Vol. 80 Friday, 

No. 224 November 20, 2015 

Part III 

Environmental Protection Agency 

40 CFR Part 50 

Treatment of Data Influenced by Exceptional Events; Proposed Rule 

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72840 Federal Register / Vol. 80, No. 224 / Friday, November 20, 2015 / Proposed Rules 

ENVIRONMENTAL PROTECTION 

AGENCY 

40 CFR Part 50 

[EPA–HQ–OAR–2013–0572, EPA–HQ–OAR– 

2015–0229; FRL–9935–73–OAR] 

RIN 2060–AS02 

Treatment of Data Influenced by 

Exceptional Events 

AGENCY: Environmental Protection 

Agency (EPA). 

ACTION: Proposed rule; notice of 

availability of related draft guidance; 

notice of hearing. 

SUMMARY: The Environmental Protection 

Agency (EPA) is proposing revisions to 

certain sections within the regulations 

that govern the exclusion of eventaffected air quality data from regulatory 

decisions. The EPA is also providing a 

notice of availability of a draft version 

of the non-binding guidance document 

titled Draft Guidance on the Preparation 

of Exceptional Events Demonstrations 

for Wildfire Events that May Influence 

Ozone Concentrations. 

DATES: Comments. Written comments 

on this proposal and draft guidance 

must be received by January 19, 2016. 

Public hearing: The EPA will hold a 

public hearing on this proposal on 

Tuesday, December 8, 2015, in Phoenix, 

Arizona. Please refer to SUPPLEMENTARY

INFORMATION for additional information 

on the comment period and public 

hearing. 

ADDRESSES: Submit your comments on 

the EPA’s proposed revisions to 40 CFR 

part 50, identified by Docket ID No. 

EPA–HQ–OAR–2013–0572, at http://

www.regulations.gov. Follow the online 

instructions for submitting comments. 

Once submitted, comments cannot be 

edited or removed from Regulations.gov. 

The EPA may publish any comment 

received to its public docket. Do not 

submit electronically any information 

you consider to be Confidential 

Business Information (CBI) or other 

information whose disclosure is 

restricted by statute. Multimedia 

submissions (audio, video, etc.) must be 

accompanied by a written comment. 

The written comment is considered the 

official comment and should include 

discussion of all points you wish to 

make. The EPA will generally not 

consider comments or comment 

contents located outside of the primary 

submission (i.e., on the Web, Cloud or 

other file sharing system). For 

additional submission methods, the full 

EPA public comment policy, 

information about CBI or multimedia 

submissions and general guidance on 

making effective comments, please visit 

http://www2.epa.gov/dockets/

commenting-epa-dockets. 

Submit your comments on the EPA’s 

Draft Guidance on the Preparation of 

Exceptional Events Demonstrations for 

Wildfire Events that May Influence 

Ozone Concentrations, identified by 

Docket ID No. EPA–HQ–OAR–2015– 

0229, at http://www.regulations.gov. 

Follow the online instructions for 

submitting comments. Once submitted, 

comments cannot be edited or removed 

from Regulations.gov. The EPA may 

publish any comment received to its 

public docket. Do not submit 

electronically any information you 

consider to be CBI or other information 

whose disclosure is restricted by statute. 

Multimedia submissions (audio, video, 

etc.) must be accompanied by a written 

comment. The written comment is 

considered the official comment and 

should include discussion of all points 

you wish to make. The EPA will 

generally not consider comments or 

comment contents located outside of the 

primary submission (i.e., on the web, 

cloud or other file sharing system). For 

additional submission methods, the full 

EPA public comment policy, 

information about CBI or multimedia 

submissions and general guidance on 

making effective comments, please visit 

http://www2.epa.gov/dockets/

commenting-epa-dockets. 

Public hearing: A public hearing will 

be held on Tuesday, December 8, 2015, 

in room 3175 in the Arizona Department 

of Environmental Quality main office 

building located at 1110 W. Washington 

Street, Phoenix, Arizona 85007. The 

public hearing will convene at 10 a.m. 

and continue until the earlier of 6 p.m. 

or 1 hour after the last registered 

speaker has spoken. We have scheduled 

a lunch break from 12:30 p.m. until 2 

p.m. People interested in presenting oral 

testimony should contact Ms. Pamela 

Long, Air Quality Planning Division, 

Office of Air Quality Planning and 

Standards (C504–01), U.S. 

Environmental Protection Agency, 

Research Triangle Park, NC 27711, 

telephone (919) 541–0641, fax number 

(919) 541–5509, email address 

long.pam@epa.gov, at least 2 days in 

advance of the public hearing (see 

DATES). People interested in attending 

the public hearing should also call Ms. 

