Document ID: EPA-HQ-OAR-2005-0159-0161
Agency: epa
Document Type: Rule
Title: Treatment of Data Influenced by Exceptional Events
Posted Date: 2007-03-22T04:00Z

[Federal Register: March 22, 2007 (Volume 72, Number 55)]
[Rules and Regulations]               
[Page 13559-13581]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr22mr07-14]                         

[[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

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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 http://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 http://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. (http://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.
---------------------------------------------------------------------------

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.
---------------------------------------------------------------------------

    \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.
---------------------------------------------------------------------------

    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 submitted to EPA, it 
is possible to ``flag'' specific values for various purposes. ``Data 
flagging'' refers to the act of making a notation in a designated field 
of an electronic data record. The principal purpose of the data 
flagging system in the AQS database is to identify those air quality 
measurements for which special attention or treatment is warranted. 
These include, but are not limited to, those measurements that are 
influenced by exceptional events.
    The preamble to the proposed rule stated: ``In the case of 
exceptional events, States place the initial flag on the data in the 
AQS database. Following an evaluation of the supporting documentation, 
EPA will decide whether to concur with the flag; concurrence will be 
marked by the placement of a second flag in the AQS database by EPA. 
Once EPA has concurred on the flag, the data will be excluded from 
regulatory decisions such as determinations of attainment or 
nonattainment.''
     ``While the flagging of data by the State is the first 
step in an exceptional events demonstration, it is insufficient by 
itself to allow for the exclusion of data. In order to have EPA concur 
on a flag, States must meet the additional requirements described 
below. As stated previously, the State has the responsibility to 
document both the occurrence of the event and the causal connection to 
the monitoring data under consideration. Because the initial step of 
flagging the data is a relatively simple one, States may flag many more 
days than the number of days for which they ultimately submit 
documentation to support exclusion.''
2. Final Rule
    In the case of exceptional events, States and Tribes place the 
initial flag on the data in the AQS database, but EPA determines the 
available flags.\14\ States may also delegate authority to local 
agencies to submit flags and documentation. In any event, States should 
work with their local agencies for the identification and review of 
exceptional events and consider requests to flag data from those 
agencies. At the time the flag is inserted into the AQS database, the 
State must also provide an initial description of the event in the AQS 
comment field. This initial description should include such information 
as the direction and distance from the event to the air quality monitor 
in question, as well as the direction of the wind on the day in 
question. The flags, and the initial event description, must be 
inserted into the AQS database prior to July 1st following the year in 
which the event occurred. Schedules for demonstrations are discussed in 
section V.D.
---------------------------------------------------------------------------

    \14\ It is EPA's intention, for purposes of consistency with 
this rule, to review the list of exceptional events that are 
currently in the AQS database following the promulgation of the 
rule.
---------------------------------------------------------------------------

    Following an evaluation of the supporting documentation, EPA will 
make a decision concerning whether to concur with the flag; concurrence 
will be marked by the placement of a second flag in the AQS database by 
EPA. If EPA has concurred on the flag, the data will be excluded from 
regulatory determinations such as determinations related to attainment 
or nonattainment, or determinations concerning SIP development. The EPA 
will use the second flag to indicate the following conditions: EPA 
concurrence, EPA non-concurrence, and documentation submitted with EPA 
decision pending.
    While flagging of the data in the AQS database by the affected 
State, local, or Tribe authority is the first step in an exceptional 
events demonstration, it is insufficient in and of itself to allow for 
the exclusion of data. In order for EPA to concur on an exceptional 
events flag, States, Tribes, and local agencies must meet the 
additional requirements described below. As explained, the State, 
Tribe, or local agency has the responsibility to document the 
occurrence of the event in question, to demonstrate that the event 
qualifies as an exceptional event in accordance with section IV.D, is 
consistent with EPA policies and guidance for certain events as 
described in section IV.E, has provided for public review in accordance 
with section V.G, and to document the causal connection between the 
measurement under consideration and the event that is claimed to have 
affected the air quality in the area. The State, Tribe, or local agency 
must also demonstrate that the event is associated with an unusual 
measured concentration beyond typical fluctuations including 
background, and that there would have been no exceedance or violation 
``but for'' the event. Because the initial step of

[[Page 13569]]

flagging the data is a relatively simple one, States, Tribes, and local 
agencies may flag more days than the number of days for which they 
ultimately intend to submit demonstrations to justify data exclusion.
3. Comments and Responses
    Comment: One commenter supported flagging data related to any fire 
that caused an exceedance.
    Response: This Rule does not preclude a State, Tribe, or Local 
agency from flagging any data allegedly influenced by exceptional 
events. However, for the data to qualify as an exceptional event and to 
exclude it from regulatory decisions, the data must meet all of the 
criteria described in this Rule and all the procedures delineated must 
be followed.

B. What Does It Mean for an Event To ``Affect Air Quality''?

1. Background
    It is important to recognize that any emissions-producing event has 
the potential to have some influence on downwind air quality. Indeed, 
on any given day, measured air quality at any given location will 
reflect the influences of a variety of activities, including both 
natural and anthropogenic emissions from both local as well as remote 
upwind sources. Given the directive in section 319(b)(3)(B)(ii), that a 
clear causal connection must exist between the ``measured exceedances'' 
and the exceptional event, EPA believes that it would be unreasonable 
to exclude data affected by an exceptional event simply because of a 
trivial contribution of an event to air quality. Furthermore, we 
believe that it would be unreasonable to exclude more significant, but 
routine background air quality impacts, as this would disregard an 
important part of the public's exposure to air pollution upon which 
EPA's air quality standards are based. The effect of such exclusion 
would be an inappropriate reduction in the stringency of the NAAQS, 
rather than providing specific relief under the circumstances provided 
in section 319 for which States should not be designated nonattainment 
or be required to prepare costly SIP control strategies.
    Neither section 319, nor its legislative history, provides precise 
guidance on what should be considered when determining whether an event 
``affects air quality'' and thus qualifies to be considered for 
exclusion or special treatment. However, section 319(b)(3)(B)(ii) and 
(iv) provides that there must be a ``clear causal relationship'' 
between a measured exceedance of a standard and the event to show that 
the event ``caused a specific air pollution concentration;'' and it 
must be shown that the data in question are ``directly due'' to an 
exceptional event. Moreover, one of the principles provided by section 
319(b)(3)(A) indicates that the protection of public health is the 
highest priority. For these reasons, we proposed three conditions under 
which an event may qualify as ``exceptional'' for purposes of special 
regulatory consideration: Its air quality impact must (1) fall both 
above the level of the applicable standard (i.e., must be an 
``exceedance'' as required by section 319), (2) be significantly beyond 
the normal fluctuating range of air quality, including background air 
quality concentrations, and (3) should be large enough such that 
without it there would have been no exceedance.
    We next provided several alternative approaches to determining 
whether and when air quality is ``affected by'' exceptional events and 
requested comment on which of these approaches was most suitable for 
demonstrating such impacts. These approaches primarily applied to 
condition (2) above. Two of the approaches involved statistical 
comparisons of existing flagged data. The final rule most closely 
reflects the third proposed option with some modifications. This option 
considered a case-by-case evaluation of the data against historical, 
seasonally adjusted air quality levels. Finally, the proposed rule 
provided details regarding what is meant by an exceedance (1) and the 
``but-for'' condition (3). These are discussed in detail in section 
V.C.
2. Final Rule
    Under the Final Rule, the demonstration to justify data exclusion 
must provide a justification that: (a) The event qualifies in 
accordance with section IV.D. and if applicable, 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) 
there would have been no exceedance or violation but for the event 
(discussed in section V.C). The second and third criteria establish 
that the event affected air quality.
    The second criterion that the event caused an air quality impact 
may be shown through a number of methods including, but not limited to, 
modeling and speciation analysis. The third criterion distinguishes 
common events from those that are exceptional and may be accomplished 
through the presentation of historical evidence.
    The final rule permits a case-by-case evaluation, without 
prescribed threshold criteria, to demonstrate that an event affected 
air quality. This demonstration would be based on the weight of 
available evidence, but must consider the historical frequency of such 
measured concentrations. While a State may determine the specific 
approach to use for such analysis, it must compare contemporary 
concentrations with the distribution of all measured data during the 
past several years. The evidence that an event affected air quality may 
be presented on a seasonal or other temporal basis to best compare 
contemporary concentrations with the distribution of historical values. 
For consistency with data reporting and computation of NAAQS 
statistics, a calendar quarter basis is suggested. Baseline data may 
also be defined differently for each event type (e.g., April and May 
data may be the most relevant information for statistical comparison 
with certain dust events).
    The general statistical approach of using all measured data during 
the past several years is independent of historical flagging practices 
and allows States to accurately represent events not likely to recur by 
including all monitoring data in analyses.
    In addition, the magnitude of the measured concentration on days 
affected by exceptional events relative to historical, temporally 
adjusted air quality levels can guide the level of necessary analysis 
and documentation to demonstrate that the event affected air quality. 
For extremely high concentrations relative to historical values (e.g., 
concentrations greater than the 95th percentile), a lesser amount of 
documentation or evidence may be required to demonstrate that the event 
affected air quality. The closer the event concentration is to typical 
levels (e.g., values less than the historical 75th percentile), the 
stronger the necessary evidence would have to be to justify exclusion 
of data for regulatory purposes. This weight of evidence approach is 
most nearly analogous to our historical treatment of exceptional 
events.
3. Comments and Responses
    Comment: One commenter noted that EPA's proposed rule concedes that 
the third option would ``provide the least definitive guidance to 
assist States in their evaluations,'' and ``may make it

