relatively
good visual air quality already.
f. Need for a Distinct Secondary
Standard To Protect Visibility
Numerous commenters questioned
whether a distinct secondary standard
for visibility is necessary in light of the
analysis described in section VI.B.1.c.vii
PO 00000
Frm 00132
Fmt 4701
Sfmt 4700
above (Kelly et al., 2012a) which
indicated that a 24-hour mass-based
PM2.5 standard of 35 mg/m3 would
protect against visibility impacts
exceeding the range of levels considered
in the proposal (28–30 dv). While this
analysis was conducted in support of
proposed implementation requirements
for a distinct secondary standard
(specifically, the modeling
demonstrations that would be required
under the PSD program), the second
prong of the analysis showed that
within the range of levels proposed by
the EPA for the visibility index NAAQS
(28–30 dv), the 24-hour PM2.5 standard
of 35 mg/m3 would generally be
controlling. Kelly et al. (2012a)
concluded that ‘‘overall, design values
based on 2008–2010 data suggest that
counties that attain 24-hour PM2.5
NAAQS level of 35 mg/m3 would attain
the proposed secondary PM2.5 visibility
index NAAQS level of 30 dv and
generally attain the level of 28 dv’’ (pp.
17–18).
Citing this conclusion, many state and
local agencies and industry commenters
argued that a visibility index standard
in the range proposed (28–30 dv) would
provide no additional protection beyond
that afforded by the existing secondary
24-hour PM2.5 NAAQS, and therefore no
distinct visibility standard was
necessary. These commenters advocated
retaining the current 24-hour PM2.5
mass-based standard to protect against
visibility effects. ‘‘Since the 24-hour
PM2.5 standard already protects the
welfare the 24-hour PM2.5 visibility
standard is designed to protect, the new
standard is duplicative and
unnecessary’’ (South Dakota DENR, p.
2). Furthermore, a number of state
commenters objected to the additional
resource burden associated with
implementing a standard which had, in
their view, no practical effect: ‘‘If the 24hour PM2.5 mass standard has the same
effect as the visibility standard, crafting
complex regulations to implement
another standard seems redundant’’
(South Carolina DHEC, p. 3). Other
states agreed: ‘‘A PM2.5-related Visibility
Index appears redundant since the
benefits achieved from the current
primary and secondary annual and 24hour PM2.5 standards already provide
reductions that would improve
visibility. Establishing a new PM2.5
secondary standard for visibility would
be an additional complication and
burden to the states that is not
warranted’’ (Indiana DEM, p. 5).
In addition, several commenters
submitted additional analyses
supporting their position that a 35 mg/
m3 24-hour PM2.5 standard would
provide at least equivalent protection to
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
a distinct 24-hour visibility standard
within the range of levels proposed
(API, Attachment 2, p. 8 and
Attachment 3, p. 1).
In responding to these comments
stating that a distinct visibility standard
is not needed, the EPA notes as an
initial matter that the Administrator
provisionally concluded at the time of
proposal that the current PM standards
were not sufficiently protective of visual
air quality, and that consideration
should be given to an alternative
secondary standard that would provide
additional protection against PM-related
visibility impairment, especially in
urban areas. This provisional
conclusion was based on the results of
public preference surveys on the
acceptability of varying degrees of
visibility impairment in urban areas,
analyses of the number of days on
which peak 1-hour or 4-hour light
extinction values were estimated to
exceed a range of CPLs under conditions
simulated to just meet the current
standards, and the advice of CASAC.
The Administrator also noted that the
current indicator of PM2.5 mass, in
conjunction with the current 24-hour
and annual averaging times, was not
well suited for purposes of protecting
visibility, since it does not incorporate
species composition or relative
humidity, both of which play a central
role in determining the impact of
ambient PM on visibility. Taking into
account the advice of CASAC and the
court’s remand of the current secondary
PM2.5 standards, the Administrator
provisionally concluded that the current
secondary standards were neither
sufficiently protective nor suitably
structured to provide an appropriate
degree of public welfare protection from
PM-related visibility impairment. As a
result, the EPA proposed a new, distinct
secondary standard that was designed to
address these deficiencies.
The EPA notes that in critiquing the
proposed secondary standard,
commenters generally did not advocate
that the form of the existing mass-based
PM2.5 standards was better suited
scientifically to the task of protecting
against visibility impairment. Rather,
the commenters’ position that a distinct
secondary standard was not needed for
purposes of protecting visibility was
based almost entirely on the relative
degree of protection likely to be afforded
by the existing standards (in particular,
the existing 24-hour PM2.5 standard) as
compared to the proposed visibility
index, along with the relatively large
uncertainties associated with the latter.
