Friday, 

March 10, 2006 

Part V 

Environmental 

Protection Agency 

40 CFR Parts 50 and 51 

The Treatment of Data Influenced by 

Exceptional Events; Proposed Rule 


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12592 Federal Register / Vol. 71, No. 47 / Friday, March 10, 2006 / Proposed Rules 

ENVIRONMENTAL PROTECTION 

AGENCY 

40 CFR Parts 50 and 51 

[EPA–HQ–OAR–2005–0159; FRL–8042–5] 

RIN 2060–AN40 

The Treatment of Data Influenced by 

Exceptional Events 

AGENCY: Environmental Protection 

Agency (EPA). 

ACTION: Proposed rule. 

SUMMARY: Today, EPA is proposing 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 proposing 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. Also, EPA is proposing 

four options with respect to whether, 

and to what extent, States should be 

required to take additional actions to 

address public health impacts related to 

the event. 

DATES: Comments must be received on 

or before May 9, 2006. Comments must 

be postmarked by the last day of the 

comment period. 

ADDRESSES: Submit your comments, 

identified by Docket ID No. EPA–HQ– 

OAR–2005–0159, by one of the 

following methods: 

• http://www.regulations.gov. Follow 

the on-line instructions for submitting 

comments. 

• E-mail: Comments may be sent by 

electronic mail (e-mail) to A–and–R– 

Docket@epa.gov, Attention Docket ID 

No. EPA–HQ–OAR–2005–0159. 

• Fax: Fax your comments to: 202– 

566–1741, Attention Docket ID no. 

EPA–HQ–OAR–2005–0159. 

• Mail: Send your comments to: Air 

and Radiation Docket and Information 

Center, U.S. Environmental Protection 

Agency, Mail Code: 6102T, 1200 

Pennsylvania Ave., NW., Washington, 

DC 20460, Attention Docket ID No. 

EPA–HQ–OAR–2005–0159. 

• Hand Delivery: Air and Radiation 

Docket and Information Center, U.S. 

Environmental Protection Agency, 1301 

Constitution Avenue, NW., Room B102, 

Washington, DC, Attention Docket ID 

No. EPA–HQ–OAR–2005–0159. Such 

deliveries are only accepted during the 

Docket’s normal hours of operation, and 

special arrangements should be made 

for deliveries of boxed information. 

Instructions: Direct your comments to 

Docket ID No. EPA–HQ–OAR–2005– 

0159. The EPA’s policy is that all 

comments received will be included in 

the public docket without change and 

may be made available online at http:// 

www.regulations.gov, including any 

personal information provided, unless 

the comment includes information 

claimed to be Confidential Business 

Information (CBI) or other information 

whose disclosure is restricted by statute. 

Do not submit information that you 

consider to be CBI or otherwise 

protected information through http:// 

www.regulations.gov, or e-mail. The 

http://www.regulations.gov Web site is 

an ‘‘anonymous access’’ system, which 

means that EPA will not know your 

identity or contact information unless 

you provide it in the body of your 

comment. If you send an e-mail 

comment directly to EPA without going 

through http://www.regulations.gov, 

your e-mail address will be 

automatically captured and included as 

part of the comment that is placed in the 

public docket and made available on the 

Internet. If you submit an electronic 

comment, EPA recommends that you 

include your name and other contact 

information in the body of your 

comment and with any disk or CD–ROM 

you submit. If EPA cannot read your 

comment due to technical difficulties 

and cannot contact you for clarification, 

EPA may not be able to consider your 

comment. Electronic files should avoid 

the use of special characters, any form 

of encryption, and be free of any defects 

or viruses. For additional instructions 

on submitting comments, go to 

SUPPLEMENTARY INFORMATION. 

Docket: All documents in the docket 

are listed in the http:// 

www.regulations.gov index. Although 

listed in the index, some information is 

not publicly available, e.g., CBI or other 

information whose disclosure is 

restricted by statute. Certain other 

material, such as copyrighted material, 

will be publicly available only in hard 

copy. Publicly available docket 

materials are available either 

electronically in http:// 

www.regulations.gov or in hard copy at 

the Office of Air and Radiation Docket 

and Information Center, EPA West, 

Room B102, 1301 Constitution Ave., 

NW., Washington, DC. The Public 

Reading Room is open from 8:30 a.m. to 

4:30 p.m., Monday through Friday, 

excluding legal holidays. The telephone 

number for the Public Reading Room is 

(202) 566–1744, and the telephone 

number for the Office of Air and 

Radiation Docket and Information 

Center is (202) 566–1742. 

FOR FURTHER INFORMATION CONTACT: 

General questions concerning this 

proposed 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, NC 

27711; telephone (919) 541–0906, and email address wallace.larry@epa.gov. 

Questions concerning technical and 

analytical issues related to this 

proposed rule should be addressed to 

Mr. Neil Frank, Office of Air Quality 

Planning and Standards, Air Quality 

Assessment Division, Mail Code C304– 

04, Research Triangle Park, NC 27711; 

telephone (919) 541–5560, and e-mail 

address frank.neil@epa.gov. 

SUPPLEMENTARY INFORMATION: 

Public Hearing 

The EPA will hold two public 

hearings on today’s proposal during the 

comment period. The details of the 

public hearings, including the times, 

dates, and locations will be provided in 

a future Federal Register notice. The 

public hearings will provide interested 

parties the opportunity to present data, 

views, or arguments concerning the 

proposed rule. The EPA may ask 

clarifying questions during the oral 

presentations, but will not respond to 

the presentations or comments at that 

time. Written statements and supporting 

information submitted during the 

comment period will be considered 

with the same weight as any oral 

comments and supporting information 

presented at the public hearings. Under 

CAA section 307(d)(1)(A), the 

procedural requirements of section 

307(d) apply to this proposal. In 

addition, under section 307(d)(1)(U), the 

Administrator determines that this 

action is subject to the provisions of 

section 307(d). Section 307(d)(1)(U) 

provides that the provisions of section 

307(d) apply to ‘‘such other actions as 

the Administrator may determine.’’ The 

EPA is including the proposals in 

today’s proposed rulemaking under 

sections 307(d)(1)(A) and (U). 

Comments 

1. Submitting CBI. Do not submit this 

information to EPA through http:// 

www.regulations.gov or e-mail. Clearly 

mark the part or all of the information 

that you claim to be CBI. For CBI 

information in a disk or CD–ROM that 


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you mail to EPA, mark the outside of the 

disk or CD–ROM as CBI and then 

identify electronically within the disk or 

CD–ROM the specific information that 

is claimed as CBI. In addition to one 

complete version of the comment that 

includes information claimed as CBI, a 

copy of the comment that does not 

contain the information claimed as CBI 

must be submitted for inclusion in the 

public docket. Information so marked 

will not be disclosed except in 

accordance with procedures set forth in 

40 CFR part 2. 

2. Tips for Preparing Your Comments. 

When submitting comments, remember 

to: 

• Identify the rulemaking by docket 

number and other identifying 

information (subject heading, Federal 

Register date and page number). 

• Follow directions—The agency may 

ask you to respond to specific questions 

or organize comments by referencing a 

Code of Federal Regulations (CFR) part 

or section number. 

• Explain why you agree or disagree; 

suggest alternatives and substitute 

language for your requested changes. 

• Describe any assumptions and 

provide any technical information and/ 

or data that you used. 

• If you estimate potential costs or 

burdens, explain how you arrived at 

your cost estimate in sufficient detail to 

allow for it to be reproduced. 

• Provide specific examples to 

illustrate your concerns, and suggest 

alternatives. 

• Explain your views as clearly as 

possible, avoiding the use of profanity 

or personal threats. 

• Make sure to submit your 

comments by the comment period 

deadline identified. 

In addition, please send a copy of 

your comments to: Mr. Larry D. Wallace, 

Ph.D., U.S. Environmental Protection 

Agency, by one of the means listed 

below: 

1. E-Mail: wallace.larry@epa.gov. 

2. Fax: (919) 541–5489, Attention: Mr. 

Larry D. Wallace, Ph.D. 

3. Mail: Mr. Larry D. Wallace, Ph.D., 

U.S. Environmental Protection Agency, 

Office of Air Quality Planning and 

Standards, Mail Code: C539–01, 

Research Triangle Park, NC 27711. 

4. Hand Delivery: Mr. Larry D. 

Wallace, Ph.D., U.S. Environmental 

Protection Agency, Office of Air Quality 

Planning and Standards, 109 T.W. 

Alexander Drive, Research Triangle 

Park, NC 27709. 

Table of Contents 

The following is an outline of the 

preamble. 

I. Preamble Glossary of Terms and Acronyms 

II. Background and Purpose of Today’s 

Rulemaking 

A. Legislative Requirements 

B. Historical Experience Concerning 

Exceptional and Natural Events 

III. Today’s Proposed Action 

A. To Whom and to What Pollutants Does 

Today’s Proposed Rule Apply? 

B. How Does This Rule Relate to Indian 

Tribes? 

C. What Is an Exceptional Event? 

D. 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 Cleanup Activities 

c. High Wind Events 

d. Unwanted Fires 

e. Stratospheric Ozone Intrusions 

IV. The Management of Air Quality Data 

Affected by Exceptional Events 

A. Flagging of Data in the AQS Database 

B. What Does It Mean for an Event To 

‘‘Affect Air Quality’’? 

1. Option 1: 95th Percentile Criterion 

2. Option 2: 75th Percentile/95th Percentile 

Tiered Approach 

3. Option 3: Case-by-Case Approach Based 

On Weight of Evidence 

C. Use of a ‘‘But For’’ Test 

D. Schedules and Procedures for Flagging 

and Requesting Exclusion of Data 

1. Option 1: Early Data Flagging and 

Demonstration Submission 

2. Option 2: Early Data Flagging and 

Delayed Demonstration Submission 

3. Option 3: Delayed Data Flagging and 

Demonstration Submission 

E. Exclusion of Entire 24-Hour Value as 

Opposed to a Partial Adjustment of the 

24-Hour Value 

F. What Should States be Required To 

Submit in Their Exceptional Events 

Demonstrations? 

