National Ambient Air Quality Standards for Particulate Matter, 2620-2708 [06-177]
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Federal Register / Vol. 71, No. 10 / Tuesday, January 17, 2006 / Proposed Rules
ENVIRONMENTAL PROTECTION
AGENCY
40 CFR Part 50
[OAR–2001–0017; FRL–8015–8]
RIN 2060–AI44
National Ambient Air Quality
Standards for Particulate Matter
Environmental Protection
Agency (EPA).
ACTION: Proposed rule.
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AGENCY:
SUMMARY: Based on its review of the air
quality criteria and national ambient air
quality standards (NAAQS) for
particulate matter (PM), EPA proposes
to make revisions to the primary and
secondary NAAQS for PM to provide
requisite protection of public health and
welfare, respectively, and to make
corresponding revisions in monitoring
reference methods and data handling
conventions for PM.
With regard to primary standards for
fine particles (particles generally less
than or equal to 2.5 micrometers (µm) in
diameter, PM2.5), EPA proposes to revise
the level of the 24-hour PM2.5 standard
to 35 micrograms per cubic meter (µg/
m3), providing increased protection
against health effects associated with
short-term exposure (including
premature mortality and increased
hospital admissions and emergency
room visits) and to retain the level of the
annual PM2.5 standard at 15 µg/m3,
continuing protection against health
effects associated with long-term
exposure (including premature
mortality and development of chronic
respiratory disease). The EPA solicits
comment on alternative levels of the 24hour PM2.5 standard (down to 25 µg/m3
and up to 65 µg/m3) and the annual
PM2.5 standard (down to 12 µg/m3), and
on alternative approaches for selecting
the standard levels.
With regard to primary standards for
particles generally less than or equal to
10 µm in diameter (PM10), EPA proposes
to revise the 24-hour PM10 standard in
part by establishing a new indicator for
thoracic coarse particles (particles
generally between 2.5 and 10 µm in
diameter, PM10-2.5), qualified so as to
include any ambient mix of PM10-2.5 that
is dominated by resuspended dust from
high-density traffic on paved roads and
PM generated by industrial sources and
construction sources, and excludes any
ambient mix of PM10-2.5 that is
dominated by rural windblown dust and
soils and PM generated by agricultural
and mining sources. The EPA proposes
to set the new PM10-2.5 standard at a
level of 70 µg/m3, continuing to provide
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a generally equivalent level of
protection against health effects
associated with short-term exposure
(including hospital admissions for
cardiopulmonary diseases, increased
respiratory symptoms and possibly
premature mortality). Also, EPA
proposes to revoke, upon finalization of
a primary 24-hour standard for PM10-2.5,
the current 24-hour PM10 standard in all
areas of the country except in areas
where there is at least one monitor
located in an urbanized area (as defined
by the U.S. Bureau of the Census) with
a minimum population of 100,000 that
violates the current 24-hour PM10
standard based on the most recent three
years of data. In addition, EPA proposes
to revoke the current annual PM10
standard upon promulgation of this
rule. The EPA solicits comment on
alternative approaches for selecting the
level of a 24-hour PM10-2.5 standard, on
alternative approaches based on
retaining the current 24-hour PM10
standard, and on revoking and not
replacing the 24-hour PM10 standard.
With regard to secondary PM
standards, EPA proposes to revise the
current standards by making them
identical to the suite of proposed
primary standards for fine and coarse
particles, providing protection against
PM-related public welfare effects
including visibility impairment, effects
on vegetation and ecosystems, and
materials damage and soiling. Also, EPA
solicits comment on adding a new subdaily PM2.5 standard to address
visibility impairment.
DATES: Written comments on this
proposed decision must be received by
April 17, 2006.
ADDRESSES: Submit your comments,
identified by Docket ID No. EPA–HQ–
OAR–2001–0017 by one of the following
methods:
• https://www.regulations.gov: Follow
the on-line instructions for submitting
comments.
• E-mail: a-and-r-Docket@epa.gov.
• Fax: 202–566–1749.
• Mail: Docket ID No. EPA–HQ–
OAR–2001–0017, Environmental
Protection Agency, Mailcode: 6102T,
1200 Pennsylvania Avenue, NW.,
Washington, DC 20460. Please include a
total of two copies.
• Hand Delivery: Environmental
Protection Agency, EPA West Building,
Room B102, 1301 Constitution Avenue,
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–2001–
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0017. 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
https://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 https://
www.regulations.gov or e-mail. The
https://www.regulations.gov Web site is
an ‘‘anonymous access’’ system, which
means EPA will not know your identity
or contact information unless you
provide it in the body of your comment.
If you send an e-mail comment directly
to EPA without going through https://
www.regulations.gov your e-mail
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, 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 EPA
cannot read your comment due to
technical difficulties and cannot contact
you for clarification, 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 at https://
www.epa.gov/epahome/dockets.htm.
Docket: All documents in the docket
are listed in the https://
www.regulations.gov index. 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,
will be publicly available only in hard
copy. Publicly available docket
materials are available either
electronically in https://
www.regulations.gov or in hard copy at
the Air and Radiation Docket and
Information Center, EPA/DC, EPA West,
Room B102, 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.
Public Hearings: The EPA intends to
hold public hearings around the end of
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February in Philadelphia, Chicago, and
San Francisco, and will announce in a
separate Federal Register notice the
date, time, and address of the public
hearings on this proposed decision.
FOR FURTHER INFORMATION CONTACT: Dr.
Erika Sasser, mail code C539–01, Air
Quality Strategies and Standards
Division, Office of Air Quality Planning
and Standards, U.S. Environmental
Protection Agency, Research Triangle
Park, North Carolina 27711, telephone:
(919) 541–3889, e-mail:
sasser.erika@epa.gov.
SUPPLEMENTARY INFORMATION:
General Information
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A. What Should I Consider As I Prepare
My Comments for EPA?
1. Submitting CBI. Do not submit this
information to EPA through https://
www.regulations.gov or e-mail. Clearly
mark the part or all of the information
that you claim to be CBI. For CBI
information in a disk or CD–ROM that
you mail to EPA, mark the outside of the
disk or CD–ROM as CBI and then
identify electronically within the disk or
CD–ROM the specific information that
is claimed as CBI. In addition to one
complete version of the comment that
includes information claimed as CBI, a
copy of the comment that does not
contain the information claimed as CBI
must be submitted for inclusion in the
public docket. Information so marked
will not be disclosed except in
accordance with procedures set forth in
40 CFR part 2.
2. Tips for Preparing Your Comments.
When submitting comments, remember
to:
• Identify the rulemaking by docket
number and other identifying
information (subject heading, Federal
Register date and page number).
• Follow directions—The agency may
ask you to respond to specific questions
or organize comments by referencing a
Code of Federal Regulations (CFR) part
or section number.
• Explain why you agree or disagree;
suggest alternatives and substitute
language for your requested changes.
• Describe any assumptions and
provide any technical information and/
or data that you used.
• If you estimate potential costs or
burdens, explain how you arrived at
your estimate in sufficient detail to
allow for it to be reproduced.
• Provide specific examples to
illustrate your concerns, and suggest
alternatives.
• Explain your views as clearly as
possible, avoiding the use of profanity
or personal threats.
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• Make sure to submit your
comments by the comment period
deadline identified.
Availability of Related Information
A number of documents are available
on EPA Web sites. The Air Quality
Criteria for Particulate Matter (Criteria
Document) (two volumes, EPA/600/P–
99/002aF and EPA/600/P–99/002bF,
October 2004) is available on EPA’s
National Center for Environmental
Assessment Web site. To obtain this
document, go to https://www.epa.gov/
ncea, and click on ‘‘Particulate Matter’’.
The Staff Paper, human health risk
assessment, and several other related
technical documents are available on
EPA’s Office of Air Quality Planning
and Standards (OAQPS) Technology
Transfer Network (TTN) Web site. The
Staff Paper is available at https://
www.epa.gov/ttn/naaqs/standards/pm/
s_pm_cr_sp.html, and the risk
assessment and technical documents are
available at https://www.epa.gov/ttn/
naaqs/standards/pm/s_pm_cr_td.html.
These and other related documents are
also available for inspection and
copying in the EPA docket identified
above.
Table of Contents
The following topics are discussed in
today’s preamble:
I. Background
A. Legislative Requirements
B. Review of Air Quality Criteria and
Standards for PM
C. Related Control Programs to Implement
PM Standards
D. Overview of Current PM NAAQS
Review
II. Rationale for Proposed Decisions on
Primary PM2.5 Standards
A. Health Effects Related to Exposure to
Fine Particles
1. Mechanisms
2. Nature of Effects
3. Integration and Interpretation of the
Health Evidence
4. Sensitive Subgroups for PM2.5-Related
Effects
5. PM2.5-Related Impacts on Public Health
B. Quantitative Risk Assessment
1. Overview
2. Scope and Key Components
3. Risk Estimates and Key Observations
C. Need for Revision of the Current
Primary PM2.5 Standards
D. Indicator of Fine Particles
E. Averaging Time of Primary PM2.5
Standards
F. Form of Primary PM2.5 Standards
1. 24-Hour PM2.5 Standard
2. Annual PM2.5 Standard
G. Level of Primary PM2.5 Standards
1. 24-Hour PM2.5 Standard
2. Annual PM2.5 Standard
H. Proposed Decisions on Primary PM2.5
Standards
III. Rationale for Proposed Decisions on the
Primary PM10 Standards
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A. Health Effects Related to Exposure to
Thoracic Coarse Particles
1. Mechanisms
2. Nature of Effects
3. Integration and Interpretation of the
Health Evidence
4. Sensitive Subgroups for Effects of
Thoracic Coarse Particle Exposure
5. Impacts on Public Health from Thoracic
Coarse Particle Exposure
B. Quantitative Risk Assessment
C. Need for Revision of the Current
Primary PM10 Standards
D. Indicator of Thoracic Coarse Particles
E. Averaging Time of Primary PM10-2.5
Standard
F. Form of Primary PM10-2.5 Standard
G. Level of Primary PM10-2.5 Standard
H. Proposed Decisions on Primary PM10-2.5
Standard
IV. Rationale for Proposed Decisions on
Secondary PM Standards
A. Visibility Impairment
1. Visibility Impairment Related to
Ambient PM
2. Need for Revision of the Current
Secondary PM Standards for Visibility
Protection
3. Indicator of PM for Secondary Standard
to Address Visibility Impairment
4. Averaging Time of a Secondary PM2.5
Standard for Visibility Protection
5. Elements of a Secondary PM2.5 Standard
for Visibility Protection
B. Other PM-related Welfare Effects
1. Nature of Effects
2. Need for Revision of Current Secondary
PM Standards to Address Other PMrelated Welfare Effects
C. Proposed Decision on Secondary PM
Standards
V. Interpretation of the NAAQS for PM
A. Proposed Amendments to Appendix
N—Interpretation of the National
Ambient Air Quality Standards for PM2.5
1. General
2. PM2.5 Monitoring and Data Reporting
Considerations
3. PM2.5 Computations and Data Handling
Conventions
4. Secondary Standard
5. Conforming Revisions
B. Proposed Appendix P—Interpretation of
the National Ambient Air Quality
Standards for PM10-2.5
1. General
2. PM2.5 Data Reporting Considerations
3. PM10-2.5 Computations and Data
Handling Conventions
4. Exceptional Events
VI. Reference Methods for the Determination
of Particulate Matter as PM2.5 and
PM10-2.5
A. Proposed Appendix O: Reference
Method for the Determination of Coarse
Particulate Matter (as PM10-2.5) in the
Atmosphere
1. Purpose of the New Reference Method
2. Rationale for Selection of the New
Reference Method
3. Consideration of Other Methods for the
Federal Reference Method
4. Consideration of Automated Method
5. Relationship of Proposed FRM to
Transportation Equity Act Requirements
6. Use of the Proposed Federal Reference
Method
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7. Basic Requirements of the Proposed
Federal Reference Method Sampler
8. Other Important Aspects of the Proposed
Federal Reference Method Sampler
B. Proposed Amendments to Appendix L—
Reference Method for the Determination
of Fine Particulate Matter (as PM2.5) in
the Atmosphere
VIII. Statutory and Executive Order
Reviews
A. Executive Order 12866: Regulatory
Planning and 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
Advancement Act
J. Executive Order 12898: Federal Actions
To Address Environmental Justice in
Minority Populations and Low-Income
Populations
References
I. Background
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A. Legislative Requirements
Two sections of the Clean Air Act
(CAA) govern the establishment and
revision of the NAAQS. Section 108 (42
U.S.C. 7408) directs the Administrator
to identify and list ‘‘air pollutants’’ that
‘‘in his judgment, may reasonably be
anticipated to endanger public health
and welfare’’ and whose ‘‘presence
* * * in the ambient air results from
numerous or diverse mobile or
stationary sources’’ and to issue air
quality criteria for those that are listed.
Air quality criteria are intended to
‘‘accurately reflect the latest scientific
knowledge useful in indicating the kind
and extent of identifiable effects on
public health or welfare which may be
expected from the presence of [a]
pollutant in ambient air * * *.’’
Section 109 (42 U.S.C. 7409) directs
the Administrator to propose and
promulgate ‘‘primary’’ and ‘‘secondary’’
NAAQS for pollutants listed under
section 108. 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
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
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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
In setting standards that are
‘‘requisite’’ to protect public health and
welfare, as provided in section 109(b),
EPA’s task is to establish standards that
are neither more nor less stringent than
necessary for these purposes. In
establishing ‘‘requisite’’ primary and
secondary standards, 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).
The requirement that primary
standards include 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. Lead Industries
Association v. EPA, 647 F.2d 1130, 1154
(D.C. Cir 1980), cert. denied, 449 U.S.
1042 (1980); American Petroleum
Institute v. Costle, 665 F.2d 1176, 1186
(D.C. Cir. 1981), cert. denied, 455 U.S.
1034 (1982). 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 include 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 Association v. EPA,
supra, 647 F.2d at 1156 n. 51), but
rather at a level that reduces risk
sufficiently so as to protect public
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, manmade 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.’’
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health with an adequate margin of
safety.
In addressing the requirement for an
adequate margin of safety, EPA
considers such factors as the nature and
severity of the health effects involved,
the size of the sensitive population(s) at
risk, 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. Lead
Industries Association v. EPA, supra,
647 F.2d at 1161–62.
Section 109(d)(1) of the CAA requires
that ‘‘not later than December 31, 1980,
and at 5-year 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 * * *.’’ This
independent review function is
performed by the Clean Air Scientific
Advisory Committee (CASAC) of EPA’s
Science Advisory Board.
B. Review of Air Quality Criteria and
Standards for PM
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.
Particles originate from a variety of
anthropogenic stationary and mobile
sources as well as from natural sources.
Particles may be emitted directly or
formed in the atmosphere by
transformations of gaseous emissions
such as sulfur oxides (SOX), nitrogen
oxides (NOX), and volatile organic
compounds (VOC). The chemical and
physical properties of PM vary greatly
with time, region, meteorology, and
source category, thus complicating the
assessment of health and welfare effects.
The last review of PM air quality
criteria and standards was completed in
July 1997 with notice of a final decision
to revise the existing standards (62 FR
38652, July 18, 1997). In that decision,
EPA revised the PM NAAQS in several
respects. While EPA determined that the
PM NAAQS should continue to focus on
particles less than or equal to 10 µm in
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diameter (PM10), EPA also determined
that the fine and coarse fractions of
PM10 should be considered separately.
The EPA added new standards, using
PM2.5 as the indicator for fine particles
(with PM2.5 referring to particles with a
nominal mean aerodynamic diameter
less than or equal to 2.5 µm), and
retained PM10 standards for the purpose
of regulating the coarse fraction of PM10
(referred to as thoracic coarse particles
or coarse-fraction particles; generally
including particles with a nominal
mean aerodynamic diameter greater
than 2.5 µm and less than or equal to
10 µm, or PM10-2.5). The EPA established
two new PM2.5 standards: an annual
standard of 15 µg/m3, based on the 3year average of annual arithmetic mean
PM2.5 concentrations from single or
multiple community-oriented monitors;
and a 24-hour standard of 65 µg/m3,
based on the 3-year average of the 98th
percentile of 24-hour PM2.5
concentrations at each populationoriented monitor within an area. Also,
EPA established a new reference
method for the measurement of PM2.5 in
the ambient air and adopted rules for
determining attainment of the new
standards. To continue to address
thoracic coarse particles, EPA retained
the annual PM10 standard, while
revising the form, but not the level, of
the 24-hour PM10 standard 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, petitions for review were
filed by a large number of parties,
addressing a broad range of issues. In
May 1999, a three-judge panel of the
U.S. Court of Appeals for the District of
Columbia Circuit issued an initial
decision that upheld 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 EPA’s decision to
regulate coarse particle pollution, but
vacated the 1997 PM10 standards,
concluding in part that PM10 is a
‘‘poorly matched indicator for coarse
particulate pollution’’ because it
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includes fine particles. Id. at 1053–55.
Pursuant to the court’s decision, EPA
removed the vacated 1997 PM10
standards from the Code of Federal
Regulations (CFR) (69 FR 45592, July 30,
2004) and deleted the regulatory
provision (at 40 CFR 50.6(d)) that
controlled the transition from the preexisting 1987 PM10 standards to the
1997 PM10 standards (65 FR 80776,
December 22, 2000). The pre-existing
1987 PM10 standards remained in place.
Id. at 80777.
More generally, the three-judge panel
held (with one dissenting opinion) that
EPA’s approach to establishing the level
of the standards in 1997, both for PM
and for 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 EPA, stating that when 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
EPA’s long-standing interpretation, the
panel also reaffirmed prior rulings
holding that in setting NAAQS EPA is
‘‘not permitted to consider the cost of
implementing those standards.’’ Id. at
1040–41.
Both sides filed cross appeals on these
issues to the United States Supreme
Court, and the Court granted certiorari.
In February 2001, the Supreme Court
issued a unanimous decision upholding
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 guided EPA’s discretion,
affirming 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 traditional
standard of judicial review that EPA’s
PM2.5 standards were reasonably
supported by the administrative record
and were not ‘‘arbitrary and capricious.’’
American Trucking Associations v.
EPA, 283 F.3d 355, 369–72 (D.C. Cir.
2002).
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In October 1997, EPA published its
plans for the current periodic review of
the PM criteria and NAAQS (62 FR
55201, October 23, 1997), including the
1997 PM2.5 standards and the 1987 PM10
standards. As part of the process of
preparing an updated Air Quality
Criteria Document for Particulate Matter
(henceforth, the ‘‘Criteria Document’’),
EPA’s National Center for
Environmental Assessment (NCEA)
hosted a peer review workshop in April
1999 on drafts of key Criteria Document
chapters. The first external review draft
Criteria Document was reviewed by
CASAC and the public at a meeting held
in December 1999. Based on CASAC
and public comment, NCEA revised the
draft Criteria Document and released a
second draft in March 2001 for review
by CASAC and the public at a meeting
held in July 2001. A preliminary draft
of a staff paper, Review of the National
Ambient Air Quality Standards for
Particulate Matter: Assessment of
Scientific and Technical Information
(henceforth, the ‘‘Staff Paper’’) prepared
by EPA’s Office of Air Quality Planning
and Standards (OAQPS) was released in
June 2001 for public comment and for
consultation with CASAC at the same
public meeting. Taking into account
CASAC and public comments, a third
draft Criteria Document was released in
May 2002 for review at a meeting held
in July 2002.
Shortly after the release of the third
draft Criteria Document, the Health
Effects Institute (HEI) 3 announced that
researchers at Johns Hopkins University
had discovered problems with
applications of statistical software used
in a number of important
epidemiological studies that had been
discussed in that draft Criteria
Document. In response to this
significant issue, EPA took steps in
consultation with CASAC to encourage
researchers to reanalyze affected studies
and to submit them expeditiously for
peer review by a special expert panel
convened at EPA’s request by HEI. The
results of this reanalysis and peerreview process were subsequently
incorporated into a fourth draft Criteria
Document, which was released in June
2003 and reviewed by CASAC and the
public at a meeting held in August 2003.
The first draft Staff Paper, based on
the fourth draft Criteria Document, was
released at the end of August 2003, and
was reviewed by CASAC and the public
at a meeting held in November 2003.
3 The HEI is an independent research institute,
jointly sponsored by EPA and a group of U.S.
manufacturers and marketers of motor vehicles and
engines, that conducts health effects research on
major air pollutants related to motor vehicle
emissions.
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During that meeting, EPA also consulted
with CASAC on a new framework for
the final chapter (integrative synthesis)
of the Criteria Document and on
ongoing revisions to other Criteria
Document chapters to address previous
CASAC comments. The EPA held
additional consultations with CASAC at
public meetings held in February, July,
and September 2004, leading to
publication of the final Criteria
Document in October 2004. The second
draft Staff Paper, based on the final
Criteria Document, was released at the
end of January 2005, and was reviewed
by CASAC and the public at a meeting
held in April 2005. The CASAC’s advice
and recommendations to the
Administrator, based on its review of
the second draft Staff Paper, were
further discussed during a public
teleconference held in May 2005 and are
provided in a June 6, 2005 letter to the
Administrator (Henderson, 2005a). The
final Staff Paper, issued in June, 2005,
takes into account the advice and
recommendations of CASAC and public
comments received on the earlier drafts
of this document. The Administrator
subsequently received additional advice
and recommendations from the CASAC,
specifically on potential standards for
thoracic coarse particles in a
teleconference on August 11, 2005, and
in a letter to the Administrator dated
September 15, 2005 (Henderson,
2005b).4
The schedule for completion of this
review is governed by a consent decree
resolving a lawsuit filed in March 2003
by a group of plaintiffs representing
national environmental organizations.
The lawsuit alleged that EPA had failed
to perform its mandatory duty, under
section 109(d)(1), of completing the
current review within the period
provided by statute. American Lung
Association v. Whitman (No.
1:03CV00778, D.D.C. 2003). An initial
consent decree was entered by the court
in July 2003 after an opportunity for
public comment. The consent decree, as
modified by the court, provides that
EPA will sign for publication notices of
proposed and final rulemaking
concerning its review of the PM NAAQS
no later than December 20, 2005 and
September 27, 2006, respectively.
C. Related Control Programs to
Implement PM Standards
States are primarily responsible for
ensuring attainment and maintenance of
4 The EPA has posted on its Web site (https://
www.epa.gov/ttn/naaqs/standards/pm/
s_pm_index.html) a second edition of the Staff
Paper which was prepared for the purpose of
including as an attachment this September 2005
letter from CASAC.
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ambient air quality standards once EPA
has established them. Under section 110
of the CAA (42 U.S.C. 7410) and related
provisions, States are to submit, for EPA
approval, State implementation plans
(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 EPA, also
administer the prevention of significant
deterioration (PSD) program (42 U.S.C.
7470–7479) for these pollutants. In
addition, Federal programs provide for
nationwide reductions in emissions of
these and other air pollutants through
the Federal Mobile Source Control
Program under title II of the CAA (42
U.S.C. 7521–7574), which involves
controls for automobile, truck, bus,
motorcycle, nonroad or off-highway,
and aircraft emissions; the new source
performance standards under section
111 (42 U.S.C. 7411); and the national
emission standards for hazardous air
pollutants under section 112 (42 U.S.C.
7412).
As described in a recent EPA report,
The Particle Pollution Report: Current
Understanding of Air Quality and
Emissions through 2003 (EPA, 2004b),
State and Federal programs have made
substantial progress in reducing ambient
concentrations of PM10 and PM2.5. For
example, PM10 concentrations have
decreased 31 percent nationally since
1988. Regionally, PM10 concentrations
decreased most in areas with
historically higher concentrations—the
Northwest (39 percent decline), the
Southwest (33 percent decline), and
southern California (35 percent decline).
Direct emissions of PM10 have decreased
approximately 25 percent nationally
since 1988.
Programs aimed at reducing direct
emissions of particles have played an
important role in reducing PM10
concentrations, particularly in western
areas. Some examples of PM10 controls
include paving unpaved roads and
using best management practices for
agricultural sources of resuspended soil.
Additionally, EPA’s Acid Rain Program
has substantially reduced sulfur dioxide
(SO2) emissions from power plants since
1995 in the eastern United States,
contributing to lower PM
concentrations. Of the 87 areas that
were designated nonattainment for PM10
in the early 1990s, 64 now meet those
standards. In cities that have not
attained the PM10 standards, the number
of days above the standards is down
significantly.
Nationally, PM2.5 concentrations have
declined by 10 percent from 1999 to
2003. Generally, PM2.5 concentrations
have also declined the most in regions
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with the highest concentrations—the
Southeast (20 percent decline), southern
California (16 percent decline), and the
Industrial Midwest (9 percent decline).
With the exception of the Northeast, the
remaining regions posted modest
declines in PM2.5 concentrations from
1999 to 2003. Direct emissions of PM2.5
have decreased by 5 percent nationally
over the past 5 years.
National programs that affect regional
emissions have contributed to lower
sulfate concentrations and,
consequently, to lower PM2.5
concentrations, particularly in the
Industrial Midwest and Southeast.
National ozone-reduction programs
designed to reduce emissions of volatile
organic compounds (VOCs) and
nitrogen oxides (NOX) also have helped
reduce carbon and nitrates, both of
which are components of PM2.5.
Nationally, SO2 emissions have
declined 9 percent, NOX emissions have
declined 9 percent, and VOC emissions
have declined by 12 percent from 1999
to 2003. In eastern States affected by the
Acid Rain Program, sulfates decreased 7
percent over the same period.
Over the next 10 to 20 years, national
and regional regulations will make
major reductions in ambient PM2.5
levels. The Clean Air Interstate Rule
(CAIR) and the NOX SIP Call will reduce
SO2 and NOX emissions from electric
generating units and industrial boilers
across the eastern half of the U.S.,
regulations to implement the current
ambient air quality standards for PM2.5
will require direct PM2.5 and PM2.5
precursor controls in nonattainment
areas, and new national mobile source
regulations affecting heavy-duty diesel
engines, highway vehicles, and other
mobile sources will reduce emissions of
NOX, direct PM2.5, SO2, and VOCs. The
EPA estimates that these regulations for
stationary and mobile sources will cut
SO2 emissions by 6 million tons
annually in 2015 from 2001 levels.
Emissions of NOX will be cut by 9
million tons annually in 2015 from 2001
levels. Emissions of VOCs will drop by
3 million tons, and direct PM2.5
emissions will be cut by 200,000 tons in
2015, compared to 2001 levels.
Modeling done by EPA indicates that
by 2010, 18 of the 39 areas currently not
attaining the PM2.5 standards will come
into attainment just based on regulatory
programs already in place, including
CAIR, the Clean Diesel Rules, and other
Federal measures. Four more PM2.5
areas are projected to attain the
standards by 2015 based on the
implementation of these programs. All
areas in the eastern U.S. will have lower
PM2.5 concentrations in 2015 relative to
present-day conditions. In most cases,
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the predicted improvement in PM2.5
ranges from 10 percent to 20 percent.
D. Overview of Current PM NAAQS
Review
This action presents the
Administrator’s proposed decisions on
the review of the current primary and
secondary PM2.5 and PM10 standards.
Primary standards for fine particles and
for thoracic coarse particles are
addressed separately below in sections
II and III, respectively, consistent with
the decision made by EPA in the last
review and with the conclusions in the
Criteria Document and Staff Paper that
fine and thoracic coarse particles should
continue to be considered as separate
subclasses of PM pollution. Thus, the
principal focus of this current review of
the air quality criteria and primary
standards for PM is on evidence of
health effects and risks related to
exposures to fine particles and to
thoracic coarse particles. Secondary
standards for fine and coarse-fraction
particles are addressed below in section
IV.
Past and current decisions to address
fine particles and thoracic coarse
particles separately are based in part on
long-established information on
differences in sources, properties, and
atmospheric behavior between fine and
coarse particles (EPA, 2005a, section
2.2). Fine particles are produced chiefly
by combustion processes and by
atmospheric reactions of various
gaseous pollutants, whereas thoracic
coarse particles are generally emitted
directly as particles as a result of
mechanical processes that crush or
grind larger particles or the
resuspension of dusts. Sources of fine
particles include, for example, motor
vehicles, power generation, combustion
sources at industrial facilities, and
residential fuel burning. Sources of
thoracic coarse particles include, for
example, resuspension of traffic-related
emissions such as tire and brake lining
materials, direct emissions from
industrial operations, construction and
demolition activities, and agricultural
and mining operations. Fine particles
can remain suspended in the
atmosphere for days to weeks and can
be transported thousands of kilometers,
whereas thoracic coarse particles
generally deposit rapidly on the ground
or other surfaces and are not readily
transported across urban or broader
areas. The approach in this review to
continue to address fine and thoracic
coarse particles separately is reinforced
by new information that advances our
understanding of differences in human
exposure relationships and dosimetric
patterns characteristic of these two
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subclasses of PM pollution, as well as
the apparent independence of health
effects that have been associated with
them in epidemiologic studies (EPA,
2004, section 3.2.3). See also American
Trucking Associations v. EPA, 175 F. 3d
at 1053–54, 1055–56 (EPA justified in
establishing separate standards for fine
and thoracic coarse particles).
Today’s proposed decisions
separately addressing fine and coarse
particles are based on a thorough review
in the Criteria Document of the latest
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
proposed decisions also take into
account: (1) Staff assessments in the
Staff Paper of the most policy-relevant
information in the Criteria Document
and as well as a quantitative risk
assessment; (2) CASAC advice and
recommendations, as reflected in the
CASAC’s letters to the Administrator,
discussions of drafts of the Criteria
Document and Staff Paper at public
meetings, and separate written
comments prepared by individual
members of the CASAC PM Review
Panel 5 (henceforth, ‘‘CASAC Panel’’),
and (3) public comments received
during the development of these
documents, either in connection with
CASAC meetings or separately.
The EPA is aware that a number of
new scientific studies on the health
effects of PM have been published since
the 2002 cutoff date for inclusion in the
Criteria Document. As in the last PM
NAAQS review, EPA intends to conduct
a review and assessment of any
significant new studies published since
the close of the Criteria Document,
including studies submitted during the
public comment period in order to
ensure that, before making a final
decision, the Administrator is fully
aware of the new science that has
developed since 2002. In this
assessment, EPA will examine these
new studies in light of the literature
evaluated in the Criteria Document.
This assessment and a summary of the
key conclusions will be placed in the
rulemaking docket. A preliminary list of
potentially significant new studies
identified to date has been compiled
and placed in the rulemaking docket for
this proposal, and EPA solicits comment
on other relevant studies that may be
added to this list. This list includes a
5 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 the types
of scientific expertise relevant to this review of the
PM NAAQS.
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wide array of different types of studies
that are potentially relevant to various
issues discussed in the following
sections, including issues related to the
elements of the standards under review.
Throughout this preamble a number
of conclusions, findings, and
determinations by the Administrator are
noted. It should be understood that
these are all provisional and proposed
in nature. While they identify the
reasoning that supports this proposal,
they are not intended to be final or
conclusive in nature. The EPA invites
comments on all issues involved with
this proposal, including all such
proposed judgments, conclusions,
findings, and determinations.
II. Rationale for Proposed Decisions on
Primary PM2.5 Standards
As discussed more fully below, the
rationale for the proposed revisions of
the primary PM2.5 NAAQS includes
consideration of: (1) Evidence of health
effects related to short- and long-term
exposures to fine particles; (2) insights
gained from a quantitative risk
assessment; and (3) specific conclusions
regarding the need for revisions to the
current standards and the elements of
PM2.5 standards (i.e., indicator,
averaging time, form, and level) that,
taken together, would be requisite to
protect public health with an adequate
margin of safety.
In developing this rationale, EPA has
drawn upon an integrative synthesis of
the entire body of evidence of
associations between exposure to
ambient fine particles and a broad range
of health endpoints (EPA, 2004, Chapter
9), focusing on those health endpoints
for which the Criteria Document
concludes that the associations are
likely to be causal. This body of
evidence includes hundreds of studies
conducted in many countries around
the world, using various indicators of
fine particles. In its assessment of the
evidence judged to be most relevant to
making decisions on elements of the
primary PM2.5 standards, EPA has
placed greater weight on U.S. and
Canadian studies using PM2.5
measurements, since studies conducted
in other countries may well reflect
different demographic and air pollution
characteristics.
As with virtually any policy-relevant
scientific research, there is uncertainty
in the characterization of health effects
attributable to exposure to ambient fine
particles. As discussed below, however,
an unprecedented amount of new
research has been conducted since the
last review, with important new
information coming from epidemiologic,
toxicologic, controlled human exposure,
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and dosimetric studies. Moreover, the
newly available research studies
evaluated in the Criteria Document have
undergone intensive scrutiny through
multiple layers of peer review and
extended opportunities for public
review and comment. While important
uncertainties remain, the review of the
health effects information has been
extensive and deliberate. In the
judgment of the Administrator, this
intensive evaluation of the scientific
evidence has provided an adequate
basis for regulatory decision making at
this time. This review also provides
important input to EPA’s research plan
for improving our future understanding
of the relationships between exposures
to ambient fine particles and health
effects.
A. Heath Effects Related to Exposure to
Fine Particles
This section outlines key information
contained in the Criteria Document
(Chapters 6–9 and the Staff Paper
(Chapter 3) on known or potential
effects associated with exposure to fine
particles and their major constituents.
The information highlighted here
summarizes: (1) New information
available on potential mechanisms for
health effects associated with exposure
to fine particles and constituents; (2) the
nature of the effects that have been
associated with ambient fine particles or
fine particle constituents; (3) an
integrative assessment of the evidence
on fine particle-related health effects; (4)
subpopulations that appear to be
sensitive to effects of exposure to fine
particles; and (5) the public health
impact of exposure to ambient fine
particles.
As was true in the last review,
evidence from epidemiologic studies
plays a key role in the Criteria
Document’s evaluation of the scientific
evidence. Some highlights of the new
epidemiologic evidence include:
(1) New multi-city studies that use
uniform methodologies to investigate
the effects of various indicators of PM
on health with data from multiple
locations with varying climate and air
pollution mixes, contributing to
increased understanding of the role of
various potential confounders,
including gaseous co-pollutants, on
observed associations with fine
particles. These studies provide more
precise estimates of the magnitude of an
effect of exposure to PM, including fine
particles, than most smaller-scale
individual city studies.
(2) More studies of various health
endpoints evaluating associations
between effects and fine particles and
thoracic coarse particles (discussed
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below in section III), as well as ultrafine
particles or specific components (e.g.,
sulfates, nitrates, metals, organic
compounds, and elemental carbon) of
fine particles.
(3) Numerous new studies of
cardiovascular endpoints, with
particular emphasis on assessment of
cardiovascular risk factors or
physiological changes.
(4) Studies relating population
exposure to fine particles and other
pollutants measured at centrally located
monitors to estimates of exposure to
ambient pollutants at the individual
level. Such studies have led to a better
understanding of the relationship
between ambient fine particles levels
and personal exposures to fine particles
of ambient origin.
(5) New analyses and approaches to
addressing issues related to potential
confounding by gaseous co-pollutants,
possible thresholds for effects, and
measurement error and exposure
misclassification.6
(6) Preliminary attempts to evaluate
the effects of fine particles from
different sources (e.g., motor vehicles,
coal combustion, vegetative burning,
crustal 7 ), using factor analysis or source
apportionment methods with fine
particle speciation data.
(7) Several new ‘‘intervention
studies’’ providing evidence for
improvements in respiratory or
cardiovascular health with reductions in
ambient concentrations of particles and
gaseous co-pollutants.
In addition, the body of evidence on
PM-related effects has greatly expanded
with findings from studies on potential
mechanisms or pathways by which
particles may result in the effects
identified in the epidemiologic studies.
These studies include important new
dosimetry, toxicologic and controlled
human exposure studies, as highlighted
below:
(8) Animal and controlled human
exposure studies using concentrated
6 ‘‘Confounding’’ occurs when a health effect that
is caused by one risk factor is attributed to another
variable that is correlated with the causal risk
factor; epidemiologic analyses attempt to adjust or
control for potential confounders (EPA, 2004,
section 8.1.3.2; EPA, 2005a, section 3.6.4). A
‘‘threshold’’ is a concentration below which it is
expected that effects are not observed (EPA, 2004,
section 8.4.7; EPA, 2005a, section 3.6.6). ‘‘Gaseous
co-pollutants’’ generally refer to other commonlyoccuring air pollutants, specifically O3, CO, SO2
and NO2. ‘‘Measurement error’’ refers to uncertainty
in the air quality measurements, while ‘‘exposure
misclassification’’ includes uncertainty in the use of
ambient pollutant measurements in characterizing
population exposures to PM (EPA, 2004, section
8.4.5; EPA, 2005a, section 3.6.2)
7 ‘‘Crustal’’ is used here to describe particles of
geologic origin, which can be found in both fineand coarse-fraction PM.
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ambient particles (CAPs), new
indicators of response (e.g., C-reactive
protein and cytokine levels, heart rate
variability), and animal models
simulating sensitive human
subpopulations. The results of these
studies are relevant to evaluation of
plausibility of the epidemiologic
evidence and provide insights into
potential mechanisms for PM-related
effects.
(9) Dosimetry studies using new
modeling methods that provide
increased understanding of the
dosimetry of different particle size
classes and in members of potentially
sensitive subpopulations, such as
people with chronic respiratory disease.
1. Mechanisms
In the last review, EPA considered the
lack of demonstrated biologic
mechanisms for the varying effects
observed in epidemiologic studies to be
an important caution in its integrated
assessment of the health evidence.
Much new evidence is now available on
potential mechanisms or pathways for
PM-related effects, ranging from effects
on the respiratory system to indicators
of cardiovascular response; these new
findings are discussed in depth in
Chapter 7 of the Criteria Document.
While questions remain, the new
findings have advanced our
understanding of the complex and
different patterns of particle deposition
and clearance in the respiratory tract
and provide insights into potential
mechanisms for PM-related effects and
support the plausibility of the findings
of epidemiologic studies.
Although there are differences among
the size fractions of particles, fine
particles, including accumulation mode
and ultrafine particles, and thoracic
coarse particles can all penetrate into
and be deposited in the
tracheobronchial and alveolar regions of
the respiratory tract (i.e., the ‘‘thoracic’’
regions).8 Penetration into the
tracheobronchial and alveolar regions is
greater for accumulation mode particles
than for coarse or ultrafine particles,
since coarse and ultrafine particles are
more efficiently removed from the air in
the extrathoracic region than are
accumulation-mode fine particles; the
evidence from dosimetric studies is
8 Particles are often classified in modes based on
their distribution by characteristics such as mass,
surface area, and particle number. ‘‘Coarse mode’’
particles are those with diameters mostly greater
than the minimum in the particle mass distribution,
which generally occurs between about 1 and 3 µm.
‘‘Accumulation mode’’ particles are those with
diameters from about 0.1 µm to between about 1
and 3 µm. Ultrafine particles are generally those
with diameters below about 0.1 µm (EPA, 2004,
pages 2–14).
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such as inflammation, might contribute
to long-term effects, it is likely that
wholly different mechanisms are
involved in the development of chronic
health responses. Some mechanistic
evidence is available, however, for
potential carcinogenic or genotoxic
effects of ambient fine particles and
combustion products of coal, wood,
diesel, and gasoline (discussed in
section 7.8 of the Criteria Document).
Overall, the findings indicate that
different health responses are linked
with different particle characteristics
and that both individual components
and complex particle mixtures appear to
be responsible for many biologic
responses relevant to fine particle
exposures. In evaluating the new body
of evidence, the Criteria Document
states: ‘‘Thus, there appear to be
multiple biologic mechanisms that may
be responsible for observed morbidity/
mortality due to exposure to ambient
PM. It also appears that many biologic
responses are produced by PM whether
it is composed of a single component or
a complex mixture’’ (EPA, 2004, p. 7–
206).
reviewed in detail in Chapter 6 of the
Criteria Document.
Fine particles have varying physical
or chemical characteristics that may
influence health responses. Physical
characteristics that may be of
importance are solubility or physical
state of the particles (e.g., solid, liquid).
Fine particle components include
metals, acids, organic compounds,
biogenic constituents, sulfate and nitrate
salts, elemental carbon, and reactive
components such as peroxides; size and
surface area of the particles can also
influence health responses. By way of
illustration, Mauderly et al. (1998)
discussed particle components or
characteristics hypothesized to
contribute to health, producing an
illustrative list of 11 components or
characteristics of interest for which
some evidence existed. The list
included: (1) Particle mass
concentration, (2) particle size/surface
area, (3) ultrafine particles, (4) metals,
(5) acids, (6) organic compounds, (7)
biogenic particles, (8) sulfate and nitrate
salts, (9) peroxides, (10) soot, and (11)
co-factors, including effects
modification or confounding by cooccurring gases and meteorology. The
authors stressed that this list is neither
definitive nor exhaustive, and note that
‘‘it is generally accepted as most likely
that multiple toxic species act by several
mechanistic pathways to cause the
range of health effects that have been
observed’’ (Mauderly et al., 1998). The
range of health outcomes linked with
fine particle exposures is also broad,
including effects on the cardiovascular
and respiratory systems, and potential
links with developmental effects in
children (e.g., low birth weight) and
death from lung cancer. It appears
unlikely that the complex mixes of
particles that are present in ambient air
would act alone through any single
pathway of response. Accordingly, it is
plausible that several physiological
responses might occur in concert to
produce reported health endpoints.
As discussed in section 7.10 of the
Criteria Document, the potential
pathways for direct effects on the
respiratory system include lung injury
and inflammation, increased airway
reactivity and asthma exacerbation, and
increased susceptibility to respiratory
infections. New toxicologic or
controlled human exposure studies have
reported some evidence of inflammatory
responses in animals, as well as
increased susceptibility to infections.
Toxicologic studies also report evidence
of lung injury, inflammation, or altered
host defenses with exposure to ambient
particles or particle constituents. Some
toxicologic evidence, particularly from
results of studies using diesel exhaust
particle exposures, also indicates that
PM can aggravate asthmatic symptoms
or increase airway reactivity.
Potential pathways for fine particlerelated effects also include systemic
effects that are secondary to effects in
the respiratory system. These include
impairment of lung function leading to
cardiac effects, pulmonary inflammation
and cytokine production leading to
systemic hemodynamic effects, lung
inflammation leading to increased blood
coagulability, and lung inflammation
leading to hematopoiesis effects. While
more limited than for direct pulmonary
effects, some new toxicologic studies
suggest that injury or inflammation in
the respiratory system can lead to
changes in heart rhythm, reduced
oxygenation of the blood, changes in
blood cell counts, and changes in the
blood that can increase the risk of blood
clot formation, a risk factor for heart
attacks and strokes. In addition, health
studies have suggested potential
pathways for effects on the heart that
include effects related to uptake of
particles or particle constituents in the
blood, and effects on the autonomic
control of the heart and circulatory
system. In the last review, little or no
evidence was available from toxicologic
studies on potential cardiovascular
effects. More recent studies have
provided some initial evidence that
particles can have direct cardiovascular
effects. Particle deposition in the
respiratory system also could lead to
cardiovascular effects, such as fine
particle-induced pulmonary reflexes
resulting in changes in the autonomic
nervous system that then could affect
heart rhythm. Also, inhaled fine
particles could affect the heart or other
organs if particles or particle
constituents are released into the
circulatory system from the lungs; some
new evidence indicates that the smaller
ultrafine particles or their soluble
constituents can move directly from the
lungs into systemic circulation.
The potential mechanisms and/or
general pathways for effects discussed
above are primarily effects related to
short-term rather than long-term
exposure to fine particles; for the most
part, air pollution toxicologic studies
are not designed to assess long-term
exposure effects. While repeated
occurrences of some short-term insults,
2. Nature of Effects
In the last review, evidence from
health studies indicated that exposure
to PM (using various indicators) was
associated with premature mortality and
indices of morbidity including
respiratory hospital admissions and
emergency room visits, school absences,
work loss days, restricted activity days,
effects on lung function and symptoms,
morphological changes, and altered host
defense mechanisms.9 As reviewed in
Chapter 8 of the Criteria Document,
recent epidemiologic studies have
continued to report associations
between short-term exposure to fine
particles or fine particle indicators, and
effects such as premature mortality,
hospital admissions or emergency
department visits for respiratory
disease, and effects on lung function
and symptoms. In addition, recent
epidemiologic studies have provided
some new evidence linking short-term
fine particle exposures to effects on the
cardivascular system, including
cardiovascular hospital admissions and
more subtle indicators of cardiovascular
health. Long-term exposure to PM2.5 and
sulfates has also been associated with
mortality from cardiopulmonary
diseases and lung cancer, and effects on
the respiratory system such as decreased
lung function or the development of
chronic respiratory disease. The
9 Historical reports of dramatic pollution
episodes, considered in the 1987 review of the PM
NAAQS, provided clear evidence of mortality
associated with high levels of PM and other
pollutants, such as the air pollution episode that
occurred in London in 1952 (EPA, 1996a, pp. 12–
28 to 12–31).
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evidence for such effects is summarized
below.
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a. Effects Associated With Short-Term
Exposure to Fine Particles
Numerous epidemiologic studies have
demonstrated statistical associations
between short-term exposure to fine
particles and health outcomes ranging
from total mortality to respiratory
symptoms, as discussed below. Figure 1
summarizes results from both multi-city
and single-city epidemiologic studies
using short-term exposures to PM2.5,
including all U.S. and Canadian studies
that used direct measurements of PM2.5
and for which effect estimates and
confidence intervals were reported.10
The central effect estimate is indicated
by a diamond for each study result, with
the vertical bar representing the 95
percent confidence interval around the
estimate. In the discussions that follow,
an individual study result is considered
to be statistically significant if the 95
percent confidence interval does not
include zero. Positive effect estimates
indicate increases in the health outcome
with PM2.5 exposure. In considering
these results as a whole, it is important
to consider not only whether statistical
significance at the 95 percent
confidence level is reported in
individual studies, but also the general
pattern of results, focusing in particular
on studies with greater statistical power
that report relatively more precise
results.
i. Mortality
Since the last review, a large number
of new time-series studies of the
relationship between short-term
exposure to PM, including PM2.5, and
mortality have been published,
including several multi-city studies that
are responsive to the recommendations
from the last review. As discussed in
section 8.2 of the Criteria Document,
these include studies that have been
conducted in single cities or locations in
the U.S. or Canada, as well as Mexico
City and locations in Europe, South
America, Asia, and Australia.
Several recent multi-city studies have
been published since the last review
that are of particular relevance for this
review. The results of multi-city studies
on associations between PM10 and
mortality across 90 U.S. cities
(Dominici, 2003) and across ten U.S.
cities (Schwartz, 2003b), while not
specifically on fine particles, have
provided important new information to
help address uncertainties regarding a
number of issues, including model
specification, potential confounding by
co-pollutants and the form of
10 In
the following discussion of specific studies,
results from single-pollutant models are referred to,
as shown in Figure 1, unless otherwise noted.
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concentration-response functions (EPA,
2004, section 8.2.2.3). Two multi-city
studies have included measurements of
PM2.5; one was conducted in six U.S.
cities (Schwartz et al., 2003a; Klemm
and Mason, 2003) and the other in eight
Canadian cities (Burnett and Goldberg,
2003). In the last review, results from
one multi-city study (the Six Cities
study) were available, in which the
authors reported significant associations
for total mortality with PM2.5 and PM10,
but not with PM10-2.5. Reanalyses of Six
Cities data have reported results
consistent with the findings of the
original study, with statistically
significant increases for total mortality
with short-term exposure to PM2.5
(Schwartz, 2003a; Klemm and Mason,
2003). In a study using data from the
eight largest Canadian cities, positive
associations were reported for PM2.5,
PM10, and PM10-2.5 with mortality, and
the association with PM2.5 was
statistically significant (Burnett and
Goldberg, 2003).
Single-city studies of mortality
associations with short-term exposures
to fine particles have also been
conducted in areas across U.S. and
Canada as well as in Europe, Australia
and Mexico (some using fine particle
indicators such as British Smoke). In
general, it can be seen in Figure 1 that
the effect estimates for associations
between mortality and short-term
exposure to PM2.5 are positive and a
number are statistically significant,
particularly when focusing on the
results of studies with greater precision.
For total nonaccidental mortality, the
effect estimates from the multi-city and
single-city studies with greater precision
generally fall in a range of 2 to 6 percent
increases per 25 µg/m3 PM2.5.11
Somewhat larger effect estimates have
been reported for associations with
cardiovascular or respiratory mortality
than with total nonaccidental mortality
although the confidence intervals may
also be larger, especially for respiratory
mortality since respiratory deaths
comprise only a small proportion of
total deaths (EPA, 2005a, p. 3–15). Some
studies evaluated seasonal variation in
effects, and there is no consistent
pattern in results. The Criteria
Document concludes that the results of
recent epidemiologic studies are
generally consistent with findings
available in the previous review (EPA,
2004, p. 8–305).
In addition, associations have been
reported between mortality and short11 In general, the results of studies conducted over
shorter time periods and/or smaller areas have a
broader range or effect estimates with larger
standard errors, as shown in Figure 1.
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term exposure to a number of fine
particle components, including sulfates,
nitrates, metals, organic compounds and
elemental carbon (EPA, 2004, Section
8.2.2.5.2), as well as gaseous precursors
such as SO2 and NO2 and other gaseous
pollutants such as CO. Further, three
recent studies have used PM2.5
speciation data to evaluate the effects of
air pollutant combinations or mixtures
using factor analysis or source
apportionment methods to evaluate
potential associations between mortality
and PM2.5 from different source
categories. These studies reported that
short-term exposures to fine particles
from combustion sources, including
motor vehicle emissions, coal
combustion, oil burning and vegetative
burning, were associated with increased
mortality (EPA, 2004, Section 8.2.2.5.3).
However, different patterns of
associations between various
components or source categories of fine
particles and total or cardiovascular
mortality are seen in different studies
(EPA, 2004, p. 8–70, Tables 8–3, 8–4).
ii. Respiratory Morbidity
As discussed in Section 8.4.6.4 of the
Criteria Document, recent epidemiologic
studies have provided further evidence
for fine particle effects on morbidity,
including effects such as hospital
admissions or emergency department
for respiratory diseases, respiratory
symptoms and lung function changes.
(a) Hospital Admissions or Emergency
Department Visits for Respiratory
Diseases
In the last review, results were
available from one study that reported
associations between PM2.5 and
hospitalization for respiratory diseases;
these findings were also supported by a
number of studies using other fine
particle indicators. Numerous studies
had also reported statistically significant
associations between hospital
admissions or emergency department
visits for respiratory diseases short-term
exposures with various indicators
ambient PM, especially PM10, in areas
where fine particles are the
predominant fraction of PM10, such as
locations in the Eastern U.S. and in
Ontario, Canada (EPA, 1996a, p. 13–39).
The body of evidence has been
expanded with numerous new studies
in the U.S. and other countries that have
reported associations between PM2.5 and
hospitalization or emergency
department visits (discussed more fully
in Section 8.3.2 of the Criteria
Document). As shown in Figure 1, all
U.S. and Canadian studies report
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associations between PM2.5 and
hospitalization for all respiratory causes
that are positive and statistically
significant. A number of studies have
also reported findings for hospital
admissions for individual disease
categories (COPD, pneumonia, and
asthma) that are positive, but not always
statistically significant, perhaps due to
smaller sample sizes for the specific
respiratory diseases. The effect
estimates for respiratory hospital
admissions tend to fall in the range of
5 to 15 percent per 25 µg/m3 PM2.5.12 In
addition, several studies have reported
positive, statistically significant
associations between exposure to PM2.5
and emergency department visits for
respiratory diseases. The effect
estimates for these associations range up
to about 25 percent per 25 µg/m3 PM2.5
(EPA, 2005a, pp. 3–20, 3–21).
both respiratory symptom incidence and
decreased lung function (EPA, 2004,
Section 8.4.6.4).
iii. Cardiovascular Morbidity
In the last review, none of the
available studies had evaluated
associations between exposure to PM
and cardiovascular morbidity, though
some studies had reported associations
with cardiopulmonary morbidity. In this
area, the evidence on PM-related effects
has been greatly expanded. Numerous
recent studies, including multi-city
analyses, have reported significant
associations between short-term
exposures to PM and health endpoints
related to cardiovascular morbidity,
including hospitalization or emergency
department visits for cardiovascular
diseases, incidence of myocardial
infarction, cardiac arrhythmia, changes
in heart rate or heart rate variability and
changes in cardiac health indicators
such as fibrinogen or C-reactive protein
(EPA, 2004, section 9.2.3.2.1).
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(b) Respiratory Symptoms and Lung
Function Changes
Associations between short-term
exposure to PM2.5 and symptoms in U.S.
and Canadian studies are presented in
Figure 1. As discussed in Section 8.3.3
of the Criteria Document, a number of
new studies have reported significant
associations between short-term
exposure to PM and increased
respiratory symptoms (e.g., cough,
wheeze, shortness of breath) and
decreased lung function in people with
asthma. In studies of nonasthmatic
subjects, there were generally positive
associations between short-term PM2.5
exposures and respiratory symptoms
that often were not statistically
significant and the results for changes in
lung function were somewhat
inconsistent. The Criteria Document
concludes that the findings of these
studies suggest associations with fine
PM in reduced lung function and
increased respiratory symptoms. For
example, significant associations were
reported between ambient PM2.5 and
lower respiratory symptoms in children
in a number of U.S. cities (Schwartz and
Neas, 2000), and significant associations
were found with reduced lung function
in Philadelphia (Neas et al., 1999).
These findings are supported by results
from numerous studies conducted in
Europe and Central and South America.
The Criteria Document finds that the
recent epidemiologic findings are
consistent with those of the previous
review in showing associations with
(a) Hospital Admissions and Emergency
Department Visits for Cardiovascular
Diseases
Several recent studies, including
multi-city analyses, have reported
significant associations between shortterm exposures to various PM indicators
and hospital admissions or emergency
department visits for cardiovascular
diseases. Among the studies using PM2.5
measurements are a number of singlecity analyses of hospitalization or
emergency department visits for
cardiovascular diseases. As shown in
Figure 1, studies conducted in Los
Angeles, Toronto and Detroit have
reported associations with hospital
admissions or emergency department
visits for all cardiovascular diseases that
are positive and statistically significant
or nearly so (Burnett et al., 1997; Ito,
2003; Moolgavkar, 2003). As was true
for respiratory diseases, the results for
specific diseases (ischemic heart
disease, dysrhythmia, congestive heart
disease or heart failure, and stroke) are
positive but often not statistically
significant. The effect estimates reported
for associations with hospitalization for
cardiovascular diseases range from
about 1 to 10 percent per 25 µg/m3 PM2.5
(EPA, 2004, p. 8–310); effect estimates
reported for associations with
emergency department visits are
generally somewhat larger.
12 Some studies have evaluated seasonal variation
in effects, and no consistent pattern is apparent in
the results. For example, stronger associations were
reported between PM2.5 and asthma hospitalization
in the warmer season in Seattle (Sheppard et al.,
2003) but in the cooler season in Los Angeles
(Nauenberg and Basu, 1999).
(b) Cardiovascular Health Indicators
In addition to the greatly expanded
body of evidence on hospitalization or
emergency department visits for
cardiovascular diseases, new
epidemiologic studies have also
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reported associations with more subtle
physiological changes in the
cardiovascular system with short-term
exposures to PM, particularly PM10 and
PM2.5 (EPA, 2004, p. 9–67). Associations
between short-term exposures to
ambient PM (often using PM10) have
been reported with measures of changes
in cardiac function such as arrhythmia,
alterations in electrocardiogram (ECG)
patterns, heart rate or heart rate
variability changes, although the
Criteria Document urges caution in
drawing conclusions regarding the
effects of PM on heart rhythm,
recognizing the need for further research
to more firmly establish and understand
links between particles and these more
subtle endpoints. Recent studies have
also reported increases in blood
components or biomarkers such as
increased levels of C-reactive protein
and fibrinogen. Several of these studies
report significant associations between
various cardiovascular endpoints and
short-term PM2.5 exposures, including
one in which statistically significant
associations were reported between
onset of myocardial infarction and
short-term PM2.5 exposures averaged
over 2 and 24 hours (EPA, 2004, p. 8–
165; Peters et al., 2001). In this study,
the effect estimates for the two
averaging periods are quite similar in
magnitude suggesting that for certain
health outcomes very short-term fine
particle concentration fluctuations are
important (EPA, 2004, p. 9–42; Peters et
al., 2001). These new epidemiologic
findings provide important insight into
potential biologic mechanisms that
could underlie associations between
short-term PM exposure and
cardiovascular mortality and
hospitalization that have been reported
previously.
b. Effects Associated With Long-Term
Exposure to Fine Particles
In the last review, results were
available from several cohort studies
that suggested associations between
long-term exposure to PM (using various
indicators) and both mortality and
respiratory morbidity. Two studies of
adult populations (the Six Cities and
ACS studies) reported associations
between increases in mortality and longterm exposure to PM2.5, and results of a
24-city study indicated that long-term
exposure to fine particles was associated
with increased respiratory illness in
children.
As discussed below, the new evidence
available in the current review includes
an extensive reanalysis of data from the
Six Cities and ACS studies, new
analyses using updated data from the
ACS and California Seventh Day
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Adventist (AHSMOG) studies, and a
new analysis using data from a cohort
of veterans. In addition, new studies
have been published on the association
between long-term exposure to fine
particles and respiratory morbidity
using data from a cohort of
schoolchildren in Southern California.
In general, the newly available evidence
has supported earlier findings, and the
results of reanalyses have increased
confidence in the associations reported
in previous prospective cohort studies.
i. Mortality
In the 1996 Criteria Document,
statistically significant associations
between long-term exposure to both
PM2.5 and sulfates and mortality were
reported in studies from the Six Cities
and ACS cohorts (Dockery et al., 1993;
Pope et al., 1995). These studies
reported effect estimates of 6.6 percent
(95 percent CI: 3.5, 9.8) increases in
total mortality per 10 µg/m3 PM2.5 in the
ACS study and 13 percent (95 percent
CI: 4.2, 23) increases in total mortality
per 10 µg/m3 PM2.5 in the Six Cities
study, with somewhat larger effect
estimates reported for cardiopulmonary
mortality (EPA, 2004, p. 8–117). A
number of reviewers raised questions
about the adequacy of adjustments for
potential confounders and other issues
(61 FR 65642, December 13, 1996).
Subsequently, as discussed in more
detail in Section 8.2.3 of the Criteria
Document, the Health Effects Institute
conducted a major reanalysis of the data
from the Six Cities and ACS studies by
a group of independent investigators to
address questions and uncertainties
raised about these prospective cohort
studies. The reanalysis included two
major components, a replication and
validation study and a sensitivity
analysis. In the first part of the
reanalysis, the investigators validated
the data used by the original
investigators in both studies, and they
were able to replicate the original
results. The results confirmed the
original investigators’ findings of
associations with both total and
cardiorespiratory mortality, and the
authors reported that the results were
not dependent on the computer
programs used in the original analyses
(EPA, 2004, p. 8–91; Krewski et al.,
2000, p. 91).
The second component of the
reanalysis project evaluated an array of
different models and variables to
determine whether the original results
would remain robust to different
analytic assumptions. This included
controlling for other individual level
variables, such as cigarette smoking,
alcohol consumption, obesity and
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occupational exposures to dusts or other
pollutants, and evaluation of the
sensitivity of results to the addition of
a range of additional city-level variables
such as population change, income,
education levels, and access to health
care. The sensitivity analysis included
assessment of effects in different
subgroups of the population. The
investigators also evaluated the
sensitivity of the results to the inclusion
of gaseous co-pollutants, and tested the
effects of different statistical modeling
approaches, including methods to adjust
for spatial patterns, such as the
correlation in pollutant levels between
cities.
The authors found that adjustment for
individual-level variables did not alter
the results for the association between
long-term PM2.5 or sulfate exposure and
mortality (Krewski et al., 2000, p. 218).
In addition, in most (but not all) cases
the associations between mortality and
long-term exposure to PM2.5 and sulfates
were unchanged when additional citylevel variables were added to the
models (Krewski et al., 2000, p. 233).
Analyses to assess the potential
modification of effects in different
subgroups of the population found, for
the most part, little difference in effects
for different subgroups. However,
education level was found to modify the
estimated effect of fine particles, in that
associations were statistically
significant for those subgroups with
lower education levels, whereas the
effect estimates from associations for the
subgroup with better than high school
education were appreciably smaller and
were statistically insignificant. The
authors suggest that educational
attainment may be a marker for lower
socioeconomic status and thus greater
vulnerability to fine particle-related
effects (EPA, 2004, p. 8–94; Krewski et
al., 2000, p. 232).13
In single-pollutant models, none of
the gaseous co-pollutants was
significantly associated with mortality
except SO2. Further reanalysis included
multi-pollutant models with the gaseous
pollutants, and the associations between
mortality and both fine particles and
sulfates were unchanged in these
models, except when SO2 was included,
which decreased the size of the effect
estimates for PM2.5 to one-sixth of its
13 In multivariate models, the association found
between mortality and long-term PM2.5 exposure
was little changed with addition of education level
to the model (Krewski et al., 2000, p. 184). This
indicates that education level was not a confounder
in the relationship between fine particles and
mortality, but the relationship between fine
particles and mortality is larger in the population
subsets with lower education in this study and not
statistically significant in the population subset
with the highest education (EPA, 2004, p. 8–100).
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original value and for sulfates to less
than one-third of its original value (EPA,
2004, p. 8–136; Krewski et al., 2000, pp.
183–184).14 However, the regional
association of SO2 and PM2.5 was
relatively high, such that the effects of
the separate pollutants could not be
distinguished. The authors conclude
that these findings support the notion
that increased mortality may be
attributable to more than one
component of ambient air pollution, and
that throughout the reanalyses, fine
particles, sulfates, and SO2
demonstrated positive associations with
mortality (Krewski et al., 2000, p. 233–
234). As discussed more generally in the
Criteria Document, this result may be
reflecting the relatively high correlation
between PM2.5 levels and SO2 levels that
would be expected in cities across the
industrial Midwest and northeastern
states, the role that SO2 has as a
precursor to sulfate components in the
mix of PM2.5, and/or the likelihood that
SO2 is part of the causal pathway
linking exposure to PM2.5 to adverse
health outcomes (EPA, 2004, section
8.1.3.2).
Finally, Krewski and colleagues used
several methods to address spatial
patterns in the data; for example,
concentrations of air pollutants may be
correlated between cities within a
region. These analyses were primarily
based on sulfate concentrations, since
more cities had data for sulfates than for
fine particles. Addressing spatial
patterns in the data generally reduced
the size of the association between
sulfates and mortality, but the models
all continued to show associations
between mortality risk and long-term
sulfate exposures, although not all were
statistically significant (Krewski et al.,
2000, p. 228). Overall, considering the
results of the extensive set of replication
and sensitivity analyses, the authors
report that the reanalysis confirmed the
association between mortality and fine
particle and sulfate exposures (EPA,
2004, p. 8–95; Krewski et al., 2000).
In addition, extended analyses were
conducted for the ACS cohort study that
included follow-up health data and air
quality data from the new fine particle
14 For a 24.5 µg/m3 change in PM , the relative
2.5
risk for the association between mortality and PM2.5
alone was 1.20 (95 percent CI: 1.11–1.29), and after
adjustment for SO2 it was 1.03 (95 percent CI: 0.95–
1.13). The relative risk for SO2 alone was 1.49 (95
percent CI: 1.36–1.64) and after adjustment for
PM2.5 was 1.46 (95 percent CI: 1.32–1.63) (Krewski
et al., 2000, p. 184). The relative risk for sulfates
alone was 1.28 (95 percent CI: 1.18–1.40) and after
adjustment for SO2 it was 1.14 (95 percent CI: 1.04–
1.25) (Krewski et al., 2000, p. 184). These relative
risks for PM2.5 are equivalent to effect estimates of
7.5 percent and 1.2 percent increases in mortality
per 10 µg/m3, in single-pollutant and two-pollutant
models, respectively.
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monitoring network for 1999–2000. In
this study of the expanded ACS cohort,
significant associations were reported
between long-term exposure to fine
particles (using various averaging
periods for air quality concentrations)
and premature mortality from all causes,
cardiopulmonary diseases, and lung
cancer (Pope et al., 2002; EPA, 2004, 8–
102). This extended analysis included
the use of more recent data on fine
particle concentrations, as well as data
on gaseous co-pollutant concentrations,
though no multi-pollutant model results
are presented. Further evaluation of the
influence of other covariates (e.g.,
dietary intake data, occupational
exposure) used methods similar to those
in the reanalysis described above, and
new statistical approaches were used for
modeling the PM-mortality relationship
as well as adjusting for spatial
correlation (EPA, 2004, section
8.2.3.2.2). The investigators reported
that the associations found with fine
particle and sulfate concentrations were
not markedly affected by adjustment for
numerous socioeconomic variables,
demographic factors, environmental
variables, indicators of access to health
services or personal health variables
(e.g., dietary factors, alcohol
consumption, body mass index). Similar
to the results of Krewski et al. (2000),
education level was found to be a
modifier in the relationship between
fine particles and mortality, in that
associations were statistically
significant for those subgroups with
lower education levels, whereas effect
estimates from associations for those
with better than a high school education
were close to zero and were statistically
insignificant.
There are also new analyses using
updated data from the AHSMOG cohort.
These include estimated PM2.5
concentrations from visibility data,
along with new health information from
continued follow-up of the Seventh Day
Adventist cohort. Positive associations
were reported for mortality with PM2.5
in males, but the estimates were
generally not statistically significant
(Abbey et al., 1999; McDonnell et al.,
2000; EPA, 2004, pp. 8–110 and 8–117).
In addition, one new set of analyses was
done using subsets of PM exposure and
mortality time periods and data from a
Veterans Administration (VA) cohort of
hypertensive men. The investigators
report inconsistent and largely
nonsignificant associations between PM
exposure (including, depending on
availability, TSP, PM10, PM2.5, PM15 and
PM15-2.5) and mortality (EPA, 2004, pp.
8–110 to 8–111; Lipfert et al., 2000b).
The Criteria Document and Staff
Paper place greatest weight on the
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findings of the Six Cities and ACS
studies (including reanalyses and
extended analyses) that include
measured fine particle data (in contrast
with AHSMOG effect estimates based on
TSP or visibility measurements), have
study populations more similar to the
general population than the VA study
cohort, and have been replicated and
examined through exhaustive reanalysis
(EPA, 2005a, at 5–22; see also EPA,
2004, at 8.2.3.2.5.). In these studies,
effect estimates for deaths from all
causes fall in a range of 6 to 13 percent
increased risk per 10 µg/m3 PM2.5, while
effect estimates for deaths from
cardiopulmonary causes fall in a range
of 6 to 19 percent per 10 µg/m3 PM2.5.
For lung cancer mortality, the effect
estimate was a 13 percent increase per
10 µg/m3 PM2.5 in the results of the
extended analysis from the ACS cohort
(Pope et al., 2002; CD, Table 8–12).
The prospective cohort studies have
used air quality measurements averaged
over long periods of time, such as
several years, to characterize the longterm ambient levels in the community.
The exposure comparisons are basically
cross-sectional in nature, and do not
provide evidence concerning any
temporal relationship between exposure
and effect (EPA, 2004, p. 9–42). As
discussed in the Criteria Document, it is
not easy to differentiate the role of
historic exposures from more recent
exposures, leading to potential exposure
measurement error that is increased if
average PM concentrations change over
time differentially between areas (EPA,
2004, p. 5–118). Several new studies
have used different air quality periods
for estimating long-term exposure and
tested associations with mortality for
the different exposure periods. As
discussed in section 3.6.5.4 of the Staff
Paper, these analyses indicate that
averaging PM concentrations over a
longer time period results in stronger
associations, and that the longer series
of data is likely a better indicator of
cumulative exposure. Thus, in
evaluating these findings, EPA has
focused on the results of analyses using
fine particle or sulfate measurements for
the longer exposure periods in the
studies.
et al., 1996). More specifically,
statistically significant associations
were reported between long-term
exposure to fine particles and decreases
in several measures of lung function
evaluated at a single point in time
(Raizenne et al., 1996). In addition,
positive but not statistically significant
associations were reported between
long-term exposure to fine particles and
prevalence of a range of respiratory
conditions (e.g., asthma, bronchitis,
chronic cough) (Dockery et al., 1996).
In the current review, new studies
conducted in the U.S. have been based
on data from cohorts of schoolchildren
in 12 Southern California Communities
and an adult cohort of Seventh Day
Adventists (AHSMOG) (EPA, 2004,
section 8.3.3.2). Information specifically
on associations with long-term PM2.5
exposures are available from the
Southern California children’s cohort
study. Early findings from crosssectional analyses done at the beginning
of the study suggested associations
between long-term PM2.5 exposures and
respiratory morbidity, but the findings
were generally not statistically
significant.15 Later publications from
this cohort have reported associations
with lung function growth in children
over four-year follow-up periods. In a
study of a cohort of children followed
from 4th to 7th grade, some measures of
decreases in lung function growth were
statistically significantly associated with
increasing exposure to PM2.5, whereas in
a second cohort of 4th graders, the
associations generally did not reach
statistical significance (Gauderman et
al., 2002). Decreases in measures of lung
function growth were also reported for
cohorts of older children, but the
associations did not reach statistical
significance (Gauderman et al., 2000).
The Criteria Document finds that these
studies ‘‘provide the best evidence’’ on
effects of long-term fine particle
exposure (EPA, 2004, p. 8–314).
However, this is the only cohort study
to have evaluated associations with
decreases in lung function growth in
children over time. Considered together,
the Criteria Document finds that the
evidence from these studies indicates
that long-term PM2.5 exposures may
ii. Respiratory Morbidity
In the last review, several studies had
reported that long-term PM exposure
was linked with increased respiratory
disease and decreased lung function.
One study, using data from 24 U.S. and
Canadian cities (‘‘24 Cities’’ study),
reported associations with these effects
and long-term exposure to fine particles
or acidic particles, but not with PM10
exposure (Dockery et al., 1996; Raizenne
15 In an initial report on the prevalence of
respiratory illnesses reported at the beginning of the
study, positive associations, though not statistically
significant, were reported between long-term PM2.5
exposure and risk of bronchitis and cough only in
the subset of children with asthma (McConnell et
al., 1999), and no significant associations with longterm PM2.5 exposure were reported for the full
cohort (Peters et al., 1999a). In addition, long-term
PM2.5 exposure was associated with decreases in
some lung function measurements made at that
time, but the associations were only statistically
significant for females (Peters et al., 1999b).
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3. Integration and Interpretation of the
Health Evidence
In evaluating the evidence from
epidemiologic studies, the Criteria
Document and Staff Paper focused on
well-recognized criteria, including the
strength of associations; robustness of
reported associations to the use of
alternative model specifications,
potential confounding by co-pollutants,
and exposure misclassification related
to measurement error; consistency of
findings in multiple studies of adequate
power, and in different persons, places,
circumstances and times; the nature of
concentration-response relationships;
and information from so-called natural
experiments or intervention studies.
These evaluations addressed key
methodological issues that are relevant
to interpretation of evidence from
epidemiologic studies. Further, findings
from epidemiologic studies were
integrated with experimental (e.g.,
dosimetric and toxicologic) studies, in
considering the extent of coherence and
biological plausibility of effects
observed in epidemiologic studies. This
integrative assessment provided the
basis for the judgments made in the
Criteria Document and Staff Paper about
the extent to which causal inferences
can be made about observed
associations between health endpoints
and PM2.5 (as well as other indicators or
constituents of ambient PM), acting
alone and/or in combination with other
pollutants. Key elements of these
evaluations are briefly summarized
below.
(1) For short-term exposures to fine
particles, in considering the magnitude
and statistical strength of the
associations, there is a pattern of
positive and often statistically
significant associations for
cardiovascular and respiratory health
outcomes with short-term exposure to
PM10 and PM2.5. Of particular note are
several multi-city studies that have
yielded relative risk estimates for
associations between short-term
exposure to various indices of PM and
mortality or morbidity. Although small
in size, the effect estimates from multicity studies have great precision due to
the statistical power of the studies. New
analyses of pre-existing cohorts with
studies of long-term exposure to fine
particles are available that confirm and
strengthen conclusions from the
previous review, although the effect
estimates are sensitive to education
level, co-pollutant effects of SO2, and
spatial correlation, as discussed above.
