Treatment of Data Influenced by Exceptional Events, 13560-13581 [E7-5156]

Agencies

• ENVIRONMENTAL PROTECTION AGENCY

[Federal Register Volume 72, Number 55 (Thursday, March 22, 2007)]
[Rules and Regulations]
[Pages 13560-13581]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E7-5156]



[[Page 13559]]

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Part II





Environmental Protection Agency





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40 CFR Parts 50 and 51



Treatment of Data Influenced by Exceptional Events; Final Rule

Federal Register / Vol. 72, No. 55 / Thursday, March 22, 2007 / Rules 
and Regulations

[[Page 13560]]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 50 and 51

[EPA-HQ-OAR-2005-0159; FRL-8289-5]
RIN 2060-AN40


Treatment of Data Influenced by Exceptional Events

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule.

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SUMMARY: This action finalizes a rule to govern the review and handling 
of air quality monitoring data influenced by exceptional events. 
Exceptional events are events for which the normal planning and 
regulatory process established by the Clean Air Act (CAA) is not 
appropriate. In this rulemaking action, EPA is finalizing the proposal 
to: Implement section 319(b)(3)(B) and section 107(d)(3) authority to 
exclude air quality monitoring data from regulatory determinations 
related to exceedances or violations of the National Ambient Air 
Quality Standards (NAAQS) and avoid designating an area as 
nonattainment, redesignating an area as nonattainment, or reclassifying 
an existing nonattainment area to a higher classification if a State 
adequately demonstrates that an exceptional event has caused an 
exceedance or violation of a NAAQS. The EPA is also requiring States to 
take reasonable measures to mitigate the impacts of an exceptional 
event.

DATES: This final rule is effective May 21, 2007.

ADDRESSES: The EPA has established a docket for this action under 
Docket ID No. EPA-HQ-OAR-2005-0159. All documents in the docket are 
listed on the https://www.regulations.gov Web site. Although listed in 
the index, some information is not publicly available, i.e., 
confidential business information (CBI) or other information whose 
disclosure is restricted by statute. Certain other material, such as 
copyrighted material, is not placed on the Internet and will be 
publicly available only in hard copy form. Publicly available docket 
materials are available either electronically through https://
www.regulations.gov or in hard copy at the OAR Docket, EPA/DC, EPA 
West, Room 3334, 1301 Constitution Ave., NW., Washington, DC. The 
Public Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday through 
Friday, excluding legal holidays. The telephone number for the Public 
Reading Room is (202) 566-1744, and the telephone number for the Air 
and Radiation Docket and Information Center is (202) 566-1742.

FOR FURTHER INFORMATION CONTACT: General questions regarding the final 
rule should be addressed to Mr. Larry D. Wallace, PhD, Office of Air 
Quality Planning and Standards, Air Quality Policy Division, Mail Code 
C539-01, Research Triangle Park, NC 27711; telephone (919) 541-0906, 
and e-mail address wallace.larry@epa.gov.
    Questions concerning technical and analytical issues related to 
this final rule should be addressed to Mr. Neil Frank, Office of Air 
Quality Planning and Standards, Air Quality Assessment Division, Mail 
Code C304-01, Research Triangle Park, NC 27711; telephone (919) 541-
5560, and e-mail address frank.neil@epa.gov.

SUPPLEMENTARY INFORMATION:

I. General Information

A. Does This Action Apply to Me?

    Regulated Entities. This final rule will affect State and local air 
quality agencies. This rule may also affect Tribal air quality agencies 
that have implemented air quality monitoring networks or have authority 
to implement air quality programs.
    This list is not intended to be exhaustive, but rather provides a 
guide for readers regarding entities likely to be regulated by this 
action. This list gives examples of the types of entities EPA is now 
aware could potentially be regulated by this action. Other types of 
entities not listed could also be affected. To determine whether your 
facility, company, business, organization, etc., is regulated by this 
action, you should examine the applicability criteria in section IV of 
this preamble. If you have any questions regarding the applicability of 
this action to a particular entity, consult the people listed in the 
preceding section.

B. How Is This Preamble Organized?

Table of Contents
    The following is an outline of the preamble.

I. General Information
    A. Does This Action Apply to Me?
    B. How Is This Preamble Organized?
II. Preamble Glossary of Terms and Acronyms
III. Background and Purpose of This Rulemaking
    A. Legislative Requirements
    B. Historical Experience Concerning Exceptional and Natural 
Events
IV. This Final Action
    A. To Whom and to What Pollutants Does This Rule Apply?
    B. How Does This Rule Relate to Indian Tribes?
    C. Comments Submitted on the Proposed Rule
    D. What Is an Exceptional Event?
    E. Examples of Exceptional Events
    1. Chemical Spills and Industrial Accidents
    2. Structural Fires
    3. Exceedances Due to Transported Pollution
    4. Exceedances Due to a Terrorist Attack
    5. Natural Events
    a. Natural Disasters and Associated Clean-Up Activities
    b. Volcanic and Seismic Activities
    c. High Wind Events
    d. Wildland Fires
    e. Stratospheric Ozone Intrusions
    6. Prescribed Fire
V. The Management of Air Quality Data Affected by Exceptional Events
    A. Flagging of Data in the AQS Database
    1. Background
    2. Final Rule
    3. Comments and Responses
    B. What Does It Mean for an Event to ``Affect Air Quality''?
    1. Background
    2. Final Rule
    3. Comments and Responses
    C. Use of a ``But For'' Test
    1. Background
    2. Final Rule
    3. Comments and Responses
    D. Schedules and Procedures for Flagging and Requesting 
Exclusion of Data
    1. Background
    2. Final Rule
    3. Comments and Responses
    E. Exclusion of Entire 24-Hour Value as Opposed to a Partial 
Adjustment of the 24-Hour Value
    1. Background
    2. Final Rule
    3. Comments and Responses
    F. What Should States Be Required To Submit in Their Exceptional 
Events Demonstrations?
    1. Background
    2. Final Rule
    3. Comments and Responses
    G. Public Availability of Air Quality Data and Demonstrations 
Related to Exceptional Events
    1. Background
    2. Final Rule
    3. Comments and Responses
VI. Additional Requirements
    A. Requirements for States To Provide Public Notification, 
Public Education, and Appropriate and Reasonable Measures To Protect 
Public Health
    1. Background
    2. Final Rule
    3. Comments and Responses
VII. Special Treatment of Certain Exceptional Events Under This 
Final Rule
    A. Volcanic and Seismic Activities
    1. Background
    2. Final Rule
    B. High Wind Events
    1. Background
    2. Final Rule
    C. Stratospheric Ozone Intrusion
    1. Background
    2. Final Rule
VIII. Treatment of Fireworks Displays

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    A. Background
    B. Final Rule
    C. Comments and Responses
    IX. 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. Congressional Review Act
    K. Petitions for Judicial Review

II. Preamble Glossary of Terms and Acronyms

    The following are abbreviations of terms used in the preamble.