G. Special Considerations Relevant to 

Proposed Standards for PM10–2.5

H. Public Availability of Air Quality Data 

and Demonstrations Related to 

Exceptional Events 

V. Additional Requirements 

A. Option 1: Proposed Option: Require 

Public Notification, Education and 

Appropriate and Reasonable Measures 

B. Option 2: The Development of a 

Mitigation Plan by States Under Section 

110 of the CAA 

C. Option 3: The Development of a 

Mitigation Plan for Episodic Events 

D. Option 4: Do Not Require States To 

Adopt and Implement Specific 

Mitigation Plans or Measures Under This 

Rule 

VI. Special Treatment of Certain Events 

Under This Rule 

A. Volcanic and Seismic Activities 

B. High Wind Events 

C. Stratospheric Ozone Intrusion 

VII. Treatment of Fireworks Displays 

VIII. Statutory and Executive Order Reviews 

A. Executive Order 12866: Regulatory 

Planning and Review 

B. Paperwork Reduction Act 

C. Regulatory Flexibility Act 

D. Unfunded Mandates Reform Act 

E. Executive Order 13132: Federalism 

F. Executive Order 13175: Consultation 

and Coordination With Indian Tribal 

Governments 

G. Executive Order 13045: Protection of 

Children From Environmental Health 

and Safety Risks 

H. Executive Order 13211: Actions that 

Significantly Affect Energy Supply, 

Distribution, or Use 

I. National Technology Transfer 

Advancement Act 

I. 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 

FMP Fire Mitigation Plan 

NAAQS National Ambient Air Quality 

Standards 

NEAP Natural Event Action Plan 

OAQPS Office of Air Quality Planning 

and Standards 

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 Plan 

TAR Tribal Authority Rule 

TIP Tribal Implementation Plan 

II. Background and Purpose of Today’s 

Rulemaking 

A. Legislative Requirements 

Today, EPA is proposing 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 EfficientTransportation Equity Act: A Legacy for 

Users (SAFE–TEA–LU) of 2005, requires 

EPA to publish this rule in the Federal 


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1All subsequent references to section 319 of the 

CAA in this proposal are to section 319 as amended 

by SAFE–TEA–LU unless otherwise noted. 

2While this document refers primarily to States 

as the entity responsible for flagging data impacted 

by exceptional events, other agencies, such as local 

or Tribal government agencies, may also have 

standing to flag data as being affected by these types 

of events, and the criteria and procedures that are 

discussed in this rulemaking also apply to these 

entities. 

3 ‘‘Guideline for Interpretation of Air Quality 

Standards,’’ U.S. Environmental Protection Agency, 

Office of Air Quality Planning and Standards, 

Research Triangle Park, N.C. OAQPS No. 1.2–008 

(Revised February 1977). The guidance indicated 

the need for a data flagging system which would 

require the submittal of detailed information 

establishing that a violation was due to 

uncontrollable natural sources and that the 

information could be used in decision-making 

related to the feasibility of modifying control 

strategies. 

4Federal Register (52 FR 24667), July 1, 1987. 

5Memorandum from Mary D. Nichols, Assistant 

Administrator for Air and Radiation, to EPA 

Regional Offices entitled, ‘‘Areas Affected by PM10

Natural Events,’’ May 30, 1996. 

Register no later than March 1, 2006.1

Further, EPA is required to issue the 

final rule no later than 1 year from the 

date of proposal. 

The EPA is proposing to establish 

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 a natural event or an event 

caused by human activity that is 

unlikely to recur at a particular location; 

and is determined by the Administrator 

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.2 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 

exceedences or violations of the 

NAAQS. 

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 base 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, 

EPA believes that 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. In addition, Congress 

indicated that States should not have to 

prepare and implement regulatory 

strategies when their air quality is 

affected by events beyond their 

reasonable control. 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. 

Section 319 also includes an interim 

provision, section 319(b)(4), that 

addresses the transition period between 

the present and the date that a final 

regulation governing the treatment of 

data related to exceptional events is 

promulgated. The provision indicates 

that following EPA guidance documents 

continues to apply until the effective 

date of a final regulation promulgated 

under section 319(b)(2): ‘‘Guidance on 

the Identification and Use of Air Quality 

Data Affected by Exceptional Events’’

(July 1986); ‘‘Areas Affected by PM10

Natural Events,’’ May 30, 1996; and 

appendices I, K, and N to 40 CFR part 

50, which describe how air quality 

monitoring data are to be used and 

interpreted to determine compliance 

with the applicable NAAQS. The statute 

requires the promulgation of the final 

rule no later than 1 year following the 

publication of this proposed rule. 

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, 

‘‘Guidelines for the Interpretation of Air 

Quality Standards,’’ Guideline No. 1.2–

008 (revised February 1977).3

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.4 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 for 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 were 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).5


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6 ‘‘Guideline on Data Handling Conventions for 

the PM NAAQS,’’ United States Environmental 

Protection Agency, Office of Air Quality Planning 

and Standards, Research Triangle Park, N.C. 27711, 

EPA–454/R–99–008, April 1999. 

‘‘Guideline on Data Handling Conventions for the 

8-hour Ozone NAAQS,’’ United States 

Environmental Protection Agency, Office of Air 

Quality Planning and Standards, Research Triangle 

Park, N.C. 27711, EPA–454/R–99–008, April 1999. 

7Following the promulgation of this rule, EPA 

will revise the ‘‘Interim Air Quality Policy on 

Wildland and Prescribed Fires’’ to be consistent 

with current policies related to wildland and 

prescribed fires as well as the final rulemaking on 

exceptional events. 

On July 18, 1997, EPA issued 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 part 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, and section 1.0(b) of 

appendix N provide the authority for 

EPA to give special consideration to 

data determined to be affected by an 

exceptional or natural event. 

Appendices K, I, and N, which are a 

part 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 base for use 

in making regulatory decisions, in some 

cases it may be appropriate for the 

Regional Administrator 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.6 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.7 The EPA will 

continue to use these policies to address 

issues related to the existing and/or 

revised PM2.5 NAAQS pending EPA’s 

final action on today’s proposed 

rulemaking. Similarly, issues related to 

exceptional and natural events affecting 

the ozone standard will continue to be 

addressed under the 1986 Exceptional 

Events Policy until EPA issues a final 

exceptional events rule. 

III. Today’s Proposed Action 

A. To Whom and to What Pollutants 

Does Today’s Proposed 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 

data base. 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, if adopted, 

today’s proposed rule would apply 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 

proposed rule would also govern 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 proposed 

rule would govern those actions as well. 

At present, only the NAAQS for ozone 

and PM contain provisions which allow 

for the special handling of air quality 

data affected by exceptional 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 proposing to only apply 

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 provision 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. 

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). 


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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 

proposed 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 proposed 

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 

proposed rule). The EPA intends to 

work with Tribes on the implementation 

of this proposed 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 proposed rule. 

C. What Is an Exceptional Event? 

In accordance with the language in 

section 319, EPA is proposing to define 

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 the 

Administrator 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 

purposes of this rule, EPA is proposing 

to define ‘‘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 this proposed 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 proposing 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. In adopting section 

188(f) of subpart 4 of the 1990 

amendments to the CAA, Congress 

recognized and provided for 

distinctions between these types of 

activities, 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). 

D. 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 proposed rule if all 

other requirements of the rule are met. 

The AQS data base also contains a more 

detailed list of other similar events that 

may be flagged for special consideration 

(http://www.epa.gov/ttn/airs/airsaqs/ 

manuals/ codedescs.htm). 

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. 

2. Structural Fires 

Structural fires include any accidental 

fire involving a manmade structure. 

3. Exceedances Due to Transported 

Pollution 

Transported pollution, whether 

national or international in origin and 

whether from natural or anthropogenic 

sources, may cause exceedances which 

are eligible for exclusion under this rule 

as long as the other criteria and 

requirements for exceptional events 

under this rule are met. 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, leading to exceedances or 

violations of the 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 at 

monitoring sites in other States. Other 

types of events may be considered on a 

case-by-case basis. 

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. 

5. Natural Events 

The natural events addressed by this 

proposed rule are: (1) Volcanic and 

seismic activities; (2) natural disasters 

and associated cleanup activities; (3) 

high wind events; (4) unwanted fires; 

and (5) stratospheric ozone intrusions. 

The EPA will consider other types of 

natural events on a case-by-case basis. 

a. Volcanic and Seismic Activities. 

Ambient concentrations of particulate 

matter for which volcanic eruptions or 

seismic activity caused or 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 

eruptions contribute to ambient 

concentrations in two ways; 

concentrations 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. 

b. Natural Disasters and Associated 

Clean-up Activities. For the purpose of 

flagging, major natural disasters, such as 

hurricanes and tornados for which 

State, local, or Federal relief has been 

granted, and clean-up activities 

associated with these events may be 

considered exceptional events. 

c. High Wind Events. High wind 

events are events that affect ambient 

particulate matter concentrations 

through re-entrainment of material, i.e., 

by raising dust. Concentrations of coarse 

particles, i.e., PM10–2.5 and PM10 in some 

locations, are most likely affected by 

these types of events, although PM2.5


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8 It should be noted that this rule does not cover 

agricultural burning. To the extent that it is 

necessary for EPA to address this issue, we will do 

so in the future via separate guidance or 

rulemaking. 

standards may be exceeded under such 

circumstances as well. 

d. Unwanted Fires. Ambient 

particulate matter concentrations caused 

by smoke from wildland fires will be 

treated as due to natural events if the 

fires are determined to be unwanted 

fires, designated wildland fire use fires, 

not designated or managed as prescribed 

fires, or requiring appropriate 

suppression action by a wildland 

manager.8

The question of what is a natural 

versus an anthropogenic fire has 

particular significance in considering 

the impacts of wildland fires on air 

quality and how they should be 

regarded under today’s proposed rule. 

Federal land managers have given 

recognition to several different types of 

wildland fires, depending on their 

causal circumstances and the role that 

such fires play in the affected 

ecosystems. ‘‘Wildfires’’ are described 

as unplanned, unwanted wildland fires, 

and include unauthorized burns (such 

as arson or acts of carelessness by 

campers), prescribed burns that escape 

control due to unforeseen 

circumstances, or other wildland fires 

where the primary objective is to 

suppress the fire as quickly as possible. 

In contrast, ‘‘wildland fire use’’ fires 

are those which were ignited naturally 

or unintentionally (e.g., as the result of 

lightning) and are allowed to continue 

burning without suppression efforts in 

locations that have been designated in 

fire management plans as areas where 

fires are necessary and desirable to 

accomplish specific resource 

management objectives. ‘‘Prescribed 

fires’’ are those ignited purposely to 

accomplish specific management 

objectives, and have been subject to 

written, approved prescribed fire plans 

(‘‘Interagency Strategy for Directives 

Task Group,’’ Memorandum from 

National Fire and Aviation Executive 

Board to Agency Personnel: Bureau of 

Indian Affairs, Bureau of Land 

Management, National Park Service, 

U.S. Fish and Wildlife Service, USDA 

Forest Service, April 18, 2005). Under 

these classifications, we believe that 

wildfires due to whatever causes them 

clearly fall within the meaning of 

‘‘natural events’’ as that term is used in 

section 319. Similarly, we believe that 

wildland fire use fires qualify as 

‘‘natural events’’ by virtue of their 

natural origins. 