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(2) The Criteria Document and Staff
Paper have evaluated the robustness of
epidemiologic associations in part by
considering the effect of differences in
statistical model specification, potential
confounding by co-pollutants and
exposure error on PM-health
associations (EPA, 2004, section 9.2.2.2;
EPA, 2005a, sections 3.4.2 and 3.6).
As discussed in section 8.4.2 of the
Criteria Document and section 3.6.3 of
the Staff Paper, the influence of
alternative modeling strategies on
epidemiologic study results was
assessed, with a particular focus on the
recent set of analyses to address
statistical modeling questions in
epidemiologic studies for short-term PM
exposures. Numerous recent studies
used a certain type of statistical method
(i.e., generalized additive methods
(GAM)) in widely used statistical
software (Splus), and it was discovered
that the default program settings could
potentially result in biased effect
estimates for associations between
pollutants and health outcomes. Results
from a number of epidemiologic studies
were reanalyzed to address this
problem. These reanalyses also more
broadly included the use of alternative
statistical models and alternative
methods of control for time-varying
effects, such as weather or season (HEI,
2003). In general, the results of the
reanalyses to address the use of default
program settings in the Splus software
showed little change in effect estimates
for some studies; in others the effect
estimates were reduced in size, though
it was observed that the reductions were
often not substantial (EPA, 2004, p. 9–
35). For example, in comparing results
for numerous studies of mortality
associations with PM10, the Criteria
Document found that the extent of
reduction in effect estimates resulting
from reanalysis was smaller than the
variation in effect estimate size across
studies (EPA, 2004, p. 8–229 and Figure
8–15). A review panel commentary on
the set of reanalysis studies (using
various PM indicators) notes that most
studies were considered to show ‘‘little
or no change’’ in results with initial
reanalyses to address questions about
the use of modeling specifications in the
statistical software package (HEI, 2003,
pp. 258–259).
In addition, the reanalyses also
refocused attention in general on the
control for relationships between health
effects and weather variables in timeseries epidemiologic studies; such
issues had been also discussed at length
in the 1996 Criteria Document (EPA,
2004, section 8.4.3.5). The reanalysis
results showed greater sensitivity to the
modeling approach used to account for
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temporal effects and weather variables
than to correcting the initial problem
with default settings in the use of GAM
in Splus software (EPA, 2004, p. 8–236).
For example, in the review panel
commentary, sixteen of the reanalyzed
studies were considered to have ‘‘little
or no change’’ in results of initial
reanalyses, while only two studies
showed ‘‘substantial’’ changes (Goldberg
and Burnett, 2003; some results in Ito,
2003; HEI, 2003, pp. 258–259). In
contrast, four of the eight studies that
were reanalyzed with additional
methods to adjust for time-related
variables were considered to show
‘‘substantial’’ changes in effect estimate
size (HEI, 2003, p. 262).
The recent time-series epidemiologic
studies evaluated in the Criteria
Document have included some degree of
control for variations in weather and
seasonal variables. As summarized in
the HEI review panel commentary,
selecting a level of control to adjust for
time-varying factors, such as
temperature, in time-series
epidemiologic studies involves a tradeoff. 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 (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
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. While recognizing the need
for further exploration of alternative
modeling approaches for time-series
analyses, the Criteria Document found
that the studies included in this part of
the reanalysis in general continued to
demonstrate associations between PM
and mortality and morbidity beyond
those attributable to weather variables
alone (EPA, 2004, pp. 8–340, 8–341).
Further, considering the full set of
reanalyses, the Criteria Document
concludes that associations between
short-term exposure to PM and various
health outcomes are generally robust to
the use of alternative modeling
strategies, again recognizing that further
evaluation of alternative modeling
strategies was warranted (EPA, 2004, p.
9–48).
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For long-term exposure to fine
particles, the reanalysis and extended
analyses of data from prospective cohort
studies, discussed above in section
II.A.2, have shown that reported
associations between mortality and
long-term exposure to fine particles are
robust to alternative modeling strategies
(Krewski et al., 2000). As stated in the
reanalysis report, ‘‘The risk estimates
reported by the Original Investigators
were remarkably robust to alternative
specifications of the underlying risk
models, thereby strengthening
confidence in the original findings’’
(Krewski et al., 2000, p. 232). In
extended analysis, Krewski et al. (2000)
identified model sensitivities related to
education level and spatial correlation,
as well as to co-pollutant effects of SO2,
as discussed below.
The Criteria Document also included
extensive evaluation of the sensitivity of
PM-health responses to confounding by
gaseous co-pollutants (EPA, 2004,
section 8.4.3, Figures 8–16 to 8–19).
Results of new multi-city short-term
exposure studies, that combine data
from locations with different mixes of
pollutants, provide important new
results. Using PM10, the NMMAPS
results indicated that associations with
mortality were not confounded by copollutant concentrations across 90 U.S.
cities (Dominici, 2003),16 and a similar
lack of confounding was observed in a
mortality study across 10 U.S. cities
(Schwartz, 2003b) (EPA, 2004, Figure 8–
16). That is, in these studies, the size of
the effect estimates are little changed
and the associations remain statistically
significant in multi-pollutant models
including one or more of the gaseous copollutants. Similar results are seen in
some single-city studies using PM2.5 for
some health outcomes in which the
single-pollutant model association was
statistically significant (EPA, 2004,
Figures 8–16 to 8–18), including the
association with mortality in Santa
Clara County, CA (Fairley, 2003);
associations with hospital admissions in
Detroit (for heart failure and pneumonia
in Ito, 2003) and Seattle (for asthma in
Sheppard et al., 2003); and associations
with cardiovascular-related biomarkers
in Boston (Gold et al., 2000). The size
of the effect estimates were little
changed in other studies as well in
which the single-pollutant model
associations were not statistically
significant (e.g., for some health
16 In the HEI Review Panel commentary on the
results of the NMMAPS multi-city analyses, the
Panel stated that the results did not show a
confounding effect of other pollutants, observing
that the PM10 effects on mortality were not changed
by addition of either O3, SO2, NO2 or CO to the
models (HEI, 2000, p. 77).
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outcomes in Ito, 2003; for mortality in
Chock et al., 2000). In yet other studies,
however, for some combinations of
pollutants in some areas, substantial
reductions in the size of the effect
estimates for PM2.5 were observed;
notably, Moolgavkar (2003) reports
substantial reductions in effect
estimates when CO is included in
models for mortality and hospitalization
in Los Angeles, and Thurston et al.
(1994) and Delfino et al. (1998) report
substantial reductions when O3 is
included in models for hospital
admissions in Toronto and emergency
department visits in Montreal,
respectively.17 It is recognized that
collinearity between co-pollutants can
make interpretation of such multipollutant model results difficult (EPA,
2004, p. 8–253). Further, associations
between long-term exposure to PM2.5
and mortality were not generally
sensitive to inclusion of co-pollutants,
with the notable exception of the
inclusion of SO2 in multipollutant
models used in the reanalysis of the
ACS study, as discussed above in
section II.A.2 (EPA, 2004, p. 8–136).
Overall, the Criteria Document
concluded that these studies indicate
that effect estimates for associations
between mortality and morbidity and
various PM indices are generally robust
to confounding by co-pollutants, while
recognizing that disentangling the
effects attributable to various pollutants
within an air pollution mixture is
challenging (EPA, 2004, p. 9–37).
Finally, as discussed in section 3.6.2,
a number of recent studies have
evaluated the influence of exposure
error on PM-health associations. This
includes both consideration of error in
measurements of PM and other copollutants, and the degree to which
measurements from an individual
monitor reflect exposures to the
surrounding community. As further
discussed in section 3.6.2, several
studies have shown that fairly extreme
conditions (e.g., very high correlation
between pollutants and no measurement
error in the ‘‘false’’ pollutant) are
needed for complete ‘‘transfer of
causality’’ of effects from one pollutant
to another (EPA, 2004, p. 9–38). In
comparing fine and thoracic coarse
particles, the Criteria Document
observes that exposure error is likely to
be more important for associations with
PM10-2.5 than with PM2.5, since there is
generally greater error in PM10-2.5
17 The correlation coefficients between
concentrations of PM2.5 and the noted co-pollutants
in these studies were high; the coefficient with CO
in Los Angeles was 0.58, and the coefficients with
O3 were 0.58 and 0.72 in Montreal and Toronto,
respectively.
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measurements, PM10-2.5 concentrations
are less evenly distributed across a
community, and less likely to penetrate
into buildings (EPA, 2004, p. 9–38).
Therefore, while the Criteria Document
concludes that associations reported
with PM10, PM2.5 and PM10-2.5 are
generally robust, it recognizes that
factors related to exposure error may
result in reduced precision for
epidemiologic associations with PM10-2.5
(EPA, 2004, p. 9–46).
(3) Consistency refers to the persistent
finding of an association between
exposure and outcome in multiple
studies of adequate power in different
persons, places, circumstances and
times (CDC, 2004). The 1996 Criteria
Document reported associations
between short-term PM exposure and
mortality or morbidity from studies
conducted in locations across the U.S.
as well as in other countries, and
concluded that the epidemiologic data
base had ‘‘general internal consistency’’
(EPA, 1996a, p. 13–30). New multi-city
studies have allowed evaluation of
consistency in effect estimates across
geographic locations, using uniform
statistical modeling approaches; the
results suggest that effect estimates
differ from one location to another, but
the extent of variation is not clear. For
example, the Canadian 8-city study
reported no evidence of heterogeneity in
city-specific results in the initial study
findings; however, in the reanalysis to
address model specification issues, the
findings suggested more evidence of
heterogeneity in associations between
mortality and short-term PM2.5 exposure
(Burnett and Goldberg, 2003; EPA, 2004,
p. 9–39). The Criteria Document
discussed a number of factors that
would be likely to cause variation in
PM-health outcomes in different
populations and geographic areas in
section 9.2.2.3, including indicators of
exposure to traffic-related pollution,
population characteristics that affect
susceptibility or exposure differences,
distribution of PM sources, or
geographic features that would affect the
spatial distribution of PM (EPA, 2004, p.
9–41). In addition, the use of data
collected on a 1-in-6 or 1-in-3 day
schedule results in reduced statistical
power, resulting in less precision for
estimated effect estimates for the
individual cities and increased potential
variability in results (EPA, 2004, p. 9–
40). Overall, the Criteria document
concluded that ‘‘[f]ocusing on the
studies with the most precision, it can
be concluded that there is much
consistency in epidemiologic evidence
regarding associations between shortterm and long-term exposures to fine
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particles and cardiopulmonary mortality
and morbidity.’’ (EPA, 2004, p. 9–47).
(4) The form of concentrationresponse relationships (e.g., linear,
sigmoid) and the potential existence of
thresholds was one of the important
research questions remaining in the
previous review. The Criteria Document
recognized that it is reasonable to expect
that there likely are biologic thresholds
for different health effects in individuals
or groups of individuals with similar
innate characteristics and health status
(EPA, 2004, Section 9.2.2.5). Individual
thresholds would presumably vary
substantially from person to person due
to individual differences in genetic-level
susceptibility and pre-existing disease
conditions (and could even vary from
one time to another for a given person).
Thus, it would be difficult to detect a
distinct threshold at the population
level, below which no individual would
experience a given effect, especially if
some members of a population are
unusually sensitive even down to very
low concentrations. The person-toperson difference in the relationship
between personal exposure to PM of
ambient origin and the concentration
observed at a monitor may also add to
the variability in observed
concentration-response relationships,
further obscuring potential population
thresholds within the range of observed
concentrations (CD, p. 9–43, 9–44).
Several new epidemiologic studies
have used different modeling methods
to address this question, and most have
been unable to detect threshold levels in
the relationship between short-term PM
exposure (generally using PM10) and
mortality; in fact, one single-city
analysis suggests that statistical
methods would allow detection of a
threshold in the epidemiologic data if a
clear threshold existed. However, a few
analyses in individual cities have
provided suggestions of some potential
threshold levels, generally at fairly low
ambient concentrations. One single-city
study used PM2.5 and PM10-2.5
measurements in Phoenix and reported
that there was suggestive evidence of a
threshold for the association between
mortality and short-term exposure to
PM2.5 in the range of 20–25 µg/m3
(Smith et al., 2000; EPA, 2004, p. 8–
322).
The shape of the concentrationresponse function for long-term
exposure to PM2.5 with mortality was
evaluated using data from the ACS
cohort. In the ACS reanalysis, the
authors report that the concentrationresponse functions for PM2.5 and allcause and cardiopulmonary mortality
demonstrate near-linear increasing
trends through the range of particle
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levels observed in the fine particle
cohort (Krewski, p. 160). However, the
HEI Review Committee concluded that
these results show no clear evidence
either for or against overall linearity
(Krewski, p. 265). In the extended ACS
study, the authors reported that the
associations for all-cause,
cardiovascular and lung cancer
mortality ‘‘were not significantly
different from linear associations’’
(Pope, et al., 2002).
Thus, evaluation of the health effects
data summarized in the Criteria
Document provides no evidence to
support selecting any particular
population threshold for PM2.5. The
Staff Paper also recognized, however,
that it is reasonable to expect that, for
individuals, there may be thresholds for
specific health responses and that it is
possible that such thresholds exist
toward the lower end of these ranges (or
below these ranges) but cannot be
detected due to variability in
susceptibility across a population. Even
in those few studies with suggestive
evidence of such thresholds, the
potential thresholds are at fairly low
concentrations (EPA, 2004, sections
8.4.7 and 9.2.2.5).
(5) Few studies are available that
assess the extent to which reductions in
ambient PM actually lead to reductions
in health effects attributable to PM. As
discussed in sections 8.2.3.4 and 9.2.2.6
of the Criteria Document, several
epidemiologic studies were done in the
Utah Valley area over a time period
when a major source of PM was closed,
resulting in markedly decreased PM10
concentrations. An epidemiologic study
reported that respiratory hospital
admissions decreased during the plant
closure time period (EPA, 2004, p. 8–
131; Pope et al., 1989). Newly available
controlled human exposure and animal
toxicology studies, using particles
extracted from stored PM10 sampling
filters from the Utah Valley, have shown
inflammatory responses that are greater
with extracts of particles collected
during the time period of source
operation than when the source was
closed, suggesting that the PM from the
steel mill was more harmful than other
ambient PM on an equal mass basis
(EPA, 2004, p. 9–73). Epidemiologic
studies in Dublin, Ireland and Hong
Kong also provides evidence for
reduced relative risks for mortality
when PM (measured as BS or PM10) and
SO2 were reduced as the result of
interventions aimed at reducing air
pollution. The Criteria Document
concluded that this small group of
studies add further support to the
results of the hundreds of other
epidemiologic studies linking ambient
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PM exposure to an array of health
effects, and provide strong evidence that
reducing emissions of PM and gaseous
pollutants has beneficial public health
impacts (EPA, 2004, p. 9–45 to 9–46).
(6) Several issues related to fine
particle exposure time periods were
assessed in the Criteria Document, as
summarized in section 3.6.5 of the Staff
Paper. As discussed above in this
section, these include the exposure time
periods used in long-term exposure
studies as well as health outcome
associations with very short time
periods (e.g., 2-hour average). An
additional issue is the time period
(‘‘lag’’) between fine particle exposure
and health outcome that is reported in
short-term exposure study results. In
these epidemiologic studies,
associations are often tested for a range
of lag periods, for example, with PM
concentrations from the same day as the
effect, and one or more days preceding
the effect. In evaluating these results, it
is important to consider the pattern of
results that is seen across the series of
lag periods. If there is an apparent
pattern of results across the different
lags, with positive associations reported
for a series of consecutive lag periods,
then selecting the single-day lag with
the largest effect from a series of
positive associations is likely to
underestimate the overall effect size,
since single-day lag effect estimates do
not fully capture the risk that may be
distributed over adjacent or other days
(EPA, 2004, sections 8.4.4 and 9.2.2.4).
For many epidemiologic studies, the
authors have reported just such a
pattern of associations across several
consecutive lag periods (EPA, 2004, p.
8–279). However, if there is no apparent
pattern or reported effects vary across
lag days, any result for a single day may
well be biased (CD, p. 9–42).
Some new studies have used a
‘‘distributed lag’’ model approach, that
captures an effect of PM over a series of
days following exposure.18 Where
effects are found for a series of lag
periods, a distributed lag model will
more accurately characterize the effect
estimate size. A number of recent
studies that have investigated
associations with distributed lags
provide effect estimates for health
responses that persist over a period of
time (days to weeks) after the exposure
period. Effect estimates from distributed
lag models are thus often, but not
always, larger in size that those for
single-day lag periods (EPA, 2004, p. 8–
281).
18 The available studies have generally used PM ,
10
but not PM2.5 or PM10-2.5.
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The Criteria Document concludes that
it is likely that the most appropriate lag
period for a study will vary depending
on the health outcome and the specific
pollutant under study. For example, for
a health outcome such as a delayed
asthma response, the lag period of a day
or several days might be expected
between exposure and outcome;
however, some cardiovascular responses
might be expected to occur within a
very short time period (e.g., an hour)
after exposure (EPA, 2004, p. 8–279). As
shown in Figures 8–24 to 8–28, the
Criteria Document notes a pattern of
stronger associations between PM10 and
mortality or cardiovascular
hospitalization with shorter lag periods
(e.g., same-day or 1-day lagged PM10).
For other effects, however, such as
respiratory symptoms, asthma
emergency department visits or
hospitalization, stronger effects were
reported with PM concentrations
averaged over several days (EPA, 2004,
pp. 8–273 to 8–279). Thus, the Criteria
Document concludes that one would
expect to see different best-fitting lags
for different health effects, based on
potentially different biological
mechanisms as well as individual
variability in responses (EPA, 2004, p.
8–342). For some health outcomes, it is
reasonable to expect associations to be
observed with PM exposures on the
same day or with very short lag periods,
but not longer lag periods. In other
cases, multi-day average exposure
periods or distributed lag models would
more appropriately estimate potential
PM-related health risks.
(7) Looking more broadly to integrate
epidemiologic evidence with that from
exposure-related, dosimetric and
toxicologic studies, EPA has considered
the coherence of the evidence and the
extent to which the new evidence
provides insights into mechanisms by
which PM, especially fine particles, may
be affecting human health. Progress
made in gaining insights into potential
mechanisms lends support to the
biologic plausibility of results observed
in epidemiologic studies. For
cardiovascular effects, the convergence
of important new epidemiologic and
toxicologic evidence (especially from
studies using concentrated ambient
particles) builds support for the
plausibility of causal associations,
especially between fine particles and
physiological endpoints indicative of
increased risk of cardiovascular disease
and changes in cardiac rhythm. This
finding is supported by new
cardiovascular effects research focused
on fine particles that has notably
advanced our understanding of
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potential mechanisms by which PM2.5
exposure, especially in susceptible
individuals, could result in changes in
cardiac function or blood parameters
that are risk factors for cardiovascular
disease. For respiratory effects,
toxicologic studies have provided
evidence that supports plausible
biologic pathways for fine particles,
including inflammatory responses,
increased airway responsiveness, or
altered responses to infectious agents.
Further, coherence across a broad range
of cardiovascular and respiratory health
outcomes is supported by evidence from
epidemiologic and toxicologic studies
done in the same location, for example,
in the series of studies conducted in or
evaluating ambient PM from Boston and
the Utah Valley (EPA, 2004, 7–42 to 43,
7–46 to 47, and 9–45). Toxicologic
studies have suggested that some
combustion-related particles, including
particles from wood burning and diesel
engine exhaust, but not others such as
coal fly ash, may have carcinogenic
effects (EPA, 2004, Section 7.8.4). This
evidence supports the plausibility of the
observed relationship between fine
particles and lung cancer mortality.
Evidence for PM-related infant mortality
and developmental effects poses an
emerging concern, but the current
information is still very limited in
support of the plausibility of potential
ambient PM relationships. More
generally, toxicologic animal studies
often test effects of exposures to
individual chemical components, and
thus the physical and chemical
characteristics may differ from those of
particles in ambient air to which
humans are exposed. These and other
differences in toxicologic and
epidemiologic study designs complicate
the assessment of coherence in results
from across disciplines (EPA, 2004,
section 9.2.3.1; Schlesinger and Cassee,
2003).
Overall, the Criteria Document finds
that much more evidence is now
available related to the coherence and
plausibility of effects than in the last
review. For short-term exposures,
integration of evidence from
epidemiologic and toxicologic studies
indicates both coherence and
plausibility of effects on the
cardiovascular and respiratory systems,
especially for fine particles (EPA, 2004,
p. 9–79). There is evidence supporting
coherence and plausibility for the
observed associations between longterm exposures to fine particles and
lung cancer mortality (EPA, 2004, p. 9–
78).
(8) In summary, as discussed in the
Staff Paper (section 3.5) and the Criteria
Document (section 9.2.2), the extensive
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body of epidemiologic evidence now
available continues to support likely
causal associations between PM2.5 and a
broad range of mortality and morbidity
health outcomes based on an assessment
of the strength of the evidence,
including the strength and robustness of
reported associations and the
consistency of the results. While the
limitations and uncertainties in the
available evidence suggest caution in
interpreting the epidemiologic studies at
the lower levels of air quality observed
in the studies, the evidence now
available provides strong support that
both short-term and long-term
exposures to fine particles are plausibly
associated with a broad range of effects
on the respiratory and cardiovascular
systems. The Criteria Document
concludes: ‘‘the epidemiological
evidence continues to support likely
causal associations between PM2.5 and
PM10 and both mortality and morbidity
from cardiovascular and respiratory
diseases, based on an assessment of
strength, robustness, and consistency in
results.’’ (EPA, 2004, p. 9–48). In its
integrative assessment, the Criteria
Document finds that health evidence
from various disciplines provides a
strong and coherent basis for concluding
that both short-term and long-term
exposure to fine particles is associated
with health effects ranging from subtle
changes in lung function to premature
mortality.
4. Sensitive Subgroups for PM2.5-Related
Effects
As described in the PM Criteria
Document, the term susceptibility refers
to innate (e.g., genetic or
developmental) or acquired (e.g.,
personal risk factors, age) factors that
make individuals more likely to
experience effects with exposure to
pollutants. A number of population
subgroups have been identified as
potentially susceptible to health effects
as a result of PM exposure, including
people with existing heart and lung
diseases, including diabetes, and older
adults and children. In addition, new
attention has been paid to the concept
of some population groups having
increased vulnerability to pollutionrelated effects due to factors such as
socioeconomic status or factors that
result in particularly elevated exposure
levels, such as residence near sources
such as roadways (EPA, 2004, p. 9–81).
A good deal of evidence indicates that
people with existing heart or lung
diseases are more susceptible to PMrelated effects. In addition, new studies
have suggested that people with
diabetes, who are at risk for
cardiovascular disease, may have
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increased susceptibility to PM
exposures. As discussed in Section
9.2.4.1 of the Criteria Document, this
body of evidence includes findings from
epidemiologic studies that associations
with mortality or morbidity are greater
in those with preexisting conditions, as
well as evidence from toxicologic
studies using animal models of
cardiopulmonary disease. In addition,
dosimetric evidence indicates that
deposition of particles is increased, and
can be focused in ‘‘hot spots’’ in the
respiratory tract, in people with chronic
respiratory diseases.
Two age groups, older adults and the
very young, are also potentially at
greater risk for PM-related effects.
Epidemiologic studies have generally
not shown striking differences between
adult age groups. However, some
epidemiologic studies have suggested
that serious health effects, such as
premature mortality, are greater among
older populations (EPA, 2005a, p. 8–
328). In addition, preexisting respiratory
or cardiovascular conditions are more
prevalent in older adults than younger
age groups; thus there is some overlap
between potentially susceptible groups
of older adults and people with heart or
lung diseases.
Epidemiologic evidence has reported
associations with emergency hospital
admissions for respiratory illness and
asthma-related symptoms in children.
Several factors may make children
susceptible to PM-related effects,
including the greater ventilation rate per
kilogram body weight in children,
greater prevalence of chronic asthma,
and the fact that children are more
likely to be active outdoors and thus
have greater exposures. In addition,
there is a more limited body of new
evidence from epidemiologic studies for
potential PM-related health effects in
infants, using various PM indicators.
Results from this body of evidence,
though mixed, are suggestive of possible
effects; more research is needed to
further elucidate the potential risks of
PM exposure for these health outcomes
(EPA, 2004, p. 8–222).
In summary, there are several
population groups that may be
especially susceptible or vulnerable to
PM-related effects. These groups
include those with preexisting heart and
lung diseases, older adults and children.
Emerging evidence indicates that people
from lower socioeconomic strata or who
have particularly elevated exposures
may be more vulnerable to PM-related
effects.
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5. PM2.5-Related Impacts on Public
Health
As just discussed, there are several
population groups that may be
especially susceptible or vulnerable to
effects from exposure to PM. These
population subgroups, such as young
children or older adults, and people
with pre-existing heart or lung diseases,
constitute a large portion of the U.S.
population. For example, approximately
22 million people, or 11 percent of the
U.S. population, have received a
diagnosis of heart disease, about 20
percent of the population has
hypertension and about 9 percent of
adults and 11 percent of children in the
U.S. have been diagnosed with asthma.
In addition, about 26 percent of the U.S.
population is under 18 years of age,19
and about 12 percent is 65 years of age
or older (EPA, 2004, Table 9–4). EPA
recognizes that combining fairly small
risk estimates and small changes in PM
concentrations with large groups of the
U.S. population would result in large
public health impacts.
One issue that is important for
interpreting the public health
implications of the associations reported
between mortality and short-term
exposure to PM is whether mortality is
occurring only in very frail individuals
(sometimes referred to as ‘‘harvesting’’),
resulting in loss of just a few days of life
expectancy. A number of new analyses
assess the likelihood of such
‘‘harvesting’’ occurring in the short-term
exposure studies. Overall, the Criteria
Document concludes from the timeseries studies that there appears to be no
strong evidence to suggest that shortterm exposure to PM is only shortening
life by a few days (EPA, 2004, Section
8.4.10). In addition to the evidence from
short-term exposure studies discussed
above, one new report used the
mortality risk estimates from the ACS
prospective cohort study to estimate
potential loss of life expectancy from
PM-related mortality in a population.
The authors estimated that the loss of
population life expectancy associated
with long-term exposure to PM2.5 was
on the order of a year or so (EPA, 2004,
p. 8–334). The Criteria Document
recognizes that these calculations were
based on studies in adult populations,
and potential population life shortening
would be increased if the new, albeit
limited, evidence from infant mortality
studies was considered (EPA, 2004, p.
8–335). The Criteria Document also
observes that the risk estimates reported
for long-term fine particle exposures
and lung cancer mortality are in about
the same range as the risk seen for a
nonsmoker living with a smoker (EPA,
2004, p. 9–94).
Large subgroups of the U.S.
population are included in
subpopulations considered to be
potentially sensitive to effects related to
fine particle exposures (EPA, 2004,
section 9.2.5.1). While individual
epidemiologic effect estimates may be
small in size, the public health impact
of the mortality and morbidity
associations can be quite large. In
addition, it appears that mortality risks
are not limited to the very frail. Taken
together, these results suggest that
exposure to ambient PM, especially
PM2.5, can have substantial public
health impacts (EPA, 2004, p. 9–93).
19 Health studies that have suggested that
children are susceptible to PM-related effects
include varying age ranges, for example, for
hospital admissions in children up to 18 years of
age, or respiratory symptoms in panels of 4th and
5th grade children.
20 The methodology, scope, and results from the
risk assessment conducted in the last review are
described in Chapter 6 of the 1996 Staff Paper (EPA,
1996b) and in several technical reports (Abt
Associates, 1996; Abt Associates, 1997a,b) and
publications (Post et al., 2000; Deck et al., 2001).
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B. Quantitative Risk Assessment
This section discusses the approach
used to develop quantitative risk
estimates associated with exposures to
PM2.5 building upon a more limited risk
assessment that was conducted during
the last review.20 At that time, EPA
conducted a very limited risk
assessment covering a portion of two
cities (i.e., Philadelphia County and
Southeast Los Angeles County) for
which ambient PM2.5 data were
available. For short-term exposure
mortality and morbidity health effects,
the prior assessment relied on either
pooled analyses that combined the
results from several studies of
individual cities or individual singleand multi-city studies, none of which
included the two urban counties for
which risks were estimated, to estimate
concentration-response relationships for
these two cities. EPA recognized that
the lack of city-specific relative risks
introduced substantial uncertainties in
the risk estimates due to inherent
differences (e.g., different population
characteristics, PM size distributions)
that might influence the concentrationresponse relationships. For long-term
exposure mortality, the prior assessment
relied on the concentration-response
relationship reported in the original
ACS study (Pope et al., 1995).
Additional important uncertainties
noted at the time of that assessment
with respect to all health effects
included: (1) The absence of clear
evidence regarding mechanisms of
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action for the various effects of interest,
(2) uncertainties about the shape of the
concentration-response relationships;
and (3) concern about whether the use
of ambient PM2.5 fixed-site monitoring
data adequately reflected the relevant
population exposures to PM that are
responsible for the reported health
effects (61 FR 65650).
In light of the substantial
uncertainties in the prior risk estimates,
EPA placed greater weight on the
overall conclusions derived from the
health effect studies—that ambient PM
was likely causing or contributing to
significant adverse effects at levels
below those permitted by the thenexisting PM10 standards—than on the
specific concentration-response
functions and quantitative risk estimates
derived from them. Nevertheless, EPA
judged that the assessment provided
reasonable estimates as to the possible
extent of risk for those effects given the
available information (62 FR at 38656).
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1. Overview
The updated risk assessment
conducted as part of this review
includes estimates of (1) risks of
mortality, morbidity, and symptoms
associated with recent ambient PM2.5
levels; (2) risk reductions and remaining
risks associated with just meeting the
current suite of PM2.5 NAAQS; and (3)
risk reductions and remaining risks
associated with just meeting various
alternative PM2.5 standards in a number
of example urban areas. This risk
assessment is more fully described and
presented in the Staff Paper (EPA,
2005a, Chapter 4) and in a technical
support document, Particulate Matter
Health Risk Assessment for Selected
Urban Areas (Abt Associates, 2005a).
The scope and methodology for this risk
assessment were developed over the last
few years with considerable input from
the CASAC PM Panel and the public.21
The information presented in these
documents included specific criteria for
the selection of health endpoints and
studies to include in the assessment. It
also addressed which alternative
statistical models (e.g., for control of
time-varying factors such as weather
21 In June 2001, OAQPS released a draft
document, PM NAAQS Risk Analysis Scoping Plan
(EPA, 2001), for CASAC consultation and public
comment, which described staff’s general plan for
this assessment. In January 2002, OAQPS released
a more detailed draft document, Proposed
Methodology for Particulate Matter Risk Analyses
for Selected Urban Areas (Abt Associates, 2002), for
CASAC review and public comment, which
described staff’s plans to assess (a) PM2.5-related
risks for several health endpoints, including
mortality, hospital admissions, and respiratory
symptoms and (b) PM10-2.5-related risks for hospital
admissions and respiratory symptoms (as discussed
below in Section III.B).
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and for various lags) to include in the
assessment, recognizing that some of the
health studies presented results from a
large number of alternative models. In
an advisory letter sent by CASAC to the
Administrator documenting its advice
in May 2002 (Hopke, 2002), CASAC
concluded that the general methodology
and framework to be used in the
assessment were appropriate.
The goals of the PM2.5 risk assessment
were: (1) To provide estimates of the
potential magnitude of mortality and
morbidity effects associated with
current PM2.5 levels, and with meeting
the current suite of PM2.5 NAAQS and
alternative PM2.5 standards, in specific
urban areas; (2) to develop a better
understanding of the influence of
various inputs and assumptions on the
risk estimates; and (3) to gain insights
into the distribution of risks and
patterns of risk reductions associated
with meeting alternative suites of PM2.5
standards. EPA recognizes that there are
many sources of uncertainty and
variability inherent in the inputs to this
assessment and that there is a high
degree of uncertainty in the resulting
PM2.5 risk estimates. While some of
these uncertainties have been addressed
quantitatively in the form of estimated
confidence ranges around central risk
estimates, other uncertainties and the
variability in key inputs are not
reflected in these confidence ranges, but
rather have been addressed through
separate sensitivity analyses or
characterized qualitatively.
2. Scope and Key Components
The risk assessment estimates risks of
various health effects associated with
exposure to ambient PM2.5 in nine urban
areas selected to illustrate the public
health impacts associated with a recent
year of air quality and potential
reductions in risk associated with just
meeting the current suite of PM2.5
standards and alternative suites of
standards. The selection of urban areas
was largely determined by identifying
areas in the U.S. for which acceptable
epidemiological studies were available
that estimated concentration-response
relationships for PM2.5, which were then
used in assessing the risks. Thus, unlike
the prior risk assessment, the current
risk assessment for short-term exposure
mortality and morbidity health effects
used concentration-response
relationships reported in studies that
included the urban areas for which risks
were estimated. Based on a review of
the evidence evaluated in the Criteria
Document and Staff Paper, as well as
the criteria discussed in Chapter 4 of the
Staff Paper, the following broad
categories of health endpoints were
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included in the risk assessment for
PM2.5 associated with short-term
exposure: Total (non-accidental),
cardiovascular, and respiratory
mortality; hospital admissions for
cardiovascular and respiratory causes;
and respiratory symptoms not requiring
hospitalization. Also included in the
PM2.5 risk assessment were total,
cardiopulmonary, and lung cancer
mortality associated with long-term
exposure.
The available long-term exposure
mortality concentration-response
functions are all based on cohort
studies, in which a cohort of individuals
is followed over time. Based on the
evaluation contained in the Criteria
Document and EPA’s assessment of the
complete data base addressing mortality
associated with long-term exposure to
PM2.5, studies based on the following
two cohorts were identified as being
particularly relevant for the PM2.5 risk
assessment: (1) The Six Cities study
cohort (referred to as Krewski et al.
(2000)—Six Cities) and (2) the ACS
cohort (referred to Krewski et al.
(2000)—ACS), which includes a much
larger number of individuals from many
more cities. In addition, Pope et al.
(2002) extended the follow-up period
for the ACS cohort to sixteen years and
published findings on the relation of
long-term exposure to PM2.5 and allcause mortality as well as
cardiopulmonary and lung cancer
mortality (referred to as Pope et al.
(2002)—ACS extended).22
The available short-term exposure
morbidity and mortality concentrationresponse functions used in the risk
assessment are all from time series
studies. The risk assessment included
only those health endpoints for which
the the Criteria Document concluded
that there is likely to be a causal
relationship with short-term exposure to
PM2.5 based on the overall weight of the
evidence from the collective body of
available studies. Also, given the large
number of endpoints and studies
addressing PM2.5-related effects, the
assessment only included the more
severe and better understood (in terms
of health consequences) health effects.
As noted above, in contrast to the prior
risk assessment, the concentrationresponse functions used in this
assessment for each urban area are
22 The use of these particular cohort studies to
estimate health risks associated with long-term
exposure to PM2.5 is consistent with the views
expressed in the National Academy of Sciences
(2002) report, ‘‘Estimating the Public Health
Benefits of Proposed Air Pollution Regulations,’’
and the Science Advisory Board Clean Air Act
Compliance Council review of the proposed
methodology to estimate the health benefits
associated with the Clean Air Act (SAB, 2004).
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based on results of studies for that
specific area or from a multi-city study
that included that specific area.
The concentration-response
relationships used in the assessment
were based on findings from human
epidemiological studies that have relied
on fixed-site, population-oriented,
ambient monitors as a surrogate for
actual ambient PM2.5 exposures. The
risk assessment addresses risks
attributable to anthropogenic sources
and activities (i.e., risk associated with
concentrations above policy-relevant
background 23 or above various selected
higher cutpoints intended as surrogates
for alternative assumed population
thresholds). This approach of estimating
risks in excess of background was
judged to be more relevant to policy
decisions regarding ambient air quality
standards than risk estimates that
include effects potentially attributable
to uncontrollable background PM
concentrations. For the base case
analyses, an estimate of the annual
average background level was used,
rather than a maximum 24-hour value,
since estimated risks were aggregated
for each day throughout the year.
In order to estimate the incidence of
a particular health effect associated with
recent conditions in a specific county or
set of counties attributable to ambient
PM2.5 exposures in excess of background
or various alternative cutpoints, as well
as the change in incidence
corresponding to a given change in
PM2.5 levels resulting from just meeting
a specified set of alternative PM2.5
standards, three elements are required.
These elements are: (1) Air quality
information (including recent air quality
data for PM2.5 from ambient monitors for
the selected location, estimates of
background PM2.5 concentrations
appropriate for that location, and a
method for adjusting the recent data to
reflect patterns of air quality estimated
to occur when the area just meets a
given set of PM2.5 standards); (2) relative
risk-based concentration-response
functions that provide an estimate of the
relationship between the health
endpoints of interest and ambient PM
concentrations; and (3) annual or
23 Background PM concentrations used in the PM
risk assessment were defined in Chapter 2 of the
Staff Paper as the PM concentrations that would be
observed in the U.S. in the absence of
anthropogenic emissions of PM and its precursors
in the U.S., Canada, and Mexico. For the initial base
case risk estimates, the midpoints of the appropriate
ranges of annual average estimates for PM2.5
background presented in the Staff Paper were used
(i.e., eastern values were used for eastern study
locations and western values were used for western
study locations). Estimated policy-relevant
background concentrations are 3.5 µg/m3 in eastern
cities, and 2.5 µg/m3 in western cities.
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seasonal baseline health effects
incidence rates and population data,
which are needed to provide an estimate
of the annual or seasonal baseline
incidence of health effects in an area
before any changes in PM air quality.
The risk assessment for PM2.5
included a series of base case analyses
that characterized the uncertainty
associated with the form of the
concentration-response relationship
drawn from the studies used in the
assessment—this uncertainty had by far
the greatest impact on estimated risks.
Other uncertainties addressed in various
sensitivity analyses (e.g., the use of
single-versus multi-pollutant models,
single-versus multi-city models, use of a
distributed lag model, alternative
assumptions about the relevant air
quality for long-term exposure
mortality, and alternative constant or
varying background levels) all have a
more moderate and often variable
impact on the risk estimates in some or
all of the cities.
In estimating health risks remaining
upon just meeting the current and
alternative PM2.5 standards, the
assessment includes a series of base
cases, while noting that the confidence
ranges in the estimates do not reflect all
the identified uncertainties. As
discussed above in section II.A.3,
additional uncertainty for short-term
exposure mortality is related to the use
of alternative statistical models and
methods to control for time-varying
effects, such as weather or season, and
to address alternative lag structures. To
provide a consistent basis for
comparison across studies and
locations, the risk assessment used
concentration-response functions based
on the most common type of analysis
(‘‘generalized additive methods’’) and
on lag structures judged to be most
appropriate for each specific health
endpoint, as discussed in the Staff Paper
(EPA, 2005a, p. 4–24). The risk
assessment included a sensitivity
analysis for one location where a wide
array of statistical models and lags was
reported in the health study for that
location (Los Angeles, as reported in
Moolgavkar, 2003). EPA recognizes that
there is additional uncertainty
associated with choices about
appropriate modeling strategy (EPA,
2004, 8.4.2) and that this uncertainty is
not included in the confidence ranges
presented for the risk estimates.
As noted earlier, EPA recognizes that
while there are likely biological
thresholds in individuals for specific
health endpoints, the available
epidemiologic studies do not support or
refute the existence of thresholds at the
population level for either long-term or
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2639
short-term PM2.5 exposures within the
range of air quality observed in the
studies (EPA, 2004, 9.2.2.5). Thus, base
case risks were estimated using not only
the linear or log-linear concentrationresponse functions reported in the
studies, but also using a series of
modified linear functions, as discussed
below, as surrogates for assumed nonlinear functions that would reflect the
possibility that thresholds may exist in
the reported associations within the
range of air quality observed in the
studies.
For short-term exposure mortality and
morbidity outcomes associated with
PM2.5, the initial base case includes
linear or log-linear concentrationresponse models reported in the
epidemiology studies which are applied
down to the estimated policy-relevant
background concentration level.
Generally, the lowest measured
concentrations in the short-term
exposure studies were relatively near or
below the estimated policy-relevant
background levels such that little or no
extrapolation was required beyond the
range of data in the studies. In the case
of the long-term exposure mortality
studies for PM2.5 that have been
included in the risk assessment, the
lowest measured levels were in the
range 7.5 to 11 µg/m3. For the initial
base case scenario for this endpoint, the
reported linear models were applied
down to 7.5 µg/m3, which is the lowest
measured level reported in the longterm studies. Going down to an
estimated policy-relevant background
level for short-term exposure studies
and to 7.5 µg/m3 for long-term studies
provides a consistent framework which
facilitates comparison of risk estimates
across urban locations within each
group of studies and avoids significant
extrapolation beyond the range of
concentrations included in these
studies.
Additional base case scenarios for
both short- and long-term exposure
health endpoints involved the use of
alternative concentration-response
functions that incorporated a modified
linear slope with an imposed cutpoint
(i.e., an assumed threshold). For
mortality associated with short-term
exposure, the base case analyses
included risk estimates associated with
cutpoints of 10, 15, and 20 µg/m. For
mortality associated with long-term
PM2.5 exposure, cutpoints of 10 and 12
µg/m3 were included. For the base case
scenarios involving alternative
cutpoints, the approach used to develop
alternative functions incorporates a
modified linear slope with an imposed
cutpoint (i.e., an assumed population
threshold) that is intended to reflect a
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hypothetical inflection point in a typical
non-linear, ‘‘hockey-stick’’ shaped
function, below which there is little or
no population response. More
specifically, the slope of the
concentration-response relationship has
been adjusted assuming that the
upward-sloping portion of the ‘‘hockey
stick’’ would be the slope estimated in
the original epidemiologic study
adjusted by the inverse of the
proportion of the range of PM levels
observed in the study that was above the
cutpoint. The Staff Paper concludes that
this simple slope adjustment approach
represents a reasonable approach to
illustrating the potential impact of
possible non-linear concentrationresponse relationships. In its review of
the Staff Paper and risk assessment, the
CASAC PM Panel commented that for
the purpose of estimating public health
impacts, it ‘‘favored the primary use of
an assumed threshold of 10 µg/m3’’ and
that ‘‘a major research need is for more
work to determine the existence and
level of any thresholds that may exist or
the shape of nonlinear concentrationresponse curves at low levels of
exposure that may exist’’ (Henderson,
2005a).
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3. Risk Estimates and Key Observations
In focusing on the five study areas
that do not meet the current PM2.5
standards based on 2001–2003 air
quality data (Detroit, Los Angeles,
Philadelphia, Pittsburgh, and St. Louis),
the total mortality risk estimates
associated with simulating air quality
reductions to just meet the current PM2.5
standards (based on associations with
long-term PM2.5 exposure, and using the
lowest cutpoint of 7.5 µg/m3) range from
several hundred to over 1500 deaths per
year, which translate into an incidence
rate of approximately 16 to 35 deaths
per year per hundred thousand
population.24 These estimated risks
associated with long-term exposure
represent approximately 2.6 to 3.2
percent of total mortality in those areas.
Estimated risks associated with longterm exposure based on an assumed
cutpoint of 10 µg/m3 are roughly half as
large as the estimates based on a
cutpoint of 7.5 µg/m3. In the same five
areas, the estimates of mortality risk
associated with short-term PM2.5
exposure, based on a cutpoint equal to
policy-relevant background or 10 µg/m,
range from less than 20 percent to over
24 The full range of quantitative risk estimates
associated with just meeting the current PM2.5
standards are presented in Tables 4–9, 4–10, 4–12,
and 4–13 in Chapter 4 of the Staff Paper.
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50 percent of the estimates associated
with long-term exposure.25
Reductions in risk associated with
simulating air quality to just meet a
range of lower alternative annual and
24-hour PM2.5 standards were also
estimated in this assessment. The
estimated risk reductions are depicted
graphically in the Staff Paper (EPA,
2005a, Figures 5–1 and 5–2 and Figures
5A–1 and 5A–2), showing patterns of
estimated risk reductions associated
with alternative suites of standards for
all the various assumed cutpoints. As
would be expected, patterns of
increasing estimated risk reductions are
observed as either the annual or 24-hour
standard, or both, are reduced over the
range considered in this assessment,
and the estimated percentage reductions
in risk are strongly influenced by the
assumed cutpoint level.
The discussion below highlights
additional observations and insights
from this PM2.5 risk assessment, together
with important caveats and limitations.
(1) With respect to short-term
exposure mortality and morbidity, this
risk assessment provides the basis for
greater confidence in the results as
compared to the prior assessment, given
that studies are now available using
PM2.5 as the indicator in a much greater
number of locations, and the assessment
is able to use city-specific functions that
are matched to the locations for which
risks are estimated. This contrasts with
the use of pooled concentrationresponse functions in the prior
assessment which did not include
studies for the specific cities included
in that assessment. However, EPA
recognizes that the confidence ranges,
which only reflect uncertainty
associated with the precision of the
study (related to the population size and
duration of the study), may be larger for
the current risk estimates due to the use
of concentration-response functions
from smaller, city-specific studies now
versus the use of concentration-response
functions from pooled sets of studies
that have greater statistical precision.
Comparing the risk estimates for the
only two specific locations that were
included in both the prior and current
assessments, the magnitude of the
estimates associated with just meeting
the current annual standard, in terms of
percentage of total incidence, is similar
in one of the locations (Philadelphia)
and the current estimate is lower in the
other location (Los Angeles).
25 In some areas, the 95 percent confidence ranges
associated with the risk estimates for short-term
exposure (but not long-term exposure) extend to
below zero, reflecting appreciably more uncertainty
in estimates based on positive but not statistically
significant associations.
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(2) With respect to long-term exposure
mortality risk estimates, the prior risk
assessment focused on the estimates
based on the original ACS study (Pope
et al., 1995). Since that time additional
cohort analyses have been published
and evaluated in the Criteria Document.
EPA has greater confidence in the
current risk estimates for long-term
exposure mortality, given the extensive
review of these studies and the
extension of the ACS study to additional
years of data, as well as improvements
in the statistical approach. However,
ACS-based risk estimates remain
sensitive to plausible changes in
statistical model specifications. The
choice of studies and concentrationresponse functions to use for the base
case risk estimates is discussed in the
Staff Paper (EPA, 2005a, p. 4–25) and
risk assessment report (Abt Associates,
2005, pp.49–50) and is consistent with
the advice provided by both the
National Academy of Sciences and the
Science Advisory board Clean Air Act
Compliance Council (see footnote 22).
At the same time, EPA recognizes that
alternative statistical models were
examined in the reanalysis of the ACS
and Six-Cities studies, and that the
uncertainty associated with model
selection (such as multipollutant
models and different effect estimates
associated with different educational
levels) is not reflected in the confidence
ranges presented in this assessment.
Thus, for long-term exposure mortality
risk estimates there are additional
unquantified uncertainties associated
with a lack of understanding as to
which statistical model best represents
the actual concentration-response
function. The relative risk estimates
used in the current risk assessment from
the ACS extended study are only
slightly smaller (1.06 with 95 percent
confidence interval of 1.02–1.11)
compared to the original ACS study
(1.07 with 95 percent confidence
interval 1.04–1.10) used in the prior
assessment. In terms of the magnitude of
the risk estimates, the estimates in terms
of percentage of total incidence are very
similar for the two specific locations
included in both the prior and current
assessments.
(3) A fairly wide range of risk
estimates are observed for PM2.5-related
morbidity and mortality risk associated
with recent air quality across the urban
areas analyzed. The impact of adding
additional co-pollutants to the models
was variable; sometimes there was
relatively little difference, while in
other cases there were larger differences.
The wide variability in risk estimates
associated with a recent year of air
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quality is to be expected given the wide
range of PM2.5 levels across the urban
areas analyzed and the variation
observed in the concentration-response
relationships obtained from the original
epidemiologic studies. Among other
factors, this variability may reflect
differences in the mixture of
components or sources of fine particles,
populations, exposure considerations
(e.g., degree of air conditioning use),
differences in co-pollutants and/or other
stressors, differences in study design,
and differences related to exposure and
monitor measurement error.
(4) The single most important factor
influencing the quantitative estimates of
risk is which of the alternative
concentration-response functions
included in this assessment are
considered to best represent the
unknown ‘‘true’’ concentration-response
relationships. In comparison, the
following uncertainties have only a
moderate impact on the risk estimates in
some or all of the cities: choice of an
alternative estimated constant
background level, use of a distributed
lag model, and alternative assumptions
about the relevant air quality for
estimating exposure levels for long-term
exposure mortality. Use of a distribution
of daily background concentrations had
very little impact on the risk estimates.
The overall pattern of risk associated
with short-term PM2.5 exposures across
the distribution of PM2.5 air quality, as
typically observed in urban areas, is
similar to that observed in the last
review. That is, on an annual basis, the
very highest days (which pose the
greatest risk in terms of deaths per day)
contribute less to the total annual health
risk associated with short-term
exposures than the middle of the
distribution, due to the much greater
number of days that occur in this part
of the air quality distribution.
(5) Risk estimates associated with just
meeting the current suite of PM2.5
standards in five urban areas that do not
meet the current PM2.5 standards
showed a wide range of PM2.5-related
risk estimates for short-term exposure
mortality and morbidity. This is likely
due, in large part, to differences in
concentration-response relationships
among single-location short-term
exposure studies, differences in baseline
incidence rates, and varying population
sizes. Results of a sensitivity analysis
which applied one multi-city
concentration-response function to all
five urban areas analyzed narrowed
considerably the range of risk estimates
when a risk metric was used that
normalized for different population
sizes. However, it is still unknown
whether the wider range of estimates
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observed using single-city
concentration-response functions reflect
methodological differences between
studies and/or real city-to-city
differences related to exposure,
population, composition of the
particles, or other factors.
(6) For the risk estimates associated
with just meeting the current suite of
PM2.5 standards and alternative suites of
standards, the single most important
factor influencing the short- and longterm exposure mortality and morbidity
estimates is again which of the
alternative concentration-response
functions included in this assessment
are considered to best represent the
unknown ‘‘true’’ concentration-response
relationships. Several additional sources
of uncertainty are introduced into this
portion of the risk assessment,
including: (1) Uncertainty in the degree
to which the pattern of air quality
concentration reductions estimated for
the risk assessment cities represents the
distribution of actual PM concentration
changes that would be observed in a
given area (‘‘rollback uncertainty’’) and
(2) uncertainty concerning the degree to
which current PM risk coefficients may
reflect contributions from other
pollutants, or uncertainty concerning
whether all of the constituents of PM2.5
would be reduced in similar proportion
to the reduction in PM2.5 as a whole,
and, if not, what impact this would have
on estimated reductions in risk. For
areas where the current annual standard
is the controlling standard, one
alternative approach to rolling back the
distribution of daily PM2.5
concentrations, in which the upper end
of the distributions of concentrations
was reduced by a greater amount than
the rest of the distribution, had little
impact on the risk estimates. This
approach or alternative approaches to
rolling back the distribution of daily
concentrations may have a greater
impact on the risk estimates in areas
where the daily standard is the
controlling standard.
(7) For the risk estimates associated
with just meeting the current or
alternative suites of PM2.5 standards,
there is a significant decrease in the
mortality risk estimates based on shortterm PM2.5 exposure remaining as one
considers alternative higher cutpoints.
There also is a significant increase
observed in the percent reduction in
estimated risk upon just meeting
alternative standards with higher
alternative cutpoints. These findings are
even more pronounced for the mortality
risk estimates associated with long-term
PM2.5 exposure as higher alternative
cutpoint levels are considered.
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C. Need for Revision of the Current
Primary PM2.5 Standards
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
reflected in the Criteria Document and
Staff Paper, the existing standards
should be revised. Based on the
information and conclusions presented
in the Criteria Document, summarized
above in section II.A., the Staff Paper
concludes that the newly available
information generally reinforces the
associations between PM2.5 and
mortality and morbidity effects observed
in the last review. While important
uncertainties and research questions
remain, much progress has been made
in reducing some key uncertainties
since the last review. The examination
of specific components, properties, and
sources of fine particles that are linked
with health effects remains an important
research need. Other important research
needs include better characterizing the
shape of concentration-response
functions, including identification of
potential threshold levels, and
methodological issues such as those
associated with selecting appropriate
statistical models in time-series studies
to address time-varying factors (such as
weather) and other factors (such as other
pollution variables), and better
characterizing population exposures.
Nonetheless, important progress has
been made in advancing our
understanding of potential mechanisms
by which ambient PM2.5, alone and in
combination with other pollutants, is
causally linked with cardiovascular,
respiratory, and lung cancer
associations observed in epidemiologic
studies. In addition, health effects
associations reported in epidemiologic
studies have been found to be generally
robust to confounding by co-pollutants,
there is now greater confidence in the
results of long-term exposure studies
due to reanalyses and extensions of the
critical studies, and there is an
increased understanding of susceptible
populations. Based on these
considerations, the Staff Paper finds
clear support in the available evidence
for fine particle standards that are at
least as protective as the current PM2.5
standards (EPA, 2005a, p. 5–6).
Having reached this initial
conclusion, the Staff Paper addresses
the question of whether the available
evidence supports consideration of
standards that are more protective than
the current PM2.5 standards. In so doing,
the Staff Paper considers whether there
is now evidence (1) that statistically
significant health effects associations
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with short-term exposures to fine
particles occur in areas that would
likely meet the current PM2.5 standards
or (2) that such associations with longterm exposures to fine particles extend
down to lower air quality levels than
had previously been observed.26 This
takes into consideration the bases for
the decisions made in 1997 in setting
the current PM2.5 standards. In generally
considering what areas would likely
meet the current PM2.5 standards, the
focus is principally on comparing the
long-term average PM2.5 level in an area
with the level of the current annual
PM2.5 standard, since in 1997 that
standard was set to be the ‘‘generally
controlling’’ standard to provide
protection against health effects related
to both short- and long-term exposures
to fine particles. In conjunction with
such an annual standard, the current 24hour standard was set to provide only
supplemental protection against days
with high peak PM2.5 concentrations,
localized ‘‘hotspots,’’ or risks arising
from seasonal emissions that might not
be well controlled by a national annual
standard.
In first considering the available
epidemiologic evidence related to shortterm exposures, the Staff Paper focuses
on specific epidemiologic studies that
show statistically significant
associations between PM2.5 and health
effects for which the Criteria Document
judges associations with PM2.5 to be
likely causal (EPA, 2005a, section
5.3.1.1). Many more U.S. and Canadian
studies are now available that provide
evidence of associations between shortterm exposure to PM2.5 and serious
health effects in areas with air quality at
and above the level of the current
annual PM2.5 standard (15 µg/m3).
Moreover, a few newly available shortterm exposure mortality studies provide
evidence of statistically significant
associations with PM2.5 in areas with air
quality levels below the levels of the
current PM2.5 standards. In considering
these studies, the Staff Paper focuses on
those that include adequate gravimetric
PM2.5 mass measurements, and where
the associations are generally robust to
alternative model specification and to
the inclusion of potentially confounding
co-pollutants. Three such studies
conducted in Phoenix (Mar et al., 2003),
26 In addressing this question, the Staff Paper first
recognizes, as discussed above in section II.A.3, that
although there are likely biologic threshold levels
in individuals for specific health responses, the
available epidemiologic evidence neither supports
nor refutes the existence of thresholds at the
population level for the effects of PM2.5 on mortality
across the range of concentrations in the studies, for
either long-term or short-term PM2.5 exposures
(EPA, 2004, section 9.2.2.5).
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Santa Clara County, CA (Fairley, 2003)
and eight Canadian cities (Burnett and
Goldberg, 2003) report statistically
significant associations between shortterm PM2.5 exposure and total and
cardiovascular mortality in areas in
which long-term average PM2.5
concentrations ranged between 13 and
14 µg/m3 and 98th percentile
concentrations ranged between 32 and
59 µg/m3.27
In also considering the new
epidemiologic evidence available from
U.S. and Canadian studies of long-term
exposure to fine particles, the Criteria
Document notes that new studies have
built upon studies available in the last
review and concludes that these studies
have confirmed and strengthened the
evidence of associations for both
mortality and respiratory morbidity
(EPA, 2004, section 9.2.3). For mortality,
the Criteria Document places greatest
weight on the reanalyses and extensions
of the Six Cities and ACS studies,
finding that these studies provide strong
evidence for associations with fine
particles (EPA, 2004, p. 9–34),
notwithstanding the lack of consistent
results in other long-term exposure
studies. For morbidity, the Criteria
Document finds that new studies of a
cohort of children in Southern
California have built upon earlier
limited evidence to provide fairly strong
evidence that long-term exposure to fine
particles is associated with development
of chronic respiratory disease and
reduced lung function growth (EPA,
2004, pp. 9–33 to 9–34). In addition to
strengthening the evidence of
association, the new extended ACS
mortality study observed statistically
significant associations with
cardiorespiratory mortality (including
lung cancer mortality) across a range of
long-term mean PM2.5 concentrations
that was lower than was reported in the
original ACS study available in the last
review.
Beyond the epidemiologic studies
using PM2.5 as an indicator of fine
particles, a large body of newly
available evidence from studies that
used PM10, as well as other indicators or
components of fine particles (e.g.,
27 As noted in the Staff Paper, these studies were
reanalyzed to address questions about the
application of the statistical software used in the
original analyses, and the study results from
Phoenix and Santa Clara County were little changed
in alternative models (Mar et al., 2003; Fairley,
2003), although Burnett and Goldberg (2003)
reported that their results were sensitive to using
different temporal smoothing methods. Two of
these studies also reported significant associations
with gaseous pollutants (Mar et al., 2003; Fairley,
2003), and the other study included multi-pollutant
model results in reanalyses, reporting that
associations with PM2.5 remained significant with
gaseous pollutants (Fairley, 2003).
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sulfates, combustion-related
components), provides additional
support for the conclusions reached in
the last review as to the likely causal
role of ambient PM, and the likely
importance of fine particles in
contributing to observed health effects.
Such studies notably include new
multi-city studies, intervention studies
(that relate reductions in ambient PM to
observed improvements in respiratory
or cardiovascular health), and sourceoriented studies (e.g., suggesting
associations with combustion- and
vehicle-related sources of fine particles).
The Criteria Document also notes that
new epidemiologic studies of asthmarelated increased physicians visits and
symptoms, as well as new studies of
cardiac-related risk factors, suggest
likely much larger public health impacts
due to ambient fine particles than just
those indexed by the mortality and
morbidity effects considered in the last
review (EPA, 2004, p. 9–94).
In reviewing this information, the
Staff Paper recognizes that important
limitations and uncertainties associated
with this expanded body of evidence for
PM2.5 and other indicators or
components of fine particles, noted
above in section II.A.2, need to be
carefully considered in determining the
weight to be placed on the body of
studies available in this review. For
example, the Criteria Document notes
that while PM-effects associations
continue to be observed across most
new studies, the newer findings do not
fully resolve the extent to which the
associations are properly attributed to
PM acting alone or in combination with
other gaseous co-pollutants, particularly
SO2, or to the gaseous co-pollutants
themselves. The Criteria Document
concludes, however, that overall the
various approaches that have now been
used to evaluate this issue substantiate
that associations for various PM
indicators with mortality and morbidity
are generally robust to confounding by
co-pollutants (EPA, 2004, p. 9–37).
While the limitations and
uncertainties in the available evidence
suggest caution in interpreting the
epidemiologic studies at the lower
levels of air quality observed in the
studies, the Staff Paper concludes that
the evidence now available provides
strong support for considering fine
particle standards that would provide
increased protection beyond that
afforded by the current PM2.5 standards.
The Staff Paper notes that a more
protective suite of PM2.5 standards
would reflect the generally stronger and
broader body of evidence of associations
with mortality and morbidity now
available in this review, both at levels
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below the current standards and
extending to lower levels of air quality
than in earlier studies, as well as
increased understanding of possible
underlying mechanisms.
In addition to this evidence-based
evaluation, the Staff Paper also
considers the extent to which health
risks estimated to occur upon
attainment of 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 Staff Paper first notes that the
risk assessment addresses a number of
key uncertainties through various base
case analyses, as well as through several
sensitivity analyses, as discussed above
in section II.B. In considering the health
risks estimated to occur upon
attainment of the current PM2.5
standards, the Staff Paper focuses in
particular on a series of base case risk
estimates, while recognizing that the
confidence ranges in the selected base
case estimates do not reflect all the
identified uncertainties. These risks
were estimated using not only the linear
or log-linear concentration-response
functions reported in the studies,28 but
also using alternative modified linear
functions as surrogates for assumed
non-linear functions that would reflect
the possibility that thresholds may exist
in the reported associations within the
range of air quality observed in the
studies. Regardless of the relative
weight placed on the risk estimates
associated with the concentrationresponse functions reported in the
studies or with the modified functions
favored by CASAC,29 the risk
assessment indicates the possibility that
thousands of premature deaths per year
would occur in urban areas across the
U.S. upon attainment of the current
PM2.5 standards.30 Beyond the estimated
incidences of premature mortality, the
28 As discussed above in section II.B.2, the
reported linear or log-linear concentration-response
functions were applied down to 7.5 µg/m3 in
estimating risk associated with long-term exposure
(i.e., the lowest measured level in the extended ACS
study), and down to the estimated policy-relevant
background level in estimating risk associated with
short-term exposure (i.e., 3.5 µg/m3 for eastern
urban areas and 2.5 µg/m3 for western urban areas).
29 The CASAC PM Panel generally favored the
primary use of an assumed threshold of 10 µg/m3
for the various concentration-response functions
used in the risk assessment (Henderson, 2005a).
30 The Staff Paper recognizes how highly
dependent any specific risk estimates are on the
assumed shape of the underlying concentrationresponse functions, noting nonetheless that
mortality risks are not completely eliminated when
current PM2.5 standards are met in a number of
example urban areas even using the highest
assumed cutpoint levels considered in the risk
assessment (EPA, 2005a, p. 5–15).
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Staff Paper also recognizes that similarly
substantial numbers of incidences of
hospital admissions, emergency room
visits, aggravation of asthma and other
respiratory symptoms, and increased
cardiac-related risk are also likely in
many urban areas, based on risk
assessment results (EPA, 2005a, Chapter
4) and on the discussion related to this
pyramid of effects in the Criteria
Document (EPA, 2004, section 9.2.5).
Based on these considerations, the Staff
Paper concludes that the estimates of
risks likely to remain upon attainment
of the current PM2.5 standards are
indicative of risks that can reasonably
be judged to be important from a public
health perspective.
In considering available evidence, risk
estimates, and related limitations and
uncertainties, the Staff Paper concludes
that the available information clearly
calls into question the adequacy of the
current suite of PM2.5 standards and
provides strong support for revising the
current PM2.5 standards to provide
increased public health protection. Also
taking into account these
considerations, the CASAC advised the
Administrator that a majority of CASAC
Panel members were in agreement that
the primary 24-hour and annual PM2.5
standards ‘‘should be modified to
provide increase public health
protection’’ (Henderson, 2005a). The
CASAC further advised that changes to
either the annual standard or the 24hour standard, or both, could be
recommended, and expressed reasons
that formed the basis for the consensus
among the Panel members for placing
more emphasis on lowering the 24-hour
standard (Henderson, 2005a).31
In considering whether the suite of
primary PM2.5 standards should be
revised to provide requisite public
health protection, the Administrator has
carefully considered the rationale and
recommendations contained in the Staff
Paper, the advice and recommendations
from CASAC, and public comments to
date on this issue. In so doing, the
Administrator places primary
consideration on the evidence obtained
from the studies, and provisionally
finds the evidence of serious health
effects reported in short-term exposure
studies conducted in areas that would
attain the current standards to be
compelling, especially in light of the
31 Of the individual Panel members who
submitted written comments expressing views on
appropriate levels of the PM2.5 standards, only one
did not suppport changes to either the 24-hour or
annual standard to provide additional public health
protection (Henderson, 2005a). In written
comments, the health scientists on the CASAC
Panel did not agree on whether the annual standard
should be lowered.
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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 Criteria Document and
Staff Paper, the Administrator
recognizes 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 PM2.5 standards. In
considering the risk assessment
presented in the Staff Paper, the
Administrator notes that the assessment
contained a sensitivity analysis but not
a formal uncertainty analysis, making it
difficult to use the risk assessment to
form a judgment of the probability of
various risk estimates. Instead, the
Administrator views the risk assessment
in light of his evaluation of the
underlying studies. Seen in this light,
the risk assessment informs the
determination of the public health
significance of risks to the extent that
the evidence is judged to support an
effect at a particular level of air quality.
Based on these considerations, the
Administrator provisionally concludes
that the current primary PM2.5
standards, taken together, are not
requisite to protect public health with
an adequate margin of safety and that
revision is needed to provide increased
public health protection.
D. Indicator of Fine Particles
In 1997, EPA established PM2.5 as the
indicator for fine particles. In reaching
this decision, the Agency first
considered whether the indicator
should be based on the mass of a sizedifferentiated sample of fine particles or
on one or more components within the
mix of fine particles. Secondly, in
establishing a size-based indicator, a
size cut needed to be selected that
would appropriately distinguish fine
particles from particles in the coarse
mode.
In addressing the first question in the
last review, EPA determined that it was
appropriate to control fine particles as a
group, as opposed to singling out any
particular component or class of fine
particles. Community health studies had
found significant associations between
various indicators of fine particles
(including PM2.5 or PM10 in areas
dominated by fine particles) and health
effects in a large number of areas that
had significant mass contributions of
differing components or sources of fine
particles, including sulfates, wood
smoke, nitrates, secondary organic
compounds and acid sulfate aerosols. In
addition, a number of animal
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toxicologic and controlled human
exposure studies had reported health
effects associations with high
concentrations of numerous fine particle
components (e.g., sulfates, nitrates,
transition metals, organic compounds),
although such associations were not
consistently observed. It also was not
possible to rule out any component
within the mix of fine particles as not
contributing to the fine particle effects
found in epidemiologic studies. For
these reasons, EPA concluded that total
mass of fine particles was the most
appropriate indicator for fine particle
standards rather than an indicator based
on PM composition (62 FR 38667, July
18, 1997).
Having selected a size-based indicator
for fine particles, the Agency then based
its selection of a specific size cut on a
number of considerations. In focusing
on a size cut within the size range of 1
to 3 µm (i.e., the intermodal range
between fine and coarse mode
particles), the Agency noted that the
available epidemiologic studies of fine
particles were based largely on PM2.5;
only very limited use of PM1 monitors
had been made. While it was recognized
that using PM1 as an indicator of fine
particles would exclude the tail of the
coarse mode in some locations, in other
locations it would miss a portion of the
fine PM, especially under high humidity
conditions, which would result in
falsely low fine PM measurements on
days with some of the highest fine PM
concentrations. The selection of a 2.5
µm size cut reflected the regulatory
importance that was placed on defining
an indicator for fine particle standards
that would more completely capture
fine particles under all conditions likely
to be encountered across the U.S.,
especially when fine particle
concentrations are likely to be high,
while recognizing that some small
coarse particles would also be captured
by PM2.5 monitoring. Thus, EPA’s
selection of 2.5 µm as the size cut for
the fine particle indicator was based on
considerations of consistency with the
epidemiologic studies, the regulatory
importance of more completely
capturing fine particles under all
conditions, and the potential for limited
intrusion of coarse particles in some
areas; it also took into account the
general availability of monitoring
technology (62 FR 38668).
In this current review, the same
considerations continue to apply for
selection of an appropriate indicator for
fine particles. As an initial matter, the
available epidemiologic studies linking
mortality and morbidity effects with
short- and long-term exposures to fine
particles continue to be largely indexed
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by PM2.5. Some epidemiologic studies
also have continued to implicate various
components within the mix of fine
particles that have been more commonly
studied (e.g., sulfates, nitrates, carbon,
organic compounds, and metals) as
being associated with adverse effects
(EPA, 2004, p. 9–31, Table 9–3). In
addition, several recent studies have
used PM2.5 speciation data to evaluate
the association between mortality and
particles from different sources
(Schwartz, 2003a; Mar et al., 2003; Tsai
et al., 2000; EPA, 2004, section 8.2.2.5).
Schwartz (2003a) reported statistically
significant associations for mortality
with factors representing fine particles
from traffic and residual oil combustion
that were little changed in reanalysis to
address statistical modeling issues, and
also an association between mortality
and coal combustion-related particles
that was reduced in size and lost
statistical significance in reanalysis. In
Phoenix, significant associations were
reported between mortality and fine
particles from traffic emissions,
vegetative burning, and regional sulfate
sources that remained unchanged in
reanalysis models (Mar et al., 2003).
Finally, a small study in three New
Jersey cities reported significant
associations between mortality and fine
particles from industrial, oil burning,
motor vehicle and sulfate aerosol
sources, though the results were
somewhat inconsistent between cities
(Tsai et al., 2000).32 No significant
increase in mortality was reported with
a source factor representing crustal
material in fine particles (CD, p. 8–85).
Recognizing that these three studies
represent a very preliminary effort to
distinguish effects of fine particles from
different sources, and that the results
are not always consistent across the
cities, the Criteria Document found that
these studies indicate that exposure to
fine particles from combustion sources,
but not crustal material, is associated
with mortality (EPA, 2004, p. 8–77).
Animal toxicologic and controlled
human exposure studies have continued
to link a variety of PM components or
particle types (e.g., sulfates, notably
primary metal sulfate emissions from
residual oil burning, metals, organic
constituents, bioaerosols, diesel
particles) with health effects, though
often at high concentrations (EPA, 2004,
section 7.10.2). In addition, some recent
studies have suggested that the ultrafine
32 More specifically, statistically significant
associations were reported with factors representing
fine particles from oil burning, industrial and
sulfate aerosol sources in Newark and with particles
from oil burning and motor vehicle sources in
Camden, and no statistically significant associations
were reported in Elizabeth.
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subset of fine particles (generally
including particles with a nominal
mean aerodynamic diameter less than
0.1 µm) may also be associated with
adverse effects (EPA, 2004, pp. 8–67 to
68).
The Criteria Document recognizes
that, for a given health response, some
fine particle components are likely to be
more closely linked with that response
than others. The presumption that
different PM constituents may have
differing biological responses is
toxicologically plausible and an
important source of uncertainty in
interpreting such epidemiologic
evidence. For specific effects there may
be stronger correlation with individual
PM components than with aggregate
particle mass. In addition, particles or
particle-bound water can act as carriers
to deliver other toxic agents into the
respiratory tract, suggesting that
exposure to particles may elicit effects
that are linked with a mixture of
components more than with any
individual PM component (EPA, 2004,
section 9.2.3.1.3).
Thus, epidemiologic and toxicologic
studies have provided evidence for
effects associated with various fine
particle components or sizedifferentiated subsets of fine particles.
The Criteria Document concludes:
‘‘These studies suggest that many
different chemical components of fine
particles and a variety of different types
of source categories are all associated
with, and probably contribute to,
mortality, either independently or in
combinations’’ (EPA, 2004, p. 9–31).
Conversely, the Criteria Document
provides no basis to conclude that any
individual fine particle component
cannot be associated with adverse
health effects (EPA, 2005a, p. 5–17). In
short, there is not sufficient evidence
that would lead toward the selection of
one or more PM components as being
primarily responsible for effects
associated with fine particles, nor is
there sufficient evidence to suggest that
any component should be eliminated
from the indicator for fine particles. The
Staff Paper continues to recognize the
importance of an indicator that not only
captures all of the most harmful
components of fine particles (i.e., an
effective indicator), but also emphasizes
control of those constituents or
fractions, including sulfates, transition
metals, and organics that have been
associated with health effects in
epidemiologic and/or toxicologic
studies, and is thus most likely to result
in the largest risk reduction (i.e., an
efficient indicator). Taking into account
the above considerations, the Staff Paper
concludes that it remains appropriate to
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control fine particles as a group; i.e.,
that total mass of fine particles is the
most appropriate indicator for fine
particle standards (EPA, 2005a, p. 5–17).
With regard to an appropriate size cut
for a size-based indicator of total fine
particle mass, the Criteria Document
concludes that advances in our
understanding of the characteristics of
fine particles continue to support the
use of particle size as an appropriate
basis for distinguishing between these
subclasses, and that a nominal size cut
of 2.5 µm remains appropriate (EPA,
2004, p. 9–22). This conclusion follows
from a recognition that within the
intermodal range of 1 to 3 µm there is
no unambiguous definition of an
appropriate size cut for the separation of
the overlapping fine and coarse particle
modes. Within this range, the Staff
Paper considered size cuts of both 1 µm
and 2.5 µm. Consideration of these two
size cuts took into account that there is
generally very little mass in this
intermodal range, although in some
circumstances (e.g., windy, dusty areas)
the coarse mode can extend down to
and below 1 µm, whereas in other
circumstances (e.g., high humidity
conditions, usually associated with very
high fine particle concentrations) the
fine mode can extend up to and above
2.5 µm. The same considerations that
led to the selection of a 2.5 µm size cut
in the last review—that the
epidemiologic evidence was largely
based on PM2.5 and that it was more
important from a regulatory perspective
to capture fine particles more
completely under all conditions likely
to be encountered across the U.S.