ARM Approved Regional Methods.
AQS Air Quality System.
BACM Best Available Control Measures.
CAA Clean Air Act.
CAAA Clean Air Act Amendments.
EPA Environmental Protection Agency.
FEM Federal Equivalent Methods.
FIP Federal Implementation Plan.
FR Federal Register.
FRM Federal Reference Methods.
NAAQS National Ambient Air Quality Standards.
NEAP Natural Events Action Plan.
NEPA National Environmental Policy Act.
NTTA National Technology Transfer Advancement Act of 1995.
OAQPS Office of Air Quality Planning and Standards.
OMB Office of Management and Budget.
PM Particulate matter.
PM10 Particles with a nominal mean aerodynamic diameter less 
than or equal to 10 micrometers.
PM10-2.5 Particles with a nominal mean aerodynamic diameter 
greater than 2.5 micrometers and less than or equal to 10 micrometers.
PM2.5 Particles with a nominal mean aerodynamic diameter 
less than or equal to 2.5 micrometers.
RACM Reasonably Available Control Measures.
SIP State Implementation Plan.
SAFE-TEA-LU Safe Accountable Flexible Efficient-Transportation Equity 
Act--A Legacy for Users.
SMP Smoke Management Program.
TAR Tribal Authority Rule.
TIP Tribal Implementation Plan.
UMRA Unfunded Mandates Reform Act.
USDA U.S. Department of Agriculture.
VCS Voluntary Consensus Standards.

III. Background and Purpose of This Rulemaking

A. Legislative Requirements

    We \1\ are finalizing a rule to govern the review and handling of 
air quality monitoring data influenced by exceptional events. As 
discussed below, these are events for which the normal planning and 
regulatory process established by the CAA is not appropriate. Section 
319 of the CAA, as amended by section 6013 of the Safe Accountable 
Flexible Efficient-Transportation Equity Act: A Legacy for Users (SAFE-
TEA-LU) of 2005, required EPA to publish the proposed rule in the 
Federal Register no later than March 1, 2006.\2\ Further, EPA must 
issue this final rule no later than 1 year from the date of proposal. 
The EPA published the proposed rule on March 10, 2006 (See 71 FR 
12592).
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    \1\ The U.S. Environmental Protection Agency.
    \2\ All subsequent references to section 319 of the CAA in this 
proposal are to section 319 as amended by SAFE-TEA-LU unless 
otherwise noted.
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    In this final rule, EPA is establishing procedures and criteria 
related to the identification, evaluation, interpretation, and use of 
air quality monitoring data related to any NAAQS where States petition 
EPA to exclude data that are affected by exceptional events.
    Section 319 defines an event as an exceptional event if the event 
affects air quality; is an event that is not reasonably controllable or 
preventable; is an event caused by human activity that is unlikely to 
recur at a particular location or a natural event; and is determined by 
EPA to be an exceptional event. The statutory definition of exceptional 
event specifically excludes stagnation of air masses or meteorological 
inversions; a meteorological event involving high temperatures or lack 
of precipitation; or air pollution relating to source noncompliance.
    Section 319(b)(3)(B)(i) requires a State air quality agency to 
demonstrate through ``reliable, accurate data that is promptly 
produced'' that an exceptional event occurred.\3\ Section 
319(b)(3)(B)(ii) requires that ``a clear causal relationship'' be 
established between a measured exceedance of a NAAQS and the 
exceptional event demonstrating ``that the exceptional event caused a 
specific air pollution concentration at a particular location.'' In 
addition, section 319(b)(3)(B)(iii) requires a public process to 
determine whether an event is an exceptional event. Finally, section 
319(b)(3)(B)(iv) requires criteria and procedures for a Governor to 
petition the Administrator to exclude air quality monitoring data that 
is directly due to exceptional events from use in determinations with 
respect to exceedances or violations of the NAAQS.
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    \3\ While this document refers primarily to States as the entity 
responsible for flagging data impacted by exceptional events, other 
agencies, such as local or Tribal government agencies, may also have 
standing to flag data as being affected by these types of events, 
and the criteria and procedures that are discussed in this 
rulemaking also apply to these entities.
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    The term exceedance refers to a measured or modeled concentration 
greater than the level of one or more for a pollutant. The NAAQS are 
also set with particular averaging periods (e.g., 3 years for ozone and 
PM2.5) such that a violation of the NAAQS for ozone and 
PM2.5 requires an average annual concentration level 
specified by appendix I and N to 40 CFR 50 to be greater than the level 
of the NAAQS. Public comments favored the consideration of data 
contributing to both exceedances and violations for data exclusion 
under this Rule. As discussed in section V.C, exceedances of any NAAQS 
will be eligible for consideration for data exclusion and any data 
contributing to violations of daily or sub-daily standards will also be 
eligible for consideration (e.g. 8-hour or 24-hour standards). Data 
contributing to annual violations without being exceedances themselves 
are considered too close to background air quality levels for exclusion 
under this Rule.
    Section 319 also contains a set of five principles for EPA to 
follow in developing regulations to implement section 319:

    (i) Protection of public health is the highest priority;
    (ii) Timely information should be provided to the public in any 
case in which the air quality is unhealthy;
    (iii) All ambient air quality data should be included in a 
timely manner in an appropriate Federal air quality database that is 
accessible to the public;
    (iv) Each State must take necessary measures to safeguard public 
health regardless of the source of the air pollution; and
    (v) Air quality data should be carefully screened to ensure that 
events not likely to recur are represented accurately in all 
monitoring data and analyses (42 U.S.C. 7619(b)(3)(A)).

    In adopting revisions to section 319, Congress sought to provide 
statutory relief to States to allow them to avoid being designated as 
nonattainment or to avoid continuing to be designated

[[Page 13562]]

nonattainment as a result of exceptional events in appropriate 
circumstances. To accomplish this goal, Congress enumerated certain 
minimum requirements for this rulemaking. In addition, Congress 
provided certain statutory principles for EPA to follow in promulgating 
regulations to exclude data affected by exceptional events.