Prescribed fires, however, cannot be 

classified as ‘‘natural,’’ given their 

clearly anthropogenic origins. 

Nonetheless, we believe that prescribed 

fires are not automatically excluded 

from the definition of exceptional 

events. If a prescribed fire meets the 

statutory criteria of being ‘‘unlikely to 

recur at the same location’’ or ‘‘not 

reasonably controllable or preventable,’’

and the measures specified below, it 

may qualify as an exceptional event. 

Prescribed fires carried out for 

resource management objectives are 

frequently designed to restore the role of 

wildland fires as they once occurred 

under natural conditions. As such, their 

expected frequency can vary widely, 

depending on the fire regenerative cycle 

of a particular landscape or wildland 

ecosystem. The natural fire cycle 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 demonstrated that the likelihood 

of recurrence is sufficiently small that 

these events should be accorded special 

consideration under the rule. 

Since a prescribed fire is being 

deliberately ignited, it does not qualify 

as ‘‘natural,’’ 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 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 result in adverse 

impacts of much greater magnitude and 

severity than would result from the 

careful use of prescribed fires. A 

particular ecosystem may also be highly 

dependent on a natural fire cycle to 

maintain a sustainable natural species 

composition. Alternatively, pest or 

disease outbreaks in an area may be 

such that there are no reasonable 

alternatives to 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 it would be 

appropriate to exclude the impacts from 

well-managed prescribed fires to 

address them. Well-managed prescribed 

fires are those that consider smoke 

impacts prior to and during the burn, 

barring unforeseen circumstances, and 

when the prescribed fire is in 

compliance with a Smoke Management 

Plan (SMP). 

The EPA is proposing in this action 

that States continue to follow the smoke 

management provisions described 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 prescribed fires 

used for purposes of resource 

management provided that the State 

certifies that it has adopted and is 

implementing a certified SMP as 

described in our policy. Under our 

proposal, if a State, local, or Tribal air 

quality agency does not certify that a 

basic SMP is being implemented, or that 

basic smoke management practices are 

being employed by burners, EPA would 

not exclude data related to exceedances 

or violations attributed to prescribed 

fires managed for resource benefits. 

We request comments on the 

interpretation of prescribed fire 

described above on the proposed 

requirements for SMPs, and on any 

additional criteria or conditions that 

should be considered in determining 

whether and under what circumstances 

prescribed fires should be considered to 

be exceptional events. 

e. Stratospheric Ozone Intrusions. 

Stratospheric ozone intrusion is 

considered to be a natural event. A 

stratospheric ozone intrusion occurs 

when a parcel of air originating in the 

stratosphere, which is at an average 

height of 20 km or 12.4 miles, is reentrained 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. 

IV. The Management of Air Quality 

Data Affected by Exceptional Events 

The EPA is proposing that, in order to 

exclude air quality data from 

consideration for regulatory purposes, 

States must follow the procedures, 

timelines, and other requirements 

described in this proposed rule. 

Specifically, States must clearly 

identify, or ‘‘flag,’’ data they believe to 

be influenced by such events; they must 

show that they have flagged days on 

which air quality has been ‘‘affected’’ by 

exceptional events according to EPA 

criteria; and they must submit 

appropriate documentation 

demonstrating that the exceptional 

event caused the exceedance or 

violation of the NAAQS in question. 

Each of these steps is described in detail 

below. 


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A. Flagging of Data in the AQS Data 

Base 

Air quality data are required, 

pursuant to 40 CFR part 58.35, 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 base is to 

identify those air quality measurements 

for which special attention or handling 

is warranted. These include, but are not 

limited to, those measurements that are 

influenced by exceptional events. In the 

case of exceptional events, States place 

the initial flag on the data in the AQS 

data base. 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 base 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 

explained, 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. 

B. What Does It Mean for an Event To 

‘‘Affect Air Quality’’? 

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 and remote upwind 

sources. The EPA believes that it would 

be unreasonable to exclude data affected 

by an exceptional event simply because 

of a trivial contribution of the event to 

air quality. Furthermore, we also 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 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) provide 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) indicate that the protection 

of public health is the highest priority. 

For these reasons, we are proposing that 

for an event to qualify as ‘‘exceptional’’

for purposes of special regulatory 

consideration, its air quality impact 

must fall both above the level of the 

applicable standard (i.e., must be an 

‘‘exceedance’’ as required by section 

319) and significantly beyond the 

normal fluctuating range of air quality, 

including background air quality 

concentrations, and should be large 

enough so that without it there would 

have been no exceedance. We next 

provide several alternative approaches 

to determining whether and when air 

quality is ‘‘affected by’’ exceptional 

events, and request comment on which 

of these approaches is most suitable for 

demonstrating such impacts. 

1. Option 1: 95th Percentile Criterion 

The first proposed approach is 

essentially a test for statistical 

deviations from the norm. For 

measurement days on which the event 

can be shown to have an air quality 

impact, the measurement would be 

compared to the 95th percentile of 

measurements typical of days in the 

particular calendar quarter that are not 

influenced by exceptional events (‘‘nonevent days’’). The typical days could be 

based on a 3–5 year period of record 

which exclude days influenced by 

exceptional events. Under this option, 

only an event whose resulting 

concentrations meet or exceed the 95th 

percentile criterion, along with meeting 

the other criteria in this proposed rule 

would qualify for exclusion from 

regulatory consideration. 

In evaluating available air quality 

data, we have found that by limiting 

consideration to those concentrations 

above the 95th percentile, only those 

concentrations that fall approximately 

two standard deviations above the mean 

of concentrations for that quarter would 

generally be excluded (See memo from 

Mark Schmidt, OAQPS, to docket 

entitled ‘‘Analysis of Flagged Particulate 

Matter Data,’’ February 10, 2006). 

Excluding days on which 

concentrations caused by exceptional 

events exceed the 95th percentile 

threshold employs a general test of 

statistical significance and has the effect 

of ensuring that such concentrations 

would clearly fall beyond the range of 

normal expectations for air quality 

during a particular time of year. 

In our analysis of flagged and 

excluded air quality data for the period 

1999–2004, we found that application of 

the 95th percentile criterion would 

result in the exclusion of approximately 

85 percent of data previously flagged by 

States and concurred on by EPA. Thus, 

this approach would result in a 

somewhat more rigorous qualification 

requirement than is reflected in EPA’s 

past case-by-case approach. Previously, 

EPA did not have a concentration 

threshold or other quantitative criteria 

to determine which days would be 

eligible for exclusion due to exceptional 

events. As indicated above, 

approximately 15 percent of the flags 

that were concurred on were 

concentrations that were not necessarily 

statistically distinguishable from routine 

levels. The 95th percentile approach 

could also help to eliminate some of the 

variability from State to State and 

Region to Region: as described in 

Schmidt (2006), rates of flagging and the 

severity of pollution on flagged days 

have varied significantly among States 

and regions in the past. For PM2.5, for 

example, many States flagged no days 

between 1999–2004, while Puerto Rico 

flagged 15 percent of all of its PM2.5

data. Also, while most PM2.5 flags 

during this period were above the 95th 

percentile, some States flagged data at 

the 75th percentile or lower. (See memo 

from Mark Schmidt, OAQPS, to docket 

entitled ‘‘Analysis of Flagged Particulate 

Matter Data,’’ February 10, 2006.) 

2. Option 2: 75th Percentile/95th 

Percentile Tiered Approach 

Under this approach, we propose to 

retain flexibility to determine whether 

concentrations less than the 95th 

percentile but above the norm should 


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qualify for exclusion as ‘‘affecting air 

quality.’’ In particular, multiple 

measurement values over time with 

relatively small individual event 

impacts may collectively affect an 

annual average concentration to a 

significant degree. States may wish to 

consider whether to exclude such 

impacts if the average concentration is 

close to the level of the annual NAAQS. 

Therefore, we are soliciting comment on 

a second approach whereby measured 

values are compared both to the 

historical 95th percentile of non-event 

days and to the 75th percentile of such 

days. 

Where concentrations caused by an 

exceptional event meet or exceed the 

95th percentile criterion, they would be 

conclusively determined to qualify for 

exclusion subject to the other 

requirements of this proposed rule. 

Where concentrations caused by an 

exceptional event do not meet the 95th 

percentile criterion, we would provide a 

further opportunity for States to make 

demonstrations which satisfy the other 

criteria in this proposed rule, so long as 

values exceeded the 75th percentile of 

non-event days. This approach would 

provide for a more flexible approach 

and would rely on a weight-of-evidence 

demonstration that would permit States 

to make other sorts of showings that the 

concentrations caused by the event were 

in some way unusual or not 

representative of normal air quality and 

thus should not result in additional 

regulatory requirements. 

When we applied the 75 percent 

percentile criterion to our analysis of 

flagged and excluded air quality data for 

the period 1999–2004, we found that 

this criterion would make nearly all of 

the data previously flagged by States 

and concurred on by EPA eligible for 

exclusion. Thus, we expect this 

approach would have a result that is 

roughly consistent with EPA’s past caseby-case approach. 

3. Option 3: Case-by-Case Approach 

Based on Weight of Evidence 

The third option is to permit the more 

general case-by-case evaluation, without 

threshold criteria, that may be guided by 

the magnitude of the measured 

concentration on days affected by 

exceptional events relative to historical, 

seasonally adjusted air quality levels. 

This approach is most nearly analogous 

to our historical treatment of 

exceptional events but, in contrast to 

Options 1 and 2, provides the least 

definitive guidance to assist States in 

their evaluations. Nevertheless, 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. In fact, 25 percent 

of days have concentrations greater than 

the median value but less than the 75th 

percentile. While such days are unlikely 

to impact short-term standards, 

discounting such days can certainly 

have an impact on an annual average 

concentration. In general, however, 

demonstration that an event caused a 

concentration which is essentially 

indistinguishable from routine air 

quality would be very difficult to 

document, and this approach may make 

it difficult for EPA regions to be 

consistent when determining whether to 

concur on a flag. 

We request comment on which of 

these proposed options should be 

included in the final rule, including the 

appropriateness of proposed statistical 

criteria, the period of record on which 

to base the 95th and 75th percentile and 

conclusions about normal air quality 

expectations (e.g., 3 years, 5 years, or 

some longer period of record), and any 

other criteria or procedures we should 

consider adopting along with one of 

these options. 

C. Use of a ‘‘But For’’ Test 

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 activities which properly 

fall within the responsibilities of States 

to manage for purposes of air quality 

attainment and maintenance. For this 

reason, we are proposing 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 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 offices to 

further discuss this issue. 