[[Page 13570]]

difficult for EPA regions to be consistent when determining whether to 
concur on a flag.'' Moreover, ``the case-by-case approach allows for 
consideration of days with ambient concentrations which are not 
necessarily among the highest concentrations that have been 
historically observed. While such days are unlikely to impact short-
term standards, discounting such days can certainly have an impact on 
an annual average concentration.'' The commenter asserted that EPA's 
description of the proposed case-by-case evaluation makes the case for 
rejecting that option because it fails to provide the guidance mandated 
by section 319, and is so vague as to be arbitrary.
    Response: The EPA disagrees with the commenter that this option 
fails to provide guidance and is so vague as to be arbitrary. The EPA 
has explained above the criteria that it will use in making its case-
by-case evaluations. The commenter's concern that the event must 
represent concentrations that are not typically observed is addressed 
by the third criterion that the event must be associated with an 
unusual measured concentration beyond typical fluctuations including 
background. Demonstration of the magnitude of the measured 
concentrations with respect to historical frequency under similar 
conditions will provide a new level of consistency across monitoring 
locations.
    Comment: If an area exceeds the NAAQS, one commenter stated that 
use of a 95th percentile criterion better ensures that the definition 
of an exceptional event is met (i.e., unlikely to recur at a particular 
location).
    Response: The EPA recognizes that extreme concentrations (e.g., 
corresponding to values greater than the 95th percentile of historical 
values) are more likely associated with exceptional events. With the 
final rule, we are not assuming that such values are definitely 
exceptional. In fact, some extreme concentrations may be associated 
with various emission sources and atmospheric conditions which are 
unrelated to a causal connection to the claimed exceptional event. 
Instead, the frequency of occurrence relative to historical 
concentrations would be used as an important part of the overall weight 
of evidence to demonstrate the exceptional nature of the claimed air 
quality impact.

C. Use of a ``But For'' Test

1. Background
    There may be instances in which exceptional events may have a 
significant impact on air quality on days when concentrations are 
already above the applicable standard in the absence of the influence 
of such events. In such cases, it is important to preserve and consider 
all valid air quality data influenced by such activities, which 
properly fall within the responsibilities of States to manage for 
purposes of air quality attainment and maintenance. For this reason, we 
proposed to require that air quality data may not be excluded except 
where States show that exceedances or violations of applicable 
standards would not have occurred ``but for'' the influence of 
exceptional events.
    In other words, to the extent that it is possible to determine that 
the resulting air quality concentrations and appropriate design values 
for an area would be above the level of the standards even without the 
influence of the exceptional event, the air quality data for the day(s) 
in question should not be excluded. However, consideration of the 
impacts of exceptional events on air quality values for control 
strategy planning purposes may be appropriate, and States are 
encouraged to consult with the appropriate EPA regional office to 
further discuss this issue.
2. Final Rule
    The EPA will maintain the proposed ``but-for'' requirement that air 
quality data may not be excluded except where States, Tribes, or local 
agencies show that exceedances or violations of applicable standards 
would not have occurred ``but for'' the influence of exceptional 
events. Through analyses, it is possible to demonstrate that an 
exceedance or violation would not have occurred but for the event [See 
sample ``but-for'' analysis in memo to docket, Husar et al. 2006 
(http://www.regulations.gov, EPA-HQ-OAR-2003-0061-0733 thru 0733.5)]. 

This analysis does not require a precise estimate of the estimated air 
quality impact from the event. The weight of evidence demonstration can 
present a range of possible concentrations which is not as technically 
demanding as justifying a specific adjustment to a measured value.
    Because there are two standards for PM2.5, clarification 
is needed regarding the measurements that contributed to an exceedance 
or a violation that are eligible to be excluded. This rule is limited 
to values above the annual standard for PM2.5 because this 
simplifies the process for determining which values are eligible for 
flagging according to the intent of section 319. The short-term 
PM2.5 NAAQS is based on a 3-year average of the annual 98th 
percentile of 24-hour values. Therefore, it is possible that one or two 
of these annual concentration values may be below the level of the 
NAAQS while the 3-year average is above the level of the NAAQS. Because 
three annual 98th percentile concentration values are included in the 
determination of a short-term PM2.5 NAAQS violation, 
individual measurements below the NAAQS may contribute to a violation.
    On the other hand, the annual PM2.5 NAAQS is also a 
standard based on a 3-year average. However, violations of the annual 
standard that are caused by measurements which are not exceedances of 
that standard will be difficult to distinguish from typical air quality 
concentrations including background. To accommodate the 3-year form of 
the PM2.5 NAAQS, this rule will allow measurements whose 
concentrations are greater than the level of the annual NAAQS to be 
flagged as being affected by exceptional events for the purposes of 
contributing to an exceedance or violation of the PM2.5 
NAAQS. Thus, we provide the following clarification that individual 
measured values greater than the annual PM2.5 NAAQS will be 
considered ``exceedances'' under this rule and therefore eligible to be 
considered for exclusion for comparisons to either the annual or 24-
hour NAAQS.
3. Comments and Responses
    Comment: One commenter stated that, while some of those 
measurements may not individually be above the NAAQS, taken together 
they might be sufficient to put an area in violation of an annual 
standard. Any ``but for'' determination must take into account the 
aggregate of exceptional events that occurred within the applicable 
NAAQS period.
    Response: The rule acknowledges that it is possible that an event 
can affect multiple days. The ``but for'' provision allows for data 
exclusion if but for the entire event there would have been no 
exceedance or violation. Therefore, for those events that can be shown 
to affect air quality on multiple consecutive days, measurements for 
the entire period are eligible for data exclusion, provided that at 
least one measurement day during the episode is an exceedance as 
defined by this rule and the air quality impact on each day are 
considered exceptional.
    Comment: One commenter cautioned EPA about using the phrase ``to 
the extent it is possible to determine'' because a ``bright line'' 
distinction between the contribution from natural and anthropogenic 
sources often does not exist.
    Response: We agree with this comment and for this reason we will 
permit a weight of evidence-based

[[Page 13571]]

approach to demonstrate that there would not have been an exceedance or 
violation but for the event.