B. Historical Experience Concerning Exceptional and Natural Events

    Since 1977, EPA guidance and regulations have either implied or 
documented the need for a flagging system for data affected by an 
exceptional event. The first EPA guidance related to the exclusion or 
discounting of data affected by an exceptional event was an Office of 
Air Quality Planning and Standards (OAQPS) guidance document entitled, 
``Guideline for the Interpretation of Air Quality Standards,'' 
Guideline No. 1.2-008 (revised February 1977).\4\
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    \4\ ``Guideline for Interpretation of Air quality Standards,'' 
U.S. Environmental Protection Agency, Office of Air quality Planning 
and Standards, Research Triangle Park, N.C. OAQPS No. 1.2-008 
(Revised February 1977). The guidance indicated the need for a data 
flagging system which would require the submittal of detailed 
information establishing that a violation was due to uncontrollable 
natural sources and that the information could be used in decision 
making related to the feasibility of modifying control strategies.
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    In July 1986, EPA issued the guidance entitled, ``Guideline On the 
Identification and Use of Air Quality Data Affected By Exceptional 
Events'' (the Exceptional Events Policy). The Exceptional Events Policy 
provided criteria for States to use in making decisions related to 
identifying data that have been influenced by an exceptional event.
    In addition to the Exceptional Events Policy, on July 1, 1987, EPA 
promulgated the NAAQS for PM10 (particulate matter with an 
aerodynamic diameter of 10 micrometers or less), which also addressed 
the issue of excluding or discounting data affected by exceptional 
events.\5\ Appendix K of that rule allows for special consideration of 
data determined to be affected by an exceptional event. Section 2.4 of 
appendix K authorizes EPA to discount from consideration in making 
attainment or nonattainment determinations air quality data that are 
attributable to ``an uncontrollable event caused by natural sources'' 
of PM10, or ``an event that is not expected to recur at a 
given location.'' Section 2.4 of appendix K, together with EPA guidance 
contained in the Exceptional Events Policy, describes the steps that 
should be taken for flagging PM10 data that a State believes 
are affected by an exceptional or natural event.
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    \5\ Federal Register (52 FR 24667), July 1, 1987.
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    In 1990, section 188(f) was added to the CAA. This section of the 
CAA provided EPA authority to waive either a specific attainment date 
or certain planning requirements for serious PM10 
nonattainment areas that are affected by nonanthropogenic sources. In 
response to section 188(f), and in consideration of the CAA 
consequences for areas affected by elevated concentrations caused by 
natural events, in 1996 EPA issued a policy to address data affected by 
natural events entitled, ``Areas Affected by PM10 Natural 
Events,'' (the PM10 Natural Events Policy).\6\
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    \6\ Memorandum from Mary D. Nicols, Assistant Administrator for 
Air and Radiation, to EPA Regional Offices entitled, ``Areas 
Affected by PM10 Natural Events,'' May 30, 1996.
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    On July 18, 1997, EPA issued a revised NAAQS for ozone and a new 
NAAQS addressing PM2.5. For ozone, the revised NAAQS 
provided for an 8-hour averaging period (versus 1 hour for the previous 
NAAQS), and the level of the standard was changed from 0.12 ppm to 0.08 
ppm (62 FR 38856). For the PM2.5 NAAQS, EPA established both 
a new 24-hour standard and a new annual standard. In that Federal 
Register, EPA also promulgated appendices I and N to 40 CFR 50. 
Appendices I and N provided the methodologies for determining whether 
an area is in attainment of the 8-hour ozone and PM2.5 NAAQS 
respectively, using ambient air quality data. Section 1.0 of appendix 
I, related to the ozone standard, addresses the treatment of data 
determined to be influenced natural events, and section 1.0(b) of 
appendix N, related to the PM2.5 standard, provides that EPA 
may give special consideration to data determined to be affected by an 
exceptional or natural event.
    Appendices K, I, and N, which are parts of the NAAQS for the 
affected pollutants as described above, provide that, while States must 
submit all valid ambient air quality data to EPA's Air Quality System 
(AQS) database for use in making regulatory decisions, in some cases it 
may be appropriate for EPA to exclude, discount, weight, or make 
adjustments to data that have been appropriately flagged from 
calculations in determining whether or not an area has attained the 
standard. These decisions are to be made on a case-by-case basis using 
all available information related to the event in question, and are 
required to be made available to the public for review. It should also 
be noted that, while it would be desirable to be able to adjust the 
daily value to exclude only those portions of the data that are 
attributable to the exceptional event, due to technical limitations, 
such subtraction has not been possible, and EPA's historical practice 
has been to exclude a daily measured value in its entirety when that 
value is found to be largely caused by an exceptional event.
    Following the promulgation of the 8-hour ozone and the 
PM2.5 NAAQS, EPA provided additional guidance to States on 
how to address data affected by exceptional and natural events.\7\ That 
guidance directed the States to follow three specific EPA guidance 
documents in making determinations related to data influenced by 
exceptional and natural events: (1) The Exceptional Events Policy; (2) 
The PM10 Natural Events Policy; and (3) The Interim Air 
Quality Policy on Wildland and Prescribed Fires, Memorandum from 
Richard D. Wilson, Acting Assistant Administrator for Air and 
Radiation, to EPA Regional Administrators, May 15, 1998. The Interim 
Air Quality Policy on Wildland and Prescribed Fires addressed the 
treatment of air quality monitoring data that are affected by wildland 
and prescribed fires that are managed for resource benefits.\8\
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    \7\ ``Guideline on Data Handling Conventions for the PM NAAQS,'' 
United States Environmental Protection Agency, Office of Air Quality 
Planning and Standards, Research Triangle Park, NC 27711, EPA-454/R-
98-017, December 1998.
    \8\ Following the promulgation of this rule, it is EPA's 
intention to begin the process to revise the ``Interim Air Quality 
Policy on Wildland and Prescribed Fires'' in calendar year 2007 to 
update the policy and to ensure that the policy is consistent with 
this final rulemaking action. In addition, it is EPA's intent that 
agricultural prescribed burning will be addressed when this policy 
is updated and will also address basic smoke management practices.
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IV. This Final Action

A. To Whom and to What Pollutants Does This Rule Apply?

    Under the statutory scheme established by the CAA, States are 
primarily responsible for the administration of air quality management 
programs within their borders. This includes the monitoring and 
analysis of ambient air quality and submission of monitoring data to 
EPA, which are then stored in EPA's AQS database. The EPA retains an 
important oversight responsibility for ensuring compliance with CAA 
requirements. With respect to the treatment of air quality monitoring 
data, States are responsible for ensuring data quality and validity and 
for identifying measurements that they believe warrant special 
consideration, while EPA is