(especially when fine particle
concentrations are likely to be high)
than to avoid some coarse-mode
intrusion into the fine fraction in some
areas—led to the same recommendation
by the Staff Paper (EPA, 2005a, p. 5–18)
and CASAC (Henderson, 2005a) in this
review. In addition, the Staff Paper
recognizes that particles can act as
carriers of water, oxidative compounds,
and other components into the
respiratory system, which adds to the
importance of ensuring that larger
accumulation-mode particles are
included in the fine particle size cut
(EPA, 2005a, p. 5–18).
Consistent with the Staff Paper and
CASAC recommendations, the
Administrator proposes to retain PM2.5
as the indicator for fine particles.
Further, the Administrator provisionally
concludes that currently available
studies do not provide a sufficient basis
for supplementing mass-based fine
particle standards with standards for
any specific fine particle component or
subset of fine particles, or for
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eliminating any individual component
or subset of components from fine
particle mass standards. Addressing the
current uncertainties in the evidence of
effects associated with various fine
particle components and types of source
categories is an important element in
EPA’s ongoing PM research program.
The Administrator notes that some
commenters have 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) are now or may be
appropriate for standards intended to
protect against the array of health effects
that have been associated with fine
particles as indexed by PM2.5.33
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. While recognizing that
the studies evaluated in the Criteria
Document provide some limited
evidence of such associations that is
helping to focus research activities, the
Administrator solicits broad public
comment on issues related to studies of
fine particle components and types of
source categories and their usefulness as
a basis for consideration of alternative
indicator(s) for fine particle standards.
In general, comment is solicited on
relevant new published research,
recommendations for studies that would
be appropriate for inclusion in future
research activities, and approaches to
assessing the available and future
research results to determine whether
alternative indicators for fine particles
are warranted to provide effective
protection of public health from effects
associated with long- and short-term
exposure to ambient fine particles.
More specifically, comment is also
solicited on a number of related issues.
One such issue is the extent to which
reducing particular types of PM
(differentiated by either size or
chemistry) might alter the size and
toxicity of remaining particles, and on
the extent to which fine particles in
urban and rural areas can be
differentiated by size or chemistry.
Another issue deals with assessment of
human exposure and its relationship
with pollution measurements at
monitors (EPA, 2004, chapter 5);
33 Such comments have focused in part on newer
studies that have become available since the close
of the Criteria Document, which EPA intends to
include in its assessment of potentially significant
new studies discussed above in section I.D.
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comment is solicited on the extent to
which the latest scientific information
can be used to improve our
understanding of the relationship of
monitored pollution levels to human
exposure. Comment is also solicited on
studies using concentrated ambient
particles (CAPs) and their use in
examining the toxicity of specific
mixtures of pollutants or of particular
source categories.
E. Averaging Time of Primary PM2.5
Standards
In the last review, EPA established
two PM2.5 standards, based on annual
and 24-hour averaging times,
respectively (62 FR at 38668–70). This
decision was based in part on evidence
of health effects related to both shortterm (from less than 1 day to up to
several days) and long-term (from a year
to several years) measures of PM. EPA
noted that the large majority of
community epidemiologic studies
reported associations based on 24-hour
averaging times or on multiple-day
averages. Further, EPA noted that a 24hour standard could also effectively
protect against episodes lasting several
days, as well as providing some degree
of protection from potential effects
associated with shorter duration
exposures. EPA also recognized that an
annual standard would provide effective
protection against both annual and
multi-year, cumulative exposures that
had been associated with an array of
health effects, and that a much longer
averaging time would complicate and
unnecessarily delay control strategies
and attainment decisions. EPA
considered the possibility of seasonal
effects, although the very limited
available evidence of such effects and
the seasonal variability of sources of
fine particle emissions across the
country did not provide an adequate
basis for establishing a seasonal
averaging time.
In considering whether the
information available in this review
supports consideration of different
averaging times for PM2.5 standards, the
Staff Paper concludes that the available
information is generally consistent with
and supportive of the conclusions
reached in the last review to set PM2.5
standards with both annual and 24-hour
averaging times. In considering the new
information, the Staff Paper makes the
following observations (EPA, 2005a,
section 5.3.3):
(1) There is a growing body of studies
that provide additional evidence of
effects associated with exposure periods
shorter than 24-hours (e.g., one to
several hours) (EPA, 2004, section
3.5.5.1). While the Staff Paper concludes
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that this information remains too
limited to serve as a basis for
establishing a shorter-than-24-hour fine
particle primary standard at this time, it
also noted that this information gives
added weight to the importance of a
standard with a 24-hour averaging time.
(2) Some recent PM10 studies have
used a distributed lag over several days
to weeks preceding the health event,
although this modeling approach has
not been extended to studies of fine
particles (EPA, 2004, section 3.5.5).
While such studies continue to suggest
consideration of a multiple day
averaging time, the Staff Paper notes
that limiting 24-hour concentrations of
fine particles will also protect against
effects found to be associated with PM
averaged over many days in health
studies. Consistent with the conclusion
reached in the last review, the Staff
Paper concludes that a multiple-day
averaging time would add complexity
without providing more effective
protection than a 24-hour average.
(3) While some newer studies have
investigated seasonal effects (EPA, 2004,
section 3.5.5.3), the Staff Paper
concludes that currently available
evidence of such effects is still too
limited to serve as a basis for
considering seasonal standards.
Based on the above considerations,
the Staff Paper and CASAC (Henderson,
2005a) recommend retaining the current
annual and 24-hour averaging times for
PM2.5 primary standards. The
Administrator concurs with the staff
and CASAC recommendations and
proposes that averaging times for PM2.5
standards should continue to include
annual and 24-hour averages to protect
against health effects associated with
short-term (hours to days) and long-term
(seasons to years) exposure periods.
F. Form of Primary PM2.5 Standards
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1. 24-Hour PM2.5 Standard
In 1997 EPA established the form of
the 24-hour PM2.5 standard as the 98th
percentile of the annual 24-hour
concentrations at each populationoriented monitor within an area,
averaged over three years (62 FR at
38671–74). EPA selected such a
concentration-based form because of its
advantages over the previously used
expected-exceedance form.34 A
concentration-based form is more
reflective of the health risk posed by
elevated PM2.5 concentrations because it
34 The form of the 1987 24-hour PM
10 standard is
based on the expected number of days per year
(averaged over 3 years) on which the level of the
standard is exceeded; thus, attainment of the oneexpected exceedance form is determined by
comparing the fourth-highest concentration in 3
years with the level of the standard.
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form because it is more robust than the
99th percentile form, such that it would
provide more stability to prevent areas
from bouncing in and out of attainment
from year to year (Henderson 2005a). In
recommending retention of the 98th
percentile form, the CASAC Panel
recognized that it is the link between
the form and level of a standard that
determines the degree of public health
protection afforded by a standard.
In considering the available
information and the Staff Paper and
CASAC recommendations, the
Administrator proposes that the form of
the 24-hour standard should be based
on the 98th percentile form. In so doing,
the Administrator has focused on the
relative stability of the 98th and 99th
percentile forms as a basis for selecting
the 98th percentile form, while
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.
gives proportionally greater weight to
days when concentrations are well
above the level of the standard than to
days when the concentrations are just
above the standard. Further, a
concentration-based form better
compensates for missing data and lessthan-every-day monitoring; and, when
averaged over 3 years, it has greater
stability and, thus, facilitates the
development of more stable
implementation programs.35 After
considering a range of concentration
percentiles from the 95th to the 99th,
EPA selected the 98th percentile as an
appropriate balance between adequately
limiting the occurrence of peak
concentrations and providing increased
stability and robustness. Further, by
basing the form of the standard on
concentrations measured at populationoriented monitoring sites (as specified
in 40 CFR part 58), EPA intended to
provide protection for people residing
in or near localized areas of elevated
concentrations.
In this review, the Staff Paper
concludes that it is appropriate to retain
a concentration-based form that is
defined in terms of a specific percentile
of the distribution of 24-hour PM2.5
concentrations at each populationoriented monitor within an area,
averaged over 3 years. This staff
recommendation is based on the same
reasons that were the basis for EPA’s
selection of this type of form in the last
review. As to the specific percentile
value to be considered, the Staff Paper
took into consideration (1) the relative
risk reduction afforded by alternative
forms at the same standard level, (2) the
relative year-to-year stability of the air
quality statistic to be used as the basis
for the form of a standard, and (3) the
implications from a public health
communication perspective of the
extent to which either form allows
different numbers of days in a year to
be above the level of the standard in
areas that attain the standard. Based on
these considerations, the Staff Paper
recommends either retaining the 98th
percentile form or revising it to be based
on the 99th percentile form, and notes
that primary consideration should be
given to the combination of form and
level, as compared to looking at the
form in isolation (EPA, 2005a, p. 5–44).
In considering the information
provided in the Staff Paper, most
CASAC Panel members favored
continued use of the 98th percentile
2. Annual PM2.5 Standard
In 1997 EPA established the form of
the annual PM2.5 standard as an annual
arithmetic mean, averaged over 3 years,
from single or multiple communityoriented monitors. This form of the
annual standard was intended to
represent a relatively stable measure of
air quality and to characterize area-wide
PM2.5 concentrations in conjunction
with a 24-hour standard designed to
provide adequate protection against
localized peak or seasonal PM2.5 levels.
The current annual PM2.5 standard level
is to be compared to measurements
made at the community-oriented
monitoring site recording the highest
level, or, if specific constraints are met,
measurements from multiple
community-oriented monitoring sites
may be averaged (Part 50 App. N section
2.1(a) and (b) and Part 58 App. D at
2.8.1.6.1; 62 FR 38,672, July 18, 1997).
Community-oriented monitoring sites
were specified to be consistent with the
intent that a spatially averaged annual
standard protect those in smaller
communities, as well as those in larger
population centers. The constraints on
allowing the use of spatially averaged
measurements were intended to limit
averaging across poorly correlated or
widely disparate air quality values.36
This approach was judged to be
consistent with the epidemiologic
studies on which the PM2.5 standard
35 See American Trucking Associations v. EPA,
283 F. 3d at 374–75 (legitimate for EPA to consider
promotion of overall effectiveness of NAAQS
implementation programs, including their overall
stability, in setting a standard that is requisite to
protect the public health).
36 The current constraints include the criteria that
the correlation coefficient between monitor pairs to
be averaged be at least 0.6, and that differences in
mean air quality values between monitors to be
averaged not exceed 20 percent (Part 58 App. D at
2.8.1.6.1).
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was primarily based, in which air
quality data were generally averaged
across multiple monitors in an area or
were taken from a single monitor that
was selected to represent communitywide exposures, not localized ‘‘hot
spots’’ (62 FR 38672). These criteria and
constraints were intended to ensure that
spatial averaging would not result in
inequities in the level of protection
afforded by the PM2.5 standards (Id.).
In this review, there now exist much
more PM2.5 air quality data than were
available in the last review.
Consideration in the Staff Paper of the
spatial variability across urban areas
that is revealed by this new database has
raised questions as to whether an
annual standard that allows for spatial
averaging, within currently specified or
alternative constraints, would provide
appropriate public health protection.
Analyses in the Staff Paper to assess
these questions, as discussed below,
have taken into account both aggregate
population risk across an entire urban
area and the potential for
disproportionate impacts on potentially
vulnerable subpopulations within an
area.
The effect of allowing the use of
spatial averaging on aggregate
population risk was considered in
sensitivity analyses included in the
health risk assessment (EPA, 2005a). In
particular, analyses were done in
several urban areas that compared
estimated mortality risks based on
calculating compliance with alternative
standards (1) using air quality values
from the highest community-oriented
monitor in an area and (2) using air
quality values averaged across all such
monitors within the constraints allowed
by the current standard.37 As expected,
estimated risks associated with longterm exposures remaining upon just
meeting the current annual standard are
greater when spatial averaging is used
than when the highest monitor is used
(i.e., the estimated reductions in risk
associated with just attaining the
current or alternative annual standards
are less when spatial averaging is used),
as the use of the highest monitor leads
37 As discussed in the Staff Paper, section 4.2.2,
the monitored air quality values were used to
determine the design value for the annual standard
in each area, as applied to a ‘‘composite’’ monitor
to reflect area-wide exposures. Changing the basis
of the annual standard design value from the
concentration at the highest monitor to the average
concentration across all monitors changes the
ambient PM2.5 levels that are needed to just meet
the current or alternative annual standards. With
averaging, less overall reduction in ambient PM2.5
is needed to just meet the standards.
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to greater modeled reductions in
ambient PM2.5 concentrations.38
In considering the potential for
disproportionate impacts on potentially
vulnerable subpopulations, analyses
were done to assess whether any such
groups are more likely to live in census
tracts in which the monitors recording
the highest air quality values in an area
are located. Data were obtained for
demographic parameters measured at
the census tract level, including
education level, income level, and
percent minority population. Data from
the census tract in each area in which
the highest air quality value was
monitored were compared to the areawide average value (consistent with the
constraints on spatial averaging
provided by the current standard) in
each area. (Schmidt et al., 2005).
Recognizing the limitations of such
cross-sectional analyses, the Staff Paper
observes that the results suggest 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
percentage minority levels (EPA, 2005a,
p. 5–41).39 Noting the intended
purposes of the form of the annual
standard, as discussed above, the Staff
Paper concludes that the existing
constraints on spatial averaging may not
be adequate to avoid substantially
greater exposures in some areas,
potentially resulting in disproportionate
impacts on potentially vulnerable
subpopulations.
In considering whether more stringent
constraints on the use of spatial
averaging may be appropriate, the Staff
Paper presents results of an analysis of
recent air quality data on the
correlations and differences between
monitor pairs in metropolitan areas
across the country (Schmidt et al.,
38 For example, based on analyses conducted in
three example urban areas, estimated mortality
incidence associated with long-term exposure based
on the use of spatial averaging is about 10 to over
40 percent higher than estimated incidence based
on the use of the highest monitor (EPA, 2005a, p.
5–41).
39 As summarized in section II.A.4 above, the
Criteria Document notes that some epidemiologic
study results, most notably the associations
between mortality and long-term PM2.5 exposure in
the ACS cohort, have shown larger effect estimates
in the cohort subgroup with lower education levels
(EPA, 2004, p. 8–103). The Criteria Document also
notes that lower education level can be a marker for
lower socioeconomic status that may be related to
increased vulnerability to the effects of fine particle
exposures, for example, as a result of greater
exposure to sources such as roadways. Lower
education level may be associated with other
potential risk factors, such as poorer health status
or access to health care, that may also result in
increased susceptibility to the effects of air
pollution exposure (EPA, 2004, section 9.2.4.5)
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2005). For all pairs of PM2.5 monitors,
the median correlation coefficient based
on annual air quality data is
approximately 0.9, which is
substantially higher than the current
criterion for correlation of at least 0.6,
which was met by nearly all monitor
pairs. Similarly, the current criterion
that differences in mean air quality
values between monitors not exceed 20
percent was met for most monitor pairs,
while the annual median and mean
differences for all monitor pairs are 5
percent and 8 percent, respectively.
This analysis also shows that in some
areas with highly seasonal air quality
patterns (e.g., due to seasonal wood
smoke emissions), substantially lower
seasonal correlations and larger seasonal
differences can occur relative to those
observed on an annual basis. This
analysis provides some perspective on
the constraints on spatial averaging that
were put in place in the last review,
before data were widely available on
spatial distributions of PM2.5 air quality
levels, based on the extensive air quality
data and related analyses that have
become available since the last review.
In considering the results of the
analyses discussed above, the Staff
Paper concludes that it is appropriate to
consider either eliminating the
provision that allows for spatial
averaging from the form of an annual
PM2.5 standard or revising the allowance
for spatial averaging to be based on
more restrictive criteria. More
specifically, based on the analyses
discussed above, the Staff Paper
recommends consideration of revised
criteria such that the correlation
coefficient between monitor pairs to be
averaged be at least 0.9, determined on
a seasonal basis, with differences
between monitor values not to exceed
10 percent (EPA, 2005a, p. 5–42).
In considering the Staff Paper
recommendations based on the results
of the analyses discussed above, and
focusing on a desire to be consistent
with the epidemiologic studies on
which the PM2.5 health effects are based
and concern over the evidence of
potential disproportionate impact on
potentially vulnerable subpopulations,
the Administrator proposes to revise the
form of the annual PM2.5 standard
consistent with the Staff Paper
recommendation to change the criteria
for use of spatial averaging such that the
correlation coefficient between monitor
pairs must be at least 0.9, determined on
a seasonal basis, with differences
between monitor values not to exceed
10 percent. The Administrator also
solicits comment on the other Staff
Paper-recommended alternative of
revising the form of the annual PM2.5
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standard to one based on the highest
community-oriented monitor in an area,
with no allowance for spatial averaging.
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G. Level of Primary PM2.5 Standards
In the last review, having concluded
that both 24-hour and annual PM2.5
standards were appropriate, EPA
selected a level for each standard that
was appropriate for the function to be
served by such standard (62 FR 38652).
As discussed above, EPA concluded at
that time that the suite of PM2.5
standards could most effectively and
efficiently protect public health by
treating the annual standard as the
generally controlling standard for
lowering both short- and long-term
PM2.5 concentrations.40 In conjunction
with such an annual standard, the 24hour standard was intended to provide
protection against days with high peak
PM2.5 concentrations, localized
‘‘hotspots,’’ and risks arising from
seasonal emissions that would not be
well controlled by an annual standard.41
In selecting the level for the annual
standard in the last review, EPA used an
evidence-based approach that
considered the evidence from both
short- and long-term exposure studies.
The risk assessment conducted in the
last review, while providing qualitative
insights about the distribution of risks,
was considered to be too limited to
serve as a quantitative basis for
decisions on the standard levels. In
accordance with Staff Paper and CASAC
views on the relative strengths of the
short- and long-term exposure studies,
greater emphasis was placed on the
short-term exposure studies. In so
doing, EPA first determined a level for
the annual standard based on the shortterm exposure studies, and then
considered whether the long-term
exposure studies suggested the need for
a lower level. While recognizing that
health effects could occur over the full
range of concentrations observed in the
studies, EPA concluded that the
strongest evidence for short-term PM2.5
effects occurs at concentrations near the
long-term (e.g., annual) average in those
40 In so doing, EPA noted that an annual standard
would focus control programs on annual average
PM2.5 concentrations, which would generally
control the overall distribution of 24-hour exposure
levels, as well as long-term exposure levels, and
would also result in fewer and lower 24-hour peak
concentrations. Alternatively, a 24-hour standard
that focused controls on peak concentrations could
also result in lower annual average concentrations.
Thus, EPA recognized that either standard could
provide some degree of protection from both shortand 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).
41 See also American Trucking Associations v.
EPA, 283 F.3d at 373 (endorsing this reasoning).
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studies reporting statistically significant
health effects. Thus, in the last review,
EPA selected a level for the annual
standard that was below the lowest
long-term average PM2.5 concentration
in a short-term exposure study that
reported statistically significant health
effects. Further consideration of the
average PM2.5 concentrations across the
cities in the key long-term exposure
studies available at that time did not
provide a basis for establishing a lower
annual standard level.
In this review, the approach used in
the Staff Paper as a basis for staff
recommendations on standard levels
builds upon and broadens the general
approach used by EPA in the last
review. This broader approach reflects
the more extensive and stronger body of
evidence now available on health effects
related to both short- and long-term
exposure to PM2.5, together with the
availability of much more extensive
PM2.5 air quality data. This newly
available information has been used to
conduct a more comprehensive risk
assessment for PM2.5. As a consequence,
the broader approach used in the Staff
Paper discusses ways to take into
account both evidence-based and
quantitative risk-based considerations
and places relatively greater emphasis
on evidence from long-term exposure
studies than was done in the last
review.
Given the extensive body of new
evidence based specifically on PM2.5
that is now available, and the resulting
broader approach presented in the Staff
Paper, the Administrator considers it
appropriate to use a different approach
from that used in the last review to
select appropriate standard levels. More
specifically, the Administrator’s
proposal relies on an evidence-based
approach that considers the much
expanded body of evidence from shortterm exposure PM2.5 studies as the
principal basis for selecting the level of
the 24-hour standard and the stronger
and more robust body of evidence from
the long-term exposure PM2.5 studies as
the principal basis for selecting the level
of the annual standard. In the
Administrator’s view, the very large
number of health effect studies that are
now available provide the most reliable
basis for standard setting. With respect
to the quantitative risk assessment, the
Administrator recognizes that it rests on
a more extensive body of data and is
more comprehensive in scope than the
assessment conducted in the last
review, but is mindful that significant
uncertainties continue to underlie the
resulting risk estimates. Such
uncertainties generally relate to a lack of
clear understanding of a number of
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important factors, including for
example: The shape of concentrationresponse functions, particularly when,
as here, effect thresholds can neither be
discerned nor determined not to exist;
issues related to selection of appropriate
statistical models for the analysis of the
epidemiologic data; the role of
potentially confounding and modifying
factors in the concentration-response
relationships; issues related to
simulating how PM2.5 air quality
distributions will likely change in any
given area upon attaining a particular
standard, since strategies to reduce
emissions are not yet defined; and
whether there would be differential
reductions in the many components
within PM2.5 and if so whether this
would result in differential reductions
in risk. In the case of fine particles, the
Administrator recognizes that such
uncertainties are likely to be unusually
large due to the complexity in the
composition of the mix of fine particles
generally present in the ambient air.
Further, in the Administrator’s view, a
risk assessment based on studies that do
not resolve the issue of a threshold is
inherently limited as a basis for
standard setting, since it will
necessarily predict that ever lower
standards result in ever lower risks,
which has the effect of masking the
increasing uncertainty inherent as lower
levels are considered. As a result, while
the Administrator views the risk
assessment as providing supporting
evidence for the conclusion that there is
a need to revise the current suite of
PM2.5 standards, he judges that it does
not provide a reliable basis to determine
what specific quantitative revisions are
appropriate.
1. 24-Hour PM2.5 Standard
Based on the approach discussed
above, the Administrator has relied
upon evidence from the short-term
exposure PM2.5 studies as the principal
basis for selecting the level of the 24hour standard. In considering these
studies as a basis for the level of a 24hour standard, and having selected a
98th percentile form for the standard,
the Administrator agrees with the focus
in the Staff Paper of looking at the 98th
percentile values in these studies. In so
doing, the Administrator recognizes that
these studies provide no evidence of
clear effect thresholds or lowestobserved-effects levels. Thus, in
focusing on 98th percentile values in
these studies, the Administrator is
seeking to establish a standard level that
will require improvements in air quality
generally in areas in which short-term
exposure to PM2.5 can reasonably be
expected to be associated with serious
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health effects. While strategies that may
be employed in the future to bring about
such improvements in air quality in any
particular area are not yet defined, most
such strategies are likely to move the
broad distribution of PM2.5 air quality
values in an area lower, resulting in
reductions in risk associated with
exposures to PM2.5 levels across a wide
range of concentrations.
Based on the information in the Staff
Paper and a supporting staff memo,42
the Administrator observes an overall
pattern of statistically significant
associations reported in studies of shortterm exposure to PM2.5 across a wide
range of 98th percentile values. More
specifically, there is a strong
predominance of studies with 98th
percentile values down to about 39 µg/
m3 (in Burnett and Goldberg, 2003)
reporting statistically significant
associations with mortality, hospital
admissions, and respiratory symptoms.
For example, within this range of air
quality, statistically significant
associations were reported for mortality
in the combined Six City study (and
three of the individual cities within that
study) (Klemm and Mason, 2003), the
Canadian 8-City Study (Burnett and
Goldberg, 2003), and in studies in Santa
Clara County, CA (Fairley, 2003) and
Philadelphia (Lipfert, 2000); for hospital
admissions and emergency department
visits in Seattle (Sheppard et al., 2003),
Toronto (Burnett et al., 1997; Thurston
et al., 1994), Detroit (Ito, 2003, for
ischemic heart disease and pneumonia,
but not for other causes), and Montreal
(Delfino et al., 1998, 1997, for some but
not all age groups and years); for
respiratory symptoms in panel studies
in a combined Six City study (Schwartz
et al., 1994) and in two Pennsylvania
cities (Uniontown in Neas et al., 1995;
State College in Neas et al., 1996); and
for lung function in Philadelphia (Neas
et al., 1999).43 Studies in this air quality
range that reported positive but not
statistically significant associations with
mortality include studies in Detroit (Ito,
2003), Pittsburgh (Chock et al., 2000),
42 As discussed in the Staff Paper (EPA, 2005a, p.
5–30) and supporting staff memo (Ross and
Langstaff, 2005), staff focused on U.S. and Canadian
short-term exposure PM2.5 studies that had been
reanalyzed as appropriate to address statistical
modeling issues and considered the extent to which
the reported associations are robust to co-pollutant
confounding and alternative modeling approaches
and the extent to which the studies used relatively
reliable air quality data.
43 Of the studies within this group that evaluated
multipollutant associations, as discussed above in
section II.A.3, the results reported in Fairley (2003),
Sheppard et al. (2003), and Ito (2003) were
generally robust to inclusion of gaseous copollutants, whereas the effect estimate in Thurston
et al. (1994) was substantially reduced with the
inclusion of O3.
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and Montreal (Goldberg and Burnett,
2003).
Within the range of 98th percentile
PM2.5 concentrations of about 35 to 30
µg/m3, this strong predominance of
statistically significant results is no
longer observed. Rather, within this
range, some studies report statistically
significant results (Mar et al., 2003;
Ostro et al., 2003), other studies report
mixed results in which some
associations reported in the study are
statistically significant and others are
not (Delfino et al., 1997; Peters et al.,
2000),44 and another study reports
associations in two of six cities that are
not statistically significant (Klemm and
Mason, 2003). Further, the very limited
number of studies in which the 98th
percentile values are below this range
do not provide a basis for reaching
conclusions about associations at such
levels (Stieb et al., 2000; Peters et al.,
2001). Thus, in the Administrator’s
view, this body of evidence provides
confidence that statistically significant
associations are occurring down close to
this range, and it provides a clear basis
for concluding that this range represents
a range of reasonable values and thus for
selecting a 24-hour standard level from
within this range. The Administrator
further notes that focusing on the range
of 35 to 30 µg/m3 is consistent with the
interpretation of the evidence held by
most CASAC Panel members as
reflected in their recommendation to
select a 24-hour PM2.5 standard level
within this range (Henderson, 2005a).
The Administrator recognizes, however,
the separate point that most CASAC
Panel members favored the range of 35
to 30 µg/m3 for the 24-hour PM2.5
standard in concert with an annual
standard set in the range of 14 to 13 µg/
m3 (Henderson, 2005a), as discussed in
section II.G.2 below.
In considering what 24-hour standard
is requisite to protect public health with
an adequate margin of safety, the
Administrator is mindful that this
choice requires judgment based on an
interpretation of the evidence that
neither overstates nor understates the
strength and limitations of the evidence
or the appropriate inferences to be
drawn from the evidence. In the absence
of evidence of any clear effect
44 For example, Delfino et al. (1997) report
statistically significant associations between PM2.5
and respiratory emergency department visits for
elderly people (>64 years old), but not children (<2
years old) in one part of the study period (summer
1993) but not the other (summer 1992). Peters et al.
(2000) report new findings of associations between
fine particles and cardiac arrhythmia, but the
Criteria Document observes that the strongest
associations were reported for a small subset of the
study population that had experienced 10 or more
defibrillator discharges (EPA, 2004, p. 8–164).
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2649
thresholds, the Administrator may
select a specific standard level from
within a range of reasonable values. In
making this judgment, the
Administrator notes that the general
uncertainties related to the shape of the
concentration-response functions and
the selection of appropriate statistical
models affect the likelihood that
observed associations are causal down
to the lowest concentrations in the
studies. Further, and more specifically,
the variation in results found in the
short-term exposure studies in which
the 98th percentile values were below
35 µg/m3 indicates an increase in
uncertainty as to whether likely causal
associations extend down below this
level.
In considering the extent to which the
quantitative risk assessment inform his
selection of a 24-hour PM2.5 standard,
the Administrator recognizes that risk
estimates based on simulating the
attainment of standards set at lower
levels within this range will inevitably
suggest some additional reductions in
risk at each lower standard level
considered. However, these quantitative
risk estimates largely depend upon
assumptions made about the lowest
level at which reported associations will
likely persist and remain causal in
nature. Thus, the Administrator is
hesitant to use such risk estimates as a
basis for proposing a standard level
below 35 µg/m3, and instead prefers to
rely on inferences that are based directly
on the evidence in the studies
themselves.
Taking the above considerations into
account, the Administrator proposes to
set the level of the primary 24-hour
PM2.5 standard at 35 µg/m3. In the
Administrator’s judgment, based on the
currently available evidence, a standard
set at this level would protect public
health with an adequate margin of safety
from serious health effects including
premature mortality and hospital
admissions for cardiorespiratory causes
that are likely causally associated with
short-term exposure to PM2.5. This
judgment by the Administrator
appropriately considers the requirement
for a standard that is neither more nor
less stringent than necessary for this
purpose and recognizes 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 with an
adequate margin of safety. Being
mindful that the available evidence does
not provide a basis for identifying a
bright line within the range of 35 to 30
µg/m3 that clearly provides the
appropriate degree of public health
protection, the Administrator also
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solicits comment on selecting a lower
level within this range.
Having reached this decision to
propose a level of 35 µg/m3 for the 24hour PM2.5 standard based on the
approach to interpreting the available
evidence described above, the
Administrator recognizes that other
approaches to selecting a standard level
have been presented to the Agency.
These other approaches reflect
alternative views, principally expressed
in public comments to date, as to the
appropriate interpretation of the
scientific evidence and the appropriate
policy response in light of that
interpretation. One such view focuses
very strongly on the uncertainties
inherent in the epidemiologic and
toxicologic studies and the quantitative
risk assessment as the basis for
concluding that no change to the current
24-hour PM2.5 standard of 65 µg/m3 is
warranted. Such commenters prefer
greater weight, for example, on issues
related to the sensitivity in the
magnitude and statistical significance of
relative risks reported in studies using
different statistical models, noting that
further research is needed to inform
modeling strategies that will
appropriately adjust for temporal trends
and weather variables in time-series
studies. Additional uncertainties arise
from the potential confounding by copollutants, and the potential differential
toxicity of components within the mix
of fine particles. These commenters
suggest that the magnitude of risks
associated with fine particle exposures
have decreased since the last review.
Some such commenters also focus on
considerations such as the absence of
clear evidence from toxicologic studies
and from studies focused on elucidating
specific physiologic mechanisms by
which PM2.5 may be causing the
observed effects. Such commenters
recognize a need for a 24-hour PM2.5
standard, but consider the evidence to
be too uncertain overall to warrant any
tightening of the standard and instead
believe the appropriate policy response
in light of this uncertainty is to retain
the current level of the 24-hour
standard.
Other commenters who also focus
strongly on the uncertainties inherent in
the epidemiologic and toxicologic
studies and the quantitative risk
assessment reach a somewhat different
conclusion as to the appropriate policy
response in light of these uncertainties.
This group of commenters sees a basis
for lowering the level of the 24-hour
PM2.5 standard, but does not believe that
a level as low as 35 µg/m3 is warranted.
Such commenters note that while many
of the studies within the range of air
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quality from approximately 39 µg/m3 up
to the level of the current standard of 65
µg/m3 report statistically significant
results, only a few such studies
independently evaluated confounding
by co-pollutants. This lack of a broader
assessment of co-pollutants, together
with other types of uncertainties as
noted above, leads such commenters to
conclude that a standard level selected
from below this range is not warranted,
and that the appropriate policy response
is to select a standard level from within
the range of about 40 to 65 µg/m3.
In sharp contrast, others view the
epidemiologic evidence and other
health studies as strong and robust, and
generally place much weight on the
results of the quantitative risk
assessment as a basis for concluding
that a much stronger policy response is
warranted, generally consistent with a
standard level at or below 25 µg/m3.
While recognizing that important
uncertainties are inherently present in
both the evidence and estimated risks,
these commenters generally support a
view that such uncertainties warrant a
highly precautionary policy response,
particularly in view of the serious
nature of the health effects at issue, and
should be addressed by selecting a
standard level that incorporates a large
margin of safety.
The Administrator recognizes that
these sharply divergent views on the
appropriate level of the standard are
based on very different interpretations
of the science itself including its relative
strengths and limitations and on very
different judgments as to how such
scientific evidence should be used in
making policy decisions on proposed
standards. Consistent with the goal of
soliciting comments on a wide array of
views, the Administrator also solicits
broad public comment on these and
other alternative approaches and on the
related standard levels, such as levels
from 35 µg/m3 up to 65 µg/m3 or from
30 µg/m3 down to 25 µg/m3, that
commenters may believe are
appropriate, along with the rationale
supporting such approaches and levels.
In addition, the Administrator solicits
comments on issues related to the
interpretation of relevant epidemiologic
and toxicologic studies, including
approaches to addressing uncertainties
related to the sensitivity of results to
alternative statistical modeling
approaches, co-pollutant confounding,
and the lack of a discernable threshold
of effects, as well as approaches to more
fully characterize uncertainties in
quantitative risk assessments based on
epidemiologic studies.
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2. Annual PM2.5 Standard
Based on the approach discussed at
the beginning of this section, the
Administrator has relied upon evidence
from the long-term exposure PM2.5
studies as the principal basis for
selecting the level of the annual
standard. In considering these studies as
a basis for the level of an annual
standard, the Administrator agrees with
the focus in the Staff Paper of looking
at the long-term mean PM2.5
concentrations across the cities
included in such studies. In so doing,
the Administrator recognizes that these
studies, like the short-term exposure
studies, provide no evidence of clear
effect thresholds or lowest-observedeffects levels. Thus, in focusing on the
cross-city long-term mean
concentrations in these studies, the
Administrator is seeking to establish a
standard level that will require
improvements in air quality in areas in
which long-term exposure to PM2.5 can
reasonably be expected to be associated
with serious health effects.
Based on the characterization and
assessment of the long-term exposure
PM2.5 studies presented in the Criteria
Document and Staff Paper, the
Administrator recognizes the
importance of the validation efforts and
reanalysis that have been done since the
last review of the original Six Cities and
ACS mortality studies. These new
assessments provide evidence of
generally robust associations and
provide a basis for greater confidence in
the reported associations than in the last
review, for example, in the extent to
which they have made progress in
understanding the importance of issues
related to co-pollutant confounding and
the specification of statistical models.
Consistent with the information
available in the last review, these two
key long-term exposure mortality
studies reported long-term mean PM2.5
concentrations across all the cities
included in the studies of 18 and 21 µg/
m3, respectively. The Administrator also
particularly recognizes the importance
of the extended ACS mortality study,
published since the last review, which
provides new evidence of mortality
related to lung cancer and further
substantiates the statistically significant
associations with cardiorespiratoryrelated mortality observed in the
original studies. The Administrator
notes that the statistically significant
associations reported in the extended
ACS study, in a large number of cities
across the U.S., provide evidence of
effects at a lower long-term mean PM2.5
concentration (17.7 µg/m3) than had
been observed in the original study,
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although the relative risk estimates are
somewhat smaller in magnitude than
those reported in the original study. The
assessment in the Criteria Document of
these mortality studies, taking into
account study design, the strength of the
study (in terms of statistical significance
and precision of result), and the
consistency and robustness of results,
concludes that it would be appropriate
to give the greatest weight to the
reanalyses of the Six Cities and ACS
studies, and in particular to the results
of the extended ACS study (EPA, 2004,
p. 9–33) in weighing the evidence of
mortality effects associated with longterm exposure to PM2.5. Consistent with
that assessment, the Administrator
places greatest weight on these studies
as a basis for selecting the level of the
annual PM2.5 standard.
In addition to these mortality studies,
the Administrator also recognizes the
availability of relevant morbidity
studies providing evidence of
respiratory morbidity, including
decreased lung function growth, in
children with long-term exposure to
PM2.5. Studies conducted in the U.S.
and Canada include the 24-city study
considered in the last review and new
studies of cohorts of children in
southern California, in which the longterm mean PM2.5 concentrations in all
the cities included in the studies are
approximately 14.5 and 15 µg/m3,
respectively. As discussed in section
II.A. above, in the 24-city study,
statistically significant associations
were reported between long-term fine
particle exposures and lung function
measures at a single point in time,
whereas positive but not statistically
significant associations were reported
with prevalence of several respiratory
conditions. As interpreted in the last
review, the results from the 24-city
study are uncertain as to the extent to
which the association extends below a
long-term mean PM2.5 concentration of
approximately 15 µg/m3. The new
southern California children’s cohort
study provides evidence of important
respiratory morbidity effects in
children, including evidence for a new
measure of morbidity, decreased growth
in lung function. Reports from this
study suggest that long-term PM2.5
exposure is associated with decreases in
lung function growth, as measured over
a four-year follow-up period, although
statistically significant associations are
not consistently reported. The
Administrator recognizes that these are
important new findings, indicating that
long-term PM2.5 exposure may be
associated with respiratory morbidity in
children. However, the Administrator
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also observes this is the only study
reporting decreased lung function
growth, conducted in just one area of
the country, such that further study of
this health endpoint in other areas of
the country would be needed to increase
confidence in the reported associations.
Thus, at this time, the Administrator
provisionally concludes that this study
provides an uncertain basis for
establishing the level of a national
standard.
As discussed in the Staff Paper (EPA,
2005a, p. 5–22), the Administrator
generally agrees that it is appropriate to
consider a level for an annual PM2.5
standard that is below the averages of
the long-term PM2.5 concentrations
across the cities in the key long-term
exposure mortality studies, recognizing
that the evidence of an association in
any such study is strongest at and
around the long-term average where the
data in the study are most concentrated.
The Administrator is mindful that
considering what standard is requisite
to protect public health with an
adequate margin of safety requires
policy judgments that neither overstate
nor understate the strength and
limitations of the evidence or the
appropriate inferences to be drawn from
the evidence. The Administrator
provisionally concludes that these key
mortality studies, together with the
morbidity studies, provide a basis for
considering a standard level no higher
than 15 µg/m3. This level is somewhat
below the long-term mean
concentrations in the key mortality
studies and consistent with the
interpretation of the evidence from the
morbidity studies discussed above.
Further, in the Administrator’s view,
these studies do not provide a clear
basis for selecting a level lower than the
current standard of 15 µg/m3.
In considering the extent to which the
quantitative risk assessment can help to
inform these judgments with regard to
the annual PM2.5 standard, the
Administrator again recognizes that risk
estimates based on simulating the
attainment of standards set at lower
levels, as expected, continue to suggest
some additional reductions in risk at the
lower standard level considered in the
assessment, and that these estimates
largely depend upon assumptions made
about the lowest level at which reported
associations will likely persist and
remain causal in nature. Thus, the
Administrator is again hesitant to use
such risk estimates as a basis for
proposing a lower annual standard level
than 15 µg/m3, the level that is based
directly on the evidence in the studies
themselves, as discussed above.
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Taking the above considerations into
account, the Administrator proposes to
retain the level of the primary annual
PM2.5 standard at 15 µg/m3. In the
Administrator’s judgment, based on the
currently available evidence, a standard
set at this level would be requisite to
protect public health with an adequate
margin of safety from serious health
effects including premature mortality
and respiratory morbidity that are likely
causally associated with long-term
exposure to PM2.5. This judgment by the
Administrator appropriately considers
the requirement for a standard that is
neither more nor less stringent than
necessary for this purpose and
recognizes 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 with an adequate
margin of safety.
In so doing, the Administrator
recognizes that the CASAC Panel did
not endorse retaining the annual
standard at the current level of 15 µg/
m3 (Henderson, 2005a, p. 7). In
weighing the recommendation of the
CASAC Panel, the Administrator has
carefully considered the stated reasons
for it. In discussing its recommendation
(Henderson, 2005a), the CASAC Panel
first noted that changes to either the
annual or 24-hour PM2.5 standard, or
both, could be recommended. Three
reasons were then given for placing
more emphasis on lowering the 24-hour
standard than the annual standard: (1)
The vast majority of studies indicating
effects of short-term PM2.5 exposure
were carried out in settings in which
PM2.5 concentrations were largely below
the current 24-hour standard level of 65
µg/m3; (2) the amount of evidence on
short-term exposure effects, at least as
reflected by the number of reported
studies, is greater than for long-term
exposure effects; and (3) toxicologic
findings are largely related to the effects
of short-term, rather than long-term,
exposures. In not endorsing the option
of retaining the level of the current
annual standard in conjunction with
lowering the 24-hour standard, the
CASAC Panel observed that some cities
have relatively high annual PM2.5
concentrations without much day-today variation and that such cities would
only rarely exceed a 24-hour standard,
even if it were set at a level below the
current standard. In such a city,
attaining a 24-hour standard would
likely have minimal if any effect on the
long-term mean PM2.5 concentration and
consequently would be less likely to
reduce health effects associated with
long-term exposures. These observations
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were taken as an indication of the
desirability of lowering the level of the
annual PM2.5 standard as well as that of
the 24-hour standard. Based on these
considerations and taking into account
the results of the risk assessment, most
CASAC Panel members favored setting
an annual standard in the range of 14 to
13 µg/m3, along with lowering the 24hour standard (Henderson, 2005a).
In considering these views, the
Administrator notes that the
appropriateness of setting an annual
standard that would lower annual PM2.5
concentrations in cities across the
country depends upon a policy
judgment as to what annual level is
required to protect public health with
an adequate margin of safety from longterm exposures to PM2.5 in light of the
available evidence. In considering the
evidence of effects associated with longterm PM2.5 exposure as a basis for
selecting an adequately health
protective annual standard, as discussed
above, the Administrator provisionally
concludes that the evidence does not
provide a basis for requiring annual
levels below 15 µg/m3. Thus, the
Administrator agrees conceptually with
the CASAC Panel that any particular 24hour standard may not result in
reductions in the level of long-term
exposures to PM2.5 in all areas with
relatively higher than typical annual
PM2.5 concentrations and lower than
typical ratios of peak-to-mean values.
Further, the Administrator agrees that
this general advice supports relying on
the annual standard, and not the 24hour standard, to achieve the
appropriate level of protection from
long-term exposures to PM2.5. However,
the Administrator does not believe that
this advice necessarily translates into a
reason for setting the annual PM2.5
standard at a level below the current
level of 15 µg/m3. As discussed above,
the Administrator believes the principal
basis for selecting the appropriate level
of an annual standard should be the
evidence provided by the long-term
studies, in conjunction with judgments
concerning whether and over what
range of concentrations reported
associations are likely causal, and this
evidence reasonably supports retaining
the current level of the annual standard.
The Administrator places great
importance on the advice of CASAC,
and therefore solicits broad public
comment on the range of 15 down to 13
µg/m3, the low end of the range
recommended by CASAC, for the level
of the annual PM2.5 standard as well as
on the reasoning that formed the basis
for that recommendation. A decision to
select a standard from within this range
would place greater weight on the
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strength of the associations reported in
the key epidemiologic mortality and
morbidity long-term exposure studies
down to the lower part of the range of
PM2.5 concentrations observed across all
the cities included in these studies.
Such a standard could also reflect
greater reliance on the results of the
quantitative risk assessment that
suggested increased reductions in risk
associated with meeting an annual
standard at such lower levels.
The Administrator recognizes that an
even stronger view of the appropriate
policy response to the currently
available evidence has been expressed
by some public commenters. These
commenters have focused principally
on the strength of the long-term
exposure studies, including the new
children’s cohort study conducted in
southern California, as well as on those
results from the quantitative risk
assessment that are based on the
assumption that there is no threshold of
effects down to the lowest levels
observed in those studies. Such
considerations generally have led these
commenters to express views that
support a highly precautionary policy
response and the selection of a standard
level that incorporates a large margin of
safety, consistent with an annual PM2.5
standard level of 12 µg/m3. The
Administrator recognizes that this view
is based on a different interpretation of
the science itself including its relative
strengths and limitations and on
different judgments as to how such
scientific evidence should be used in
making policy decisions on proposed
standards. Consistent with the goal of
soliciting comments on a wide array of
views, the Administrator also solicits
broad public comment on this
alternative approach and on the related
standard level of 12 µg/m3.
The Administrator also recognizes a
contrasting view as to the interpretation
of and weight to be accorded to the
results from the ACS-based studies
(Pope et al., 1995; Krewski et al., 2000;
Pope et al., 2002). In this view, the ACSbased studies are not sufficiently robust
to support a policy response that would
tighten the annual PM2.5 standard based
on the evidence. This view emphasizes
the sensitivity of the results of these
studies to plausible changes in model
specification with regard to accounting
for the geographical proximity of cities
and the correlation of air pollutant
concentrations within a region, effect
modification by education level, and
inclusion of SO2 in the model. In this
view, these sensitivities suggest
potential confounding or effect
modification that has not been taken
into account. For example, concern has
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been raised about the sensitivity of
results in the reanalysis of data from the
ACS cohort study (Krewski et al., 2000)
to inclusion of SO2 in the models. As
discussed in section II.A.2.b above, the
reanalysis found that PM2.5, sulfates,
and SO2 were each associated with
mortality in single-pollutant models.
However, in two-pollutant models with
SO2 and PM2.5, the relative risk for PM2.5
was substantially smaller and no longer
statistically significant, whereas the
effect estimates for SO2 were not
sensitive to inclusion of PM2.5 or
sulfates in two-pollutant models. In this
view, the ACS-based risk estimates are
more robust for SO2 than for PM2.5 or
sulfates. In further extended analyses,
Pope et al. (2002) reported that effect
estimates were not highly sensitive to
spatial smoothing approaches intended
to address spatial autocorrelation, while
findings of effect modification by
education level were reaffirmed. Results
of multi-pollutant models were not
reported by Pope et al. (2002). Because
the correlation coefficient between
PM2.5 and SO2 was 0.50 in the ACS data,
in this view it is plausible to believe
that the independent effects of the two
pollutants could be disentangled with
additional study.
In this view, there is a separate but
related concern that tightening the
annual standard now, without a clear
understanding of which specific PMrelated pollutants are most toxic, will
have very uncertain public health
payoffs. In response to the advice of the
National Research Council (NRC) and
other scientists, the Agency is
undertaking, as one of its higher
priorities, a substantial research
program to clarify which aspects of PMrelated pollution are responsible for
elevated risks of mortality and
morbidity. For example, the Health
Effects Institute has issued a request for
applications to analyze the largest
database on specific components of PM
that has ever been assembled for public
health and medical researchers. The
time line for this multi-million dollar
research program is well designed to
inform the Agency’s next periodic
reevaluation of the primary ambient air
quality standard for PM2.5. In light of the
degree of sensitivity of the ACS-based
relative risk estimates to model
specifications and the significant
research underway, in this view, it
would be wiser to consider modification
of the annual standard with a fuller
body of information in hand rather than
initiate a change in the annual standard
at this time.
The Administrator solicits comment
on this view and on the issues raised in
interpreting the results of the ACS-based
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studies. For example, comment is
solicited on the extent to which the
associations reported in the ACS-based
studies suggest that SO2 should be
considered as a surrogate for fine
particles and/or the broader mix of air
pollutants or as an independent
pollutant exhibiting separate effects.
Comment is also solicited on relevant
research that would improve our
understanding of issues related to model
specification and alternative analytic
approaches that would better inform
judgments based on such epidemiologic
studies in the future.
H. Proposed Decisions on Primary PM2.5
Standards
For the reasons discussed above, and
taking into account the information and
assessments presented in the Criteria
Document and Staff Paper, the advice
and recommendations of CASAC, and
public comments to date, the
Administrator proposes to revise the
current primary PM2.5 standards.
Specifically, the Administrator proposes
to revise (1) the level of the 24-hour
PM2.5 standard to 35 µg/m3, and (2) the
form of the annual PM2.5 standard by
changing the constraints on the use of
spatial averaging to include the criterion
that the minimum correlation
coefficient between monitor pairs to be
averaged be 0.9 or greater, determined
on a seasonal basis, and the criterion
that differences between monitor values
not exceed 10 percent. Data handling
conventions are specified in proposed
revisions to Appendix N, as discussed
in Section V below, and the reference
method for monitoring PM as PM2.5 is
specified in proposed minor revisions to
Appendix L, as discussed in Section VI
below.
In recognition of alternative views of
the science and the appropriate policy
response based on the currently
available information, the Administrator
also solicits comments on (1) alternative
levels of the 24-hour PM2.5 standard
within the range of 35 to 30 µg/m3, and
alternative approaches for selecting the
level of the 24-hour PM2.5 standard, and
related levels (such as approaches that
suggest retaining the current level of 65
µg/m3, setting a level no higher than 25
µg/m3, or setting a level within the range
of 65 down to 35 µg/m3); (2) alternative
levels of the annual PM2.5 standard
below 15 µg/m3 down to12 µg/m3; (3)
issues related to consideration of
alternative indicators of fine particle
components; and (4) an alternative form
of the annual PM2.5 standard based on
the highest community-oriented
monitor in an area. Based on the
comments received and the
accompanying rationales, the
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Administrator may adopt other
standards within the range of the
alternatives identified above in lieu of
the standards he is proposing today.
The Administrator solicits comment
on all aspects of this proposed decision.
Comment is specifically invited on the
methodology for evaluating the
uncertainty and significance of risks to
public health. The Administrator
believes that it is important to further
develop ways of addressing uncertainty
when estimating such risk, recognizing
the wide variety of information
available in the underlying health
effects and other studies. The Agency
seeks comment on methods and
approaches for conducting a more
formalized uncertainty analysis. In
addition, the Agency seeks comment on
how to evaluate the results from a
formalized uncertainty analysis or from
the Staff Paper’s risk assessment, which
addresses multiple health effects across
multiple populations, in the context of
judging the public health importance of
such risks and determining the requisite
level of public health protection for the
PM standards.
To address issues related to the
transition from the current PM2.5
standards to revised PM2.5 standards,
the Administrator intends to seek public
comment on EPA’s implementation
plans for the revised PM2.5 standards,
including its plans for assuring an
effective transition, as part of an
advance notice of proposed rulemaking
(ANPR) on NAAQS implementation that
will be published in an early in 2006.
In this ANPR, EPA will be discussing
issues related to the timing and
regulatory implications of this
transition. The EPA intends to present
and take comment on the need and
potential approaches for revocation of
the current 24-hour PM2.5 standard, and
on issues related to the establishment of
no-backsliding requirements, such as
those adopted by the Agency in 1997
with respect to the ozone NAAQS. The
EPA also expects to address a variety of
implementation issues concerning
revised PM2.5 standards in the ANPR.
The ANPR will explain the designation
process and its timing, and the timing
of SIP submittals for both attainment
and nonattainment areas. The EPA also
expects to address issues regarding the
attainment dates for areas designated
nonattainment. The EPA will also
discuss new source permitting
requirements for both attainment and
nonattainment areas, i.e., the PSD and
Part D NSR programs. If the
Administrator promulgates a revised
PM2.5 standard, EPA will determine the
final implementation approach for that
standard.
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III. Rationale for Proposed Decisions on
Primary PM10 Standards
This action presents the
Administrator’s proposed decisions on
revision to the primary NAAQS for
PM10. The rationale for the proposed
revisions of the primary PM10 NAAQS
includes consideration of: (1) Evidence
of health effects related to short- and
long-term exposures to thoracic coarse
particles; (2) insights gained from a
quantitative risk assessment prepared by
EPA; and (3) specific conclusions
regarding the need for revisions to the
current standards and the elements of
PM10 standards (i.e., indicator,
averaging time, form, and level) that,
taken together, would be requisite to
protect public health with an adequate
margin of safety.
In developing this rationale, EPA has
taken into account the information
available from a growing, but still
limited, body of evidence on health
effects associated with thoracic coarse
particles from studies that use PM10-2.5
as a measure of thoracic coarse particles.
The EPA has drawn upon an integrative
synthesis of the body of evidence on
associations between exposure to
ambient thoracic coarse particles and a
range of health endpoints (EPA, 2004,
Chapter 9), focusing on those health
endpoints for which the Criteria
Document concludes that the
associations are suggestive of possible
causal relationships. In its policy
assessment of the evidence judged to be
most relevant to making decisions on
elements of the standards, EPA has
placed greater weight on U.S. and
Canadian epidemiological studies using
thoracic coarse particles measurements,
since studies conducted in other
countries may well reflect different
demographic and air pollution
characteristics.
While there is little question that
particles in the thoracic coarse particle
size range can present a risk of adverse
effects to the most sensitive regions of
the respiratory tract, the
characterization of health effects
attributable to various levels of exposure
to ambient thoracic coarse particles is
subject to uncertainties that are
markedly greater than is the case for fine
particles. As discussed below, however,
there is a growing body of evidence
available since the last review of the PM
NAAQS, with important new
information coming from epidemiologic,
toxicologic, and dosimetric studies.
Moreover, the newly available research
studies have undergone intensive
scrutiny through multiple layers of peer
review and extended opportunities for
public review and comment. While
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important uncertainties remain, the
review of the health effects information
has been extensive and deliberate. In the
judgment of the Administrator, this
intensive evaluation of the scientific
evidence has provided an adequate
basis for proposing regulatory decisions
at this time. This review also provides
important input to EPA’s research plan
for improving our future understanding
of the relationships between exposures
to ambient thoracic coarse particles and
health effects.
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A. Evidence of Health Effects Related to
Thoracic Coarse Particle Exposure
The first PM NAAQS (36 FR 8186)
used an indicator based solely on a
preexisting monitor for total suspended
particles (TSP) that was not designed to
focus on particles of greatest risk to
health. In preparing for the initial
review of those standards, EPA placed
a major emphasis on developing a new
indicator that considered the significant
amount of evidence on particle size,
composition, and relative risk of effects
from penetration and deposition to the
major regions of the respiratory tract
(Miller et al., 1979). The development
and assessment of these lines of
evidence in the PM Criteria Document
and PM Staff Paper published between
1979 and 1986 culminated in revised
standards for PM that used PM10 as the
indicator (52 FR 24634). The major
conclusion from that review, which
remained unchanged in the 1997
review, was that ambient particles
smaller than or equal to 10 µm in
aerodynamic diameter are capable of
penetrating to the deeper ‘‘thoracic’’ 45
regions of the respiratory tract and
present the greatest concern to health
(61 FR 65648). While considerable
advances have been made, the available
evidence in this review continues to
support the basic conclusions reached
in the 1987 and 1997 reviews regarding
penetration and deposition of fine and
thoracic coarse particles. As discussed
in the Criteria Document, both fine and
thoracic coarse particles penetrate to
and deposit in the alveolar and
tracheobronchial regions. For a range of
typical ambient size distributions, the
total deposition of thoracic coarse
particles to the alveolar region can be
comparable to or even larger than that
for fine particles. For areas with
appreciable coarse particle
concentrations, thoracic coarse particles
45 The ‘thoracic’ regions of the respiratory tract
are located in the chest (thorax) and are comprised
of the tracheo-bronchial region with connecting
airways and the alveolar, or gas-exchange region of
the lung. For ease of communications, ‘thoracic’
particles penetrating to these regions are often
called ‘inhalable’ particles.
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would tend to dominate particle
deposition to the tracheobronchial
region for mouth breathers (EPA, 2004,
p. 6–16). Deposition of particles to the
tracheobronchial region is of particular
concern with respect to aggravation of
asthma.
In the last review, little new
toxicologic evidence was available on
potential effects of thoracic coarse
particles and there were few
epidemiologic studies that had included
direct measurements of thoracic coarse
particles. Evidence of associations
between health outcomes and PM10 that
were conducted in areas where PM10
was predominantly composed of
thoracic coarse particles was an
important part of the basis for reaching
conclusions about the requisite level of
protection provided against coarse
particles for the final standards. The
new studies available in this review
include a number of epidemiologic
studies that have reported associations
with health effects using direct
measurements of PM10-2.5, as well as a
number of new toxicologic studies.
This section outlines key information
contained in the Criteria Document
(Chapters 6–9 and the Staff Paper
(Chapter 3) on known or potential
effects associated with exposure to
thoracic coarse particles and their major
constituents. The information
highlighted here summarizes: (1) New
information available on potential
mechanisms for health effects associated
with exposure to thoracic coarse
particles or their constituents; (2) the
nature of the effects that have been
associated with ambient thoracic coarse
particles or their constituents; (3) an
integrative assessment of the evidence
on health effects related to thoracic
coarse particles; (4) subpopulations that
appear to be sensitive to effects of
exposure to thoracic coarse particles;
and (5) the public health impact of
exposure to ambient thoracic coarse
particles.
1. Mechanisms
As summarized above, the first review
of the PM NAAQS found a strong basis
for concluding that thoracic coarse
particles could be plausibly linked to
health effects. This was based on an
integrated assessment of the physical
and chemical characteristics of ambient
coarse particles, the evidence regarding
health effects that could be associated
with deposition of coarse particulate
substances in the different regions of the
respiratory tract, and the relative
potential for penetration and deposition
of ambient distributions of coarse
particles in the human respiratory tract
(52 FR 24634). In the 1987 review, EPA
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found that occupational and toxicologic
studies provided ample cause for
concern related to higher levels of
thoracic coarse particles. Such findings
indicated that elevated levels of thoracic
coarse particles were linked with effects
such as aggravation of asthma and
increases in upper respiratory illness,
which was consistent with dosimetric
evidence of enhanced deposition of
thoracic coarse particles in the
respiratory tract (61 FR 65649).
Toxicologic and controlled human
exposure studies available in previous
reviews have generally used particle
exposures at levels higher than ambient
levels, relying on various particle
components or surrogates. Such studies
reported some effects on the respiratory
tract, indicative of inflammatory or
irritant effects for particles in both the
fine and thoracic coarse particle size
range (EPA, 1982, chapters 12 and 13;
EPA, 1996, chapters 10 and 11). As
discussed above in section II.A, the
results of numerous new toxicologic and
controlled human exposure studies have
implicated a number of potential
mechanisms or pathways for effects
associated with PM. Many of these
studies have used particle exposures
that are generally more relevant to
studying the effects of fine particles
than those of thoracic coarse particles.
However, several studies, discussed
more fully below, have suggested
mechanisms or pathways for thoracic
coarse particles to cause inflammatory
and other effects on the respiratory
system. This evidence generally
supports previous conclusions that
thoracic coarse particles can affect the
respiratory system.
Some limited evidence is available
from recent toxicologic studies on
effects of exposure to thoracic coarse
particles, specifically using PM10-2.5, for
either acute or chronic exposures (EPA,
2004, p. 9–55). This toxicologic
evidence includes results from studies
where respiratory cell cultures were
exposed to ambient particles, thus
providing insight into potential
mechanisms for respiratory effects of
thoracic coarse particles. The types of
effects reported include inflammatory
and allergic effects. For example, two
recent studies report inflammatory
responses in cells exposed to extracts of
water-soluble and water-insoluble
materials from thoracic coarse particles
and fine particles collected in Chapel
Hill, NC (Monn and Becker, 1999;
Soukup and Becker, 2001). One study
focused on water-soluble materials, and
reported significant immune system
effects with water-soluble extracts of
ambient PM10-2.5, in contrast to the lack
of effects observed with extracts from
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ambient PM2.5 as well as indoorcollected PM10-2.5 and PM2.5. The
authors report that different components
of PM10-2.5 appeared to have different
effects, with endotoxin implicated in
inflammatory effects, while coarse
particulate metals appeared to have a
role in cytotoxicity effects (Monn and
Becker, 1999). A followup study in the
same laboratory (Soukup and Becker,
2001) reports that the insoluble
materials from thoracic coarse particles
resulted in several effects on immune
system cells.46 In this extract of thoracic
coarse particles, endotoxin appeared to
be the most pro-inflammatory
component, but components other than
endotoxin or metals appeared to
contribute to other effects. Using
particles collected in two urban areas in
the Netherlands, Becker et al. (2003)
reported that thoracic coarse particles,
but not fine or ultrafine particles,
resulted in effects related to
inflammation and decreased pulmonary
defenses. This small group of studies
thus suggests that exposure to thoracic
coarse particles may cause proinflammatory effects, as well as
cytotoxicity and oxidant generation
(EPA, 2004, section 7.4.2). While still
limited, these emerging new studies
provide additional insight into potential
mechanisms for respiratory effects of
thoracic coarse particles. The results
also indicate that different health
responses may be linked with different
components of thoracic coarse particles.
In contrast, one recent study exposed
human red blood cell cultures to
ambient coarse particles collected in
Italy and found only limited effects on
blood cells (Diociaiuti et al., 2001). The
addition of thoracic coarse particles that
were collected in Italy to human
respiratory tract cell cultures produced
only limited evidence of carcinogenic
effects; some response was seen with
thoracic coarse particles but greater
response was reported with fine particle
exposures (Hornberg et al., 1998). These
latter results are consistent with the
evidence from epidemiologic studies,
which provide no direct evidence for
carcinogenicity of thoracic coarse
particles.
As noted in past reviews (EPA, 1981b,
1996b), deposition of a variety of
particle types in the tracheobronchial
region, including resuspended urban
dust and coarse-fraction organic
materials, has the potential to affect
lung function and aggravate symptoms,
particularly in asthmatics. Of particular
note are limited toxicologic studies that
46 Examples of such effects include cytokine
production, decreased phagocytic ability and
oxidant generation.
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found urban road dust can produce
cellular and immunological effects (e.g.,
Kleinman et al., 1995; Steerenberg et al.,
2003). Road dust is a major source of
thoracic coarse particles in urban areas
and is therefore representative of the
components expected to be found in
resuspended thoracic coarse particles.
In the 1996 Staff Paper, results from the
study by Kleinman and colleagues
(1995) were highlighted in which effects
were observed in rats with inhalation
exposure to road dust. These effects
included changes in the structure of the
rat airways as well as effects on immune
cells. Higher concentrations of road dust
were needed to cause effects, compared
with exposures to fine particle
components (e.g., sulfates, nitrates), in
part because of the limited penetration
of coarse-sized particles past the nose of
the rats studied (EPA, 1996b, p. V–70).47
Another study used a standard
toxicologic approach to studying
allergic responses, and the authors
concluded that exposure to road tunnel
dust particles resulted in greater allergyrelated effects than did exposure to
several other particle samples, including
residual oil fly ash and diesel exhaust
particles (Steerenberg et al., 2003).48 In
this study, the particles were collected
in a road tunnel and placed directly in
the animal respiratory tract, so
differences in inhalability of larger
particles in rodents was not an issue. In
contrast, a number of studies have
reported that Mt. St. Helens volcanic
ash, which is generally in the size range
of thoracic coarse particles, has very
little toxicity in animal or in vitro
toxicologic studies (EPA, 2004, p. 7–
216).
The Criteria Document finds that the
limited number of recent toxicologic
studies using PM10-2.5 provide some
evidence that coarse fraction particle
exposures can result in effects primarily
linked to the respiratory system, related
to inflammation or aggravation of
allergic effects. Toxicologic studies have
suggested potential pathways for effects
from a few sources or components of
thoracic coarse particles, such as road
dust particles, metals or organic
constituents. The need to better
understand the relationship between
different components or sources of
thoracic coarse particles remains a key
47 The particles used in this study were collected
by vacuum sweeping of freeway surfaces in
California, and were generally 5 µm in diameter or
lower (Kleinman et al., 1995).
48 This approach, using ovalbumin-sensitized
mice, is commonly used for comparing allergic
potency of air pollutants. The authors also tested
responses in an additional toxicologic model, based
on pollen-sensitized rats, and reported responses
only with diesel exhaust particles (Steerenberg et
al., 2003, p. 1436).
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area of uncertainty with regard to the
effects of thoracic coarse particles.
2. Nature of Effects
In the last review, EPA considered a
substantial number of epidemiological
studies using PM10, which contains both
fine and coarse particles, as a measure
of exposure to PM. In many such studies
in which fine and coarse particles occur
at similar levels, it is difficult or
impossible to determine whether fine
and coarse particles both played major
roles in the associations. Accordingly,
considerable emphasis was placed on
the more limited body of evidence from
PM10 studies in locations where coarse
particles were a much greater fraction of
PM10 than were fine particles. These
findings indicated that short-term
exposure to thoracic coarse particles in
such areas was linked with respiratory
morbidity effects, such as aggravation of
asthma, increases in respiratory
symptoms and respiratory infections (62
FR 38677). The single available shortterm exposure study that compared
associations between mortality and fine
and coarse particles reported a
significant association between shortterm exposure to PM10-2.5 and mortality
in one of six cities (Steubenville, OH).
In this location, an unusually high
correlation between high levels of fine
and thoracic coarse particles suggested
a common industrial source, and a clear
conclusion about the relative
contribution was not possible. The
study found no association with
thoracic coarse particles in a combined
multi-city analysis (Schwartz et al.,
1996; CD, p. 8–40 to 8–41).49 No studies
in the past review provided clear
epidemiologic evidence of mortality or
morbidity effects related to long-term
exposure to PM10-2.5. EPA observed that
toxicologic studies offered some
qualitative evidence suggesting the
potential for effects on the respiratory
system with long-term exposure to
coarse particles or coarse particle
constituents (62 FR 38678).
In this review, epidemiologic studies
have continued to support a
relationship between short-term
exposure to thoracic coarse particles
and respiratory morbidity, with effects
ranging from increased respiratory
symptoms to hospitalization for
respiratory diseases. As discussed
below, the new studies also suggest
associations with effects on the
cardiovascular system and possibly with
49 Note that in more recent reanalyses of this
study to investigate statistical modeling issues, the
association for Steubenville was not statistically
significant in most models reported in the two
reanalyses (Klemm and Mason, 2003; Schwartz,
2003a).
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mortality. Figure 2 summarizes results
from both multi-city and single-city
epidemiologic studies using short-term
exposures to PM10-2.5, including all U.S.
and Canadian studies that used direct
measurements of PM10-2.550 and for
which effect estimates and confidence
intervals were reported. Consistent with
the presentation of fine particle study
results in Figure 1, the central effect
estimate is indicated by a diamond for
each study result, with the vertical bar
representing the 95 percent confidence
interval around the estimate. The results
of these epidemiologic studies are
discussed below.
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provided plausible evidence that shortterm exposure to thoracic coarse
particles was associated with such
effects. This is followed by a discussion
of new findings on potential
cardiovascular effects of thoracic coarse
particles, as well as new evidence from
studies of mortality.
Investigators have sometimes also used prediction
models to ‘‘fill’’ or estimate PM concentrations
where measurements are not available (most often
where data are collected less frequently than daily).
In one particular study in Coachella Valley,
measurements were made of fine and thoracic
coarse particle concentrations for two and a half
years. The investigators predicted PM10-2.5
concentrations for a longer time series, based on a
ten-year data set for PM10 for use in the health study
(Ostro et al., 2003).
The discussion below focuses first on
evidence related to respiratory
morbidity effects, since information
available in the previous review
50 All epidemiologic studies discussed below
included measurements of thoracic coarse particles
either through monitors that collected thoracic
coarse particles separately (e.g., dichotomous
monitors) or using data from side-by-side (colocated) monitors for fine particles and PM10.
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i. Morbidity
(a) Effects on the Respiratory System
Evidence available in the last review
suggested that aggravation of asthma
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a. Effects Associated With Short-Term
Exposure to Thoracic Coarse Particles
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and respiratory infections and
symptoms were associated with PM10 in
areas where thoracic coarse particles
were a much greater fraction of PM10
than were fine particles, such as
Anchorage, AK, and southeast
Washington (62 FR 38679). Only one
epidemiologic study had used PM10-2.5
data; it reported a positive, but not
statistically significant, association
between respiratory hospital admissions
and PM10-2.5 in Toronto (Thurston et al.,
1994).
Several new studies of respiratory
symptoms and lung function have
included both PM10-2.5 and PM2.5 data,
and these results suggest a role for
thoracic coarse particles as well as for
fine particles in associations with
respiratory symptoms (EPA, 2004, p. 8–
311). In the Six Cities study, a
statistically significant increase in
cough for children was found with
PM10-2.5 but not with PM2.5, while the
reverse was true for lower respiratory
symptoms. When both PM10-2.5 and
PM2.5 were included in models, the
effect estimates were reduced for each,
but PM10-2.5 retained significance in the
association with cough and PM2.5
retained significance in the association
with lower respiratory symptoms
(Schwartz and Neas, 2000).51 Changes in
lung function were evaluated in three
cities in Pennsylvania, and in all three,
short-term exposure to thoracic coarse
particles was not significantly
associated with peak flow rate, although
some statistically significant
associations were found with exposure
to fine particles (EPA, 2004, p. 8–312).
Three new U.S. and Canadian
epidemiologic studies have reported
associations between short-term
exposure to PM10-2.5 with hospital
admissions for respiratory diseases,
including asthma, pneumonia and
COPD (Burnett et al., 1997; Ito, 2003;
Sheppard et al., 2003). As shown in
Figure 2, the effect estimates for these
associations are positive and some are
statistically significant. In these
associations with respiratory
hospitalization, the risk estimates tend
to fall in the range of 5 to 15 percent per
25 µg/m3 PM10-2.5 (EPA, 2004, p. 8–193).
Because fine particles and ozone, as
well as other gaseous air pollutants, are
known to cause respiratory effects, a key
consideration for assessing this body of
studies is assessment of potential
confounding by these co-pollutants, as
discussed in detail in Section 8.4.3 of
the Criteria Document. The associations
51 The authors conclude that for acute asthmarelated responses as well as daily mortality, fine
particles are a stronger predictor of health response
that are thoracic coarse particles (Schwartz and
Neas, 2000, p. 8).
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reported between respiratory hospital
admissions and short-term exposure to
PM10-2.5 were largely unchanged in most
cases when gaseous co-pollutants were
included in the models (EPA, 2004,
Figure 8–18; Burnett et al., 1997; Ito,
2003).52 Few investigators have
evaluated potential confounding of
PM10-2.5 effects with adjustment for
PM2.5 in multi-pollutant models. Only
the study conducted in Detroit included
such multi-pollutant models for
respiratory hospitalization and was
reanalyzed to address potential
statistical modeling questions. In this
study, the simultaneous consideration
of PM10-2.5 and PM2.5 resulted in
reduction in the size of the effect
estimate, as well as loss of statistical
significance, for both pollutants. The
authors report that the correlation
between the two pollutants was
‘‘modest’’ (correlation coefficient of
0.42) (Lippmann et al., 2000, p. 33). The
results in this study vary by health
outcome; for example, for pneumonia
hospitalization, effect estimates for
PM2.5 were little changed but those for
PM10-2.5 decreased substantially in
magnitude in two-pollutant models. In
contrast, effect estimates for PM2.5 with
COPD hospitalization decreased
dramatically, whereas those for PM10-2.5
were only slightly decreased in size in
two-pollutant models (Ito, 2003, pp.
152, 153).
Additional insight into the respiratory
effects of coarse particles is provided by
studies using PM10 in locations where
thoracic coarse particles were a much
greater fraction of PM10 than were fine
particles. This review includes new
PM10 studies in such relatively high
coarse-fraction areas, such as Reno, NV
and Anchorage, AK.53 In these areas,
statistically significant associations have
been reported between PM10 and
52 More specifically, the effect estimates for
associations between PM10-2.5 and hospitalization
for COPD and pneumonia in Detroit are largely
unchanged with the addition of gaseous copollutants to the models, except in one case where
the PM10-2.5 effect estimate for COPD hospitalization
is substantially reduced in size with the inclusion
of O3 in the model (Ito, 2003). Results for the study
in Toronto also show relatively consistent effect
estimate size for associations between PM10-2.5 and
respiratory hospitalization, except for the models
including NO2 and all four gaseous pollutants
(Burnett et al., 1997).
53 For example, Anchorage, AK and Reno, NV do
not currently attain the PM10 24-hour standard
which is set at 150 µg/m3. Based on 2002–2004
data, the 98th percentile PM2.5 concentrations in
these areas were 21 and 25 µg/m3, respectively. As
noted in the fine particle discussion above, no
short-term exposure studies to date have shown
statistically significant associations between fine
particles and effects with 98th percentile values this
low. This suggests that coarse particles either
caused or contributed to the observed PM10
associations.
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hospitalization for respiratory diseases
(Chen et al., 2000) and outpatient
medical visits for asthma (Choudhury et
al., 1997). These findings support the
evidence from the limited group of
studies discussed above that have
reported associations between measured
PM10-2.5 and respiratory morbidity.