D. Schedules and Procedures for 

Flagging and Requesting Exclusion of 

Data 

In establishing procedures and 

timetables 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 are proposing three 

alternatives for public review and 

comment. 

1. Option 1: Early Data Flagging and 

Demonstration Submission 

The first approach would establish a 

two-step process for identification of 

data and submission of demonstrations. 

This process provides for the early 

flagging of data and the notification of 

the appropriate EPA Regional Office 

concerning the State’s intention to seek 

exclusion of data, followed by a longer 

timeframe for States to prepare and 

submit their demonstrations. 

Under this approach, we would 

require a State 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 base, 

in accordance with the schedule 

described in 40 CFR part 50.35, which 

is generally no later than 90 days after 

the end of the calendar quarter. This 

approach would ensure that the flagging 

process remains consistent with the 

timeline set forth in rules governing 

data submission requirements. 

Just as the scope and substance of 

demonstrations in support of requests 

for exclusion will vary depending on 

facts and circumstances (see section 

IV.F. below), so, too, will the time 

required for such demonstrations. 

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 


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unusual ones, more time and effort will 

be needed for a State to provide an 

adequate demonstration in support of its 

request. 

For these reasons, we are proposing 

under this option to require States to 

notify the appropriate EPA Regional 

Office of their intent to seek exclusion 

of data due to exceptional events at the 

time of submission of quarterly air 

quality data to the AQS data base. We 

are also proposing to require the State 

to consult with the EPA Regional Office 

as soon as reasonably possible after 

notification about the event, its 

suspected air quality impact, and the 

demonstration needed to justify a 

decision to exclude the data from 

regulatory consideration. This is 

intended to enable the State and EPA to 

work together during the process of data 

analysis and documentation to ensure 

that a complete and well-supported 

demonstration is submitted in a timely 

manner. 

With respect to demonstrations in 

support of requests for exclusion of 

data, we are proposing under this option 

to provide States with more time to 

submit the necessary demonstration. We 

propose that States submit complete 

demonstrations to EPA not later than 

180 days following the close of the 

quarter in which the event occurred. 

Based on past experience with 

exceptional events and associated data 

analyses, we believe that this will 

provide adequate time in most cases for 

States to identify, compile, and evaluate 

all relevant factors pertaining to an 

exceptional event and its impacts. 

However, in special circumstances 

where additional time is required to 

make a complete submission, and where 

the outcome of such additional efforts is 

likely to have a substantial impact on 

the demonstration, we are proposing to 

allow States to request extensions of up 

to 90 additional days. We expect that 

such extensions under this option 

would be the exception, rather than the 

rule, and that they will be limited to 

special circumstances necessitating 

more complex and sophisticated 

analyses, such as where the collection 

and analysis of species-specific data in 

urban areas may be needed in order to 

characterize and quantify an event’s 

contribution to air quality at a particular 

location. Under this option, as well as 

the options addressed below, once EPA 

receives a State’s demonstration, EPA 

will then have a 30-day period to review 

the demonstration and provide a 

concurrence or nonconcurrence on the 

flag in the AQS data base. The EPA 

expects that, in most cases, a period of 

30 days will 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 more time for its review. In 

such cases, EPA may extend the time for 

its review by not more than an 

additional 30 days. 

2. Option 2: Early Data Flagging and 

Delayed Demonstration Submission 

Under this option, we are proposing 

the same requirements for the flagging 

of data and notification of the 

appropriate EPA Regional Office as 

described in Option 1. However, under 

Option 2, we propose to allow up to 3 

years following the quarter in which the 

event occurred for the submission of 

exceptional events demonstrations. The 

reason for providing more time under 

this option is that for most existing air 

quality standards, 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 

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. 

3. Option 3: Delayed Data Flagging and 

Demonstration Submission 

Under this option, we are proposing 

to decouple the process of flagging and 

demonstrations from the regular 

submission of air quality data to the 

AQS data base and to require instead 

that data be flagged and exceptional 

events demonstrations be submitted not 

later than 6 months prior to the date 

when regulatory decisions using the air 

quality data must be made. This option 

is based on the recognition that while 

data flagging itself may not be a 

particularly burdensome exercise, it 

triggers a more extensive process of 

collection and analysis of other 

information to determine and 

demonstrate whether, in fact, an 

exceptional event has occurred which 

affects air quality data in a way that 

justifies exclusion of the data. It may be 

that although certain events occurred 

which do indeed affect air quality in 

significant ways, their impact on 

regulatory decisions may not be known 

for a significant period of time, i.e., until 

a relevant 3-year period of record is 

compiled and the need for a regulatory 

decision is identified. Thus under this 

option, it would be less burdensome for 

the States and EPA if demonstrations 

were not required unless and until it 

became apparent that potentially 

affected measurements would be used 

in making regulatory findings of 

attainment or nonattainment (e.g., 

where a State with an existing area 

designated as nonattainment seeks to 

have that area redesignated as 

attainment and the existence of one or 

more exceptional events may affect its 

ability to provide the requisite 3 years 

of clean air quality data). 

We request comment on which of the 

above three proposed options EPA 

should promulgate and on what, if any, 

modifications to these options we 

should make prior to the final rule. 

E. Exclusion of Entire 24-Hour Value as 

Opposed to a Partial Adjustment of the 

24-Hour Value 

The 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, 

and we are proposing to retain this 

approach in today’s 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

PM2.5 and is associated with a nearby 

forest fire, then EPA would 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 day 

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 which 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 universally 


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applicable techniques that are 

administratively and technically 

feasible and that could support partial 

adjustment of air quality data except 

perhaps in limited cases, such as where 

the number and type of pollutant 

species and contributing sources are 

relatively less complex or potentially, 

when sufficient spatial, temporal, 

meteorological and chemical data are 

available [See memo to docket, Husar et 

al. 2006, (http://www.regulations.gov, 

Epa–HQ–Oar–2003–0061–0733 thru 

0733.5)]. When we determine that 

techniques for adjustment of air quality 

data are sufficiently well-demonstrated 

for use in exceptional events 

determinations, we will publish a notice 

of proposed rulemaking to seek 

comment on the appropriateness and 

scope of such use. 

F. What Should States Be Required To 

Submit in Their Exceptional Events 

Demonstrations? 

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 base, 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 speciesspecific 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. Depending on which 

option is finalized pursuant to section V 

below, States may 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: 

1. 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. 

2. 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. 

3. 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. 

4. 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. 

5. Extremely high wind speeds, or 

unusual transport conditions 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 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. 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 proposing to specify 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. However, we request comment 

on whether we should adopt a set of 

minimum demonstration requirements 

to ensure a reasonable degree of national 

consistency in approaches to 

demonstrating exceptional events, and if 

so, what elements should be included in 

the demonstration. We believe, 

however, that at a minimum, the 

elements of such a demonstration 


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9The demonstrations related to PM10–2.5 are 

contingent upon the final outcome related to the 

rulemaking on the NAAQS for PM10–2.5. 

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. 

G. Special Considerations Relevant to 

Proposed Standards for PM10–2.5

As noted in EPA’s notice of proposed 

rulemaking reviewing the NAAQS for 

particulate matter (71 FR 2620; January 

17, 2006), fine particles (PM2.5) are 

produced chiefly by combustion 

processes and by atmospheric reactions 

of various gaseous pollutants, whereas 

thoracic coarse particles (PM10–2.5) are 

generally emitted directly as particles as 

a result of mechanical processes that 

crush or grind larger particles or the 

resuspension of dusts. Sources of fine 

particles include, for example, motor 

vehicles, power generation, combustion 

sources at industrial facilities, and 

residential fuel burning. Sources of 

thoracic coarse particles include, for 

example, resuspension of traffic-related 

emissions such as tire and brake lining 

materials, and direct emissions from 

industrial operations, construction and 

demolition activities. Fine particles can 

remain suspended in the atmosphere for 

days to weeks and can be transported 

thousands of kilometers, whereas 

thoracic coarse particles generally 

deposit rapidly on the ground or other 

surfaces and are not readily transported 

across urban or broader areas (71 FR 

2620, 2625; January 17, 2006). 

Based on preliminary analysis, we 

generally anticipate that demonstrations 

that ambient concentrations of PM10–2.5

have been affected by exceptional 

events will involve similar analytical 

steps to demonstrations for PM2.5 but 

will be simpler than demonstrations for 

PM2.5.9 This conclusion is based on 

preliminary evaluation of estimated 

PM10–2.5 concentrations derived from 

historical PM10 and PM2.5 data. We 

examined those days on which PM10

exceedances were flagged as due to 

exceptional events but where PM2.5

concentrations were not also flagged, 

indicating that the event in question 

was dominated by coarse particles. The 

results of this analysis suggest that 

exceptional events related to PM10–2.5

are relatively infrequent, occur 

predominantly in the western States and 

are overwhelmingly high wind events. 

Thus, with the exception of western 

areas, we do not anticipate that 

exceptional events will be a 

predominate factor in decisions made 

related to attainment or nonattainment 

determinations for the proposed 

PM10–2.5 standards (See memo from 

Mark Schmidt, OAQPS, to docket 

entitled ‘‘Analysis of Flagged Particulate 

Matter Data,’’ February 10, 2006). 

Moreover, in light of the above analysis 

and the evidence on which it is based, 

we believe that exceptional events 

demonstrations for PM10–2.5 will involve 

relatively straightforward showings that 

when high concentrations occurred at 

the affected monitors, concentrations at 

available rural monitors (e.g., IMPROVE 

network monitors) were also elevated 

and that meteorological conditions (i.e., 

wind speed and wind direction) were 

conducive to transport from upwind 

sources of re-entrained coarse particles. 

It may be beneficial to examine 

continuous PM10–2.5 monitoring data as 

well, as they may indicate extremely 

high short-term values (e.g., 1 hour or 

less) that heavily influence 24-hour 

concentrations and are consistent with 

extreme high wind events. For instance, 

when we examined air quality 

concentrations recorded in El Paso, 

Texas during a dust storm that occurred 

on April 26–27, 2002 we found two 

consecutive 24-hour average 

concentrations of PM10 (654 μg/m3) and 

PM2.5 (56 μg/m3) which were dominated 

by a peak 1-hour concentration of 2700 

μg/m3 which occurred in the late 

evening of April 26–27. 

H. Public Availability of Air Quality 

Data and Demonstrations Related to 

Exceptional Events 

Sections 40 CFR parts 58.35 and 58.28 

of EPA’s air quality monitoring rules 

state that all data, flagged or unflagged, 

should be available to the public for 

comparison to the NAAQS to determine 

if exceedances have occurred. The EPA 

is proposing to require 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 public review 

and comment prior to the 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 is not proposing to 

require that public hearings be held on 

exceptional events demonstrations, but 

leaves this matter to the States’

discretion. 