[[Page 13563]]

responsible for reviewing and approving or disapproving any requests 
for such consideration. Therefore, this final rule applies to all 
States; to local air quality agencies to whom a State has delegated 
relevant responsibilities for air quality management, including air 
quality monitoring and data analysis; and, as discussed below, to 
Tribal air quality agencies where appropriate. This rule governs EPA's 
actions in reviewing and approving or disapproving the relevant actions 
taken or requested by States. Where EPA implements air quality 
management programs on Tribal lands, this rule would govern those 
actions as well.
    At present, only the NAAQS for ozone and particulate matter (PM) 
contain provisions which allow for the special handling of air quality 
data affected by exceptional and natural events (40 CFR part 50, 
appendices K, I, and N). The language of section 319 of the CAA is 
broad in terms of making its provisions applicable to events that 
``affect air quality'' and to exceedances or violations of ``the 
national ambient air quality standards'' (42 U.S.C. 7619(b)(1)(A)(i), 
(b)(3)(B)(iv)). Thus, its provisions can apply to the NAAQS for any 
criteria pollutant. Because the NAAQS established for other criteria 
pollutants do not currently contain provisions permitting the 
discounting or exclusion of data due to exceptional events, we are only 
applying the provisions of this rule initially to ozone and PM.\9\ As 
we review and consider the need for revisions to the NAAQS for other 
pollutants, we will include provisions to address exceptional events in 
those NAAQS in accordance with section 319, as appropriate at that 
time. Because issuance of a new or revised NAAQS will necessitate the 
initiation of the designation process, EPA believes that the NAAQS 
rules are an appropriate place to make provisions for exceptional 
events in the evaluation of air quality data. In the interim, where 
exceptional events result in exceedances or violations of NAAQS that do 
not currently provide for special treatment of the data, we intend to 
use our discretion as outlined under section 107(d)(3) not to 
redesignate affected areas as nonattainment based on these events. We 
also intend to use our discretion under this rule to address 
determinations for the ozone standard related to the treatment of data 
influenced by both exceptional and natural events. Currently, appendix 
I, only addresses the treatment of data determined to be influenced by 
a stratospheric ozone intrusion and other natural events, but does not 
address the handling of data influenced by other exceptional events.
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    \9\ Section IV.G of the preamble to the Proposed Rule discussed 
special considerations relevant to a new NAAQS for 
PM10-2.5 proposed by EPA on December 20, 2005. This 
proposed standard would have drawn a distinction between coarse 
particles of urban versus non-urban origin, which raised new issues 
about the handling of exceedances of the coarse particle standard 
caused by exceptional events. However, in EPA's final rule on the PM 
NAAQS, issued September 21, 2006, EPA retained the existing 24-hour 
PM10 standard instead of promulgating the proposed 
PM10-2.5 standard. Thus, section IV.G of the preamble to 
the Proposed Rule is no longer relevant and has been removed from 
this Preamble.
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B. How Does This Rule Relate to Indian Tribes?

    Under the CAA and the Tribal Authority Rule (TAR), eligible Indian 
Tribes may develop and submit Tribal Implementation Plans (TIPs) for 
EPA approval, to administer requirements under the CAA on their 
reservations and other areas under their jurisdiction. However, Tribes 
are not required to develop TIPs or otherwise implement relevant 
programs under the CAA. The EPA has stated that it will continue to 
ensure the protection of air quality throughout the nation, including 
in Indian country, and will issue Federal Implementation Plans (FIPs) 
as necessary or appropriate to fill gaps in program implementation in 
affected areas of Indian country (63 FR 7254, 7265; February 12, 1998).
    In cases where a Tribal air quality agency has implemented an air 
quality monitoring network, which is affected by emissions from 
exceptional events, the criteria and procedures identified in this 
final rule may be used to exclude or discount data for regulatory 
purposes. Certain Tribes may implement all relevant components of an 
air quality program for purposes of meeting the various requirements of 
this rule. In some cases, however, a Tribe may implement only portions 
of the relevant program and may not be in a position to address each of 
the procedures and requirements associated with excluding or 
discounting emissions data (e.g., a particular Tribe may operate a 
monitoring network for purposes of gathering and identifying 
appropriate data, but may not implement relevant programs for the 
purpose of mitigating the effects of exceptional events required under 
this rule). The EPA intends to work with Tribes on the implementation 
of this rule, which may include appropriate implementation by EPA of 
program elements ensuring that any exclusion or discounting of data in 
Indian country areas with air quality affected by exceptional events 
comports with the procedures and requirements of this rule.

C. Comments Submitted on the Proposed Rule

    The proposed rule on the ``Treatment of Data Influenced by 
Exceptional Events'' was issued on March 10, 2006 (71 FR 12592). We 
received 98 letters from commenters representing 587 comments from 
private citizens, State and local governments, industry, environmental 
groups, and Federal agencies. Sections V, VI, VII, and VIII of this 
notice describe the primary elements and requirements concerning the 
process for the handling of data influenced by exceptional events. Each 
section summarizes the relevant issues and options discussed in the 
proposed rule and provides the final decisions related to the issues 
for each section. In this preamble, we have provided responses to 
certain significant comments to elaborate or provide clarification for 
EPA's decision on an issue discussed in the relevant section of the 
rule. We have developed a response to comments document which addresses 
all of the timely comments received on the proposed rule. Following the 
promulgation of this rule, the response to comments document will be 
placed into the docket of this rulemaking action for public review (See 
Docket No. EPA-HQ-OAR-2005-0159).

D. What Is an Exceptional Event?

    In accordance with the language in section 319, EPA is defining the 
term ``exceptional event'' to mean an event that:

    (i) Affects air quality;
    (ii) Is not reasonably controllable or preventable;
    (iii) Is an event caused by human activity that is unlikely to 
recur at a particular location or a natural event; and
    (iv) Is determined by EPA through the process established in 
these regulations to be an exceptional event.