D. Schedules and Procedures for Flagging and Requesting Exclusion of 
Data

1. Background
    In establishing procedures and time tables for States to request, 
and EPA to grant, exclusion of data affected by exceptional events, we 
are guided by two competing considerations: Ensuring States have 
adequate time and opportunity to compile and evaluate all relevant and 
available information in support of such requests; and making 
determinations in a timely manner so that all pertinent and valid air 
quality data would be appropriately considered in regulatory 
determinations. To assist EPA in determining the best approach to 
managing the data flagging process and submissions of demonstrations 
for the final rule, we proposed three alternatives for public review 
and comment. Public comments showed that each option had desirable 
aspects, and these are incorporated into the final rule.
2. Final Rule
    A multi-step process will be established for identification of data 
and submission of demonstrations. The process is designed to ensure 
that States, Tribes, and local agencies have adequate opportunity to 
compile and present evidence of exceptional and natural events but also 
ensures timely submittals in order to make regulatory decisions and 
ensure the protection of human health through NAAQS determinations. The 
steps include State flagging, annual State submission of an initial 
event description, State submission of a demonstration to justify data 
exclusion and EPA review followed by approval or disapproval. Where air 
quality in an area is influenced by a relatively small set of emission 
sources with well-defined emission profiles and limited pollutant 
species, a demonstration that an air quality measurement influenced by 
a particular event merits exclusion may be relatively simple to make. 
In other cases, such as where the number and types of sources 
contributing to measured air quality concentrations are extremely 
complex and varied, making it more difficult to distinguish between the 
effects of routine activities and unusual ones, more time and effort 
will be needed for a State, Tribe, or local agency to provide an 
adequate demonstration in support of its request.
    States, Tribes, and local agencies are encouraged to flag the data 
that they believe to be affected by exceptional events at the time of 
submission of the air quality data to EPA's AQS database, in accordance 
with the schedule described in 40 CFR 58.16, which is generally no 
later than 90 days after the end of the calendar quarter. This includes 
both flagging of data and insertion of the initial event description 
into the AQS comment field. This constitutes notification of the 
appropriate EPA Regional Office concerning the State's intention to 
seek exclusion of data. This approach would ensure that the flagging 
process remains consistent with the timeline set forth in rules 
governing data submission requirements. The EPA recognizes that 
laboratory analyses may delay these submissions and therefore is 
extending the required time period for submission to 180 days after the 
end of the calendar year (i.e., all flags, along with initial event 
descriptions, for a calendar year must be reported by July 1 of the 
following year).
    We encourage States, Tribes, and local agencies to submit the 
demonstration to justify data exclusion annually for exceedances of 
short-term NAAQS by July 1. However, the demonstration to justify data 
exclusion must also be submitted no later than 12 months prior to a 
regulatory decision. For all flagged events, the demonstration to 
justify data exclusion must be submitted within 3 years of the calendar 
quarter following an event, but no later than 12 months prior to a 
regulatory decision. This period should be used primarily to support 
NAAQS compliance with annual averages and violations of the short-term 
standard that were not anticipated. For nonattainment designations, 
this would occur with the Governor's letter recommending the list of 
nonattainment areas. We also recognize that special circumstances could 
dictate more expedited data delivery, flagging, and minimal 
demonstrations (e.g., PM2.5 designations using 2002-2004 
data). The submitted demonstration to justify data exclusion as well as 
the EPA responses and the rationale for the EPA decision will be made 
publicly available through EPA. The reason for providing the 3-year 
timeframe is that for ozone and PM, decisions regarding whether or not 
an area is attaining the applicable standard are based on the most 
recent 3 years of air quality data. Providing 3 years for submission of 
demonstrations would provide States, Tribes, and local agencies with an 
opportunity to evaluate whether the influence of one or more 
exceptional events will be relevant to determinations of attainment or 
nonattainment before undertaking the effort of preparing and submitting 
demonstrations.
    Once EPA receives a State's demonstration, EPA generally will 
undertake to review the demonstration and provide a concurrence or 
nonconcurrence on the flag in the AQS database within 60 days. The EPA 
expects that, in most cases, this time period should be enough time to 
review and provide a concurrence or non-concurrence related to a 
State's request to exclude data affected by an exceptional event. 
However, for more complex demonstrations, EPA may require additional 
time to make its decision and will notify the State of the additional 
time required.
3. Comments and Responses
    Comment: One commenter supported arguments on why the proposed rule 
must include a procedure for retrospective flagging that addresses the 
full set of the State's needs so that the end result is that the State 
can flag any and all events impacted by natural events.
    Response: With the Final Rule, EPA requires annual submittal of 
flags. States may, if they so choose, submit them sooner. This schedule 
ensures that data are collected and retained shortly after the event 
and identification of potential (non-routine) events is done in a 
timely fashion to ensure that appropriate corrective actions can be 
taken. States would only maintain minimal documentation supporting the 
decision to flag the data. The full demonstrations, however, can come 
later, in order to allow States time to focus efforts on those events 
that are determined to have an impact on attainment. The Agency notes 
that the Exceptional Events Rule does not apply to routine natural 
events that are part of background air quality.
    Comment: One commenter was concerned that a State may have failed 
to flag data impacted by a natural event because the data values were 
below the current NAAQS, only to find the State threatened with 
nonattainment after NAAQS revisions.
    Response: For data collected before the effective date of this 
rule, States may include a demonstration to justify data exclusion with 
the Governor's recommendation letter on nonattainment areas, provided 
that there was notice and opportunity for public comment. After 
considering this and other comments, for PM2.5 data 
collected during calendar years 2004-2006, that the State identifies as 
resulting from an exceptional event,

[[Page 13572]]

EPA is permitting the State to flag and submit an initial description 
of the event provided that these are submitted no later than October 1, 
2007. In cases where the State is able to show that this time period is 
inadequate, a State may submit a request for an extension and EPA will 
grant this request for an extension up to but no later than December 1, 
2007. This procedure should accommodate States concerned about 
potential PM2.5 nonattainment areas using the 2004-2006 data 
sets. The EPA may consider a similar exemption of the schedules for 
submittal of data for future revision of standards.
    Comment: One commenter stated that EPA should also make allowances 
for those situations when a State neglects to flag a value or submit 
documentation within the required timeframes. In these cases, the 
commenter asserted that EPA should provide some type of petitioning 
process.
    Response: If a State fails to meet the schedule for flagging or 
document submittal, late petitions will not be considered. Policy 
decisions, SIP planning, and dissemination of data should not be 
delayed or altered based on a State's failure to submit documentation 
or follow the regulatory procedures in a timely manner.

E. Exclusion of Entire 24-Hour Value as Opposed to a Partial Adjustment 
of the 24-Hour Value

1. Background
    In general, EPA's historical practice has been to exclude a daily 
measured value in its entirety when an exceptional event causes that 
value, and we retained this approach in the proposed rule. With this 
approach, a determination is made that emissions from the event are 
largely responsible for the resultant ambient air pollutant 
concentration. For example, if the observed concentration is 200 [mu]g/
m3 for PM2.5 and is associated with a nearby 
forest fire, then EPA is likely to concur with the claim that the event 
was responsible for the ambient concentration. The measured value would 
be excluded in its entirety from the data used to judge attainment (as 
per 40 CFR 50, appendix N), although the measurement would still count 
towards meeting minimum data capture requirements.
    We believe it would be desirable to adjust the daily value to 
exclude only those portions of the data that are attributable to the 
exceptional event in question, and to retain the remainder of the day's 
measurement if appropriate and accurate methods were available to make 
such adjustments. For example, if an area affected by a wildfire had a 
measured 24-hour PM2.5 concentration of 50 [mu]g/
m3 and the estimated event impact was 30 [mu]g/
m3, then the expected value that would have occurred but for 
the event would have been 20 [mu]g/m3. Normal air quality 
for this location might be 16 [mu]g/m3 and, therefore, the 
``but-for'' concentration of 20 [mu]g/m3 is above average. 
Discounting the entire event day could, therefore, inappropriately bias 
a determination of nonattainment with the annual PM2.5 NAAQS 
(currently set at 15 [mu]g/m3). We are currently seeking to 
develop and evaluate new analytical methods that would allow us to 
discount only the portion of the daily value attributable to the 
exceptional event. However, at present, we are not aware of the 
existence of precise and universally applicable techniques that are 
administratively and technically feasible and that could support 
partial adjustment of air quality data except perhaps in limited cases, 
such as where the number and type of pollutant species and contributing 
sources are relatively less complex or potentially when sufficient 
spatial, temporal, meteorological and chemical data are available [See 
memo to docket, Husar et al. 2006, (http://www.regulations.gov, EPA-HQ-

OAR-2003-0061-0733 thru 0733.5)]. When we determine that techniques for 
adjustment of air quality data are sufficiently well-demonstrated for 
use in exceptional events determinations, we will publish a notice of 
proposed rulemaking to seek comment on the appropriateness and scope of 
such use and its impact on the requirements set forth in this rule for 
determining an exceptional event.
2. Final Rule
    We are retaining in this rule EPA's historical practice to exclude 
a daily measured value in its entirety when that value is found to be 
caused by a qualifying exceptional event that affected air quality in 
accordance with the conditions described in sections V.B and V.D. If 
precise and universally applicable techniques that are administratively 
and technically feasible and that could support partial adjustment of 
air quality data become available in the future, EPA will, through a 
rulemaking, propose, and as appropriate, finalize a technique for 
partial adjustment of data as well as any other matters in this rule 
which may be affected by the availability of this technology.
    One exception may be made to this exclusion of the entire daily 
value for monitoring locations with hourly measurements by Federal 
Reference Methods (FRM), Federal Equivalent Methods (FEM), and/or 
Approved Regional Methods (ARM) where such data are submitted routinely 
to AQS. For example, in cases where stratospheric ozone intrusion 
occurs, those hourly (but not sub-hourly) measurements affected by the 
intrusion may be excluded in order to calculate the ozone measurements 
for the day. The individual hours are to be excluded however, if the 
resulting calculated NAAQS averaging time value exceeds the level of 
the standard, not just if the individual hourly values exceed that 
level. Thus, in the case of ozone, the resulting 8-hour average must 
exceed 0.08 ppm, and the resulting 24-hour average must exceed 15.0 
[mu]g/m3 for PM2.5. Incomplete data substitution 
protocols shall also be considered when evaluating the original and 
revised NAAQS averaging time value. In other words, an 8-hour ozone 
period is considered valid when fewer than six valid hours are present 
if one half the minimum detection limit can be substituted for the 
missing hours and the resultant 8-hour value still exceeds 0.08 ppm; a 
daily (24-hour) PM2.5 value is considered valid when fewer 
than eighteen valid hours are present if zeroes can be substituted for 
the missing hours and the resultant 24-hour value still exceeds 15.0 
[mu]g/m3.
3. Comments and Responses
    Comment: One commenter supported value adjustment rather than 
exclusion when, and only when, such adjustment can be accomplished by 
the application of various quantitative or semi-quantitative 
approaches. When this is not possible, the value in question should be 
replaced with a long-term seasonal mean value.
    Response: The EPA will consider such analyses as part of the weight 
of evidence to judge ``but-for,'' but will not make quantitative 
adjustments to reported measured values because EPA does not believe 
sufficient quantitative methods are available at this time.