Thus, for all the reasons discussed in
the proposal with regard to the scientific
appropriateness of an indicator that
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
takes into account both species
composition and relative humidity, the
EPA continues to conclude that the
proposed standard based on a visibility
index would be appropriate
scientifically to provide targeted
protection of visibility, since it would
provide a measure of PM-related light
extinction that directly takes into
account the factors (i.e., species
composition and relative humidity) that
influence the relationship between
PM2.5 in the ambient air and PM-related
visibility impairment.
Furthermore, the EPA disagrees with
commenters who stated that
implementation concerns, in particular
the additional resource burden
associated with implementing a distinct
secondary standard, should alter the
Agency’s decision making with regard
to a standard to protect visibility. The
EPA may not take the costs of
implementation into account in setting
or revising the NAAQS.
However, in light of the results of the
Kelly et al. (2012a) analysis and the
views expressed by commenters on the
implications of this analysis for
conclusions regarding the adequacy of
the current secondary 24-hour PM2.5
standard, the EPA has reconsidered
some of the conclusions drawn at the
time of proposal, in particular with
regard to the degree of protection that
would be provided by the current
secondary standard. Based on a review
of comments related to indicator,
averaging time, form and level, the
Agency has concluded that (as
described in sections VI.C.1b-e above) a
standard defined in terms of a PM2.5
visibility index (based on speciated
PM2.5 mass concentrations and relative
humidity data to calculate PM2.5 light
extinction), a 24-hour averaging time,
and a 90th percentile form, averaged
over 3 years, and a level of 30 dv, would
provide sufficient but not more than
necessary protection of the public
welfare with regard to visual air quality.
Having identified this target level of
protection, the EPA is now in a position
to compare it specifically to the existing
secondary 24-hour PM2.5 standard of 35
mg/m3 for purposes of determining
whether it would provide more, the
same, or less protection from visibility
impairment. The EPA must consider
both whether the existing secondary 24hour PM2.5 standard of 35 mg/m3 is
sufficient (i.e. not under-protective) and
whether it is more stringent than
necessary (i.e. over-protective).
With regard to the degree to which the
existing secondary 24-hour PM2.5
standard provides sufficient but not
more than necessary protection for
visibility, the EPA first notes that the
PO 00000
Frm 00133
Fmt 4701
Sfmt 4700
3217
kind of area-specific analysis conducted
in Kelly et al. (2012a) is essential for
addressing the court remand of the 2006
secondary standards. In the case of the
2006 secondary standards, the EPA had
argued that the 35 mg/m3 24-hour PM2.5
standard was requisite because one part
of the proposed range for a distinct
secondary standard the Agency had
considered would affect the attainment
status of a somewhat fewer counties
than the 35 mg/m3 24-hour PM2.5
standard. The court rejected this kind of
rough balancing, finding that the EPA’s
equivalency analysis based on
percentages of counties demonstrated
nothing about the relative protection
offered by the different standards. Based
on this, an area-by-area evaluation of the
relative degree of protection offered by
different standards should be conducted
to the extent air quality data is available.
Kelly et al. (2012a) performed such an
evaluation. Based on 2008–2010 data,
there are no areas that would have
exceeded a 30 dv, 24-hour visibility
index standard that would not also have
exceeded a 24-hour PM2.5 standard of 35
mg/m3. Stated another way, all areas that
met the 24-hour PM2.5 standard of 35
mg/m3 would have had visual air quality
at least as good as 30 dv (24-hour
average, based on 90th percentile form
averaged over 3 years). The Kelly
(2012a) analysis also showed that for
some areas, particularly in the West,
areas that would have met a 24-hour
PM2.5 standard of 35 mg/m3 would have
had visual air quality better than 30 dv
for the PM2.5 visibility index standard,
and that at sites that violated both the
24-hour level and the visibility index 30
dv level, the visibility index level of 30
dv would likely be attained if PM2.5
concentrations were reduced such that
the 24-hour PM2.5 level of 35 mg/m3 was
attained.
The EPA has conducted a reanalysis
(Kelly et al., 2012b) to update the areaby-area analysis in the original Kelly et
al. (2012a) analysis in three respects.
First, noting that the original Kelly at al.