Considering evidence from across a
range of respiratory morbidity health
outcomes, the Criteria Document
concludes that the epidemiologic
evidence indicates that both fine and
thoracic coarse particles impact
respiratory health (EPA, 2004, p. 8–311).
(b) Effects on the Cardiovascular System
Two new studies conducted in the
U.S. and Canada have also reported
associations between short-term
exposure to PM10-2.5 and hospital
admissions for various cardiovascular
diseases. The results of these studies are
included in Figure 2, where it can be
seen that the associations are generally
positive and the results of the larger
studies with more statistical power are
statistically significant (Burnett et al.,
1997, cardiovascular disease
hospitalization; Ito, 2003, ischemic
heart disease hospitalization). The
excess risks for hospital admissions for
cardiovascular diseases range from
about 1 to 10 percent per 25 µg/m3
PM10-2.5, as seen in the Detroit study
(EPA, 2004, p. 8–310). In addition, a
statistically significant association was
reported between PM10 and increased
hospitalization for cardiovascular
diseases in Tucson, AZ, an urban area
where thoracic coarse particles are a
much greater fraction of PM10 than are
fine particles (Schwartz, 1997).54 The
Criteria Document finds that
associations between cardiovascular
hospitalization and short-term PM10-2.5
exposure were relatively unchanged
when gaseous co-pollutants were
included in the models (EPA, 2004,
Figure 8–17; Burnett et al., 1997; Ito,
2003).55 In assessing potential
confounding between PM2.5 and
PM10-2.5, one new study in Detroit
reported that simultaneous
consideration of PM10-2.5 and PM2.5
resulted in a reduction in effect estimate
54 Tucson currently attains the PM
10 standard,
and the 98th percentile 24-hour average
concentrations reported for PM2.5 are 15 and 17µg/
m3 at two monitoring sites in the area.
55 The effect estimates for associations between
PM10-2.5 and hospitalization for ischemic heart
disease and heart failure in Detroit are largely
unchanged with the addition of gaseous copollutants to the models (Ito, 2003). Results
presented for the study in Toronto also show
relatively consistent effect estimate size for
associations between PM10-2.5 and cardiovascular
hospitalization, except for the models including
NO2 and all four gaseous pollutants (Burnett et al.,
1997).
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size and a lack of statistical significance
for both PM indicators (Ito, 2003). In the
reanalysis for this study, for example, a
significant association was reported
between PM10-2.5 and hospitalization for
ischemic heart disease in a singlepollutant model, and in a two-pollutant
model the effect estimates for PM2.5 and
PM10-2.5 were both reduced in
magnitude and neither remained
statistically significant (Ito, 2003, pp.
152, 153).
Epidemiologic studies have also
reported associations between shortterm exposures to ambient PM
(generally using PM10 or PM2.5) and
more subtle cardiovascular health
outcomes (e.g., changes in heart rhythm
or cardiovascular biomarkers) (EPA,
2004, p. 8–169). Only one of this new
set of epidemiologic studies included
PM10-2.5, and no significant associations
were reported between onset of
myocardial infarction and short-term
PM10-2.5 exposures (EPA, 2005a, p. 8–
165; Peters et al., 2001).
ii. Mortality
In the few epidemiologic studies
available for the last review, only the
Six City study summarized above
evaluated the relationship between
short-term exposure to PM10-2.5 and
mortality. That study provided a
suggestion of a potential effect of
thoracic coarse particles only in the city
with the highest coarse and fine particle
concentrations, but it was not possible
to separate fine and thoracic coarse
particle contributions.
As shown in Figure 2 for U.S. and
Canadian studies, effect estimates for
associations between mortality and
short-term exposure to PM10-2.5 are
generally positive and similar in
magnitude to those for PM2.5 and PM10
though most are not statistically
significant. In general, the confidence
intervals (indicating uncertainty) are
greater for associations between
mortality and PM10-2.5 than for
associations with PM2.5, as is apparent
when directly comparing results from
numerous studies as shown in Figure 8–
5 of the Criteria Document (EPA, 2004,
p. 8–61). In the same comparison, it can
be seen that the size of the effect
estimates for the associations are in the
same range. In general, effect estimates
are somewhat larger for respiratory and
cardiovascular mortality than for total
mortality. Two of the five effect
estimates for cardiovascular mortality
with short-term PM10-2.5 exposure are
positive and statistically significant
(Mar et al., 2003; Ostro et al., 2003)
while none of the effect estimates for
total mortality reach statistical
significance. The new studies include a
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multi-city study that uses data from the
eight largest Canadian cities and
reported associations between total
mortality and PM10-2.5 as well as PM2.5
and PM10. The effect estimates were of
similar magnitude for each PM indicator
(Burnett and Goldberg, 2003), but the
association with PM10-2.5 did not reach
statistical significance. The magnitude
of the effect estimates for PM10-2.5 are
similar to those for PM2.5, generally
falling in the range of 3 to 8 percent for
cardiovascular mortality per 25 µg/m3
PM10-2.5.
Potential confounding by co-pollutant
gases has been assessed in some of these
mortality studies. As shown in Figures
8–16 through 8–18 of the Criteria
Document, the associations reported
with PM10-2.5 are generally unchanged in
effect size when co-pollutant gases are
included in multi-pollutant models. The
evidence available on potential
confounding between PM2.5 and PM10-2.5
is limited, but the Criteria Document
includes results from two studies that
showed effects of the two PM indicators
to be relatively independent in multipollutant models, however, these
particular analyses were not included in
reanalyses to address statistical
modeling questions.56
iii. Effects of Thoracic Coarse Particle
Components or Sources in
Epidemiologic Studies
In considering the epidemiologic
evidence on morbidity or mortality
associations with short-term exposure to
thoracic coarse particles, EPA
recognizes that the issue of the relative
toxicity of different PM components,
discussed above in section II.A.1 for fine
particles, is an important uncertainty for
thoracic coarse particles as well. Several
toxicologic studies, discussed above in
section III.A.1, have reported evidence
of effects with different components or
sources of thoracic coarse particles.
However, the available epidemiologic
studies that have used PM10-2.5 did not
evaluate associations with specific
components of thoracic coarse particles
(EPA, 2004, section 8.2.2.5.2). As
discussed in section II.A, several studies
have reported that PM2.5 from
combustion-related sources is more
strongly linked with mortality than
PM2.5 of crustal origin. However, these
findings are not directly relevant to
findings related to thoracic coarse
particles. Combustion sources are a
major contributor to PM2.5 emissions,
but not to emissions of PM10-2.5, while
crustal material is an important
component of PM10-2.5 but only a small
portion of PM2.5 (EPA, 2005a, Table 2–
2).
One study that does have relevance to
considering the effects of PM10-2.5 from
different sources assessed the
contribution of dust storms to PM10related mortality. The authors focused
on days when dust storms or high wind
events occurred in Spokane, during
which thoracic coarse particles from
surrounding rural soils are the dominant
fraction of PM10. No evidence was
reported of increased mortality on days
with high PM10 levels related to these
dust storms (average PM10 level was 221
µg/m3 higher on dust storm days than
on other study days) (Schwartz, et al.,
1999), suggesting that PM10-2.5 from
wind-blown rural dust is also not likely
associated with mortality.57 EPA has
also observed that the available
epidemiologic studies using PM10-2.5
have been conducted in urban areas,
such as Phoenix, Detroit and Seattle.
Coarse particles are generally not
distributed over broad areas, but rather
reflect contributions from more
localized sources, thus it is more
difficult than for fine particles to
generalize the results of these studies to
areas with other types of sources.
The Criteria Document finds that the
new epidemiologic studies support the
conclusions drawn in the previous
review, and indicate that short-term
exposure to thoracic coarse particles is
likely associated with respiratory
morbidity. The epidemiologic studies
report statistically significant
associations between short-term PM10-2.5
exposure and outcomes ranging from
respiratory symptoms to hospitalization
for respiratory diseases (EPA, 2004, p.
8–312). A limited body of new
56 One study was the Canadian 8-city study, in
which multi-pollutant models included PM2.5 and
PM10-2.5 and gaseous co-pollutants, with moderate
reductions in the effect estimate size for both PM
indicators (Burnett et al., 2000). Moolgavkar (2000)
presented results of two-pollutant models for PM2.5
and PM10-2.5 with COPD hospitalization in Los
Angeles, and again, effect estimates for both
pollutants were generally reduced somewhat in
size. The author also reports that associations with
PM10-2.5 were generally reduced in size and lost
statistical significance in two-pollutant models
including CO. These two studies were reanalyzed
to address potential issues with statistical model
specification, but these multi-pollutant model
results were not included in the reanalysis reports.
57 In addition, studies conducted in several areas
in the western U.S. have reported that associations
between PM10 and mortality or morbidity remained
unchanged or became larger and more precise when
days indicative of wind-blown dust or high PM10
concentration days were excluded from the
analyses (Pope et al., 1999; Schwartz, 1997; Chen
et al., 2000; Hefflin et al., 1994). This group of
studies does not provide conclusive evidence of any
effects or lack of effects associated with wind-blown
dust or high concentration days, nor were the
studies designed specifically for that purpose. The
results do, however, indicate that associations
between PM10 and health outcomes in these
western areas are not overly influenced or ‘‘driven
by’’ such days.
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associated with long-term exposure to
thoracic coarse particles (EPA, 1996b, p.
V–67a) . In this group of cities, mean
thoracic coarse particle concentrations
ranged from approximately 4 to 15 µg/
m3. Several new studies have used data
from the Southern California children’s
cohorts, one of which included PM10-2.5
data; in these cities, mean thoracic
coarse particle concentrations ranged
from 6 to 39 µg/m3. In this study,
decreases in several measures of lung
function growth were associated with
long-term exposure to PM10-2.5 (as well
as PM10 and PM2.5) though not all
associations reached statistical
significance (Gauderman et al., 2000).
Further, in analyses for a second cohort
of children, no statistically significant
associations were reported between lung
function growth and long-term PM10-2.5
exposure (Gauderman et al., 2002, p.
81). The correlation reported between
PM10-2.5 and PM2.5 in this area was
unusually high (r=0.76); in twopollutant models, the authors observe
that the effects reported with both
pollutants were reduced in magnitude,
b. Effects Related to Long-Term
and did not remain statistically
Exposure to Thoracic Coarse Particles
significant, with somewhat larger
In the last review, the available
reductions for PM10-2.5 associations than
prospective cohort study results had
for PM2.5 (Gauderman et al., 2000, p.
shown no evidence of associations
1387). Thus, results from one children’s
between long-term exposure to thoracic
cohort study provide no evidence of
coarse particles and either mortality
associations between long-term to
(Dockery et al., 1993; Pope et al., 1995)
exposure to PM10-2.5 and respiratory
or morbidity (Dockery et al., 1996;
morbidity, while findings from a more
Raizenne et al., 1996). As discussed
recent cohort study provide only very
above for PM2.5, new studies available in limited evidence for such effects.
this review include the reanalyses and
Overall, EPA finds that the available
extended analyses for the Six Cities and evidence provides little support to link
ACS cohort studies of mortality, and
long-term exposures to thoracic coarse
new analyses from the southern
particles with respiratory morbidity
California children’s cohorts of
(EPA, 2004, p. 9–34).
morbidity effects.
3. Integration and Interpretation of the
In both the reanalyses and extended
Health Evidence
analyses of the ACS cohort study, longterm exposure to PM10-2.5 was not
As discussed in section II.A.3, the
significantly associated with mortality
Criteria Document and Staff Paper
(CD, p. 8–105; Krewski et al., 2000; Pope focused on well-recognized criteria in
et al., 2002). Based on evidence from
evaluating the epidemiologic evidence,
reanalyses and extended analyses using including the strength of associations;
ACS cohort data, the Criteria Document robustness of reported associations to
concludes that the long-term exposure
the use of alternative model
studies find no associations between
specifications, potential confounding by
long-term exposure to thoracic coarse
co-pollutants, and exposure
particles and mortality (EPA, 2004, p. 8– misclassification related to
measurement error; consistency of
307).
In the previous review, results from
findings in multiple studies of adequate
the Harvard 24-city study had shown
power, and in different persons, places,
associations between respiratory illness circumstances and times; and the nature
prevalence and decreased lung function of concentration-response relationships.
in children with fine particles or fine
These evaluations addressed key
particle indicators, but not with the
methodological issues that are relevant
larger size fractions (Dockery et al.,
to interpretation of evidence from
1996; Raizenne et al., 1996). Further
epidemiologic studies. Further, findings
EPA staff evaluation of the data from
from epidemiologic studies were
this study that suggested that lung
integrated with available experimental
function decrements were not
evidence (e.g., dosimetric and
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epidemiologic evidence suggests that
short-term exposure to thoracic coarse
particles is associated with effects on
the cardiovascular system. Finally, the
Criteria Document finds that evidence
from health studies on associations
between short-term exposure to PM10-2.5
and mortality is ‘‘limited and clearly not
as strong’’ as evidence for associations
with PM2.5 or PM10 but nonetheless is
suggestive of associations with mortality
(EPA, 2004, p. 9–28, 9–32). As
discussed briefly above, some
epidemiologic evidence suggests that
there are components of thoracic coarse
particles (e.g., crustal material in nonurban areas) that are less likely to have
adverse effects, at least at lower
concentrations, than other components.
Based on the epidemiologic evidence,
the Criteria Document concluded that
the limited body of evidence provided
suggestive evidence for associations
between throacic coarse particles and
various mortality and morbidity effects
‘‘in some locations’’ (EPA, 2004, p. 8–
338).
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2659
toxicologic), in considering the extent of
coherence and biological plausibility of
effects observed in epidemiologic
studies. This integrative assessment
formed the basis for the Criteria
Document and Staff Paper to draw
judgments about the extent to which
causal inferences can be made about
observed associations between health
endpoints and thoracic coarse particles
combination with other pollutants. The
key elements of these evaluations are
summarized below. Many of these
issues are discussed in section II.A.3
above for fine particles, and are thus
only briefly summarized here with
regard to implications for thoracic
coarse particles.
(1) Effect estimates from associations
between short-term exposures to
thoracic coarse particles and various
health outcomes are generally small in
size. The Criteria Document observes
that the associations are similar in size
to those reported for PM2.5, but with less
precision as the measurement error for
PM10-2.5 is greater than that for PM2.5.
Thus, the Criteria Document concludes
that the magnitude of PM10-2.5
associations is similar to those for fine
particles, but the lesser precision of the
associations reduces the strength of the
evidence for thoracic coarse particles
(EPA, 2004, p. 9–41).
(2) EPA has evaluated the robustness
of epidemiologic associations in part by
considering the effect of differences in
statistical model specification, exposure
error on PM-health associations, and
potential confounding by co-pollutants.
Sensitivity to model specification was
discussed above for fine particles, and,
in general, similar conclusions apply to
studies using PM10-2.5. Section 8.4.2 of
the Criteria Document discusses a series
of reanalyses that address issues related
to a specific type of statistical model
(‘‘generalized additive methods’’) used
in some recent epidemiologic studies.
The results of the reanalyses showed
little change in effect estimates for some
studies; in others the effect estimates
were reduced in size though it was
observed that the reductions were often
not substantial (EPA, 2004, p. 9–35).
Overall, the Criteria Document
concludes that associations between
short-term exposure to PM and various
health outcomes are generally robust to
the use of alternative modeling
strategies, recognizing that further
evaluation of alternative modeling
strategies is warranted. It was also
observed that the results of reanalyses
indicated that effect estimates were
more sensitive to the modeling
approach used to account for temporal
effects and weather variables than to the
specific model specifications, and thus
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recommended further exploration of
alternative modeling approaches for
time-series analyses (EPA, 2004, pp. 8–
236 to 8–237).
Recent epidemiologic studies have
also evaluated the influence of exposure
error on PM-health associations. This
includes both consideration of error in
measurements of PM, and the degree to
which measurements from an
individual monitor reflect exposures to
the surrounding community. As
discussed in section 8.4.5 of the Criteria
Document, several studies have shown
that fairly extreme conditions (e.g., very
high correlation between pollutants and
no measurement error in the ‘‘false’’
pollutant) are needed for complete
‘‘transfer of causality’’ of effects from
one pollutant to another (EPA, 2004, p.
9–38). Exposure error is likely to be
more important for associations with
PM10-2.5 than with PM2.5, since there is
generally greater error in PM10-2.5
measurements, PM10-2.5 concentrations
are less evenly distributed across a
community, and thoracic coarse
particles are less likely to penetrate into
buildings (EPA, 2004, p. 9–38). Thus,
factors related to exposure error likely
result in reduced precision for
epidemiologic associations with
PM10-2.5.
There are two key implications of this
uncertainty for this review. First, for an
individual epidemiologic association,
the increased uncertainty in
measurements would tend to increase
the standard error about the effect
estimate, possibly reducing statistical
significance of the findings. This would
mean that a set of positive but generally
not statistically significant associations
between PM10-2.5 and a health outcome
could be reflecting a true association
that is measured with error (EPA, 2004,
p. 5–126). Second, this uncertainty
about measurements is an important
consideration in evaluating the air
quality concentrations with which a
statistical association is reported. The
air quality levels reported in these
studies, as measured by ambient
concentrations at monitoring sites
within the study areas, are not
necessarily good surrogates for the
population exposures that are likely
associated with the observed effects in
the study areas or that would likely be
associated with effects in other urban
areas across the country. The
concentrations measured at one
particular site may over-or underestimate air quality levels in other parts
of the area. In evaluating the air quality
data from the locations in which
epidemiologic associations were
reported, as discussed in the Staff Paper
and below in section III.G, examples of
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both cases are seen. For example, in
Coachella Valley, mortality was
statistically significantly associated with
PM10-2.5 measurements made at one site
(Ostro et al., 2003), but these air quality
measurements appear to represent
concentrations on the high end of
PM10-2.5 levels for Coachella Valley
communities. In contrast, statistically
significant associations were reported
with PM10-2.5 measurements in Detroit
(Ito, 2003), and in this case the data
appear to represent concentrations on
the low end of PM10-2.5 levels for the
Detroit area (EPA, 2005a, p. 5–65, 5–66).
Finally, some investigators have
assessed the robustness of associations
between health outcomes and shortterm exposures to PM10-2.5 in multipollutant models to potential
confounding by the gaseous copollutants or fine particles. A high
degree of correlation between the
concentrations of thoracic coarse
particles and other pollutants (either
gaseous co-pollutants or fine particles)
can make interpretation of the study
results difficult. Multi-pollutant models
including PM10-2.5 and gaseous copollutants are included in Figures 8–16
through 8–18 of the Criteria Document,
where it can be seen that associations
with PM10-2.5 are largely unchanged
when gaseous co-pollutants are added to
the models (EPA, 2004, section 8.4.3).
Further, in the available epidemiologic
studies, it can be seen that correlations
between the gaseous co-pollutants (CO,
NO2, O3, SO2) and PM10-2.5
concentrations are often lower than
correlations between the gases and fine
particles.58 While recognizing that
disentangling the effects attributable to
various pollutants within an air
pollution mixture is challenging, the
Criteria Document concludes that effect
estimates for associations between PM,
including PM10-2.5, and health endpoints
are generally robust to confounding by
gaseous co-pollutants (EPA, 2004, p. 9–
37).
Less information is available from
studies that specifically assessed
potential confounding between fine and
thoracic coarse particles, as noted
above. The reported correlation
coefficients between PM10-2.5 and PM2.5
are in the low to moderate range for
most such studies, i.e., generally in a
range of below 0.3 to 0.5, with some
notably higher correlation coefficients
reported in Phoenix (0.59) and
58 For example, from the studies included in
Figures 8–16 through 8–18, correlation coefficients
reported in Detroit between PM10-2.5 and the four
gaseous co-pollutants ranged from 0.13 to 0.32,
whereas the correlation coefficients between PM2.5
and the gaseous co-pollutants range from 0.38–0.49
(Ito, 2003).
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Steubenville (0.69). As observed
previously, one study in Detroit
evaluated the effects of both PM2.5 and
PM10-2.5 simultaneously where the
correlation between the two pollutants
was ‘‘modest’’ (correlation coefficient of
0.42). The authors report a reduction in
coefficients for both PM10-2.5 and PM2.5
in associations with mortality and
hospital admissions for respiratory or
cardiovascular diseases (Ito, 2003, pp.
152–153); the degree of reduction in size
varied for different health outcomes.
Similarly, Schwartz and Neas (2000)
report some reduction in effect estimate
size for both PM10-2.5 and PM2.5
associations across six cities in twopollutant models, but the association
reported between PM10-2.5 and cough
remains statistically significant.59 Two
studies reported associations between
PM10-2.5 and mortality (Ostro et al.,
2003, Coachella Valley; Mar et al., 2003,
Phoenix); stronger associations were
reported with PM10-2.5 than PM2.5 by
Ostro et al., although the authors note
the reduced sample size for PM2.5 may
have influenced the statistical power
(Ostro et al., 2003). Both areas have
relatively low fine particle
concentrations, with 98th percentile
PM2.5 concentrations of about 32 µg/m3
in Phoenix and 34 µg/m3 in Coachella
Valley, while the correlation coefficient
reported between PM2.5 and PM10-2.5
was low in Coachella Valley (0.28) and
fairly high in Phoenix (0.59). This
limited body of evidence suggests that
PM10-2.5 and PM2.5 have associations
with health outcomes that are likely
independent of one another, but further
work is needed to help distinguish the
contributions of thoracic coarse
particles on health outcomes from those
of fine particles.
Overall, the Criteria Document
concludes that associations reported
between health outcomes and shortterm exposure to PM10-2.5 are generally
robust to the use of alternative modeling
strategies, to adjustment for the
potential confounding effects of gaseous
co-pollutants, and in terms of exposure
error (EPA, 2004, p. 9–46). However, the
remaining uncertainties are larger in
assessing the degree to which effects
observed with thoracic coarse particle
exposures are independent from effects
of fine particles. In addition, in
interpreting the results of epidemiologic
studies, it is difficult to determine how
well PM10-2.5 concentrations measured
at ambient monitoring stations
59 The correlation coefficients between PM
10-2.5
and PM2.5 range from 0.23 to 0.45 in five of the six
cities (Boston, Knoxville, Portage, Topeka, and St.
Louis), with a correlation coefficient of 0.69 in
Steubenville.
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characterize the magnitude of
population exposures to thoracic coarse
particles.
(3) In assessing consistency in effect
estimates, the epidemiologic study
results suggest that effect estimates may
differ from one location to another, but
the extent of variation is not clear. For
example, in one multi-city study, some
limited evidence was reported in the
reanalysis to address model
specification issues that suggested some
heterogeneity among the 8 largest
Canadian cities for associations with
PM10-2.5, although there had been no
evidence of heterogeneity in initial
study findings (Burnett and Goldberg,
2003; EPA, 2004, p. 9–39). As was
observed for fine particles, there are a
number of factors that would be likely
to cause variation in PM-health
outcomes in different populations and
geographic areas. The Criteria Document
discusses such factors, including the
mix of PM sources and composition, the
mix of other gaseous pollutants,
geographic features that would affect the
spatial distribution of ambient PM, and
population characteristics that affect
susceptibility or exposure levels (EPA,
2004, p. 9–41). In addition, the use of
data collected on a 1-in-6 or 1-in-3 day
schedule results in reduced statistical
power, resulting in less precision for
estimated effect estimates for the
individual cities and increased potential
variability in results (EPA, 2004, p. 9–
40). Overall, the Criteria Document
concludes that there is some
consistency in effect estimates for
hospitalization for respiratory and
cardiovascular causes with short-term
exposure to thoracic coarse particles,
though fewer studies are available on
which to make such an assessment than
are available for fine particles (EPA,
2004, p. 9–47).
(4) Of the group of new epidemiologic
studies that have evaluated the shape of
concentration-response functions, many
(generally using PM10) have been unable
to detect threshold levels in the
relationship between short-term PM
exposure and mortality. One single-city
study used PM10-2.5 and PM2.5
measurements in Phoenix and reported
that there was no indication of a
threshold in the association between
PM10-2.5 and mortality (Smith et al.,
2000; EPA, 2004, p. 8–322). However, a
few analyses have provided suggestions
of some potential threshold levels,
generally at fairly low ambient
concentrations. Thus, the Criteria
Document concludes that the evidence
did not support selecting any particular
population threshold for PM10-2.5,
recognizing that there may be thresholds
for specific health responses in
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individuals, and that it is possible that
such thresholds exist toward the lower
end of the range of air quality
measurements in the health studies, but
cannot be detected due to variability in
susceptibility across a population. Even
in those few studies with suggestive
evidence of such thresholds, the
potential thresholds are at fairly low
concentrations (EPA, 2004, sections
8.4.7 and 9.2.2.5).
(5) Several issues related to exposure
time periods were assessed in the
Criteria Document, as summarized in
section 3.6.5 of the Staff Paper. One key
issue is the lag period between thoracic
coarse particle exposure and health
outcome in short-term exposure studies.
In many epidemiologic studies, the
authors have reported a pattern of
positive associations across several
consecutive lag periods for thoracic
coarse particles, such that an effect
estimate for any individual lag day for
thoracic coarse particles likely
underestimates the magnitude of the
PM-health response. A number of recent
studies that have investigated
associations with distributed lags
provide effect estimates for health
responses that persist over a period of
time (days to weeks) after the exposure
period and the effect estimates are often,
but not always, larger in size that those
for single-day lag periods; however,
available studies have generally not
included PM10-2.5 (EPA, 2004, p. 8–281).
As reported for fine particles, the
Criteria Document concludes that it is
likely that the most appropriate lag
period for a study will vary, depending
on the health outcome and the specific
pollutant under study. (EPA, 2004, p. 8–
279).
(6) In integrating evidence from across
scientific disciplines, the Criteria
Document and Staff Paper observed that
the body of epidemiologic evidence on
thoracic coarse particles is smaller than
that for fine particles and the evidence
available from toxicologic studies is also
more limited. The clearest case for a
causal relationship for coarse particles
is for effects on the respiratory system.
The epidemiologic results showing
respiratory effects is consistent with the
assessment of regional particle
penetration and deposition, as well the
observations from more limited
toxicologic studies. The fractional
deposition of elevated coarse particle
concentrations is significant in the
tracheobronchial region, which is
particularly sensitive in asthmatic
individuals. From the limited number of
toxicologic studies using PM10-2.5, as
noted above in section III.A.1, there is
some evidence that exposure to thoracic
coarse particles results in respiratory-
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related effects such as inflammation or
oxidative stress. In addition, allergic
adjuvant effects were linked with road
dust exposures. These findings are
generally consistent with epidemiologic
evidence linking PM10-2.5 with
respiratory morbidity, such as increased
respiratory symptoms and
hospitalization for respiratory diseases
such as asthma or COPD.
The evidence is less coherent for
effects on the cardiovascular system.
Some epidemiologic studies have
reported significant associations with
hospital admissions for cardiovascular
diseases, and associations reported with
cardiovascular mortality are positive
and some are statistically significant
(see Figure 2). However, the very
limited available evidence from
toxicologic studies or epidemiologic
studies on more subtle cardiovascular
effects has not provided evidence that
demonstrates plausible mechanisms or
pathways for these effects.
Based on an integrative assessment of
the evidence, the Criteria Document
concludes that this growing but still
limited body of health evidence is
suggestive of causality in associations
between short-term (but not long-term)
exposures to thoracic coarse particles
and health effects, particularly for
associations with respiratory morbidity.
(7) In summary, based on the
available evidence and the evaluation of
that evidence in the Criteria Document
and Staff Paper, the Criteria Document
concludes that the body of evidence on
effects related to exposure to thoracic
coarse particles is less strong than that
for fine particles, but provides
suggestive evidence of causality for
short-term exposure to PM10-2.5 and
morbidity, including hospitalization for
respiratory diseases, increased
respiratory symptoms and decreased
lung function, and possibly mortality
(EPA, 2004, pp. 9–79, 9–80). The Staff
Paper recognizes, however, that the
substantial uncertainties associated with
this limited body of evidence suggest
that it should be interpreted with a high
degree of caution (EPA, 2005a, p. 5–70).
4. Sensitive Subgroups for Effects of
Thoracic Coarse Particle Exposure
As described in section II.A.4, there
are several population groups that may
be susceptible or vulnerable to PMrelated effects. These groups include
those with preexisting lung diseases,
such as asthma, and children and older
adults. Emerging evidence indicates that
people from lower socioeconomic strata
or who have particularly elevated
exposures may be more vulnerable to
PM-related effects. However, the
available evidence does not generally
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allow distinctions to be drawn between
the PM indicators, in terms of which
groups might have greater susceptibility
or vulnerability to PM2.5 or PM10-2.5
(EPA, 2005a pp. 3–35 to 36).
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5. Impacts on Public Health From
Thoracic Coarse Particle Exposure
While recognizing that the health
evidence regarding effects of thoracic
coarse particles is more limited, the
Criteria Document has concluded that
the evidence suggests causal
associations between short-term
exposure to thoracic coarse particles
and morbidity effects, such as
respiratory symptoms or hospital
admissions for respiratory diseases, and
possibly mortality. As observed above,
the potentially susceptible populations
for such effects include people with
preexisting respiratory diseases,
including asthma, and children and
older adults. In focusing on respiratory
effects likely associated with PM10-2.5, it
can be observed that population groups
with respiratory diseases such as asthma
or COPD include tens of millions of
people (EPA, 2004; Tables 9–4 and 9–
5). Considering the magnitude of these
subpopulations and risks identified in
health studies, the Criteria Document
concludes that exposure to thoracic
coarse particles can have an important
public health impact.
B. Quantitative Risk Assessment
The general overview and discussion
of key components of the risk
assessment used to develop risk
estimates for PM2.5 presented in section
II.B above is also applicable to the
assessment done for PM10-2.5 in this
review. However, the scope of the risk
assessment for PM10-2.5 is much more
limited than that for PM2.5, reflecting the
much more limited body of
epidemiologic evidence and air quality
information available for PM10-2.5. As
discussed in chapter 4 of the Staff
Paper, the PM10-2.5 risk assessment
includes risk estimates for just three
urban areas for two categories of health
endpoints related to short-term
exposure to PM10-2.5: hospital
admissions for cardiovascular and
respiratory causes and respiratory
symptoms.
Consistent with the approach used in
the PM2.5 risk assessment, discussed
above in section II.B, PM10-2.5-related
health risks attributable to
anthropogenic sources and activities
(i.e., risk associated with concentrations
above background or above various
selected higher cutpoints intended as
surrogates for alternative assumed
population thresholds) were estimated
by using the reported linear or log-linear
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concentration-response functions from
epidemiologic studies and available air
quality data from the locations in which
the studies had been conducted. A
series of base case analyses were
conducted, using the same assumed
cutpoints as were used in the
assessment of short-term exposures to
PM2.5.
Estimates of hospital admissions
attributable to short-term exposure to
PM10-2.5 have been developed for Detroit
(cardiovascular and respiratory
admissions) and Seattle (respiratory
admissions), and estimates of
respiratory symptoms have been
developed for St. Louis.60 Base case
estimates of respiratory-related hospital
admissions under recent air quality
levels in Detroit are on the order of
several hundred admissions per year
across the range of assumed cutpoints
considered in this assessment. The
Detroit estimates are roughly one to two
orders of magnitude greater than the
range of estimated asthma-related
admissions in Seattle, which can be
attributed in part to differences in
baseline risks related to respiratoryrelated health endpoints as well as to
differences in PM10-2.5 air quality levels
in these two areas. More specifically,
recent (e.g., 2001-2003) PM10-2.5
concentrations are substantially higher
in Detroit, where the current 24-hour
PM10 standard is not met, than they are
in Seattle (where the 24-hour PM10
design value is well below the level of
the current PM10 standard). In
considering risk estimates for
respiratory symptoms in St. Louis, the
number of days of cough in children
living in St. Louis associated with
recent PM10-2.5 levels range from
approximately 27,000 days per year 61 at
the lowest assumed cutpoint to almost
3,000 days per year at the highest
assumed cutpoint. For the same time
period, PM10-2.5 air quality levels in St.
Louis are high, where, like Detroit, the
current 24-hour PM10 standard is not
met.
While one of the goals of the PM10-2.5
risk assessment was to provide
estimates of the risk reductions
associated with just meeting alternative
PM10-2.5 standards, the nature and
magnitude of the uncertainties and
concerns associated with this portion of
the risk assessment weigh against use of
these risk estimates as a basis for
recommending specific standard levels
60 Quantitative risk estimates associated with
recent air quality levels for these three cities are
presented in Figures 4–11 and 4–12 in Chapter 4
of the Staff Paper.
61 This represents roughly 1100 days of cough per
100,000 people in the general population, of which
approximately 12 percent are children.
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(EPA, 2005a, p. 5–69). These
uncertainties and concerns include, but
are not limited to the following:
(1) As noted above in section II.A and
discussed more fully below in section
III.G, the PM10-2.5 levels measured at
ambient monitoring sites in recent years
may be quite different from the levels
used to characterize exposure in the
original epidemiologic studies based on
monitoring sites in different location,
thus possibly over- or underestimating
population risk levels.
(2) There is greater uncertainty about
the reasonableness of the use of
proportional rollback to simulate just
meeting alternative PM10-2.5 standards in
any urban area relative to that for PM2.5
due to the limited availability of historic
PM10-2.5 air quality data.
(3) The locations used in the PM10-2.5
risk assessment are not representative of
urban areas in the U.S. that experience
the most significant 24-hour peak
PM10-2.5 concentrations, and thus,
observations about relative risk
reductions associated with alternative
standards may not be relevant to the
areas expected to have the greatest
health risks associated with elevated
ambient PM10-2.5 levels.
(4) The health effects database that
supplies the concentration-response
relationships used in the PM10-2.5 risk
assessment is much smaller than that
available for PM2.5, which limits EPA’s
ability to evaluate the robustness of the
risk estimates for the same health
endpoints across different locations.
C. Need for Revision of the Current
Primary PM10 Standards
The initial issue to be addressed in
the current review of the primary PM10
standards is whether, in view of the
advances in scientific knowledge
reflected in the Criteria Document and
Staff Paper, the existing standards
should be revised. The Staff Paper
addresses this question by first
considering the conclusions reached in
the last review, the subsequent litigation
of that decision, and the nature of the
new information available in this
review.
In 1997, in conjunction with
establishing new PM2.5 standards, EPA
concluded that continued protection
against potential effects associated with
thoracic coarse particles in the size
range of 2.5 to 10 µm was warranted
based on particle dosimetry, toxicologic
information, and limited epidemiologic
evidence (62 FR 38,677). This
information indicated that thoracic
coarse particles can deposit in the
sensitive regions of the lung of most
concern (e.g., the tracheobronchial and
alveolar regions, which together make
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up the thoracic region),62 and that they
can be expected to aggravate effects in
individuals with asthma and contribute
to increased upper respiratory illness
(62 FR 38,666–8).
Further, EPA decided that the new
function of PM10 standard(s) would be
to provide such protection against
effects associated with particles in this
narrower size range between 2.5 to 10
µm. Although some consideration had
been given to a more narrowly defined
indicator that did not include fine
particles (e.g., PM10-2.5), EPA decided
that it was more appropriate to continue
to use PM10 as the indicator for
standards to control thoracic coarse
particles. 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
in areas where the coarse fraction was
the dominant fraction of PM10, namely
two studies conducted in areas that
substantially exceeded the 24-hour PM10
standard (62 FR 38,679). The decision
also reflected the fact that there were
only very limited ambient air quality
data then available specifically on
thoracic coarse particles, in contrast to
the extensive monitoring network
already in place for PM10. In essence,
EPA concluded at that time that it was
appropriate to continue to control
thoracic coarse particles, but that the
only information available upon which
to base such standards was indexed in
terms of PM10.
In subsequent litigation regarding the
1997 PM NAAQS revisions, however,
the court held in part that PM10 is a
‘‘poorly matched indicator’’ for thoracic
coarse particles in the context of a rule
that also includes PM2.5 standards
because PM10 includes PM2.5. American
Trucking Associations v. EPA, 175 F.3d.
at 1054. Although the court found
‘‘ample support’’ (id.) for EPA’s decision
to regulate thoracic coarse particles, it
vacated the 1997 revised PM10 standards
for that reason. The result of subsequent
EPA actions, discussed above in section
I.C, is that the 1987 PM10 standards
remain in place (65 FR 80776, 80777,
Dec. 22, 2000) and the present review is
consequently of those 1987 standards.
In this review, the Staff Paper focuses
on the information now available from
a growing, but still limited, body of
62 EPA further concluded at that time that the
risks of adverse health effects associated with
deposition of particles in the thoracic region are
‘‘markedly greater than for deposition in the
extrathoracic (head) region,’’ and that risks from
extrathoracic deposition are ‘‘sufficiently low that
particles which deposit only in that region can
safely be excluded from the standard indicator’’ (62
FR 38,666).
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evidence on health effects associated
with thoracic coarse particles from
studies that use PM10-2.5 as the measure
of thoracic coarse particles. In addition,
there is now much more information
available to characterize air quality in
terms of PM10-2.5 than was available in
the last review.63 In considering this
information, the Staff Paper finds that
the major considerations that formed the
basis for EPA’s 1997 decision to retain
PM10 as the indicator for thoracic coarse
particles, rather than a more narrowly
defined indicator that does not include
fine particles, no longer apply. More
specifically, the continued use of PM10
as an indicator for standards intended to
protect against health effects associated
with thoracic coarse particles is no
longer appropriate since information is
now available that supports the use of
a more directly relevant indicator,
PM10-2.5. Further, continuing to rely
principally on health effects evidence
indexed by PM10 to determine the
appropriate averaging time, form, and
level of a standard is no longer
necessary or appropriate since a number
of more directly relevant studies,
indexed by PM10-2.5, are also now
available. Thus, separate from any legal
considerations, the Staff Paper
concludes it is appropriate to revise the
current PM10 standards in part by
revising the indicator for thoracic coarse
particles, and by basing any such
revised standard principally on the
currently available evidence and air
quality information indexed by PM10-2.5,
but also considering evidence from
studies using PM10 in locations where
PM10-2.5 is the predominant fraction
(EPA, 2005a, section 5.4.1).
Recognizing that dosimetric evidence
formed the principal basis for the initial
establishment of the PM10 indicator in
1987, and supported the decision in
1997 to retain the PM10 indicator, the
Staff Paper also considers whether
currently available dosimetric evidence
continues to support the basic
conclusions reached in those reviews of
the standards. In particular,
consideration is given to available
information about patterns of
penetration and deposition of thoracic
coarse particles in the sensitive thoracic
region of the lung and to whether an
aerodynamic size of 10 µm remains a
reasonable separation point for particles
that penetrate and potentially deposit in
the thoracic regions. The Staff Paper
concludes that while considerable
advances have been made in
understanding particle dosimetry, the
available evidence continues to support
those basic conclusions from past
reviews. More specifically, both fine
particles, indexed by PM2.5, and thoracic
coarse particles, indexed by PM10-2.5,
penetrate to and deposit in the thoracic
regions. Further, for a range of typical
ambient size distributions, the total
deposition of thoracic coarse particles to
the alveolar region can be comparable to
or even larger than that for fine particles
(EPA, 2004, p. 6–16).
Beyond the dosimetric evidence, as
noted in past reviews (EPA, 1981b,
1996b), toxicologic studies show that
the deposition of a variety of particle
types in the tracheobronchial region,
including resuspended urban dust and
coarse-fraction organic materials, has
the potential to affect lung function and
aggravate respiratory symptoms,
particularly in asthmatics. Of particular
note are limited toxicologic studies that
found urban road dust can produce
cellular and immunological effects (e.g.,
Kleinman, et al., 1995; Steerenberg et
al., 2003).64 In addition, some very
limited in vitro toxicologic studies show
some evidence that coarse particles may
elicit pro-inflammatory effects (EPA,
2004, section 7.4.4). Further, the Staff
Paper assessment of the
physicochemical properties and
occurrence of ambient coarse particles
suggests that both the chemical makeup
and the spatial distribution of coarse
particles are likely to be more
heterogeneous than for fine particles
(EPA, 2005a, chapter 2). In particular, as
discussed below in section III.D, coarse
particles in urban areas can contain all
of the components found in more rural
areas, but be contaminated by a number
of additional materials, from motor
vehicle-related emissions to metals and
transition elements associated with
industrial operations. The Staff Paper
concludes that the weight of the
dosimetric, limited toxicologic, and
atmospheric science evidence, taken
together, lends support to the
plausibility of the PM10-2.5-related
effects reported in urban epidemiologic
studies, and provides support for
retaining some standard for thoracic
coarse particles so as to continue
programs to protect public health from
such effects (EPA, 2005a, p. 5–49).
The available epidemiologic evidence,
discussed above in section III.A,
includes studies of associations between
short-term exposure to thoracic coarse
particles, indexed by PM10-2.5, and
63 Coarse particle concentrations from EPA’s
monitoring network are currently determined using
a difference method in locations with same-day
data from co-located PM10 and PM2.5 FRM monitors.
64 The Criteria Document notes that toxicologic
studies, in general, use exposure concentrations
that are generally much higher than ambient
concentrations (EPA, 2004, p. 9–51).
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health endpoints, as well as evidence
from PM10 studies conducted in areas in
which the coarse fraction is dominant.
More specifically, several U.S. and
Canadian studies now provide evidence
of associations between short-term
exposure to PM10-2.5 and various
morbidity endpoints. Three such studies
conducted in Toronto (Burnett et al.,
1997), Seattle (Sheppard et al., 2003),
and Detroit (Ito, 2003) report
statistically significant associations
between short-term PM10-2.5 exposure
and respiratory- and cardiac-related
hospital admissions, and a fourth study
(Schwartz and Neas, 2000) conducted in
six U.S. cities including Boston, St.
Louis, Knoxville, Topeka, Portage, and
Steubenville reports statistically
significant associations across these six
areas with respiratory symptoms in
children. These studies were mostly
done in areas in which PM2.5, rather
than PM10-2.5, is the larger fraction of
ambient PM10, and they are not
representative of areas with relatively
high levels of thoracic coarse particles
(EPA, 2005a, p. 5–49).
In evaluating the epidemiologic
evidence from health studies on
associations between short-term
exposure to PM10-2.5 and mortality, the
Criteria Document concluded that such
evidence was ‘‘limited and clearly not
as strong’’ as that for associations with
PM2.5 or PM10 but nonetheless was
suggestive of associations with mortality
(EPA, 2004, p. 9–28, 9–32). Statistically
significant mortality associations were
reported in short-term exposure studies
conducted in areas with relatively high
PM10-2.5 concentrations, including
Phoenix (Mar et al., 2003), Coachella
Valley, CA (Ostro et al., 2003), and in
the initial analysis of data from
Steubenville (as part of the Six Cities
study, Schwartz et al., 1996), although
in a reanalysis of this study, the results
were generally not statistically
significant (Klemm and Mason, 2003).
In areas with lower PM10-2.5
concentrations, no statistically
significant associations were reported
with mortality, though most were
positive.
The Staff Paper also considers
relevant epidemiologic studies indexed
by PM10 that were conducted in areas
where the coarse fraction of PM10 is
typically much greater than the fine
fraction. Such studies include findings
of associations between short-term
exposure to PM10 and hospitalization for
cardiovascular diseases in Tucson, AZ
(Schwartz, 1997), hospitalization for
COPD in Reno/Sparks, NV (Chen et al.,
2000), and medical visits for asthma or
respiratory diseases in Anchorage, AK
(Gordian et al., 1996; Choudhury et al.,
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1997). In addition, a number of
epidemiologic studies have reported
significant associations with mortality,
respiratory hospital admissions and
respiratory symptoms in the Utah Valley
area (e.g., Pope et al., 1989; 1991; 1992).
This group of studies provides
additional supportive evidence for
associations between short-term
exposure to thoracic coarse particles
and health effects, particularly
morbidity effects, generally in areas not
meeting the PM10 standards (EPA,
2005a, p. 5–50).65
In contrast to the findings from the
short-term exposure studies discussed
above, available epidemiologic studies
do not provide evidence that long-term
exposure to thoracic coarse particles is
associated with mortality or morbidity
(EPA, 2005a, p. 3–25). More specifically,
no association is found between longterm exposure to thoracic coarse
particles and mortality in the reanalyses
and extended analysis of the ACS cohort
(EPA, 2005a, p. 8–307). Further, little
evidence is available on potential
respiratory and cardiovascular
morbidity effects of long-term exposure
to thoracic coarse particles (EPA, 2005a,
p. 3–23–24).
Taken together, the Staff Paper
concludes that the health evidence,
including dosimetric, toxicologic and
epidemiologic study findings, supports
retaining some standard to protect
against effects associated with shortterm exposure to thoracic coarse
particles. However, the substantial
uncertainties associated with this
limited body of epidemiologic evidence
on health effects related to exposure to
PM10-2.5, including the difficulty in
separating the effects of fine and
thoracic coarse particles, suggest a high
degree of caution in interpreting this
evidence, especially at the lower levels
of ambient particle concentrations in the
morbidity studies discussed above
(EPA, 2004, p. 5–50).
Beyond this evidence-based
evaluation, the Staff Paper also
considers the extent to which PM10-2.5related health risks estimated to occur at
current levels of ambient air quality may
be judged to be important from a public
health perspective, taking into account
key uncertainties associated with the
estimated risks. Consistent with the
approach used to address this issue for
65 Based on recent air quality data, as well as the
summary information provided for PM
concentrations used in the studies, the existing
PM10 standards are not met in any of these study
cities except Tucson, AZ. Based on 2002–2004 air
quality data, the 98th percentile PM2.5
concentrations in three of these areas range from 15
to 25 µg/m3, while in Utah Valley the
concentrations range from 37 to 54 µg/m3.
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PM2.5-related health risks, discussed
above in section II.B, the Staff Paper
considers the results of a series of base
case analyses that reflect in part the
uncertainty associated with the form of
the concentration-response functions
drawn from the studies used in the
assessment. In this assessment, which is
much more limited than the risk
assessment conducted for PM2.5, health
risks were estimated for three urban
areas by using the reported linear or loglinear concentration-response functions
as well as modified functions that
incorporate alternative assumed
cutpoints as surrogates for potential
population thresholds (discussed above
in section III.B). In considering the risk
estimates from this limited assessment,
and recognizing the very substantial
uncertainties inherent in basing an
assessment on such limited information,
the Staff Paper concludes that the
results for the two areas in the
assessment that did not meet the current
PM10 standards are indicative of risks
that can reasonably be judged to be
important from a public health
perspective, in contrast to the
appreciably lower risks estimated for
the area that did meet the current
standards (EPA, 2005a, p. 5–52).
The Staff Paper recognizes the
substantial uncertainties associated with
the limited available epidemiologic
evidence and the inherent difficulties in
interpreting the evidence for purposes
of setting appropriate standards for
thoracic coarse particles. Nonetheless,
in considering the available evidence,
the public health implications of
estimated risks associated with current
levels of air quality, and the related
limitations and uncertainties, the Staff
Paper concludes that this information
supports (1) revising the current PM10
standards in part by revising the
indicator for thoracic coarse particles,
and (2) consideration of a standard that
will continue to provide public health
protection from short-term exposure to
thoracic coarse particles of concern that
have been associated with morbidity
effects and possibly mortality at current
levels in some urban areas (EPA, 2005a,
p. 5–52).
In CASAC’s review of these Staff
Paper recommendations, there was
general concurrence among CASAC
Panel members that there is a need to
revise the current PM10 standards and
establish a primary standard specifically
targeted to address particles in the size
range of 2.5 to 10 µm (Henderson,
2005b). In making this recommendation,
CASAC indicated its agreement with the
summary of the scientific data regarding
the potential adverse health effects from
exposures to thoracic coarse particles in
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section 5.4 of the Staff Paper upon
which the EPA staff recommendations
were based.
In considering whether the primary
PM10 standards should be revised, the
Administrator has carefully considered
the rationale and recommendations
contained in the Staff Paper, the advice
and recommendations of CASAC, and
public comments to date on this issue.
The Administrator provisionally
concludes that the health evidence,
including dosimetric, toxicologic and
epidemiologic study findings, supports
retaining a standard to protect against
effects associated with short-term
exposure to thoracic coarse particles.
Further, the Administrator believes that
the new evidence on health effects from
studies that use PM10-2.5 as a measure of
thoracic coarse particles, together with
the much more extensive data now
available to characterize air quality in
terms of PM10-2.5, provide an appropriate
basis for revising the current PM10
standards in part by revising the
indicator to focus more narrowly on
particles between 2.5 and 10 µm. The
Administrator also notes that the need
for a standard for thoracic coarse
particles has already been upheld based
upon evidence of health effects
considerably more limited than now
available. American Trucking
Associations v. EPA, 175 F. 3d at 1054.
Based on these considerations, the
Administrator provisionally concludes
that the current suite of PM10 standards
should be revised, and that the revised
standard(s) should provide more
targeted protection from short-term
exposure to those thoracic coarse
particles that are of concern to public
health.
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D. Indicator of Thoracic Coarse Particles
In considering an appropriate
indicator for a standard intended to
afford protection from health effects
associated with exposure to thoracic
coarse particles of concern, the Staff
Paper starts by making the following
observations:
(1) The most obvious choice for a
thoracic coarse particle standard is the
size-differentiated, mass-based indicator
used in the epidemiologic studies that
provide the most direct evidence of
such health effects, PM10-2.5.
(2) The upper size cut of a PM10-2.5
indicator is consistent with dosimetric
evidence that continues to reinforce the
finding from past reviews that an
aerodynamic size of 10 µm is a
reasonable separation point for particles
that penetrate to and potentially deposit
in the thoracic regions of the respiratory
tract.
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(3) The lower size cut of such an
indicator is consistent with the choice
of 2.5 µm as a reasonable separation
point between fine and coarse fraction
particles.
(4) Further, the limited available
information is not sufficient to define an
indicator for thoracic coarse particles
solely in terms of metrics other than
size-differentiated mass, such as specific
chemical components.
(5) The available epidemiologic
evidence for effects of PM10-2.5 exposure
is quite limited and is inherently
characterized by large uncertainties,
reflective in part of the more
heterogeneous nature of the spatial
distribution and chemical composition
of thoracic coarse particles and the more
limited and generally uncertain
measurement methods that have
historically been used to characterize
their ambient concentrations.
In evaluating relevant information
from atmospheric sciences, toxicology,
and epidemiology related to thoracic
coarse particles, the Staff Paper notes
that there appears to be clear
distinctions between (1) the character of
the ambient mix of particles generally
found in urban areas as compared to
that found in nonurban and, more
specifically, rural areas, and (2) the
nature of the evidence concerning
health effects associated with thoracic
coarse particles generally found in
urban versus rural areas. Based on such
information, and on specific initial
advice from CASAC (Henderson,
2005a), the Staff Paper considers a more
narrowly defined indicator for thoracic
coarse particles that focuses on the mix
of such particles that is characteristic of
that generally found in urban areas
where thoracic coarse particles are
strongly influenced by traffic-related or
industrial sources. In so doing, the Staff
Paper focuses on comparing the
potential health effects associated with
thoracic coarse particles in urban and
rural settings, as discussed below.
Atmospheric science and monitoring
information indicates that exposures to
thoracic coarse particles tend to be
higher in urban areas than in nearby
rural locations. Further, the mix of
thoracic coarse particles typically found
in urban areas contains a number of
contaminants that are not commonly
present to the same degree in the mix of
natural crustal particles that is typical of
rural areas. The elevation of PM10-2.5
levels in urban locations as compared to
those at nearby rural sites suggests that
sources located within urban areas are
generally the cause of elevated urban
concentrations; conversely, PM10-2.5
concentrations in such urban areas are
not largely composed of particles blown
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in from more distant regions (EPA,
2005a, sections 2.4.5 and 5.4.2.1).
Important sources of thoracic coarse
particles in urban areas include dense
traffic that suspends significant
quantities of dust from paved roads, as
well as industrial and combustion
sources and construction activities that
contribute to ambient coarse particles
both directly and through deposition to
soils and roads (EPA, 2005a, Table 2–2).
It follows that the mix of thoracic coarse
particles in urban areas would differ in
composition from that in rural areas,
being influenced to a relatively greater
degree by components from urban
mobile and stationary source emissions.
While detailed composition data are
more limited for PM10-2.5 than for PM2.5,
available measurements from some
areas as well as studies of road dust
components do show a significant
influence of urban sources on both the
composition and mass of thoracic coarse
particles generally found in urban areas.
Although crustal elements and natural
biological materials represent a
significant fraction of thoracic coarse
particles in urban areas, both their
relative quantity and character may be
altered by urban sources. For example,
in industrial cities, primary particle
emissions from industrial sources and
resuspended road dust can increase the
relative amount of iron in the mix of
PM10-2.5, one of the metals that has been
noted as being of some interest in the
studies of mechanisms of toxicity for
PM, as well as other industrial processrelated and potentially toxic materials
such as nickel, cadmium, and
chromium (EPA, 2005a, p. 5–54).
Traffic-related activities can also grind
and resuspend vegetative materials into
forms not as common in more natural
areas (Rogge et al., 1993). Studies of
urban road dusts find that levels of a
variety of components are increased
from traffic as well as from other
anthropogenic urban sources, including
products of incomplete combustion (e.g.
polycyclic aromatic hydrocarbons) from
motor vehicle emissions and other
sources, brake and tire wear, rust, salt
and biological materials (EPA, 2004, p.
3D–3). Limited ambient coarse fraction
composition data from various
comparisons find that metals and
sometimes elemental carbon contribute
a greater proportion of thoracic coarse
particle mass in urban areas than in
nearby rural areas. In addition, while
large uncertainties exist in emissions
inventory data, the Staff Paper observes
that major sources of PM10-2.5 emissions
in the urban counties in which
epidemiologic studies have been
conducted are paved roads and ‘‘other’’
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sources (largely construction), and that
such areas also have larger contributions
from industrial emissions, whereas
unpaved roads and agriculture are the
main sources of PM10-2.5 emissions
outside of urban areas.
Toxicologic studies, although quite
limited, support the view that thoracic
coarse particles from sources common
in urban areas are of greater concern
than uncontaminated materials of
geologic origin. One major source of
thoracic coarse particles in urban areas
is paved road dust; the Criteria
Document discusses results from a
recent toxicologic study in which road
tunnel dust particles had greater allergic
adjuvant activity than several other
particle samples (Steerenberg et al.,
2003; EPA, 2004, pp. 7–136, 137). This
study supports evidence available in the
last review regarding potential effects of
road dust particles (EPA, 1996b, p. V–
70). In contrast, a number of studies
have reported that Mt. St. Helens
volcanic ash, an example of natural
crustal material of geologic origin, has
very little toxicity in animal or in vitro
toxicologic studies (EPA, 2004, p. 7–
216).
A few toxicologic studies have used
ambient thoracic coarse particles from
urban/suburban locations (PM10-2.5), and
the results suggest that effects can be
linked with several components of
PM10-2.5. These in vitro toxicologic
studies linked thoracic coarse particles
with effects including cytotoxicity,
oxidant formation, and inflammatory
effects (EPA, 2005a, sections 3.2 and
5.4.1). These studies suggest that several
components (e.g., metals, endotoxin,
other materials) may have roles in
various health responses but do not
suggest a focus on any individual
component.
Although largely focused on
undifferentiated PM10, the series of
epidemiologic observations and
toxicologic experiments related to the
Utah Valley suggest that directly
emitted (fine and coarse) and
resuspended (coarse) urban industrial
emissions are of concern. Of particular
interest are area studies spanning a 13month period when a major source of
PM10 in the area, a steel mill, was not
operating. Observational studies found
that respiratory hospital admissions for
children were lower when the plant was
shut down (Pope et al., 1989). More
recently, a set of toxicologic and
controlled human exposure studies have
used particles extracted from filters
from ambient PM10 monitors from
periods when the plant did and did not
operate. In both human volunteers and
animals, greater lung inflammatory
responses were reported with particles
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collected when the source was
operating, as compared to the period
when the plant was closed (EPA, 2004,
p. 9–73). In addition, in some studies it
was suggested that the metal content of
the particles was most closely related to
the effects reported (EPA, 2004, p. 9–
74). While peak days in the Utah Valley
occur in conditions that enhance fine
particle concentrations, over the long
run, over half of the PM10 was in the
coarse fraction. The aggregation of
particles collected on the filters during
the study period reflect this long-term
composition and represent the kinds of
industrial components that would be
incorporated in road dusts in the area.
Epidemiologic studies that have
examined exposures to thoracic coarse
particles generally found in urban
environments, together with studies that
have taken into account exposures to
natural crustal materials typical of rural
areas, generally support the view that
the mix of thoracic coarse particles
generally found in urban areas is of
concern to public health, in contrast to
natural crustal dusts of geologic origin.
With respect to the urban results,
several recent studies have shown
associations between PM10-2.5 and health
outcomes in a few sites across the U.S.
and Canada. Associations have been
reported with morbidity in a few urban
areas, some of which had relatively low
PM10-2.5 concentrations. For mortality,
statistically significant associations have
been reported only for two urban areas
that have notably higher ambient
PM10-2.5 concentrations. These
associations are with short-term
exposures to aggregated PM10-2.5 mass,
and no epidemiologic evidence is
available on associations with different
components or sources of PM10-2.5.
However, these studies have all been
conducted in urban areas of the U.S.,
and thus reflect effects associated with
the ambient mix of thoracic coarse
particles generally present in urban
environments.
In contrast, recent evidence from
epidemiologic studies has suggested
that mortality and possibly other health
effects are not associated with thoracic
coarse particles from dust storms or
other such wind-related events that
result in suspension of natural crustal
materials of geologic origin. The clearest
example is provided by a study in
Spokane, WA, which specifically
assessed whether mortality was
increased on dust-storm days using
case-control analysis methods. The
average PM10 level was more than 200
µg/m3 higher on dust storm days than
on control days, and the authors report
no evidence of increased mortality on
these specific days (Schwartz et al.,
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1999). One caveat of note is the
possibility that people may reduce their
exposure to ambient particles on the
most dusty days (e.g., Gordian et al.,
1996; Ostro et al., 2000). Nevertheless,
these studies provide no suggestion of
significant health effects from
uncontaminated natural crustal
materials that would typically form a
major fraction of coarse particles in nonurban or rural areas.
Beyond the urban and rural
distinctions discussed above, the Staff
Paper also considers the extent to which
there is evidence of effects with
exposure to the ambient thoracic coarse
particles in communities predominantly
influenced by agricultural or mining
sources.66 For example, in the last
review, EPA considered health evidence
related to long-term silica exposures
from mining activities, but found that
there was a lack of evidence that such
emissions contribute to effects linked
with ambient PM exposures (EPA,
1996b, p. V–28). Similarly in this
review, there is an absence of evidence
related to such community exposures.
While crustal and organic dusts
generated from agricultural activity can
include a variety of biological materials,
and some occupational studies
discussed in the Criteria Document
report effects at occupational exposure
levels (EPA, 2004, Table 7B–3, p. 7B–
11), such studies do not provide
relevant evidence for effects at much
lower levels of community exposures.
Further, it is unlikely that such sources
contribute to the effects that have been
observed in the recent urban
epidemiologic studies.
The Criteria Document concludes its
integrated assessment of the effects of
natural crustal materials as follows:
Certain classes of ambient particles appear
to be distinctly less toxic than others and are
unlikely to exert human health effects at
typical ambient exposure concentrations (or
perhaps only under special circumstances).
For example, particles of crustal origin,
which are predominately in the coarse
fraction, are relatively non-toxic under most
circumstances, compared to combustionrelated particles (such as from coal and oil
combustion, wood burning, etc.) However,
under some conditions, crustal particles may
become sufficiently toxic to cause human
health effects. (EPA, 2004, p. 8–344)
The Staff Paper assessment of the
available evidence relevant to the
appropriate scope of an indicator for
coarse particles can be summarized as
follows. Ambient concentrations of
thoracic coarse particles generally
66 Mining sources are intended to include all
activities that encompass extraction and/or
mechanical handling of natural geologic crustal
materials.
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reflect contributions from local sources,
and the limited information available
from speciation of thoracic coarse
particles and emissions inventory data
indicate that the sources of thoracic
coarse particles in urban areas generally
differ from those found in nonurban
areas. As a result, the mix of thoracic
coarse particles people are typically
exposed to in urban areas can be
expected to differ appreciably from the
mix typically found in non-urban or
rural areas. Ambient PM10-2.5 exposure
is associated with health effects in
studies conducted in urban areas, and
the limited available health evidence
more strongly implicates the ambient
mix of thoracic coarse particles that is
dominated by traffic-related and
industrial sources than that from
uncontaminated soil or geologic
sources. The limited evidence does not
support either the existence or the lack
of causative associations for community
exposures to thoracic coarse particles
from agricultural or mining industries.
Given the apparent differences in
composition and in the epidemiologic
evidence, the Staff Paper concludes that
it is not appropriate to generalize the
available evidence of associations with
health effects that have been related to
thoracic coarse particles generally found
in urban areas and apply it to the mix
of particles typically found in nonurban
or rural areas (EPA, 2005a, p. 5–57).
Collectively, this evidence suggests
that a more narrowly defined indicator
for thoracic coarse particles should be
considered that would protect public
health against effects that have been
linked with the mix of thoracic coarse
particles generally present in urban
areas. Such an indicator would be
principally based on particle size, but
also reflect a focus on the mix of
thoracic coarse particles that is
generally present in urban environments
and the sources that principally
generate that mix. The Staff Paper
recommends consideration of thoracic
coarse urban particulate matter 67 as an
indicator for a thoracic coarse particle
standard, referring to the mix of
airborne particles between 2.5 and 10
µm in diameter that are generally
present in urban environments, which,
as discussed above, are principally
comprised of resuspended road dust
typical of high traffic-density areas and
emissions from industrial sources and
construction activities (EPA, 2005a, p.
5–54, 5–57–58). The Staff Paper
concludes that such an indicator would
more likely be an effective indicator for
standards to protect against health
67 The acronym ‘‘UPM
10-2.5’’ is used in the Staff
Paper to refer to this indicator.
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effects that have been associated with
thoracic coarse particles than a more
broadly focused PM10-2.5 indicator. This
indicator would also be consistent with
an appropriately cautious interpretation
of the epidemiologic evidence that does
not potentially over-generalize the
results of the limited available studies.
In conjunction with this
recommendation of an indicator defined
in terms of the mix of thoracic coarse
particles that are generally present in
urban areas, the Staff Paper also
discusses the importance of a
monitoring network designed so as to be
consistent with the intent of such an
indicator and that would facilitate
implementation of such a standard. EPA
has historically used implementation
policies to address elevations in
thoracic coarse particle levels that may
occur in urban areas as a result of dust
storms or other such events for which
this staff-recommended indicator is not
intended to apply. Both new criteria for
monitor network design and revised
natural/exceptional events policies
should work in concert with a revised
thoracic coarse particle indicator to
ensure the most effective application of
a thoracic coarse particle standard.
In its review of the Staff Paper
recommendation for a thoracic coarse
particle indicator (Henderson, 2005b),
the CASAC generally agreed that
‘‘thoracic coarse particles in urban areas
can be expected to differ in composition
from those in rural areas;’’ that ‘‘coarse
particles in urban or industrial areas are
likely to be enriched by anthropogenic
pollutants that tend to be inherently
more toxic than the windblown crustal
material which typically dominates
coarse particle mass in arid rural areas;’’
and that ‘‘evidence of associations with
health effects related to urban coarsemode particles would not necessarily
apply to non-urban or rural coarse
particles.’’ Further, most CASAC Panel
members concurred that ‘‘the current
scarcity of information on the toxicity of
rural dusts makes it necessary’’ for EPA
to base its standard for thoracic coarse
particles ‘‘on the known toxicity of
urban-derived coarse particles.’’ While
most Panel members concurred with the
thoracic coarse particle indicator
recommended in the Staff Paper, a few
members recommended specifying a
PM10-2.5 indicator in conjunction with
monitoring network design criteria and
natural/exceptional events policies that
would emphasize urban influences. In
either case, CASAC indicated that the
intent of any such indicator should be
to ‘‘provide protection against those
components of PM10-2.5 that arise from
anthropogenic activities occurring in or
near urban and industrial areas.’’
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In considering an appropriate
indicator for a standard intended to
afford protection from health effects
associated with exposure to thoracic
coarse particles of concern, the
Administrator has carefully considered
the rationale and recommendations
contained in the Staff Paper, the advice
and recommendations from CASAC,
and public comments to date on this
issue. In so doing, the Administrator
believes, despite the substantial
limitations and uncertainties in the
relevant information available, that it is
appropriate to propose a new indicator
for such particles at this time. Further,
the Administrator believes that any such
indicator should be defined not only by
particle size, to generally include those
particles between 2.5 and 10 µm in
diameter, but also by qualifications that
narrow the scope of the indicator. In
considering an indicator that is
intended to focus on the mix of thoracic
coarse particles generally present in
urban environments and commonly
derived from sources typically found in
urban environments, consistent with
Staff Paper and CASAC
recommendations, the Administrator
notes that identifying it as an ‘‘urban’’
thoracic coarse particle indicator could
be misconstrued as meaning that the
standard is limited to certain geographic
locations and, thus, not a national
standard. To avoid this semantic
problem, the Administrator has sought
to define the indicator in a way that
more clearly focuses on the nature of the
mix of thoracic coarse particles
intended to be included and the sources
that principally generate that mix, rather
than just where they are found, and that
also explicitly focuses on what would
be excluded from such an indicator. In
so doing, the Administrator intends the
proposed indicator to be equivalent to
the one recommended in the Staff Paper
and endorsed by CASAC, but to do so
in a manner that will be more clearly
understood and less likely to be
misinterpreted.
Taking into account the
considerations discussed above, the
Administrator proposes to establish a
new indicator for thoracic coarse
particles in terms of PM10-2.5, the
definition of which includes
qualifications that identify both the mix
of such particles that are of concern to
public health, and are thus included in
the indicator, and those for which
currently available information is not
sufficient to infer a public health
concern, and are thus excluded. More
specifically, the proposed PM10-2.5
indicator is qualified so as to include
any ambient mix of PM10-2.5 that is
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dominated by resuspended dust from
high-density traffic on paved roads and
PM generated by industrial sources and
construction sources, and excludes any
ambient mix of PM10-2.5 that is
dominated by rural windblown dust and
soils and PM generated by agricultural
and mining sources. In short, the
indicator is not defined by nor limited
to any specific geographic area, but
includes the mix of PM10-2.5 in any
location that is dominated by these
sources.
With the indicator as defined above,
each area in the country would fall into
one or the other of these two categories:
(1) Either the majority of the ambient
mix of PM10-2.5 in an area is
resuspended dust from high-density
traffic on paved roads and PM generated
by industrial sources and construction
sources, or (2) the majority of the
ambient mix is rural windblown dust
and soils and PM generated by
agricultural and mining sources. The
indicator would apply when PM10-2.5
generated by one or more of these
named sources in the first category
constitutes a majority of the ambient
mix of PM10-2.5. The EPA recognizes that
in many cases it will be clear which of
these two categories applies, while in
other cases it may be difficult to
determine the appropriate category. As
described in more detail in the preamble
to EPA’s proposed monitor network
design rule, published elsewhere in
today’s Federal Register, the proposed
minimum monitor siting criteria would
provide guidance on distinguishing
between areas where the mix of PM10-2.5
of concern would likely be dominated
by the named sources in the first
category and those areas where it would
not. Consequently, all PM10-2.5 captured
by a monitor that is properly sited in
light of the indicator described above, as
discussed in the proposed monitoring
rule, would be considered in applying
the standard, since the monitor would
be capturing the mix of ambient PM10-2.5
covered by the proposed indicator. As
such, the proposed indicator does not
present the type of over-inclusion or
under-inclusion problems noted by the
court with respect to a PM10 indicator
(see American Trucking Associations v.
EPA, 175 F.3d at 1054), since the
application of the proposed indicator
would result in compliance being based
on measurement of the mix of ambient
PM10-2.5 at which the standard is
directed.
The regulation for the proposed
thoracic coarse particle indicator states
that ‘‘[a]gricultural sources, mining
sources, and other similar sources of
crustal material shall not be subject to
control in meeting this standard.’’ This
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proposed language reflects that the
information supporting the proposed
standard for thoracic coarse particles
does not support extending controls to
thoracic coarse particles from
agricultural, mining sources, and other
similar sources of crustal material. This
statement in the regulations therefore is
designed to make clear that there is no
need nor basis to control these sources
to obtain the public health benefits
intended by the proposed indicator.
Although the Administrator believes
that an indicator qualified through
reference to these categories and named
sources appropriately identifies the
ambient mixes that the epidemiologic
studies indicate are of concern to public
health, he solicits comment as to
whether there may be other classes of
sources which should also be included
or excluded from the indicator. More
generally, comment is also solicited on
the approach of defining the indicator in
terms of both particle size and
categories of named sources.
The Administrator recognizes that the
proposed indicator, which includes
considerations beyond particle size in
its definition, represents a shift in the
way in which PM indicators have been
defined historically, and thus poses new
challenges in ensuring a common
understanding of how it can be
appropriately and consistently
implemented in areas across the
country. In the Administrator’s view,
the application of this proposed
indicator in conjunction with the
proposed monitoring network design
criteria, published elsewhere in today’s
Federal Register, and proposed rules for
the treatment of air quality data
influenced by exceptional events that
will be published in the near future,
will facilitate appropriate and consistent
implementation.
E. Averaging Time of Primary PM10-2.5
Standard
In the last review, EPA retained both
24-hour and annual PM10 standards to
provide protection against the known
and potential effects of short- and longterm exposures to thoracic coarse
particles (62 FR at 38,677–79). That
decision was based in part on
qualitative considerations related to the
expectation that deposition of thoracic
coarse particles in the respiratory
system could aggravate effects in
individuals with asthma. In addition,
quantitative support for retaining a 24hour standard came from limited
epidemiologic evidence suggesting that
aggravation of asthma and respiratory
infection and symptoms may be
associated with daily or episodic
increases in PM10, where dominated by
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thoracic coarse particles including
fugitive dust. The decision to retain an
annual standard as well was generally
based on considerations of the
plausibility of the potential build-up of
insoluble thoracic coarse particles in the
lung after long-term exposures to high
levels of such particles.
New information available in this
review on thoracic coarse particles,
discussed above, includes several
epidemiologic studies that report
statistically significant associations
between short-term (24-hour) exposure
to PM10-2.5 and various morbidity effects
and mortality. With regard to long-term
exposure studies, while one recent
study conducted in southern California
reported a link between reduced lung
function growth and long-term exposure
to PM10-2.5 and PM2.5, other such studies
reported no associations (EPA, 2005a, p.
3–19, 3–23–24). Thus, the Criteria
Document concludes that the available
evidence does not suggest an association
with long-term exposure to PM10-2.5
(EPA, 2004, p. 9–79).
Based on these considerations, the
Staff Paper concludes that the newly
available evidence continues to support
a 24-hour averaging time for a standard
intended to control thoracic coarse
particles, based primarily on evidence
suggestive of associations between
short-term (24-hour) exposure and
morbidity effects and, to a lesser degree,
mortality. Noting the absence of
evidence judged to be suggestive of an
association with long-term exposures,
the Staff Paper concludes that there is
no quantitative evidence that directly
supports an annual standard, while
recognizing that it could be appropriate
to consider an annual standard to
provide a margin of safety against
possible effects related to long-term
exposure to thoracic coarse particles
that future research may reveal. The
Staff Paper observes, however, that a 24hour standard that would reduce 24hour exposures would also likely reduce
long-term average exposures, thus
providing some margin of safety against
the possibility of health effects
associated with long-term exposures
(EPA, 2005a, p. 5–61).
Based on its review of the Staff Paper,
CASAC recommends retention of a 24hour averaging time and agrees that an
annual averaging time for PM10-2.5 is not
currently warranted (Henderson,
2005b). Based on these considerations,
the Administrator concurs with staff
and CASAC recommendations, and
provisionally concludes that the newly
available evidence continues to support
a 24-hour averaging time for a PM10-2.5
standard, based primarily on evidence
suggestive of associations between
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short-term (24-hour) exposure and
morbidity effects and, to a lesser degree,
mortality. Further, the Administrator
agrees that an annual PM10-2.5 standard
is not warranted at this time. Thus, the
Administrator proposes to revoke the
annual PM10 standard and is not
proposing an annual PM10-2.5 standard.