    It is important to note that natural events, which are one form of 
exceptional events according to this definition, may recur, sometimes 
frequently (e.g., western wildfires). For the purposes of this rule, 
EPA is defining ``natural event'' as an event in which human activity 
plays little or no direct causal role to the event in question. We 
recognize that over time, certain human activities may have had some 
impact on the conditions which later give rise to a ``natural'' air 
pollution event. However, we do not believe that small historical human 
contributions should preclude an event from being deemed ``natural.'' 
In adopting section 188(f) of part D, subpart 4, of the 1990 amendments 
to

[[Page 13564]]

the CAA, Congress recognized and provided for distinctions between 
these types of events with respect to waiver of applicable requirements 
and the extension of otherwise applicable attainment dates for the 
PM10 standard. In approving section 188(f) of the CAA, the 
House committee of jurisdiction discussed a circumstance in which 
recurring emissions from a source should be considered to be 
anthropogenic. The House report noted EPA statements that, in the cited 
case, high concentrations of dust from a lakebed were due to human 
activity, i.e., the long-term diversion of water from a lake. (See Pub. 
L. 101-549, CAA Amendments of 1990 House Report No. 101-290(l), May 17, 
1990; and discussion of Mono Lake, California therein). Also, EPA 
recognized, in recently acting to retain PM10 as a measure 
of coarse particulate, that in some instances exceedances of this NAAQS 
``may be caused in whole or in part, by exceptional events, including 
natural events such as windstorms * * *. (and that) an exceedance may 
be treated as an exceptional event even though anthropogenic sources 
such as agricultural and mining emissions contribute to the 
exceedance.'' (71 FR 61216; October 17, 2006).
    In this final rule, EPA also defines the term ``exceedance'' with 
respect to compliance with the NAAQS and establishes criteria for 
determining when an event can be said to ``affect air quality.'' We are 
not finalizing more detailed requirements for determining when an event 
is ``not reasonably controllable or preventable'' because we believe 
that such determinations will necessarily be dependent on specific 
facts and circumstances that cannot be prescribed by rule.

E. Examples of Exceptional Events

    The EPA believes that the following types of events meet the 
definition of exceptional events, as defined above. This means that air 
quality data affected by these types of events may qualify for 
exclusion under this rule provided that all other requirements of the 
rule are met. By providing the examples listed below, EPA is not 
determining that such events are the only types of events that may 
qualify for exclusion under the rule as exceptional events. Other 
events that meet the statutory criteria for an exceptional event as 
defined in this rule may also qualify for exclusion. The AQS user 
documentation contains a list of other similar events that may be 
flagged for special consideration. (https://www.epa.gov/ttn/airs/
airsaqs/manuals/qualifiers.htm).\10\
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    \10\ The EPA will be revising the list of events contained in 
the AQS database following the promulgation of this rule to ensure 
that the list is consistent with the requirements of the rule.
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    In addition, in the sections below, we have provided responses to 
certain significant comments received during the comment period for the 
proposed rule regarding the examples of events that may meet the 
definition of an exceptional event in order to elaborate upon or 
provide clarification about what constitutes an exceptional event.
1. Chemical Spills and Industrial Accidents
    Emissions that result from accidents such as fires, explosions, 
power outages, train derailments, vehicular accidents, or combinations 
of these may be flagged as an exceptional event.

Comments and Responses

    Comment: Several commenters stated that ``Chemical Spills and 
Industrial Accidents'' should generally not be considered exceptional 
events. Commenters stated that most industrial accidents and chemical 
spills are reasonably controllable and preventable with proper planning 
and mitigation efforts. These commenters stated that allowing for 
accidents or spills that could have been avoided is inconsistent with 
the CAA.
    Response: It is EPA's belief that air quality data that has been 
affected by emissions from chemical spills, industrial accidents, or 
structural fires may be flagged by a State as an exceptional event and 
reviewed by EPA for exclusion on a case-by-case basis to determine 
whether it meets the criteria for exceptional events as defined in this 
rule. In particular, data influenced by chemical spills or industrial 
accidents must be demonstrated to have ``affected air quality'' and 
must be demonstrated to be due to circumstances that were not 
reasonably controllable or preventable and are events that are unlikely 
to recur in a particular location. The EPA agrees with the commenters 
that industrial or point source emissions due to malfunctions or non-
compliance would not be considered exceptional events and should be 
addressed through the normal State Implementation Planning process.
2. Structural Fires
    Structural fires include any accidental fire involving a manmade 
structure.

Comments and Responses

    Comment: Several commenters indicated that ``Structural Fires'' 
should generally not be considered exceptional events. Commenters 
stated that these types of events should be considered as emissions 
from anthropogenic sources and handled within the form of the 
respective air quality standards where a certain number of exceedances 
of the standards are allowed over a 3-year period. Commenters assert 
that structural fires, lasting for several hours, are unlikely to cause 
an area to reach the level of nonattainment. In cases where structural 
fires are determined to be the cause of a monitored violation of the 
NAAQS, commenters stated that EPA should adopt a case-by-case review of 
these events.
    Response: The definition of structural fires under this rule 
pertains to any accidental fire involving a manmade structure. The EPA 
believes that structural fires could be an exceptional event under this 
rule, provided all other requirements of the rule are met, because they 
could ``affect air quality,'' could be an event that is not 
``reasonably controllable'' or ``preventable,'' and could be events 
that are caused by human activity that are unlikely to recur at the 
same location. However, EPA agrees with the commenters that these types 
of events, as well as other similar types of events, should be reviewed 
on a case-by-case basis to determine whether they meet the criteria for 
an exceptional event as defined by this rule.
3. Exceedances Due to Transported Pollution
    Transported pollution, whether national or international in origin, 
and whether from natural or anthropogenic sources, may cause 
exceedances eligible for exclusion under this rule, as long as all of 
the criteria and requirements related to exceptional events are met as 
defined in this rule. For example, States may flag, and EPA may 
exclude, data associated with fires occurring outside of the borders of 
the United States, such as forest fires in Mexico, Central America, and 
Canada; or transport events such as African dust and Asian dust which 
contribute significantly to ambient concentrations of a pollutant in an 
area, leading to exceedances or violations of a NAAQS. An example of 
interstate transported emissions which may be flagged as due to an 
exceptional event would be emissions due to smoke from wildfires or 
wildland fire use fires which cause exceedances or violations of the 
NAAQS at monitoring sites in other States. Other examples could include 
data affected by emissions from mining and agricultural activities when 
such emissions are subjected to long-range transport, and the criteria 
and

[[Page 13565]]

requirements related to an exceptional event are met as defined in this 
rule. In general, events due to transported pollution may be considered 
on a case-by-case basis.

Comments and Responses

    Comment: Several commenters expressed concern over EPA allowing the 
exceptional events rule to be used to exclude data that has been 
affected by emissions emanating from sources outside the borders of the 
United States.
    Response: States may flag data that has been affected by sources 
emanating from outside the United States that meet the criteria for an 
exceptional event as defined under this rule, including requirements 
for causation and documentation. In cases where an area is impacted by 
emissions from sources outside of the United States which do not meet 
the criteria for an exceptional event under this rule, and these 
emissions contribute to an area being designated as nonattainment, the 
emissions may be addressed under section 179B of the CAA related to 
``International Border Areas.'' Section 179B provides that where a 
State is required to submit a State Implementation Plan (SIP) to 
address issues related to a nonattainment designation, EPA may approve 
the SIP for the area provided that the plan (1) meets all the 
applicable requirements called for under the CAA, other than the 
requirement that the plan demonstrate attainment or maintenance of the 
NAAQS, and (2) the SIP must demonstrate that the affected area would be 
able to attain the standard by the applicable attainment date ``but 
for'' emissions emanating from outside the United States.
4. Exceedances Due to a Terrorist Attack
    Emissions that result from a terrorist attack such as smoke from 
fires, dust, explosions, power outages, train derailments, vehicular 
accidents, or combinations of these may be flagged as an exceptional 
event.