V. Additional Requirements 

Pursuant to section 319, EPA is 

proposing new regulations to address 

exceptional events. Also EPA is 

proposing one option, and is taking 

comments on three alternative options, 

to address the issue of whether, and to 

what extent, States might be required to 

adopt specific mitigation plans or 

measures. 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 proposing 

to exclude trivial and more routine 

background air quality impacts from 

qualifying as an exceptional event and 

is also proposing a ‘‘but for’’ test as a 

precondition to qualification as an 

exceptional event (See: section IV). In 

addition, EPA is also proposing one 

approach and is taking comments on 

three other alternative options 

concerning State actions in anticipation 

of or in response to exceptional events. 

These proposed options range from 

being very detailed and more 

prescriptive to very flexible and less 

prescriptive. While EPA does not 

believe section 319(b)(3)(A) explicitly 

requires, in and of itself, that States 

develop mitigating measures or plans 

under options (1), (2), and (3) as 

discussed below, EPA solicits comment 

on whether this subparagraph supports 

the exertion of other legal authority to 

require mitigating actions or plans and 

solicits comment on issues regarding its 

legal authority to require mitigation 

measures and plans, and the legal basis 

for not requiring mitigation measures or 

plans. We are also requesting comments 

on the proposed approach and the three 

alternatives, and on any modifications 

to or combinations of any of the four 

approaches. 

A. Option 1: Proposed Option: Require 

Public Notification, Education and 

Appropriate and Reasonable Measures 

In cases where exceedances or 

violations of a NAAQS are caused by an 

exceptional event, EPA is proposing that 

once a State becomes aware that an 

exceptional event is occurring, is 

predicted to occur, or has occurred, the 

State must take appropriate action to: 


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Federal Register / Vol. 71, No. 47 / Friday, March 10, 2006 / Proposed Rules 12603 

10 In the case of the proposed NAAQS for 

PM10–2.5, these options would not apply to sources 

which are proposed to be excluded from 

consideration, e.g., agriculture and mining 

activities. 

1. 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. 

2. 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. 

3. 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 include, but is not limited to, 

taking reasonable and appropriate 

actions to implement control measures 

on significant contributing 

anthropogenic sources to reduce 

potential exposure of the public to 

emissions associated with natural 

events. 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 reentrainment. 

Under this option, where a State is 

requesting that air quality data be 

excluded as an exceptional event, the 

State must submit, as part of its 

demonstration, the appropriate 

documentation to show that the State 

provided appropriate public notice and 

public education concerning the event 

in question, and that the State took 

reasonable measures to abate or 

minimize the exposure of the public, 

where appropriate. 

The concept of having States take 

steps to reduce emissions, where 

appropriate, and to develop mitigation 

plans to address impacts associated 

with exceptional events was first 

instituted under the PM10 Natural 

Events Policy. The mitigation plans 

required under the PM10 Natural Events 

Policy were called Natural Events 

Action Plans (NEAPS). In instances 

where a State requested that air quality 

data influenced by a natural event be 

excluded, the State was required to 

develop and implement a NEAP. 

In developing a NEAP, States were 

expected to: Establish a public 

notification and education program 

related to natural events; minimize 

public exposure to high concentrations 

of pollutants related to natural events; 

provide a process for abatement of 

controllable anthropogenic sources 

related to natural events; identify, study, 

and implement practical mitigation 

measures as necessary; and provide for 

a periodic re-evaluation of the NEAP 

every 3–5 years. 

Due to past success with the 

implementation of NEAPs, EPA is 

proposing to base the requirements to 

mitigate the impact of exceptional 

events on the general concepts and 

elements described above from the PM10

Natural Events Policy. The EPA is 

proposing this approach to provide 

flexibility to the States to implement 

those measures that it considers to be 

reasonable and appropriate under 

particular circumstances to protect 

public health in the event of an 

exceptional event. The EPA believes 

that this approach allows States to use 

their experience in addressing those 

exceptional events that occur most 

frequently in their respective 

jurisdictions, and in providing notice to 

sensitive populations concerning the 

harmful effects of prolonged exposure to 

high concentrations of pollution 

associated with various types of 

exceptional events, yet could be 

consistent with both the principles and 

requirements of section 319. The 

proposed approach also allows EPA to 

fulfill its oversight responsibility, while 

still providing flexibility to States to 

implement reasonable measures to 

address the effects of exceptional events 

on public health. A possible 

disadvantage of this option is that it has 

the potential to result in inconsistencies 

in the way that exceptional events are 

addressed by States and in the actions 

that are taken to mitigate public health 

impacts associated with exceptional 

events, although such inconsistencies 

exist in any program that allows 

flexibility of any kind. We believe that 

despite this, such flexibility makes for a 

better and more efficient program in 

terms of taking specific mitigation 

actions that fit the circumstances of 

each case. 

B. Option 2: The Development of a 

Mitigation Plan by States Under Section 

110 of the CAA 

Under this option, States would be 

required to adopt a general mitigation 

plan to address exceptional events 

before the occurrence of an event as a 

part of the State’s SIP required under 

section 110(a)(1) of the CAA. Section 

110(a)(1) requires States to adopt and 

submit to EPA, within 3 years following 

the promulgation of a new or revised 

NAAQS, a plan which provides for the 

implementation, maintenance, and 

enforcement of the standard in each air 

quality region within the State. The EPA 

believes that section 110(a)(1) of the 

CAA provides EPA with the statutory 

authority to require States to submit 

plans to address the mitigation of public 

health impacts due to exceptional 

events that cause exceedances or 

violations of the NAAQS, because such 

plans assist in the maintenance and 

enforcement of the NAAQS and could 

be consistent with both the principles 

and requirements of section 319. Under 

this alternative, States would be 

required to develop and adopt the 

general requirements and procedures 

necessary for the implementation of a 

mitigation plan as a part of its section 

110(a)(1) SIP to address a new or revised 

NAAQS. As a part of this plan, EPA 

would require States to identify the 

actions the State intends to take to 

reduce the impact of exceptional events 

on public health. Since the precise 

nature and cause of exceptional events 

may not be foreseeable, in many cases, 

these requirements would be general, 

and similar to the types of actions that 

States have already identified and 

adopted in their section 110 plans 

intended to address emergency episodes 

as required under section 110(g) and 40 

CFR part 51.152. Once the general 

requirements of the mitigation plan are 

in place under section 110, the State 

would only need to take action on an 

episodic basis to implement the 

requirements of the mitigation plan for 

the affected area following the 

occurrence of an exceptional event. 

The general plan requirements would 

include provisions for providing public 

notification of an event; providing a 

program to educate the public on the 

harmful effects of prolonged exposure to 

emissions associated with an 

exceptional event; and implementing 

reasonable measures to mitigate the 

public health impacts of an exceptional 

event (e.g., the implementation of 

control measures to abate or minimize 

the effect of high concentrations of 

emissions associated with an 

exceptional event). In cases where 

control measures are required to address 

the impacts associated with an 

exceptional event, the State would 

implement the required measures on an 

episodic basis, meaning in response to 

a specific event that affects the air 

quality of a particular area. 

In cases where anthropogenic sources 

contribute to emissions related to a 

recurring natural event, appropriate 

control measures would have to be 

implemented on all significant 

contributing anthropogenic sources 

related to the event in the affected 

area.10 Natural events, which are 


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defined as a class of exceptional events 

under this rule, may recur frequently in 

affected areas. Under this option, as 

well as under Option 3 below, after a 

natural event occurs, and it is 

determined that anthropogenic sources 

have significantly contributed to the 

emissions associated with that event, 

EPA is proposing that at a minimum, 

Reasonably Available Control Measures 

(RACM) must be implemented on the 

anthropogenic sources that contributed 

to the emissions associated with the 

event. Reasonable Available Control 

Measures are defined as those control 

measures that are considered to be 

reasonable, and economically feasible, 

to implement in an area for a given 

source type. States should consult the 

most recent EPA control guidance for 

the affected pollutant to determine what 

control measures might be considered as 

RACM for the affected source types 

associated with emissions due to a 

natural event. This requirement is also 

consistent with the policy currently 

being implemented under the ‘‘PM10

Natural Events Policy.’’

Also, EPA requests comments on 

whether, instead of RACM, the 

appropriate level of controls that should 

be implemented on these source types is 

Best Available Control Measures 

(BACM). Best Available Control 

Measures is a term first identified in the 

CAA under part D, subpart 4, related to 

the implementation of the PM10

standard. For PM10, BACM are defined 

as techniques that achieve the 

maximum degree of emissions 

reductions from a source as determined 

on a case-by-case basis, considering 

both the technological and economic 

feasibility of implementing the control 

measures for the affected source (59 FR 

42010; August 16, 1994). Currently, EPA 

requires the implementation of BACM 

on contributing anthropogenic sources 

under the PM10 Natural Events Policy 

for high wind events. Under this option, 

as well as under Option 3 below, the 

State would also be required to submit 

the mitigation plan for the affected area 

to the appropriate EPA Regional Office 

for review and concurrence. Once the 

State has received concurrence from the 

Regional Office on the control measures 

identified for the anthropogenic sources 

contributing to exceedances associated 

with natural events, the State would be 

required to include the measures as a 

part of its section 110(a)(1) SIP related 

to the mitigation plan for the area. As is 

the case with the control plans required 

for emergency episode plans under 

section 110(g), the State will not be 

required to submit the specific control 

measures as a part of the mitigation plan 

to EPA to be made federally enforceable. 

Pursuant to section 107(d)(3)and section 

319 (b)(3)(B) of the CAA, it is EPA’s 

intention to adopt a flexible approach 

and not redesignate an area as 

nonattainment, or seek a SIP call for an 

area, so long as the State continues to 

implement the requirements related to 

the mitigation plan for the area, as well 

as the control measures for significant 

contributing anthropogenic sources 

related to a natural event. 

Where a State provides adequate 

documentation to show that RACM was 

being implemented for the affected 

sources at the time that the natural 

event in question occurred, a State need 

not implement further control measures 

in the area related to the natural event. 

In cases where RACM was not 

implemented for contributing 

anthropogenic sources at the time of the 

natural event, the State would be 

required to implement RACM as 

expeditiously as practicable, but in no 

case later than 18 months from the end 

of the calendar quarter in which the 

event occurred. The EPA requests 

comments on whether this proposed 

time period is appropriate for the 

implementation of RACM for significant 

contributing anthropogenic sources 

under this option or whether another 

time period is more appropriate. 