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F. Form of Primary PM10-2.5 Standard
For reasons similar to those discussed
above in section II.F.2 on the form of the
24-hour PM2.5 standard, the Staff Paper
also recommends consideration of either
the 98th or 99th percentile form for a
24-hour PM10-2.5 standard. The relative
year-to-year stability of the air quality
statistic to be used as the basis for the
form of a PM10-2.5 standard is of
particular importance for a PM10-2.5
standard, since the nature and
magnitude of the uncertainties in the
risk assessment conducted for thoracic
coarse particles weighed against
considering risk estimates as a basis for
comparing alternative combinations of
specific forms and levels of standards.
In considering the information
provided in the Staff Paper, CASAC
strongly recommends use of the 98th
percentile form because it is more
statistically robust than the 99th
percentile form, together with the use of
a three-year average of this statistic
(Henderson 2005b). In making this
recommendation, CASAC notes that the
use of this statistic will tend to
minimize ‘‘measurement error and
spatial variability, which are larger for
coarse-mode particles than for fine PM’’
as well as ‘‘the influence in arid areas
of occasional but extreme excursion
contributions from rural, coarse-mode
dust sources that are thought to be
inherently less toxic than coarse-mode
particles heavily enriched with urban
source contaminants’’ (Henderson,
2005b).
In considering the available
information, the Administrator concurs
with the CASAC recommendation and
proposes that the form of the 24-hour
PM10-2.5 standard be based on the annual
98th percentile statistic, averaged over
three years.
G. Level of Primary PM10-2.5 Standard
In considering the available evidence
on associations between short-term
PM10-2.5 concentrations and morbidity
and mortality effects as a basis for
setting a 24-hour standard for thoracic
coarse particles, the Staff Paper focuses
on relevant U.S. and Canadian
epidemiologic studies, as discussed
above in section II.A. As an initial
matter, the Staff Paper recognizes that
these individual short-term exposure
studies provide no evidence of clear
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population thresholds, or lowestobserved-effects levels, in terms of 24hour average concentrations. As a
consequence, this body of evidence is
difficult to translate directly into a
specific 24-hour standard that would
protect against the range of effects that
have been associated with short-term
exposures.
In considering the evidence, the Staff
Paper notes the significant uncertainties
and the limited nature of the available
evidence. In examining the available
evidence to identify a basis for a range
of standard levels that would be
appropriate for consideration, the Staff
Paper focuses on the upper end of the
distributions of daily PM10-2.5
concentrations in the relevant studies in
terms of the 98th and 99th percentile
values.68
In looking first at the morbidity
studies that report statistically
significant associations with respiratoryand cardiac-related hospital admissions
in Toronto (Burnett et al., 1997), Seattle
(Sheppard et al., 2003), and Detroit (Ito,
2003), the 98th percentile values
reported in these studies range from
approximately 30 to 36 µg/m3. To
provide some perspective on these
PM10-2.5 levels, the Staff Paper notes that
the level of the 24-hour PM10 standard
was exceeded only on a few occasions
during the time periods of the studies in
Detroit and Seattle.69 In looking also at
the mortality studies that report
statistically significant and generally
robust associations with short-term
exposures to PM10-2.5 in Phoenix (Mar et
al., 2003) and Coachella Valley, CA
(Ostro et al., 2003), the reported 98th
percentile values were approximately 70
and 107 µg/m3, respectively. These
studies were conducted in areas with air
quality levels that did not meet the
current PM10 standards. In addition, a
statistically significant association was
reported between PM10-2.5 and mortality
in Steubenville as part of the original
Six Cities study (Schwartz et al., 1996),
although in more recent reanalyses, the
association did not remain statistically
significant in most models (Schwartz,
2003a; Klemm and Mason, 2003)—the
PM10-2.5 concentrations in this eastern
city were fairly high, with a reported
98th percentile value of 53 µg/m3. In
68 This examination of the evidence is based on
air quality information and analyses presented in
two staff memos which were part of the materials
reviewed by CASAC (Ross and Langstaff, 2005;
Ross, 2005).
69 As shown in air quality data trends reports: for
Seattle, 1997 Air Quality Annual Report for
Washington State, p. 17, at https://www.ecy.wa.gov/
pubs/97208.pdf; for Detroit, Michigan’s 2003
Annual Air Quality Report, p. 46, at https://
www.deq.state.mi.us/documents/deq-aqd-airreports-03AQReport.pdf.
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contrast to the statistically significant
mortality associations with PM10-2.5
reported in these studies, the Staff Paper
notes that no such associations were
reported in a number of other studies,
including those in the five other cities
that were part of the Six Cities study
(Boston, St. Louis, Knoxville, Topeka,
and Portage), Santa Clara County, CA,
Detroit, Philadelphia, and Pittsburgh.
With the exception of Pittsburgh, these
cities had much lower 98th percentile
PM10-2.5 values, ranging from 18 to 49
µg/m3. Thus, in mortality studies that
reported statistically significant
associations, the reported 98th
percentile PM10-2.5 values were all above
50 µg/m3, whereas in the mortality
studies that reported no statistically
significant associations, the reported
98th percentile PM10-2.5 values were
generally below 50 µg/m3.
In looking more closely at air quality
data used in the morbidity and mortality
studies discussed above, however, the
Staff Paper recognizes that the
uncertainty related to exposure
measurement error associated with
using ambient concentrations to
represent area-wide population
exposure levels can be potentially quite
large. For example, in looking
specifically at the Detroit study, the
Staff Paper notes that the PM10-2.5 air
quality values were based on air quality
monitors located in Windsor, Canada.
While the study authors concluded that
these monitors were appropriate for use
in exploring the association between air
quality and hospital admissions in
Detroit, a close examination of air
quality levels at Detroit and Windsor
sites in recent years led to the
conclusion that the statistically
significant, generally robust association
with hospital admissions in Detroit
likely reflects population exposures that
may be appreciably higher in the central
city area, but not necessarily across the
broader study area, than would be
estimated using data from the Windsor
monitors (EPA, 2005a, p. 5–64).
The EPA staff also looked more
specifically at the Coachella Valley
mortality study (Ostro et al., 2003), in
which data were used from a single
monitoring site in one city, Indio,
within the study area where daily
measurements were available. A close
examination of air quality levels across
the Coachella Valley suggests that while
the association of mortality with
PM10-2.5 measurements made at the
Indio site was statistically significant, a
portion of the study population would
have been expected to experience
appreciably lower ambient exposure
levels. In contrast to the Detroit study,
air quality data used in the mortality
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study conducted in Coachella Valley
appear to represent concentrations on
the high end of PM10-2.5 levels for
Coachella Valley communities. On the
other hand, a close examination of the
air quality data used in the other studies
discussed above generally shows less
disparity between air quality levels at
the monitoring sites used in the studies
and the broader pattern of air quality
levels across the study areas than that
described above in the Detroit and
Coachella Valley studies.
This close examination of air quality
information generally reinforces the
view that exposure measurement error
is potentially quite large in these
PM10-2.5 studies. As a consequence, the
air quality levels reported in these
studies, as measured by ambient
concentrations at monitoring sites
within the study areas, are not
necessarily good surrogates for
population exposures that are likely
associated with the observed effects in
the study areas or that would likely be
associated in other urban areas across
the country. The Detroit example
suggests that population exposures were
probably appreciably underestimated in
the Detroit morbidity study, such that
the observed effects are likely associated
with higher PM10-2.5 levels than
reported. In contrast, the Coachella
Valley mortality study provides an
example in which population levels
were probably appreciably
overestimated, such that the observed
effects may well be associated with
lower PM10-2.5 levels than reported. At
relatively low levels of air quality,
population exposures implied by these
studies as being associated with the
observed effects likely become more
uncertain, suggesting a high degree of
caution in interpreting the group of
morbidity studies as a basis for
identifying a standard level that would
protect against the observed effects.
Taking into account this close
examination of the studies, the Staff
Paper concludes that this evidence
suggests that EPA could consider a
standard for urban thoracic coarse
particles at a PM10-2.5 level at least down
to 50 µg/m3, in conjunction with a 98th
percentile form. This view takes into
account the conclusion that this
evidence is particularly uncertain as to
population exposures, especially from
the morbidity studies reporting effects at
relatively low concentrations, as well as
the general lack of evidence of
associations from the group of mortality
studies with reported concentrations
below these levels.
Another view that reflects a more
cautious or restrained approach to
interpreting the limited body of PM10-2.5
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epidemiologic evidence would be to
judge that the uncertainties in this
whole group of studies as to population
exposures that are associated with the
observed effects are too large to use the
reported air quality levels directly as a
basis for setting a specific standard
level. Such a judgment would be
consistent with concluding that these
studies, together with other dosimetric
and toxicologic evidence, provide
support for retaining standards for
thoracic coarse particles at some level to
protect against the morbidity and
mortality effects observed in the studies,
regardless of whether an associated
population exposure level can be clearly
discerned from the studies.
Based on this more cautious
approach, the Staff Paper concludes that
it would be reasonable to interpret the
available epidemiologic evidence more
qualitatively. Considering the available
evidence in this way leads to the
following observations:
(1) The statistically significant
mortality associations with short-term
exposure to PM10-2.5 reported in the
Phoenix and Coachella Valley studies
were observed in areas that did not meet
the current PM10 standards.
(2) The statistically significant
morbidity associations with short-term
exposure to PM10-2.5 reported in the
Detroit and Seattle studies were
observed in areas that exceeded the
level of the current 24-hour PM10
standard on just a few occasions during
the time periods of the studies.
(3) All but one of the statistically
significant morbidity and mortality
associations with short-term exposure to
PM10 reported in areas in which the
thoracic coarse particle fraction of PM10
was much greater than was the fine
fraction (including Reno/Sparks, NV,
Tucson, AZ, Anchorage, AK, and the
Utah Valley area) were observed in areas
that did not meet the current PM10
standards.
Based on these considerations, the
Staff Paper finds 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 standards,
but have not been associated with air
quality levels that would generally meet
the current standards, and morbidity
effects have been associated with air
quality levels that exceeded the current
standards only a few times. Further, the
Staff Paper finds little basis for
concluding that a greater degree of
protection is warranted in light of the
very high degree of uncertainty in the
relevant population exposures implied
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by the morbidity studies. The Staff
Paper concludes, therefore, that it is
reasonable to interpret the available
evidence as supporting consideration of
a short-term standard for thoracic coarse
particles, so as to provide generally
‘‘equivalent’’ protection to that afforded
by the current PM10 standards,
recognizing that no one PM10-2.5 level
will be strictly equivalent to a specific
PM10 level in all areas (EPA, 2005a, p.
5–67). Such a standard would likely
provide protection against morbidity
effects especially in urban areas where,
unlike the study areas, PM10 is generally
dominated by coarse-fraction rather
than fine-fraction particles. Such a
standard would also likely provide
protection against the more serious, but
more uncertain, PM10-2.5-related
mortality effects generally observed at
somewhat higher air quality levels.
To identify a range of levels for
consideration for a 24-hour PM10-2.5
standard, based on the indicator
proposed above and set so as to afford
generally ‘‘equivalent’’ protection as the
current PM10 standards, the Staff Paper
presents the results of analyses of
relevant data on PM10-2.5 and PM10 24hour average concentrations.70 In one
such analysis of 205 monitoring sites
(Schmidt et al., 2005),71 a PM10-2.5 level
of approximately 60 µg/m3, in terms of
a 98th percentile form, would be
roughly equivalent on average across the
U.S. to the current PM10 standard level
of 150 µg/m3, in terms of the current
one-expected-exceedance form.72 While
noting appreciable variability in the
estimated point of equivalence across
individual sites, these levels of
approximate average equivalence are
quite consistent across each of the five
regions in which all of the areas that do
not meet the current PM10 standards are
located (including the southern
California, southwest, northwest, upper
mid-west, and southeast regions).
Notably different average equivalence
70 Consistent with PM
10-2.5 monitoring network
design criteria discussed in section 5.4.2.2 of the
Staff Paper, monitors included in this analysis are
those in CBSAs with at least 100,000 population
and in census block groups with a population
density of at least 500, and that also had 3 years
of complete data in each quarter for both PM10 and
PM10-2.5 (EPA, 2005a, p. 5–67).
71 These analyses were based on collocated PM
10
and PM10-2.5 data, and used linear regression
methods to predict PM10-2.5 concentrations (98th
percentile form) equivalent to the 24-hour PM10
standard level of 150 µg/m3 (one expected
exceedence form) at a national and at regional
levels.
72 Across the U.S., the 95 percent confidence
intervals around these point estimates are
approximately ± 3 µg/m3, while region-specific
intervals are approximately ± 10 µg/m3 in the five
regions in which all of the areas that do not meet
the current PM10 standards are located (EPA, 2005a,
p. 5–68).
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levels were observed in the other two
regions, i.e., approximately 40 µg/m3 in
the northeast and over 70 µg/m3 in the
industrial mid-west.
Another such analysis was based on
comparing the number of areas, and the
population in those areas, that would
likely not meet a specific PM10-2.5
standard, set at a given level and form,
with the same measures in areas that do
not meet the current PM10 standards.
This analysis, based on 2001 to 2003
data, provides some rough indication of
the breadth of protection potentially
afforded by alternative standards. The
results of this analysis indicate that a
PM10-2.5 standard of about 70 or 65 µg/
m3, 98th percentile form, would impact
approximately the same number of
counties or number of people,
respectively, as would the current PM10
standards.73
In considering the relevant
dosimetric, toxicologic, and
epidemiologic evidence, related
limitations and uncertainties, and
analyses of relevant air quality
information, the Staff Paper concludes
that it is appropriate to consider a 24hour PM10-2.5 standard in the range of 50
to 70 µg/m3, with a 98th percentile
form.74 The lower end of this range is
based on a close examination of the air
quality patterns related to the limited
number of relevant epidemiologic
studies. The upper part of this range is
based on a more cautious approach to
interpreting the available information
and reflects a generally ‘‘equivalent’’
degree of protection to that afforded by
the current PM10 standards. The upper
end of this range is also below the 98th
percentile PM10-2.5 concentrations in the
two mortality studies that reported
statistically significant associations.
Consideration of a generally
‘‘equivalent’’ PM10-2.5 standard would
reflect a judgment that while the
73 As shown in Tables 5B–2(a) and (b) of the Staff
Paper, there are 585 counties with PM10 monitoring
sites used in determining compliance with the PM10
standards, whereas only 309 of those counties have
monitor sites that would be included in the
monitoring network design criteria discussed in
section 5.4.2.2 of the Staff Paper. Of these 309
counties, 259 have PM10 and PM10-2.5 air quality
data that meet the data completeness criteria
defined for this analysis, which are somewhat less
restrictive than the criteria that were applied in the
regression analysis described above.
74 Beyond looking directly at the relevant
epidemiologic evidence and related air quality
information, the Staff Paper also considers the
extent to which the PM10-2.5 risk assessment,
discussed above in section III.B, can help inform
consideration of alternative 24-hour PM10-2.5
standards. The Staff Paper concludes that the nature
and magnitude of the uncertainties and concerns
associated with this portion of the risk assessment
weigh against use of these risk estimates as a basis
for recommending specific standard levels (EPA,
2005a, p. 5–69).
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epidemiologic evidence supports
establishing a short-term standard for
urban thoracic coarse particles at such
a generally ‘‘equivalent’’ level, the
evidence concerning air quality levels of
thoracic coarse particles in the studies
is not strong enough to provide a basis
for changing the level of protection
generally afforded by the current PM10
standards.
Based on its review of the Staff Paper,
there was general agreement among the
CASAC Panel members that the Staff
Paper-recommended range of 50 to 70
µg/m3, with a 98th percentile form, for
a 24-hour PM10-2.5 standard was
reasonably justified. Most CASAC Panel
members favored levels at the upper end
of that range, while several members
supported the lower end of the range
(Henderson, 2005b). Because of the
significant uncertainties resulting from
the limited number of studies to date in
which PM10-2.5 has been measured and
the potentially large exposure
measurement errors in such studies, the
CASAC Panel did not generally support
a level below the Staff Paperrecommended range.
In considering an appropriate level for
a 24-hour PM10-2.5 standard intended to
afford requisite protection of public
health from health effects associated
with exposure to thoracic coarse
particles of concern, the Administrator
has carefully considered the rationale
and recommendations contained in the
Staff Paper, the advice and
recommendations of CASAC, and public
comments to date on this issue. Taking
these considerations into account, the
Administrator proposes to set the level
of the primary 24-hour PM10-2.5 standard
at 70 µg/m3. In the Administrator’s
provisional judgment, based on the
currently available evidence, a standard
set at this level would be requisite to
protect public health with an adequate
margin of safety from the morbidity and
possibly mortality effects that have been
associated with short-term exposures to
thoracic coarse particles of concern.
This proposed standard is expected to
have the most impact in areas that do
not meet the current 24-hour PM10
standard.
In reaching this judgment, the
Administrator recognizes that the
epidemiologic evidence on morbidity
and possible mortality effects related to
PM10-2.5 exposure is very limited at this
time, and that there are potentially quite
large uncertainties inherent in
interpreting the available evidence for
PM10-2.5 as compared with the evidence
related to fine particles. For example,
PM10-2.5 concentrations can vary
substantially across a metropolitan area
and thoracic coarse particles are less
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able to penetrate into buildings than
fine particles; thus, the ambient
concentrations reported in
epidemiologic studies may not well
represent area-wide population
exposure levels. It may also be difficult
to disentangle effects associated with
PM10-2.5 and PM2.5 in epidemiologic
studies. Further, the Administrator is
mindful that considering what standard
is requisite to protect public health with
an adequate margin of safety requires
judgments that neither overstate nor
understate the strength and limitations
of the evidence or the appropriate
inferences to be drawn from the
evidence. Thus, the Administrator
provisionally concludes that the
selection of a level that provides
generally equivalent protection to that
provided by the current PM10 standards
is an appropriate policy response to the
very limited body of evidence that is
available at this time. The EPA intends
to address the considerable
uncertainties in the currently available
information on thoracic coarse particles
as part of the Agency’s ongoing PM
research program.
The Administrator also recognizes
that there is no one level for a PM10-2.5
standard that would be equivalent to the
current PM10 standards in every area
across the country, and that there are
likely additional approaches to
identifying a generally equivalent
standard level beyond those approaches
considered in the Staff Paper upon
which the proposed level is based.
Thus, the Administrator also solicits
comment on alternative approaches to
identifying a generally ‘‘equivalent’’
standard level. While proposing to set
the PM10-2.5 standard at a level that is
generally equivalent to the 1987 PM10
standard, the Administrator solicits
comment on whether it would be more
appropriate to set the PM10-2.5 standard
at a level that is generally equivalent to
the PM10 standard set in 1997.
Having decided to propose the 24hour PM10-2.5 standard described above,
the Administrator recognizes that there
are important views on the information
relating to the effects of coarse fraction
PM that warrant consideration. For
example, an alternative interpretation of
the available health evidence presented
in the Criteria Document and the Staff
Paper questions the conclusions about
PM10-2.5 associations drawn from onepollutant models. This interpretation of
the available epidemiological evidence
suggests that the results from onepollutant PM10-2.5 models are
confounded by fine particles and
gaseous co-pollutants.
The key PM10-2.5 epidemiologic results
discussed in the Criteria Document and
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Staff Paper are drawn from onepollutant models; i.e., PM10-2.5 is the
only variable used in the statistical
model reflecting exposure to air
pollution. There are four studies cited in
these documents as being suggestive of
a statistically significant role for PM10-2.5
in the reported associations: Ito (2003),
Burnett et al. (1997), Mar et al. (2003),
and Ostro et al. (2003). However, there
is strong evidence that adverse health
effects similar to those observed in these
studies, including both cardiovascular
and/or respiratory health effects are
associated with exposure to PM2.5. The
authors of several of these studies focus
on fine particles (and in some cases one
or more of the gaseous pollutants) as
playing an important role in
‘‘explaining’’ the association between
PM and various health endpoints. For
example, in these key epidemiologic
studies, the correlation coefficients
between PM2.5 and PM10-2.5
concentrations range from moderate to
high (i.e., 0.4 to 0.7), which increases
the likelihood that associations between
health effects and PM10-2.5 identified in
one-pollutant models may instead
simply reflect the effects of exposure to
PM2.5 rather than independent health
effects. With the positive correlations
between pollutants and similar health
effects, it generally would be
appropriate for any assessment of the
effect of exposure to PM10-2.5 to control
for exposure to the PM2.5.
In this light, it is important to review
how the authors of the four key PM10-2.5
epidemiology studies have accounted
for co-pollutants in their analysis. Ito
(2003) noted significant estimates of the
health effects of associations in onepollutant models, but in a two-pollutant
model with PM2.5 the PM10-2.5
associations lost statistical significance.
Burnett et al. (1997) concluded that the
effect of PM10-2.5 in a one-pollutant
model could be explained by gaseous
co-pollutants. Mar et al. (2003) found
PM10-2.5 to be positively associated with
adverse health effects in a one-pollutant
model, but also found similar
associations with a range of other air
pollutants. In addition, Mar et al. (2003)
noted that even though all PM mass
metrics included in the study were
associated with an excess risk of
cardiovascular death, the strongest
associations were with PM2.5, followed
by PM10 and PM10-2.5. Ostro et al. (2003)
used a one-pollutant model to estimate
the association between PM10-2.5 on
mortality using an effectively linear
construct of PM10 (as observed in Indio,
CA) to represent PM10-2.5 for the entire
study area. By using such a construct of
PM10, the estimated associations simply
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reflect a PM10 association (i.e., the
construct does not provide additional
information on the effect of PM10-2.5).
Moreover, roughly 75 percent of the
cardiovascular mortality in this study
occurred in or near Palm Springs, CA
and PM characteristics differ
significantly between Palm Springs and
Indio (e.g., average PM10 concentrations
are roughly 30 percent lower in Palm
Springs and PM2.5 represents a higher
fraction of PM10, with a correlation
coefficient between PM2.5 and PM10-2.5
of 0.46 in Palm Springs). Thus, the
Ostro et al. (2003) study suggests a
positive association between PM10
monitored in Indio and mortality in
Palm Springs, but some view this study
as offering little basis for attributing
significant mortality association to
PM10-2.5 as observed in either city.
The Criteria Document and Staff
Paper also present and discuss other
epidemiology studies in support of the
proposal for both the PM2.5 and PM10-2.5
standards (as shown in Figure 2 and
discussed in Section III.A above):
Burnett (1997), Fairley (2003), Ito
(2003), Lipfert et al (2000), Mar et al
(2003), Moolgavkar (2000), Sheppard et
al (2003), Thurston et al (1994), Burnett
(2000, 2003), Klemm and Mason (2003),
and Schwartz and Neas (2000).
However, these studies report positive,
statistically significant associations with
PM2.5 that are more consistent and
robust than the associations thus far
identified for PM10-2.5. Indeed, several of
these and other studies that specifically
considered PM10-2.5, but did not find
statistically significant associations,
including Schwartz et al (1996),
Thurston et al. (1994), Sheppard et al.
(2003), Fairley (2003), Schwartz et al
(1996) and Lipfert et al. (2000). With
respect to mortality effects in the SixCity study, Schwartz et al. (1996)
concluded that the PM associations (in
the six metropolitan areas—including
Steubenville) were specifically
associated with PM2.5, with little
additional contribution from the
PM10-2.5. Sheppard et al. (2003) noted
that bias in model selection and
reporting can result in inflated excess
risk estimates for PM. Fairley (1999)
noted that PM10-2.5 effects become
negative and insignificant when
modeled jointly with PM2.5. Lipfert et al.
(2000) showed insignificant effects for
PM10-2.5 in one- and two-pollutant
models with O3. The authors also
caution against drawing causal
interpretations from results when
comparing health effects from one
region in a metropolitan area to air
quality observations in another region.
In addition, several of these studies also
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report positive, statistically significant
associations with one or more of the
gaseous pollutants. Both Thurston et al.
(1994) and Burnett et al. (1997) reported
substantial confounding with gaseous
co-pollutants in Toronto, and Thurston
et al. (1994, p. 282) reported that ‘‘it
seems clear that these apparent
associations were merely a statistical byproduct of interpollutant confounding
resulting from the shared day-to-day
variations in dispersion conditions.’’ In
addition, Burnett et al. (2000) concluded
that gaseous pollutants played an
important role in explaining the effect of
urban air pollution on health. Similarly,
Moolgavkar (2000) concludes that gases
were more strongly associated with
respiratory effects than PM in Los
Angeles.
Taken as a whole, evidence from
PM10-2.5 epidemiologic studies could be
interpreted to suggest that one-pollutant
PM10-2.5 models suffer from bias due to
omitting co-pollutants in the statistical
model, especially given the much
stronger evidence (discussed above) that
these effects are associated with
exposure to PM2.5. As noted by many of
the aforementioned authors, while
significant health associations may be
noted for coarse fraction PM in onepollutant models, the actual association
may be insignificant from zero due to
confounding co-pollutants. Of course,
the Administrator must conclude in the
final rule that the evidence about the
health effects of PM10-2.5 is sufficiently
robust to finalize a standard for PM10-2.5.
The Administrator, recognizing
notably large uncertainties in the
underlying evidence and information
that formed the basis for this proposal
as well as the challenges associated with
moving toward a new PM10-2.5 indicator
and a related new monitoring network,
solicits comment on this and other
alternative interpretations of the
available health evidence and
alternative policy responses. Several
such alternative interpretations and
policy responses are discussed below.
(1) In light of the large uncertainties
in the evidence and the challenges of
moving to a new indicator, and
provisionally recognizing the need for a
standard to provide a requisite level of
protection from the risks associated
with thoracic coarse particles, the
Administrator also believes it
appropriate to consider a policy option
that would retain the current 24-hour
PM10 standard (with a one-expectedexceedance form), while addressing
issues such as the appropriateness of the
indicator and the level of the standard.
As discussed in section I.D, in
response to a challenge to the 1997
standards for thoracic coarse PM, the
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U.S. Court of Appeals for the District of
Columbia vacated the Agency’s 1997
PM10 standards. In its decision the Court
noted that use of PM10 as an indicator
to protect against the public health risks
associated with thoracic coarse particles
resulted in double regulation of PM2.5,
since this size fraction is both a
component of PM10 and the subject of
its own standard. The Court further
reasoned that, since PM2.5
concentrations vary from area to area,
use of PM10 as a thoracic coarse particle
indicator results in an arbitrary level of
protection in public health from the
risks associated with thoracic coarse
particles on a national basis, as the level
of protection would vary based on the
concentration of PM2.5 in an area. See
American Trucking Associations v.
EPA, 175 F.3d at 1054–55.
Under this option to retain the 24hour PM10 standard, EPA would modify
the standard to exclude the doublecounted PM2.5 contribution in
circumstances where this could present
a concern. First, there will be some
areas that may be in nonattainment with
the PM10 standard because, and only
because, they are in nonattainment with
the PM2.5 standard. To remedy the
double counting in this situation, EPA
is requesting comment on subtracting
from a daily measured PM10
concentration the value by which the
concentration of PM2.5 measured at a
collocated monitor is in excess of 35 µg/
m3 (i.e., the proposed level for the 24hour PM2.5 standard). This adjustment
would need to be made only on days
when a 24-hour average PM10
concentration is measured in excess of
150 µg/m3. In such a case, the amount
by which the PM2.5 concentration
exceeds 35 µg/m3 would be subtracted
from the measured PM10 concentration.
The EPA would then use this adjusted
value in any comparison to the PM10
standard.
The second situation where the
overlap between the PM2.5 and PM10
standards may cause some concern is in
areas where a daily PM2.5 level is below
35 µg/m3. In those areas, the level of the
PM10 standard would allow a higher
concentration of thoracic coarse
particles before triggering an exceedance
than it would in other areas. The EPA
is requesting comment on not requiring
any adjustment to the daily measured
PM10 concentration in this situation, on
the basis that any additional risk to
public health that may be associated
with this higher allowable concentration
of thoracic coarse particles would
reasonably be expected to present less
concern from a public health
perspective than would the otherwise
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allowable equivalent increase in the
concentration of PM2.5.
The EPA also believes that it would
be appropriate in this option to focus
the PM10 standard in a manner similar
to that proposed above for the PM10-2.5
standard. While the indicator would
remain specified as PM10, the focus
would be on including only the mix of
ambient thoracic coarse particles that
are of concern to public health (and to
exclude the mix for which information
is not sufficient to infer a public health
concern) and would be achieved in
practice through the data handling
requirements associated with the
standard, which are linked to the
proposed monitoring network design
criteria (in the part 58 rule proposed
elsewhere in today’s Federal Register).
The EPA invites comment on whether
this option would provide the requisite
level of public health protection from
risks associated with thoracic coarse
particles. Given the difference in form
between the 24-hour PM10 standard
(one-expected-exceedance form) and the
proposed PM10-2.5 standard (98th
percentile form), and the adjustments
noted above, in practice there may not
be an appreciable difference in the
degree of public health protection
afforded by this option relative to that
afforded by the proposed PM10-2.5
standard. The EPA invites comment on
whether this approach addresses one of
the concerns about use of a PM10
indicator for thoracic coarse particles
noted by the Court in its ATA decision,
namely that the level of public health
protection from thoracic coarse particles
in an area would vary depending on the
relative proportions of fine and thoracic
coarse particles, by recognizing that the
PM10 indicator and standard would
cover both fine and thoracic coarse
particles.
With respect to revocation of the 1987
24-hour PM10 standard, under this
option EPA would apply the same
approach to revocation as that proposed
below in section III.H. in conjunction
with the proposed PM10-2.5 standard.
Since the 24-hour PM10 standard would
be focused in basically the same manner
as the proposed PM10-2.5 standard, it
would be appropriate to follow the same
approach to revocation of the current
24-hour PM10 standard under this
option as well.
The EPA solicits comment on all
aspects of this approach, including
views on whether a 24-hour PM10
standard revised as noted above would
be requisite to protect public health
from the risks associated with thoracic
coarse particles, with an adequate
margin of safety, as well as views on any
legal, scientific, or policy issues
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2673
associated with this alternative, and
including comments on the consistency
of this option with CASAC’s
recommendations. The EPA also solicits
comment on whether a 98th percentile
form should be considered for a 24-hour
PM10 standard and on the appropriate
level of such a standard.
(2) The Administrator recognizes that
some commenters hold the view that the
uncertainties that exist at the present
time are so great that no standards for
thoracic coarse particles are warranted.
Some such commenters point to
conclusions reached in the Staff Paper
in part as a basis for their view,
including, for example, the conclusion
that the ‘‘substantial uncertainties
associated with this limited body of
epidemiological evidence on health
effects related to PM10-2.5 * * * suggests
a high degree of caution in interpreting
this evidence * * *.’’ (EPA 2005, pp. 5–
50). This view generally places
significant weight on the issue of
confounding between PM2.5 and PM10-2.5
(discussed above in section III.A), with
some commenters stating that the
correlation coefficients between fine
and thoracic coarse particle levels are
modest to high for all studies for which
such data are available, increasing the
possibility that the positive association
identified in the PM10-2.5 one-pollutant
models may instead reflect the effects of
fine particles. Noting that the Staff
Paper puts little weight on the health
risk assessment because of the
significant uncertainties in the
underlying health studies, some
commenters suggest that the risk
assessment therefore does not provide a
basis for determining whether the health
effects possibly associated with PM10-2.5
constitute a meaningful public health
risk. Some commenters take the view
that, based either on the studies or the
risk assessment, the magnitude of the
health effects possibly associated with
PM10-2.5 do not constitute a meaningful
risk to public health. These commenters
also maintain that significant
uncertainty remains as to an appropriate
level of a standard, even assuming that
a meaningful public health risk exists.
In consideration of these views, the
Administrator also solicits comment on
revoking the current 24-hour PM10
standard at this time (as well as the
current annual PM10 standard, as
proposed above), not adopting a
thoracic coarse particle standard at this
time, and taking into account any new
relevant research that becomes available
as a basis for considering a more
targeted standard for thoracic coarse
particles in the next periodic review of
the PM NAAQS.
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(3) In sharp contrast to the views
noted above, another view that the
Administrator takes note of would place
greater weight on the available
epidemiologic evidence as a basis for
selecting a level down to 50 µg/m3 or
below and/or for selecting an
unqualified PM10-2.5 indicator. While
recognizing that important uncertainties
are present in the available evidence,
this view would support incorporating a
larger margin of safety consistent with a
more highly precautionary policy
response. In soliciting comments on a
wide array of views, the Administrator
solicits comment on this view and on
standard levels that are consistent with
this view.
H. Proposed Decisions on Primary
PM10-2.5 Standard
For the reasons discussed above, and
taking into account the information and
assessments presented in the Criteria
Document and Staff Paper, the advice
and recommendations of CASAC, and
public comments to date, the
Administrator proposes to revise the
current primary PM10 standards. In
particular, to provide more targeted
protection from thoracic coarse particles
that are of concern to public health, the
Administrator proposes to establish a
new indicator for thoracic coarse
particles in terms of PM10-2.5, the
definition of which includes
qualifications that identify both the mix
of such particles that are of concern to
public health, and are thus included in
the indicator, and those for which
currently available information is not
sufficient to infer a public health
concern, and are thus excluded. More
specifically, the proposed PM10-2.5
indicator is qualified so as to include
any ambient mix of PM10-2.5 that is
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. The
Administrator proposes to replace the
current primary 24-hour PM10 standard
with a 24-hour standard defined in
terms of this new PM10-2.5 indicator and
set at a level of 70 µg/m3, which would
generally maintain the degree of public
health protection afforded by the
current PM10 standards from short-term
exposure to thoracic coarse particles of
concern. The proposed new standard
would be met at an ambient air quality
monitoring site 75 when the 3-year
75 Monitoring sites that are appropriate for
determining compliance with this standard are
those that are consistent with the proposed
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average of the annual 98th percentile
24-hour average PM10-2.5 concentration
is less than or equal to 70 µg/m3.76 The
Administrator also proposes to revoke
and not replace the annual PM10
standard.
In recognition of alternative views of
the currently available scientific
information and the appropriate policy
response to this information, the
Administrator also solicits comments on
(1) alternative approaches to selecting
the level of a 24-hour PM10-2.5 standard
or to selecting an unqualified PM10-2.5
indicator, and (2) alternative approaches
to providing continued protection from
thoracic coarse particles based on
retaining the current 24-hour PM10
standard. Alternatively, the
Administrator also solicits comment on
revoking and not replacing the 24-hour
PM10 standard. Based on the comments
received and the accompanying
rationale, the Administrator may adopt
other standards within the range of the
alternatives identified above in lieu of
the standard he is proposing today.
The Administrator is also proposing
to revoke the current annual PM10
standard upon promulgation of this
rule. Further, if EPA finalizes a 24-hour
primary PM10-2.5 standard, the
Administrator is proposing to revoke the
current 24-hour PM10 standard
everywhere except in areas where there
is at least one monitor that is located in
an urbanized area 77 with a minimum
population of 100,000 people and that
violates the 24-hour PM10 standard
based on the most recent three years of
data.
EPA specifically proposes that the 24hour PM10 standard would be revoked
in this rulemaking in all areas except
the following:
1. Birmingham urban area (Jefferson
County, AL)
2. Maricopa and Pinal Counties;
Phoenix planning area (AZ)
3. Riverside, Los Angeles, Orange and
San Bernardino Counties; South Coast
Air Basin (CA)
indicator. Guidance on this can be found in the
proposed monitoring network design criteria
published elsewhere in today’s Federal Register.
76 Data handling conventions are specified in a
new proposed Appendix P, as discussed in Section
V below, and the reference method for monitoring
PM as PM10-2.5 is specified in a new proposed
Appendix L, as discussed in Section VI below.
77 As defined by the U.S. Bureau of the Census,
an urbanized area has ‘‘a minimum residential
population of at least 50,000 people’’ and generally
includes ‘‘core census block groups or blocks that
have a population density of at least 1,000 people
per square mile and surrounding census blocks that
have an overall density of at least 500 people per
square mile.’’ The Census Bureau notes that ‘‘under
certain conditions, less densely settled territory
may be part of each UA.’’ See https://
www.census.gov/geo/www/ua/ua_2k.html.
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4. Fresno, Kern, Kings, Tulare, San
Joaquin, Stanislaus, Maderia
Counties; San Joaquin Valley
planning area (CA)
5. San Bernardino County (part);
excluding Searles Valley Planning
Area and South Coast Air Basin (CA)
6. Riverside County; Coachella Valley
Planning Area (CA)
7. Simi Valley urban area (CA)
8. Lake County; Cities of East Chicago,
Hammond, Whiting, and Gary (IN)
9. Wayne County (part) (MI)
10. St. Louis urban area (MO)
11. Albuquerque urban area (NM)
12. Clark County; Las Vegas planning
area (NV)
13. Columbia urban area (SC)
14. El Paso urban area (including those
portions in TX and those portions in
NM)
15. Salt Lake County (UT)
A separate memorandum explaining
the factual basis for our proposed
determinations regarding each PM10
area where we are proposing to retain
the current 24-hour standard is part of
the administrative record for this
proposed rule (Rosendahl, 2005).
In essence, we are proposing to retain
the current 24-hour PM10 standard only
in areas which could be in violation of
the proposed PM10-2.5 standard. While it
is possible that some existing PM10
monitors may not be sited in accordance
with all of the criteria for PM10-2.5
monitor siting proposed elsewhere in
today’s Federal Register (see section
IV.E.2.b.ii of the preamble to the
proposed changes to Part 53/58), it is
not possible for EPA to make a case-bycase assessment of monitor placement
within each area at this time. Therefore,
EPA believes that all areas with
violating PM10 monitors located in
urbanized areas with a minimum
population of 100,000 people should be
considered areas that may violate the
PM10-2.5 standard.
For those areas where we propose to
retain the 24-hour PM10 standard which
were previously designated
nonattainment for PM10 or which are
currently designated nonattainment for
PM10, EPA proposes, in the alternative,
either that the standard would continue
to apply in the entire attainment/
nonattainment area, or that the area to
which the standard would continue to
apply should be limited to the
urbanized area containing the violating
monitor(s). For areas with violating
monitor(s) which were never designated
nonattainment, EPA proposes that the
boundaries of the area to which the
standard would continue to apply
should be limited to the urbanized area
containing the violating monitor(s). For
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all areas in which the 24-hour PM10
standard would be retained, EPA invites
comments on the appropriate
boundaries within which the standard
should continue to apply.
Consistent with our request for
comment in the Part 53/58 proposal,
section IV.E.2.b.ii, on whether we
should establish criteria for locating
discretionary monitors appropriate for
comparison with the proposed 24-hour
PM10-2.5 standard in locations other than
urbanized areas with population of at
least 100,000 people, we also request
comment on whether the 24-hour PM10
standard should be retained in areas
that are either urbanized areas with a
population less than 100,000 people or
non-urbanized areas (i.e. population less
than 50,000) but where the majority of
the ambient mix of PM10-2.5 is generated
by high density traffic on paved roads,
industrial sources, and construction
activities, and which have at least one
monitor that violates the 24-hour PM10
standard. The EPA requests comment on
the criteria that should be used to
determine whether such an area with a
violating monitor must retain the 24hour PM10 standard. Such criteria could
include whether the area has one (or
more) industrial source(s) listed in
either the National Emissions Inventory
or the Toxics Release Inventory located
within a certain radius of the violating
monitor, and whether these sources are
in industrial categories that do not
include agricultural or mining sources.
One approach to defining such
categories would be to utilize the U.S.
Census Bureau’s North American
Industry Classification System,78 which
defines separate classifications for
agricultural and mining activities such
as Crop Production (111), Animal
Production (112), and Mining (112). The
EPA requests comments on how this or
another classification system, combined
with information on the location of
sources relative to the violating PM10
monitor, could be used to identify
additional areas to which the 24-hour
PM10 standard should continue to apply
due to the presence of industrial
sources. The EPA also requests
comments on which areas would meet
these criteria or other criteria that may
be appropriate to determine in which, if
any, areas the 24-hour PM10 standard
should be retained, and the appropriate
boundaries within which the standard
should continue to apply for these areas.
A more detailed example of criteria that
could be used to identify areas to which
the standard should continue to apply,
along with a list of all areas with
78 https://www.census.gov/epcd/naics02/
naicod02.htm#N21.
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violating PM10 monitors that meet these
criteria, are part of the administrative
record for this proposed rule
(Rosendahl, 2005). For all areas where
the 24-hour PM10 standard would be
retained under this proposal, we
contemplate that the 24-hour PM10
standard would be revoked after
designations are completed under a
final 24-hour PM10-2.5 standard.
The EPA also recognizes that it is
possible that some areas for which we
are proposing to retain the PM10 daily
standard would, upon a case-specific
investigation (see section IV.E.2.c of the
Part 53/58 preamble), warrant
revocation as not being an area where
the ambient coarse PM mix is
dominated by the type of coarse PM
described by the proposed indicator.
The EPA is not in a position to conduct
such case-by-case evaluation for this
proposal, but could address revocation
in such situations in a future
rulemaking. The EPA invites comment
on this issue.
To address issues related to the
transition from the current PM10
standards to a new PM10-2.5 standard,
the Administrator intends to seek public
comment on EPA’s plans for assuring an
effective transition as part of an ANPR
that EPA intends to issue by the end of
January 2006. In the forthcoming ANPR
dealing with transition issues, EPA
intends to address, among other things,
the timing for revocation of the PM10
standard in areas in which we are
proposing to retain that standard, and
the consequences of revoking the PM10
standards on the PM10 PSD program
(including PM10 increments), on the
PM10 nonattainment New Source
Review (NSR) program, and on our
existing policy of using PM10 as a
surrogate for the PM2.5 NSR program.
IV. Rationale for Proposed Decisions on
Secondary PM Standards
The Criteria Document and Staff
Paper examined the effects of PM on
such aspects of public welfare as
visibility, vegetation and ecosystems,
materials damage and soiling, and
climate change. The existing suite of
secondary PM standards, which is
identical to the suite of primary PM
standards, includes annual and 24-hour
PM2.5 standards and annual and 24-hour
PM10 standards. This existing suite of
secondary standards is intended to
address visibility impairment associated
with fine particles and materials damage
and soiling related to both fine and
coarse particles. The following
discussion of the rationale for the
proposed decisions on secondary PM
standards focuses on those
considerations most influential in the
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Administrator’s proposed decisions,
first addressing visibility impairment
followed by the other welfare effects
considered in this review.79
A. Visibility Impairment
This section presents the rationale for
the Administrator’s proposed revision of
the current secondary PM2.5 standard to
address PM-related visibility
impairment. As discussed below, the
rationale includes consideration of: (1)
The latest scientific information on
visibility effects associated with PM; (2)
insights gained from assessments of
correlations between ambient PM2.5 and
visibility impairment prepared by EPA
staff; 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.
1. Visibility Impairment Related to
Ambient PM
This section outlines key information
contained in the Criteria Document and
Staff Paper on: (1) The nature of
visibility impairment, including trends
in visual air quality and the
characterization of current visibility
conditions; (2) quantitative
relationships between ambient PM and
visibility; (3) the impacts of visibility
impairment on public welfare; and (4)
approaches to evaluating public
perceptions and attitudes about
visibility impairment.
a. Nature of Visibility Impairment
Visibility can be defined as the degree
to which the atmosphere is transparent
to visible light. Visibility conditions are
determined by the scattering and
absorption of light by particles and
gases, from both natural and
anthropogenic sources. Visibility is
often described in terms of visual range,
light extinction, or deciviews.80 The
classes of fine particles principally
responsible for visibility impairment are
sulfates, nitrates, organic matter,
elemental carbon, and soil dust. Fine
79 As noted in section I.A above, in establishing
secondary standards that are requisite to protect the
public welfare from any known or anticipated
adverse effects, EPA may not consider the costs of
implementing the standards.
80 Visual range can be defined as the maximum
distance at which one can identify a black object
against the horizon sky. It is typically described in
kilometers or miles. Light extinction is the sum of
light scattering and absorption by particles and
gases in the atmosphere. It is typically expressed in
terms of inverse megameters (Mm¥1), with larger
values representing poorer visibility. The deciview
metric describes perceived visual changes in a
linear fashion over its entire range, analogous to the
decibel scale for sound.
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particles are more efficient per unit
mass at scattering light than coarse
particles. The scattering efficiency of
certain classes of fine particles, such as
sulfates, nitrates, and some organics,
increases as relative humidity rises
because these particles can absorb water
and grow to sizes comparable to the
wavelength of visible light. In addition
to limiting the distance that one can see,
the scattering and absorption of light
caused by air pollution can also degrade
the color, clarity, and contrast of scenes.
Visibility impairment is manifested in
two principal ways: As local visibility
impairment and as regional haze. Local
visibility impairment may take the form
of a localized plume, a band or layer of
discoloration appearing well above the
terrain that results from complex local
meteorological conditions.
Alternatively, local visibility
impairment may manifest as an urban
haze, sometimes referred to as a ‘‘brown
cloud.’’ A ‘‘brown cloud’’ is
predominantly caused by emissions
from multiple sources in the urban area
and is not typically attributable to a
single nearby source or to long-range
transport from more distant sources.
The second type of visibility
impairment, regional haze, generally
results from pollutant emissions from a
multitude of sources located across a
broad geographic region. Regional haze
impairs visibility in every direction over
a large area, in some cases over multistate regions. It is regional haze that is
principally responsible for impairment
in national parks and wilderness areas
across the country (NRC, 1993).
While visibility impairment in urban
areas at times may be dominated by
local sources, it often may be
significantly affected by long-range
transport of haze due to the multi-day
residence times of fine particles in the
atmosphere. Fine particles transported
from urban and industrialized areas, in
turn, may, in some cases, be significant
contributors to regional-scale
impairment in Class I areas 81 and other
rural areas.
As discussed in the Staff Paper (EPA,
2004, section 6.2), in Class I areas,
visibility levels on the 20 percent
haziest days in the West are about equal
to levels on the 20 percent best days in
the East. Despite improvement through
the 1990’s, visibility in the rural East
remains significantly impaired, with an
81 There are 156 mandatory Class I Federal areas
protected by the visibility provisions in sections
169A and 169B of the Act. These areas are defined
in section 163 of the Act as those national parks
exceeding 6000 acres, wilderness areas and
memorial parks exceeding 5000 acres, and all
international parks which were in existence on
August 7, 1977.
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average visual range of approximately
20 km on the 20 percent haziest days
(compared to the naturally occurring
visual range in the eastern U.S. of about
150 ± 45 km). In the rural West, the
average visual range showed little
change over this period, with an average
visual range of approximately 100 km
on the 20 percent haziest days
(compared to the naturally occurring
visual range in the western U.S. of about
230 ± 40 km).
In urban areas, visibility levels show
far less difference between eastern and
western regions. For example, the
average visual ranges on the 20 percent
haziest days in eastern and western
urban areas are approximately 20 km
and 27 km, respectively (Schmidt et al.,
2005). Even more similarity is seen in
considering 4-hour (12 to 4 p.m.)
average PM2.5 concentrations, for which
the average visual ranges on the 20
percent haziest days in eastern and
western urban areas are approximately
26 km and 31 km, respectively (Schmidt
et al., 2005).
Data on visibility conditions indicate
that urban areas generally have higher
loadings of PM2.5 and, thus, higher
visibility impairment than monitored
Class I areas. Since efforts are now
underway to address all human-caused
visibility in Class I areas through the
regional haze program (EPA, 1999; 65
FR 35713), implemented under sections
169A and 169B of the CAA, and since
the Clean Air Interstate Rule (CAIR) (70
FR 25162) is expected to result in
improvements to visual air quality,
particularly in eastern Class I and nonurban areas, new assessments included
in the Staff Paper were primarily
focused on visibility impairment in
urban areas.
b. Correlations Between Urban Visibility
and PM2.5 Mass
Direct relationships exist between
measured ambient pollutant
concentrations and their contributions
to light extinction and thus to visibility
impairment. The contribution of each
PM constituent to total light extinction
is derived by multiplying the
constituent concentration by its
extinction efficiency to calculate a
‘‘reconstructed’’ light extinction.82 For
82 Extinction efficiencies vary by type of
constituent and have been obtained for typical
atmospheric aerosols by a combination of empirical
approaches and theoretical calculations. As
discussed in the Staff Paper, EPA’s guidance for
tracking progress under the regional haze program
specifies an algorithm for calculating total light
extinction as a function of the major fine particle
components (EPA, 2005a, section 2.8.1).
‘‘Reconstructed’’ light extinction simply refers to
the calculation of PM-related light extinction by the
use of that formula.
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certain fine particle constituents,
extinction efficiencies increase
significantly with increases in relative
humidity. As a consequence, while
higher PM2.5 mass concentrations
generally indicate higher levels of
visibility impairment, it is not as precise
a metric as the light extinction
coefficient. Nonetheless, by using
historic averages, regional estimates, or
actual day-specific measurements of the
component-specific percentage of total
mass, one can develop reasonable
estimates of light extinction from PM
mass concentrations. As discussed
below, the Staff Paper concludes that
fine particle mass concentrations can be
used as a general surrogate for visibility
impairment (EPA, 2005a, p. 2–74).
In an effort to better characterize
urban visibility, the Staff Paper presents
results of analyses of the extensive new
data now available on PM2.5 primarily in
urban areas. This rapidly expanding
national database includes federal
reference method (FRM) 83
measurements of PM2.5 mass,
continuous measurements of hourly
PM2.5 mass, and PM2.5 chemical
speciation measurements. These data
allowed for analyses that explored
factors that have historically
complicated efforts to address visibility
impairment nationally, including
regional differences related to levels of
primarily fine particles and to relative
humidity. These analyses show a
consistently high correlation between
visibility, in terms of reconstructed light
extinction, and hourly PM2.5
concentrations for urban areas in a
number of regions across the U.S. and,
more generally, in the eastern and
western U.S. These correlations in
urban areas are generally similar in the
East and West, in sharp contrast to the
East/West differences observed in rural
areas.
While the average daily relative
humidity levels are generally higher in
the East than in the West, in both
regions relative humidity levels are
appreciably lower during daylight as
compared to night time hours. The
reconstructed light extinction
coefficient, for a given mass and
concentration, increases sharply as
relative humidity rises. Thus, with
lower relative humidity levels, visibility
impacts related to East/West differences
in average relative humidity are
minimized during daylight hours, when
relative humidity is generally lower.
Both 24-hour and shorter-term
daylight hour averaging periods were
83 The PM
2.5 Federal Reference Method (FRM)
monitoring network provides 24-hour average PM2.5
concentrations.
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considered in evaluations of
correlations between PM2.5
concentrations in urban areas and
visibility in eastern and western areas,
as well as nationwide. Clear and
similarly strong correlations are found
between visibility and 24-hour average
PM2.5 in eastern, western, and all urban
areas (EPA, 2005a, Figure 6–3).
Somewhat stronger correlations are
observed between visibility and PM2.5
concentrations averaged over a 4-hour
time period (EPA, 2005a, Figure 6–5).
The correlations between visibility and
PM2.5 concentrations during daylight
hours in urban areas are relatively more
reflective of PM2.5 mass rather than
relative humidity effects, in comparison
to correlations based on a 24-hour
averaging time.
c. Impacts of Urban Visibility
Impairment on Public Welfare
EPA has long recognized that
impairment of visibility is an important
effect of PM on public welfare, and that
it is experienced throughout the U.S. in
urban areas as well as in remote Class
I areas (62 FR 38680). Visibility is an
important welfare effect because it has
direct significance to people’s
enjoyment of daily activities in all parts
of the country. Individuals value good
visibility for the sense of well-being it
provides them directly, both in places
where they live and work, and in places
where they enjoy recreational
opportunities.
Survey research on public awareness
of visual air quality using direct
questioning typically reveals that 80
percent or more of the respondents are
aware of poor visual air quality (Cohen
et al., 1986). The importance of visual
air quality to public welfare across the
country has been demonstrated by a
number of studies designed to quantify
the benefits (or willingness to pay)
associated with potential improvements
in visibility (Chestnut and Dennis, 1997;
Chestnut and Rowe, 1991). Economists
have performed many studies in an
attempt to quantify the economic
benefits associated with improvements
in current visibility conditions both in
national parks and in urban areas
(Chestnut and Dennis, 1997). These
economic benefits may include the
value of improved aesthetics during
daily activities (e.g., driving or walking,
daily recreations), for special activities
(e.g., visiting parks and scenic vistas,
hiking, hunting), and for viewing scenic
photography. They may also include the
value of improved road and air safety,
and/or preservation of the resource for
its own sake. As discussed in the Staff
Paper and below, the value placed on
protecting visual air quality is further
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demonstrated by the existence of a
number of programs, goals, standards,
and planning efforts that have been
established in the U.S. and abroad to
address visibility concerns in urban and
non-urban areas.
Protection against visibility
impairment in special areas is provided
for in sections 169A, 169B, and 165 of
the CAA, in addition to that provided by
the secondary NAAQS. Section 169A,
added by the 1977 CAA Amendments,
established a national visibility goal to
‘‘remedy existing impairment and
prevent future impairment’’ in 156
national parks and wilderness areas
(Class I areas). The Amendments also
called for EPA to issue regulations
requiring States to develop long-term
strategies to make ‘‘reasonable progress’’
toward the national goal. EPA issued
initial regulations in 1980 focusing on
visibility problems that could be linked
to a single source or small group of
sources. The 1990 CAA Amendments
placed additional emphasis on regional
haze issues through the addition of
section 169B. In accordance with this
section, EPA established the Grand
Canyon Visibility Transport
Commission (GCVTC) in 1991 to
address adverse visibility impacts on 16
Class I national parks and wilderness
areas on the Colorado Plateau. The
GCVTC issued its recommendations to
EPA in 1996, triggering a requirement in
section 169B for EPA issuance of
regional haze regulations.
EPA accordingly promulgated a final
regional haze rule in 1999 (U.S. EPA,
1999; 65 FR 35713). Under the regional
haze program, States are required to
establish goals for improving visibility
on the 20 percent most impaired days in
each Class I area, and for allowing no
degradation on the 20 percent least
impaired days. Each state must also
adopt emission reduction strategies
which, in combination with the
strategies of contributing States, assure
that Class I area visibility improvement
goals are met. The first State
implementation plans are to be adopted
in the 2003–2008 time period, with the
first implementation period extending
until 2018. Five multi-state planning
organizations are evaluating the sources
of PM2.5 contributing to Class I area
visibility impairment to lay the
technical foundation for developing
strategies, coordinated among many
States, in order to make reasonable
progress in Class I areas across the
country.
A number of other programs, goals,
standards, and planning efforts have
also been established in the U.S. and
abroad to address visibility concerns in
urban and non-urban areas. These
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regulatory and planning activities are of
interest because they are illustrative of
the significant value that the public
places on improving visibility, and
because they have developed and
applied methods for evaluating public
perceptions and judgments about the
acceptability of varying degrees of
visibility impairment, as discussed
below in the next section.
Several state and local governments
have developed programs to improve
visual air quality in specific urban areas,
including Denver, CO; Phoenix, AZ;
and, Lake Tahoe, CA. At least two States
have established statewide standards to
protect visibility. In addition, interest in
visibility protection in other countries,
including Canada, Australia, and New
Zealand has resulted in various studies,
surveys, and programs. Examples of
these efforts are highlighted below.
In 1990, the State of Colorado adopted
a visibility standard for the city of
Denver. The Denver standard is a shortterm standard that establishes a limit of
a four-hour average light extinction
level of 76 Mm¥1 (equivalent to a visual
range of approximately 50 km) during
the hours between 8 a.m. and 4 p.m.
(Ely et al., 1991). In 2003, the Arizona
Department of Environmental Quality
created the Phoenix Region Visibility
Index, which focuses on an averaging
time of 4 hours during actual daylight
hours. This visibility index establishes
visual air quality categories (i.e.,
excellent to very poor) and establishes
the goals of moving days in the poor/
very poor categories up to the fair
category, and moving days in the fair
category up to the good/excellent
categories (Arizona Department of
Environmental Quality, 2003). This
approach results in a focus on
improving visibility to a visual range of
approximately 48–36 km. In 1989, the
state of California revised the visibility
standard for the Lake Tahoe Air Basin
and established an 8-hour visibility
standard equal to a visual range of 30
miles (approximately 48 km) (California
Code of Regulations).
California and Vermont each have
standards to protect visibility, though
they are based on different measures.
Since 1959, the state of California has
had an air quality standard for particle
pollution where the ‘‘adverse’’ level was
defined as the ‘‘level at which there will
be * * * reduction in visibility or
similar effects.’’ California’s general
statewide visibility standard is a visual
range of 10 miles (approximately 16 km)
(California Code of Regulations). In
1985, Vermont established a state
visibility standard that is expressed as a
summer seasonal sulfate concentration
of 2 µg/m3, that equates to a visual range
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of approximately 50 km. This standard
was established to represent ‘‘reasonable
progress’’ toward attaining the
congressional visibility goal for the
Class 1 Lye Brook National Wilderness
Area, and applies to this Class 1 area
and to all other areas of the state with
elevations greater than 2500 ft.
Outside of the U.S., efforts have also
been made to protect visibility. The
Australian state of Victoria has
established a visibility objective (State
Government of Victoria, 1999 and 2000),
and a visibility guideline is under
consideration in New Zealand (New
Zealand National Institute of Water &
Atmospheric Research, 2000a and
2000b; New Zealand Ministry of
Environment, 2000). A survey was
undertaken for the Lower Fraser Valley
in British Columbia, with responses
from this pilot study being supportive of
a standard in terms of a visual range of
approximately 40 km for the suburban
township of Chilliwack and 60 km for
the suburban township of Abbotsford,
although no visibility standard has been
adopted for the Lower Fraser Valley at
this time.
d. Approaches to Evaluating Public
Perceptions and Attitudes
New methods and tools have been
developed to communicate and evaluate
public perceptions of varying visual
effects associated with alternative levels
of visibility impairment relative to
varying pollution levels and
environmental conditions. New survey
methods have been applied and
evaluated in various studies, such as
those done in Denver, Phoenix, and the
Lower Fraser Valley in British
Columbia. These methods are intended
to assess public perceptions as to the
acceptability of varying levels of visual
air quality, considered in these studies
to be an appropriate basis for
developing goals and standards for
visibility protection. A pilot study was
also conducted in Washington, DC by
EPA staff.84 Even with variations in
each study’s approaches, the public
perception survey methods used for the
Denver, Phoenix, and British Columbia
studies produced reasonably consistent
results from location to location, with
each study indicating that a majority of
participants find visual ranges within
about 40 to 60 km to be acceptable.
These public perception studies use
images of urban and distant scenic
views under different visibility
conditions together with survey
techniques designed to elicit judgments
84 This small pilot study was briefly discussed in
the preliminary draft staff paper (Abt Associates,
2001).
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from members of the public about the
acceptability of differing levels of visual
air quality. Images used are either
photographs or computer simulations
using the WinHaze program.85
Examples of images that illustrate visual
air quality in Denver, Phoenix,
Washington, DC, and Chicago under a
range of visibility conditions associated
with a range of PM2.5 concentrations are
available at https://www.epa.gov/ttn/
naaqs/standards/pm/s_pm_cr_sp.html
(labeled as Appendix 6A: Images of
Visual Air Quality in Selected Urban
Areas in the U.S.). These examples
include simulated images for Denver,
Phoenix, and Washington, DC, and
photographs of Chicago.
Survey techniques were developed in
conjunction with the Denver study and
relied on citizen judgments of
acceptable and unacceptable levels of
visual air quality (Ely et al., 1991; EPA,
2005a, section 6.2.6.2). The studies in
Phoenix and British Columbia, and the
pilot study in Washington, DC used
survey approaches based on that used in
Denver. This approach involves
conducting a series of meetings with
civic and community groups to elicit
individual ratings of a number of images
of well-known local vistas having
varying levels of visual air quality.
Participants are told that the results are
intended to provide input on setting a
visibility standard, and they are asked to
base their judgments on three factors: (1)
The standard is for an urban area, not
a pristine national park area where the
standards might be more strict; (2)
standard violations should be at visual
air quality levels considered to be
unreasonable, objectionable, and
unacceptable visually; and (3)
judgments of standard violations should
be based on visual air quality only, not
on any health effects that some may
perceive as being linked with poor
visual air quality. The Denver visibility
survey process produced the following
findings: (1) Individuals’ judgments of
an images’s visual air quality and
whether the image should be considered
to violate a visibility standard are highly
correlated with the group average; (2)
when participants judged duplicate
slides, group averages of the first and
second ratings were highly correlated;
85 The Criteria Document discusses methods
available to represent different levels of visual air
quality (EPA, 2004, p. 4–174). In particular,
Molenar et al. (1994) describe a sophisticated visual
air quality simulation technique, incorporated into
the WinHaze program developed by Air Resources
Specialists, Inc., which combined various modeling
systems under development for the past 20 years to
produce images that standardize non-pollution
related effects on visibility so that perceptions of
these images are not biased due to these other
factors.
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and (3) group averages of visual air
quality ratings and ‘‘standard
violations’’ were highly correlated. The
strong relationship of standard violation
judgments with the visual air quality
ratings is cited as the best evidence
available from this study for the validity
of this approach as input to a standard
setting process (Ely et al., 1991).
The Denver visibility standard was
established based on a 50 percent
acceptability criterion. That is, under
this approach, the standard was
identified as the light extinction level
that divides the images into two groups:
those found to be acceptable and those
found to be unacceptable by a majority
of study participants. In fact, when
researchers evaluated all citizen
judgments made on all the photographic
images at this level and above as a
single group, more than 85 percent of
the participants found visibility
impairment at and above the level of the
selected standard to be unacceptable.
Generally consistent results were
found in the Phoenix study, which used
simulated images from the WinHaze
program. The study carefully selected
participants to be demographically
representative of the Phoenix
population. The Phoenix survey
demonstrates that the rating
methodology developed for gathering
citizen input for establishing the Denver
visibility standard can be reliably
transferred to another city while relying
on updated imaging technology to
simulate a range of visibility
impairment levels. Similarly, the British
Columbia study reinforces the
conclusion that the methodology
originally developed for the Denver
standard setting process is a sound and
effective one for obtaining public
participation in a standard setting
process (EPA, 2005a, p. 6–22).
2. Need for Revision of the Current
Secondary PM Standards for Visibility
Protection
The initial issue to be addressed in
the current review of the secondary PM
standards is whether, in view of the
information now available, the existing
secondary standards should be revised
to provide requisite protection from PMrelated adverse effects on visual air
quality. As discussed in the Criteria
Document and Staff Paper, while new
research has led to improved
understanding of the optical properties
of particles and the effects of relative
humidity on those properties, it has not
changed the fundamental
characterization of the role of PM,
especially fine particles, in visibility
impairment from the last review.
However, extensive new information
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now available from visibility and fine
particle monitoring networks has
allowed for updated characterizations of
visibility trends and current levels in
urban areas, as well as Class I areas. As
discussed above, these new data are a
critical component of analyses that
better characterize visibility impairment
in urban areas and the relationships
between visibility and PM2.5
concentrations, finding that PM2.5
concentrations can be used as a general
surrogate for visibility impairment in
urban areas.
Taking into account the most recent
monitoring information and analyses,
and recognizing that efforts are now
underway to address all human-caused
visibility impairment in Class I areas
through the regional haze program
implemented under sections 169A and
169B of the CAA, as discussed above,
this review focuses on visibility
impairment primarily in urban areas. In
so doing, consideration is first given to
the question of whether visibility
impairment in urban areas allowed by
the current 24-hour secondary PM2.5
standard can be considered adverse to
public welfare.
As discussed above, studies in the
U.S. and abroad have provided the basis
for the establishment of standards and
programs to address specific visibility
concerns in a number of local areas.
These studies (e.g., in Denver, Phoenix,
British Columbia) have produced
reasonably consistent results in terms of
the visual ranges found to be generally
acceptable by the participants in the
various studies, which ranged from
approximately 40 to 60 km in visual
range. Standards targeting protection
within this range have also been set by
the State of Vermont and by California
for the Lake Tahoe area, in contrast to
the statewide California standard that
targets a visual range of approximately
16 km.
In addition to the information
available from such programs,
photographic representations (simulated
images and actual photographs) of
visibility impairment are available, as
discussed above, to help inform
judgments about the acceptability of
varying levels of visual air quality in
urban areas across the U.S. In
considering these images for Phoenix,
Washington, DC, and Chicago (for
which PM2.5 concentrations are
reported), the Staff Paper observes that:
(1) At concentrations at or near the
level of the current 24-hour PM2.5
standard (65 µg/m3), which equates to
visual ranges roughly around 10 km,
scenic views (e.g., mountains, historic
monuments), as depicted in these
images around and within the urban
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areas, are significantly obscured from
view.
(2) Appreciable improvement in the
visual clarity of the scenic views
depicted in these images occurs at PM2.5
concentrations below 35 to 40 µg/m3,
which equate to visual ranges generally
above 20 km for the urban areas
considered (EPA, 2005a, p. 7–6).
(3) Visual air quality appears to be
good in these images at PM2.5
concentrations generally below 20 µg/
m3, corresponding to visual ranges of
approximately 25 to 35 km (EPA, 2005a,
p. 7–8).
While being mindful of the
limitations in using visual
representations from a small number of
areas as a basis for considering national
visibility-based secondary standards,
the Staff Paper nonetheless concludes
that these observations, together with
information from the analyses and other
programs discussed above, support
revising the current secondary PM2.5
standards to improve visual air quality,
particularly in urban areas. As
discussed in the following sections, the
Staff Paper recommends the
establishment of a new short-term
secondary PM2.5 standard to provide
increased and more targeted protection
primarily in urban areas from visibility
impairment related to fine particles
(EPA, 2005a, p. 7–12). Based on its
review of the Staff Paper, the CASAC
advised the Administrator that most
CASAC PM Panel members strongly
supported the Staff Paper
recommendation to establish a new,
secondary PM2.5 standard to protect
urban visibility (Henderson, 2005a).86
Most Panel members considered such a
standard to be a reasonable complement
to the Regional Haze Rules that protect
Class I areas.
In considering whether the secondary
PM standards should be revised to target
PM-related visibility impairment
primarily in urban areas, the
Administrator has carefully considered
the rationale and recommendation in
the Staff Paper, the advice and
recommendations from CASAC, and
public comments to date on this issue.
In so doing, the Administrator first
recognizes that PM-related visibility
impairment is principally related to fine
particle levels, such that it is
appropriate to focus in this review on
the current secondary PM2.5 standards to
provide such targeted protection. The
Administrator also recognizes that
visibility is most directly related to
86 A dissenting view was expressed in one Panel
member’s invididual review comments to the effect
that any urban visibility standard should be
voluntary and locally adopted (Henderson, 2005a).
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instantaneous levels of visual air
quality, such that it is appropriate to
focus on a standard with a short-term
averaging time (e.g., 24-hours or less).
Thus, the Administrator has considered
whether the current 24-hour secondary
PM2.5 standard should be revised to
provide a requisite level of protection
from visibility impairment, principally
in urban areas, in conjunction with the
regional haze program for protection of
visual air quality in Class I areas. The
Administrator observes that at
concentrations at or near the level of the
current 24-hour PM2.5 standard (65 µg/
m3), corresponding to visual ranges of
about 10 km, images of scenic views
(e.g., mountains, historic monuments,
urban skylines) around and within a
number of urban areas are significantly
obscured from view. Further, the
Administrator notes the various State
and local standards and programs that
have been established protect visual air
quality beyond the degree of protection
that would be afforded by the current
24-hour secondary PM2.5 standard.
Based on all of the above
considerations, the Administrator
provisionally concludes that it is
appropriate to revise the current 24hour secondary PM2.5 standard to
provide requisite protection from
visibility impairment principally in
urban areas.
3. Indicator of PM for Secondary
Standard To Address Visibility
Impairment
As discussed in the Staff Paper, fine
particles contribute to visibility
impairment directly in proportion to
their concentration in the ambient air.
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. In analyzing how well
PM2.5 concentrations correlate with
visibility in urban locations across the
U.S. (see EPA, 2005a, section 6.2.3), the
Staff Paper concludes that the observed
correlations are strong enough to
support the use of PM2.5 as the indicator
for such standards. More specifically,
clear correlations exist between 24-hour
average PM2.5 concentrations and
reconstructed light extinction, which is
directly related to visual range. These
correlations are similar in the eastern
and western regions of the U.S.. Further,
these correlations are less influenced by
relative humidity and more consistent
across regions when PM2.5
concentrations are averaged over
shorter, daylight time periods (e.g., 4 to
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8 hours). Thus, the Staff Paper
concludes that it is 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 of
daylight hours. Based on its review of
the Staff Paper, most CASAC PM Panel
members endorsed a PM2.5 indicator for
a secondary standard to address
visibility impairment.
The Administrator concurs with the
EPA staff and CASAC
recommendations, and concludes that
PM2.5 should be retained as the
indicator for fine particles as part of a
secondary standard to address visibility
protection. In the Administrator’s view,
PM2.5 is the appropriate indicator for
any such standard, whether averaged
over 24-hours or over a shorter, subdaily time period.
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4. Averaging Time of a Secondary PM2.5
Standard for Visibility Protection
As discussed in the Staff Paper,
averaging times from 24 to 4 hours have
been considered for a standard to
address visibility impairment. Within
this range, as noted above, clear and
similarly strong correlations are found
between visibility and 24-hour average
PM2.5 concentrations in eastern and
western areas, while somewhat stronger
correlations are found with PM2.5
concentrations averaged over a 4-hour
time period. In general, correlations
between PM2.5 concentrations and light
extinction are generally less influenced
by relative humidity and more
consistent across regions as shorter, subdaily averaging times, within daylight
hours from approximately 10 a.m. to 6
p.m., are considered. The Staff Paper
concludes that an averaging time from 4
to 8 hours, generally within this
daylight time period, should be
considered for a standard to address
visibility impairment.
In reaching this conclusion, the Staff
Paper recognizes that the PM2.5 Federal
Reference Method (FRM) monitoring
network provides 24-hour average
concentrations, and, in some cases, on
a third- or sixth-day sample schedule,
such that implementing a standard with
a less-than-24-hour averaging time
would necessitate the use of continuous
monitors that can provide hourly time
resolution. Given that the data used in
the analysis discussed above are from
commercially available PM2.5
continuous monitors, such monitors
clearly could provide the hourly data
that would be needed for comparison
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with a potential visibility standard with
a less-than-24-hour averaging time.87
Most CASAC PM Panel members
supported the Staff Paper
recommendation of a sub-daily (4 to 8
daylight hours) averaging time, finding
it to be an innovative approach that
strengthens the quality of the PM2.5
indicator by targeting the driest part of
the day (Henderson, 2005a). In its
advice to the Administrator, CASAC
noted an indirect but important benefit
to advancing EPA’s monitoring program
goals that would come from the direct
use of hourly data from a network of
continuous PM2.5 mass monitors.
In considering the Staff Paper
recommendation and CASAC’s advice,
the Administrator provisionally
concludes that averaging times from 24
hours to 4 daylight hours would
represent a reasonable range of choices
for a standard to address urban visibility
impairment. A 24-hour averaging time
could be selected and applied based on
the extensive data base currently
available from the existing PM2.5 FRM
monitoring network, whereas a subdaily averaging time would necessarily
depend upon an expanded network of
continuous PM2.5 mass monitors. While
the Administrator agrees that broader
deployment of continuous PM2.5 mass
monitors is a desirable goal, working
toward that goal does not depend upon
nor provide a basis for setting a subdaily standard. The Administrator
believes that it is appropriate to evaluate
averaging time in conjunction with
reaching decisions on the form and level
of a standard, as discussed below.
5. Elements of a Secondary PM2.5
Standard for Visibility Protection
In considering PM2.5 standards that
would provide requisite protection
against PM-related impairment of
visibility primarily in urban areas, the
Administrator has taken into account
the results of public perception and
attitude surveys 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
provide 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
87 Decisions as to which PM
2.5 continuous
monitors are providing data of sufficient quality to
be used in a sub-daily visibility standard would
follow protocols for approval of Federal equivalent
methods (FEMs) that can provide data in at least
hourly intervals, as proposed in the revisions to
Part 53, published elsewhere in today’s Federal
Register.
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subjective nature of the public welfare
effect involved. In considering
alternative forms for such standards, the
Administrator has also taken into
account the same general factors that
were considered in selecting an
appropriate form for the 24-hour
primary PM2.5 standard, as well as
additional information on the percent of
areas not likely to meet various
alternative PM2.5 standards, consistent
with CASAC advice to consider such
information (Henderson, 2005a).