(2012a) analysis used a 1.4 multiplier to
convert OC to OM at those monitors not
using the new CSN monitoring protocol,
the EPA recalculated the visibility index
design values for 2008–2010 using a
higher multiplier for converting OC to
OM at monitors not already using the
new CSN monitoring protocol
SANDWICH approach, consistent with
the Agency’s view that it is more
appropriate to use a multiplier of 1.6 at
such monitors as compared to 1.4, as
described in section VI.C.1.a.ii,
E:\FR\FM\15JAR2.SGM
15JAR2
3218
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
tkelley on DSK3SPTVN1PROD with
above.197 The recomputed visibility
design index values for 2008–2010 show
the same overall relationship to 24-hour
PM2.5 design values as presented in
Kelly et al., 2012a.
Second, the EPA repeated the
calculations comparing visibility index
design values with 24-hour PM2.5 design
values using 2009–2011 data, the most
recent three years of air quality
information currently available.198
Third, the EPA modified the area-byarea evaluation to ensure consistency
with the data completeness criteria of 40
CFR part 50, Appendix N, including the
removal of data approved by EPA as
exceptional events, for the current 24hour PM2.5 standard and the proposed
visibility index standard.
The results of this reanalysis, as
presented in Kelly et al. (2012b), show
a similar pattern to that described in the
original Kelly memo. Specifically, the
analysis indicates that there were no
areas with visibility impairment above
30 dv that did not also exceed the 24hour PM2.5 standard of 35 mg/m3. The
updated memo concludes that the
results for 2009–2011 corroborate the
findings for 2008–2010.
Based on these analyses (Kelly et al.,
2012a; 2012b), the EPA concludes with
a high degree of confidence that having
air quality that meets the 24-hour PM2.5
standard of 35 mg/m3 would be
sufficient to ensure areas would not
exceed 30 dv. The EPA notes that this
conclusion from Kelly et al. (2012a) is
supported by two analyses submitted by
industry commenters (API, Attachments
2 and 3).
At the time of proposal, the EPA had
reached a different conclusion,
specifically that the 35 mg/m3 24-hour
PM2.5 standard was not sufficiently
protective. This conclusion was based,
in part, on the analyses conducted for
the Visibility Assessment and Policy
Assessment regarding 1- to 4-hour peak
light extinction values based on 2007–
2009 data. For the reasons outlined
above in sections VI.B.1.c and VI.C.1.c,
the EPA originally focused on hourly or
sub-daily timeframes for evaluating
visibility conditions. However, data
quality concerns effectively precluded
adoption of a 1-hour or sub-daily
averaging time in this review, and
ultimately the EPA has concluded that
a 24-hour averaging time can serve as an
appropriate surrogate. In reaching this
conclusion, the EPA has recognized that
adopting a 24-hour averaging time will
197 Some of the OC measurements were produced
with CSN’s newer monitoring protocol and did not
require a change in the computed OM.
198 The 2011 air quality data were not yet
available at the time of proposal.
VerDate Mar<15>2010
20:39 Jan 14, 2013
Jkt 229001
likely smooth out some of the hour-byhour variability in visibility index
values, and will effectively reduce peak
values by averaging them together with
other hours. In concluding it is
appropriate to adopt a 24-hour
averaging time, which limits the impact
of hour-specific influences, the Agency
is now placing less weight on the results
of the 1-hour and 4-hour analyses
presented in the Visibility Assessment
and the Policy Assessment which
focused on identifying the percent of
days with peak hourly light extinction
above various CPLs. In light of the
Agency’s conclusion that a 24-hour
averaging time would be appropriate,
the Agency has determined to place
more weight on analyses of visibility
conditions over a 24-hour time period,
especially the results in Kelly et al.
(2012a and 2012b). In addition, the EPA
notes that the Kelly et al. analyses
reflects updated air quality information
from more recent years of data (2008–
2010 for Kelly et al., 2012a; 2009–2011
for Kelly et al. 2012b) as compared to
the air quality information used in the
Visibility Assessment and Policy
Assessment.
In light of all of these considerations,
including the results of the Kelly et al.
(2012a; 2012b) analyses, and the
supporting comments provided by a
broad range of public commenters, the
EPA now concludes that the 24-hour
PM2.5 standard of 35 mg/m3 provides
sufficient protection in all areas against
the effects of visibility impairment. The
EPA concludes that the existing 24-hour
PM2.5 standard would provide at least
the target level of protection for visual
air quality defined by a visibility index
set at 30 dv, as described above, which
the EPA judges appropriate.