Comments and Responses

    No comments were received on this topic.
5. Natural Events
    The natural events addressed by this final rule are: (1) Natural 
disasters and associated cleanup activities; (2) volcanic and seismic 
activities; (3) high wind events; (4) wildfires and wildland fire use 
fires; and (5) stratospheric ozone intrusions. The EPA will consider 
other types of natural events on a case-by-case basis.
a. Natural Disasters and Associated Clean-Up Activities
    For the purpose of flagging, major natural disasters such as 
hurricanes and tornadoes for which State, local, or Federal relief has 
been granted, and clean-up activities associated with these events, may 
be considered exceptional events. The EPA believes that for a major 
natural disaster, a timeframe up to 12 months is a reasonable time 
period to allow for clean-up activities associated with these types of 
activities. In cases where the damage caused by the event is so 
substantial that a 12-month period is inadequate to address the clean 
up that is necessary, a State may submit a request to EPA for an 
extension of the 12-month time period. The EPA will grant requests for 
extensions of the time period related to such events on a case-by-case 
basis if the States submit adequate supporting information concerning 
the reason for the extension as well as the length of time being 
requested for the extension.

Comments and Responses

    Comment: Several commenters indicated that EPA should limit the 
time period associated with clean-up activities due to a natural 
disaster. One commenter indicated that the exceptional events rule as 
proposed would allow States to apply the term ``natural disaster'' very 
broadly to include circumstances that would circumvent the intent of 
the CAA. For example, declaring an episode of high summer temperatures 
to be a natural disaster could potentially allow a State to exclude 
high ozone levels which commonly occur during hot weather.
    Response: A time period up to 12 months for clean-up activities is 
permitted for major natural disasters, such as hurricanes and 
tornadoes, for which State, local, or Federal relief has been granted, 
may be flagged for exclusion as exceptional events under this rule. The 
clean-up activities associated with these types of events may also be 
flagged for exclusion as being due to an exceptional event. Given the 
nature of a major natural disaster, the 12-month time period allowed 
for clean-up activities following such disaster is a reasonable time 
period, and is consistent with the time period being allowed for 
volcanic and seismic activities under this rule. The period of high 
summer temperatures noted in the comment would not represent a major 
natural disaster, as described above, subject to the 12-month clean-up 
period.
b. Volcanic and Seismic Activities
    Ambient concentrations of particulate matter for which volcanic or 
seismic activity caused or significantly contributed to high levels of 
particulate matter in an affected area will be treated as natural 
events. While generally not occurring frequently, volcanic and seismic 
activity can affect air quality data related to the particulate matter 
NAAQS for an extended period of time after an event. Volcanic 
activities can contribute to ambient concentrations in several ways: it 
may influence concentrations of particulate matter due to primary 
emissions (e.g., ash), and emissions of precursor pollutants (e.g., 
sulfur dioxide) that contribute to the secondary formation of 
particulate matter. Seismic activity (e.g., earthquakes) can also 
contribute to ambient particulate matter concentrations by shaking the 
ground, causing structures to collapse, and otherwise raising dust 
which may lead to exceedances or violations of the NAAQS.

Comments and Responses

    Comment: Several commenters indicated that the rule should provide 
sufficient flexibility for data to be excluded where the duration of 
the event may last for a long period of time. An example of such an 
event is where volcanic activities last for several days.
    Response: The EPA agrees with the commenters and notes that the 
rule allows for States to flag data and submit documentation related to 
events such as long-term volcanic and seismic activities. States may 
also submit requests to EPA to extend the time period up to 12 months 
for major natural disasters, for clean-up activities following volcanic 
and seismic events. States are encouraged to submit supporting 
information related to the reasons for the requested extension and the 
length of time being requested for the extension.
c. High Wind Events
    High wind events are events that affect ambient particulate matter 
concentrations through the raising of dust or through the re-
entrainment of material that has been deposited. In some locations, 
concentrations of coarse particles like PM10 are most likely 
affected by these types of events, although PM2.5 standards 
may be exceeded under such circumstances as well. Section VII.B. also 
includes a discussion of this issue.

Comments and Responses

    Comment: Several commenters suggested that EPA replace the term

[[Page 13566]]

``high winds'' with the term ``wind-generated dust'' because (1) it 
places the emphasis on the natural mechanism, (2) dust may become 
entrained at relatively low wind velocities, and (3) the change will 
eliminate confusion between the wind speeds associated with a natural 
event and wind speeds needed to qualify for a ``high wind'' exceptional 
event under EPA's 1986 guidance.
    Response: The EPA is retaining the term ``high wind'' event because 
it accurately connotes the type of natural event that should be 
excluded under this rule, as well as the action which caused the 
exceedance or violation of the standard. The term also serves as an 
indicator concerning the level of wind which caused the exceedance or 
violation of the standard and indicates that it was unusually high for 
the affected area during the time period that the event occurred. 
Therefore, States must provide appropriate documentation to 
substantiate why the level of wind speed associated with the event in 
question should be considered unusual for the affected area during the 
time of year that the event occurred. The EPA will evaluate such 
instances on a case-by-case basis, including factors such as 
historically typical windspeed levels for the season of the year that 
the event is claimed.\11\
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    \11\ As described elsewhere in the preamble, EPA is adopting a 
weight of evidence approach to demonstrate that an exceptional event 
caused an exceedance or violation. Therefore, in instances where the 
level of the wind speed results in exceedances or violations of 
particulate matter, for data affected by these events to be 
considered for exclusion under the weight of evidence approach, a 
clear causal relationship must be demonstrated between the 
exceedances measured at the air quality monitoring site and the high 
wind event in question. EPA will consider in the weight of evidence 
analysis winds that produce emissions contributed to by 
anthropogenic activities that have been controlled to the extent 
possible through use of all reasonably available reasonable and 
appropriate measures.
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d. Wildland Fires
    Federal land managers have afforded recognition to several 
different types of wildland fires (i.e., wildfire, wildland fire use 
fire and prescribed fire), depending on their causal circumstances and 
the role that such fires play in the affected ecosystems. Prescribed 
fire is addressed more fully in the following section.
    The question of what is a natural versus an anthropogenic fire has 
particular significance when considering the impacts of wildland fires 
(wildfire, wildland fire use fire and prescribed fire) on air quality 
and how these impacts should be regarded under this rule. A 
``wildfire'' is defined as an unplanned, unwanted wildland fire (such 
as a fire caused by lightning), and include unauthorized human-caused 
fires (such as arson or acts of carelessness by campers), escaped 
prescribed fire projects (escaped control due to unforeseen 
circumstances), where the appropriate management response includes the 
objective to suppress the fire. In contrast, a ``wildland fire use'' 
fire is the application of the appropriate management response to a 
naturally-ignited (e.g., as the result of lightning) wildland fire to 
accomplish specific resource management objectives in predefined and 
designated areas where fire is necessary and outlined in fire 
management or land management plans.
    Using these definitions, we believe that both wildfires and 
wildland fire use fires fall within the meaning of ``natural events'' 
as that term is used in section 319. Therefore, ambient particulate 
matter and ozone concentrations due to smoke from a wildland fire will 
be considered for treatment as an exceptional event if the fire is 
determined to be either a wildfire or wildland fire use fire.

