OMB DRAFT 3: February 147, 2007  SEQ CHAPTER \h \r 1

				         				6560-50-P

ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 50 and 51

[EPA-HQ-OAR-2005-0159; FRL-    ]

RIN 2060-AN40

Final Rule on the Treatment of Data Influenced by Exceptional Events

AGENCY:  	Environmental Protection Agency (EPA).

ACTION: 	Final Rule.

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.

DATES: 	This rule is effective [Insert date 60 days after publication in
the Federal Register].

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 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 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<PHONE_NUMBER>, 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, Ph.D., Office
of Air Quality Planning and Standards, Air Quality Policy Division, Mail
Code C539-01, Research Triangle Park, N.C. 27711; telephone (919)
541-0906, and e-mail address   HYPERLINK<EMAIL_ADDRESS><EMAIL_ADDRESS>.

	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, N.C. 27711; telephone<PHONE_NUMBER>,
and e-mail address   HYPERLINK<EMAIL_ADDRESS><EMAIL_ADDRESS>.

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.

  	General Information

  	Does this Action Apply to Me?

  	How is This Preamble Organized?

 	Preamble Glossary of Terms and Acronyms

	Background and Purpose of This Rulemaking

A.	Legislative Requirements

	Historical Experience Concerning Exceptional and Natural Events

IV.  This Final Action

	To Whom and to What Pollutants Does This Rule

                           Apply?

	How Does This Rule Relate to Indian Tribes?

   Comments Submitted on the Proposed Rule.

	What is an Exceptional Event?

	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. 	Volcanic and Seismic Activities

		b.	Natural Disasters and Associated Clean-up Activities

	c. 	High Wind Events

d.	Forest Fires

e.	The Treatment of Prescribed Fires

f.	Stratospheric Ozone Intrusions

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

A.	Flagging of Data in the AQS Data base

1.	Background

2.	Final Rule

3.	Comment and Responses

B.   What Does it Mean for an Event to “Affect Air Quality”?

	1.	Background

	2.	Final Rule

	3.	Comment and Responses

C.	Use of a “But For” Test

	1.	Background

	2.	Final Rule

	3.	Comment and Responses

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

	1.	Background

	2.	Final Rule

	3.	Comment 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.	Comment 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.	Comment and Responses

VI.	Additional Requirements

	Requirements for States to Provide Public

Notification, Public Education, and Appropriate and Reasonable Measures
to Protect Public Health

1.	Background

2.	Final Rule

3.	Comment 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

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.

AQS 			Air Quality System

BACM			Best Available Control Measures

CAA			Clean Air Act

CAAA			Clean Air Act Amendments

EPA			Environmental Protection Agency

FIP			Federal Implementation Plan

FR			Federal Register

FMP			Fire Mitigation Plan

NAAQS		National Ambient Air Quality Standards

NEAP			Natural Events Action Plan

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 Programlan

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 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.  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).

	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 caused by human activity that is
unlikely to recur at a particular location or a natural event; and is
determined by the 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 temperature 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.  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.

The term exceedance refers to a measured or modeled concentration
greater than the level of one or more national ambient air quality
standards for a pollutant.  The NAAQS are also set with particular
averaging periods (e.g., three years for ozone and PM2.5) such that a
violation of the NAAQS 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 data exclusion and any data contributing to violations
of daily or sub-daily standards will also be eligible (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 data basedatabase 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 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).

	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.  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.

	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).

	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)
data basedatabase 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.  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.

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 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.  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 the treatment of data influenced by both
exceptional and natural events. Currently, appendix I, only addresses
the treatment of data determined to be influenced a stratospheric ozone
intrusion and other natural events, but does not address the handling of
data influenced by exceptional events.

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 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
has no substantial or direct causal connection 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 the CAA, Congress recognized and provided for distinctions between
these types of events, while discussing circumstances under which events
should or should not be considered natural (see Public Law 101-549, CAA
Amendments of 1990 House Report No. 101-290(l), May 17, 1990; and
discussion of Mono Lake, California therein).

	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 also contains a more
detailed list of other similar events that may be flagged for special
consideration.

(  HYPERLINK
"http://www.epa.gov/ttn/airs/airsaqs/manuals/qualifiers.htm"
http://www.epa.gov/ttn/airs/airsaqs/manuals/qualifiers.htm ).