The advantage of this particular 

option is that all States would have a 

general plan in place for how to address 

exceptional events once they occur and 

could take immediate action to protect 

public health. It would also allow States 

to evaluate proactively what actions 

need to be taken to address 

anthropogenic sources related to 

exceptional events, and to consider the 

most efficient and effective ways to 

educate the sensitive populations most 

likely to be harmed should an event 

occur. 

It is important to note that if we 

selected Option 3 regarding the timeline 

for flagging of data and submission of 

demonstrations, a disadvantage would 

be that flagging and demonstrations 

could potentially be delayed 

significantly past the time when States 

would be required to implement RACM 

under this option for mitigation plans. 

We request comment on when RACM 

should be implemented by States in the 

event that we select Flagging and 

Demonstration Option 3. 

C. Option 3: The Development of a 

Mitigation Plan for Episodic Events 

Under this option, 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 of the CAA containing the general 

provisions of a mitigation plan in 

advance of the occurrence of any 

exceptional event. Under this third 

option, the mitigation plan would only 

be developed by the State following the 

occurrence of an exceptional event for 

which a State requested exclusion of air 

quality data. The mitigation plan would 

be required to address the actions that 

would be taken by the State related to 

future similar events, yet could be 

consistent with the principles and 

requirements of section 319. The 

mitigation plan under this option would 

have the same provisions to 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. The mitigation 

plan must include a detailed description 

of planned actions that would be 

implemented if the event recurs. It 

would also provide for an 

implementation schedule which 

identifies the actions that would be 

taken related to the recurrence of an 

event, and it should identify the 

principal parties that would be 

responsible for carrying out the stated 

actions under the mitigation plan. 

In cases where a State intends to 

request that EPA exclude data from 

regulatory consideration that has been 

affected by an exceptional event under 

this option, the State must submit the 

plan to EPA for review and concurrence. 

However, EPA will not take action to 

make the mitigation plan federally 

enforceable. Under this option States 

would develop a mitigation plan for an 

area where an exceptional event has 

caused an exceedance or violation of a 

NAAQS no later than 18 months 

following the end of the calendar 

quarter in which the event occurred. 

The EPA requests comments on whether 

18 months is an appropriate time period 

for the development and adoption of a 

mitigation plan under this option or 

whether another time period is more 

appropriate. 

As stated in Option 2 above, in cases 

where anthropogenic sources contribute 

to emissions related to a recurring 

natural event, RACM must be 

implemented for all significant 

contributing anthropogenic sources. 

Where a State provides adequate 

documentation to show that RACM was 

being implemented for the affected 


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11As discussed in rules proposed at 71 FR 2665–

2668, January 17, 2006, and 71 FR 2710 and 2731, 

Continued 

sources in the area at the time that the 

event occurred, no action would be 

required by the State to implement 

further control measures related to the 

event for the affected area. In cases 

where a determination is made that 

RACM was not being implemented for 

significant contributing anthropogenic 

sources at the time of the event, the 

State would be required to adopt and 

implement RACM as expeditiously as 

practicable, but in no case later than 3 

years following the end of the calendar 

quarter in which the event occurred. 

The EPA requests comment on the 

appropriateness of the time period being 

proposed for the implementation of 

control measures related to significant 

contributing anthropogenic sources 

associated with a recurring natural 

event under this option. 

An advantage of this alternative is 

that a State can more carefully tailor the 

actions that it will take to mitigate the 

effect of the exceptional event based on 

its prior experience, which will help 

ensure protection of public health. 

However, the disadvantage of this 

particular option is that it would apply 

more specifically to one type of event, 

so that if a new or different type of 

exceptional event occurred, there would 

be no provisions in place under the 

mitigation plan to address it. Each time 

a new type of event occurs, the State 

would need to submit or revise the plan 

to address the new event. 

D. Option 4: Do Not Require States To 

Adopt and Implement Specific 

Mitigation Plans or Measures Under 

This Rule 

Under this option, 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 

because it results from an exceptional 

event. This approach would 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, States would not be obligated to 

take any particular actions to mitigate 

exposures such as those in Option 1, to 

develop and implement a formal 

mitigation plan as part of the SIP such 

as that in proposed Option 2, or to 

develop a more formal plan with 

requirements not a part of the SIP such 

as that in proposed Option 3. 

This proposed approach would 

require a much less formal method for 

States to take necessary measures to 

safeguard public health, yet could be 

consistent with both the principles and 

requirements of section 319. The statute 

does not identify specific ways in which 

EPA must satisfy its principles and 

requirements. Moreover, as detailed 

above, EPA is proposing to exclude only 

certain types of exceptional events from 

regulatory determinations with respect 

to the NAAQS. In section IV, EPA is 

proposing options for percentile criteria, 

case-by-case evaluation, and 

establishment of a ‘‘but for’’ test in order 

for an event to qualify as an exceptional 

event for which data can be excluded 

with respect to exceedences or 

violations of the NAAQS. These 

requirements, in and of themselves, may 

offer appropriate protection of public 

health. Under this view, EPA should 

give States broad flexibility in 

determining how best to respond to 

individual exceptional events. Given the 

States’ concern with the health of their 

citizens, and taking into consideration 

the other requirements of this rule, in 

this view States would have sufficient 

incentive to take appropriate actions to 

protect public health. 

One benefit of this option is that it 

would allow States to maintain the 

maximum degree of flexibility to 

respond to exceptional events and to 

take appropriate actions to protect 

public health without unnecessarily 

limiting their ability to seek exceptional 

events treatment for the data. One 

potential limitation of this proposed 

approach is that it might result in 

inconsistencies among States in 

addressing exceptional events and in 

mitigating the impacts of those events. 

The EPA requests comments on all 

options described above. Additionally, 

EPA requests comments on specific 

modifications that should be made to 

one or more of the options provided 

above, or on any combination of these 

options. 

VI. Special Treatment of Certain Events 

Under This Rule 

As stated in section III.C., above, this 

proposed 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 

or violations of the NAAQS in an 

affected area. This proposed rule applies 

to several types of natural events, 

including volcanic and seismic actives, 

natural disasters, high wind events, 

unwanted fires, and stratospheric ozone 

intrusions, and 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 which 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 

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 it is appropriate to consider an 

extended timeframe for flagging and 

exclusion of data associated with such 

events. Specifically, EPA is proposing 

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. Based on prior 

experiences, and on consultation with 

States, we believe that 1 year is an 

adequate amount of time for cleaning 

ash deposits from areas where 

anthropogenic activities (e.g., vehicle 

traffic) may cause re-entrainment and 

possible exceedances of the particulate 

matter NAAQS. After a year, however, 

exceedances or violations due to reentrainment of ash deposits will not be 

provided special consideration under 

this rule. The EPA, however, requests 

comments on whether another time 

period is more appropriate and 

reasonable to allow for clean up of ash 

deposits following volcanic or seismic 

activity. 

B. High Wind Events 

Where high wind events result in 

exceedances or violations of PM2.5

standards, we are proposing that they 

will be treated as natural events 

pursuant to this proposed rule if there 

is a clear causal relationship 

demonstrated between the exceedances 

measured and the high wind event in 

question, and if anthropogenic activities 

which contribute to PM2.5 emissions in 

conjunction with the high wind event 

are reasonably well controlled. 

For the proposed 24-hour PM10–2.5

standard, we propose to exclude 

measured exceedances from 

consideration if it is demonstrated that 

high winds resulted in the transport of 

airborne particulate matter in 

concentrations that caused an 

exceedance or violation of the 

NAAQS.11 States would be expected to 


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2736–40, January 17, 2006, where properly sited 

monitors show exceedances or violations of 

proposed PM10–2.5 standards, it will generally be 

presumed that such concentrations are due to 

emissions of urban origin and therefore subject to 

regulations, unless shown to be due to an 

exceptional event. 

control emissions from contributing 

anthropogenic sources as appropriate 

under the definition of the proposed 

PM10–2.5 indicator. 

C. Stratospheric Ozone Intrusion 

Consideration of stratospheric ozone 

intrusions applies only to the 8-hour 

ozone standard. The occurrence of such 

inversions is extremely difficult to 

measure or document given currently 

measured meteorological parameters. 

The infrequence, short duration, and 

localized nature of such events makes it 

difficult to use currently available, 

general meteorological data, which are 

usually collected at isolated locations 

like airports, to determine whether a 

stratospheric ozone intrusion has 

occurred. The EPA believes 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. 

VII. Treatment of Fireworks Displays 

While we are not including fireworks 

displays in our proposed rule governing 

exceptional events, we are proposing as 

a policy matter to address certain 

displays in a manner similar to 

exceptional events. Some national and/ 

or cultural traditions, such as July 4th 

Independence Day and Chinese New 

Year, have long included fireworks 

displays as important—indeed, many 

might assert essential—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 to prohibit these 

activities. 

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 have 

significant impact in the areas where 

these events are held. Such actions 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. States are 

encouraged, too, to explore the use of 

lower-emitting fireworks, such as those 

developed for frequent use at 

amusement parks. 

For these reasons, where States can 

show that the use of fireworks displays 

is integral to significant traditional 

national, ethnic, or other cultural 

events, we are proposing that air quality 

data associated with such events could 

be excluded. We request comments on 

alternative approaches to addressing 

emissions from fireworks at such events. 

VIII. Statutory and Executive Order 

Reviews 

A. Executive Order 12866: Regulatory 

Planning and Review 

Under Executive Order 12866 (58 FR 

51735, October 4, 1993), EPA must 

determine whether the regulatory action 

is ‘‘significant’’ and, therefore, subject to 

the Office of Management and Budget 

(OMB) review and the requirements of 

the Executive Order. The order defines 

‘‘significant regulatory action’’ as one 

that is likely to result in a rule that may: 

(1) Have an annual effect on the 

economy of $100 million or more or 

adversely affect in a material way the 

economy, a sector of the economy, 

productivity, competition, jobs, the 

environment, public health or safety, or 

State, local, or Tribal governments or 

communities; 

(2) Create a serious inconsistency or 

otherwise interfere with an action taken 

or planned by another agency; 

(3) Materially alter the budgetary 

impact of entitlements, grants, user fees, 

or loan programs or the rights and 

obligations of recipients thereof; or 

(4) Rraise novel legal or policy issues 

arising out of legal mandates, the 

President’s priorities, or the principles 

set forth in the Executive Order. 

Pursuant to the terms of Executive 

Order 12866, it has been determined 

that the proposed rule is a ‘‘significant 

regulatory action.’’ As such, this 

proposed rule was submitted to OMB 

for review under Executive Order 

12866. 