F. What Should States Be Required To Submit in Their Exceptional Events 
Demonstrations?

1. Background
    Section 319 requires that, in order to have a flagged value 
excluded from regulatory determinations, a State must make an 
affirmative demonstration that an event occurred (as shown by reliable 
and accurate data that is promptly produced) and that there is a clear 
causal relationship between measured exceedances or violations of a 
standard and the exceptional event in question to

[[Page 13573]]

``demonstrate that the exceptional event caused a specific air 
pollution concentration'' (42 U.S.C. 7619(b)(3)(B)(ii), (iv)). Section 
319 also indicates that regulations promulgated under the section 
should provide for criteria and procedures to exclude air quality 
monitoring data ``directly due to exceptional events from use in 
determinations by the Administrator with respect to exceedances or 
violations of the national ambient air quality standards.''
    Therefore, after flagging data in the AQS database, States are 
expected to develop appropriate documentation to support each 
individual flag. As a general matter, we believe that such 
demonstrations should include documentation showing that the event in 
fact occurred and that emissions related to the event were transported 
in the direction of the monitor(s) where measurements were recorded; 
the size of the area affected by the transported emissions; the 
relationship in time between the event, transport of emissions, and 
recorded concentrations; and, as appropriate, pollutant species-
specific information supporting a causal relationship between the event 
and the measured concentration. The latter information could be based 
on available data provided by routine speciation, monitoring networks, 
or from selective laboratory analysis of archived particulate matter 
filters for the day thought to be impacted by specific events. In 
certain situations, such data might be useful for evaluation of impacts 
from exceptional events, e.g., to distinguish between impacts caused by 
natural fires versus impacts caused by industrial sources. States also 
need to show that appropriate mitigation actions were taken at the time 
that the event occurred, or after an event occurred in order to protect 
public health.
    The following examples are intended to further illustrate the kinds 
of information that States could consider in preparing their 
demonstrations:
     Information demonstrating the occurrence of the event and 
its subsequent transport to the affected monitors. This could include, 
for instance, documentation from land owners/managers, satellite-
derived pixels (portions of digital images) indicating the presence of 
fires; satellite images of the dispersing smoke and smoke plume 
transport or trajectory calculations (calculations to determine the 
direction of transport of pollutant emissions from their point of 
origin) connecting fires with the receptors.
     Identification of the spatial pattern of the affected area 
(the size, shape, and area of geographic coverage). This could include, 
for instance, the use of satellite or surface measurement data.
     Information about temporal patterns (e.g., the time and 
duration of an event in relation to measured downwind concentrations, 
air quality trends over time and space). This could include, for 
instance, observed sequential concentration spikes at multiple 
locations in a downwind direction.
     Identification of the chemical composition of measured 
concentrations. This could include, for instance, organic or crustal 
material in excess of typically observed quantities to differentiate 
from other high concentration events.
     High wind speeds relative to historically typical levels 
for the season of the year in which the claimed event occurred.
    This list is not exhaustive and not all of these kinds of 
information and/or documentation will need to be provided in every 
instance. A particular instance may require more or less documentation, 
depending on the particular facts or circumstances in that instance. 
The simplest demonstrations could consist of newspaper accounts or 
satellite images to demonstrate that an event occurred together with 
daily and seasonal average ambient concentrations to demonstrate an 
unusually high ambient concentration level, which is clearly indicative 
of an exceptional impact. Such is the case with events such as volcanic 
eruptions and nearby forest fires. In one instance, we determined that 
wildfires upwind of the San Diego area very likely caused high 
concentrations of particulate matter measured in October 2003 based on 
the actual physical damage caused by fire to the ambient monitor. 
Depending on the nature of the event, meteorological conditions, 
severity and spatial extent of measured ambient concentrations 
(including relevant chemical components when available) relative to 
what typically occurs in the area, and on emissions of pollutants from 
the exceptional event which have similar characteristics to those of 
other sources in the area, additional showings could be required on a 
case-by-case basis. In particular, we anticipate that significantly 
more effort will be needed to establish that an exceptional event 
caused a particular concentration in an urban area in which there are 
numerous and diverse sources and complex meteorology and topography, 
and where the emissions from the event in question may well be similar 
to those from other sources contributing to measured concentrations, as 
compared to an area that has relatively few sources, simple terrain and 
less complex meteorology, and where emissions associated with the event 
are both substantially greater than and different in composition from 
those of other nearby sources.
2. Final Rule
    The demonstration to justify data exclusion will address specific 
monitor readings reported to the AQS database. As stated in the 
previous sections, a complete demonstration shall justify 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, (d) there would have been no exceedance or violation but 
for the event, and (e) the State has provided an opportunity for the 
public to comment as required under section V.G. The level of 
documentation may vary by the type of event and can be guided in part 
by the relative magnitude of the observed concentrations. To obtain 
concurrence, EPA must determine that the demonstration is complete and 
provides a reasonable technical demonstration.
    Because of the variability in the nature of exceptional events and 
the resulting demonstration requirements, States should consult with 
the appropriate EPA Regional Office early in the process of preparing 
their demonstrations. We are not specifying what will be required as a 
minimum level of documentation in all cases because facts and 
circumstances will vary significantly based on, among other things, 
geography, meteorology and the relative complexity of source 
contributions to measured concentrations in any particular location. We 
believe, however, that at a minimum, the elements of such a 
demonstration should include a showing that an event occurred at a time 
when meteorological conditions were conducive to transporting emissions 
from the event downwind to the monitor recording a high concentration 
of one or more criteria pollutants. Acceptable documentation will be 
determined through consultation with the EPA regional offices. However, 
certain minimum requirements (e.g., ``but for'' test) will be necessary 
as discussed in the earlier sections of this rule.

[[Page 13574]]

3. Comments and Responses
    Comment: In cases where high wind data cannot be found, one 
commenter stated that EPA should use a ``weight of evidence'' approach, 
and should recognize that not accepting a demonstration that such 
exceedances are exceptional events is equivalent to a determination 
that the exceedances were caused by recurring anthropogenic sources.
    Response: The EPA agrees that a weight of evidence approach is the 
most appropriate for demonstrations of exceptional impact.
    Comment: One commenter asserted that States should be allowed to 
choose not to submit any demonstration, if the flagged value does not 
impact a regulatory determination or if more detailed investigation 
indicates that the value may not have been caused by an exceptional 
event after all. In these cases, the agency should have the option to 
remove the flag.
    Response: We agree that the flag can be removed in these 
circumstances or left for informational purposes only.
    Comment: One commenter stated that EPA must provide a reasonable 
explanation and documentation for their decision to deny any request 
for the flagging of data.
    Response: The EPA regional offices will work with the States, 
Tribes, and local agencies to ensure that proper documentation is 
submitted to justify data exclusion. The EPA will make the response and 
associated explanation publicly available.
    Comment: One commenter stated that EPA must establish a 
technically-based appellate process for States to follow when Regional 
Offices do not concur with a data flag.
    Response: The EPA does not believe that an appellate process is 
necessary because we anticipate that the States and Regional Offices 
will be working closely through the data and documentation submission 
process.

G. Public Availability of Air Quality Data and Demonstrations Related 
to Exceptional Events

1. Background
    Section 40 CFR part 58.16 of EPA's air quality monitoring rules 
state that all ambient air quality data and associated quality 
assurance data, including metadata records and information specified by 
the AQS Data Coding Manual epa.gov/ttn/airs/airsaqs/manuals/manuals.htm 
must be reported to EPA via AQS. This information includes exceptional 
event flags.
2. Final Rule
    We are requiring that all relevant flagged data, along with the 
reasons for the data being flagged, and a demonstration that the 
flagged data are caused by exceptional events be made available by the 
State for 30 days of public review and comment. The State or designated 
local agency should consider the public comments prior to the final 
demonstration being submitted to EPA for a decision concerning whether 
to exclude the data from regulatory consideration. Notice and 
availability of such data and demonstrations must be adequate and 
consistent with States' administrative procedures governing similar 
submissions. The EPA does not require that public hearings be held on 
exceptional events demonstrations but leaves this matter to the States' 
discretion consistent with their administrative procedures. With the 
submission of the demonstration, the State should document that the 
public comment process was followed.
3. Comments and Responses
    Comment: One commenter stated that any new rules related to the 
flagging of exceptional events should be consistent with prior EPA 
policies and provide sufficient time for States to engage the public in 
the process prior to data being flagged in the AQS.
    Response: The EPA believes that the data demonstration requirements 
of the final rule provide sufficient time to engage the public. Not 
only does the final rule require that the public be accorded an 
opportunity to comment on the State's findings, but in some instances 
there will be further opportunities for public review and comment at 
the time that EPA proposes to base specific actions, e.g., approval or 
disapproval of SIP revisions. Thus, we do not believe that additional 
public review and comment provisions are necessary or appropriate.

VI. Additional Requirements

    Pursuant to section 319, EPA is finalizing this rule to address 
data that has been influenced by exceptional events. Also, EPA is 
finalizing one of four options put forth in the proposed rule to 
address the issue of whether, and to what extent, States are required 
to adopt specific mitigation plans or measures to protect the public 
from emissions due to exceptional events. Section 319 states that in 
promulgating regulations under the section, EPA shall follow certain, 
enumerated principles and that regulations must contain certain 
requirements. Section 319(b)(3)(A) contains five principles, including 
the principle that each State ``must take necessary measures to 
safeguard public health regardless of the source of air pollution.'' In 
order to address this principle, EPA is finalizing its proposal to 
exclude trivial and more routine air quality impacts from qualifying as 
an exceptional event and is also finalizing a ``but for'' test as a 
precondition to qualification as an exceptional event (See: section V.C 
above).