Long to verify the time, date and 

location of the hearing. 

FOR FURTHER INFORMATION CONTACT: For 

additional information regarding this 

proposed rule, please contact: Beth W. 

Palma, U.S. EPA, Office of Air Quality 

Planning and Standards, Air Quality 

Policy Division, Mail Code C539–04, 

Research Triangle Park, NC 27711, 

telephone (919) 541–5432, email at 

palma.elizabeth@epa.gov. For 

additional information regarding the 

Draft Guidance on the Preparation of 

Exceptional Events Demonstrations for 

Wildfire Events that May Influence 

Ozone Concentrations, please contact 

Melinda Beaver, U.S. EPA, Office of Air 

Quality Planning and Standards, Air 

Quality Policy Division, Mail Code 

C539–04, Research Triangle Park, NC 

27711, telephone (919) 541–1062, email 

at beaver.melinda@epa.gov. For 

information on the public hearing or to 

register to speak at the hearing, contact 

Ms. Pamela Long, U.S. Environmental 

Protection Agency, Office of Air Quality 

Planning and Standards, Air Quality 

Planning Division, Mail Code C504–01, 

Research Triangle Park, NC 27711, 

telephone (919) 541–0641, fax number 

(919) 541–5509, email at long.pam@

epa.gov (preferred method for 

registering). 

SUPPLEMENTARY INFORMATION: 

I. General Information 

A. Does this action apply to me? 

Entities potentially directly affected 

by this proposal and the draft guidance 

document include all state air agencies 

and any local air quality agency to 

whom a state has delegated relevant 

responsibilities for air quality 

management, including air quality 

monitoring and data analysis. Tribal air 

agencies operating ambient air quality 

monitors that produce regulatory data 

may also be directly affected. Entities 

potentially affected indirectly by this 

proposal and the draft guidance 

document include federal land 

managers (FLMs) of Class I areas, other 

federal agencies and other entities that 

operate ambient air quality monitors 

and submit collected data to the EPA’s 

Air Quality System (AQS) database. 

B. What should I consider as I prepare 

my comments for the EPA? 

1. Docket. The EPA has established 

one docket for the proposed revisions to 

the 2007 Exceptional Events Rule and 

another docket for the draft guidance 

document. All documents in these 

dockets are listed on the http://

www.regulations.gov Web site in the 

respective docket. The rulemaking 

docket is Docket ID No. EPA–HQ–OAR– 

2013–0572. The separate docket 

established for the Draft Guidance on 

the Preparation of Exceptional Events 

Demonstrations for Wildfire Events that 

May Influence Ozone Concentrations is 

Docket No. EPA–HQ–OAR–2015–0229. 

The EPA will not respond to comments 

relating to the guidance document as 

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part of this rulemaking, but will 

consider these comments in the 

development of the final guidance 

document. If comments on the draft 

guidance document are submitted to the 

rulemaking docket, the EPA will 

respond only to the portion of such 

comments that are relevant to the 

rulemaking. The EPA also relies on the 

documents in Docket ID No. EPA–HQ– 

OAR–2011–0887, the docket established 

for the July 2012 notice of availability 

for the Draft Exceptional Events 

Implementation Guidance, and 

incorporates this docket into the record 

for this action. However, no new 

comments may be directed to Docket ID 

No. EPA–HQ–OAR–2011–0887 and the 

EPA will not respond to comments that 

have already been submitted to this 

docket unless they are resubmitted to 

Docket ID No. EPA–HQ–OAR–2013– 

0572. Although listed in the indices to 

the rulemaking docket and the guidance 

docket associated with this action (i.e., 

Docket ID No. EPA–HQ–OAR–2013– 

0572 and Docket No. EPA–HQ–OAR– 

2015–0229), 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 not be placed on the Internet but 

may be viewed, with prior arrangement, 

at the EPA Docket Center. Publicly 

available docket materials are available 

either electronically in 

www.regulations.gov or in hard copy at 

the Air and Radiation Docket and 

Information Center, EPA/DC, EPA 

William Jefferson Clinton West 

Building, Room 3334, 1301 Constitution 

Avenue NW., Washington, DC. The 

Public Reading Room is open from 8:30 

a.m. to 4:30 p.m., Monday through 

Friday, excluding legal holidays. The 

telephone number for the Public 

Reading Room is (202) 566–1744 and 

the telephone number for the Air and 

Radiation Docket and Information 

Center is (202) 566–1742. For additional 

information about the EPA’s public 

docket, visit the EPA Docket Center 

homepage at: http://www.epa.gov/

epahome/dockets.htm. 