B. Paperwork Reduction Act 

This action does not impose an 

information collection burden. The 

information being requested under this 

rule is consistent with current 

requirements related to information 

needed to verify the authenticity of 

monitoring data submitted to EPA’s 

AQS data base, and to justify data that 

has been flagged as being affected by 

exceptional or natural events. The OMB 

has previously approved the 

information collection requirements 

contained in the existing regulations at 

40 CFR part 58.01, 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. 


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C. Regulatory Flexibility Act 

The Regulatory Flexibility Act (RFA) 

generally requires an agency to prepare 

a regulatory flexibility analysis of any 

rule subject to notice and comment 

rulemaking requirements under the 

Administrative Procedures Act (APA) 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 

today’s proposed rule on small entities, 

small entity is defined as: (1) A small 

business that is a small industry entity 

as defined in the U.S. Small Business 

Administration (SBA) size standards. 

(See 13 CFR 121); (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-forprofit enterprise which is independently 

owned and operated and is not 

dominate in its field. 

Courts have interpreted the RFA to 

require a regulatory flexibility analysis 

only when small entities will be subject 

to the requirements of the rule. See, 

Michigan v. EPA, 213 F.3d 663, 668–69 

(D.C. Cir., 2000), cert. den., 532 U.S. 903 

(2001). This rule would not establish 

requirements applicable to small 

entities. Instead, this rule provides the 

criteria necessary for State, local, or 

Tribal air quality agencies to meet in 

order to properly flag data as being 

influenced by an exceptional or natural 

event. The rule also provides 

information concerning what action 

should be taken by a State, local, or 

Tribal air quality agency to protect 

public health once EPA has provided a 

concurrence on data that has been 

flagged as being influenced by an 

exceptional or natural event. Because 

affected States would have discretion to 

choose the sources that may need to be 

regulated and the emissions reductions 

each selected source would have to 

achieve using RACM or BACM related 

to anthropogenic sources in the area 

determined to be influenced by an 

exceptional or natural event, EPA could 

not predict the effect of the rule on 

small entities. 

After considering the economic 

impacts of today’s proposed rule on 

small entities, I certify that this rule will 

not have a significant economic impact 

on a substantial number of small 

entities. 

D. Unfunded Mandates Reform Act 

Title II of the Unfunded Mandates 

Reform Act of 1995 (UMRA), Public 

Law 104–4, establishes requirements for 

Federal Agencies to assess the effects of 

their regulatory actions on State, local 

and Tribal governments and the private 

sector. Under section 202 of the UMRA, 

EPA generally must prepare a written 

statement, including a cost-benefit 

analysis, for proposed and final rules 

with ‘‘Federal mandates’’ that may 

result in expenditures to State 

governments, in the aggregate, or to the 

private sector, of $100 million or more 

in any 1 year. Before promulgating an 

EPA rule for which a written statement 

is needed, section 205 of the UMRA 

generally requires EPA to identify and 

consider a reasonable number of 

regulatory alternatives and adopt the 

least costly, most cost-effective or least 

burdensome alternative that achieves 

the objectives of the rule. The 

provisions of section 205 do not apply 

when they are inconsistent with 

applicable law. Moreover, section 205 

allows EPA to adopt an alternative other 

than the least costly, most cost-effective 

or least burdensome alternative if the 

Administrator publishes with the final 

rule an explanation of why that 

alternative was not adopted. Before EPA 

establishes any regulatory requirements 

that may significantly or uniquely affect 

small governments, including Tribal 

governments, it must have developed 

under section 203 of the UMRA a small 

government agency plan. The plan must 

provide for notifying potentially 

affected small governments to have 

meaningful and timely input in the 

development of EPA regulatory 

proposals with significant Federal 

intergovernmental mandates, and 

informing, educating, and advising 

small government on compliance with 

regulatory requirements. 

Today’s action does not include a 

Federal mandate within the meaning of 

UMRA that may result in expenditures 

of $100 million or more in any 1 year 

by either State, local, or Tribal 

governments in the aggregate or to the 

private sector, and therefore, is not 

subject to the requirements of sections 

202 and 205 of the UMRA. 

Inasmuch as this action simply 

provides the criteria for State, local, or 

Tribal air quality agencies to flag data to 

be discounted for regulatory purposes 

that is being influenced by exceptional 

or natural events, this proposed Federal 

action will not impose mandates that 

will require expenditures of $100 

million or more in the aggregate in any 

1 year. 

E. Executive Order 13132: Federalism 

Executive Order 13132, entitled 

‘‘Federalism’’ (64 FR 43255, August 10, 

1999), requires EPA to develop an 

accountable process to ensure 

‘‘meaningful and timely input by State 

and local officials in the development of 

regulatory policies that have federalism 

implications.’’ ‘‘Policies that have 

federalism implications’’ is defined in 

the Executive Order to include 

regulations that have ‘‘substantial direct 

effects on the States, or the relationship 

between the national government and 

the States, or on the distribution of 

power and responsibilities among the 

various levels of government.’’

This proposed rule does not have 

federalism implications. It will not have 

substantial direct effects on the States, 

on the relationship between the national 

government and the States, or on the 

distribution of power and 

responsibilities among the various 

levels of government, as specified in 

Executive Order 13132. The CAA 

establishes the scheme whereby States 

take the lead in developing plans to 

meet the NAAQS. This rule will not 

modify the relationship of the States 

and EPA for purposes of developing 

programs to implement the NAAQS. 

Thus, Executive Order 13132 does not 

apply to this rule. 

F. Executive Order 13175: Consultation 

and Coordination With Indian Tribal 

Governments 

Executive Order 13175, entitled 

‘‘Consultation and Coordination with 

Indian Tribal Governments’’ (65 FR 

67249, November 9, 2000), requires EPA 

to develop an accountable process to 

ensure ‘‘meaningful and timely input by 

Tribal officials in the development of 

regulatory policies that have Tribal 

implications.’’ This proposed rule does 

not have ‘‘Tribal implications’’ as 

specified in Executive Order 13175. The 

rule provides information concerning 

what action should be taken by a State, 

local, or Tribal air quality agency 

implementing relevant air quality 

programs to protect public health once 

EPA has provided a concurrence on data 

that has been flagged as being 

influenced by an exceptional or natural 

event. The CAA and the Tribal 

Authority Rule (TAR) give Tribes the 

opportunity to develop and implement 

CAA programs, but it leaves to the 

discretion of the Tribe whether to 

develop these programs and which 

programs, or appropriate elements of a 

program, the Tribe will adopt. 

This rule does not have Tribal 

implications as defined by Executive 

Order 13175. It does not have a 


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substantial direct effect on one or more 

Indian Tribes, because no Tribe has 

implemented an air quality management 

program related to the PM NAAQS at 

this time. Furthermore, this rule does 

not affect the relationship or 

distribution of power and 

responsibilities between the Federal 

government and Indian Tribes. The 

CAA and the TAR establish the 

relationship of the Federal government 

and Tribes in developing plans to attain 

the NAAQS, and this rule does nothing 

to modify that relationship. Because this 

rule does not have Tribal implications, 

Executive Order 13175 does not apply. 

G. Executive Order 13045: Protection of 

Children From Environmental Health 

and Safety Risks 

Executive Order 13045: ‘‘Protection of 

Children From Environmental Health 

and Safety Risks’’ (62 FR 19885, April 

23, 1997) applies to any rule that (1) is 

determined to be ‘‘economically 

significant’’ as defined under Executive 

Order 12866, and (2) concerns an 

environmental health and safety risk 

that EPA has reason to believe may have 

a disproportionate effect on children. If 

the regulatory action meets both criteria, 

EPA must evaluate the environmental 

health or safety effects of the planned 

rule on children, and explain why the 

planned regulation is preferable to other 

potentially effective and reasonably 

feasible alternatives considered by EPA. 

This action is not subject to Executive 

Order 13045 because it is not 

economically significant as defined in 

Executive Order 12866, and because 

EPA does not have reason to believe that 

the environmental health risks or safety 

risks addressed by this rule present a 

disproportionate risk or safety risk to 

children. The rule provides information 

concerning what action should be taken 

by a State, local, or Tribal air quality 

agency to protect public health once 

EPA has provided a concurrence on data 

that has been flagged as being 

influenced by an exceptional or natural 

event. 

H. Executive Order 13211: Actions That 

Significantly Affect Energy Supply, 

Distribution, or Use 

This rule is not a ‘‘significant energy 

action’’ as defined in Executive Order 

13211, ‘‘Actions that Significantly 

Affect Energy Supply, Distribution, or 

Use,’’ (66 FR 28355, May 22, 2001) 

because it is not likely to have a 

significant adverse effect on the supply, 

distribution, or use of energy. Further, 

we have concluded that this rule is not 

likely to have any adverse energy 

effects. 

I. National Technology Transfer 

Advancement Act 

Section 12(d) of the National 

Technology Transfer Advancement Act 

of 1995 (NTTAA), Public Law No. 104–

113, section 12(d) (15 U.S.C. 272 note) 

directs EPA to use voluntary consensus 

standards (VCS) in its regulatory 

activities unless to do so would be 

inconsistent with applicable law or 

otherwise impracticable. Voluntary 

consensus standards are technical 

standards (e.g., materials specifications, 

test methods, sampling procedures, and 

business practices) that are developed or 

adopted by VCS bodies. The NTTAA 

directs EPA to provide Congress, 

through OMB, explanations when EPA 

decides not to use available and 

applicable VCS. 

This action does not involve technical 

standards. Therefore, EPA did not 

consider the use of any VCS. 

List of Subjects in 40 CFR Parts 50 and 

51 

Environmental protection, Air 

pollution control, National parks, 

Wilderness areas. 

Dated: March 1, 2006. 

Stephen L. Johnson, 

Administrator. 

In consideration of the foregoing, the 

Environmental Protection Agency 

proposes to amend 40 CFR parts 50 and 

51 as follows: 

PART 50—NATIONAL PRIMARY AND 

SECONDARY AMBIENT AIR QUALITY 

STANDARDS 

1. The authority citation for part 50 

continues to read as follows: 

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

2. Amend § 50.1 to add paragraphs (j), 

(k), and (l) to read as follows: 

§ 50.1 Definitions. 

* * * * * 

(j) Exceptional event means an event 

that affects air quality; is not reasonably 

controllable or preventable; is a natural 

event or an event caused by human 

activity that is unlikely to recur at a 

particular location; and is determined 

by the Administrator in accordance with 

40 CFR 50.13 to be an exceptional event; 

it does not include stagnation of air 

masses or meteorological inversions; a 

meteorological event involving high 

temperatures or lack of precipitation; or 

air pollution relating to source 

noncompliance. 

(k) Natural event means an event in 

which human activity plays little or no 

direct causal role. 

(l) Exceedance with respect to a 

national ambient air quality standard 

means one occurrence of a measured or 

modeled concentration that exceeds the 

specified concentration level of such 

standard for the averaging period 

specified by the standard. 