Comments and Responses

    Comment: In general, commenters strongly supported exempting 
wildfires as exceptional events under the rule.
    Response: The EPA acknowledges support for the proposal to classify 
wildfires as a potential exceptional event. As noted above, the Agency 
states that wildland fires will be excluded as exceptional events if 
they meet the criteria and requirements of the exceptional events rule.
    Comment: The Agency received comments both supporting and opposing 
the proposal allowing wildland fire use fires to qualify as an 
exceptional event.
    Response: After reviewing Congress' revisions to section 319, the 
various Agency policies cited in the proposal, and comments received, 
the Agency has determined that wildland fire use fires may also qualify 
as an exceptional event. However, these types of fires must also meet 
certain criteria. For example, these fires must occur on lands that 
have been designated in fire management or land management plans as 
areas where fires are necessary and desirable to accomplish specific 
resource management objectives.
    Comment: Many commenters supported EPA's commitment to update the 
1998 Interim Air Quality Policy on Wildland and Prescribed Fires to be 
consistent with this rule.
    Response: The Agency plans to begin revising this policy in 2007 as 
part of its overall Fire Strategy after promulgation of this rule.

e. Stratospheric Ozone Intrusions

    Stratospheric ozone intrusion is considered to be a natural event. 
A stratospheric ozone intrusion occurs when a parcel of air originating 
in the stratosphere, which is at an average height of 20 km or 12.4 
miles, is transported directly to the surface of the earth. 
Stratospheric ozone intrusions are very infrequent, localized events of 
short duration. They are typically associated with strong frontal 
passages and, thus, may occur primarily during the spring season.

Comments and Responses

    Comment: One commenter stated that EPA should update its approach 
to stratospheric events, establish criteria by which such events may be 
determined, and credit States for the impact of intrusion events on 
non-compliant ozone monitor readings.
    Response: Stratospheric ozone intrusion is identified as a natural 
event under 40 CFR part 50, appendix I, for ozone, and will be 
considered for treatment as an exceptional event.
6. Prescribed Fire
    A ``prescribed fire'' is defined as any fire ignited by management 
actions to meet specific resource management objectives. According to 
existing Federal policy, prior to ignition a prescribed fire must have 
an approved prescribed fire plan and must meet the National 
Environmental Policy Act (NEPA) requirements (where applicable)(see 
National Wildland Fire Coordination Group Glossary of Wildland Fire 
Terminology, 2003). For purposes of section 319, a prescribed fire 
cannot be classified as ``natural,'' given the extent of the direct 
human causal connection, however, a prescribed fire may meet the 
statutory criteria defined in section 319 of ``affect[ing] air 
quality,'' being ``unlikely to recur at a particular location'' and is 
``not reasonably controllable or preventable.'' The determination of 
whether a prescribed fire can be considered an exceptional event should 
be made on a case-by-case basis taking into account the factors 
described below.
    A prescribed fire carried out for resource management objectives is 
frequently designed to restore essential ecological processes of fire 
and mimic fire under natural conditions. As such, a prescribed fire's 
expected frequency can vary widely, depending on the natural fire 
return interval of a particular landscape or wildland ecosystem. The 
natural fire return

[[Page 13567]]

interval can range from once every year to less frequently than once in 
more than 200 years. Thus, in many, though not all cases, it may be 
possible to demonstrate that the likelihood of recurrence is 
sufficiently small enough to show that a prescribed fire under these 
conditions meets the ``unlikely to recur at a particular location'' 
requirement of the statutory language.
    A prescribed fire may also meet the condition of ``not reasonably 
controllable or preventable'' by examining whether there are reasonable 
alternatives to the use of fire in light of the needs and objectives to 
be served by it. For instance, there may be a significant build-up of 
forest fuels in a particular area that if left unaddressed would pose 
an unacceptable risk of catastrophic wildfire, which could result in 
adverse impacts of much greater magnitude, duration, and severity than 
would result from careful use of prescribed fire. A particular 
ecosystem may also be highly dependent on a natural fire return 
interval to maintain a sustainable natural species composition. 
Alternatively, pest or disease outbreaks in an area may be such that 
there are no reasonable alternatives to prescribed fire. In some cases, 
other legal requirements may preclude the use of mechanical fuel 
reduction methods such as in designated wilderness or National Parks. 
Where such ecological conditions exist, or where mechanical or other 
treatments are not reasonably feasible for reasons that include, but 
are not limited to, a lack of access, or severe topography, we believe 
that prescribed fire qualifies as being ``not reasonably controllable 
or preventable.'' Thus, we believe that a prescribed fire, conducted by 
Federal, State, Tribal or private wildland managers or owners, under 
the conditions described above may qualify as an exceptional event.
    In addition, one of the principles contained in SAFE-TEA-LU, 
section 6013(b)(3)(A), includes the principle that States must take 
necessary measures to safeguard public health regardless of the source 
of air pollution. We believe it reasonable to tie the qualifying 
criteria for an anthropogenically generated prescribed fire to State 
accountability for public health protection. Consistent with historical 
practice governed by the guidance contained in the ``Interim Air 
Quality Policy on Wildland and Prescribed Fires,'' issued on May 15, 
1998, EPA approval of exceedances linked to a prescribed fire used for 
resource management purposes is contingent on the State certifying that 
it has adopted and is implementing a Smoke Management Program (SMP) as 
described in that policy. A State SMP establishes a basic framework of 
procedures and requirements for managing smoke from a prescribed fire 
managed for resource benefits. A SMP is typically developed by a State 
or Tribe with cooperation and participation by wildland managers, both 
public and private, and the general public. As reflected in the Interim 
Air Quality Policy on Wildland and Prescribed Fires, States are 
provided flexibility on the structure of a SMP. Thus, a SMP can be 
extensive and detailed, or simply identify the basic smoke management 
practices for minimizing emissions, and controlling impacts from a 
prescribed fire.\12\ In the proposal to this rule, EPA proposed to 
continue the use of that approach. We also proposed to expand the 
criteria for contingent approval to a prescribed fire where, in lieu of 
a SMP, basic smoke management practices, that minimize emissions and 
control impacts, are being employed by burners. In order to protect 
public health in areas where a SMP has not been adopted, in the final 
rule, the Agency has elected to expand, on a case-by-case basis, the 
qualifying criteria by which a prescribed fire may qualify as an 
exceptional event. In those cases, the Agency will judge on a case-by-
case basis whether the State has ensured that appropriate basic smoke 
management practices have been employed in determining whether the 
prescribed fire qualifies as an exceptional event. If an exceptional 
event occurs using the basic smoke management practices approach, the 
State must undertake a review of their approach to ensure public health 
is being protected and must include consideration of development of a 
SMP.
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    \12\ Basic smoke management practices could include, among other 
practices, steps that will minimize air pollutant emissions during 
and after the burn, evaluate dispersion conditions to minimize 
exposure of sensitive populations, actions to notify populations and 
authorities at sensitive receptors and contingency actions during 
the fire to reduce exposure of people at such receptors, identify 
steps taken to monitor the effects of the fire on air quality, and 
identify procedures to ensure that burners are using basic smoke 
management practices.
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Comments and Responses