A. Requirements for States To Provide Public Notification, Public 
Education, and Appropriate and Reasonable Measures To Protect Public 
Health

1. Background
    The EPA proposed one approach and took comments on three 
alternative options concerning what actions a State should take in 
anticipation of, or in response to, the occurrence of an exceptional 
event. The options that were proposed ranged from being very detailed 
and prescriptive to being very flexible and less prescriptive in terms 
of the actions that States should take to mitigate the impact of an 
exceptional event on the public. While EPA does not believe that 
section 319(b)(3)(A) explicitly requires, in and of itself, that States 
must develop mitigating measures or plans, EPA solicited comment in the 
proposed rule on whether this subparagraph supports the use of other 
legal authority to require mitigating actions or plans when an 
exceptional event occurs, and solicited comment on issues regarding its 
legal authority to require mitigation measures and plans, and the legal 
basis for not requiring mitigation measures or plans.
    Option 1 in the proposed rule provided that in cases where 
exceedances of a NAAQS are caused by an exceptional event, once a State 
becomes aware that an exceptional event is occurring, is predicted to 
occur, or has occurred, the State must take reasonable and appropriate 
actions to:
     Provide notice to the public of the event. This may 
include, but is not limited to, using the media to alert the public of 
the event.
     Provide public education concerning the potential health 
risks associated with being exposed to high ambient concentrations of 
pollutant(s) related to the event. This may include, but is not limited 
to, providing information to sensitive populations related to the 
health risks associated with the event.
     Take appropriate and reasonable measures to abate or 
minimize the exposure of the public to high

[[Page 13575]]

concentrations of air pollution associated with the exceptional event. 
This may include, but is not limited to, taking reasonable and 
appropriate actions to implement control measures on significant 
contributing anthropogenic sources to reduce potential exposure of the 
public to emissions associated with natural events. States must review 
the need to implement controls on contributing anthropogenic sources on 
a case-by-case basis. For example, in the case of volcanic or seismic 
activity, this may include, but is not limited to, providing for prompt 
clean-up of the ash deposits related to the event to prevent re-
entrainment.
    Under option 1, EPA also proposed that, where a State is requesting 
that air quality data be excluded as an exceptional event, the State 
must submit, as a part of its demonstration, appropriate documentation 
to show that the State provided public notice and public education 
concerning the event in question, and that the State took reasonable 
and appropriate measures to abate or minimize the exposure of the 
public to the emissions from the event, where appropriate.
    Option 2 in the proposed rule provided that, States are required to 
adopt a general mitigation plan to address exceptional events before 
the occurrence of an event as a part of the State's SIP required under 
section 110(a)(1) of the CAA. Section 110(a)(1) requires States to 
adopt and submit to EPA, within 3 years following the promulgation of a 
new or revised NAAQS, a plan which provides for the implementation, 
maintenance, and enforcement of the standard in each air quality region 
within the State. Under this option, States would be required to 
develop and adopt the general requirements and procedures necessary for 
the implementation of a mitigation plan to address exceptional events 
as a part of its section 110(a)(1) SIP to address a new or revised 
NAAQS. The general plan related to exceptional events would include 
provisions providing for public notice, public education related to an 
event, and provide a requirement for a State to take reasonable and 
appropriate measures to mitigate the public health impacts of an 
exceptional event. Under this option, in cases where control measures 
are required to address the impacts associated with an exceptional 
event, the State would be required to implement appropriate measures on 
an episodic basis, meaning in response to a specific event that affects 
the air quality of a particular area.
    Option 3 in the proposed rule required that, where appropriate, EPA 
would require a State to develop and implement a mitigation plan for an 
area following the occurrence of an exceptional event. This is in 
contrast to option 2 above, which would require each State to adopt a 
plan under section 110(a)(1) of the CAA which would contain the general 
provisions of a mitigation plan in advance of the occurrence of any 
exceptional event. Under option 3, the mitigation plan would only be 
developed by the State following the occurrence of an exceptional event 
for which the State requested exclusion of the air quality data, and 
would not be submitted as a part of the SIP. The mitigation plan would 
be required to address the actions that would be taken by the State 
related to future similar events. The mitigation plan under this option 
would have the same provisions as required of plans developed under 
Option 2 above, including the requirements to notify the public that an 
event is expected to occur, or is occurring, or has occurred, to 
provide for public education related to the health effects associated 
with the event, and to identify the actions that would be taken by the 
State to mitigate the impact of any recurrence of the event on public 
health.
    Option 4 provided that EPA would not require a State to develop and 
implement a mitigation plan for exceptional events, or to take specific 
mitigation measures as described in options 1-3 in order for EPA to 
exclude data from regulatory consideration. This approach proposed to 
allow States to have the maximum degree of flexibility in determining 
what actions should be taken to mitigate the impacts of exceptional 
events, e.g., public notification, public education, efforts to reduce 
exposures, or other necessary measures to safeguard public health. 
Thus, under this proposed option States would not be obligated to take 
any particular actions to mitigate exposures such as those contained in 
Option 1, to develop and implement a formal mitigation plan as part of 
the SIP such as those contained in Option 2, or to develop a more 
formal plan with requirements not a part of the SIP such as those 
contained in Option 3.
2. Final Rule
    The EPA is adopting a modified version of Option 1 from the 
proposed rule, as described above. This option does not require States 
to submit formal mitigation plans; however, States must provide public 
notice, public education, and must provide for implementation of 
reasonable measures to protect public health when an event occurs.
3. Comments and Responses
    Comment: Several commenters supported option 1 because they stated 
that it provides more flexibility for States to determine the 
appropriate measures to be implemented related to the occurrence of an 
exceptional event. Other commenters supported option 1 for well 
defined, well understood events that are non-recurring or unlikely to 
recur. The majority of the commenters who commented on option 2 
strongly opposed that option. The commenters indicated that option 2 
would waste scarce local resources in developing a mitigation plan. 
Other commenters stated that issues concerning exceptional events 
should be dealt with outside the SIP process and section 110 of the 
CAA. With regard to Option 3, one commenter indicated that a preemptive 
plan similar to a Natural Events Action Plan (NEAP) (which includes 
Reasonably Available Control Measures (RACM)/Best Available Control 
Measures (BACM) is necessary to mitigate the poor air quality impacts 
associated with exceptional events. The commenter stated that BACM, not 
RACM, must be implemented on all contributing anthropogenic sources 
related to an exceptional event. Several commenters supported option 3 
for addressing public health impacts related to recurring natural 
events. The commenters stated that mitigation plans should include BACM 
for contributing anthropogenic sources, not RACM. The majority of 
commenters who commented on option 4 stated that they supported the 
implementation of option 4 because it allows States the most 
flexibility for developing and tailoring programs for public 
notification of exceptional events, the implementation of education 
programs on exceptional events, and implementation of reasonable 
measures to protect public health.
    Response: States have an inherent responsibility to protect its 
citizens and as such to provide appropriate and reasonable actions to 
mitigate the impact of exceptional events on the public health. This 
includes alerting the public when such events occur, providing public 
education concerning the health effects of such events, and 
implementing reasonable measures to mitigate the impact of such events 
on public health. Consistent with this inherent responsibility, it is 
EPA's belief that States are in a better position to make decisions 
concerning what actions should be taken to protect the public when an 
exceptional event occurs. This

[[Page 13576]]

being the case, States should have the necessary flexibility to take 
appropriate actions when exceptional events occur. The EPA is adopting 
a modified version of its proposed preferred option 1, which requires 
States to provide public notification, public education, and provides 
that States should take ``reasonable and appropriate measures'' to 
protect public health related to the occurrence of an event. Because 
States are inherently responsible for the public health of its 
citizens, and are capable of making the determinations of what actions 
should be taken to mitigate the impact of such events on the public 
when they occur. The EPA has modified option 1 from the proposed rule 
and will not be requiring States to submit documentation concerning the 
actions that it took to mitigate the impact of exceptional events, in 
order for EPA to exclude data from regulatory consideration. As 
proposed in option 1, States may still make determinations regarding 
reasonable measures in a particular instance, which may or may not 
include the implementation of control measures on contributing 
anthropogenic sources related to an event, and are not limited to any 
particular measure. Therefore, under this option the implementation of 
RACM or BACM is not required, but a State has the necessary flexibility 
to determine if, and what, controls should be implemented following an 
event, as well as the level of control that is required. The EPA 
believes that this modified option 1 provides suitable flexibility to 
allow States to take those actions that it deems necessary and 
appropriate to protect public health. While section 319, as revised by 
SAFE-TEA-LU, does not specifically provide that States must implement 
mitigation plans, in developing the exceptional events rule, EPA is 
required to consider the enumerated principles including the principle 
that States must take necessary measures to protect public health 
regardless of the source of air pollution. Therefore, under the 
modified version of option 1 adopted in this final rule, States must 
take reasonable and appropriate actions to protect public health.
    Comment: Several commenters stated that the exceptional events rule 
should be consistent with the current requirements under existing 
policies with respect to the need for a NEAP to address recurring 
natural events such as high wind events.
    Response: The EPA believes that it is advantageous for States to 
keep NEAPs in place that are currently being implemented in order to 
address the public health impacts associated with recurring natural 
events such as high wind events. However, following the promulgation of 
this rule, States will no longer be required to keep NEAPs in place 
that were not approved as a part of a SIP for an area. Where a NEAP, as 
well as BACM, has been approved as a part of a nonattainment SIP for an 
area, the NEAP, as well as the associated BACM, must remain in place. 
States may, however, submit a request to EPA to remove the NEAP and 
BACM from the SIP. The request must contain an approvable 
demonstration, as required by section 110(l), which shows that the 
removal of the NEAP and BACM will not interfere with any applicable 
requirement concerning attainment or maintenance of the NAAQS for an 
area, reasonable further progress, or any other applicable requirement 
for the area.