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. EPA agrees with the commenters that other types
of 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 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
three-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. EPA, however, 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 and are within the effective control of States or other
authorities seeking to flag and exclude such data.  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 wildland 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 requirements for an exceptional event is met as
defined in this rule. Other types ofIn 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 influenced 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 Act 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, the EPA may approve the
SIP for the area provided that the plan (1) meets all the applicable
requirements called for under the Act, 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) volcanic and
seismic activities; (2) natural disasters and associated cleanup
activities; (3) high wind events; (4) forest 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 time frame 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 Clean Air
Act. 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 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 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 "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: 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 theat 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. Extremely high wind speeds relative to historically typical
levels for the season of the year in which the claimed event
occurred.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.

d.  ForestWildland 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 lightening), 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), and other wildland fires where the objective is 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 are outlined in fire
management or land use 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
concentrations due to smoke from a wildland fire will be treated 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 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 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 as part of its
overall Fire Strategy after promulgation of this rule.

e. 	The Treatment of Prescribed Fire

A “prescribed fire” is defined as any fire ignited by management
actions to meet specific resource management objectives.  A written,
approved prescribed fire plan must exist, and National Environmental
Policy Act (NEPA) requirements (where applicable) must be met, prior to
ignition (National Wildland Fire Coordination Group Glossary of Wildland
Fire Terminology, 2003). A prescribed fire cannot be classified as
“natural,” given its anthropogenic origins, nonetheless, we believe
that a prescribed fire should not automatically be excluded from the
definition of exceptional events as defined under this rule.  Therefore,
if a prescribed fire meets the statutory criteria defined in section 319
of being “unlikely to recur at the same location” and “not
reasonably controllable or preventable,” and it meets the measures
specified below and the requirements of this rule, it may qualify as an
exceptional event. However, the determination of whether a prescribed
fire can be considered as 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 interval can range from once every year to less frequently
than once in 35-60 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 the same location”
requirement of the statutory language.

	As stated previously, since a prescribed fire is ignited deliberately,
it does not qualify as “natural,” under this rule and one view is
that it cannot qualify as “not reasonably controllable or
preventable.”  However, a different interpretation of this provision
of section 319 examines whether there are any reasonable alternatives to
the use of prescribed fire in light of the needs and objectives to be
served by it.  For instance, there may be a sufficient 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 the 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.  Alternately,
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 under the conditions described
above and designed to achieve resource benefits on public, Indian, and
privately owned lands may qualify as an exceptional event.  The EPA
believes States should continue to address prescribed fire issues by
following the guidance contained in the “Interim Air Quality Policy on
Wildland and Prescribed Fires,” issued May 15, 1998 (Wildland and
Prescribed Fire Policy).  This policy provides that EPA will allow
exceedances to be discounted that have been flagged by a State as having
been caused by a prescribed fire used for resource management purposes
provided that the State certifies that it has adopted and is
implementing a Smoke Management Program (SMP) as described in our
policy. EPA will continue to use that approach and a State, local, or
Tribal air quality agency that requests exclusion of data related to
exceedances or violations attributed to a prescribed fire managed for
resource benefits should continue to certify that a SMP is being
implemented.

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 these types of fires
should be considered as an exceptional event.  A number of commenters
also disapproved of allowing prescribed fires to be considered as
exceptional events because they believe that these types of fires are
anthropogenic and do not meet the statutory definition of exceptional
event.

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 being “not reasonably controllable or
preventable” and “unlikely to recur at the same location”.  In
those instances where a prescribed fire meets the criteria for an
exceptional event, the State must also provide appropriate documentation
to show that an approved SMP was in place and being followed at the time
that the event occurred.

Comment:  The Agency received comments on expanding the criteria used to
qualify a prescribed fire as an exceptional event.  Currently, a State
must certify to EPA that it has a SMP and that the fire was conducted in
accordance with the SMP.  Commenters recommended expanding the criteria
for a potentially qualifying prescribed fire as one that is either in
compliance with a SMP or when basic smoke management practices are used.

Response:  Several commenters addressed the criteria by which the
ambient air quality data impacted by a prescribed fire qualifies for
exemption under this rule.  The Agency requires that a State must
certify that it has a SMP and that the fire was conducted in accordance
with the plan in order for the exceedence to be considered under that
policy.  Some commenters interpreted the proposed rule as expanding the
criteria to include either a SMP or the use of basic smoke management
practices and recommended expanding the qualifying criteria.  However,
several commenters opposed expanding the criteria.  In the final rule,
the Agency reaffirms that the qualifying criteria have not been expanded
and that a SMP is required before ambient air quality data impacted by a
prescribed fire may qualify for exemption.

f. 	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 must be
considered as an exceptional event.

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.  For
data exclusion, States must clearly identify, or “flag,” 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.

The SAFE-TEA-LU key requirements for exclusion of data from exceptional
events are: (1) 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 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.F states the requirements
for determination submittals if the agency requests EPA to exclude the
data from consideration for regulatory purposes.  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.E discusses the applicability to hourly readings.  Section V.G
describes the public review requirements, and Section V.D the schedules
and procedures for the flagging and demonstration submittals.

Some commenters suggested that all data occurring from exceptional
events should be flagged, and the 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 Data BaseDatabase

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 data basedatabase 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 proposed rule stated: “In the case of exceptional events, States
place the initial flag on the data in the AQS data basedatabase.
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 data basedatabase 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 and natural events, States and Tribes place
the initial flag on the data in the AQS data basedatabase, but EPA
determines the available flags.  States may also delegate authority to
local agencies to submit flags and documentation.  At the time the flag
is inserted into the AQS data basedatabase, 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 data
basedatabase prior to July 1st following the year in which the event
occurred.  Schedules for demonstrations are discussed in Section V.D.