    Comment: Several commenters supported classifying prescribed fire 
as qualifying as an exceptional event. However, some commenters 
indicated that there should be limitations placed on when this type of 
fire should be considered as an exceptional event. A number of 
commenters also disapproved of allowing prescribed fire to be 
considered as an exceptional event because they believe that this type 
of fire is anthropogenic and does not meet the statutory definition of 
exceptional event. Some commenters also favored expanding the criteria 
for contingent approval to include instances where basic smoke 
management practices are used in lieu of a SMP, while other commenters 
did not favor this expansion.
    Response: The EPA believes that a prescribed fire may be excluded 
as an exceptional event under this rule only in cases where the event 
meets the criteria for an exceptional event as defined in this rule, if 
documentation is submitted to show that the fire meets the requirement, 
as described above, of ``affect[ing] air quality,'' being ``not 
reasonably controllable or preventable'' and ``unlikely to recur at 
location'' and provided the other requirements of the rule including, 
among others, the schedules and procedures for flagging and 
demonstration are met. In those instances where a prescribed fire meets 
the criteria for an exceptional event, the State must also provide 
appropriate documentation to show that a certified SMP was in place or 
that the burner employed basic smoke management practices and that the 
appropriate practices were being followed at the time that the event 
occurred. Because a prescribed fire is an anthropogenic source of 
emissions for purposes of section 319, even though it may qualify as an 
exceptional event, a State can attempt to limit the health impact of a 
prescribed fire through the thoughtful development and implementation 
of a SMP or ensuring that basic smoke management practices were 
employed that minimize emissions and control impacts from prescribed 
fires.

V. The Management of Air Quality Data Affected by Exceptional Events

    The EPA proposed that, in order to exclude air quality data from 
consideration for regulatory purposes, States must follow the 
procedures, timelines, and other requirements described in the proposed 
rule. Under the Final Rule, if an event is determined to be a 
qualifying exceptional event according to section IV.D, a State, Tribe, 
or designated local agency may petition EPA to classify the event as 
exceptional and submit a demonstration to justify data exclusion.\13\ 
For data exclusion, States must clearly identify, or ``flag,''

[[Page 13568]]

data they believe to be influenced by such events. The demonstration to 
justify data exclusion shall provide evidence that: (a) The event 
qualifies in accordance with section IV.D and with EPA policies and 
guidance for certain events as described in section IV.E, (b) there is 
a clear causal relationship between the measurement under consideration 
and the event that is claimed to have affected the air quality in the 
area, (c) the event is associated with an unusual measured 
concentration beyond typical fluctuations including background, and (d) 
that there would have been no exceedance or violation but for the 
event.
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    \13\ Although a single qualifying exceptional event may affect 
air quality for multiple days and at multiple monitors, the 
discussions below consider an individual demonstration as justifying 
exclusion of a single AQS data point. The EPA encourages State 
submittals to package demonstrations about single exceptional events 
to expedite the review process.
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    The SAFE-TEA-LU requirements for exclusion of data from exceptional 
events are: (1) The occurrence of the exceptional event must be 
demonstrated by reliable and accurate data; (2) the State must show 
that there is a ``clear causal relationship'' between the NAAQS 
exceedances and the event; (3) there must be a public review process 
related to the exceptional event determination; and (4) the rule must 
set criteria and procedures for States to petition EPA to exclude data 
directly affected by an exceptional event. The sections below describe 
how each of these requirements must be met.
    The sections below address the flagging of data as exceptional 
events that are determined to have affected air quality, submittal of 
demonstrations to request data exclusion, public review, and the 
schedule and timing for these processes. After an exceptional event 
occurs (judged according to section IV.D) and an agency determines that 
the event affected ambient air quality, flagging may occur according to 
section V.A. Section V.B describes the evaluation of whether or not the 
event affected ambient air quality. Section V.C describes the necessary 
``but-for'' test that data would have complied with the applicable 
standard but for the occurrence of the exceptional event. Section V.D 
explains the schedules and procedures for the flagging and 
demonstration submittals, section V.E discusses the applicability to 
hourly readings, section V.F states the requirements for determination 
submittals if the agency requests EPA to exclude the data from 
consideration for regulatory purposes, and section V.G describes the 
public review requirements. Some commenters suggested that all data 
occurring from exceptional events should be flagged, and EPA will allow 
these flags for informational purposes, even if the data do not qualify 
for exclusion. If EPA concurs on the exclusion of data from qualifying 
exceptional events, the data will be excluded from regulatory 
consideration but will still count toward data capture requirements.

A. Flagging of Data in the AQS Database

1. Background
    Air quality data are required, pursuant to 40 CFR 58.16, to be 
submitted to EPA by each State on a calendar quarterly basis, with 
submissions due not later than 90 days after the end of a quarterly 
reporting period. Once air quality data have been submitte