VII. Special Treatment of Certain Exceptional Events Under This Final 
Rule

    As stated in section IV.D above, this final rule applies to data 
affected by natural events (which are a subset of exceptional events) 
at air quality monitoring sites where it has been determined that 
concentrations due to these events have caused, or substantially 
contributed to, exceedances of the NAAQS in an affected area. This 
final rule applies to several types of natural events, including, but 
not limited to, volcanic and seismic activities, natural disasters, 
high wind events, certain fires, and stratospheric ozone intrusions. It 
also applies to transported pollution originating from national and 
international sources that otherwise meets the criteria and 
requirements for exceptional events. Some types of exceptional events 
have unusual characteristics that require special consideration in the 
context of this final rulemaking. We discuss each of these special 
issues, and the necessary accommodations, below.

A. Volcanic and Seismic Activities

1. Background
    Volcanic and seismic activities may affect air quality for an 
extended period of time after the initial occurrence of the event in 
question. Therefore, EPA believes that it is appropriate to consider an 
extended timeframe for flagging and exclusion of data associated with 
such events. Specifically, EPA believes that emissions attributed to 
anthropogenic activities associated with clean-up that re-entrain 
volcanic ash and dust from seismic activity during the first year (12 
months) following an event will be treated as due to the natural event.
2. Final Rule
    The EPA is finalizing its proposal with regards to volcanic and 
seismic activities. The EPA will allow up to 12 months for the clean-up 
of ash deposits due to volcanic/seismic events. During that time 
period, emissions of re-entrained dust due to anthropogenic activities 
associated with cleanup may be treated as exceptional events. 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 for an extension of the 12-month time period to 
EPA. As stated elsewhere in this rule, EPA will grant requests for 
extensions of the time period related to such events on a case-by-case 
basis. States are encouraged to submit supporting information 
concerning the reason for the extension and the length of time being 
requested for the extension.

B. High Wind Events

1. Background
    Where high wind events result in exceedances or violations of the 
particulate matter standards, EPA proposed that they be treated as 
natural events if there is a clear causal relationship demonstrated 
between the exceedances measured at the air quality monitoring site and 
the high wind event in question, and if anthropogenic activities which 
contribute to particulate matter emissions in conjunction with the high 
wind event are reasonably well-controlled.
2. Final Rule
    The EPA's final rule concerning high wind events states that 
ambient particulate matter concentrations due to dust being raised by 
unusually high winds will be treated as due to uncontrollable natural 
events where (1) the dust originated from nonanthropogenic sources, or 
(2) the dust originated from anthropogenic sources within the State, 
that are determined to have been reasonably well-controlled at the time 
that the event occurred, or from anthropogenic sources outside the 
State. These events are also discussed in section IV.E.5.c above. In 
cases where anthropogenic sources are determined to have contributed to 
exceedances or violations due to high wind events at air quality 
monitoring sites, per our decision in this rulemaking concerning the 
action that States must take to mitigate the impact of exceptional 
events on public

[[Page 13577]]

health (See section VI above), States must take reasonable and 
appropriate measures to mitigate the impact associated with the event 
on public health. As stated in section VI of this rule, States have the 
flexibility to implement reasonable measures to protect public health 
when an exceptional event occurs. These actions may or may not include 
the implementation of controls on contributing anthropogenic sources 
related to an event. However, where anthropogenic sources have 
contributed to the exceedances of the PM NAAQS at an air quality 
monitoring site due to a high wind event, a State must take reasonable 
and appropriate measures to protect public health.
    Since the conditions that cause or contribute to high wind events 
vary from area to area with soil type, precipitation, and the speed of 
wind gusts, States should provide appropriate documentation which 
indicates what types of circumstances contributed to the exceedances or 
violations at the monitoring site in question.\15\ In this rule, EPA is 
not identifying a specific wind speed which should be considered when 
making a determination concerning whether an event should qualify as 
exceptional. Instead, EPA is requiring that States submit appropriate 
documentation which demonstrates why a particular event should be 
considered exceptional for the affected area. The EPA will review the 
documentation submitted by States concerning high wind events and will 
make decisions concerning whether to exclude the data as being 
influenced by an exceptional event on a case-by-case basis.
---------------------------------------------------------------------------

    \15\ Section 319(b)(1)(B) states: ``In this subsection, the term 
`exceptional event' does not include (i) stagnation of air masses or 
meteorological inversions; (ii) a meteorological events involving 
high temperatures or a lack of precipitation; or (iii) air pollution 
relating to source noncompliance.'' In terms of the exclusion 
related to ``a meteorological event involving high temperatures or a 
lack of precipitation'' EPA believes that this statutory language 
prohibits EPA from treating a typical dry day(s) or a dry season for 
an area as an exceptional event. However, EPA believes that Congress 
did not intend that the above quoted language to prevent a State 
from submitting compelling documentation which shows that severe 
drought conditions may have contributed to an exceptional event, but 
instead was designed to prevent the indiscriminate exclusion of data 
on days characterized by ``high temperature and a lack of 
precipitation.'' Therefore, EPA is permitting States to submit 
documentation which shows that ``severe drought'' conditions may 
have contributed to the occurrence of a high wind event. The 
documentation must, however, be compelling enough to show that the 
conditions present at the time of the event were more substantial 
than a typical dry day(s) or dry season for the area in question, 
but were related to severe drought conditions. The EPA will review 
this information and make decisions concerning the exclusion of the 
data related to the event on a case-by-case basis.
---------------------------------------------------------------------------

C. Stratospheric Ozone Intrusion

1. Background
    Consideration of stratospheric ozone intrusions applies only to the 
8-hour ozone standard. The occurrence of such intrusions are extremely 
difficult to measure or document given currently measured 
meteorological parameters and the locations of these measurements. The 
infrequency, short durations, and localized nature of such events makes 
it difficult to use currently available, general meteorological data, 
which are usually collected at isolated locations such as airports, to 
determine whether a stratospheric ozone intrusion has occurred. The EPA 
believes that it is important to differentiate between stratospheric 
ozone intrusion, which is an exceptional event for the purpose of 
flagging data, and other non-exceptional meteorological events. 
Although data have been identified in the past showing the result of 
stratospheric ozone intrusion, no standard definition or criteria have 
been established for concrete identification. Therefore, EPA's 
determination of whether a stratospheric ozone intrusion has occurred 
is a case-by-case decision based on reasonable judgment considering the 
season of the year, time of day, persistence, duration, type and 
severity of accompanying meteorological conditions associated with the 
ozone measurement in question, and other data showing that conditions 
were not conducive to local high ozone production but for this 
intrusion.
2. Final Rule
    The EPA is finalizing its rule as proposed. The EPA's determination 
of whether a stratospheric ozone intrusion has occurred will be made on 
a case-by-case basis based on reasonable judgment considering the 
criteria as noted above. It is our intention to review this type of 
exceptional event during the next review of the NAAQS for ozone. A 
review of historical data related to the flagging of stratospheric 
ozone intrusion as an exceptional event shows that the event has only 
been flagged on a few isolated occasions.

VIII. Treatment of Fireworks Displays

A. Background

    The EPA proposed to treat emissions due to fireworks displays in a 
manner similar to exceptional events. Some national and/or cultural 
traditions, such as July 4th Independence Day and the Chinese New Year, 
have long included fireworks displays as important elements of their 
observances. While this issue is not specifically covered in CAA 
section 319, EPA believes that Congress did not intend to require EPA 
to consider air quality violations associated with such cultural 
traditions in regulatory determinations.
    We are not aware of any information showing adverse air quality 
impacts caused by individual use of fireworks in relatively small 
quantities. However, analyses of monitoring data collected on July 4th 
and July 5th indicates that large fireworks displays, in combination 
with other sources, can in some circumstances be potentially 
significant sources of air pollutant emissions. For this reason, States 
are encouraged to take reasonable precautions to minimize exposures to 
emissions from fireworks displays, to explore the use of lower emitting 
fireworks, as well as to manage associated activities that may also 
have significant air quality impacts in the areas where these events 
are held. Such precautions may include alerting the public to the 
potential for short-term air quality impacts that may result from the 
discharge of fireworks at large displays, monitoring prevailing winds, 
and locating displays downwind of concentrations of people. For these 
reasons, where States can show that the use of fireworks displays was 
integral to significant traditional national, ethnic, or other cultural 
events, we proposed that air quality data associated with such events 
could be excluded similar to exceptional events under this rule.