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 data base 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.  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 data base 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 both the occurrence of the
event in question, to demonstrate that the event qualifies as an
exceptional event in accordance with section IV.D and with EPA policies
and guidance for certain events as described in section IV.E, 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, and to more specifically 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 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 only information permitted 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 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:  EPA disagrees with the commenter that this option fails to
provide guidance and is so vague as to be arbitrary.  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:  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

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, (
HYPERLINK "http://www.regulations.gov"  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 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.

Comment:  One commenter cautioned the 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 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.  PHowever, 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 data basedatabase, 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.  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 three years of an event,
and 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 three year time frame 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 data basedatabase within 60 days.
The EPA expects that, in most cases, this time period should be enough
time to review and provide a 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 and they may
flag the data at that time.  Any data that is flagged prior to or
following the effective date of the rule will be addressed under this

exceptional events rule.  This procedure should accommodate States
concerned about potential PM2.5 nonattainment areas using the 2004-2006
data sets.

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 time frames. 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.

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

1.	Background

In general, the 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 μg/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 forest fire had
a measured 24-hour PM2.5 concentration of 50 μg/m3 and the estimated
event impact was 30 μg/m3, then the expected value that would have
occurred but for the event would have been 20 μg/m3.  Normal air
quality for this location might be 16 μg/m3 and, therefore, the
“but-for” concentration of 20 μg/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 μg/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 adequate and generally
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, (
HYPERLINK "http://www.regulations.gov"  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 will retain 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
adequate and generally 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 µg/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 µg/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:  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 “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 data basedatabase, 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.

Extremely hHigh 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 data basedatabase.  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, (cb) the event is associated with an unusual
measured concentration beyond typical fluctuations including background,
and (dc) there would have been no exceedance or violation but for the
event.  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.

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:  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:  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.  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:  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 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.

Additional Requirements

Pursuant to section 319, EPA is finalizing this rule to address data
that has been influenced by exceptional events.  EPA is also 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 EPA must promulgate
regulations that are consistent with paragraph 3, which enumerates
certain principles and minimum regulatory requirements.  The first part
of paragraph 3 states that in promulgating regulations under section
319, EPA shall follow five principles, including the principle that each
State “must take necessary measures to safeguard public health
regardless of the source of air pollution”,  section 319(b)(3)(A).
This section does not, however, specify what measures may be
“necessary” in this context.  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 concentrations of air pollution
associated with the exceptional event.  This may or may not include
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, submit 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 Act.  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, yet would be consistent with the
principles and requirements of section 319.  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 contained in the proposed rule 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 finalizes Option 1 from the proposed rule, as stated 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.  States must also provide documentation
which shows what actions were taken to mitigate the affects of an
exceptional event on the public.  This information must be submitted
along with the State’s request for exclusion of data affected by an
exceptional event.

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.  Several The majority of
commenters who commented on option 4 also 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 educate programs on
exceptional events, and implementation of reasonable measures to protect
public health.

Response:  EPA believes that States should take appropriate action to
mitigate the public health impacts associated with exceptional events.
It is EPA’s belief as well 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 being the case, EPA
believes that States should have the necessary flexibility to take
appropriate actions when exceptional events occur.  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.  A State
may determine that reasonable measures in a particular instance, 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 controls should be implemented following an event, as
well as the level of control that is required. EPA believes that 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, EPA believes that the
principles requiring the development of an exceptional events rule do
specify that States must take appropriate action to protect public
health with regard to the impacts of exceptional events irrespective of
the NAAQS pollutants that are involved.  Therefore, under the modified
version of option 1 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:  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 proposed 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 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 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 that are determined to have been
reasonably well controlled at the time that the event occurred.  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 health (See section VI above), States must provide
documentation to show that reasonable and appropriate measures were
taken to mitigate the impact associated with the event on public health
although, as noted, the documentation will not be used as a basis for
approval or disapproval of a State’s request for exclusion of data.
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 provide appropriate documentation to
show that reasonable and appropriate measures were taken to protect
public health, and whether or not the implementation of control measures
was necessary to mitigate or prevent future impacts associated with the
event in question.

	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.  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.  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.

C.	Stratospheric Ozone Intrusion

1.	Background

	Consideration of stratospheric ozone intrusions applies only to the
8-hour ozone standard.  The occurrence of such intrusionsversions is 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 like 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 the need for
recognizing 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

	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, 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 from
regulatory determinations data that has been determined to be affected
by emissions from fireworks displays on a case-by-case basis in a
similar manner as other exceptional events under this rule.  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 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
the 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 it was not the intent of Congress 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. Emissions from
fireworks displays that are determined to be non-culturally significant,
such as fireworks displays associated with amusement parks and sporting
events, are not be subject to exclusion under this rule, unless they
otherwise qualify as exceptional events as defined by this rule.

IX. 	Statutory and Executive Order Reviews

	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 EO 12866 and any changes made in response to OMB recommendations
have been documented in the docket for this action.

	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.

	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