In considering elements of a
secondary PM2.5 standard, the
Administrator has looked to the
rationale presented in the Staff Paper
and to CASAC’s advice and
recommendations for such a standard.
Based on photographic representations
of varying levels of visual air quality,
public perception studies, and local and
State visibility standards, as discussed
above, the Staff Paper concludes that 30
to 20 µg/m3 PM2.5 represents a
reasonable range for a national visibility
standard primarily for urban areas,
based on a sub-daily averaging time.
The upper end of this range is below the
levels at which the illustrative scenic
views are significantly obscured, and
the lower end is around the level at
which visual air quality generally
appears to be good based on observation
of the illustrative views. Analyses of 4hour average PM2.5 concentrations
indicate that this concentration range
can be expected generally to correspond
to median visual ranges in urban areas
within regions across the U.S. of
approximately 25 to 35 km (see EPA,
2005a, Figure 7–1).88 This range of
visual range values is 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 Staff Paper
concludes that a concentration-based
percentile form is appropriate for the
same reasons as discussed above in
section II.F.1 (on the form of the 24-hour
primary PM2.5 standard). The Staff Paper
also concludes that the upper end of the
range of concentration percentiles
should be consistent with the percentile
used for the primary standard, which is
proposed to be the 98th percentile, and
that the lower end of the range should
be the 92nd percentile, which
represents the mean of the distribution
88 The Staff Paper notes that a standard set at any
specific PM2.5 concentration will 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 (EPA, 2005a, p. 7–8).
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of the 20 percent worst day, as targeted
in the regional haze program (EPA,
2005a, p. 7–11 to 12).
In its letter to the Administrator
(Henderson, 2005a), the CASAC PM
Panel recognizes that it is difficult to
select any specific level and form based
on currently available information.
Some Panel members felt that the range
of levels recommended in the Staff
Paper was on the high side, but
recognized that developing a more
specific (and more protective) level in
future reviews would require updated
and refined public visibility valuation
studies, which CASAC strongly
encouraged the Agency to support prior
to the next review. With regard to the
form of the standard, the
recommendations in the final Staff
Paper reflected CASAC’s advice to
consider percentiles in the range of the
92nd to the 98th percentile. Some Panel
members recommend considering a
percentile within this range in
conjunction with a level toward the
upper end of the range recommended in
the Staff Paper.89
Based on the above considerations,
the Administrator believes that it is
appropriate to first consider the level of
protection that would be afforded by the
suite of primary PM2.5 standards
proposed today. The limited and
uncertain evidence currently available
for use in evaluating the appropriate
level of protection suggests that a
cautious approach is warranted in
establishing a secondary standard.
While significantly more information is
available since the last review
concerning the relationship between
fine PM levels and visibility across the
country, there is still little available
information for use in making the
relatively subjective value judgment
needed in setting the secondary
standard. Given this, it is appropriate to
first evaluate the level of protection that
the proposed primary standards would
likely provide, and then determine
whether the available evidence warrants
adopting a standard with a different
level, form, or averaging time. In
comparing 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, the
Administrator has looked to information
on the predicted percent of areas not
89 Some CASAC Panel members also recommend
that such a standard be implemented in conjunction
an ‘‘exceptional events’’ policy so as to avoid
having non-compliance with the standard be driven
by natural source influences such as dust storms
and wild fires (Henderson, 2005a).
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likely to meet various alternative
secondary and primary PM2.5 standards
(EPA, 2005a, Tables 7A–1 and 5B–
1(a) 90). In so doing, the Administrator
observes that the predicted percent of
counties with monitors not likely to
meet the proposed suite of primary
PM2.5 standards (i.e., a 24-hour standard
set at 35 µg/m3, with a 98th percentile
form, and an annual standard of 15 µg/
m3) is somewhat higher (27 percent)
than the predicted percent of counties
with monitors not likely to meet a subdaily secondary standard with an
averaging time of 4 to 8 daylight hours,
a level toward the upper end of the
range recommended in the Staff Paper
(e.g., up to 30 µg/m3), and a form within
the recommended range (e.g., around
the 95th percentile) (24 percent). A
similar comparison is seen in
considering the predicted percentages of
the population living in such areas.
The Administrator provisionally
concludes that revising the current
secondary PM2.5 to be identical to the
proposed suite of primary PM2.5
standards is a reasonable policy
approach to addressing visibility
protection primarily in urban areas.
Such an approach would result in
improvements in visual air quality in as
many or more urban areas across the
country as would the alternative
approach of setting a sub-daily standard
consistent with that generally
recommended by CASAC. Such an
approach also takes into account the
substantial limitations in the available
hourly air quality data and in available
studies of public perception and
attitudes with regard to the acceptability
of various degrees of visibility
impairment in urban areas across the
country. Given these limitations, the
Administrator concludes, subject to
consideration of public comment, that a
secondary standard with a different
averaging time, level, or form is not
warranted, because the available
evidence does not support a decision to
achieve a level of protection different
from that provided by the current
primary standards, and because no
change in averaging time, level, or form
appears needed to achieve a comparable
level of protection.
The Administrator believes that a
secondary NAAQS should be
considered in conjunction with the
90 The information in these Tables is based on
analysis of 2001–2003 air quality data, including
562 counties with FRM monitors that met specific
data completeness criteria for developing predicted
percentages of counties not likely to meet the suite
of primary PM2.5 standards and 168 counties with
continuous PM2.5 monitors that met less restrictive
data completeness criteria for developing predicted
percentages for a 4-hour secondary PM2.5 standard.
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regional haze program as a means of
achieving appropriate levels of
protection against PM-related visibility
impairment in urban, non-urban, and
Class I areas across the country.
Programs implemented to meet a
national standard focused primarily on
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 rule
established for protection of visual air
quality in Class I areas. The
Administrator further believes that the
development of local programs
continues to be an effective and
appropriate approach to provide
additional protection for unique scenic
resources in and around certain urban
areas that are particularly highly valued
by people living in those areas. Based
on these considerations, and taking into
account the observations, analyses, and
recommendations discussed above, the
Administrator proposes to revise the
current secondary PM2.5 standards by
making them identical in all respects to
the proposed suite of primary PM2.5
standards.
As discussed above, most CASAC PM
Panel members strongly supported a
sub-daily (4- to 8-hour averaging time)
PM2.5 standard. The Administrator
places great importance on the advice of
CASAC, and therefore solicits public
comment on such a standard.
B. Other PM-Related Welfare Effects
This section presents the rationale for
the Administrator’s proposed revision of
the current secondary PM standards to
address PM-related effects other than
visibility impairment, including
vegetation and ecosystems, materials
damage and soiling, and climate change.
In considering the currently available
evidence on each of these types of PMrelated welfare effects, the Staff Paper
notes that there is much information
linking ambient PM to potentially
adverse effects on materials and
ecosystems and vegetation, and on
characterizing the role of atmospheric
particles in climatic and radiative
processes. However, given the
evaluation of this information in the
Criteria Document and Staff Paper
which highlighted the substantial
limitations in the evidence, especially
the lack of evidence linking various
effects to specific levels of ambient PM,
the Administrator provisionally
concludes that the available evidence
does not provide a sufficient basis for
establishing distinct secondary
standards for PM based on any of these
effects alone.
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The Administrator has also addressed
the question of whether reductions in
PM likely to result from the current
secondary PM standards, or from the
range of proposed revisions to the
primary PM standards, would provide
requisite protection against any of these
PM-related welfare effects. As discussed
below, these considerations include the
latest scientific information
characterizing the nature of these PMrelated effects and judgments as to
whether revision of the current
secondary standards are appropriate
based on that information.
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1. Nature of Effects
Particulate matter contributes to
adverse effects on a number of welfare
effects categories other than visibility
impairment, including vegetation and
ecosystems, soiling and materials
damage and climate. These welfare
effects result predominantly from
exposure to excess amounts of specific
chemical species, regardless of their
source or predominant form (particle,
gas or liquid). Reflecting this fact, the
Criteria Document concludes that
regardless of size fraction, particles
containing nitrates and sulfates have the
greatest potential for widespread
environmental significance, while
effects are also related to other chemical
constituents found in ambient PM, such
as trace metals and organics.91 The
following characterizations of the nature
of these welfare effects are based on the
information contained in the Criteria
Document and Staff Paper.
a. Effects on Vegetation and Ecosystems
Potentially adverse PM-related effects
on vegetation and ecosystems are
principally associated with particulate
nitrate and sulfate deposition. In
characterizing such effects, it is
important to recognize that nitrogen and
sulfur are necessary and beneficial
nutrients for most organisms that make
up ecosystems, with optimal amounts of
these nutrients varying across
organisms, populations, communities,
ecosystems and time scales. Therefore,
it is impossible to generalize to all
species in all circumstances as to the
amount at which inputs of these
nutrients or acidifying compounds
become stressors. The Staff Paper
recognizes that the public welfare
benefits from the use of nitrogen (N) and
sulfur (S) nutrients in fertilizers in
managed agricultural and commercial
forest settings. The focus of this review,
therefore, is on identifying risks to
91 The Staff Paper notes that some of these other
components are regulated under separate statutory
authorities, e.g., section 112 of the CAA.
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sensitive species and ecosystems where
unintentional additions of these
atmospherically derived nutrient and
acidifying compounds may be
contributing to undesired change in the
nation’s ecosystems and resulting in
adverse impacts on essential ecological
attributes such as species shifts, loss of
species richness and diversity, impacts
on threatened and endangered species,
and alteration of native fire cycles. In
these cases, deposited particulate nitrate
and sulfate are appropriately termed
ecosystem ‘‘stressors.’’
i. Vegetation Effects
At current ambient levels, risks to
vegetation from short-term exposures to
dry deposited particulate nitrate or
sulfate are low. However, when found
in acid or acidifying deposition, such
particles do have the potential to cause
direct foliar injury. Specifically, the
responses of forest trees to acid
precipitation (rain, snow) include
accelerated weathering of leaf cuticular
surfaces, increased permeability of leaf
surfaces to toxic materials, water, and
disease agents; increased leaching of
nutrients from foliage; and altered
reproductive processes—all which serve
to weaken trees so that they are more
susceptible to other stresses (e.g.,
extreme weather, pests, pathogens).
Acid deposition with levels of acidity
associated with the foliar effects
described above are currently found in
some locations in the eastern U.S. (EPA,
2003). Even higher concentrations of
acidity can be present in occult
deposition (e.g. fog, mist or clouds)
which more frequently impacts higher
elevations. Thus, the risks of foliar
injury occurring from acid deposition in
some areas of the eastern U.S. is high.
However, based on currently available
information, the contribution of
particulate sulfates and nitrates to the
total acidity found at these locations is
not clear.
ii. Ecosystem Effects
The N- and S-containing components
of PM have been associated with a broad
spectrum of terrestrial and aquatic
ecosystem impacts that result from
either the nutrient or acidifying
characteristics of the deposited
compounds.
Reactive nitrogen (Nr) is the form of
N that is available to support the growth
of plants and microorganisms. Since the
mid-1960’s, Nr creation through natural
terrestrial processes has been overtaken
by Nr creation as a result of human
processes, and is now accumulating in
the environment on all spatial scales—
local, regional and global. Some Nr
emissions are transformed into ambient
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PM and deposited onto sensitive
ecosystems. Some of the most
significant detrimental effects associated
with excess Nr deposition are those
associated with a syndrome known as
‘‘nitrogen saturation.’’ These effects
include: (1) Decreased productivity,
increased mortality, and/or shifts in
terrestrial plant community
composition, often leading to decreased
biodiversity in many natural habitats
wherever atmospheric Nr deposition
increases significantly and critical
thresholds are exceeded; (2) leaching of
excess nitrate and associated base
cations from terrestrial soils into
streams, lakes and rivers and
mobilization of soil aluminum; and (3)
alteration of ecosystem processes such
as nutrient and energy cycles through
changes in the functioning and species
composition of beneficial soil organisms
(Galloway and Cowling 2002). Thus,
through its effects on habitat suitability,
genetic diversity, community dynamics
and composition, nutrient status, energy
and nutrient cycling, and frequency and
intensity of natural disturbance regimes
(fire), excess Nr deposition is having
profound and adverse impact on the
essential ecological attributes associated
with terrestrial ecosystems. In the U.S.,
numerous forests now show severe
symptoms of nitrogen saturation. For
other forested locations, ongoing
expansion in nearby urban areas will
increase the potential for nitrogen
saturation unless there are improved
emission controls.
Excess nutrient inputs into aquatic
ecosystems (e.g., streams, rivers, lakes,
estuaries or oceans) either from direct
atmospheric deposition, surface runoff,
or leaching from nitrogen saturated soils
into ground or surface waters can
contribute to conditions of severe water
oxygen depletion (hypoxia);
eutrophication and algae blooms;
altered fish distributions, catches, and
physiological states; loss of biodiversity;
habitat degradation; and increases in the
incidence of disease. Estuaries are
among the most intensely fertilized
systems on Earth.
Reactive nitrogen moves from one
environmental reservoir to another
through a number of sequential
environmental processes. Though strong
correlation between the stressor and
adverse environmental response exists
in many locations, and N-addition
studies have confirmed the relationship
between stressor and response, the
ability to determine the temporal and
spatial distribution of environmental
effects for a given input of Nr are
extremely limited by the large
uncertainties associated with the rates at
which Nr cascades through and
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accumulates in various environmental
reservoirs.
Acid and acidifying deposition is
another significant source of stress to
forest and aquatic ecosystems. It
changes the chemical composition of
soils by depleting the content of
available plant nutrient cations such as
calcium (Ca2∂), increasing the mobility
of aluminum (Al), and increasing the S
and N content (Driscoll et al., 2001).
Leaching of soil nutrients is often of
major importance in cation cycles, and
many forest ecosystems show a net loss
of base cations. In sensitive forest soils,
acid deposition leads to a shift in
chemical speciation of Al from organic
to inorganic forms that are toxic to
terrestrial and aquatic biota, and
increases inorganic Al mobilization and
transport into surface waters. The toxic
effect of Al on forest vegetation is
attributed to its interference with plant
uptake of essential nutrients, such as Ca
and Mg. There are large variations in Al
sensitivity among ecotypes, between
and within species, due to differences in
nutritional demands and physiological
status, that are related to age and
climate, and which change over time.
Acid deposition has been firmly
implicated as a causal factor in the
decline of red spruce in high elevation
sites in the Northeast. Red spruce is
valued commercially, for recreation and
aesthetics, and as habitat for unique and
endangered species. Dieback of red
spruce trees has also been observed in
mixed hardwood-conifer stands at
relatively low elevations in the western
Adirondack Mountains, where inputs of
acid deposition are high. Exposure to
acidic mist or cloud water reduces foliar
calcium levels in red spruce needles,
leading to increased susceptibility to
freezing (winter injury). There is also
the strong possibility that acid
deposition altering of foliar calcium
levels leading to reduced cold tolerance
is not unique to red spruce but has been
demonstrated in many other northern
temperate forest tree species including
yellow birch, white spruce, red maple,
eastern white pine, and sugar maple.
Less sensitive forests throughout the
U.S. are experiencing gradual losses of
base cation nutrients, which in many
cases will reduce the quality of forest
nutrition in the future (National Science
and Technology Council, 1998).
Inputs of acid deposition to regions
with base-poor soils have also resulted
in the acidification of soil waters,
shallow ground waters, streams, and
lakes in a number of locations within
the U.S. Acidification has marked
effects on the trophic structure of
surface waters. Decreases in pH and
increases in Al concentrations
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contribute to declines in species
richness and in the abundance of
zooplankton, macroinvertebrates, and
fish. Numerous studies have shown that
decreases in pH result in decreases in
fish species richness (the number of fish
species in a water body) by eliminating
acid-sensitive species including
important recreational fishes plus
ecologically important minnows that
serve as forage for sport fishes.
Though significant decreases in sulfur
emissions have occurred in the U.S. and
Europe in recent decades, these
decreases have not been accompanied
by equivalent declines in net acidity
related to sulfate in precipitation, and
may have, to varying degrees, been
offset by steep declines in atmospheric
base cation concentrations over the past
10 to 20 years (Hedin et al., 1994;
Driscoll et al. 2001). Projections made
using an acidification model (PnETBGC) 92 indicate that full
implementation of the 1990 CAA
Amendments will not afford substantial
chemical recovery at Hubbard Brook
Experimental Forest and at many
similar acid-sensitive locations (Driscoll
et al., 2001). Model calculations indicate
that the magnitude and rate of recovery
from acid deposition in the northeastern
U.S. are directly proportional to the
magnitude of emissions reductions.
Model evaluations of policy proposals
calling for additional reductions in
utility SO2 and NOX emissions, year
round emissions controls, and early
implementation indicate greater success
in facilitating the recovery of sensitive
ecosystems (Driscoll et al., 2001).
Driscoll et al. (2001) envision a
recovery process that will involve two
phases: chemical and biological.
Initially, a decrease in acid deposition
following emissions controls will
facilitate a phase of chemical recovery
in forest and aquatic ecosystems.
Recovery time for this phase will vary
widely across ecosystems and will be a
function of a number of factors. In most
cases, it seems likely that chemical
recovery will require decades, even with
additional controls on emissions. The
second phase in ecosystem recovery is
biological recovery, which can occur
only if chemical recovery is sufficient to
allow survival and reproduction of
plants and animals. The time required
for biological recovery is uncertain. For
92 PnET–BGC is designed to simulate element
cycling in forest and interconnected aquatic
ecosystems. The model PnET is a simple,
generalized, and well validated model that provides
estimates of forest net primary productivity,
nutrient uptake by vegetation, and water balances.
Recently, PnEt was coupled with a soil model that
simulates abiotic soil processes, resulting in a
comprehensive forest-soil-water model, PnET–BGC
(Driscoll et al., 2001).
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terrestrial ecosystems, it is likely to be
at least decades after soil chemistry is
restored because of the long life of tree
species and the complex interactions of
soil, roots, microbes, and soil biota. For
aquatic systems, research suggests that
stream macroinvertebrate populations
may recover relatively rapidly
(approximately 3 years), whereas lake
populations of zooplankton are likely to
recover more slowly (approximately 10
years) (Gunn and Mills, 1998). Some
fish populations may recover in 5 to 10
years after the recovery of zooplankton
populations, perhaps sooner with fish
stocking (Driscoll et al., 2001).
iii. Ecosystem Exposure to PM
Deposition
In order to establish exposureresponse profiles useful in ecological
risk assessments, two types of
monitoring networks need to be in
place. First, a deposition network is
needed that can track changes in
deposition rates of PM stressors
(nitrates/sulfates) occurring in sensitive
or symptomatic areas/ecosystems.
Secondly, a network or system of
networks should be established that
measures the response of key sensitive
ecological indicators over time to
changes in atmospheric deposition of
PM stressors.
Data from existing deposition
networks in the U.S. demonstrate that N
and S compounds are being deposited
in amounts known to be sufficient to
affect sensitive terrestrial and aquatic
ecosystems over time. Though the
percentages of N and S containing
compounds in PM vary spatially and
temporally, nitrates and sulfates make
up a substantial portion of the chemical
composition of PM. In the future,
speciated data from these networks may
allow better understanding of the
specific components of total deposition
that are most strongly influencing PMrelated ecological effects.
At this time, however, there are only
a few sites where long-term monitoring
of sensitive indicators of ecosystem
response to excess nitrogen and/or
acidic and acidifying deposition is
taking place within the U.S. Because the
complexities of ecosystem response
make predictions of the magnitude and
timing of chemical and biotic recovery
uncertain, it is important that this type
of long-term monitoring network be
continued, and that biological
monitoring be enhanced to support
future evaluations of the response of
forested watersheds and surface waters
to a host of research and regulatory
issues related to nutrient and acid and
acidifying deposition.
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iv. Critical Loads
The critical load (CL) has been
defined as a ‘‘quantitative estimate of an
exposure to one or more pollutants
below which significant harmful effects
on specified sensitive elements of the
environment do not occur according to
present knowledge’’ (Lokke et al., 1996).
The concept is useful for estimating the
amounts of pollutants that ecosystems
can absorb on a sustained basis without
experiencing measurable degradation.
The estimation of ecosystem critical
loads requires an understanding of how
an ecosystem will respond to different
loading rates in the long term and is a
direct function of the level of sensitivity
of the ecosystem to the pollutants in
question and its ability to ameliorate
pollutant stress.
The CL approach is very dataintensive, and, at the present time, there
is a paucity of ecosystem-level data for
most sites. However, for a limited
number of areas which already have a
long-term record of ecosystem
monitoring, (e.g., Rocky Mountain
National Park in Colorado and the Lye
Brook Wilderness in Vermont), Federal
Land Managers may be able to develop
site specific CLs. More specifically, with
respect to PM deposition, there are
insufficient data for the vast majority of
U.S. ecosystems that differentiate the
PM contribution to total N or S
deposition to allow for practical
application of this approach as a basis
for developing national standards to
protect sensitive U.S. ecosystems from
adverse effects related to PM deposition.
Though atmospheric sources of Nr and
acidifying compounds, including
ambient PM, are clearly contributing to
the overall excess load or burden
entering ecosystems annually,
insufficient data are available at this
time to quantify the contribution of
ambient PM to total Nr or acid
deposition as its role varies both
temporally and spatially along with a
number of other factors. Thus, at the
present time, a CL could not be
developed that would address the
portion of the total N or S input that is
contributed by ambient PM.
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b. Effects on Materials Damage and
Soiling
As discussed in the Staff Paper, the
effects of the deposition of atmospheric
pollution, including ambient PM, on
materials are related to both physical
damage and impaired aesthetic
qualities. The deposition of PM
(especially sulfates and nitrates) can
physically affect materials, adding to the
effects of natural weathering processes,
by potentially promoting or accelerating
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the corrosion of metals, by degrading
paints, and by deteriorating building
materials such as concrete and
limestone. As noted in the last review,
only chemically active fine-mode or
hygroscopic coarse-mode particles
contribute to these physical effects. In
addition, the deposition of ambient PM
can reduce the aesthetic appeal of
buildings and culturally important
articles through soiling. Particles
consisting primarily of carbonaceous
compounds cause soiling of commonly
used building materials and culturally
important items such as statues and
works of art. Available data indicate that
particle-related soiling can result in
increased cleaning frequency and
repainting, and may reduce the useful
life of the soiled materials. However, to
date, no quantitative relationships
between particle characteristics (e.g.,
concentrations, particle size, and
chemical composition) and the
frequency of cleaning or repainting have
been established. Thus, the
Administrator concludes that PM effects
on materials can play no quantitative
role in considering whether any
revisions of the secondary PM standards
are appropriate at this time.
c. Effects on Climate
As discussed in the Staff Paper,
atmospheric particles can alter the
earth’s energy balance by both scattering
and absorbing radiation transmitted
through the earth’s atmosphere. Most
components of ambient PM (especially
sulfates) scatter and reflect incoming
solar radiation back into space, thus
tending to have a cooling effect on
climate. In contrast, some components
of ambient PM (especially black carbon)
absorb incoming solar radiation or
outgoing terrestrial radiation, thus
tending to have a warming effect on
climate. Other impacts of atmospheric
particles are associated with their role
in affecting the radiative properties of
clouds, through changes in the number
and size distribution of cloud droplets
(which can have an effect on the climate
in either direction), and by altering the
amount of ultraviolet solar radiation
(especially UV–B) penetrating through
the atmosphere to ground level, where
it can exert a variety of effects on human
health, plant and animal biota, and
other environmental components.
The available information, however,
provides no basis for estimating how
localized changes in the temporal,
spatial, and composition patterns of
ambient PM likely to occur as a result
of expected future emissions of particles
and their precursor gases across the
U.S., would affect local, regional, or
global changes in climate or UV–B
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radiation penetration. Even the
direction of such effects on a local scale
remains uncertain. Moreover, similar
concentrations of different particle
components can produce opposite net
effects, depending on other atmospheric
parameters such as humidity. The
Administrator thus concludes that,
given this uncertainty, the potential
indirect effects of ambient PM on public
health and welfare, secondary to
potential PM-related changes in climate
and UV–B radiation, can play no
quantitative role in considering whether
any revisions of the primary or
secondary PM standards are appropriate
at this time.
2. Need for Revision of Current
Secondary PM Standards To Address
Other PM-Related Welfare Effects
In considering the currently available
evidence on each type of PM-related
welfare effects discussed above, the
Administrator notes that there is much
information linking the S- and Ncontaining components of ambient PM
to potentially adverse effects on
ecosystems and vegetation, materials
damage and soiling, and on climatic and
radiative processes. However, after
reviewing the extent of relevant studies
and other information provided since
the 1997 review of the PM standards,
which highlighted the substantial
limitations in the evidence, especially
with regard to the lack of evidence
linking various effects to specific levels
of ambient PM, the Administrator
concurs with conclusions reached in the
Staff Paper and by CASAC (Henderson,
2005a) that the available data do not
provide a sufficient basis for
establishing separate and distinct
secondary PM standards based on any of
these non-visibility PM-related welfare
effects.
While recognizing that PM-related
impacts on vegetation and ecosystems
and PM-related soiling and materials
damage are associated with chemical
components in both fine and coarsefraction PM, the Administrator
provisionally concludes that sufficient
information is not available at this time
to consider either an ecologically based
indicator or an indicator based
distinctly on soiling and materials
damage, in terms of specific chemical
components of PM. Further, consistent
with the rationale and recommendations
in the Staff Paper, the Administrator
agrees that it is appropriate to continue
control of ambient fine and coarsefraction particles, especially long-term
deposition of particles such as
particulate nitrates and sulfates that
contribute to adverse impacts on
vegetation and ecosystems and/or to
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materials damage and soiling. The
Administrator also agrees with the Staff
Paper that the available information
does not provide a sufficient basis for
the development of distinct national
secondary standards to protect against
such effects beyond the protection likely
to be afforded by the proposed suite of
primary PM standards. In considering
those proposed standards in
combination, including the proposed
more protective 24-hour standard for
PM2.5 and the proposed 24-hour
standard for PM10-2.5, which is intended
to provide an equivalent degree of
protection to the current PM10 standards
in areas where the proposed PM10-2.5
indicator applies (which tend to be
more densely populated areas where
materials damage would be of greater
concern), the Administrator believes
that this proposed suite of standards
would afford at least the degree of
protection as that afforded by the
current secondary PM standards.
Finally, the Administrator believes, as
noted above, that such standards should
be considered in conjunction with the
protection afforded by other programs
intended to address various aspects of
air pollution effects on ecosystems and
vegetation, such as the Acid Deposition
Program and other regional approaches
to reducing pollutants linked to nitrate
or acidic deposition. Based on these
considerations, and taking into account
the information and recommendations
discussed above, the Administrator
therefore proposes to revise the current
secondary PM2.5 and PM10 standards to
address these other welfare effects by
making them identical in all respects to
the proposed suite of primary PM2.5 and
PM10-2.5 standards.
C. Proposed Decisions on Secondary PM
Standards
For the reasons discussed above, and
taking into account the information and
assessments presented in the Criteria
Document and Staff Paper, the advice
and recommendations of CASAC, and
public comments to date, the
Administrator proposes to revise the
current secondary PM2.5 and PM10
standards by making them identical in
all respects to the proposed primary
PM2.5 and PM10-2.5 standards to address
PM-related welfare effects including
visibility impairment, effects on
vegetation and ecosystems, materials
damage and soiling, and effects on
climate change. In recognition of an
alternative view expressed by most
members of the CASAC PM Panel, the
Administrator also solicits comments on
a sub-daily (4- to 8-hour averaging time)
PM2.5 standard to address visibility
impairment, within the range of 20 to 30
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µg/m3 and with a form within the range
of the 92nd to 98th percentile. Based on
the comments received and the
accompanying rationale, the
Administrator may adopt other
standards within the range of
alternatives identified above in lieu of
the standards he is proposing today.
V. Interpretation of the NAAQS for PM
A. Proposed Amendments to Appendix
N—Interpretation of the National
Ambient Air Quality Standards for
PM2.5
The EPA is proposing to revise the
data handling procedures for the annual
and 24-hour primary PM2.5 standards in
appendix N to 40 CFR part 50. The
proposed amendments to appendix N
would detail the computations
necessary for determining when the
proposed primary and secondary PM2.5
national ambient air quality standards
(NAAQS) are met. The proposed
amendments also would address data
reporting, monitoring considerations,
and rounding conventions. Key
elements of the proposed revisions to
appendix N are summarized below in
sections V.A.1 through V.A.5 of this
preamble.
1. General
Several new definitions would be
added to section 1.0 and utilized
throughout the appendix, most notably
ones for ‘‘design values’’. Also, the 24hour time would be clarified as
representing ‘‘local standard (word
inserted) time’’. This proposal reflects
EPA’s previous intent as well as
majority practice, and also avoids
ambiguity since local clock time varies
according to daylight savings periods.
2. PM2.5 Monitoring and Data Reporting
Considerations
Two new sections would be added to
appendix N to more specifically
stipulate and highlight monitoring and
data considerations. New section 2.0
would include statistical requirements
for spatial averaging (which is part of
the form of the current and proposed
annual standard for PM2.5). As
explained in section II.F.2 above, we are
proposing to tighten the constraints on
use of spatial averaging to reflect
enhanced knowledge of typical monitor
correlation coefficients in metropolitan
areas. As also set out in section II.F.2,
the Administrator is further soliciting
comment on the other staffrecommended alternative of revising the
form of the annual PM2.5 standard to one
based on the highest communityoriented monitor in an area, with no
allowance for spatial averaging.
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New section 3.0 would codify aspects
of raw data reporting and raw data time
interval aggregation including
specifications of number of decimal
places. Previously, these reporting
instructions resided only in associated
guidance documents. Section 3.0 would
also note the process for assimilating
monitored concentration data from
collocated instruments into a single
‘‘site’’ record; data for the site record
would originate mainly from the
designated ‘‘primary’’ monitor at the site
location, but would be augmented with
collocated Federal reference method
(FRM) or Federal equivalent method
(FEM) monitor data whenever valid data
are not generated by the primary
monitor. This procedure would enhance
the opportunity for sites to meet data
completeness requirements. This
proposed language likewise would
codify existing practice, since the
technique was previously documented
in guidance documentation and
implemented as EPA standard operating
procedure.
3. PM2.5 Computations and Data
Handling Conventions
The EPA is proposing a spatiallyaveraged annual mean as the form of the
annual PM2.5 standard and a 98th
percentile concentration as the form of
the 24-hour PM2.5 standard. Although
no actual computational change is
proposed for a spatially-averaged annual
mean, the proposed Appendix N now
differentiates, in language and formulae,
between a spatial average of more than
one site and a spatial average of only
one site. The intent of this change is to
alleviate confusion caused by the
current ‘‘catch-all’’ generic reference.
The proposed revisions to appendix N
would identify the NAAQS metrics and
explain data capture requirements and
comparisons to the standards for the
annual PM2.5 standard and the 24-hour
standard (in sections 4.1, and 4.2,
respectively); data rounding
conventions (in section 4.3); and
formulas for calculating the annual and
24-hour metrics (in sections 4.4 and 4.5,
respectively).
With regard to the annual PM2.5
standard, we are proposing to retain
current data capture requirements for
the annual standard with two
exceptions. Current appendix N has
reduced data capture requirements for
years that exceed the level of the annual
NAAQS; specifically, a minimum of 11
valid samples per quarter as opposed to
a more stringent 75 percent (of
scheduled samples) is currently
considered sufficient in those instances
where the annual mean exceeded the
NAAQS level. See existing Part 50 App.
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N 2.1(b). The EPA is proposing to also
allow 11 or more samples per quarter as
an acceptable minimum if the
calculated annual standard design value
exceeds the level of the standard. The
EPA solicits comments on this proposed
change.
A second proposed change in the data
completeness requirements would
incorporate data substitution logic for
situations where the proposed 11
sample per quarter minimum is not met.
Consistent with existing guidance and
practice (implementing current App. N
2.1(c)), EPA proposes to incorporate the
following requirement into appendix N:
a quarter with less than 11 samples
would be complete and valid if, by
substituting a historically low 24-hr
value for the missing samples (up to the
11 minimum), the results yield an
annual mean, spatially averaged annual
mean, and/or annual standard design
value that exceeds the levels of the
standard. The EPA proposes to
implement this procedure for making
comparisons to the NAAQS and not to
permanently alter the reported data. The
EPA considers this a very conservative
means of inputing data (and increasing
the opportunities for using monitoring
data that otherwise are valid), but
solicits comment on the proposed
approach.
With regard to the 24-hour PM2.5
standard, the proposed revisions to
appendix N would include a special
formula (Equation 6 in the proposed
rule) for computing annual 98th
percentile values when a site operates
on an approved seasonal sampling
schedule. This formula was previously
stated only in guidance documentation
(‘‘Guideline on Data Handling
Conventions for the PM NAAQS’’, April
1999) but was utilized, where
appropriate, in official OAQPS design
value calculations. Seasonal sampling
has traditionally been implemented in
periods that do not divide months; this
criterion is explicitly stated in the
proposed amendments.
The proposed revisions to appendix N
would also incorporate language
explicitly stating that 98th percentiles
(for both regular and seasonal sampling
schedules) is to be based on the
applicable number of samples rather
than the actual number of samples. Both
annual 98th percentile equations
(proposed Equations 5 and 6) would
now reflect this approach. To
accommodate seasonal sampling, the
calculation of ‘‘annual applicable
number of samples’’ would be changed
from the sum of the ‘‘quarterly
applicable number of samples’’ to a sum
of the ‘‘monthly applicable number of
samples’’. The EPA welcomes comment
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on the ‘‘applicable number of samples’’
concept and calculation.
To simplify the regulatory language,
another proposed change to appendix N
would eliminate the equation
computational examples. The EPA will
provide extensive computational
examples in forthcoming guidance
documents.
4. Secondary Standard
The EPA is proposing that the
secondary standards for PM2.5 be the
same as the primary standards.
However, the Administrator is soliciting
comment on the alternative of a distinct
4-hour secondary standard for visibility
protection with a form of an annual
percentile, in the range 92nd to 98th, for
a 12 p.m. to 4 p.m. local standard time
daily average, averaged over 3 years.
The same basic data handling approach
as used for the 24-hour 98th percentile
primary standard would also be utilized
for a 4-hour percentile-based secondary
standard (should EPA ultimately adopt
such a standard). For example, 75
percent of the hours in the averaging
time (i.e., 3 hours) would be required to
produce a valid daily measurement.
Also, 75 percent capture of sample days
in a quarter would always make a
complete quarter and four complete
quarters, a complete year. Reduced
capture (i.e., as little as one sample per
year) would also suffice for high
concentration years or 3-year periods.
However, the percentile computational
variation permitted for seasonal
sampling for the 24-hour 98th percentile
would not be needed for the 4-hour 95th
percentile since the predominant (if not
only) monitoring instrument used for
this standard would be a continuous
PM2.5 sampler and EPA expects these
continuous instruments to operate
throughout the entire year. For this
same reason, distinction between
applicable number of samples and
actual number of samples would not be
necessary.
5. Conforming Revisions
Terminology and data handling
procedures associated with exceptional
events would be revised to conform to
rules which EPA plans to propose in the
near future to implement the recent
amendment to CAA section 319 (42
U.S.C. 7619) by section 6013 of the Safe,
Accountable, Flexible Efficient
Transportation Equity Act: A Legacy for
Users (SAFETEA–LU) (PL 109–59). At
this time, EPA is proposing to replace
the term currently used in Appendix
N.1.(b)—‘‘uncontrollable or natural
events’’—with ‘‘exceptional events,’’
corresponding with the term used in the
recent amendment. (Because this
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proposal would make only a semantic
change to existing Appendix N, EPA
believes the proposal is consistent with
section 6013 (b) (4) of SAFETEA–LU,
which provides that EPA shall continue
to apply existing Appendix N of part 50
(among others) until the effective date of
rules implementing the exceptional
event provisions in amended section
319 of the CAA.)
B. Proposed Appendix P—Interpretation
of the National Ambient Air Quality
Standards for PM10-2.5
The EPA is proposing to add
appendix P to 40 CFR part 50 in order
to add data handling procedures for the
proposed 24-hour PM10-2.5 standard. The
proposed appendix P would detail the
computations necessary for determining
when the proposed PM10-2.5 NAAQS is
met. The proposed appendix also would
address data reporting, sampling
frequency considerations, and rounding
conventions. The protocols described in
proposed appendix P would mirror the
general and 24-hour specific protocols
proposed for the PM2.5 NAAQS in
appendix N of 40 CFR part 50. Key
elements of the proposed appendix P
are summarized below in sections V.B.1
through V.B.3 of this preamble.
1. General
Terms utilized throughout the
proposed appendix would be defined in
section 1.0.
2. PM2.5 Data Reporting Considerations
Section 2.0 of the proposed appendix
P would specify the input data to be
used in the NAAQS computations. The
section would address raw data
reporting and raw data time interval
aggregation (i.e., report/calculate to one
decimal place, truncate additional
digits). Section 2.0 would also note the
process for assimilating monitored
concentration data into a ‘‘site’’ record;
data for the site record would originate
mainly from the designated ‘‘primary’’
monitor at the site location, but would
be augmented with collocated Federal
reference method or Federal equivalent
method monitor data whenever valid
data are not generated by the primary
monitor. This procedure would enhance
the opportunity for sites to meet data
completeness requirements.
3. PM10-2.5 Computations and Data
Handling Conventions
The EPA is proposing a site-based
98th percentile concentration as the
form of the 24-hour PM2.5. The proposed
appendix P would explain data
handling conventions and computations
for the 24-hour primary (and secondary)
PM10-2.5 standards in section 3.1; data
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rounding conventions in section 3.2;
and sampling frequency considerations
in section 3.3. The formulas used for
calculating the 24-hour NAAQS metric
would be specified in section 3.4.
The proposed appendix would
include a special formula (Equation 2)
for use in computing annual 98th
percentile values when a site operates
on an approved seasonal sampling
schedule. The proposed appendix P also
would incorporate language explicitly
stating that 98th percentiles (for both
regular and seasonal sampling
schedules) is to be based on the
applicable number of samples rather
than actual number of samples. Both
annual 98th percentile equations
(Equations 1 and 2 of proposed
appendix P) would reflect this
approach. This approach parallels that
proposed in appendix N for PM2.5
described in V.A.3. above, and is based
on the same considerations.
4. Exceptional Events
The EPA plans to use the terminology
and adopt the data handling procedures
associated with exceptional events
consistent with rules which would
implement the recent amendment to
CAA section 319 discussed in section
V.A.5 above. The EPA expects to
propose such rules in the near future. In
the present proposal, the term
‘‘exceptional events’’ is used, consistent
with the term used in the recent
amendment as well as the term EPA
proposes to use in the parallel provision
in Appendix N (see section V.A.5).
VI. Reference Methods for the
Determination of Particulate Matter As
PM2.5 and PM10-2.5
A. Proposed Appendix O: Reference
Method for the Determination of Coarse
Particulate Matter (as PM10-2.5) in the
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1. Purpose of the New Reference
Method
The EPA is proposing a new Federal
reference method (FRM) for the
measurement of coarse particles (as
PM10-2.5) in ambient air for the purpose
of determining attainment of the
proposed new PM10-2.5 standards. The
FRM would also serve as the standard
of comparison for determining the
adequacy of alternative ‘‘equivalent’’
methods for use in lieu of the FRM. The
method is described in a proposed new
appendix O to 40 CFR part 50, where it
would join other FRM (or measurement
principles) specified for the other
criteria pollutants.
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2. Rationale for Selection of the New
Reference Method
The proposed FRM for measuring
PM10-2.5 is based on the combination of
two conventional low-volume methods,
one for measuring PM10 and the other
for measuring PM2.5, and determining
the PM10-2.5 measurement by subtracting
the PM2.5 measurement from the
concurrent PM10 measurement. The
proposed PM2.5 measurement method is
identical to the PM2.5 FRM currently
specified in appendix L to 40 CFR part
50, and the proposed PM10
measurement method is similar,
utilizing the same sampler but without
the PM2.5 particle size separator. (Both
samplers use identical PM10 sizeselective inlets.) Thus, this PM10-2.5 FRM
is based on the same aerodynamic
particle size separation and filter-based,
gravimetric technology that is also the
basis for FRMs for PM2.5 and (in a
somewhat less rigorously specified
form) for PM10.
In selecting the FRM methodology,
EPA’s primary considerations were the
ability of the method to provide: (1)
Credible and reliable measurements of
PM10-2.5; (2) reliable assessment of the
quality of monitoring data; and (3) a
credible and practical reference
standard of comparison for candidate
alternative measurement methods to
determine their qualification as
equivalent methods. In concept, a direct
method for measuring PM10-2.5 would
seem to be desirable for the FRM, rather
than the indirect method proposed. The
EPA tested and evaluated various types
of direct measurement technology
(Vanderpool et al., 2005), including
other conventional, filter-based
gravimetric methods. The results of
these tests and other evaluations
indicate that none of the available
methods or alternative technologies was
more suitable as a reference method for
PM10-2.5 than the method proposed.
Perhaps the most fundamental
requirement for the PM10-2.5 FRM is the
capability of the method to measure the
subject particulate matter with a high
degree of fidelity and faithfulness to the
definition of PM10-2.5. In proposed
appendix O, PM10-2.5 is defined as the
mass concentration of ambient particles
in the coarse-mode fraction of PM10,
specifically the (nominal) size range of
2.5 to 10 micrometers. The lower and
upper limits of this size range are
formally defined by the existing FRMs
for PM2.5 (40 CFR part 50, appendix L)
and for PM10 (40 CFR part 50, appendix
J). In both cases, the particle sizes are
defined in terms of aerodynamic size,
not actual physical size. Further, the
particle size limits are not simple step
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functions but instead are defined by the
corresponding PM2.5 and PM10
measurement methodologies, which
have inherent size fractionation curves
with characteristic shapes and cutoff
sharpness. The proposed PM10-2.5 FRM
would utilize these same measurement
methodologies to determine the PM10-2.5
concentration as the difference between
separate PM10 and PM2.5 measurements,
thereby preserving and replicating the
same particular PM10 and PM2.5
aerodynamic particle size limit
characteristics previously established by
the PM10 and PM2.5 FRMs.
Also, the proposed PM10-2.5 FRM
utilizes the same conventional
integrated-sample, filter-collection, and
mass-based gravimetric measurement
technology that has been chosen for all
previous FRM for the various formal
particulate matter indicators. This wellestablished and reliable technology
provides a high degree of credibility in
the PM10-2.5 measurements, derived from
its gravimetric basis and its extensive
track record from wide utilization over
many years in many government
monitoring networks. Further, it allows
for maximum compatibility and
comparability among new and existing
PM10-2.5, PM10, and PM2.5 data sets and
thus to much of the health effects data
used as a basis for the proposed
NAAQS. No costly studies are needed to
assess the impact, effect, or degree of
comparability of a new or changed
measurement technology relative to
previously acquired measurement data.
Extensive wind tunnel tests have shown
that the inlet, used on both the PM2.5
and PM10 samplers, is capable of
aspirating large particles efficiently,
even at high wind speeds. The presence
of PM2.5 aerosols on the PM10 sample
collection filter increases the adhesion
of larger particles to the filter to
minimize losses of large particles from
the PM10 filters during handling and
transport. Such losses can be a problem
with filter samples collected with a
virtual impactor-type sampler, where
the PM2.5 aerosols are not present on the
PM10-2.5 filter in sufficient quantities to
eliminate loss of coarse mode particles.
An inherent advantage of a difference
method is that some (additive) biases
may be eliminated or substantially
reduced by the subtraction. In the
proposed PM10-2.5 FRM, the two
samplers and their operational
procedures are very closely matched
(except for the particle size separator) to
take maximum advantage of this feature,
which helps to compensate for the
additional variability resulting from
dual measurement systems. Although a
difference method could produce
negative measurements on occasion,
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considerable field testing of the method
indicates that negative readings are rare,
due in substantial part to the excellent
precision of the base methods
(Vanderpool et al., 2005). Moreover,
measured negative PM10-2.5
concentrations, if observed, would
likely occur only at low concentrations
near the detection limit of the method
and would thus be unlikely to adversely
affect the accuracy of PM10-2.5
attainment decisions based on the
proposed 24-hour NAAQS.
The proposed method also has a
number of secondary advantages. The
samplers and operational procedures of
the proposed FRM are similar to those
of the PM2.5 FRM and will be familiar
to most State monitoring agencies. In
fact, the nature of the method allows for
the possibility of readily and
economically obtaining PM10-2.5
samplers (actually sampler pairs) by
reconfiguring existing PM2.5 samplers.
PM10-2.5 sampler pairs based on
currently designated PM2.5 FRM
samplers could be quickly designated by
EPA as PM10-2.5 FRM, as no additional
qualification testing would be required.
Existing PM2.5 FRM samplers can be
easily reconfigured as PM10-2.5 FRM
sampler pairs by converting some of
them to the special PM10 (PM10c)
samplers by simply replacing the WINS
impactor with the specified straight
downtube adaptor. Thus, the PM10-2.5
method could be rapidly and
economically implemented into new or
existing monitoring networks to begin
collection of PM10-2.5 monitoring data
expeditiously, with minimal
requirements for operator retraining or
pilot operational periods.
The proposed FRM provides readily
accessible aerosol samples for
subsequent chemical analyses, and the
sampler’s design allows use of a wide
variety of filter materials including
Teflon, quartz, nylon, and
polycarbonate. Compared to PM2.5, the
chemical composition of coarse-mode
aerosols has not yet been extensively
evaluated. The ability of the proposed
FRM to provide speciated analyses of
coarse aerosol samples would be an
important tool for the States during
development of effective
implementation plans.
In developing this new FRM for
PM10-2.5, EPA staff consulted with a
number of individuals and groups in the
monitoring community, including
instrument manufacturers, academics,
consultants, and experts in State and
local agencies. The approach and key
specifications of the method were
submitted for peer review to the Clean
Air Scientific Advisory Committee
(CASAC) Ambient Air Monitoring and
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Methods Subcommittee, which held
public meetings to discuss methods and
related monitoring issues on July 22,
2004 and September 21 and 22, 2005.
Comments on the proposed method
were provided orally and in writing by
Subcommittee members and by
interested public entities. In a letter
dated November 30, 2005 (Henderson,
2005c) forwarded by the CASAC to the
Administrator, the CASAC provided its
peer review consensus report stating
that ‘‘in general, the CASAC agrees that
there are several important scientific or
operational strengths of the proposed
difference method PM10-2.5 to be used as
the FRM, while noting that there are
several prominent weaknesses as well.
Despite these weaknesses, no other
better, currently available candidate
FRM method has been identified.’’ The
CASAC report noted that ‘‘A majority of
the Subcommittee members expressed
the opinion that the demonstrated data
quality of the PM10-2.5 difference method
and its documented value in
correlations with health effects data
support its being proposed as the PM
coarse FRM’’. However, the CASAC also
indicated that the proposed FRM should
not be intended for extensive
implementation in national monitoring
networks. Instead, it should be used
primarily as a benchmark for evaluating
the performance of continuous as well
as other direct-measuring, filter-based,
integrated methods and determining
their acceptability for use in routine
monitoring of PM10-2.5. As explained
more fully below, this is the approach
we intend to adopt for the national
monitoring network.
3. Consideration of Other Methods for
the Federal Reference Method
Other measurement technologies
considered for the FRM include a
variety of alternative integrated-sample,
filter-based methods as well as various
automated methods providing
continuous or semi-continuous
measurements of PM10-2.5. One
methodology that warranted particular
consideration is integrated, filter
sampling using a virtual impactor
particle size separator (also known as a
dichotomous fractionator). This
technology provides for measuring
PM10-2.5 more directly than the proposed
difference method and also provides
associated PM2.5 measurements, as well
as PM10 measurements by addition. Like
the proposed difference method,
dichotomous samplers have been used
in health studies that supported the
basis for both the PM2.5 and proposed
PM10-2.5 NAAQS. A dichotomous
sampler can utilize the same PM10
sampler inlet, the same types of filters
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and filter processing, and similar quality
assurance procedures as the proposed
method. It also has a very important
advantage in providing PM10-2.5 filter
samples for chemical analysis. Such
‘‘speciation’’ analysis is a critical tool
used by States for developing effective
PM10-2.5 control strategies. Speciated
PM2.5 and PM10-2.5 data have supported
epidemiological studies used to develop
associations between exposure to
ambient particulate matter and
increased mortality and morbidity
(Dockery, et al., 1993, Schwartz, 1994).
Collected speciated samples from
dichotomous samplers can also be used
to conduct toxicological studies of the
adverse health effects of PM exposure as
a function of particle size (Demokritou,
et al., 2003).
However, some aspects of virtual
impactor technology raise concerns
regarding the technology’s current
suitability for use as a PM10-2.5 reference
method. Various versions of virtual
impactors have been designed and used,
but their particle size separation
characteristics have not been fully
evaluated and independently
characterized as extensively as those of
the proposed method, resulting in
considerable uncertainty about their
performance relative to the conventional
low-volume PM2.5 and PM10 FRMs.
There is also concern about the impact
and potential need to compensate for
some inherent fine particle
contamination on the PM10-2.5 filter. For
example, for a virtual impactor which
employs a 10 to 1 total flow rate to
coarse flow rate ratio, 10 percent of the
fine particles deposit on the coarse
filter. Following each sampling event,
the presence of these fine particles must
be accounted for during subsequent
calculation of the PM10-2.5 mass
concentration. Depending upon the
analyte of interest, the collected mass of
the analyte, and the method detection
limit of the analytical technique for that
analyte, proper compensation for fine
particle contamination will also need to
be made when conducting speciation
analysis of the coarse channel filter.
Allen et al. (1999) also reported the
tendency for some fraction (up to 16
percent) of coarse mode particles to
penetrate to the fine channel filter and
thus positively bias calculated PM2.5
mass concentrations as well as
concentrations of specific analytes.
Because the level of coarse particle
contamination depends upon the size
distribution of the sampled aerosol and
the physical nature of the coarse
particles, this contamination cannot be
accurately predicted and thus cannot be
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accounted for during subsequent
calculations.
Loss of particles within virtual
impactors is also well documented
(Forney et al., 1982, Chen et al., 1985,
Loo and Cork, 1988, Li and Lundgren,
1997, Allen, et al., 1999, Kim and Lee,
2000) and can substantially bias
measured mass and species
concentrations. As reported by Loo and
Cork (1988), losses up to 50 percent
have been reported during laboratory
calibration of various virtual impactor
designs when using liquid calibration
aerosols. Moreover, these losses cannot
be predicted and are very sensitive to
virtual impactor geometry and
component misalignment. Unlike
conventional impactors where internal
particle loss can be readily minimized,
the design of virtual impactors must be
optimized to ensure that particle loss is
sufficiently low to enable accurate mass
and species measurements during field
use.
In the proposed difference method,
the high concentration of fine particles
on the PM10 filter provides additional
adhesive force for retaining large
particles to the filter’s surface. In the
dichotomous sampler, however, the low
concentration of fine particles on the
coarse channel filter results in a
significantly reduced adhesive force. If
inertial forces (applied to the filter
during its post-sampling handling and
transport) are greater than the adhesive
force, then coarse particles will be
dislodged from the coarse channel filter
and not be subsequently quantified.
Depending upon the virtual impactor
design, the nature of the collected
aerosol, and the magnitude of the
applied inertial force, large particle
losses up to 50 percent have been
documented (Dzubay and Barbour,
1983, Spengler and Thurston, 1983). As
in the case of coarse particle intrusion
into the fine channel, the magnitude of
this measurement bias is variable and
cannot be accurately predicted nor
compensated for.
The CASAC, in their peer review
report (Hendersen, 2005c) supports
‘‘* * * the possibility of specifying
more than one FRM for PM10-2.5 (as it
did for PM10) , if one or more of the
current or evolving dichotomous
sampler designs shows reasonable
agreement with the difference method
(assuming filter-handling procedures
can be developed to minimize losses of
coarse-only particles prior to
weighing).’’ We agree that the filterhandling procedures need to be
investigated in addition to other issues
described above. Therefore, at this point
we believe the proposed FRM, based on
the difference method, offers less
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uncertainty in PM10-2.5 measurements
and is the more prudent choice for the
reference method. However, CASAC
and EPA are both interested in utilizing
dichotomous samplers in support of
other monitoring objectives, such as
providing samples for chemical
speciation analysis, once a number of
issues are worked through. Therefore,
the Agency wishes to solicit public
comment regarding consideration of a
PM10-2.5 reference method or equivalent
method based on the use of the virtual
impactors to aerodynamically separate
fine mode aerosols from coarse mode
aerosols.
Concerns have been expressed to EPA
regarding the fact that the size
separation devices of both the PM2.5 and
PM10 FRMs, which are the basis of the
proposed difference-based PM10-2.5
FRM, have inherent size fractionation
curves with characteristic shapes and
cutoff sharpness rather than creating a
perfectly sharp cutpoint at a specific
aerodynamic particle size. For example,
a portion of all ambient particles larger
than 10 micrometers are included in the
PM10-2.5 sample, while some particles
smaller than 10 micrometers are not. A
larger effect on measured PM10-2.5 will
occur in environments with high
concentrations of particles above 10
micrometers than in environments with
low concentrations.
Some commenters who have been
concerned about this aspect of the PM2.5
and PM10 FRMs have supported the
adoption of a PM10-2.5 FRM that would
directly measure the coarse fraction of
particles. We invite comment on this
topic, in the context of today’s proposal
for a PM10-2.5 NAAQS and a FRM that
would employ both PM2.5 and PM10 size
separators.
4. Consideration of Automated Methods
for the Federal Reference Method
Other measurement technologies
considered for the FRM included
various types of automated analyzer
methods that provide continuous or
semi-continuous measurements of
PM10-2.5. Such methods are particularly
desirable for use in PM10-2.5 monitoring
networks because they potentially offer
substantially lower operational and
maintenance costs, hourly averages or
other short-term measurements in
addition to 24-hour averages, and nearly
real-time electronic, remote reporting of
measurement data. However, recent
field testing of many of these
instruments (Vanderpool et al., 2005)
indicated that none can yet achieve
performance commensurate to that of
the proposed method. The technologies
employed by these methods usually
represent a substantial, if not radical,
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departure from the well-characterized,
conventional filter-collection and
gravimetric determination. This
departure raises inevitable questions of
representativeness of particle size
discrimination, treatment of volatile
components, variability with differing
site and climatic conditions, and the
degree of comparability to
conventionally obtained measurements.
Also, since EPA is proposing a daily
standard for PM10-2.5, hourly
measurements are not required to
support such a standard, although they
would be of value to more closely
investigate impacts of sources and
exceptional events.
Most, if not all, of these automated
measurement technologies are
proprietary. While that alone is not
sufficient reason to preclude their
consideration as FRM or as a ‘‘reference
measurement principle,’’ it would be in
the best interest of all stakeholders if
multiple manufacturers could compete
for this market. Adoption of the
proposed FRM along with reasonable
qualification requirements for
equivalent methods leaves a fair and
level playing field for any manufacturer
to either produce the specified FRM
samplers or to pursue the development
and EPA approval of innovative new
methods and technologies to strive for
competitive marketing advantages.
5. Use of the Proposed Federal
Reference Method
The EPA acknowledges that the
proposed FRM is quite labor-intensive
and has other disadvantages that make
it less than ideal for routine use in large
monitoring networks. At the same time,
as just described, alternative, automated
methods are under continuing research
and development, and some may soon
demonstrate adequate performance and
comparability to the FRM for use in
monitoring networks. Accordingly, and
consistent with the recommendations of
the CASAC (Hendersen, 2005c), EPA is
providing for the possible designation of
alternative methods as equivalent
methods for PM10-2.5, as set forth in
proposed amendments to 40 CFR part
53 published elsewhere in this Federal
Register. Under these proposed
equivalent method provisions, EPA
anticipates that alternative methods—
particularly filter based, virtualimpactor samplers as well as selfcontained, automated analyzers—can be
designated as equivalent methods. The
dichotomous samplers could potentially
lead to better speciation data, while
automated equivalent methods would
ease the potential PM10-2.5 monitoring
burdens of monitoring agencies and
would potentially provide substantial
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monitoring advantages such as reduced
operational cost, availability of 1-hour
(or other less-than-24-hour) average
concentration measurements, and near
real-time telemetered monitoring data.
As explained in the preamble to the
proposed Part 58 rule, if such automated
methods are designated as equivalent,
they would likely be used
predominantly for much of the required
PM10-2.5 network monitoring. The new
PM10-2.5 FRM would thus be used
primarily as the reference standard for
designating qualified equivalent
methods and for quality assurance
activities, but used only minimally for
routine network monitoring.
Encouraging the further development
of automated analyzers by providing for
their designation as equivalent methods
for PM10-2.5 could eventually lead to
commercial, direct-reading instruments
that would meet multiple monitoring
objectives better than the FRM proposed
today. In that event, the Agency may
consider adopting such an automated
method for the FRM (or as a
‘‘measurement principle and calibration
procedure’’) under the provisions of 40
CFR 53.16, ‘‘Supersession of reference
methods.’’
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6. Relationship of Proposed FRM to
SAFETEA–LU Requirements
Section 6012 of the SAFETEA–LU in
part requires the Administrator, within
two years, to ‘‘develop a Federal
reference method to measure directly
particles that are larger than 2.5
micrometers in diameter without
reliance on subtracting from coarse
particle measurements those particles
that are equal to or smaller than 2.5
micrometers in diameter.’’ We believe
that our proposed action today is
consistent with the goals of the new
legislation, in that it actively promotes
use of non-difference methods through
the Part 53 equivalency designation
process, and states our ultimate
expectation that the monitoring network
for PM10-2.5 will utilize primarily nondifference method monitors.
Furthermore, we are actively
investigating the possibility that a
dichotomous method could be an
alternative FRM within the time frame
prescribed by this Act. However, we are
proposing a difference method as the
FRM for PM10-2.5, for the reasons
explained above as we believe this is the
only approach technically justified at
this time. Since the new statutory
language does not require that EPA
promulgate a non-difference method as
either the sole or alternative FRM, we
believe this proposed approach is
consistent with the express language of
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the provision as well as with its
objectives.
7. Basic Requirements of the Proposed
Federal Reference Method Sampler
The proposed PM10-2.5 FRM
‘‘sampler’’ is actually a collocated pair
of samplers, one for PM10 and one for
PM2.5, operated simultaneously. The
PM2.5 sampler is exactly as specified in
the PM2.5 FRM (appendix L to 40 CFR
part 50). The operational and procedural
requirements would be the same as
those for PM2.5 FRM measurements.
PM2.5 measurements obtained as part of
PM10-2.5 FRM measurements would be
indistinguishable from conventional
PM2.5 FRM measurements and would be
usable for any PM2.5 monitoring
purpose, provided they are sited at the
appropriate spatial scale (e.g.,
neighborhood scale).
In contrast, the PM10 sampler of the
PM10-2.5 sampler pair would be required
to be identical in design and
construction to the PM2.5 sampler,
except that the PM2.5 particle size
separator (WINS impactor) would be
removed from the sampler and replaced
with a straight downtube, thereby
converting it to a PM10 sampler. This
PM10 sampler would have to meet the
higher standards of manufacture and
performance of appendix L to 40 CFR
part 50 rather than the standards for
conventional PM10 FRM samplers
(which meet the lesser requirements of
appendix J to 40 CFR part 50). Thus,
PM10 measurements obtained as part of
or incidental to the PM10-2.5 FRM
measurements must be distinguished
from conventional PM10 measurements
and need to be identified by a unique
descriptor such as ‘‘PM10c.’’ Since PM10c
measurements would meet a higher
standard than conventional PM10
measurements, such measurements
would also be acceptable for any
conventional PM10 monitoring purpose.
However, one subtle issue regarding
conventional PM10 measurements and
new PM10c measurements needs
clarification. Conventional PM10
measurement flow systems operate on
conditions of standard temperature and
pressure (STP). Flow systems for PM2.5
and the new PM10-2.5 FRM as proposed
today and peer reviewed by the CASAC,
all operate under conditions of actual
local conditions.
PM10-2.5 sampler pairs would be
required to be specifically designated as
PM10-2.5 FRM samplers by EPA under
amendments to 40 CFR 53 proposed
elsewhere in this Federal Register. The
two samplers of the PM10-2.5 FRM
sampler pair would be required to be of
like manufacturer and of matched
design and fabrication so that they are
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essentially identical, except that one
would have a PM2.5 particle size
separator while the other would not.
Either single-filter samplers or multiplefilter, sequential samplers could
constitute a PM10-2.5 sampler pair, as
long as both were of the same type and
design. For a manufacturer’s sampler
model that has already been designated
as a PM2.5 FRM, no further testing
would be required for designation as a
PM10-2.5 FRM, although the sampler
manufacturer would have to submit a
formal application under 40 CFR part
53. Users could assemble their own
PM10-2.5 sampler pair using existing
PM2.5 samplers of the same model or
design by converting one of the
samplers to a PM10c sampler, provided
the specific sampler pair has been
previously designated by the EPA as a
PM10-2.5 FRM under 40 CFR part 53.
Pairings of qualified PM2.5 samplers
that are dissimilar or have some minor
design or model variations (and one
sampler is converted to a PM10c
sampler) could be designated by the
EPA as Class I equivalent methods
under proposed amendments to 40 CFR
part 53. Again, an application for an
equivalent method determination for the
sampler combination would have to be
submitted to the EPA under 40 CFR part
53, and not all combinations would
necessarily be designated without
further testing. For example,
supplemental test or operational
performance information would likely
be required for designation of a PM10-2.5
sampler pair consisting of a single-filter
sampler and a multiple-filter, sequential
sampler. A pairing of dissimilar PM2.5
samplers that has not been designated as
a Class I equivalent method for PM10-2.5
under 40 CFR part 53 could be
considered by the EPA for approved use
in PM10-2.5 monitoring networks as a
user modification under section 2.8 of
appendix C to 40 CFR part 58.
8. Other Important Aspects of the
Proposed Federal Reference Method
Sampler
The proposed method would require
that both samplers of the PM10-2.5
sampler pair be located in close
proximity and operated simultaneously.
Operational procedures for both
samplers of the pair would be similar or
identical to those specified for PM2.5
FRM, and both samplers should be
operated, serviced, and maintained
similarly. Quality assurance procedures
would parallel those for the PM2.5 FRM,
although data quality assessment
procedures would apply to the
calculated PM10-2.5 measurement data
rather than (or in addition to) the
individual PM10 and PM2.5
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would also apply to the proposed
PM10-2.5 FRM, so the benefits would be
realized for PM10-2.5 measurements as
well, and uniformity between the PM2.5
FRM and the PM2.5 portion of the
PM10-2.5 FRM would be maintained.
The most significant proposed change
is the addition of an alternative PM2.5
particle size separator. Since the
promulgation of the PM2.5 FRM in 1997,
a new, very sharp cut cyclone separator
(VSCCTM) manufactured by BGI
Incorporated, Waltham, MA has been
shown to have performance equivalent
to that of the originally specified
separator (WINS impactor) (Kenny, et
al., 2001; Kenny et al., 2004; EPA,
2002b). Although the original WINS
impactor continues to show fully
adequate performance in PM2.5
samplers, the new VSCC provides the
same level of performance and has a
considerably longer service interval.
Generally, the VSCC separator is also
physically interchangeable with the
WINS where both are manufactured for
the same sampler. The proposed change
would allow either the WINS or the
VSCC separator to be used in a PM2.5
FRM sampler. Currently, EPA has
designated seven PM2.5 samplers
configured with VSCC separators as
Class II equivalent methods.93 Upon
promulgation of this change to appendix
L, those seven methods would be redesignated as PM2.5 FRM.
Another minor change proposed for
the PM2.5 FRM (and, hence, also
applicable to the proposed PM10-2.5
FRM) would require an improved
impactor oil for the PM2.5 WINS
impactor particle size separator. The
new oil corrects an occasional problem
of crystallization of the original oil
B. Proposed Amendments to Appendix
during sampling in cold and damp
L—Reference Method for the
Determination of Fine Particulate Matter weather and has been tested and
approved as a national user
(as PM2.5) in the Atmosphere
modification (EPA, 2000b). Also, the
In connection with the proposal of a
time limit specified for sample filter
new Federal reference method (FRM) for retrieval time would be increased from
PM10-2.5, EPA is proposing minor
96 hours to 177 hours following the end
changes to the FRM for PM2.5 in
of the sample period. This change
appendix L to 40 CFR part 50. These
would allow the filter to be retrieved by
proposed changes are based on new test the morning of the eighth day after
information and extensive operational
sampling to permit recovery of up to
experience with the PM2.5 FRM acquired three samples from a sequential sampler
subsequent to its promulgation in 1997. operating on a 1-in-3 day sample
Through the increased flexibility
schedule. Based on a study (Papp, et al.,
afforded by the proposed changes,
2002) at six sampling sites, this change
significant improvements in the
has already been approved as a national
efficiency of the PM2.5 method in
user modification (EPA, 2002a). An
monitoring network operations are
associated change to ease the filter
expected without altering the
retrieval burden on monitoring agencies
performance of the method. In fact, the
would modify the current requirement
changes have already been implemented that retrieved filters be weighed within
in the national PM2.5 monitoring
network through designated equivalent
93 List of designated reference and equivalent
methods or duly approved user
methods available at https://www.epa.gov/ttn/amtic/
criteria.html.
modifications. Further, the changes
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measurements. The proposed sample
period would be nominally 24 hours (±1
hour).
Expected performance of the PM10-2.5
FRM—as measured by precision, lower
concentration limit, and completeness—
is similar to that of the PM2.5 FRM, but
may be somewhat inferior because of
the dual measurement components.
Precision, defined as a goal for
acceptable measurement uncertainty, is
given as 15 percent coefficient of
variation, as assessed according to
quality assurance procedures for
PM10-2.5 monitoring described in
proposed revisions to appendix A of 40
CFR part 58, published elsewhere in
this Federal Register.
The lower concentration limit
proposed for the method is 3 µg/m3.
This value can vary with the level of
quality control and precision achieved
in implementing the method. It should
not be interpreted as a specification but
rather as a simple guide to the general
significance of low-level measured
concentrations. However, this proposed
value may be used as a lower range limit
for excluding low-concentration data
from composite performance
calculations that use percentages (where
very low values in a denominator need
to be avoided) or in types of statistical
calculations of monitoring data that
cannot accept zero or negative values
(such as geometric distributions, where
1⁄2 of this lower concentration limit may
be substituted for any measurements
less than that value). Comments are
solicited on the usefulness of this lower
concentration limit, its value, or how its
value should be established and
interpreted.
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10 days after sampling, unless they are
maintained at a temperature of 4°C or
less at all times during transport. The
filter recovery extension study (Papp, et
al., 2002) showed that these limits can
be relaxed somewhat (EPA, 2000a) to
allow up to 30 days for weighing the
filter if it is maintained below the
average ambient temperature during the
sampling period prior to the postcollection sample equilibration.
Finally, some of the sampler data
output reporting requirements specified
in Table L–1 of appendix L to 40 CFR
part 50 (e.g. flow rate CV, sample
volume, minimum and maximum
temperature, minimum and maximum
pressure) have been determined to be
unnecessary to report to the Air Quality
System, and the reporting requirement
for these data would be deleted. These
data will be retained and available at the
monitoring agency, if needed.
VII. Statutory and Executive Order
Reviews
A. Executive Order 12866: Regulatory
Planning and Review
Under Executive Order 12866 (58 FR
51735, October 4, 1993), the Agency
must determine whether a regulatory
action is ‘‘significant’’ and therefore
subject to Office of Management and
Budget (OMB) review and the
requirements of the Executive Order.
The Order defines ‘‘significant
regulatory action’’ as one that is likely
to result in a rule that may:
1. Have an annual effect on the
economy of $100 million or more or
adversely affect in a material way the
economy, a sector of the economy,
productivity, competition, jobs, the
environment, public health or safety, or
State, local, or Tribal governments or
communities;
2. Create a serious inconsistency or
otherwise interfere with an action taken
or planned by another agency;
3. Materially alter the budgetary
impact of entitlements, grants, user fees,
or loan programs or the rights and
obligations of recipients thereof; or
4. Raise novel legal or policy issues
arising out of legal mandates, the
President’s priorities, or the principles
set forth in the Executive Order.
In view of its important policy
implications and potential effect on the
economy of over $100 million, this
action has been judged to be an
economically ‘‘significant regulatory
action’’ within the meaning of the
Executive Order. As a result, today’s
action was submitted to OMB for
review. Changes made in response to
OMB suggestions or recommendations
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will be documented in the public
record.
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B. Paperwork Reduction Act
This action does not impose an
information collection burden under the
provisions of the Paperwork Reduction
Act, 44 U.S.C. 3501 et seq. There are no
information collection requirements
directly associated with the
establishment of a NAAQS under
section 109 of the CAA.
Burden means the total time, effort, or
financial resources expended by persons
to generate, maintain, retain, or disclose
or provide information to or for a
Federal agency. This includes the time
needed to review instructions; develop,
acquire, install, and utilize technology
and systems for the purposes of
collecting, validating, and verifying
information, processing and
maintaining information, and disclosing
and providing information; adjust the
existing ways to comply with any
previously applicable instructions and
requirements; train personnel to be able
to respond to a collection of
information; search data sources;
complete and review the collection of
information; and transmit or otherwise
disclose the information.
An agency may not conduct or
sponsor, and a person is not required to
respond to a collection of information
unless it displays a currently valid OMB
control number. The OMB control
numbers for EPA’s regulations in 40
CFR are listed in 40 CFR part 9.
C. Regulatory Flexibility Act
The Regulatory Flexibility Act (RFA)
generally requires an agency to prepare
a regulatory flexibility analysis of any
rule subject to notice and comment
rulemaking requirements under the
Administrative Procedure Act or any
other statute unless the agency certifies
that the rule will not have a significant
economic impact on a substantial
number of small entities. Small entities
include small businesses, small
organizations, and small governmental
jurisdictions.
For purposes of assessing the impacts
of today’s rule on small entities, small
entity is defined as: (1) A small business
that is a small industrial entity as
defined by the Small Business
Administration’s (SBA) regulations at 13
CFR 121.201; (2) a small governmental
jurisdiction that is a government of a
city, county, town, school district or
special district with a population of less
than 50,000; and (3) a small
organization that is any not-for-profit
enterprise which is independently
owned and operated and is not
dominant in its field.
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After considering the economic
impacts of today’s proposed rule on
small entities, I certify that this action
will not have a significant economic
impact on a substantial number of small
entities. This proposed rule will not
impose any requirements on small
entities. Rather, this rule establishes
national standards for allowable
concentrations of particulate matter in
ambient air as required by section 109
of the CAA. See also American Trucking
Associations v. EPA. 175 F. 3d at 1044–
45 (NAAQS do not have significant
impacts upon small entities because
NAAQS themselves impose no
regulations upon small entities). We
continue to be interested in the
potential impacts of the proposed rule
on small entities and welcome
comments on issues related to such
impacts.
D. Unfunded Mandates Reform Act
Title II of the Unfunded Mandates
Reform Act of 1995 (UMRA), Public
Law 104–4, establishes requirements for
Federal agencies to assess the effects of
their regulatory actions on State, local,
and Tribal governments and the private
sector. Under section 202 of the UMRA,
EPA generally must prepare a written
statement, including a cost-benefit
analysis, for proposed and final rules
with ‘‘Federal mandates’’ that may
result in expenditures to State, local,
and Tribal governments, in the
aggregate, or to the private sector, of
$100 million or more in any 1 year.
Before promulgating an EPA rule for
which a written statement is needed,
section 205 of the UMRA generally
requires EPA to identify and consider a
reasonable number of regulatory
alternatives and adopt the least costly,
most cost-effective or least burdensome
alternative that achieves the objectives
of the rule. The provisions of section
205 do not apply when they are
inconsistent with applicable law.
Moreover, section 205 allows EPA to
adopt an alternative other than the least
costly, most cost-effective or least
burdensome alternative if the
Administrator publishes with the final
rule an explanation why that alternative
was not adopted. Before EPA establishes
any regulatory requirements that may
significantly or uniquely affect small
governments, including Tribal
governments, it must have developed
under section 203 of the UMRA a small
government agency plan. The plan must
provide for notifying potentially
affected small governments, enabling
officials of affected small governments
to have meaningful and timely input in
the development of EPA regulatory
proposals with significant Federal
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intergovernmental mandates, and
informing, educating, and advising
small governments on compliance with
the regulatory requirements.