B. Final Rule

    The EPA is finalizing the approach as stated in the proposed rule 
to treat emissions from fireworks similar to the treatment of 
exceptional events in the final rule provided that the event meets the 
other criteria as stated in this rulemaking. For example, the event 
must be determined to have affected air quality. Where a State can show 
that the use of fireworks is significantly integral to traditional 
national, ethnic, or other cultural events (e.g., July Fourth 
celebrations, Chinese New Year celebrations, Diwali, etc.), EPA will 
exclude data from regulatory determinations for monitoring stations 
whose exceedances or violations has been determined to be caused by 
emissions from fireworks displays on a case-by-case basis. As stated in 
other parts of the rule, States must assure that reasonable measures 
were taken to protect the public from the emissions created by the 
fireworks display. Under this rule, States are also strongly encouraged 
to institute educational programs that alert the public to the

[[Page 13578]]

health effects associated with exposure to emissions from fireworks 
displays.

C. Comments and Responses

    Comment: The majority of commenters who commented on this issue 
agreed that emissions from fireworks should be treated as an 
exceptional event. However, some commenters disagreed with EPA's 
proposal to treat fireworks as an exceptional event. Several commenters 
believed that fireworks are neither an exceptional event nor a natural 
event and that EPA should not make provisions for fireworks to be 
excluded as an exceptional event.
    Response: In considering the intent of the SAFETEA-LU legislation, 
it is EPA's belief that Congress did not intend to prohibit the 
exclusion of data affected by emissions from fireworks related to 
celebrations of national or cultural traditions. It is EPA's belief 
that data influenced by fireworks displays should be subject to the 
same provisions as other exceptional events identified under this rule. 
Therefore, the mitigation actions described in section VI.A above would 
also apply to emissions related to fireworks displays.

IX. Statutory and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Review

    Under Executive Order 12866 (58 FR 51735, October 4, 1993), this 
action is a significant regulatory action because it raises novel legal 
or policy issues arising out of legal mandates. Accordingly, EPA 
submitted this action to the Office of Management and Budget (OMB) for 
review under Executive Order 12866 and any changes made in response to 
OMB recommendations have been documented in the docket for this action.

B. Paperwork Reduction Act

    This action does not impose an information collection burden. The 
information being requested under this rule is consistent with current 
requirements related to information needed to verify the authenticity 
of monitoring data submitted to EPA's AQS database, and to justify data 
that has been flagged as being affected by exceptional or natural 
events. However, the OMB has previously approved the information 
collection requirements regulations for ambient air monitoring 
contained in 40 CFR part 58, subparts A through E, under the provisions 
of the Paperwork Reduction Act, 44 U.S.C. 3501 et seq. and assigned OMB 
control number 2060-0084, EPA ICR number 940.17. A copy of the OMB 
approved Information Collection Request (ICR) may be obtained from 
Susan Auby, Collection Strategies Division; U.S. Environmental 
Protection Agency (2822T); 1200 Pennsylvania Ave., NW., Washington, DC 
20460 or by calling (202) 566-1672.
    Burden means that 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 the 
CFR are listed in 40 CFR part 9.

C. Regulatory Flexibility Act

    The Regulatory Flexibility Act generally requires an agency to 
prepare a regulatory flexibility analysis of any rule subject to notice 
and comment rulemaking requirements under the Administrative Procedures 
Act or any other statute unless the EPA 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 the purpose of assessing the 
impacts of this final rule on small entities, small entity is defined 
as: (1) A small business as defined by the Small Business 
Administration's 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 
dominate in its field.
    Courts have interpreted the RFA to require a regulatory flexibility 
analysis only when small entities will be subject to the requirements 
of the rule. See, Michigan v. EPA, 213 F.3d 663, 668-69 (DC Cir., 
2000), cert. den., 532 U.S. 903 (2001). This rule would not establish 
requirements applicable to small entities. Instead, this rule provides 
the criteria necessary for State, local, or Tribal air quality agencies 
to meet in order to properly flag data as being influenced by an 
exceptional or natural event. The rule also provides information 
concerning what action should be taken by a State, local, or Tribal air 
quality agency to protect public health during and following an 
exceptional or natural event. Because affected States would have 
discretion to implement controls on sources that may need to be 
regulated due to anthropogenic contribution in the area determined to 
be influenced by an exceptional or natural event, EPA could not predict 
the effect of the rule on small entities.
    After considering the economic impacts of this final rule on small 
entities, I certify that this rule will not have a significant economic 
impact on a substantial number of small entities.

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 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 of 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 to have 
meaningful and timely input in the

[[Page 13579]]

development of EPA regulatory proposals with significant Federal 
intergovernmental mandates, and informing, educating, and advising 
small government on compliance with regulatory requirements.
    We have determined that this rule does not contain a Federal 
mandate that may result in expenditures of $100 million or more for 
State, local, and Tribal governments, in the aggregate, or the private 
sector in any 1 year. This action simply provides the criteria for 
State, local, or Tribal air quality agencies to flag data to be 
discounted for regulatory purposes that is being influenced by 
exceptional or natural events. Thus, this rule is not subject to the 
requirements of sections 202, 203, and 205 of the UMRA.

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, or the relationship between the national 
government and the States, or on the distribution of power and 
responsibilities among the various levels of government.''
    This final rule does not have federalism implications. It will not 
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, 
as specified in Executive Order 13132. The CAA establishes the scheme 
whereby States take the lead in developing plans to meet the NAAQS. 
Thus, Executive Order 13132 does not apply to this rule.

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 final rule does not have 
``Tribal implications'' as specified in Executive Order 13175. The rule 
provides information concerning what action should be taken by a State, 
local, or Tribal air quality agency implementing relevant air quality 
programs to protect public health once EPA has provided a concurrence 
on data that has been flagged as being influenced by an exceptional or 
natural event. The CAA and the Tribal Authority Rule (TAR) give Tribes 
the opportunity to develop and implement CAA programs, but it leaves to 
the discretion of the Tribe whether to develop these programs and which 
programs, or appropriate elements of a program, the Tribe will adopt 
through the Tribal Implementation Plan (TIP).
    This rule does not have Tribal implications as defined by Executive 
Order 13175. It does not have a substantial direct effect on one or 
more Indian Tribes, because no Tribe has implemented a TIP related to 
the PM or the 8-hour ozone NAAQS at this time. Furthermore, this rule 
does not affect the relationship or distribution of power and 
responsibilities between the Federal government and Indian Tribes. The 
CAA and the TAR establish the relationship of the Federal government 
and Tribes in developing plans to attain the NAAQS, and this rule does 
nothing to modify that relationship. Because this rule does not have 
Tribal implications, Executive Order 13175 does not apply. However, 
even though we found that this rule does not have Tribal implications, 
we nevertheless were aware of Tribes that had an interest in this rule. 
Therefore, we conducted communications and outreach related to the rule 
with the Tribes through discussions via conference calls with the 
Tribal Association. We also provided information to the Tribes on the 
rule via the Quarterly Tribal Air Newsletter.

G. Executive Order 13045: Protection of Children From Environmental 
Health and Safety Risks

    Executive Order 13045: ``Protection of Children From Environmental 
Health 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 and safety risk that EPA has reason to believe may have a 
disproportionate effect on children. If the regulatory action meets 
both criteria, EPA 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 EPA.
    This action is not subject to Executive Order 13045 because it is 
not economically significant as defined in Executive Order 12866, and 
because EPA does not have reason to believe that the environmental 
health risks or safety risks addressed by this rule present a 
disproportionate risk or safety risk to children. The rule provides 
information concerning what action should be taken by a State, local, 
or Tribal air quality agency to protect public health once EPA has 
provided a concurrence on data that has been flagged as being 
influenced by an exceptional or natural event.

H. Executive Order 13211: Actions That Significantly Affect Energy 
Supply, Distribution, or Use

    This rule is not a ``significant energy action'' as defined in 
Executive Order 13211, ``Actions 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. Further, we have concluded that this 
rule is not likely to have any adverse energy effects.

I. National Technology Transfer Advancement Act

    Section 12(d) of the National Technology Transfer Advancement Act 
of 1995 (NTTAA), Public Law No. 104-113, section 12(d) (15 U.S.C. 272 
note) directs EPA to use voluntary consensus standards (VCS) in its 
regulatory activities unless to do so would be inconsistent with 
applicable law or otherwise impracticable. Voluntary consensus 
standards are technical standards (e.g., materials specifications, test 
methods, sampling procedures, and business practices) that are 
developed or adopted by VCS bodies. The NTTAA directs EPA to provide 
Congress, through OMB, explanations when EPA decides not to use 
available and applicable VCS.
    This action does not involve technical standards. Therefore, EPA 
did not consider the use of any VCS.