3. Add § 50.14 to read as follows: 

§ 50.14 Treatment of air quality monitoring 

data influenced by exceptional events. 

(a) Requirements. (1) A State may 

request EPA to exclude data showing 

exceedances or violations of the 

national ambient air quality standards 

that are directly due to an exceptional 

event from use in determinations by 

demonstrating to EPA’s satisfaction that 

such event caused a specific air 

pollution concentration at a particular 

air quality monitoring location. 

(2) Demonstrations may include any 

reliable and accurate data, but must 

demonstrate a clear causal relationship 

between the measured exceedance or 

violation of such standards and the 

event. 

(b) Determinations by EPA. (1) EPA 

shall exclude data due to such event 

from use in determinations where a 

State demonstrates: 

(i) That an exceptional event caused 

a specific air pollution concentration 

resulting in an exceedance or violation 

of the national ambient air quality 

standards at a particular air quality 

monitoring location; and 

(ii) That it has taken appropriate 

actions to protect public health. 

(2) [Reserved] 

(c) Schedules and procedures—(1) 

Public notification. (i) All States and, 

where applicable, their political 

subdivisions must notify the public 

promptly whenever an event occurs or 

is reasonably anticipated to occur which 

may result in the exceedance of an 

applicable air quality standard. 

(ii) [Reserved] 

OPTION 1 for paragraphs (c)(2) 

through (c)(4): 

(2) Flagging of data. (i) A State shall 

notify EPA of its intent to exclude one 

or more measured exceedances of an 

applicable ambient air quality standard 

as being due to an exceptional event by 

placing a flag in the appropriate field for 

the data record of concern in accordance 

with the schedules for submission of 

data to the AQS data base in 40 CFR 

58.35. 

(ii) Flags placed on data in accordance 

with this section shall be deemed 

informational only, and the data shall 

not be excluded from determinations 

with respect to exceedances or 

violations of the national ambient air 

quality standards unless and until EPA 

notifies the State of its concurrence by 

placing a concurrence flag in the 

appropriate field for the data record in 

the AQS data base. 


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(3) Submission of demonstrations. (i) 

A State that has flagged data as being 

due to an exceptional event shall, after 

notice and opportunity for public 

comment, submit a complete 

demonstration to EPA in support of its 

request for exclusion not later than 180 

days following the end of the calendar 

quarter in which the flagged 

concentration was recorded. 

(A) Extensions. Where a State 

demonstrates to the satisfaction of EPA 

that additional time is needed to obtain 

information or complete analyses to 

demonstrate that an exceptional event 

caused an exceedance or violation of an 

ambient air quality standard, and that 

such information is likely to have 

significant probative value, then EPA 

may grant an extension of the date for 

submission of demonstrations of not 

more than an additional 90 days. 

(B) [Reserved] 

(ii) [Reserved] 

(4) EPA review and concurrence or 

nonconcurrence. (i) EPA shall complete 

its review and concur or nonconcur 

with a State’s request for exclusion not 

later than 30 days following receipt of 

a complete submission from the State. 

EPA shall notify the State of its 

concurrence or nonconcurrence by 

placing a flag in the appropriate field for 

the data record in the AQS data base. 

(A) Extensions. Where additional time 

is needed to complete its review of the 

State’s demonstration, EPA may extend 

the time for review by not more than an 

additional 30 days. 

(B) [Reserved] 

(ii) [Reserved] 

OPTION 2 for paragraphs (c)(2) 

through (c)(4): 

(2) Flagging of data. (i) A State shall 

notify EPA of its intent to exclude one 

or more measured exceedances of an 

applicable ambient air quality standard 

as being due to an exceptional event by 

placing a flag in the appropriate field for 

the data record of concern in accordance 

with the schedules for submission of 

data to the AQS data base in 40 CFR 

58.35. 

(ii) Flags placed on data in accordance 

with this section shall be deemed 

informational only, and the data shall 

not be excluded from determinations 

with respect to exceedances or 

violations of the national ambient air 

quality standards unless and until EPA 

notifies the State of its concurrence by 

placing a concurrence flag in the 

appropriate field for the data record in 

the AQS data base. 

(3) Submission of demonstrations. (i) 

A State that has flagged data as being 

due to an exceptional event shall, after 

notice and opportunity for public 

comment, submit a complete 

demonstration to EPA in support of its 

request for exclusion not later than 3 

years following the end of the calendar 

quarter in which the flagged 

concentration was recorded. 

(ii) [Reserved] 

(4) EPA review and concurrence or 

nonconcurrence. (i) EPA shall complete 

its review and concur or nonconcur 

with a State’s request for exclusion not 

later than 30 days following receipt of 

a complete submission from the State. 

EPA shall notify the State of its 

concurrence or nonconcurrence by 

placing a flag in the appropriate field for 

the data record in the AQS data base. 

(A) Extensions. Where additional time 

is needed to complete its review of the 

State’s demonstration, EPA may extend 

the time for review by not more than an 

additional 30 days. 

(B) [Reserved] 

(ii) [Reserved] 

OPTION 3 for paragraphs (c)(2) 

through (c)(4): 

(2) Flagging of data. (i) A State shall 

notify EPA of its intent to exclude one 

or more measured exceedances of an 

applicable ambient air quality standard 

as being due to an exceptional event by 

placing a flag in the appropriate field for 

the data record of concern not later than 

180 days prior to the date on which EPA 

intends to propose determinations with 

respect to violations of applicable 

national ambient air quality standards. 

(ii) Flags placed on data in accordance 

with this section shall be deemed 

informational only, and the data shall 

not be excluded from determinations 

with respect to exceedances or 

violations of the national ambient air 

quality standards unless and until EPA 

notifies the State of its concurrence by 

placing a concurrence flag in the 

appropriate field for the data record in 

the AQS data base. 

(3) Submission of demonstrations. (i) 

A State that has flagged data as being 

due to an exceptional event shall, after 

notice and opportunity for public 

comment, submit a complete 

demonstration to EPA in support of its 

request for exclusion not later than 180 

days prior to the date on which EPA 

intends to propose determinations with 

respect to violations of applicable 

national ambient air quality standards. 

(ii) [Reserved] 

(4) EPA review and concurrence or 

nonconcurrence. (i) EPA shall complete 

its review and concur or nonconcur 

with a State’s request for exclusion not 

later than 30 days following receipt of 

a complete submission from the State. 

EPA shall notify the State of its 

concurrence or nonconcurrence by 

placing a flag in the appropriate field for 

the data record in the AQS data base. 

(A) Extensions. Where additional time 

is needed to complete its review of the 

State’s demonstration, EPA may extend 

the time for review by not more than an 

additional 30 days. 

(B) [Reserved] 

(ii) [Reserved] 

PART 51—NATIONAL PRIMARY AND 

SECONDARY NATIONAL AMBIENT AIR 

QUALITY STANDARDS 

1. The authority citation for part 51 

continues to read as follows: 

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

2. Add Subpart Y consisting of 

§ 51.920 to read as follows: 

Subpart Y—Exceptional Events 

OPTION 1 for § 51.920: 

§ 51.920 Mitigation of exceptional events. 

(a) As a condition for EPA’s approval 

of a request to exclude air quality data 

due to exceptional events from use, each 

State must take appropriate and 

reasonable actions to protect public 

health from exceedances or violations of 

the national ambient air quality 

standards due to exceptional events. 

The State must: 

(1) Provide for prompt public 

notification whenever air quality 

concentrations exceed or are expected to 

exceed an applicable ambient air quality 

standard. 

(2) Provide for public education 

concerning actions that individuals may 

take to reduce exposures to unhealthy 

levels of air quality during and 

following an exceptional event. 

(3) Provide for the implementation of 

reasonable measures to protect public 

health from exceedances or violations of 

ambient air quality standards caused by 

exceptional events. 

(a) [Reserved] 

OPTION 2 for § 51.920: 

§ 51.920 Mitigation of exceptional events. 

(a) As a condition for EPA’s approval 

of a request to exclude air quality data 

due to exceptional events from use, each 

plan must include a mitigation action 

plan which provides for appropriate 

actions to protect public health from 

exceedances or violations of the 

national ambient air quality standards 

due to exceptional events. Each 

mitigation action plan must: 

(1) Provide for prompt public 

notification whenever air quality 

concentrations exceed or are expected to 

exceed an applicable ambient air quality 

standard. 

(2) Provide for public education 

concerning actions that individuals may 

take to reduce exposures to unhealthy 


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12610 Federal Register / Vol. 71, No. 47 / Friday, March 10, 2006 / Proposed Rules 

levels of air quality during and 

following an exceptional event. 

(3) Describe the procedures by which 

appropriate actions will be identified 

and taken to prevent or mitigate public 

health threats associated with 

exceptional events. 

(4) Provide for the implementation of 

reasonably available control measures to 

reduce emissions from those 

anthropogenic sources which are not 

exempt under § 50.13(a)(2)(ii) of this 

chapter and which interact with 

recurring natural events to contribute to 

exceedances or violations of applicable 

national ambient air quality standards. 

(b) States should periodically 

reevaluate mitigation action plans for 

adequacy and revise them as necessary 

and appropriate. 

OPTION 3 for § 51.920: 

§ 51.920 Mitigation of exceptional events. 

(a) As a condition for EPA’s approval 

of a request to exclude air quality data 

due to exceptional events from use in 

determinations with respect to 

exceedances or violations of the 

national ambient air quality standards, 

each State must adopt and implement a 

mitigation action plan for an affected 

area which provides for appropriate 

actions to protect public health from 

exceedances or violations of national 

ambient air quality standards due to 

exceptional events which is to be 

implemented in an affected area on an 

episodic basis. Mitigation action plans 

need not be incorporated into the 

applicable implementation plan, but 

each mitigation action plan must: 

(1) Provide for prompt public 

notification whenever air quality 

concentrations exceed or are expected to 

exceed an applicable ambient air quality 

standard. 

(2) Provide for public education 

concerning actions that individuals may 

take to reduce exposures to unhealthy 

levels of air quality during and 

following an exceptional event. 

(3) Describe the procedures by which 

appropriate actions will be identified 

and taken to prevent or mitigate public 

health threats associated with 

exceptional events. 

(4) Provide for the implementation of 

reasonably available control measures to 

reduce emissions from those 

anthropogenic sources which are not 

exempt under § 50.13(a)(2)(ii) of this 

chapter and which interact with 

recurring natural events to contribute to 

exceedances or violations of applicable 

national ambient air quality standards. 

(b) States should periodically 

reevaluate mitigation action plans for 

adequacy and revise them as necessary 

and appropriate. 

[FR Doc. 06–2179 Filed 3–9–06; 8:45 am] 

BILLING CODE 6560–50–P 


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