However, the EPA also recognizes that
it is important to evaluate whether such
a standard would be over-protective (i.e.
more stringent than necessary to protect
public welfare). The analyses presented
in Kelly et al. (2012a; 2012b) indicates
that the 24-hour PM2.5 standard of 35
mg/m3 would achieve more than the
target level of protection of visual air
quality (30 dv) in some areas. That is,
when meeting a mass-based standard of
35 mg/m3, some areas would have levels
of PM-related visibility impairment far
below 30 dv. Thus, when considered by
itself and without consideration of the
secondary standards adopted for
purposes of non-visibility welfare
effects, the 24-hour PM2.5 standard of 35
mg/m3 would be over-protective of
visibility in some areas. However, it is
important to note that as long as the
current secondary 24-hour PM2.5
standard of 35 mg/m3 remains in effect,
this overprotection for visibility would
PO 00000
Frm 00134
Fmt 4701
Sfmt 4700
occur, regardless of whether a distinct
secondary standard based on a visibility
index set at 30 dv were adopted. These
issues are discussed more fully in
section VI.D, which outlines the
Administrator’s final conclusions on the
secondary PM standards, below.
g. Legal Issues
Some commenters opposed the
proposal to establish a distinct
secondary standard that would be
defined in terms of a PM2.5 visibility
index. The proposed standard would
use measured PM2.5 mass concentration,
in combination with speciated PM2.5
mass concentration and relative
humidity data, to calculate PM2.5 light
extinction, translated to the deciview
(dv) scale. The standard would also be
defined in terms of a specified averaging
time and form, and a level for the PM2.5
visibility index set at one of two
options—either 30 dv or 28 dv. The
commenters argued that the entire
approach proposed by the EPA is
inconsistent with the requirements of
CAA section 109(b). They pointed to a
number of different aspects of the
proposal which in their view made it
incompatible with the CAA. For
example, the Utility Air Resources
Group (UARG) stated:
In the past, EPA has always used a measure
of PM mass as the indicator for both primary
and secondary PM NAAQS. Such a standard
is, as a general matter, consistent with the
directive in the CAA that the NAAQS
‘‘specify a level of air quality’’ and targets for
control the listed criteria air pollutant. CAA
§ 109(b)(2). The standard contained in EPA’s
proposed rule does neither of these things.
Instead, it would (1) regulate relative
humidity, which is not a criteria pollutant;
(2) fail to ‘‘specify a level of air quality’’ as
required by section 109(b)(2) of the CAA; and
(3) result in a standard necessitating
nationally variable PM concentrations
instead of a standard establishing a
nationally uniform, minimally acceptable PM
concentration. (UARG, p. 22–23)
Other commenters raised similar or
related issues, arguing that the EPA
improperly set a visibility standard, and
not a PM2.5 standard, and that NAAQS
can only be set in terms of a level or
concentration of the air pollutant.
Commenters also argued that an
endangerment finding and air quality
criteria would be needed before the EPA
could set a standard based on PM
components. Each of these comments is
discussed below.
As an initial matter, the commenters
argued that the proposed standard is
unlawful because it is ‘‘not a PM2.5
standard at all, but rather a visibility
standard, and visibility is neither an air
pollutant nor a criteria pollutant for
which a NAAQS may be promulgated’’
E:\FR\FM\15JAR2.SGM
15JAR2
tkelley on DSK3SPTVN1PROD with
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations
(NMA/NCBA, p. 21). According to these
commenters, the CAA requires that
NAAQS be established as limits on the
concentration of an air pollutant in
ambient air, not limits on the
‘‘identifiable effects’’ caused by that air
pollutant. These commenters claimed
that reduced visibility due to light
extinction is not an air pollutant but
instead is an effect, noting that ‘‘the
Act’s definition of ‘air pollutant’ speaks
in terms of specific substances or matter
in the ambient air’’ (NSSGA, p. 8). The
commenters pointed to the use of the
term ‘‘air pollutant’’ in sections
109(a)(1)(A) and (b)(2) as support for
their argument, as these provisions refer
to setting standards for the ‘‘air
pollutant’’ to address the effects
associated with the presence of the air
pollutant in the ambient air. They
likewise pointed to section 108(a)(2)’s
reference to the presence of the air
pollutant in the ambient air. Since
reduced visibility is not an air pollutant,
they argue the EPA cannot set a NAAQS
that is a standard for visibility. They
argue that the proposed secondary
standard it is not a PM2.5 standard as it
does not limit the concentration of PM2.5
or any other fraction of particulate
matter in the ambient air and therefore
is not an ‘‘ambient air quality standard’’
for any pollutant.
One commenter argued that the EPA
is required to ‘‘specif