J. Congressional Review Act

    The Congressional Review Act, 5 U.S.C. 801 et seq., as added by the 
Small Business Regulatory Enforcement Fairness Act of 1996, generally 
provides that before a rule may take effect, the agency promulgating 
the rule must submit a rule report, which includes a copy of the rule, 
to each House of the Congress and to the Comptroller General of the 
United States. The EPA will submit a report containing this rule and 
other required information to the U.S. Senate, the U.S. House of 
Representatives, and the Comptroller General of the United States prior 
to publication of the rule in the Federal

[[Page 13580]]

Register. A major rule cannot take effect until 60 days after it is 
published in the Federal Register. This action is not a ``major rule'' 
as defined by 5 U.S.C. 804(2). This rule will be effective May 21, 
2007.

K. Petitions for Judicial Review

    Under section 307(b)(1) of the CAA, petitions for judicial review 
of this action must be filed in the United States Court of Appeals for 
the District of Columbia Circuit by May 21, 2007. Filing a petition for 
reconsideration by the Administrator of this final rule does not affect 
the finality of this rule for the purposes of judicial review nor does 
it extend the time within which a petition for judicial review must be 
filed, and shall not postpone the effectiveness of such rule or action. 
This action may not be challenged later in proceedings to enforce its 
requirements. See CAA Section 307(b)(2).

List of Subjects

40 CFR Part 50

    Environmental protection, Air pollution control, National parks, 
Wilderness areas.

40 CFR Part 51

    Environmental protection, Air pollution control, Administrative 
practice and procedure, Reporting and recordkeeping requirements.

    Dated: March 14, 2007.
Stephen L. Johnson,
Administrator.

0
In consideration of the foregoing, the Environmental Protection Agency 
amends 40 CFR parts 50 and 51 as follows:

PART 50--NATIONAL PRIMARY AND SECONDARY AMBIENT AIR QUALITY 
STANDARDS

0
1. The authority citation for part 50 continues to read as follows:

    Authority: 42 U.S.C. 7401 et seq.

0
2. Amend Sec.  50.1 to add paragraphs (j) and (k) to read as follows:

Sec.  50.1  Definitions.

* * * * *
    (j) Exceptional event means an event that affects air quality, 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 the Administrator in accordance 
with 40 CFR 50.14 to be an exceptional event. It does not include 
stagnation of air masses or meteorological inversions, a meteorological 
event involving high temperatures or lack of precipitation, or air 
pollution relating to source noncompliance.
    (k) Natural event means an event in which human activity plays 
little or no direct causal role.
    (l) Exceedance with respect to a national ambient air quality 
standard means one occurrence of a measured or modeled concentration 
that exceeds the specified concentration level of such standard for the 
averaging period specified by the standard.

0
3. Add Sec.  50.14 to read as follows:

Sec.  50.14  Treatment of air quality monitoring data influenced by 
exceptional events.

    (a) Requirements. (1) A State may request EPA to exclude data 
showing exceedances or violations of the national ambient air quality 
standard that are directly due to an exceptional event from use in 
determinations by demonstrating to EPA's satisfaction that such event 
caused a specific air pollution concentration at a particular air 
quality monitoring location.
    (2) Demonstration to justify data exclusion may include any 
reliable and accurate data, but must demonstrate a clear causal 
relationship between the measured exceedance or violation of such 
standard and the event in accordance with paragraph (c)(3)(iii) of this 
section.
    (b) Determinations by EPA. (1) EPA shall exclude data from use in 
determinations of exceedances and NAAQS violations where a State 
demonstrates to EPA's satisfaction that an exceptional event caused a 
specific air pollution concentration in excess of one or more national 
ambient air quality standards at a particular air quality monitoring 
location and otherwise satisfies the requirements of this section.
    (2) EPA shall exclude data from use in determinations of 
exceedances and NAAQS violations where a State demonstrates to EPA's 
satisfaction that emissions from fireworks displays caused a specific 
air pollution concentration in excess of one or more national ambient 
air quality standards at a particular air quality monitoring location 
and otherwise satisfies the requirements of this section. Such data 
will be treated in the same manner as exceptional events under this 
rule, provided a State demonstrates that such use of fireworks is 
significantly integral to traditional national, ethnic, or other 
cultural events including, but not limited to July Fourth celebrations 
which satisfy the requirements of this section.
    (3) EPA shall exclude data from use in determinations of 
exceedances and NAAQS violations, where a State demonstrates to EPA's 
satisfaction that emissions from prescribed fires caused a specific air 
pollution concentration in excess of one or more national ambient air 
quality standards at a particular air quality monitoring location and 
otherwise satisfies the requirements of this section provided that such 
emissions are from prescribed fires that EPA determines meets the 
definition in Sec.  50.1(j), and provided that the State has certified 
to EPA that it has adopted and is implementing a Smoke Management 
Program or the State has ensured that the burner employed basic smoke 
management practices. If an exceptional event occurs using the basic 
smoke management practices approach, the State must undertake a review 
of its approach to ensure public health is being protected and must 
include consideration of development of a SMP.
    (4) [Reserved]
    (c) Schedules and Procedures. (1) Public notification.
    (i) All States and, where applicable, their political subdivisions 
must notify the public promptly whenever an event occurs or is 
reasonably anticipated to occur which may result in the exceedance of 
an applicable air quality standard.
    (ii) [Reserved.]
    (2) Flagging of data.
    (i) A State shall notify EPA of its intent to exclude one or more 
measured exceedances of an applicable ambient air quality standard as 
being due to an exceptional event by placing a flag in the appropriate 
field for the data record of concern in accordance with the schedules 
for submission of data to the AQS database in 40 CFR 58.16.
    (ii) Flags placed on data in accordance with this section shall be 
deemed informational only, and the data shall not be excluded from 
determinations with respect to exceedances or violations of the 
national ambient air quality standards unless and until, following the 
State's submittal of its demonstration pursuant to paragraph (c)(3) of 
this section and EPA review, EPA notifies the State of its concurrence 
by placing a concurrence flag in the appropriate field for the data 
record in the AQS database.
    (iii) Flags placed on data as being due to an exceptional event 
together with an initial description of the event shall be submitted to 
EPA not later than July 1st of the calendar year following the year in 
which the flagged measurement occurred, except as allowed under 
paragraph (c)(2)(iv) of this section.
    (iv) For PM2.5 data collected during calendar years 
2004-2006, that the State identifies as resulting from an

[[Page 13581]]

exceptional event, the State must notify EPA of the flag and submit an 
initial description of the event no later than October 1, 2007. EPA may 
grant an extension, if a State requests an extension, and permit the 
State to submit the notification of the flag and initial description by 
no later than December 1, 2007.
    (v) When EPA sets a NAAQS for a new pollutant, or revises the NAAQS 
for an existing pollutant, it may revise or set a new schedule for 
flagging data for the initial designation of areas for those NAAQS.
    (3) Submission of demonstrations.
    (i) A State that has flagged data as being due to an exceptional 
event and is requesting exclusion of the affected measurement data 
shall, after notice and opportunity for public comment, submit a 
demonstration to justify data exclusion to EPA not later than the 
lesser of, 3 years following the end of the calendar quarter in which 
the flagged concentration was recorded or, 12 months prior to the date 
that a regulatory decision must be made by EPA. A State must submit the 
public comments it received along with its demonstration to EPA.
    (ii) A State that flags data collected during calendar years 2004-
2006, pursuant to paragraph (c)(2)(iv) of this section, must adopt the 
procedures and requirements specified in paragraph (c)(3)(i) of this 
section and must include a demonstration to justify the exclusion of 
the data not later than the submittal of the Governor's recommendation 
letter on nonattainment areas.
    (iii) The demonstration to justify data exclusion shall provide 
evidence that:
    (A) The event satisfies the criteria set forth in 40 CFR 50.1(j);
    (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 a measured concentration in excess 
of normal historical fluctuations, including background; and
    (D) There would have been no exceedance or violation but for the 
event.
    (iv) With the submission of the demonstration, the State must 
document that the public comment process was followed.
    (v) [Reserved.]
    (A) [Reserved]

PART 51--NATIONAL PRIMARY AND SECONDARY NATIONAL AMBIENT AIR 
QUALITY STANDARDS

0
4. The authority citation for part 51 continues to read as follows:

    Authority: 23 U.S.C. 101; 42 U.S.C. 7401-7671q.

0
5. Adding Subpart Y consisting of Sec.  51.930 to read as follows:

Subpart Y--Mitigation Requirements

Sec.  51.930  Mitigation of Exceptional Events.

    (a) A State requesting to exclude air quality data due to 
exceptional events must take appropriate and reasonable actions to 
protect public health from exceedances or violations of the national 
ambient air quality standards. At a minimum, the State must:
    (1) Provide for prompt public notification whenever air quality 
concentrations exceed or are expected to exceed an applicable ambient 
air quality standard;
    (2) Provide for public education concerning actions that 
individuals may take to reduce exposures to unhealthy levels of air 
quality during and following an exceptional event; and
    (3) Provide for the implementation of appropriate measures to 
protect public health from exceedances or violations of ambient air 
quality standards caused by exceptional events.
    (b) [Reserved]

[FR Doc. E7-5156 Filed 3-21-07; 8:45 am]

BILLING CODE 6560-50-P