Today’s rule contains no Federal
mandates (under the regulatory
provisions of Title II of the UMRA) for
State, local, or Tribal governments or
the private sector. The rule imposes no
new expenditure or enforceable duty on
any State, local or Tribal governments or
the private sector, and EPA has
determined that this rule contains no
regulatory requirements that might
significantly or uniquely affect small
governments. Furthermore, as indicated
previously, in setting a NAAQS EPA
cannot consider the economic or
technological feasibility of attaining
ambient air quality standards, although
such factors may be considered to a
degree in the development of State
plans to implement the standards. See
also American Trucking Associations v.
EPA, 175 F. 3d at 1043 (noting that
because EPA is precluded from
considering costs of implementation in
establishing NAAQS, preparation of a
Regulatory Impact Analysis pursuant to
the Unfunded Mandates Reform Act
would not furnish any information
which the court could consider in
reviewing the NAAQS). Accordingly,
EPA has determined that the provisions
of sections 202, 203, and 205 of the
UMRA do not apply to this proposed
decision. The EPA acknowledges,
however, that any corresponding
revisions to associated SIP requirements
and air quality surveillance
requirements, 40 CFR part 51 and 40
CFR part 58, respectively, might result
in such effects. Accordingly, EPA has
addressed unfunded mandates in the
notice that announces the proposed
revisions to 40 CFR part 58, and will, as
appropriate, address unfunded
mandates when it proposes any
revisions to 40 CFR part 51.
E. Executive Order 13132: Federalism
Executive Order 13132, entitled
‘‘Federalism’’ (64 FR 43255, August 10,
1999), requires EPA to develop an
accountable process to ensure
‘‘meaningful and timely input by State
and local officials in the development of
regulatory policies that have federalism
implications.’’ ‘‘Policies that have
federalism implications’’ is defined in
the Executive Order to include
regulations that have ‘‘substantial direct
effects on the States, on the relationship
between the national government and
the States, or on the distribution of
power and responsibilities among the
various levels of government.’’
This proposed rule does not have
federalism implications. It will not have
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substantial direct effects on the States,
on the relationship between the national
government and the States, or on the
distribution of power and
responsibilities among the various
levels of government, as specified in
Executive Order 13132. The rule does
not alter the relationship between the
Federal government and the States
regarding the establishment and
implementation of air quality
improvement programs as codified in
the CAA. Under section 109 of the CAA,
EPA is mandated to establish NAAQS;
however, CAA section 116 preserves the
rights of States to establish more
stringent requirements if deemed
necessary by a State. Furthermore, this
rule does not impact CAA section 107
which establishes that the States have
primary responsibility for
implementation of the NAAQS. Finally,
as noted in section E (above) on UMRA,
this rule does not impose significant
costs on State, local, or Tribal
governments or the private sector. Thus,
Executive Order 13132 does not apply
to this rule.
However, as also noted in section E
(above) on UMRA, EPA recognizes that
States will have a substantial interest in
this rule and any corresponding
revisions to associated SIP requirements
and air quality surveillance
requirements, 40 CFR part 51 and 40
CFR part 58, respectively. Therefore, in
the spirit of Executive Order 13132, and
consistent with EPA policy to promote
communications between EPA and State
and local governments, EPA specifically
solicits comment on this proposed rule
from State and local officials.
F. Executive Order 13175: Consultation
and Coordination With Indian Tribal
Governments
Executive Order 13175, entitled
‘‘Consultation and Coordination with
Indian Tribal Governments’’ (65 FR
67249, November 9, 2000), requires EPA
to develop an accountable process to
ensure ‘‘meaningful and timely input by
tribal officials in the development of
regulatory policies that have tribal
implications.’’ This rule concerns the
establishment of PM NAAQS. The
Tribal Authority Rule gives Tribes the
opportunity to develop and implement
CAA programs such as the PM NAAQS,
but it leaves to the discretion of the
Tribe whether to develop these
programs and which programs, or
appropriate elements of a program, they
will adopt.
This proposed rule does not have
Tribal implications, as specified in
Executive Order 13175. It does not have
a substantial direct effect on one or
more Indian Tribes, since Tribes are not
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obligated to adopt or implement any
NAAQS. Thus, Executive Order 13175
does not apply to this rule.
Although Executive Order 13175 does
not apply to this rule, EPA contacted
tribal environmental professionals
during the development of this rule. The
EPA staff participated in the regularly
scheduled Tribal Air call sponsored by
the National Tribal Air Association
during the summer and fall of 2005 as
this proposal was under development.
Also, EPA is sending notice and an
opportunity for comment to Tribal
Leaders within the lower 48 states.
Specifically, EPA solicits additional
comment on this proposed rule from
Tribal officials.
G. Executive Order 13045: Protection of
Children From Environmental Health
Risks and Safety Risks
Executive Order 13045, ‘‘Protection of
Children from Environmental Health
Risks and Safety Risks’’ (62 FR 19885,
April 23, 1997) applies to any rule that:
(1) is determined to be ‘‘economically
significant’’ as defined under Executive
Order 12866, and (2) concerns an
environmental health or safety risk that
EPA has reason to believe may have a
disproportionate effect on children. If
the regulatory action meets both criteria,
the Agency must evaluate the
environmental health or safety effects of
the planned rule on children, and
explain why the planned regulation is
preferable to other potentially effective
and reasonably feasible alternatives
considered by the Agency.
This proposed rule is subject to
Executive Order 13045 because it is an
economically significant regulatory
action as defined by Executive Order
12866, and we believe that the
environmental health risk addressed by
this action may have a disproportionate
effect on children. The proposed
NAAQS will establish uniform, national
standards for PM pollution; these
standards are designed to protect public
health with an adequate margin of
safety, as required by CAA section 109.
However, the protection offered by these
standards may be especially important
for children because children, along
with other sensitive population
subgroups such as the elderly and
people with existing heart or lung
disease, are potentially susceptible to
health effects resulting from PM
exposure. Because children are
considered a potentially susceptible
population, we have carefully evaluated
the environmental health effects of
exposure to PM pollution among
children. These effects and the size of
the population affected are summarized
in section 9.2.4 of the Criteria Document
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2693
and section 3.5 of the Staff Paper, and
the results of our evaluation of the effect
of PM pollution on children are
discussed in sections II.A, B, and C and
III.A, B, and C of this preamble.
H. Executive Order 13211: Actions That
Significantly Affect Energy Supply,
Distribution or Use
This proposed rule is not a
‘‘significant energy action’’ as defined in
Executive Order 13211, ‘‘Actions
Concerning Regulations That
Significantly Affect Energy Supply,
Distribution, or Use’’ (66 FR 28355 (May
22, 2001)) because it is not likely to
have a significant adverse effect on the
supply, distribution, or use of energy.
The purpose of this rule is to establish
NAAQS for PM. The rule does not
prescribe specific pollution control
strategies by which these ambient
standards will be met. Such strategies
will be developed by States on a caseby-case basis, and EPA cannot predict
whether the control options selected by
States will include regulations on
energy suppliers, distributors, or users.
Thus, EPA concludes that this rule is
not likely to have any adverse energy
effects and does not constitute a
significant energy action as defined in
Executive Order 13211.
I. National Technology Transfer
Advancement Act
Section 12(d) of the National
Technology Transfer Advancement Act
of 1995 (NTTAA), Public Law No. 104–
113, § 12(d) (15 U.S.C. 272 note) directs
EPA to use voluntary consensus
standards in its regulatory activities
unless to do so would be inconsistent
with applicable law or otherwise
impractical. Voluntary consensus
standards are technical standards (e.g.,
materials specifications, test methods,
sampling procedures, and business
practices) that are developed or adopted
by voluntary consensus standards
bodies. The NTTAA directs EPA to
provide Congress, through OMB,
explanations when the Agency decides
not to use available and applicable
voluntary consensus standards.
The proposed rule establishes
requirements for environmental
monitoring and measurement.
Specifically, it would establish the FRM
for PM10-2.5 measurement (and slightly
amend the FRM for PM2.5). The FRM is
the benchmark against which all
ambient monitoring methods are
measured. While the FRM is not a
voluntary consensus standard, the
proposed revisions to the FEM in 40
CFR part 53 do allow for the utilization
of voluntary consensus standards if they
meet the specified performance criteria.
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To the extent feasible, EPA employs a
Performance-Based Measurement
System (PBMS), which does not require
the use of specific, prescribed analytic
methods. The PBMS is defined as a set
of processes wherein the data quality
needs, mandates or limitations of a
program or project are specified, and
serve as criteria for selecting appropriate
methods to meet those needs in a costeffective manner. It is intended to be
more flexible and cost effective for the
regulated community; it is also intended
to encourage innovation in analytical
technology and improved data quality.
Though the FRM defines the particular
specifications for ambient monitors,
there is some variability with regard to
how monitors measure PM, depending
on the type and size of PM and
environmental conditions. Therefore, it
is not practically possible to fully define
the FRM in performance terms.
Nevertheless, our approach in the past
has resulted in multiple brands of
monitors qualifying as FRM for PM, and
we expect this to continue. Also, the
FRM described in this proposal and the
equivalency criteria contained in the
proposed revisions to 40 CFR part 53 do
constitute performance based criteria for
the instruments that will actually be
deployed for monitoring PM10-2.5.
Therefore, for most of the measurements
that will be made and most of the
measurement systems that make them,
EPA is not precluding the use of any
method, whether it constitutes a
voluntary consensus standard or not, as
long as it meets the specified
performance criteria.
The EPA welcomes comments on this
aspect of the proposed rulemaking and,
specifically, invites the public to
identify potentially applicable voluntary
consensus standards and to explain why
such standards should be used in this
regulation.
J. Executive Order 12898: Federal
Actions To Address Environmental
Justice in Minority Populations and
Low-Income Populations
Executive Order 12898, ‘‘Federal
Actions to Address Environmental
Justice in Minority Populations and
Low-Income Populations,’’ requires
Federal agencies to consider the impact
of programs, policies, and activities on
minority populations and low-income
populations. According to EPA
guidance, agencies are to assess whether
minority or low income populations
face risks or a rate of exposure to
hazards that are significant and that
‘‘appreciably exceed or is likely to
appreciably exceed the risk or rate to the
general population or to the appropriate
comparison group.’’ (EPA, 1998)
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In accordance with Executive Order
12898, the Agency has considered
whether these proposals, if
promulgated, may have
disproportionate negative impacts on
minority or low income populations.
The Agency expects these proposals
would lead to the establishment of
uniform NAAQS for PM.
References
Abbey, D. E.; Nishino, N.; McDonnell, W. F.;
Burchette, R. J.; Knutsen, S. F.; Beeson,
L.; Yang, J. X. (1999) Long-term inhalable
particles and other air pollutants related
to mortality in nonsmokers. Am. J.
Respir. Crit. Care Med. 159:373–382.
Abt Associates Inc. (1996). ‘‘A Particulate
Matter Risk Assessment for Philadelphia
and Los Angeles.’’ Bethesda, MD.
Prepared for the Office of Air Quality
Planning and Standards, U.S.
Environmental Protection Agency,
Contract No. 68–W4–0029. July 3
(revised November). Available: https://
www.epa.gov/ttn/naaqs/standards/pm/
s_pm_pr_td.html.
Abt Associates Inc. (1997a). Abt Associates
Memorandum to U.S. EPA. Subject:
Revision of Mortality Incidence
Estimates Based on Pope et al. (1995) in
the Abt Particulate Matter Risk
Assessment Report. June 5, 1997.
Abt Associates Inc. (1997b). Abt Associates
Memorandum to U.S. EPA. Subject:
Revision of Mortality Incidence
Estimates Based on Pope et al. (1995) in
the December 1996 Supplement to the
Abt Particulate Matter Risk Assessment
Report. June 6, 1997.
Abt Associates, Inc. (2001). Assessing Public
Opinions on Visibility Impairment Due
to Air Pollution: Summary Report.
Prepared for EPA Office of Air Quality
Planning and Standards; funded under
EPA Contract No. 68–D–98–001.
Bethesda, Maryland. January 2001.
Abt Associates Inc. (2002). Proposed
Methodology for Particulate Matter Risk
Analyses for Selected Urban Areas: Draft
Report. Bethesda, MD. Prepared for the
Office of Air Quality Planning and
Standards, U.S. Environmental
Protection Agency, Contract No. 68–D–
03–002. Available: https://www.epa.gov/
ttn/naaqs/standards/pm/
s_pm_cr_td.html.
Abt Associates Inc. (2005). Particulate Matter
Health Risk Assessment for Selected
Urban Areas. Draft Report. Bethesda,
MD. Prepared for the Office of Air
Quality Planning and Standards, U.S.
Environmental Protection Agency,
Contract No. 68–D–03–002. Available:
https://www.epa.gov/ttn/naaqs/
standards/pm/s_pm_cr_td.html.
Allen, G., Oh, J., Koutrakis, P., Sioutus, C.
(1999). Techniques for High-Quality
Ambient Coarse Particle Mass
Measurements. J. Air Waste Manage.
Assoc. 49:133–141.
Arizona Department of Environmental
Quality (2003). Visibility Index
Oversight Committee Final Report:
Recommendation for a Phoenix Area
PO 00000
Frm 00076
Fmt 4701
Sfmt 4702
Visibility Index. March 5, 2003. https://
www.phoenixvis.net/PDF/
vis_031403final.pdf.
Becker, S.; Soukup, J. M.; Sioutas, C.; Cassee,
F. R. (2003). Response of human alveolar
macrophages to ultrafine, fine and coarse
urban air pollution particles. Exp. Lung
Res. 29: 29–44.
Burnett, R. T.; Cakmak, S.; Brook, J. R.;
Krewski, D. (1997). The role of
particulate size and chemistry in the
association between summertime
ambient air pollution and hospitalization
for cardiorespiratory diseases. Environ.
Health Perspect. 105:614–620.
Burnett, R. T.; Brook, J.; Dann, T.; Delocla, C.;
Philips, O.; Cakmak, S.; Vincent, R.;
Goldberg, M. S.; Krewski, D. (2000).
Association between particulate- and
gas-phase components of urban air
pollution and daily mortality in eight
Canadian cities. Inhalation Toxicol. 12
(suppl. 4): 15–39.
Burnett, R. T.; Goldberg, M. S. (2003). Sizefractionated particulate mass and daily
mortality in eight Canadian cities. In:
Revised analyses of time-series studies of
air pollution and health. Special report.
Boston, MA: Health Effects Institute; pp.
85–90. Available: https://
www.healtheffects.org/news.htm. May
16, 2003.
California Code of Regulations. Title 17,
Section 70200, Table of Standards.
Centers for Disease Control and Prevention
(2004). The health consequences of
smoking: a report of the Surgeon
General. Atlanta, GA: U.S. Department of
Health and Human Services, National
Center for Chronic Disease Prevention
and Health Promotion, Office on
Smoking and Health. Available: https://
www.cdc.gov/tobacco/sgr/sgr_2004/
chapters.htm. August 18, 2004.
Chen, B.T., Yeh, H.C., Cheng, Y.S. (1985). A
Novel Virtual Impactor: Calibration and
Use. J. Aerosol Sci. 16:343–354.
Chen, L.; Yang, W.; Jennison, B. L.; Omaye,
S. T. (2000). Air particulate pollution
and hospital admissions for chronic
obstructive pulmonary disease in Reno,
Nevada. Inhalation Toxicol. 12:281–298.
Chestnut , L. G.; Rowe, R. D. (1991).
Economic valuation of changes in
visibility: A state of the science
assessment. Sector B5 Report 27. In
Acidic Depositions: State of Science and
Technology Volume IV Control
Technologies, Future Emissions and
Effects Valuation. P.M. Irving (ed.). The
U.S. National Acid Precipitation
Assessment Program. GPO, Washington,
DC.
Chestnut, L. G.; Dennis, R. L. (1997).
Economic benefits of improvements in
visibility: acid rain provisions of the
1990 clean air act amendments. J. Air
Waste Manage. Assoc. 47:395–402.
Chock, D. P.; Winkler, S.; Chen, C. (2000). A
study of the association between daily
mortality and ambient air pollutant
concentrations in Pittsburgh,
Pennsylvania. J. Air Waste Manage.
Assoc. 50:1481–1500.
Choudhury, A. H.; Gordian, M. E.; Morris, S.
S. (1997) Associations between
E:\FR\FM\17JAP2.SGM
17JAP2
cchase on PROD1PC60 with PROPOSALS2
Federal Register / Vol. 71, No. 10 / Tuesday, January 17, 2006 / Proposed Rules
respiratory illness and PM10 air
pollution. Arch. Environ. Health 52:113–
117.
Cohen, S.; Evans, G.W.; Stokols, D.; Krantz,
D.S. (1986). Behavior, Health, and
Environmental Stress. Plenum Press.
New York, NY.
Deck, L. B.; Post, E.S.; Smith, E.; Wiener, M.;
Cunningham, K.; Richmond, H. (2001).
Estimates of the health risk reductions
associated with attainment of alternative
particulate matter standards in two U.S.
cities. Risk Anal. 21(5):821–835.
Delfino, R. J.; Murphy-Moulton, A. M.;
Burnett, R. T.; Brook, J. R.; Becklake, M.
R. (1997). Effects of air pollution on
emergency room visits for respiratory
illnesses in Montreal, Quebec. Am. J.
Respir. Crit. Care Med. 155:568–576.
Delfino, R. J.; Zeiger, R. S.; Seltzer, J. M.;
Street, D. G. (1998). Symptoms in
pediatric asthmatic and air pollution:
differences in effects by symptom
severity, anti-inflammatory medication
use and particulate averaging time.
Environ. Health Perspect. 106:751–761.
Demokritou, P., Tarun, G., Ferguson, S.,
Koutrakis, P. (2003). Development of a
High-Volume Concentrated Ambient
Particles System (CAPS) for Human and
Animal Inhalation Toxicological Studies.
Inhalation Toxicol. 15:111–129.
Diociaiuti, M.; Balduzzi, M.; De Berardis, B.;
Cattani, G.; Stacchini, G.; Ziemacki, G.;
Marconi, A.; Paoletti, L. (2001) The two
PM2.5 (fine) and PM2.5–10 (coarse)
fractions: evidence of different biological
activity. Environ. Res. A 86:254–262.
Dockery, D. W.; Pope, C. A., III; Xu, X.;
Spengler, J. D.; Ware, J. H.; Fay, M. E.;
Ferris, B. G., Jr.; Speizer, F. E. (1993). An
association between air pollution and
mortality in six U.S. cities. N. Engl. J.
Med. 329:1753–1759.
Dockery, D. W.; Cunningham, J.; Damokosh,
A. I.; Neas, L. M.; Spengler, J. D.;
Koutrakis, P.; Ware, J. H.; Raizenne, M.;
Speizer, F. E. (1996). Health effects of
acid aerosols on North American
children: respiratory symptoms. Environ.
Health Perspect. 104:500–505.
Dominici, F.; McDermott, A.; Daniels, M.;
Zeger, S. L.; Samet, J. M. (2003).
Mortality among residents of 90 cities.
In: Revised analyses of time-series
studies of air pollution and health.
Special report. Boston, MA: Health
Effects Institute; pp. 9–24. Available:
https://www.healtheffects.org/Pubs/
TimeSeries.pdf. May 12, 2004.
Driscoll, C. T.; Lawrence, G. B.; Bulger, A. J.;
Butler, T. J.; Cronan, C. S.; Eagar, C.;
Lambert, K. F.; Likens, G. E.; Stoddard,
J. L.; Weathers, K. C. (2001). Acidic
deposition in the northeastern United
States: sources and inputs, ecosystem
effects, and management strategies.
BioScience 51:180–198.
Dzubay, T.G., Barbour, R.K. (1983). A Method
to Improve the Adhesion of Aerosol
Particles on Teflon Filters. JAPCA, 33:
692–695.
Ely, D.W.; Leary, J.T.; Stewart, T.R.; Ross,
D.M. (1991). The Establishment of the
Denver Visibility Standard. For
presentation at the 84th Annual Meeting
VerDate Aug<31>2005
15:50 Jan 13, 2006
Jkt 208001
& Exhibition of the Air and Waste
Management Association, June 16–21,
1991.
Environmental Protection Agency (1996a).
Air Quality Criteria for Particulate
Matter. Research Triangle Park, NC:
National Center for Environmental
Assessment-RTP Office; report no. EPA/
600/P–95/001aF–cF. 3v
Environmental Protection Agency (1996b).
Review of the National Ambient Air
Quality Standards for Particulate Matter:
Policy Assessment of Scientific and
Technical Information, OAQPS Staff
Paper. Research Triangle Park, NC
27711: Office of Air Quality Planning
and Standards; report no. EPA–452\R–
96–013.
Environmental Protection Agency (1999).
Regional Haze Regulations. 40 CFR Part
51.300–309. 64 Federal Register 35713.
Environmental Protection Agency (2000a).
Memorandum from David Mobley, EPA–
OAQPS to EPA Regional Office Air
Directors, dated January 19, regarding
Additional Guidance on PM2.5 Cassette
Handling and Transportation. Available:
https://www.epa.gov/ttn/amtic/files/
ambient/pm25/pm25caset.pdf.
Environmental Protection Agency (2000b).
Memorandum from Elizabeth Hunike,
EPA–NERL–Process Modeling Research
Branch to Lee Ann Byrd, EPA–OAQPS–
MQAG, dated November 30, regarding
Alternative WINS oil. Available: https://
www.epa.gov/ttn/amtic/files/cfr/recent/
letter.pdf.
Environmental Protection Agency (2001).
Particulate Matter NAAQS Risk Analysis
Scoping Plan, Draft. Research Triangle
Park, NC: Office of Air Quality Planning
and Standards. Available: https://
www.epa.gov/ttn/naaqs/standards/pm/
s_pm_cr_td.html.
Environmental Protection Agency (2002a).
Memorandum from David Mobley, EPA–
OAQPS to EPA Regional Office Air
Directors, dated February 22, regarding
‘‘Extension of Filter Retrieval Time for
PM2.5 Samples.’’ Available: https://
www.epa.gov/ttn/amtic/files/ambinet/
pm25/filtere.pdf.
Environmental Protection Agency (2002b). 67
Federal Register 15566. April 2, 2002.
Environmental Protection Agency (2003).
Response Of Surface Water Chemistry to
the Clean Air Act Amendments of 1990.
National Health and Environmental
Effects Research Laboratory, Office of
Research and Development, U.S.
Environmental Protection Agency.
Research Triangle Park, NC. EPA 620/R–
03/001.
Environmental Protection Agency (2004). Air
Quality Criteria for Particulate Matter.
Research Triangle Park, NC: National
Center for Environmental AssessmentRTP Office; report no. EPA/600/P–99/
002aD.
Environmental Protection Agency. (2005a)
Review of the National Ambient Air
Quality Standards for Particulate Matter:
Policy Assessment of Scientific and
Technical Information, OAQPS Staff
Paper. Research Triangle Park, NC
27711: Office of Air Quality Planning
PO 00000
Frm 00077
Fmt 4701
Sfmt 4702
2695
and Standards; report no. EPA–452/R–
05–005. June 2005.
Environmental Protection Agency. (2005b)
Review of the National Ambient Air
Quality Standards for Particulate Matter:
Policy Assessment of Scientific and
Technical Information, OAQPS Staff
Paper. Research Triangle Park, NC
27711: Office of Air Quality Planning
and Standards; report no. EPA EPA–452/
R–05–005a. December 2005.
Fairley, D. (2003). Mortality and air pollution
for Santa Clara County, California, 1989–
1996. In: Revised analyses of time-series
studies of air pollution and health.
Special report. Boston, MA: Health
Effects Institute; pp. 97–106. Available:
https://www.healtheffects.org/Pubs/
TimeSeries.pdf. October 18, 2004.
Forney, L.J., Ravenhall, D.G., Lee, S.S. (1982).
Experimental and Theoretical Study of a
Two-Dimensional Virtual Impactor.
Environ. Sci. Technol. 16: 492–497.
Galloway, J. N.; Cowling, E. B. (2002).
Reactive nitrogen and the world: 200
years of change. Ambio 31: 64–71.
Gauderman, W. J.; McConnell, R.; Gilliland,
F.; London, S.; Thomas, D.; Avol, E.;
Vora, H.; Berhane, K.; Rappaport, E. B.;
Lurmann, F.; Margolis, H. G.; Peters, J.
(2000). Association between air pollution
and lung function growth in southern
California children. Am. J. Respir. Crit.
Care Med. 162: 1383–1390.
Gauderman, W. J.; Gilliland, G. F.; Vora, H.;
Avol, E.; Stram, D.; McConnell, R.;
Thomas, D.; Lurmann, F.; Margolis, H.
G.; Rappaport, E. B.; Berhane, K.; Peters,
J. M. (2002). Association between air
pollution and lung function growth in
southern California children: results
from a second cohort. Am. J. Respir. Crit.
Care Med. 166: 76–84.
Gold, D. R.; Litonjua, A.; Schwartz, J.; Lovett,
E.; Larson, A.; Nearing, L.; Allen, G.;
Verrier, M.; Cherry, R.; Verrier, R. (2000)
Ambient pollution and heart rate
variability. Circulation 101:1267–1273.
Goldberg, M. S.; Burnett, R. T. (2003) Revised
analysis of the Montreal time-series
study. In: Revised analyses of time-series
studies of air pollution and health.
Special report. Boston, MA: Health
Effects Institute; pp. 113–132. Available:
https://www.healtheffects.org/Pubs/
TimeSeries.pdf [18 October, 2004].
¨
Gordian, M. E.; Ozkaynak, H.; Xue, J.; Morris,
S. S.; Spengler, J. D. (1996) Particulate air
pollution and respiratory disease in
Anchorage, Alaska. Environ. Health
Perspect. 104:290–297.
Grand Canyon Visibility Transport
Commission (1996). Report of the Grand
Canyon Visibility Transport Commission
to the United States Environmental
Protection Agency.
Gunn, J.M. and Mills, K.H. (1998). The
potential for restoration of acid-damaged
lake trout lakes. Restoration Ecology.
6:390–397.
Health Effects Institute (2000). Commentary
on the National Morbidity, Mortality and
Air Pollution Study. Part II: morbidity,
mortality and air pollution in the United
States. Boston, MA: Health Effects
Institute; research report no. 94, pp. 73–
E:\FR\FM\17JAP2.SGM
17JAP2
cchase on PROD1PC60 with PROPOSALS2
2696
Federal Register / Vol. 71, No. 10 / Tuesday, January 17, 2006 / Proposed Rules
81. Available: https://
www.healtheffects.org/Pubs/Samet2.pdf.
June, 2000.
Health Effects Institute (2003). Commentary
on revised analyses of selected studies.
In: Revised analyses of time-series
studies of air pollution and health.
Special report. Boston, MA: Health
Effects Institute; pp. 255–290. Available:
https://www.healtheffects.org/Pubs/
TimeSeries.pdf. October 18, 2004.
Hedin, L. O.; Granat, L.; Likens, G. E.;
Buishand, T. A.; Galloway, J. N.; Butler,
T. J.; Rodhe, H. (1994). Steep declines in
atmospheric base cations in regions of
Europe and North America. Nature
(London) 367:351–354.
Hefflin, B. J.; Jalaludin, B.; McClure, E.; Cobb,
N.; Johnson, C. A.; Jecha, L.; Etzel, R. A.
(1994). Surveillance for dust storms and
respiratory diseases in Washington State,
1991. Arch. Environ. Health 49:170–174.
Henderson, R. (2005a). EPA’s Review of the
National Ambient Air Quality Standards
for Particulate Matter (Second Draft PM
Staff Paper, January 2005): A review by
the Particulate Matter Review Panel of
the EPA Clean Air Scientific Advisory
Committee. June 6, 2005. Available:
https://www.epa.gov/sab/pdf/casac05007.pdf.
Henderson, R. (2005b). Clean Air Scientific
Advisory Committee (CASAC) Review of
the EPA Staff Recommendations
Concerning a Potential Thoracic Coarse
PM Standard in the Review of the
National Ambient Air Quality Standards
for Particulate Matter: Policy Assessment
of Scientific and Technical Information
(Final PM OAQPS Staff Paper, EPA–452/
R–05–005). September 15, 2005.
Available: https://www.epa.gov/sab/
panels/casacpmpanel.html.
Henderson, R. (2005c). Letter to the EPA
Administrator from the Clean Air
Scientific Advisory Committee, dated
November 30, 2005, regarding peer
review of the proposed Federal reference
method for PM10-2.5. Available: https://
www.epa.gov/sab/pdf/casac_06001.pdf.
Hopke, P. (2002). Letter from Dr. Phil Hopke,
Chair, Clean Air Scientific Advisory
Committee (CASAC) to Honorable
Christine Todd Whitman, Administrator,
U.S. EPA. Final advisory review report
by the CASAC Particulate Matter Review
Panel on the proposed particulate matter
risk assessment. May 23, 2002.
Available: https://www.epa.gov/sab/pdf/
casacadv02002.pdf.
Hornberg, C.; Maciuleviciute, L.; Seemayer,
N. H.; Kainka, E. (1998). Induction of
sister chromatid exchanges (SCE) in
human tracheal epithelial cells by the
fractions PM¥10 and PM¥2.5 of airborne
particulates. Toxicol. Lett. 96/97: 215–
220.
Ito, K. (2003). Associations of particulate
matter components with daily mortality
and morbidity in Detroit, Michigan. In:
Revised analyses of time-series studies of
air pollution and health. Special report.
Boston, MA: Health Effects Institute; pp.
143–156. Available: https://
www.healtheffects.org/Pubs/
TimeSeries.pdf. May 12, 2004.
VerDate Aug<31>2005
15:50 Jan 13, 2006
Jkt 208001
Kenny L.C.; Thorp, A. (2001). Evaluation of
VSCC Cyclones. Health & Safety
Laboratory Report # IR/L/EXM/01/01
(2001). Available: https://
www.bgiusa.com/aam/vsccref6.pdf.
Kenny, L; Merrifield, T.; Gussman, R.; Thorp,
A. (2004). The Development and
Designation of a New USEPA-Approved
Fine Particle Inlet: A Study of the
USEPA Designation Process. Aerosol
Science & Technology, 38 (supplement
2): 15–22.
Kim, M.C., Lee, K.W. (2000). Design
Modification of Virtual Impactor for
Enhancing Particle Concentration
Performance. Aerosol Sci. Technol. 32:
233–242.
Kleinman, M.T.; Bhalla, D.K.; Mautz, W.J.;
Phalen, R.F. (1995) Cellular and
immunologic injury with PM–10
inhalation. Inhalation Toxicol. 7:589–
602.
Klemm, R. J.; Mason, R. (2003). Replication
of reanalysis of Harvard Six-City
mortality study. In: Revised analyses of
time-series studies of air pollution and
health. Special report. Boston, MA:
Health Effects Institute; pp. 165–172.
Available: https://www.healtheffects.org/
Pubs/TimeSeries.pdf. May 12, 2004.
Krewski, D.; Burnett, R. T.; Goldberg, M. S.;
Hoover, K.; Siemiatycki, J.; Jerrett, M.;
Abrahamowicz, M.; White, W. H. (2000).
Reanalysis of the Harvard Six Cities
Study and the American Cancer Society
Study of particulate air pollution and
mortality. A special report of the
Institute’s particle epidemiology
reanalysis project. Cambridge, MA:
Health Effects Institute.
Li, S., Lundgren, D.A. (1997). Effect of Clean
Air Core Geometry on Fine Particle
Contamination and Calibration of a
Virtual Impactor. Aerosol Sci. Technol.
27: 625–635.
Lipfert, F. W.; Morris, S. C.; Wyzga, R. E.
(2000a). Daily mortality in the
Philadelphia metropolitan area and sizeclassified particulate matter. J. Air Waste
Manage. Assoc. 50:1501–1513.
Lipfert, J. W.; Perry, H. M., Jr.; Miller, J. P.;
Baty, J. D.; Wyzga, R. E.; Carmody, S. E.
(2000b). The Washington UniversityEPRI veteran’s cohort mortality study:
preliminary results. Inhalation Toxicol.
12(Suppl. 4):41–73.
Lippmann, M.; Ito, K.; Nadas, A.; Burnett, R.
T. (2000). Association of particulate
matter components with daily mortality
and morbidity in urban populations.
Cambridge, MA: Health Effects Institute;
research report 95.
Lokke, H.; Bak, J.; Falkengren-Grerup, U.;
Finlay, R. D.; Ilvesniemi, H.; Nygaard, P.
H.; Starr, M. (1996). Critical loads of
acidic deposition for forest soils: is the
current approach adequate. Ambio 25:
510–516.
Loo, B.W.; Cork, C.P. (1988). Development of
High Efficiency Virtual Impactors.
Aerosol Sci. Technol. 9: 167–176.
Mar, T. F.; Norris, G. A.; Larson, T. V.;
Wilson, W. E.; Koenig, J. Q. (2003). Air
pollution and cardiovascular mortality in
Phoenix, 1995–1997. In: Revised
analyses of time-series studies of air
PO 00000
Frm 00078
Fmt 4701
Sfmt 4702
pollution and health. Special report.
Boston, MA: Health Effects Institute; pp.
177–182. Available: https://
www.healtheffects.org/Pubs/
TimeSeries.pdf. October 18, 2004.
Mauderly, J.; Neas, L.; Schlesinger, R. (1998)
PM monitoring needs related to health
effects. In: Atmospheric observations:
helping build the scientific basis for
decisions related to airborne particulate
matter; Report of the PM measurements
research workshop, July 22–23, 1998.
Available from ‘‘PM Measurements
Report’’, Health Effects Institute, 955
Massachusetts Ave., Cambridge, MA
02139.
McConnell, R.; Berhane, K.; Gilliland, F.;
London, S. J.; Vora, H.; Avol, E.;
Gauderman, W. J.; Margolis, H. G.;
Lurmann, F.; Thomas, D. C.; Peters, J. M.
(1999). Air pollution and bronchitic
symptoms in southern California
children with asthma. Environ. Health
Perspect. 107: 757–760.
McDonnell, W. F.; Nishino-Ishikawa, N.;
Petersen, F. F.; Chen, L. H.; Abbey, D. E.
(2000). Relationships of mortality with
the fine and coarse fractions of long-term
ambient PM10 concentrations in
nonsmokers. J. Exposure Anal. Environ.
Epidemiol. 10:427–436.
Miller, F.J.; Gardner, D.E.; Graham, J.A.; Lee,
R.E.; Wilson, W.E.; Bachmann, J.D.
(1979) Size considerations for
establishing a standard for inhalable
particles. J Air Pollution Control Assoc.
29:610–615.
Molenar, J.V. (2000). Visibility Science and
Trends in the Lake Tahoe Basin: 1989–
1998. Report by Air Resource Specialists,
Inc., to Tahoe Regional Planning Agency.
February 15, 2000.
Monn, C.; Becker, S. (1999). Cytotoxicity and
induction of proinflammatory cytokines
from human monocytes exposed to fine
(PM2.5) and coarse particles (PM10-2.5) in
outdoor and indoor air. Toxicol. Appl.
Pharmacol. 155: 245–252.
Moolgavkar, S. H. (2000c). Air pollution and
hospital admissions for chronic
obstructive pulmonary disease in three
metropolitan areas of the United States.
Inhalation Toxicol. 12 (Suppl. 4):75–90.
Moolgavkar, S. H. (2003). Air pollution and
daily deaths and hospital admissions in
Los Angeles and Cook counties. In:
Revised analyses of time-series studies of
air pollution and health. Special report.
Boston, MA: Health Effects Institute; pp.
183–198. Available: https://
www.healtheffects.org/news.htm. May
16, 2003.
National Academy of Sciences (2002).
Estimating the Public Health Benefits of
Proposed Air Pollution Regulations.
Washington, D.C.: The National
Academy Press. Available: https://
www.nap.edu/books/0309086094/html/.
National Research Council (1993). Protecting
Visibility in National Parks and
Wilderness Areas. National Academy of
Sciences Committee on Haze in National
Parks and Wilderness Areas. National
Academy Press: Washington, DC.
National Science and Technology Council
(1998). National acid precipitation
E:\FR\FM\17JAP2.SGM
17JAP2
cchase on PROD1PC60 with PROPOSALS2
Federal Register / Vol. 71, No. 10 / Tuesday, January 17, 2006 / Proposed Rules
assessment program biennial report to
Congress: an integrated assessment;
executive summary. Silver Spring, MD:
U.S. Department of Commerce, National
Oceanic and Atmospheric
Administration. Available: https://
www.nnic.noaa.gov/CENR/NAPAP/
NAPAP_96.htm. November 24, 1999.
Nauenberg, E.; Basu, K. (1999). Effect of
insurance coverage on the relationship
between asthma hospitalizations and
exposure to air pollution. Public Health
Rep. 114: 135–148.
Neas, L. M.; Dockery, D. W.; Koutrakis, P.;
Tollerud, D. J.; Speizer, F. E. (1995). The
association of ambient air pollution with
twice daily peak expiratory flow rate
measurements in children. Am. J.
Epidemiol. 141: 111–122.
Neas, L. M.; Dockery, D. W.; Burge, H.;
Koutrakis, P.; Speizer, F. E. (1996).
Fungus spores, air pollutants, and other
determinants of peak expiratory flow rate
in children. Am. J. Epidemiol. 143: 797–
807.
Neas, L. M.; Dockery, D. W.; Koutrakis, P.;
Speizer, F. E. (1999). Fine particles and
peak flow in children: acidity versus
mass. Epidemiology 10:550–553.
New Zealand Ministry for the Environment.
(2000). Proposals for Revised and New
Ambient Air Quality Guidelines:
Discussion Document. Air Quality
Report No. 16. December.
New Zealand National Institute of Water &
Atmospheric Research (NIWAR) (2000a).
Visibility in New Zealand: Amenity
Value, Monitoring, Management and
Potential Indicators. Air Quality
Technical Report 17. Prepared for New
Zealand Ministry for the Environment.
Draft report.
New Zealand National Institute of Water &
Atmospheric Research (NIWAR) (2000b).
Visibility in New Zealand: National Risk
Assessment. Air Quality Technical
Report 18. Prepared for New Zealand
Ministry for the Environment. Draft
report.
Ostro, B. (1995). Fine particulate air
pollution and mortality in two Southern
California counties. Environ. Res. 70: 98–
104.
Ostro, B. D.; Lipsett, M. J.; Mann, J. K.;
Braxton-Owens, H.; White, M. C. (1995).
Air pollution and asthma exacerbations
among African-American children in Los
Angeles. Inhalation Toxicol. 7:711–722.
Ostro, B. D.; Broadwin, R.; Lipsett, M. J.
(2000). Coarse and fine particles and
daily mortality in the Coachella Valley,
CA: a follow-up study. J. Exposure Anal.
Environ. Epidemiol. 10:412–419.
Ostro, B. D.; Broadwin, R.; Lipsett, M. J.
(2003). Coarse particles and daily
mortality in Coachella Valley, California.
In: Revised analyses of time-series
studies of air pollution and health.
Special report. Boston, MA: Health
Effects Institute; pp. 199–204. Available:
https://www.healtheffects.org/Pubs/
TimeSeries.pdf. October 18, 2004.
Papp, M.; Eberly, S.; Hanley, T.; Watkins, N.;
Barden, H.; Noah, G.; Bermudez, R.;
Eden, R.; Franks, B.; Johnson, A.
Marriner, R.; Michel, E. (2002).
VerDate Aug<31>2005
15:50 Jan 13, 2006
Jkt 208001
Evaluation of Filter Recovery Period for
the Determination of Fine Particulate
Matter as PM2.5 in the Atmosphere. EPAOAQPS Test Report. Available: https://
www.epa.gov/ttn/amtic/files/ambient/
pm25/qa/initdraft.pdf.
Peters, A.; Liu, E.; Verrier, R. L.; Schwartz,
J.; Gold, D. R.; Mittleman, M.; Baliff, J.;
Oh, J. A.; Allen, G.; Monahan, K.;
Dockery, D. W. (2000). Air pollution and
incidence of cardiac arrhythmia.
Epidemiology 11:11–17.
Peters, A.; Dockery, D. W.; Muller, J. E.;
Mittleman, M. A. (2001). Increased
particulate air pollution and the
triggering of myocardial infarction.
Circulation 103:2810–2815.
Peters, J. M.; Avol, E.; Navidi, W.; London,
S. J.; Gauderman, W. J.; Lurmann, F.;
Linn, W. S.; Margolis, H.; Rappaport, E.;
Gong, H., Jr.; Thomas, D. C. (1999a). A
study of twelve southern California
communities with differing levels and
types of air pollution. I. Prevalence of
respiratory morbidity. Am. J. Respir. Crit.
Care Med. 159: 760–767.
Peters, J. M.; Avol, E.; Navidi, W.; London,
S. J.; Gauderman, W. J.; Lurmann, F.;
Linn, W. S.; Margolis, H.; Rappaport, E.;
Gong, H., Jr.; Thomas, D. C. (1999b). A
study of twelve southern California
communities with differing levels and
types of air pollution. II. Effects on
pulmonary function. Am. J. Respir. Crit.
Care Med. 159: 768–775.
Pope, C. A., III. (1989). Respiratory disease
associated with community air pollution
and a steel mill, Utah Valley. Am. J.
Public Health 79: 623–628.
Pope, C. A., III. (1991). Respiratory hospital
admissions associated with PM10
pollution in Utah, Salt Lake, and Cache
Valleys. Arch. Environ. Health 46: 90–
97.
Pope, C. A., III; Schwartz, J.; Ransom, M. R.
(1992). Daily mortality and PM10
pollution in Utah valley. Arch. Environ.
Health 47: 211–217.
Pope, C. A., III; Thun, M. J.; Namboodiri, M.
M.; Dockery, D. W.; Evans, J. S.; Speizer,
F. E.; Heath, C. W., Jr. (1995). Particulate
air pollution as a predictor of mortality
in a prospective study of U.S. adults.
Am. J. Respir. Crit. Care Med. 151: 669–
674.
Pope, C. A., III; Hill, R. W.; Villegas, G. M.
(1999). Particulate air pollution and
daily mortality on Utah’s Wasatch Front.
Environ. Health Perspect. 107: 567–573.
Pope, C. A., III; Burnett, R. T.; Thun, M. J.;
Calle, E. E.; Krewski, D.; Ito, K.;
Thurston, G. D. (2002). Lung cancer,
cardiopulmonary mortality, and longterm exposure to fine particulate air
pollution. J. Am. Med. Assoc. 287:1132–
1141.
Post, E.; Deck, L.; Larntz, K.; Hoaglin. D.
(2001). An application of an empirical
Bayes estimation technique to the
estimation of mortality related to shortterm exposure to particulate matter. Risk
Anal. 21(5): 837–842.
Raizenne, M.; Neas, L. M.; Damokosh, A. I.;
Dockery, D. W.; Spengler, J. D.;
Koutrakis, P.; Ware, J. H.; Speizer, F. E.
(1996). Health effects of acid aerosols on
PO 00000
Frm 00079
Fmt 4701
Sfmt 4702
2697
North American children: pulmonary
function. Environ. Health Perspect. 104:
506–514.
Rogge, W.F.; Hildemann, L.M.; Mazurek,
M.A.; Cass, G.R.; Simoneit, B.R.T. (1993).
Sources of fine organic aerosol. 3. Road
dust, tire debris, and organometallic
brake lining dust: roads as sources and
sinks. Environ. Sci. Technol. 27:1982–
1904.
Rosendahl, T. (2005). Basis for proposed
determinations regarding retention of the
existing 24-hour PM10 standard.
Memorandum to the PM NAAQS review
docket, EPA–HQ–OAR–2001–0017.
December 20, 2005.
Ross, M. (2005). Updated information on air
quality monitoring data for thoracic
coarse particles used in epidemiologic
studies. Memorandum to the PM
NAAQS review docket, EPA–HQ–OAR–
2001–0017. June 30, 2005.
Ross, M.; Langstaff, J. (2005). Updated
statistical information on air quality data
from epidemiologic studies.
Memorandum to PM NAAQS review
docket EPA–HQ–OAR–2001–0017.
January 31, 2005.
Schlesinger, R.B., Cassee, F. (2003)
Atmospheric secondary inorganic
particulate matter: the toxicological
perspective as a basis for health effects
risk assessment. Inhalation Toxicol.
15:197–235.
Schmidt. M; Frank, N.; Mintz, D.; Rao, T.;
McCluney, L. (2005). Analyses of
particulate matter (PM) data for the PM
NAAQS review. Memorandum to PM
NAAQS review docket EPA–HQ–OAR–
2001–0017. June 30, 2005.
Schwartz, J. (1997). Air pollution and
hospital admissions for cardiovascular
disease in Tucson. Epidemiology 8: 371–
377.
Schwartz, J. (2003a). Daily deaths associated
with air pollution in six U.S. cities and
short-term mortality displacement in
Boston. In: Revised analyses of timeseries studies of air pollution and health.
Special report. Boston, MA: Health
Effects Institute; pp. 219–226. Available:
https://www.healtheffects.org/Pubs/
TimeSeries.pdf. October 18, 2004.
Schwartz, J. (2003b). Airborne particles and
daily deaths in 10 U.S. cities. In: Revised
analyses of time-series studies of air
pollution and health. Special report.
Boston, MA: Health Effects Institute; pp.
211–218. Available: https://
www.healtheffects.org/Pubs/
TimeSeries.pdf. October 18, 2004.
Schwartz, J.; Dockery, D. W.; Neas, L. M.
(1996). Is daily mortality associated
specifically with fine particles? J. Air
Waste Manage. Assoc. 46:927–939.
Schwartz, J.; Norris, G.; Larson, T.; Sheppard,
L.; Claiborne, C.; Koenig, J. (1999).
Episodes of high coarse particle
concentrations are not associated with
increased mortality. Environ. Health
Perspect. 107: 339–342.
Schwartz, J.; Neas, L. M. (2000). Fine
particles are more strongly associated
than coarse particles with acute
respiratory health effects in
schoolchildren. Epidemiology 11:6–10.
E:\FR\FM\17JAP2.SGM
17JAP2
cchase on PROD1PC60 with PROPOSALS2
2698
Federal Register / Vol. 71, No. 10 / Tuesday, January 17, 2006 / Proposed Rules
Science Advisory Board (2004). Advisory for
plans on health effects analysis in the
analytical plan for EPA’s second
prospective analysis—benefits and costs
of the clean air act, 1990–2000. Advisory
by the Health Effects Subcommittee of
the Advisory Council for Clean Air
Compliance Analysis. EPA SAB
Council—ADV–04–002. March, 2004.
Available: https://www.epa.gov/science1/
pdf/council_adv_04002.pdf.
Sheppard, L. (2003). Ambient air pollution
and nonelderly asthma hospital
admissions in Seattle, Washington,
1987–1994. In: Revised analyses of timeseries studies of air pollution and health.
Special report. Boston, MA: Health
Effects Institute; pp. 227–230. Available:
https://www.healtheffects.org/Pubs/
TimeSeries.pdf. October 18, 2004.
Smith, R. L.; Spitzner, D.; Kim, Y.; Fuentes,
M. (2000). Threshold dependence of
mortality effects for fine and coarse
particles in Phoenix, Arizona. J. Air
Waste Manage. Assoc. 50: 1367–1379.
Soukup, J. M.; Becker, S. (2001). Human
alveolar macrophage responses to air
pollution particulates are associated with
insoluble components of coarse material,
including particulate endotoxin. Toxicol.
Appl. Pharmacol. 171: 20–26.
Spengler, J.D., Thurston, G.D. (1983). Mass
and Elemental Composition of Fine and
Coarse Particles in Six U.S. Cities. J. Air
& Waste Manage. Assoc. 33: 1162–1171.
State Government of Victoria, Australia
(2000a). Draft Variation to State
Environment Protection Policy (Air
Quality Management) and State
Environment Protection Policy (Ambient
Air Quality) and Draft Policy Impact
Assessment. Environment Protection
Authority. Publication 728. Southbank,
Victoria.
State Government of Victoria, Australia
(2000b). Year in Review. Environment
Protection Authority. Southbank,
Victoria.
Steerenberg, P. A.; Withagen, C. E.; Dormans,
J. A. M. A.; Van Dalen, W. J.; Van
Loveren, H.; Casee, F. R. (2003).
Adjuvant activity of various diesel
exhaust and ambient particle in two
allergic models. J. Toxicol. Environ.
Health A 66: 1421–1439.
Stieb, D. M.; Beveridge, R. C.; Brook, J. R.;
Smith-Doiron, M.; Burnett, R. T.; Dales,
R. E.; Beaulieu, S.; Judek, S.; Mamedov,
A. (2000). Air pollution, aeroallergens
and cardiorespiratory emergency
department visits in Saint John, Canada.
J. Exposure Anal. Environ. Epidemiol.:
10: 461–477.
Thurston, G. D.; Ito, K.; Hayes, C. G.; Bates,
D. V.; Lippmann, M. (1994). Respiratory
hospital admissions and summertime
haze air pollution in Toronto, Ontario:
Consideration of the role of acid
aerosols. Environ. Res. 65:271–290.
Tsai, F. C.; Apte, M. G.; Daisey, J. M. (2000).
An exploratory analysis of the
relationship between mortality and the
chemical composition of airborne
particulate matter. Inhalation Toxicol. 12
(suppl.): 121–135.
Vanderpool, R.; Hanley, T.; Dimmick, F.;
Hunike, E. (2005). Multi-Site Evaluations
VerDate Aug<31>2005
15:50 Jan 13, 2006
Jkt 208001
of Candidate Methodologies for
Determining Coarse Particulate Matter
(PM10-2.5) Concentrations: August 2005.
Updated Report Regarding SecondGeneration and New PM10-2.5 Samplers.
In press.
List of Subjects in 40 CFR Part 50
Environmental protection, Air
pollution control, Carbon monoxide,
Lead, Nitrogen dioxide, Ozone,
Particulate matter, Sulfur oxides.
Dated: December 20, 2005.
Stephen L. Johnson,
Administrator.
For the reasons set forth in the
preamble, part 50 of chapter 1 of title 40
of the Code of Federal Regulations is
proposed to be amended as follows:
PART 50—NATIONAL PRIMARY AND
SECONDARY AMBIENT AIR QUALITY
STANDARDS
1. The authority citation for part 50
continues to read as follows:
Authority: 42 U.S.C. 7401 et seq.
2. Section 50.3 is revised to read as
follows:
§ 50.3
Reference conditions.
All measurements of air quality that
are expressed as mass per unit volume
(e.g., micrograms per cubic meter) other
than for the particulate matter (PM2.5
and PM10-2.5) standards contained in
§§ 50.7 and 50.13 shall be corrected to
a reference temperature of 25 [deg] C
and a reference pressure of 760
millimeters of mercury (1,013.2
millibars). Measurements of PM2.5 and
PM10-2.5 for purposes of comparison to
the standards contained in §§ 50.7 and
50.13 shall be reported based on actual
ambient air volume measured at the
actual ambient temperature and
pressure at the monitoring site during
the measurement period.
3. Section 50.6 is amended by adding
new paragraphs (d) and (e) to read as
follows:
§ 50.6 National primary and secondary
ambient air quality standards for PM10.
*
*
*
*
*
(d) The national primary and
secondary 24-hour ambient air quality
standards for particulate matter set forth
in paragraph (a) of this section will no
longer apply except in the following
areas as of [effective date of final rule]:
(1) Birmingham urban area (Jefferson
County, AL).
(2) Maricopa and Pinal Counties;
Phoenix planning area (AZ).
(3) Riverside, Los Angeles, Orange
and San Bernardino Counties; South
Coast Air Basin (CA).
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(4) Fresno, Kern, Kings, Tulare, San
Joaquin, Stanislaus, Maderia Counties;
San Joaquin Valley planning area (CA).
(5) San Bernardino County (part);
excluding Searles Valley Planning Area
and South Coast Air Basin (CA).
(6) Riverside County; Coachella
Valley Planning Area (CA).
(7) Simi Valley urban area (CA).
(8) Lake County; Cities of East
Chicago, Hammond, Whiting, and Gary
(IN).
(9) Wayne County (part) (MI).
(10) St. Louis urban area (MO).
(11) Albuquerque urban area (NM).
(12) Clark County; Las Vegas planning
area (NV).
(13) Columbia urban area (SC).
(14) El Paso urban area (including
those portions in TX and those portions
in NM).
(15) Salt Lake County (UT).
(e) The national primary and
secondary annual ambient air quality
standards for particulate matter set forth
in paragraph (b) of this section will no
longer apply in an area as of [effective
date of final rule.]
4. A new § 50.13 is added, to read as
follows:
§ 50.13 National primary and secondary
ambient air quality standards for PM2.5 and
PM10-2.5.
(a) The national primary and
secondary ambient air quality standards
for particulate matter are:
(1) 15.0 micrograms per cubic meter
(µg/m3) annual arithmetic mean
concentration, and 35 µg/m3 24-hour
average concentration measured in the
ambient air as PM2.5 (particles with an
aerodynamic diameter less than or equal
to a nominal 2.5 micrometers) by either:
(i) A reference method based on
appendix L of this part and designated
in accordance with part 53 of this
chapter; or
(ii) An equivalent method designated
in accordance with part 53 of this
chapter.
(2)(i) 70 µg/m3 24-hour average
concentration measured in the ambient
air as PM10-2.5 (particles with an
aerodynamic diameter less than or equal
to a nominal 10 micrometers and greater
than a nominal 2.5 micrometers) by
either:
(A) A reference method based on
appendix O of this part and designated
in accordance with part 53 of this
chapter; or
(B) An equivalent method designated
in accordance with part 53 of this
chapter.
(ii) The standard for PM10-2.5 includes
any ambient mix of PM10-2.5 that is
dominated by resuspended dust from
high-density traffic on paved roads and
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Federal Register / Vol. 71, No. 10 / Tuesday, January 17, 2006 / Proposed Rules
PM generated by industrial sources and
construction sources, and excludes any
ambient mix of PM10-2.5 that is
dominated by rural windblown dust and
soils and PM generated by agricultural
and mining sources. Agricultural
sources, mining sources, and other
similar sources of crustal material shall
not be subject to control in meeting this
standard.
(b) The annual primary and secondary
PM2.5 standards are met when the
annual arithmetic mean concentration,
as determined in accordance with
appendix N of this part, is less than or
equal to 15.0 µg/m3.
(c) The 24-hour primary and
secondary PM2.5 standards are met when
the 98th percentile 24-hour
concentration, as determined in
accordance with appendix N of this
part, is less than or equal to 35 µg/m3.
The 24-hour primary and secondary
PM10-2.5 standards are met when the
98th percentile 24-hour concentration,
as determined in accordance with
appendix P of this part, is less than or
equal to 70 µg/m3. ′
5. Appendix L to part 50 is amended
by:
a. Revising section 1.1;
b. Revising the heading of section
7.3.4 and adding introductory text;
revising paragraph (a) of section 7.3.4.3,
adding section 7.3.4.4; and revising
Table L–1 in section 7.4.19;
c. Revising section 8.3.6;
d. Revising the first sentence in
section 10.10 and revising section 10.13;
and
e. Revising reference 2 in section 13.0.
The revisions and addition read as
follows:
Appendix L to Part 50—Reference
Method for the Determination of Fine
Particulate Matter as PM2.5 in the
Atmosphere
1.0 Applicability.
1.1 This method provides for the
measurement of the mass concentration of
fine particulate matter having an
aerodynamic diameter less than or equal to
a nominal 2.5 micrometers (PM2.5) in ambient
air over a 24-hour period for purposes of
determining whether the primary and
secondary national ambient air quality
standards for fine particulate matter specified
in § 50.7 and § 50.13 of this part are met. The
measurement process is considered to be
nondestructive, and the PM2.5 sample
obtained can be subjected to subsequent
physical or chemical analyses. Quality
assessment procedures are provided in part
58, appendix A of this chapter, and quality
assurance guidance are provided in
references 1, 2, and 3 in section 13.0 of this
appendix.
*
*
7.3
*
*
*
*
Design specifications. * * *
*
*
*
*
7.3.4 Particle size separator. The sampler
shall be configured with either one of the two
alternative particle size separators described
in this section 7.3.4. One separator is an
impactor-type separator (WINS impactor)
described in sections 7.3.4.1, 7.3.4.2, and
7.3.4.3 of this appendix. The alternative
separator is a cyclone-type separator
(VSCCTM) described in section 7.3.4.4 of this
appendix.
*
*
*
*
*
7.3.4.3 Impactor oil specifications:
(a) Composition. Dioctyl sebacate (DOS),
single-compound diffusion oil.
*
*
*
*
*
7.3.4.4 The cyclone-type separator is
identified as a BGI VSCCTM Very Sharp Cut
Cyclone particle size separator specified as
part of EPA-designated equivalent method
EQPM–0202–142 (67 FR 15567, April 2,
2002) and as manufactured by BGI
Incorporated, 58 Guinan Street, Waltham,
Massachusetts 20451.
*
*
7.4.19
*
*
*
Data reporting requirements. * * *
TABLE L–1 TO APPENDIX L OF PART 50.—SUMMARY OF INFORMATION TO BE PROVIDED BY THE SAMPLER
Availability
Appendix L
section reference
Anytime 1
Flow rate, 30 second maximum interval ................
Flow rate, average for the sample period ..............
Flow rate, CV, for sample period ...........................
Flow rate, 5-min. average out of spsec. (FLAG 6)
Sample volume, total .............................................
Temperature, ambient, 30-second interval ............
Temperature, ambient, min., max., average for
the sample period.
Baro. pressure, ambient, 30-second interval .........
Baro. pressure, ambient, min., max., average for
the sample period.
Filter temperature, 30-second interval ...................
Filter temp. differential, 30-second interval, out of
spec. (FLAG 6).
Filter temp., maximum differential from ambient,
date, time of occurrence.
7.4.5.1
7.4.5.2
7.4.5.2
7.4.5.2
7.4.5.2
7.4.8
7.4.8
✔
(*)
(*)
✔
(*)
✔
(*)
7.4.9
7.4.9
Information to be provided
Visual
display 3
Data output 4
(*)
✔
✔
✔I
✔
✔
✔
(*)
(*)
✔
✔
✔
✔
✔
(*)
✔
7.4.11
7.4.11
✔
(*)
7.4.11
(*)
Date and Time .......................................................
7.4.12
✔
Sample start and stop time settings ......................
7.4.12
✔
Sample period start time ........................................
cchase on PROD1PC60 with PROPOSALS2
End of
period 2
Format
7.4.12
Elapsed sample time .............................................
Elapsed sample time, out of spec. (FLAG 6) .........
Power interruptions ≤1 min., start time of first 10
7.4.13
7.4.13
7.4.15.5
(*)
User-entered information, such as sampler and
site identification.
7.4.16
16:32 Jan 13, 2006
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* Provision of this information is optional. If information related to the entire sample period is optionally provided prior to the end of the sample
period, the value provided should be the value calculated for the portion of the sampler period completed up to the time the information is provided.
I Indicates that this information is also required to be provided to the Air Quality System (AQS) data bank; see § 58.16 of this chapter. For ambient temperature and barometric pressure, only the average for the sample period must be reported.
1. Information is required to be available to
the operator at any time the sampler is
operating, whether sampling or not.
2. Information relates to the entire sampler
period and must be provided following the
end of the sample period until reset manually
by the operator or automatically by the
sampler upon the start of a new sample
period.
3. Information shall be available to the
operator visually.
4. Information is to be available as digital
data at the sampler’s data output port
specified in section 7.4.16 of this appendix
following the end of the sample period until
reset manually by the operator or
automatically by the sampler upon the start
of a new sample period.
5. Digital readings, both visual and data
output, shall have not less than the number
of significant digits and resolution specified.
6. Flag warnings may be displayed to the
operator by a single flag indicator or each flag
may be displayed individually. Only a set
(on) flag warning must be indicated; an off
(unset) flag may be indicated by the absence
of a flag warning. Sampler users should refer
to section 10.12 of this appendix regarding
the validity of samples for which the sampler
provided an associated flag warning.
*
*
8.3
*
*
*
*
Weighing procedure.
*
*
*
*
8.3.6 The post-sampling conditioning and
weighing shall be completed within 240
hours (10 days) after the end of the sample
period, unless the filter sample is maintained
at temperatures below the average ambient
temperature during sampling (or 4°C or
below for average sampling temperatures less
than 4°C) during the time between retrieval
from the sampler and the start of the
conditioning, in which case the period shall
not exceed 30 days. Reference 2 in section
13.0 of this appendix has additional guidance
on transport of cooled filters.
*
*
*
*
*
10.0 PM2.5 Measurement Procedure.
* * *
*
*
*
*
*
10.10 Within 177 hours (7 days, 9 hours)
of the end of the sample collection period,
the filter, while still contained in the filter
cassette, shall be carefully removed from the
sampler, following the procedure provided in
the sampler operation or instruction manual
and the quality assurance program, and
placed in a protective container. * * *
cchase on PROD1PC60 with PROPOSALS2
*
*
*
*
*
10.13 After retrieval from the sampler,
the exposed filter containing the PM2.5
sample should be transported to the filter
conditioning environment as soon as
possible, ideally to arrive at the conditioning
environment within 24 hours for
conditioning and subsequent weighing.
During the period between filter retrieval
from the sampler and the start of the
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15:50 Jan 13, 2006
Jkt 208001
conditioning, the filter shall be maintained as
cool as practical and continuously protected
from exposure to temperatures over 25°C to
protect the integrity of the sample and
minimize loss of volatile components during
transport and storage. See section 8.3.6 of
this appendix regarding time limits for
completing the post-sampling weighing. See
reference 2 in section 13.0 of this appendix
for additional guidance on transporting filter
samplers to the conditioning and weighing
laboratory.
*
*
*
*
*
13.0 References.
*
*
*
*
*
2. Quality Assurance Guidance Document
2.12. Monitoring PM2.5 in Ambient Air Using
Designated Reference or Class I Equivalent
Methods. U.S. EPA, National Exposure
Research Laboratory. Research Triangle Park,
NC, November 1988 or later edition.
Currently available at: https://www.epa.gov/
ttn/amtic/pmqainf.html.
*
*
*
*
*
6. Appendix N to part 50 is revised to
read as follows:
Appendix N to Part 50—Interpretation
of the National Ambient Air Quality
Standards for PM2.5
1. General.
(a) This appendix explains the data
handling conventions and computations
necessary for determining when the annual
and 24-hour primary and secondary national
ambient air quality standards (NAAQS) for
PM2.5 specified in § 50.7 and § 50.13 of this
part are met. PM2.5, defined as particles with
an aerodynamic diameter less than or equal
to a nominal 2.5 micrometers, is measured in
the ambient air by a Federal reference
method (FRM) based on appendix L of this
part, as applicable, and designated in
accordance with part 53 of this chapter, or by
a Federal equivalent method (FEM)
designated in accordance with part 53 of this
chapter. Data handling and computation
procedures to be used in making
comparisons between reported PM2.5
concentrations and the levels of the PM2.5
NAAQS are specified in the following
sections.
(b) Data resulting from exceptional events,
for example structural fires or high winds,
may be given special consideration. In some
cases, it may be appropriate to exclude these
data in whole or part because they could
result in inappropriate values to compare
with the levels of the PM2.5 NAAQS. In other
cases, it may be more appropriate to retain
the data for comparison with the levels of the
PM2.5 NAAQS and then for EPA to formulate
the appropriate regulatory response.
(c) The terms used in this appendix are
defined as follows:
Annual mean refers to a weighted
arithmetic mean, based on quarterly means,
as defined in section 4.4 of this appendix.
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Daily values for PM2.5 refers to the 24-hour
average concentrations of PM2.5 calculated
(averaged from hourly measurements) or
measured from midnight to midnight (local
standard time).
Designated monitors are those monitoring
sites designated in a State or local agency PM
Monitoring Network Description in
accordance with part 58 of this chapter.
Design values are the metrics (i.e.,
statistics) that are compared to the NAAQS
levels to determine compliance, calculated as
shown in section 4 of this appendix:
(1) The 3-year average of annual means for
a single monitoring site or a group of
monitoring sites (referred to as the ‘‘annual
standard design value’’). If spatial averaging
has been approved by EPA for a group of
sites which meet the criteria specified in
section 2(b) of this appendix and section
4.7.5 of appendix D of 40 CFR part 58, then
3 years of spatially averaged annual means
will be averaged to derive the annual
standard design value for that group of sites
(further referred to as the ‘‘spatially averaged
annual standard design value’’). Otherwise,
the annual standard design value will
represent the 3-year average of annual means
for a single site (further referred to as the
‘‘single site annual standard design value’’).
(2) The 3-year average of annual 98th
percentile 24-hour average values recorded at
each monitoring site (referred to as the ‘‘24hour standard design value’’).
98th percentile is the daily value out of a
year of PM2.5 monitoring data below which
98 percent of all daily values fall.
Year refers to a calendar year.
2.0 Monitoring Considerations.
(a) Section 58.30 of this chapter specifies
which monitoring locations are eligible for
making comparisons with the PM2.5
standards.
(b) To qualify for spatial averaging,
monitoring sites must meet the criterion
specified in section 4.7.5 of appendix D of 40
CFR part 58 as well as the following
requirements:
(1) The annual mean concentration at each
site shall be within 10 percent of the spatially
averaged annual mean.
(2) The daily values for each site pair shall
yield a correlation coefficient of at least 0.9
for each calendar quarter.
(3) All of the monitoring sites should
principally be affected by the same major
emission sources of PM2.5. This can be
demonstrated by site-specific chemical
speciation profiles confirming all major
component concentration averages to be
within 10 percent for each calendar quarter.
(4) The requirements in paragraphs (b)(1)
through (3) of this section shall be met for 3
consecutive years in order to produce a valid
spatially averaged annual standard design
value. Otherwise, the individual (single) site
annual standard design values shall be
compared directly to the level of the annual
NAAQS.
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(c) Section 58.12 of this chapter specifies
the required minimum frequency of sampling
for PM2.5. Exceptions to the specified
sampling frequencies, such as a reduced
frequency during a season of expected low
concentrations (i.e., ‘‘seasonal sampling’’),
are subject to the approval of EPA. Annual
98th percentile values are to be calculated
according to equation 6 in section 4.5 of this
appendix when a site operates on a ‘‘seasonal
sampling’’ schedule.
3.0 Requirements for Data Used for
Comparisons With the PM2.5 NAAQS and
Data Reporting Considerations.
(a) Except as otherwise provided in this
appendix, only valid FRM/FEM PM2.5 data
required to be submitted to EPA’s Air Quality
System (AQS) shall be used in the design
value calculations.
(b) PM2.5 measurement data (typically
hourly for continuous instruments and daily
for filter-based instruments) shall be reported
to AQS in micrograms per cubic meter (µg/
m3) to one decimal place, with additional
digits to the right being truncated.
(c) Block 24-hour averages shall be
computed from available hourly PM2.5
concentration data for each corresponding
day of the year and the result shall be stored
in the first, or start, hour (i.e., midnight, hour
‘0’) of the 24-hour period. A 24-hour average
shall be considered valid if at least 75
percent (i.e., 18) of the hourly averages for
the 24-hour period are available. In the event
that less than all 24 hourly averages are
available (i.e., less than 24, but at least 18),
the 24-hour average shall be computed on the
basis of the hours available using the number
of available hours as the divisor (e.g., 19). 24hour periods with seven or more missing
hours shall be considered valid if, after
substituting zero for all missing hourly
concentrations, the 24-hour average
concentration is greater than the level of the
standard. The computed 24-hour average
PM2.5 concentrations shall be reported to one
decimal place (the insignificant digits to the
right of the third decimal place are truncated,
consistent with the data handling procedures
for the reported data).
(d) Except for calculation of spatially
averaged annual means and spatially
averaged annual standard design values, all
other calculations shown in this appendix
shall be implemented on a site-level basis.
Site level data shall be processed as follows:
(1) The default dataset for a site shall
consist of the measured concentrations
recorded from the designated primary FRM/
FEM monitor. The primary monitor shall be
designated in the appropriate State or local
agency PM Monitoring Network Description.
(2) Data for the primary monitor shall be
augmented as necessary with data from
collocated FRM/FEM monitors. If a valid 24hour measurement is not produced from the
primary monitor for a particular required
sampling day, but a valid sample is generated
by a collocated FRM/FEM instrument (and
recorded in AQS), then that collocated value
shall be considered part of the site data
record. If more than one valid collocated
FRM/FEM value is available, the average of
those valid collocated values shall be used as
the site value for the day.
4.0 Comparisons with the PM2.5 NAAQS.
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15:50 Jan 13, 2006
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4.1 Annual PM2.5 NAAQS.
(a) The annual PM2.5 NAAQS is met when
the annual standard design value is less than
or equal to 15.0 micrograms per cubic meter
(µg/m3).
(b) For single site comparisons, 3 years of
valid annual means are required to produce
a valid annual standard design value. In the
case of spatial averaging, 3 years of valid
spatially averaged annual means are required
to produce a valid annual standard design
value. Designated sites with less than 3 years
of data shall be included in annual spatial
averages for those years that data
completeness requirements are met. A year
meets data completeness requirements when
at least 75 percent of the scheduled sampling
days for each quarter have valid data.
However, years with high concentrations and
at least 11 samples in each quarter shall be
considered valid, notwithstanding quarters
with less than complete data, if the resulting
annual mean, spatially averaged annual mean
concentration, or resulting annual standard
design value concentration (rounded
according to the conventions of section 4.3 of
this appendix) is greater than the level of the
standard. Furthermore, where the explicit 11
sample per quarter requirement is not met,
the site annual mean shall still be considered
valid if, by substituting a low value
(described below) for the missing data in the
deficient quarters (substituting enough to
meet the 11 sample minimum), the
computation still yields a recalculated
annual mean, spatially averaged annual mean
concentration, or annual standard design
value concentration over the level of the
standard. The low value used for this
substitution test shall be the lowest reported
value in the site data record for that calendar
quarter over the most recent 3-year period. If
an annual mean is deemed complete using
this test, the original annual mean (without
substituted low values) shall be considered
the official mean value for this site, not the
result of the recalculated test using the low
values.
(c) The use of less than complete data is
subject to the approval of EPA, which may
consider factors such as monitoring site
closures/moves, monitoring diligence, and
nearby concentrations in determining
whether to use such data.
(d) The equations for calculating the
annual standard design values are given in
section 4.4 of this appendix.
4.2 24-Hour PM2.5 NAAQS.
(a) The 24-hour PM2.5 NAAQS is met when
the 24-hour standard design value at each
monitoring site is less than or equal to 35 µg/
m3. This comparison shall be based on 3
consecutive, complete years of air quality
data. A year meets data completeness
requirements when at least 75 percent of the
scheduled sampling days for each quarter
have valid data. However, years with high
concentrations shall be considered valid,
notwithstanding quarters with less than
complete data (even quarters with less than
11 samples), if the resulting annual 98th
percentile value or resulting 24-hour
standard design value (rounded according to
the conventions of section 4.3 of this
appendix) is greater than the level of the
standard.
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(b) The use of less than complete data is
subject to the approval of EPA which may
consider factors such as monitoring site
closures/moves, monitoring diligence, and
nearby concentrations in determining
whether to use such data.
(c) The equations for calculating the 24hour standard design values are given in
section 4.5 of this appendix.
4.3 Rounding Conventions. For the
purposes of comparing calculated values to
the applicable level of the standard, it is
necessary to round the final results of the
calculations described in sections 4.4 and 4.5
of this appendix. Results for all intermediate
calculations shall not be rounded.
(a) Annual PM2.5 standard design values
shall be rounded to the nearest 0.1 µg/m3
(decimals 0.05 and greater are rounded up to
the next 0.1, and any decimal lower than 0.05
is rounded down to the nearest 0.1).
(b) 24-hour PM2.5 standard design values
shall be rounded to the nearest 1 µg/m3
(decimals 0.5 and greater are rounded up to
the nearest whole number, and any decimal
lower than 0.5 is rounded down to the
nearest whole number).
4.4 Equations for the Annual PM2.5
NAAQS.
(a) An annual mean value for PM2.5 is
determined by first averaging the daily values
of a calendar quarter using equation 1 of this
appendix:
Equation 1
X q , y ,s =
1
nq
nq
∑X
i , q , y ,s
i =1
Where:
¯
xq, y, s = the mean for quarter q of year y for
site s;
nq = the number of monitored values in the
quarter; and
xi, q, y, s = the ith value in quarter q for year
y for site s.
(b) Equation 2 of this appendix is then
used to calculate the site annual mean:
Equation 2
X y ,s =
1 4
∑ X q , y ,s
4 q =1
Where:
¯
xy,s = the annual mean concentration for year
y (y = 1, 2, or 3) and for site s; and
¯
xq,y,s = the mean for quarter q of year y for
site s.
(c) If spatial averaging is utilized, the sitebased annual means will then be averaged
together to derive the spatially averaged
annual mean using equation 3 of this
appendix. Otherwise (i.e., for single site
comparisons), skip to equation 4.b of this
appendix.
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Where:
¯
xy = the spatially averaged mean for year y,
¯
xy,s = the annual mean for year y and site s,
and
ns = the number of sites designated to be
averaged.
(d) The annual standard design value is
calculated using equation 4A of this
appendix when spatial averaging and
equation 4B of this appendix when not
spatial averaging:
Where:
¯
x = the annual standard design value (the
spatially averaged annual standard
design value for equation 4A of this
appendix and the single site annual
standard design value for equation 4B of
this appendix); and
xy = the spatially averaged annual mean for
year y (result of equation 3 of this
appendix) when spatial averaging is
used, or
¯
xy,s = the annual mean for year y and site s
(result of equation 2 of this appendix)
when spatial averaging is not used.
(e) The annual standard design value is
rounded according to the conventions in
section 4.3 of this appendix before a
comparison with the standard is made.
4.5 Equations for the 24-Hour PM2.5
NAAQS.
(a) When the data for a particular site and
year meet the data completeness
requirements in section 4.2 of this appendix,
calculation of the 98th percentile is
accomplished by the steps provided in this
subsection. Equation 5 of this appendix shall
be used to compute annual 98th percentile
values, except that where a site operates on
an approved seasonal sampling schedule,
equation 6 of this appendix shall be used
instead. Seasonal sampling, when approved,
will be implemented in periods of calendar
quarters or months; seasonal sampling
seasons shall not divide months. Calculations
of all annual 98th percentile values are based
on the applicable number of samples (as
described below), rather than on the actual
number of samples. For the 24-hour NAAQS,
credit will not be granted for more samples
than the maximum number of scheduled
sampling days in the sampling period. For
each month, the applicable number of
samples is the lower of the actual number of
samples and the scheduled number of
samples. The applicable number of samples
for a year is the sum of the twelve monthly
‘‘applicable number of samples’; the
applicable number of samples for a season is
the sum of the corresponding monthly
‘‘applicable number of samples’’. 98th
percentile values shall be calculated as in
equations 5 or 6 of this appendix using the
applicable number of samples for the year or
season. [The applicable number of samples
will determine how deep to go into the data
distribution, but all samples (scheduled or
not) will be considered when making the
percentile assignment.]
(1) Regular formula for computing annual
98th percentile values. Sort all the daily
values from a particular site and year by
ascending value. (For example: (x[1], x[2],
x[3], * * *, x[n]). In this case, x[1] is the
smallest number and x[n] is the largest
value.) The 98th percentile is determined
from this sorted series of daily values which
is ordered from the lowest to the highest
number. Compute (0.98) × (an) as the number
‘‘i.d’’, where ‘an’ is the annual applicable
number of samples, ‘‘i’’ is the integer part of
the result, and ‘‘d’’ is the decimal part of the
result. The 98th percentile value for year y,
P0.98,y, is calculated using equation 5 of this
appendix:
Where:
dHigh = number of calendar days in the
‘‘High’’ season;
dLow = number of calendar days in the ‘‘Low’’
season;
dHigh + dLow = days in a year; and
Equation 3
1
ns
ns
∑x
y ,s
s =1
Where:
P0.98,y = 98th percentile for year y;
x[i+1] = the (i+1)th number in the ordered
series of numbers; and
i = the integer part of the product of 0.98 and
an.
(2) Formula for computing annual 98th
percentile values when sampling frequencies
are seasonal. Calculate the annual 98th
percentiles by determining the smallest
measured concentration, x, that makes W(x)
greater than 0.98 using equation 6 of this
appendix:
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xy =
Such that ‘‘a’’ can be either ‘‘High’’ or ‘‘Low’’
‘‘x’’ is the measured concentration; and
‘‘dHigh/(dHigh + dLow) and dLow/(dHigh + dLow)’’
are constant and are called seasonal
‘‘weights.’’
(b) The 24-hour standard design value is
then calculated by averaging the annual 98th
percentiles using equation 7 of this appendix:
(c) The 24-hour standard design value (3year average 98th percentile) is rounded
according to the conventions in section 4.3
of this appendix before a comparison with
the standard is made.
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7. Appendix O to part 50 is added to
read as follows:
Appendix O to Part 50—Reference
Method for the Determination of Coarse
Particulate Matter as PM10-2.5 in the
Atmosphere
1.0 Applicability and Definition.
1.1 This method provides for the
measurement of the mass concentration
of coarse particulate matter (PM10-2.5) in
ambient air over a 24-hour period for
purposes of determining whether the
primary and secondary NAAQS for
coarse particulate matter specified in
§ 50.13 of this chapter are met.
1.2 For the purpose of this method,
PM10-2.5 is defined as particulate matter
having an aerodynamic diameter in the
nominal range of 2.5 to 10 micrometers,
inclusive.
1.3 For this reference method,
PM10-2.5 concentrations shall be
measured as the arithmetic difference
between separate but concurrent,
collocated measurements of PM10 and
PM2.5, where the PM10 measurements
are obtained with a specially approved
sampler, identified as a ‘‘PM10c
sampler,’’ that meets more demanding
performance requirements than
conventional PM10 samplers described
in appendix J of this part. Measurements
obtained with a PM10c sampler are
identified as ‘‘PM10c measurements’’ to
distinguish them from conventional
PM10 measurements obtained with
conventional PM10 samplers. Thus,
PM10-2.5 = PM10c ¥ PM2.5.
1.4 The PM10c and PM2.5 gravimetric
measurement processes are considered
to be nondestructive, and the PM10c and
PM2.5 samples obtained in the PM10-2.5
measurement process can be subjected
to subsequent physical or chemical
analyses.
1.5 Quality assessment procedures
are provided in part 58, appendix A of
this chapter. The quality assurance
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procedures and guidance provided in
reference 1 in section 13 of this
appendix, although written specifically
for PM2.5, are generally applicable for
PM10c, and, hence, PM10-2.5
measurements under this method, as
well.
1.6 A method based on specific
model PM10c and PM2.5 samplers will be
considered a reference method for
purposes of part 58 of this chapter only
if:
(a) The PM10c and PM2.5 samplers and
the associated operational procedures
meet the requirements specified in this
appendix and all applicable
requirements in part 53 of this chapter,
and
(b) The method based on the specific
samplers and associated operational
procedures has been designated as a
reference method in accordance with
part 53 of this chapter.
1.7 PM10-2.5 methods based on
samplers that meet nearly all
specifications set forth in this method
but have one or more significant but
minor deviations or modifications from
those specifications may be designated
as ‘‘Class I’’ equivalent methods for
PM10-2.5 in accordance with part 53 of
this chapter.
1.8 PM2.5 measurements obtained
incidental to the PM10-2.5 measurements
by this method shall be considered to
have been obtained with a reference
method for PM2.5 in accordance with
appendix L of this part.
1.9 PM10c measurements obtained
incidental to the PM10-2.5 measurements
by this method shall be considered to
have been obtained with a reference
method for PM10 in accordance with
appendix J of this part, provided that:
(a) The PM10c measurements are
adjusted to EPA reference conditions
(25°C and 760 millimeters of mercury),
and
(b) Such PM10c measurements are
appropriately identified to differentiate
them from PM10 measurements obtained
with other (conventional) methods for
PM10 designated in accordance with
part 53 of this chapter as reference or
equivalent methods for PM10.
2.0 Principle.
2.1 Separate, collocated, electrically
powered air samplers for PM10c and
PM2.5 concurrently draw ambient air at
identical, constant volumetric flow rates
into specially shaped inlets and through
one or more inertial particle size
separators where the suspended
particulate matter in the PM10 or PM2.5
size range, as applicable, is separated for
collection on a polytetrafluoroethylene
(PTFE) filter over the specified sampling
period. The air samplers and other
aspects of this PM10-2.5 reference method
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are specified either explicitly in this
appendix or by reference to other
applicable regulations or quality
assurance guidance.
2.2 Each PM10c and PM2.5 sample
collection filter is weighed (after
moisture and temperature conditioning)
before and after sample collection to
determine the net weight (mass) gain
due to collected PM10c or PM2.5. The
total volume of air sampled by each
sampler is determined by the sampler
from the measured flow rate at local
ambient temperature and pressure and
the sampling time. The mass
concentrations of both PM10c and PM2.5
in the ambient air are computed as the
total mass of collected particles in the
PM10 or PM2.5 size range, as appropriate,
divided by the total volume of air
sampled by the respective samplers, and
expressed in micrograms per cubic
meter (µ/m3)at local temperature and
pressure conditions. The mass
concentration of PM10-2.5 is determined
as the PM10c concentration value less
the corresponding, concurrently
measured PM2.5 concentration value.
2.3 Most requirements for PM10-2.5
reference methods are similar or
identical to the requirements for PM2.5
reference methods as set forth in
appendix L to this part. To insure
uniformity, applicable appendix L
requirements are incorporated herein by
reference in the sections where
indicated rather than repeated in this
appendix.
3.0 PM10-2.5 Measurement Range.
3.1 Lower concentration limit. The
lower detection limit of the mass
concentration measurement range is
estimated to be approximately 3 µg/m3,
based on the observed precision of PM2.5
measurements in the national PM2.5
monitoring network, the probable
similar level of precision for the
matched PM10c measurements, and the
additional variability arising from the
differential nature of the measurement
process. This value is provided merely
as a guide to the significance of low
PM10-2.5 concentration measurements.
3.2 Upper concentration limit. The
upper limit of the mass concentration
range is determined principally by the
PM10c filter mass loading beyond which
the sampler can no longer maintain the
operating flow rate within specified
limits due to increased pressure drop
across the loaded filter. This upper limit
cannot be specified precisely because it
is a complex function of the ambient
particle size distribution and type,
humidity, the individual filter used, the
capacity of the sampler flow rate control
system, and perhaps other factors. All
PM10c samplers are estimated to be
capable of measuring 24-hour mass
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concentrations of at least 200 µg/m3
while maintaining the operating flow
rate within the specified limits. The
upper limit for the PM10-2.5
measurement is likely to be somewhat
lower because the PM10-2.5 concentration
represents only a fraction of the PM10
concentration.
3.3 Sample period. The required
sample period for PM10-2.5 concentration
measurements by this method shall be
at least 1,380 minutes but not more than
1,500 minutes (23 to 25 hours), and the
start times of the PM2.5 and PM10c
samples are within 10 minutes and the
stop times of the samples are also
within 10 minutes (see section 10.4 of
this appendix). However, a PM10-2.5
measured concentration where the
actual sample period for PM10c sample
is less than 1,380 minutes, but the
corresponding PM2.5 sample period is at
least 1,380 minutes, may be used as if
it were a valid concentration
measurement for the specific purpose of
determining an exceedance of the
NAAQS. For this purpose, the measured
PM10c concentration is determined as
the PM10c mass collected divided by the
actual sampled air volume, multiplied
by the actual number of minutes in the
PM10c sample period and divided by
1,440; the PM10-2.5 concentration is then
calculated as prescribed in section 12.4
of this appendix. This value represents
the minimum nominal PM10-2.5
concentration that could have been
measured for the full sample period.
Accordingly, if the value thus calculated
is high enough to be an exceedance,
such an exceedance would be a valid
exceedance for the sample period. When
reported to AQS, this data value should
receive a special data qualifier code to
identify it as having an insufficient
sample period.
4.0 Accuracy (bias).
4.1 Because the size, density, and
volatility of the particles making up
ambient particulate matter vary over
wide ranges and the mass concentration
of particles varies with particle size, it
is difficult to define the accuracy of
PM10-2.5 measurements in an absolute
sense. Furthermore, generation of
credible PM10-2.5 concentration
standards at field monitoring sites and
presenting or introducing such
standards reliably to samplers or
monitors to assess accuracy is still
generally impractical. The accuracy of
PM10-2.5 measurements is therefore
defined in a relative sense as bias,
referenced to measurements provided
by other reference method samplers or
based on flow rate verification audits or
checks, or on other performance
evaluation procedures.
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4.2 Measurement system bias for
monitoring data is assessed according to
the procedures and schedule set forth in
part 58, appendix A of this chapter. The
goal for the measurement uncertainty
(as bias) for monitoring data is defined
in part 58, appendix A of this chapter
as an upper 95 percent confidence limit
for the absolute bias of 15 percent.
Reference 1 in section 13 of this
appendix provides additional
information and guidance on flow rate
accuracy audits and assessment of bias.
5.0 Precision.
5.1 Tests to establish initial
measurement precision for each sampler
of the reference method sampler pair are
specified as a part of the requirements
for designation as a reference method
under part 53 of this chapter.
5.2 Measurement system precision is
assessed according to the procedures
and schedule set forth in appendix A to
part 58 of this chapter. The goal for
acceptable measurement uncertainty, as
precision, of monitoring data is defined
in part 58, appendix A of this chapter
as an upper 95 percent confidence limit
for the coefficient of variation (CV) of 15
percent. Reference 1 in section 13 of this
appendix provides additional
information and guidance on this
requirement.
6.0 Filters for PM10c and PM2.5
Sample Collection. Sample collection
filters for both PM10c and PM2.5
measurements shall be identical and as
specified in section 6 of appendix L to
this part.
7.0 Sampler. The PM10-2.5 sampler
shall consist of a PM10c sampler and a
PM2.5 sampler, as follows:
7.1 The PM2.5 sampler shall be as
specified in section 7 of appendix L to
this part.
7.2 The PM10c sampler shall be of
like manufacturer, design,
configuration, and fabrication to that of
the PM2.5 sampler and as specified in
section 7 of appendix L to this part,
except as follows:
7.2.1 The particle size separator
specified in section 7.3.4 of appendix L
to this part shall be eliminated and
replaced by a downtube extension
fabricated as specified in Figure O–1 of
this appendix.
7.2.2 The sampler shall be identified
as a PM10c sampler on its identification
label required under § 53.9(d) of this
chapter.
7.2.3 The average temperature and
average barometric pressure measured
by the sampler during the sample
period, as described in Table L–1 of
appendix L to this part, need not be
reported to EPA’s AQS data base, as
required by section 7.4.19 and Table L–
1 of appendix L to this part, provided
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such measurements for the sample
period determined by the associated
PM2.5 sampler are reported as required.
7.3 In addition to the operation/
instruction manual required by section
7.4.18 of appendix L to this part for each
sampler, supplemental operational
instructions shall be provided for the
simultaneous operation of the samplers
as a pair to collect concurrent PM10c and
PM2.5 samples. The supplemental
instructions shall cover any special
procedures or guidance for installation
and setup of the samplers for PM10-2.5
measurements, such as synchronization
of the samplers’ clocks or timers, proper
programming for collection of
concurrent samples, and any other
pertinent issues related to the
simultaneous, coordinated operation of
the two samplers.
7.4 Capability for electrical
interconnection of the samplers to
simplify sample period programming
and further ensure simultaneous
operation is encouraged but not
required. Any such capability for
interconnection shall not supplant each
sampler’s capability to operate
independently, as required by section 7
of appendix L of this part.
8.0 Filter Weighing.
8.1 Conditioning and weighing for
both PM10c and PM2.5 sample filters
shall be as specified in section 8 of
appendix L to this part. See reference 1
of section 13 of this appendix for
additional, more detailed guidance.
8.2 Handling, conditioning, and
weighing for both PM10c and PM2.5
sample filters shall be matched such
that the corresponding PM10c and PM2.5
filters of each filter pair receive uniform
treatment. The PM10c and PM2.5 sample
filters should be weighed on the same
balance, preferably in the same
weighing session and by the same
analyst.
8.3 Due care shall be exercised to
accurately maintain the paired
relationship of each set of concurrently
collected PM10c and PM2.5 sample filters
and their net weight gain data and to
avoid misidentification or reversal of
the filter samples or weight data. See
Reference 1 of section 13 of this
appendix for additional guidance.
9.0 Calibration. Calibration of the
flow rate, temperature measurement,
and pressure measurement systems for
both the PM10c and PM2.5 samplers shall
be as specified in section 9 of appendix
L to this part.
10.0 PM10-2.5 Measurement
Procedure.
10.1 The PM10c and PM2.5 samplers
shall be installed at the monitoring site
such that their ambient air inlets differ
in vertical height by not more than 0.2
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maintained as described in section 11 of
appendix L to this part.
12.0 Calculations.
12.1 Both concurrent PM10c and
PM2.5 measurements must be available,
valid, and meet the conditions of
section 10.4 of this appendix to
determine the PM10-2.5 mass
concentration.
12.2 The PM10c mass concentration
is calculated using equation 1 of this
section:
Where:
PM10c = mass concentration of PM10c,
µg/m3;
Wf, Wi = final and initial masses
(weights), respectively, of the filter
used to collect the PM10c particle
sample, µg;
Va = total air volume sampled by the
PM10c sampler in actual volume
units measured at local conditions
of temperature and pressure, as
provided by the sampler, m3.
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Note: Total sample time must be between
1,380 and 1,500 minutes (23 and 25 hrs) for
a fully valid PM10c sample; however, see also
section 3.3 of this appendix.
12.3 The PM2.5 mass concentration
is calculated as specified in section 12
of appendix L to this part.
12.4 The PM10-2.5 mass
concentration, in µg/m3, is calculated
using Equation 2 of this section:
13.0 Reference.
1. Quality Assurance Guidance
Document 2.12. Monitoring PM2.5 in
Ambient Air Using Designated
Reference or Class I Equivalent
Methods. Draft, November 1998 (or later
version or supplement, if available).
Available at: https://www.epa.gov/ttn/
amtic/pgqa.html.
14.0 Figures.
Figures O–1 is included as part of this
appendix O.
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meter, if possible, but in any case not
more than 1 meter, and the vertical axes
of their inlets are separated by at least
1 meter but not more than 4 meters,
horizontally.
10.2 The measurement procedure for
PM10c shall be as specified in section 10
of appendix L to this part, with ‘‘PM10c’’
substituted for ‘‘PM2.5’’ wherever it
occurs in that section.
10.3 The measurement procedure for
PM2.5 shall be as specified in section 10
of appendix L to this part.
10.4 For the PM10-2.5 measurement,
the PM10c and PM2.5 samplers shall be
programmed to operate on the same
schedule and such that the sample
period start times are within 5 minutes
and the sample duration times are
within 5 minutes.
10.5 Retrieval, transport, and storage
of each PM10c and PM2.5 sample pair
following sample collection shall be
matched to the extent practical such
that both samples experience uniform
conditions.
11.0 Sampler Maintenance. Both
PM10c and PM2.5 samplers shall be
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8. Appendix P is added to part 50 to
read as follows:
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Appendix P to Part 50—Interpretation
of the National Ambient Air Quality
Standards for PM10-2.5
1.0 General.
(a) This appendix explains the data
handling conventions and computations
necessary for determining when the 24-hour
primary and secondary national ambient air
quality standards (NAAQS) for PM10-2.5
specified in § 50.13 of this part are met.
PM10-2.5, defined as particles with an
aerodynamic diameter more than a nominal
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2.5 micrometers and less than or equal to a
nominal 10.0 micrometers, is measured in
the ambient air by a Federal reference
method (FRM) based on appendix O of this
part, as applicable, and designated in
accordance with part 53 of this chapter, or by
a Federal equivalent method (FEM)
designated in accordance with part 53 of this
chapter. Data handling and computation
procedures to be used in making
comparisons between reported PM10-2.5
concentrations and the levels of the PM10-2.5
NAAQS are specified in the following
sections.
(b) Data resulting from exceptional events,
for example structural fires or high winds,
may require special consideration. In some
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cases, it may be appropriate to exclude these
data in whole or part because they could
result in inappropriate values to compare
with the levels of the PM10-2.5 NAAQS. In
other cases, it may be more appropriate to
retain the data for comparison with the levels
of the PM10-2.5 NAAQS and then allow EPA
to formulate the appropriate regulatory
response.
(c) The terms used in this appendix are
defined as follows:
Daily values for PM10-2.5 refers to the 24hour average concentrations of PM10-2.5
calculated (averaged) or measured from
midnight to midnight (local standard time).
Designated monitors are those monitoring
sites designated in a State or local agency PM
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Monitoring Network Description in
accordance with part 58 of this chapter.
Design values are the metrics that are
compared to the NAAQS levels to determine
compliance and are comprised of the 3-year
average of annual 98th percentile 24-hour
average values recorded at each monitoring
location, are referred to as ‘‘24-hour standard
design values,’’ and are calculated as shown
in section 3 of this appendix.
Geographic area design value (e.g., one for
a county or defined metropolitan area) is the
highest valid site-level design value in that
area.
98th percentile means the daily value out
of a year of PM10-2.5 monitoring data below
which 98 percent of all values in the group
fall.
Year refers to a calendar year.
2.0 Requirements for data used for
comparisons with the PM10-2.5 NAAQS and
data reporting considerations.
(a) Appendix D to part 58 of this chapter
specifies which monitors are eligible for
making comparisons with the PM10-2.5
standards.
(b) Except as otherwise provided in this
appendix, only valid FRM/FEM PM10-2.5 data
required to be submitted to EPA’s Air Quality
System (AQS) shall be used in the design
value calculations.
(c) Raw concentration data (typically
hourly for automated continuous instruments
and daily for manual, filter-based
instruments) shall be reported to AQS in
micrograms per cubic meter (µg/m3) to one
decimal place, with additional digits to the
right being truncated.
(d) Block 24-hour averages shall be
computed from available hourly PM10-2.5
concentration data for each corresponding
day of the year and the result shall be stored
in the first, or start, hour (i.e., midnight, hour
‘‘0’’) of the 24-hour period. A 24-hour average
shall be considered valid if at least 75
percent (i.e., 18) of the hourly averages for
the 24-hour period are available. In the event
that less than all 24 hourly averages are
available (i.e., less than 24, but at least 18),
the 24-hour average shall be computed on the
basis of the hours available using the number
of available hours as the divisor (e.g., 19). 24hour periods with 7 or more missing hours
shall be considered valid if, after substituting
zero for the missing hourly concentrations,
the 24-hour average concentration is greater
than the level of the standard. The computed
24-hour average PM10-2.5 concentrations shall
be reported to one decimal place (the
insignificant digits to the right of the third
decimal place are truncated, consistent with
the data handling procedures for the reported
data).
(e) All calculations shall be implemented
on a site-level basis. Site level data shall be
processed as follows:
(1) The default dataset for a site shall
consist of the measured concentrations
recorded from the designated primary FRM/
FEM monitor. The primary monitor shall be
designated in the appropriate State or local
agency PM Monitoring Network Description.
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(2) Data for the primary monitor shall be
augmented as necessary with data from
collocated FRM/FEM monitors. If a valid 24hour measurement is not produced from the
primary monitor for a particular required
sampling day, but a valid sample is generated
by a collocated FRM/FEM instrument (and
recorded in AQS), then that collocated value
shall be considered part of the site data
record. If more than one valid collocated
FRM/FEM value is available, the average of
those valid collocated values shall be used as
the site value for the day.
3.0 Comparisons with the PM10-2.5
NAAQS.
3.1 24-Hour PM10-2.5 NAAQS.
(a) The 24-hour PM10-2.5 NAAQS is met
when the 24-hour standard design value at
each monitoring site is less than or equal to
70 µg/m3. This comparison shall be based on
3 consecutive, complete years of air quality
data. A year meets data completeness
requirements when at least 75 percent of the
scheduled sampling days for each quarter
have valid data. However, years or 3-year
periods with high concentrations shall be
considered valid, notwithstanding quarters
with less than complete data (even quarters
with less than 11 samples), if the resulting
annual 98th percentile value or resulting 24hour standard design value (rounded
according to the conventions of section 3.2 of
this appendix) is greater than the level of the
standard.
(b) The use of less than complete data is
subject to the approval of EPA, which may
consider factors such as monitoring site
closures/moves, monitoring diligence, and
nearby concentrations in determining
whether to use such data.
(c) The equations for calculating the 24hour standard design values are given in
section 3.4 of this appendix.
3.2 Rounding Conventions. For the
purposes of comparing calculated values to
the applicable level of the standard, it is
necessary to round the final results of the
calculations described in sections 3.4 of this
appendix. 24-hour PM10-2.5 standard design
values shall be rounded to the nearest 1 µg/
m3 (decimals 0.5 and greater are rounded up
to nearest whole number, and any decimal
lower than 0.5 is rounded down to the
nearest whole number).
3.3 Sampling Frequency Considerations.
Section 58.12 of this chapter specifies the
required minimum frequency of sampling for
PM10-2.5. Exceptions to the specified sampling
frequencies, such as a reduced frequency
during a season of expected low
concentrations (i.e., ‘‘seasonal sampling’’),
are subject to the approval of EPA. Annual
98th percentile values are to be calculated
according to equation 2 in section 3.4 of this
appendix when a site operates on a ‘‘seasonal
sampling’’ schedule.
3.4 Equations for the 24-Hour PM10-2.5
NAAQS.
(a) When the data for a particular site and
year meet the data completeness
requirements in section 3.1 of this appendix,
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calculation of the 98th percentile is
accomplished by the steps provided in
paragraphs (a) through (c) of this section.
Equation 1 of this appendix shall be used to
compute annual 98th percentile values,
except that where a site operates on an
approved seasonal sampling schedule,
equation 2 of this appendix shall be used
instead. Seasonal sampling, when approved,
will be implemented in periods of calendar
quarters or months; seasonal sampling
seasons shall not divide months. Calculations
of all annual 98th percentile values are based
on the applicable number of samples (as
described below), rather than on the actual
number of samples. For the 24-hour NAAQS,
credit will not be granted for more samples
than the maximum number of scheduled
sampling days in the sampling period. For
each month, the applicable number of
samples is the lower of the actual number of
samples and the scheduled number of
samples. The applicable number of samples
for a year is the sum of the twelve monthly
‘‘applicable number of samples;’’ the
applicable number of samples for a season is
the sum of the corresponding monthly
‘‘applicable number of samples.’’ 98th
percentile values shall be calculated as in
equations 5 or 6 of this appendix using the
applicable number of samples for the year or
season. The applicable number of samples
will determine how deep to go into the data
distribution, but all samples (scheduled or
not) will be considered when making the
percentile assignment.
(1) Regular formula for computing annual
98th percentile values. Sort all the daily
values from a particular site and year by
ascending value. (For example: x[1], x[2],
x[3], * * *, x[n]. In this case, x[1] is the
smallest number and x[n] is the largest
value.) The 98th percentile is determined
from this sorted series of daily values.
Compute (0.98) x (an) as the number ‘‘i.d,’’
where ‘‘an’’ is the applicable number of
samples, ‘‘i’’ is the integer part of the result,
and ‘‘d’’ is the decimal part of the result. The
98th percentile value for year y, P0.98,y, is
calculated using equation 1 of this appendix:
Where:
P0.98,y = 98th percentile for year y;
x[i+1] = the (i+1)th number in the ascending
ordered series of numbers for year y; and
i = the integer part of the product of 0.98 and
an.
(2) Formula for computing annual 98th
percentile values when sampling frequencies
are seasonal. Calculate the annual 98th
percentiles by determining the smallest
measured concentration, x, that makes W(x)
greater than 0.98 using equation 2 of this
appendix:
E:\FR\FM\17JAP2.SGM
17JAP2
EP17JA06.062
cchase on PROD1PC60 with PROPOSALS2
Federal Register / Vol. 71, No. 10 / Tuesday, January 17, 2006 / Proposed Rules
2708
Federal Register / Vol. 71, No. 10 / Tuesday, January 17, 2006 / Proposed Rules
dHigh = number of calendar days in the
‘‘High’’ season;
dLow = number of calendar days in the ‘‘Low’’
season;
dHigh + dLow = days in a year); and
Such that ‘‘a’’ can be either ‘‘High’’ or
‘‘Low; ’’ ‘‘x’’ is the measured concentration;
and ‘‘dHigh/(dHigh + dLow) and dLow /(dHigh +
dLow)’’ are constant and are called seasonal
‘‘weights.’’
(b) The 3-year average 98th percentile (24hour standard design value) is then
calculated by averaging the annual 98th
percentiles using equation 3 of this appendix:
(c) The 24-hour standard design value (3year average 98th percentile) is rounded
according to the conventions in section 3.2
of this appendix before a comparison with
the standard is made.
[FR Doc. 06–177 Filed 1–13–06; 8:45 am]
EP17JA06.065
BILLING CODE 6560–50–P
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Jkt 208001
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Where:
Agencies
[Federal Register Volume 71, Number 10 (Tuesday, January 17, 2006)]
[Proposed Rules]
[Pages 2620-2708]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 06-177]
[[Page 2619]]
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Part II
Environmental Protection Agency
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40 CFR Part 50
National Ambient Air Quality Standards for Particulate Matter; Proposed
Rule
Federal Register / Vol. 71, No. 10 / Tuesday, January 17, 2006 /
Proposed Rules
[[Page 2620]]
-----------------------------------------------------------------------
ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 50
[OAR-2001-0017; FRL-8015-8]
RIN 2060-AI44
National Ambient Air Quality Standards for Particulate Matter
AGENCY: Environmental Protection Agency (EPA).
ACTION: Proposed rule.
-----------------------------------------------------------------------
SUMMARY: Based on its review of the air quality criteria and national
ambient air quality standards (NAAQS) for particulate matter (PM), EPA
proposes to make revisions to the primary and secondary NAAQS for PM to
provide requisite protection of public health and welfare,
respectively, and to make corresponding revisions in monitoring
reference methods and data handling conventions for PM.
With regard to primary standards for fine particles (particles
generally less than or equal to 2.5 micrometers ([mu]m) in diameter,
PM2.5), EPA proposes to revise the level of the 24-hour
PM2.5 standard to 35 micrograms per cubic meter ([mu]g/
m3), providing increased protection against health effects
associated with short-term exposure (including premature mortality and
increased hospital admissions and emergency room visits) and to retain
the level of the annual PM2.5 standard at 15 [mu]g/
m3, continuing protection against health effects associated
with long-term exposure (including premature mortality and development
of chronic respiratory disease). The EPA solicits comment on
alternative levels of the 24-hour PM2.5 standard (down to 25
[mu]g/m3 and up to 65 [mu]g/m3) and the annual
PM2.5 standard (down to 12 [mu]g/m3), and on
alternative approaches for selecting the standard levels.
With regard to primary standards for particles generally less than
or equal to 10 [mu]m in diameter (PM10), EPA proposes to
revise the 24-hour PM10 standard in part by establishing a
new indicator for thoracic coarse particles (particles generally
between 2.5 and 10 [mu]m in diameter, PM10-2.5), qualified
so as to include any ambient mix of PM10-2.5 that is
dominated by resuspended dust from high-density traffic on paved roads
and PM generated by industrial sources and construction sources, and
excludes any ambient mix of PM10-2.5 that is dominated by
rural windblown dust and soils and PM generated by agricultural and
mining sources. The EPA proposes to set the new PM10-2.5
standard at a level of 70 [mu]g/m3, continuing to provide a
generally equivalent level of protection against health effects
associated with short-term exposure (including hospital admissions for
cardiopulmonary diseases, increased respiratory symptoms and possibly
premature mortality). Also, EPA proposes to revoke, upon finalization
of a primary 24-hour standard for PM10-2.5, the current 24-
hour PM10 standard in all areas of the country except in
areas where there is at least one monitor located in an urbanized area
(as defined by the U.S. Bureau of the Census) with a minimum population
of 100,000 that violates the current 24-hour PM10 standard
based on the most recent three years of data. In addition, EPA proposes
to revoke the current annual PM10 standard upon promulgation
of this rule. The EPA solicits comment on alternative approaches for
selecting the level of a 24-hour PM10-2.5 standard, on
alternative approaches based on retaining the current 24-hour
PM10 standard, and on revoking and not replacing the 24-hour
PM10 standard.
With regard to secondary PM standards, EPA proposes to revise the
current standards by making them identical to the suite of proposed
primary standards for fine and coarse particles, providing protection
against PM-related public welfare effects including visibility
impairment, effects on vegetation and ecosystems, and materials damage
and soiling. Also, EPA solicits comment on adding a new sub-daily
PM2.5 standard to address visibility impairment.
DATES: Written comments on this proposed decision must be received by
April 17, 2006.
ADDRESSES: Submit your comments, identified by Docket ID No. EPA-HQ-
OAR-2001-0017 by one of the following methods:
https://www.regulations.gov: Follow the on-line
instructions for submitting comments.
E-mail: a-and-r-Docket@epa.gov.
Fax: 202-566-1749.
Mail: Docket ID No. EPA-HQ-OAR-2001-0017, Environmental
Protection Agency, Mailcode: 6102T, 1200 Pennsylvania Avenue, NW.,
Washington, DC 20460. Please include a total of two copies.
Hand Delivery: Environmental Protection Agency, EPA West
Building, Room B102, 1301 Constitution Avenue, 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-
2001-0017. 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 https://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 https://
www.regulations.gov or e-mail. The https://www.regulations.gov Web site
is an ``anonymous access'' system, which means EPA will not know your
identity or contact information unless you provide it in the body of
your comment. If you send an e-mail comment directly to EPA without
going through https://www.regulations.gov your e-mail 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, 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 EPA cannot read your comment due to
technical difficulties and cannot contact you for clarification, 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 at https://www.epa.gov/
epahome/dockets.htm.
Docket: All documents in the docket are listed in the https://
www.regulations.gov index. 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, will be publicly available only in hard copy.
Publicly available docket materials are available either electronically
in https://www.regulations.gov or in hard copy at the Air and Radiation
Docket and Information Center, EPA/DC, EPA West, Room B102, 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.
Public Hearings: The EPA intends to hold public hearings around the
end of
[[Page 2621]]
February in Philadelphia, Chicago, and San Francisco, and will announce
in a separate Federal Register notice the date, time, and address of
the public hearings on this proposed decision.
FOR FURTHER INFORMATION CONTACT: Dr. Erika Sasser, mail code C539-01,
Air Quality Strategies and Standards Division, Office of Air Quality
Planning and Standards, U.S. Environmental Protection Agency, Research
Triangle Park, North Carolina 27711, telephone: (919) 541-3889, e-mail:
sasser.erika@epa.gov.
SUPPLEMENTARY INFORMATION:
General Information
A. What Should I Consider As I Prepare My Comments for EPA?
1. Submitting CBI. Do not submit this information to EPA through
https://www.regulations.gov or e-mail. Clearly mark the part or all of
the information that you claim to be CBI. For CBI information in a disk
or CD-ROM that you mail to EPA, mark the outside of the disk or CD-ROM
as CBI and then identify electronically within the disk or CD-ROM the
specific information that is claimed as CBI. In addition to one
complete version of the comment that includes information claimed as
CBI, a copy of the comment that does not contain the information
claimed as CBI must be submitted for inclusion in the public docket.
Information so marked will not be disclosed except in accordance with
procedures set forth in 40 CFR part 2.
2. Tips for Preparing Your Comments. When submitting comments,
remember to:
Identify the rulemaking by docket number and other
identifying information (subject heading, Federal Register date and
page number).
Follow directions--The agency may ask you to respond to
specific questions or organize comments by referencing a Code of
Federal Regulations (CFR) part or section number.
Explain why you agree or disagree; suggest alternatives
and substitute language for your requested changes.
Describe any assumptions and provide any technical
information and/or data that you used.
If you estimate potential costs or burdens, explain how
you arrived at your estimate in sufficient detail to allow for it to be
reproduced.
Provide specific examples to illustrate your concerns, and
suggest alternatives.
Explain your views as clearly as possible, avoiding the
use of profanity or personal threats.
Make sure to submit your comments by the comment period
deadline identified.
Availability of Related Information
A number of documents are available on EPA Web sites. The Air
Quality Criteria for Particulate Matter (Criteria Document) (two
volumes, EPA/600/P-99/002aF and EPA/600/P-99/002bF, October 2004) is
available on EPA's National Center for Environmental Assessment Web
site. To obtain this document, go to https://www.epa.gov/ncea, and click
on ``Particulate Matter''. The Staff Paper, human health risk
assessment, and several other related technical documents are available
on EPA's Office of Air Quality Planning and Standards (OAQPS)
Technology Transfer Network (TTN) Web site. The Staff Paper is
available at https://www.epa.gov/ttn/naaqs/standards/pm/s_pm_cr_
sp.html, and the risk assessment and technical documents are available
at https://www.epa.gov/ttn/naaqs/standards/pm/s_pm_cr_td.html. These
and other related documents are also available for inspection and
copying in the EPA docket identified above.
Table of Contents
The following topics are discussed in today's preamble:
I. Background
A. Legislative Requirements
B. Review of Air Quality Criteria and Standards for PM
C. Related Control Programs to Implement PM Standards
D. Overview of Current PM NAAQS Review
II. Rationale for Proposed Decisions on Primary PM2.5
Standards
A. Health Effects Related to Exposure to Fine Particles
1. Mechanisms
2. Nature of Effects
3. Integration and Interpretation of the Health Evidence
4. Sensitive Subgroups for PM2.5-Related Effects
5. PM2.5-Related Impacts on Public Health
B. Quantitative Risk Assessment
1. Overview
2. Scope and Key Components
3. Risk Estimates and Key Observations
C. Need for Revision of the Current Primary PM2.5
Standards
D. Indicator of Fine Particles
E. Averaging Time of Primary PM2.5 Standards
F. Form of Primary PM2.5 Standards
1. 24-Hour PM2.5 Standard
2. Annual PM2.5 Standard
G. Level of Primary PM2.5 Standards
1. 24-Hour PM2.5 Standard
2. Annual PM2.5 Standard
H. Proposed Decisions on Primary PM2.5 Standards
III. Rationale for Proposed Decisions on the Primary PM10
Standards
A. Health Effects Related to Exposure to Thoracic Coarse
Particles
1. Mechanisms
2. Nature of Effects
3. Integration and Interpretation of the Health Evidence
4. Sensitive Subgroups for Effects of Thoracic Coarse Particle
Exposure
5. Impacts on Public Health from Thoracic Coarse Particle
Exposure
B. Quantitative Risk Assessment
C. Need for Revision of the Current Primary PM10
Standards
D. Indicator of Thoracic Coarse Particles
E. Averaging Time of Primary PM10-2.5 Standard
F. Form of Primary PM10-2.5 Standard
G. Level of Primary PM10-2.5 Standard
H. Proposed Decisions on Primary PM10-2.5 Standard
IV. Rationale for Proposed Decisions on Secondary PM Standards
A. Visibility Impairment
1. Visibility Impairment Related to Ambient PM
2. Need for Revision of the Current Secondary PM Standards for
Visibility Protection
3. Indicator of PM for Secondary Standard to Address Visibility
Impairment
4. Averaging Time of a Secondary PM2.5 Standard for
Visibility Protection
5. Elements of a Secondary PM2.5 Standard for
Visibility Protection
B. Other PM-related Welfare Effects
1. Nature of Effects
2. Need for Revision of Current Secondary PM Standards to
Address Other PM-related Welfare Effects
C. Proposed Decision on Secondary PM Standards
V. Interpretation of the NAAQS for PM
A. Proposed Amendments to Appendix N--Interpretation of the
National Ambient Air Quality Standards for PM2.5
1. General
2. PM2.5 Monitoring and Data Reporting Considerations
3. PM2.5 Computations and Data Handling Conventions
4. Secondary Standard
5. Conforming Revisions
B. Proposed Appendix P--Interpretation of the National Ambient
Air Quality Standards for PM10-2.5
1. General
2. PM2.5 Data Reporting Considerations
3. PM10-2.5 Computations and Data Handling
Conventions
4. Exceptional Events
VI. Reference Methods for the Determination of Particulate Matter as
PM2.5 and PM10-2.5
A. Proposed Appendix O: Reference Method for the Determination
of Coarse Particulate Matter (as PM10-2.5) in the
Atmosphere
1. Purpose of the New Reference Method
2. Rationale for Selection of the New Reference Method
3. Consideration of Other Methods for the Federal Reference
Method
4. Consideration of Automated Method
5. Relationship of Proposed FRM to Transportation Equity Act
Requirements
6. Use of the Proposed Federal Reference Method
[[Page 2622]]
7. Basic Requirements of the Proposed Federal Reference Method
Sampler
8. Other Important Aspects of the Proposed Federal Reference
Method Sampler
B. Proposed Amendments to Appendix L--Reference Method for the
Determination of Fine Particulate Matter (as PM2.5) in
the Atmosphere
VIII. Statutory and Executive Order Reviews
A. Executive Order 12866: Regulatory Planning and 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 Advancement Act
J. Executive Order 12898: Federal Actions To Address
Environmental Justice in Minority Populations and Low-Income
Populations
References
I. Background
A. Legislative Requirements
Two sections of the Clean Air Act (CAA) govern the establishment
and revision of the NAAQS. Section 108 (42 U.S.C. 7408) directs the
Administrator to identify and list ``air pollutants'' that ``in his
judgment, may reasonably be anticipated to endanger public health and
welfare'' and whose ``presence * * * in the ambient air results from
numerous or diverse mobile or stationary sources'' and to issue air
quality criteria for those that are listed. Air quality criteria are
intended to ``accurately reflect the latest scientific knowledge useful
in indicating the kind and extent of identifiable effects on public
health or welfare which may be expected from the presence of [a]
pollutant in ambient air * * *.''
Section 109 (42 U.S.C. 7409) directs the Administrator to propose
and promulgate ``primary'' and ``secondary'' NAAQS for pollutants
listed under section 108. 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\
---------------------------------------------------------------------------
\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-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.''
---------------------------------------------------------------------------
In setting standards that are ``requisite'' to protect public
health and welfare, as provided in section 109(b), EPA's task is to
establish standards that are neither more nor less stringent than
necessary for these purposes. In establishing ``requisite'' primary and
secondary standards, 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).
The requirement that primary standards include 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. Lead Industries Association v. EPA, 647 F.2d 1130, 1154
(D.C. Cir 1980), cert. denied, 449 U.S. 1042 (1980); American Petroleum
Institute v. Costle, 665 F.2d 1176, 1186 (D.C. Cir. 1981), cert.
denied, 455 U.S. 1034 (1982). 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 include
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 Association v. EPA, supra, 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, EPA
considers such factors as the nature and severity of the health effects
involved, the size of the sensitive population(s) at risk, 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. Lead
Industries Association v. EPA, supra, 647 F.2d at 1161-62.
Section 109(d)(1) of the CAA requires that ``not later than
December 31, 1980, and at 5-year 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 * *
*.'' This independent review function is performed by the Clean Air
Scientific Advisory Committee (CASAC) of EPA's Science Advisory Board.
B. Review of Air Quality Criteria and Standards for PM
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.
Particles originate from a variety of anthropogenic stationary and
mobile sources as well as from natural sources. Particles may be
emitted directly or formed in the atmosphere by transformations of
gaseous emissions such as sulfur oxides (SOX), nitrogen
oxides (NOX), and volatile organic compounds (VOC). The
chemical and physical properties of PM vary greatly with time, region,
meteorology, and source category, thus complicating the assessment of
health and welfare effects.
The last review of PM air quality criteria and standards was
completed in July 1997 with notice of a final decision to revise the
existing standards (62 FR 38652, July 18, 1997). In that decision, EPA
revised the PM NAAQS in several respects. While EPA determined that the
PM NAAQS should continue to focus on particles less than or equal to 10
[mu]m in
[[Page 2623]]
diameter (PM10), EPA also determined that the fine and
coarse fractions of PM10 should be considered separately.
The EPA added new standards, using PM2.5 as the indicator
for fine particles (with PM2.5 referring to particles with a
nominal mean aerodynamic diameter less than or equal to 2.5 [mu]m), and
retained PM10 standards for the purpose of regulating the
coarse fraction of PM10 (referred to as thoracic coarse
particles or coarse-fraction particles; generally including particles
with a nominal mean aerodynamic diameter greater than 2.5 [mu]m and
less than or equal to 10 [mu]m, or PM10-2.5). The EPA
established two new PM2.5 standards: an annual standard of
15 [mu]g/m3, based on the 3-year average of annual
arithmetic mean PM2.5 concentrations from single or multiple
community-oriented monitors; and a 24-hour standard of 65 [mu]g/
m3, based on the 3-year average of the 98th percentile of
24-hour PM2.5 concentrations at each population-oriented
monitor within an area. Also, EPA established a new reference method
for the measurement of PM2.5 in the ambient air and adopted
rules for determining attainment of the new standards. To continue to
address thoracic coarse particles, EPA retained the annual
PM10 standard, while revising the form, but not the level,
of the 24-hour PM10 standard 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, petitions for
review were filed by a large number of parties, addressing a broad
range of issues. In May 1999, a three-judge panel of the U.S. Court of
Appeals for the District of Columbia Circuit issued an initial decision
that upheld 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 EPA's decision to regulate coarse particle
pollution, but vacated the 1997 PM10 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, EPA removed the vacated 1997
PM10 standards from the Code of Federal Regulations (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
standards remained in place. Id. at 80777.
More generally, the three-judge panel held (with one dissenting
opinion) that EPA's approach to establishing the level of the standards
in 1997, both for PM and for 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 EPA, stating that when 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 EPA's long-standing interpretation, the panel also
reaffirmed prior rulings holding that in setting NAAQS EPA is ``not
permitted to consider the cost of implementing those standards.'' Id.
at 1040-41.
Both sides filed cross appeals on these issues to the United States
Supreme Court, and the Court granted certiorari. In February 2001, the
Supreme Court issued a unanimous decision upholding 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 guided EPA's discretion, affirming 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 traditional standard of judicial review that EPA's
PM2.5 standards were reasonably supported by the
administrative record and were not ``arbitrary and capricious.''
American Trucking Associations v. EPA, 283 F.3d 355, 369-72 (D.C. Cir.
2002).
In October 1997, EPA published its plans for the current periodic
review of the PM criteria and NAAQS (62 FR 55201, October 23, 1997),
including the 1997 PM2.5 standards and the 1987
PM10 standards. As part of the process of preparing an
updated Air Quality Criteria Document for Particulate Matter
(henceforth, the ``Criteria Document''), EPA's National Center for
Environmental Assessment (NCEA) hosted a peer review workshop in April
1999 on drafts of key Criteria Document chapters. The first external
review draft Criteria Document was reviewed by CASAC and the public at
a meeting held in December 1999. Based on CASAC and public comment,
NCEA revised the draft Criteria Document and released a second draft in
March 2001 for review by CASAC and the public at a meeting held in July
2001. A preliminary draft of a staff paper, Review of the National
Ambient Air Quality Standards for Particulate Matter: Assessment of
Scientific and Technical Information (henceforth, the ``Staff Paper'')
prepared by EPA's Office of Air Quality Planning and Standards (OAQPS)
was released in June 2001 for public comment and for consultation with
CASAC at the same public meeting. Taking into account CASAC and public
comments, a third draft Criteria Document was released in May 2002 for
review at a meeting held in July 2002.
Shortly after the release of the third draft Criteria Document, the
Health Effects Institute (HEI) \3\ announced that researchers at Johns
Hopkins University had discovered problems with applications of
statistical software used in a number of important epidemiological
studies that had been discussed in that draft Criteria Document. In
response to this significant issue, EPA took steps in consultation with
CASAC to encourage researchers to reanalyze affected studies and to
submit them expeditiously for peer review by a special expert panel
convened at EPA's request by HEI. The results of this reanalysis and
peer-review process were subsequently incorporated into a fourth draft
Criteria Document, which was released in June 2003 and reviewed by
CASAC and the public at a meeting held in August 2003.
---------------------------------------------------------------------------
\3\ The HEI is an independent research institute, jointly
sponsored by EPA and a group of U.S. manufacturers and marketers of
motor vehicles and engines, that conducts health effects research on
major air pollutants related to motor vehicle emissions.
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The first draft Staff Paper, based on the fourth draft Criteria
Document, was released at the end of August 2003, and was reviewed by
CASAC and the public at a meeting held in November 2003.
[[Page 2624]]
During that meeting, EPA also consulted with CASAC on a new framework
for the final chapter (integrative synthesis) of the Criteria Document
and on ongoing revisions to other Criteria Document chapters to address
previous CASAC comments. The EPA held additional consultations with
CASAC at public meetings held in February, July, and September 2004,
leading to publication of the final Criteria Document in October 2004.
The second draft Staff Paper, based on the final Criteria Document, was
released at the end of January 2005, and was reviewed by CASAC and the
public at a meeting held in April 2005. The CASAC's advice and
recommendations to the Administrator, based on its review of the second
draft Staff Paper, were further discussed during a public
teleconference held in May 2005 and are provided in a June 6, 2005
letter to the Administrator (Henderson, 2005a). The final Staff Paper,
issued in June, 2005, takes into account the advice and recommendations
of CASAC and public comments received on the earlier drafts of this
document. The Administrator subsequently received additional advice and
recommendations from the CASAC, specifically on potential standards for
thoracic coarse particles in a teleconference on August 11, 2005, and
in a letter to the Administrator dated September 15, 2005 (Henderson,
2005b).\4\
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\4\ The EPA has posted on its Web site (https://www.epa.gov/ttn/
naaqs/standards/pm/s_pm_index.html) a second edition of the Staff
Paper which was prepared for the purpose of including as an
attachment this September 2005 letter from CASAC.
---------------------------------------------------------------------------
The schedule for completion of this review is governed by a consent
decree resolving a lawsuit filed in March 2003 by a group of plaintiffs
representing national environmental organizations. The lawsuit alleged
that EPA had failed to perform its mandatory duty, under section
109(d)(1), of completing the current review within the period provided
by statute. American Lung Association v. Whitman (No. 1:03CV00778,
D.D.C. 2003). An initial consent decree was entered by the court in
July 2003 after an opportunity for public comment. The consent decree,
as modified by the court, provides that EPA will sign for publication
notices of proposed and final rulemaking concerning its review of the
PM NAAQS no later than December 20, 2005 and September 27, 2006,
respectively.
C. Related Control Programs to Implement PM Standards
States are primarily responsible for ensuring attainment and
maintenance of ambient air quality standards once EPA has established
them. Under section 110 of the CAA (42 U.S.C. 7410) and related
provisions, States are to submit, for EPA approval, State
implementation plans (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
EPA, also administer the prevention of significant deterioration (PSD)
program (42 U.S.C. 7470-7479) for these pollutants. In addition,
Federal programs provide for nationwide reductions in emissions of
these and other air pollutants through the Federal Mobile Source
Control Program under title II of the CAA (42 U.S.C. 7521-7574), which
involves controls for automobile, truck, bus, motorcycle, nonroad or
off-highway, and aircraft emissions; the new source performance
standards under section 111 (42 U.S.C. 7411); and the national emission
standards for hazardous air pollutants under section 112 (42 U.S.C.
7412).
As described in a recent EPA report, The Particle Pollution Report:
Current Understanding of Air Quality and Emissions through 2003 (EPA,
2004b), State and Federal programs have made substantial progress in
reducing ambient concentrations of PM10 and
PM2.5. For example, PM10 concentrations have
decreased 31 percent nationally since 1988. Regionally, PM10
concentrations decreased most in areas with historically higher
concentrations--the Northwest (39 percent decline), the Southwest (33
percent decline), and southern California (35 percent decline). Direct
emissions of PM10 have decreased approximately 25 percent
nationally since 1988.
Programs aimed at reducing direct emissions of particles have
played an important role in reducing PM10 concentrations,
particularly in western areas. Some examples of PM10
controls include paving unpaved roads and using best management
practices for agricultural sources of resuspended soil. Additionally,
EPA's Acid Rain Program has substantially reduced sulfur dioxide
(SO2) emissions from power plants since 1995 in the eastern
United States, contributing to lower PM concentrations. Of the 87 areas
that were designated nonattainment for PM10 in the early
1990s, 64 now meet those standards. In cities that have not attained
the PM10 standards, the number of days above the standards
is down significantly.
Nationally, PM2.5 concentrations have declined by 10
percent from 1999 to 2003. Generally, PM2.5 concentrations
have also declined the most in regions with the highest
concentrations--the Southeast (20 percent decline), southern California
(16 percent decline), and the Industrial Midwest (9 percent decline).
With the exception of the Northeast, the remaining regions posted
modest declines in PM2.5 concentrations from 1999 to 2003.
Direct emissions of PM2.5 have decreased by 5 percent
nationally over the past 5 years.
National programs that affect regional emissions have contributed
to lower sulfate concentrations and, consequently, to lower
PM2.5 concentrations, particularly in the Industrial Midwest
and Southeast. National ozone-reduction programs designed to reduce
emissions of volatile organic compounds (VOCs) and nitrogen oxides
(NOX) also have helped reduce carbon and nitrates, both of
which are components of PM2.5. Nationally, SO2
emissions have declined 9 percent, NOX emissions have
declined 9 percent, and VOC emissions have declined by 12 percent from
1999 to 2003. In eastern States affected by the Acid Rain Program,
sulfates decreased 7 percent over the same period.
Over the next 10 to 20 years, national and regional regulations
will make major reductions in ambient PM2.5 levels. The
Clean Air Interstate Rule (CAIR) and the NOX SIP Call will
reduce SO2 and NOX emissions from electric
generating units and industrial boilers across the eastern half of the
U.S., regulations to implement the current ambient air quality
standards for PM2.5 will require direct PM2.5 and
PM2.5 precursor controls in nonattainment areas, and new
national mobile source regulations affecting heavy-duty diesel engines,
highway vehicles, and other mobile sources will reduce emissions of
NOX, direct PM2.5, SO2, and VOCs. The
EPA estimates that these regulations for stationary and mobile sources
will cut SO2 emissions by 6 million tons annually in 2015
from 2001 levels. Emissions of NOX will be cut by 9 million
tons annually in 2015 from 2001 levels. Emissions of VOCs will drop by
3 million tons, and direct PM2.5 emissions will be cut by
200,000 tons in 2015, compared to 2001 levels.
Modeling done by EPA indicates that by 2010, 18 of the 39 areas
currently not attaining the PM2.5 standards will come into
attainment just based on regulatory programs already in place,
including CAIR, the Clean Diesel Rules, and other Federal measures.
Four more PM2.5 areas are projected to attain the standards
by 2015 based on the implementation of these programs. All areas in the
eastern U.S. will have lower PM2.5 concentrations in 2015
relative to present-day conditions. In most cases,
[[Page 2625]]
the predicted improvement in PM2.5 ranges from 10 percent to
20 percent.
D. Overview of Current PM NAAQS Review
This action presents the Administrator's proposed decisions on the
review of the current primary and secondary PM2.5 and
PM10 standards. Primary standards for fine particles and for
thoracic coarse particles are addressed separately below in sections II
and III, respectively, consistent with the decision made by EPA in the
last review and with the conclusions in the Criteria Document and Staff
Paper that fine and thoracic coarse particles should continue to be
considered as separate subclasses of PM pollution. Thus, the principal
focus of this current review of the air quality criteria and primary
standards for PM is on evidence of health effects and risks related to
exposures to fine particles and to thoracic coarse particles. Secondary
standards for fine and coarse-fraction particles are addressed below in
section IV.
Past and current decisions to address fine particles and thoracic
coarse particles separately are based in part on long-established
information on differences in sources, properties, and atmospheric
behavior between fine and coarse particles (EPA, 2005a, section 2.2).
Fine particles are produced chiefly by combustion processes and by
atmospheric reactions of various gaseous pollutants, whereas thoracic
coarse particles are generally emitted directly as particles as a
result of mechanical processes that crush or grind larger particles or
the resuspension of dusts. Sources of fine particles include, for
example, motor vehicles, power generation, combustion sources at
industrial facilities, and residential fuel burning. Sources of
thoracic coarse particles include, for example, resuspension of
traffic-related emissions such as tire and brake lining materials,
direct emissions from industrial operations, construction and
demolition activities, and agricultural and mining operations. Fine
particles can remain suspended in the atmosphere for days to weeks and
can be transported thousands of kilometers, whereas thoracic coarse
particles generally deposit rapidly on the ground or other surfaces and
are not readily transported across urban or broader areas. The approach
in this review to continue to address fine and thoracic coarse
particles separately is reinforced by new information that advances our
understanding of differences in human exposure relationships and
dosimetric patterns characteristic of these two subclasses of PM
pollution, as well as the apparent independence of health effects that
have been associated with them in epidemiologic studies (EPA, 2004,
section 3.2.3). See also American Trucking Associations v. EPA, 175 F.
3d at 1053-54, 1055-56 (EPA justified in establishing separate
standards for fine and thoracic coarse particles).
Today's proposed decisions separately addressing fine and coarse
particles are based on a thorough review in the Criteria Document of
the latest 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 proposed decisions
also take into account: (1) Staff assessments in the Staff Paper of the
most policy-relevant information in the Criteria Document and as well
as a quantitative risk assessment; (2) CASAC advice and
recommendations, as reflected in the CASAC's letters to the
Administrator, discussions of drafts of the Criteria Document and Staff
Paper at public meetings, and separate written comments prepared by
individual members of the CASAC PM Review Panel \5\ (henceforth,
``CASAC Panel''), and (3) public comments received during the
development of these documents, either in connection with CASAC
meetings or separately.
---------------------------------------------------------------------------
\5\ 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 the types of
scientific expertise relevant to this review of the PM NAAQS.
---------------------------------------------------------------------------
The EPA is aware that a number of new scientific studies on the
health effects of PM have been published since the 2002 cutoff date for
inclusion in the Criteria Document. As in the last PM NAAQS review, EPA
intends to conduct a review and assessment of any significant new
studies published since the close of the Criteria Document, including
studies submitted during the public comment period in order to ensure
that, before making a final decision, the Administrator is fully aware
of the new science that has developed since 2002. In this assessment,
EPA will examine these new studies in light of the literature evaluated
in the Criteria Document. This assessment and a summary of the key
conclusions will be placed in the rulemaking docket. A preliminary list
of potentially significant new studies identified to date has been
compiled and placed in the rulemaking docket for this proposal, and EPA
solicits comment on other relevant studies that may be added to this
list. This list includes a wide array of different types of studies
that are potentially relevant to various issues discussed in the
following sections, including issues related to the elements of the
standards under review.
Throughout this preamble a number of conclusions, findings, and
determinations by the Administrator are noted. It should be understood
that these are all provisional and proposed in nature. While they
identify the reasoning that supports this proposal, they are not
intended to be final or conclusive in nature. The EPA invites comments
on all issues involved with this proposal, including all such proposed
judgments, conclusions, findings, and determinations.
II. Rationale for Proposed Decisions on Primary PM2.5 Standards
As discussed more fully below, the rationale for the proposed
revisions of the primary PM2.5 NAAQS includes consideration
of: (1) Evidence of health effects related to short- and long-term
exposures to fine particles; (2) insights gained from a quantitative
risk assessment; and (3) specific conclusions regarding the need for
revisions to the current standards and the elements of PM2.5
standards (i.e., indicator, averaging time, form, and level) that,
taken together, would be requisite to protect public health with an
adequate margin of safety.
In developing this rationale, EPA has drawn upon an integrative
synthesis of the entire body of evidence of associations between
exposure to ambient fine particles and a broad range of health
endpoints (EPA, 2004, Chapter 9), focusing on those health endpoints
for which the Criteria Document concludes that the associations are
likely to be causal. This body of evidence includes hundreds of studies
conducted in many countries around the world, using various indicators
of fine particles. In its assessment of the evidence judged to be most
relevant to making decisions on elements of the primary
PM2.5 standards, EPA has placed greater weight on U.S. and
Canadian studies using PM2.5 measurements, since studies
conducted in other countries may well reflect different demographic and
air pollution characteristics.
As with virtually any policy-relevant scientific research, there is
uncertainty in the characterization of health effects attributable to
exposure to ambient fine particles. As discussed below, however, an
unprecedented amount of new research has been conducted since the last
review, with important new information coming from epidemiologic,
toxicologic, controlled human exposure,
[[Page 2626]]
and dosimetric studies. Moreover, the newly available research studies
evaluated in the Criteria Document have undergone intensive scrutiny
through multiple layers of peer review and extended opportunities for
public review and comment. While important uncertainties remain, the
review of the health effects information has been extensive and
deliberate. In the judgment of the Administrator, this intensive
evaluation of the scientific evidence has provided an adequate basis
for regulatory decision making at this time. This review also provides
important input to EPA's research plan for improving our future
understanding of the relationships between exposures to ambient fine
particles and health effects.
A. Heath Effects Related to Exposure to Fine Particles
This section outlines key information contained in the Criteria
Document (Chapters 6-9 and the Staff Paper (Chapter 3) on known or
potential effects associated with exposure to fine particles and their
major constituents. The information highlighted here summarizes: (1)
New information available on potential mechanisms for health effects
associated with exposure to fine particles and constituents; (2) the
nature of the effects that have been associated with ambient fine
particles or fine particle constituents; (3) an integrative assessment
of the evidence on fine particle-related health effects; (4)
subpopulations that appear to be sensitive to effects of exposure to
fine particles; and (5) the public health impact of exposure to ambient
fine particles.
As was true in the last review, evidence from epidemiologic studies
plays a key role in the Criteria Document's evaluation of the
scientific evidence. Some highlights of the new epidemiologic evidence
include:
(1) New multi-city studies that use uniform methodologies to
investigate the effects of various indicators of PM on health with data
from multiple locations with varying climate and air pollution mixes,
contributing to increased understanding of the role of various
potential confounders, including gaseous co-pollutants, on observed
associations with fine particles. These studies provide more precise
estimates of the magnitude of an effect of exposure to PM, including
fine particles, than most smaller-scale individual city studies.
(2) More studies of various health endpoints evaluating
associations between effects and fine particles and thoracic coarse
particles (discussed below in section III), as well as ultrafine
particles or specific components (e.g., sulfates, nitrates, metals,
organic compounds, and elemental carbon) of fine particles.
(3) Numerous new studies of cardiovascular endpoints, with
particular emphasis on assessment of cardiovascular risk factors or
physiological changes.
(4) Studies relating population exposure to fine particles and
other pollutants measured at centrally located monitors to estimates of
exposure to ambient pollutants at the individual level. Such studies
have led to a better understanding of the relationship between ambient
fine particles levels and personal exposures to fine particles of
ambient origin.
(5) New analyses and approaches to addressing issues related to
potential confounding by gaseous co-pollutants, possible thresholds for
effects, and measurement error and exposure misclassification.\6\
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\6\ ``Confounding'' occurs when a health effect that is caused
by one risk factor is attributed to another variable that is
correlated with the causal risk factor; epidemiologic analyses
attempt to adjust or control for potential confounders (EPA, 2004,
section 8.1.3.2; EPA, 2005a, section 3.6.4). A ``threshold'' is a
concentration below which it is expected that effects are not
observed (EPA, 2004, section 8.4.7; EPA, 2005a, section 3.6.6).
``Gaseous co-pollutants'' generally refer to other commonly-occuring
air pollutants, specifically O3, CO, SO2 and
NO2. ``Measurement error'' refers to uncertainty in the
air quality measurements, while ``exposure misclassification''
includes uncertainty in the use of ambient pollutant measurements in
characterizing population exposures to PM (EPA, 2004, section 8.4.5;
EPA, 2005a, section 3.6.2)
---------------------------------------------------------------------------
(6) Preliminary attempts to evaluate the effects of fine particles
from different sources (e.g., motor vehicles, coal combustion,
vegetative burning, crustal \7\ ), using factor analysis or source
apportionment methods with fine particle speciation data.
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\7\ ``Crustal'' is used here to describe particles of geologic
origin, which can be found in both fine- and coarse-fraction PM.
---------------------------------------------------------------------------
(7) Several new ``intervention studies'' providing evidence for
improvements in respiratory or cardiovascular health with reductions in
ambient concentrations of particles and gaseous co-pollutants.
In addition, the body of evidence on PM-related effects has greatly
expanded with findings from studies on potential mechanisms or pathways
by which particles may result in the effects identified in the
epidemiologic studies. These studies include important new dosimetry,
toxicologic and controlled human exposure studies, as highlighted
below:
(8) Animal and controlled human exposure studies using concentrated
ambient particles (CAPs), new indicators of response (e.g., C-reactive
protein and cytokine levels, heart rate variability), and animal models
simulating sensitive human subpopulations. The results of these studies
are relevant to evaluation of plausibility of the epidemiologic
evidence and provide insights into potential mechanisms for PM-related
effects.
(9) Dosimetry studies using new modeling methods that provide
increased understanding of the dosimetry of different particle size
classes and in members of potentially sensitive subpopulations, such as
people with chronic respiratory disease.
1. Mechanisms
In the last review, EPA considered the lack of demonstrated
biologic mechanisms for the varying effects observed in epidemiologic
studies to be an important caution in its integrated assessment of the
health evidence. Much new evidence is now available on potential
mechanisms or pathways for PM-related effects, ranging from effects on
the respiratory system to indicators of cardiovascular response; these
new findings are discussed in depth in Chapter 7 of the Criteria
Document. While questions remain, the new findings have advanced our
understanding of the complex and different patterns of particle
deposition and clearance in the respiratory tract and provide insights
into potential mechanisms for PM-related effects and support the
plausibility of the findings of epidemiologic studies.
Although there are differences among the size fractions of
particles, fine particles, including accumulation mode and ultrafine
particles, and thoracic coarse particles can all penetrate into and be
deposited in the tracheobronchial and alveolar regions of the
respiratory tract (i.e., the ``thoracic'' regions).\8\ Penetration into
the tracheobronchial and alveolar regions is greater for accumulation
mode particles than for coarse or ultrafine particles, since coarse and
ultrafine particles are more efficiently removed from the air in the
extrathoracic region than are accumulation-mode fine particles; the
evidence from dosimetric studies is
[[Page 2627]]
reviewed in detail in Chapter 6 of the Criteria Document.
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\8\ Particles are often classified in modes based on their
distribution by characteristics such as mass, surface area, and
particle number. ``Coarse mode'' particles are those with diameters
mostly greater than the minimum in the particle mass distribution,
which generally occurs between about 1 and 3 [mu]m. ``Accumulation
mode'' particles are those with diameters from about 0.1 [mu]m to
between about 1 and 3 [mu]m. Ultrafine particles are generally those
with diameters below about 0.1 [mu]m (EPA, 2004, pages 2-14).
---------------------------------------------------------------------------
Fine particles have varying physical or chemical characteristics
that may influence health responses. Physical characteristics that may
be of importance are solubility or physical state of the particles
(e.g., solid, liquid). Fine particle components include metals, acids,
organic compounds, biogenic constituents, sulfate and nitrate salts,
elemental carbon, and reactive components such as peroxides; size and
surface area of the particles can also influence health responses. By
way of illustration, Mauderly et al. (1998) discussed particle
components or characteristics hypothesized to contribute to health,
producing an illustrative list of 11 components or characteristics of
interest for which some evidence existed. The list included: (1)
Particle mass concentration, (2) particle size/surface area, (3)
ultrafine particles, (4) metals, (5) acids, (6) organic compounds, (7)
biogenic particles, (8) sulfate and nitrate salts, (9) peroxides, (10)
soot, and (11) co-factors, including effects modification or
confounding by co-occurring gases and meteorology. The authors stressed
that this list is neither definitive nor exhaustive, and note that ``it
is generally accepted as most likely that multiple toxic species act by
several mechanistic pathways to cause the range of health effects that
have been observed'' (Mauderly et al., 1998). The range of health
outcomes linked with fine particle exposures is also broad, including
effects on the cardiovascular and respiratory systems, and potential
links with developmental effects in children (e.g., low birth weight)
and death from lung cancer. It appears unlikely that the complex mixes
of particles that are present in ambient air would act alone through
any single pathway of response. Accordingly, it is plausible that
several physiological responses might occur in concert to produce
reported health endpoints.
As discussed in section 7.10 of the Criteria Document, the
potential pathways for direct effects on the respiratory system include
lung injury and inflammation, increased airway reactivity and asthma
exacerbation, and increased susceptibility to respiratory infections.
New toxicologic or controlled human exposure studies have reported some
evidence of inflammatory responses in animals, as well as increased
susceptibility to infections. Toxicologic studies also report evidence
of lung injury, inflammation, or altered host defenses with exposure to
ambient particles or particle constituents. Some toxicologic evidence,
particularly from results of studies using diesel exhaust particle
exposures, also indicates that PM can aggravate asthmatic symptoms or
increase airway reactivity.
Potential pathways for fine particle-related effects also include
systemic effects that are secondary to effects in the respiratory
system. These include impairment of lung function leading to cardiac
effects, pulmonary inflammation and cytokine production leading to
systemic hemodynamic effects, lung inflammation leading to increased
blood coagulability, and lung inflammation leading to hematopoiesis
effects. While more limited than for direct pulmonary effects, some new
toxicologic studies suggest that injury or inflammation in the
respiratory system can lead to changes in heart rhythm, reduced
oxygenation of the blood, changes in blood cell counts, and changes in
the blood that can increase the risk of blood clot formation, a risk
factor for heart attacks and strokes. In addition, health studies have
suggested potential pathways for effects on the heart that include
effects related to uptake of particles or particle constituents in the
blood, and effects on the autonomic control of the heart and
circulatory system. In the last review, little or no evidence was
available from toxicologic studies on potential cardiovascular effects.
More recent studies have provided some initial evidence that particles
can have direct cardiovascular effects. Particle deposition in the
respiratory system also could lead to cardiovascular effects, such as
fine particle-induced pulmonary reflexes resulting in changes in the
autonomic nervous system that then could affect heart rhythm. Also,
inhaled fine particles could affect the heart or other organs if
particles or particle constituents are released into the circulatory
system from the lungs; some new evidence indicates that the smaller
ultrafine particles or their soluble constituents can move directly
from the lungs into systemic circulation.
The potential mechanisms and/or general pathways for effects
discussed above are primarily effects related to short-term rather than
long-term exposure to fine particles; for the most part, air pollution
toxicologic studies are not designed to assess long-term exposure
effects. While repeated occurrences of some short-term insults, such as
inflammation, might contribute to long-term effects, it is likely that
wholly different mechanisms are involved in the development of chronic
health responses. Some mechanistic evidence is available, however, for
potential carcinogenic or genotoxic effects of ambient fine particles
and combustion products of coal, wood, diesel, and gasoline (discussed
in section 7.8 of the Criteria Document).
Overall, the findings indicate that different health responses are
linked with different particle characteristics and that both individual
components and complex particle mixtures appear to be responsible for
many biologic responses relevant to fine particle exposures. In
evaluating the new body of evidence, the Criteria Document states:
``Thus, there appear to be multiple biologic mechanisms that may be
responsible for observed morbidity/mortality due to exposure to ambient
PM. It also appears that many biologic responses are produced by PM
whether it is composed of a single component or a complex mixture''
(EPA, 2004, p. 7-206).
2. Nature of Effects
In the last review, evidence from health studies indicated that
exposure to PM (using various indicators) was associated with premature
mortality and indices of morbidity including respiratory hospital
admissions and emergency room visits, school absences, work loss days,
restricted activity days, effects on lung function and symptoms,
morphological changes, and altered host defense mechanisms.\9\ As
reviewed in Chapter 8 of the Criteria Document, recent epidemiologic
studies have continued to report associations between short-term
exposure to fine particles or fine particle indicators, and effects
such as premature mortality, hospital admissions or emergency
department visits for respiratory disease, and effects on lung function
and symptoms. In addition, recent epidemiologic studies have provided
some new evidence linking short-term fine particle exposures to effects
on the cardivascular system, including cardiovascular hospital
admissions and more subtle indicators of cardiovascular health. Long-
term exposure to PM2.5 and sulfates has also been associated
with mortality from cardiopulmonary diseases and lung cancer, and
effects on the respiratory system such as decreased lung function or
the development of chronic respiratory disease. The
[[Page 2628]]
evidence for such effects is summarized below.
\9\ Historical reports of dramatic pollution episodes,
considered in the 1987 review of the PM NAAQS, provided clear
evidence of mortality associated with high levels of PM and other
pollutants, such as the air pollution episode that occurred in
London in 1952 (EPA, 1996a, pp. 12-28 to 12-31).
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BILLING CODE 6560-50-P
[GRAPHIC] [TIFF OMITTED] TP17JA06.048
BILLING CODE 6560-50-C
[[Page 2629]]
a. Effects Associated With Short-Term Exposure to Fine Particles
Numerous epidemiologic studies have demonstrated statistical
associations between short-term exposure to fine particles and health
outcomes ranging from total mortality to respiratory symptoms, as
discussed below. Figure 1 summarizes results from both multi-city and