2. Submitting CBI. Do not submit this 

information to the EPA through http:// 

www.regulations.gov or email. Clearly 

mark the part or all of the information 

that you claim to be CBI. For CBI 

information in a disk or CD–ROM that 

you mail to the 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. 

3. Tips for Preparing Your Comments. 

When submitting comments, remember 

to: 

• Identify the rulemaking and/or draft 

guidance document by docket number 

and other identifying information 

(subject heading, Federal Register date, 

page number and guidance document 

title, if applicable). 

• 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 in the guidance. 

• Explain why you agree or disagree; 

suggest alternatives and substitute 

language for your requested changes. 

• Describe any assumptions and 

provide any technical information and/ 

or data that you used. 

• If you estimate potential costs or 

burdens, explain how you arrived at 

your estimate in sufficient detail to 

allow for it to be reproduced. 

• Provide specific examples to 

illustrate your concerns, and suggest 

alternatives. 

• Explain your views as clearly as 

possible, avoiding the use of profanity 

or personal threats. 

• Make sure to submit your 

comments by the identified comment 

period deadline. 

C. Where can I get a copy of these 

documents and other related 

information? 

In addition to being available in the 

docket, an electronic copy of this notice 

and the draft guidance will be posted at 

http://www2.epa.gov/air-qualityanalysis/treatment-data-influencedexceptional-events. 

D. What should I know about the public 

hearing? 

The EPA intends to hold a public 

hearing on Tuesday, December 8, 2015, 

in room 3175 in the Arizona Department 

of Environmental Quality main office 

building located at 1110 W. Washington 

Street, Phoenix, Arizona 85007. If you 

would like to attend or speak at the 

public hearing, please contact Ms. 

Pamela Long, U.S. Environmental 

Protection Agency, Office of Air Quality 

Planning and Standards, Air Quality 

Planning Division, Mail Code C504–01, 

Research Triangle Park, NC 27711, 

telephone (919) 541–0641, fax number 

(919) 541–5509, email at long.pam@

epa.gov (preferred method for 

registering) at least 2 days in advance of 

the public hearing (see DATES). 

Interested parties may submit oral and/ 

or written comments. Interested parties 

do not need to attend the public hearing 

to submit written comments. Additional 

details concerning any public hearing 

for this proposed rule will be posted on 

the EPA’s Web site for this rulemaking 

at http://www2.epa.gov/air-qualityanalysis/treatment-data-influencedexceptional-events. 

The public hearing will provide 

interested parties the opportunity to 

present data, views or arguments 

concerning the proposed revisions to 

the 2007 Exceptional Events Rule. The 

EPA will make every effort to 

accommodate all speakers who arrive 

and register. Individuals planning to 

attend the hearing will be required to 

sign in, and may be required to show 

valid picture identification to the 

security staff to gain access to the 

meeting room. In addition, no weapons 

will be allowed in the facility. Any 

weapons brought to the site will be 

stored in a locker at the facility. No large 

signs will be allowed in the building, 

and cameras may only be used outside 

of the building. The EPA may ask 

clarifying questions during the oral 

presentations but will not respond to 

the presentations at that time. Written 

statements and supporting information 

submitted during the comment period 

will be considered with the same weight 

as oral comments and supporting 

information presented at the public 

hearing. Commenters must submit 

written comments on the proposed rule 

and/or draft guidance by January 19, 

2016. Commenters should notify Ms. 

Long if they will need specific 

equipment, or if there are other special 

needs related to providing comments at 

the hearing. The EPA will provide 

equipment for commenters to show 

overhead slides or make computerized 

slide presentations if we receive special 

requests in advance. Oral testimony will 

be limited to 5 minutes for each 

commenter. The EPA encourages 

commenters to provide the EPA with a 

copy of their oral testimony 

electronically (via email or CD) or in 

hard copy form. The hearing schedule, 

including the list of speakers, will be 

posted on the EPA’s Web site at 

http://www2.epa.gov/air-qualityanalysis/treatment-data-influencedexceptional-events. Verbatim transcripts 

of the hearing and written statements 

will be included in the docket for the 

rulemaking. The EPA will make every 

effort to follow the schedule as closely 

as possible on the day of the hearing; 

however, please plan for the hearing to 

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run either ahead of schedule or behind 

schedule. 

E. How is this document organized? 

The information presented in this 

document is organized as follows: 

I. General Information 

A. Does this action apply to me? 

B. What should I consider as I prepare my 

comments for the EPA? 

C. Where can I get a copy of these 

documents and other related 

information? 

D. What should I know about the public 

hearing? 

E. How is this document organized? 

II. Glossary of Terms and Acronyms 

III. Executive Summary 

IV. Background for Proposal 

A. Purpose of and Statutory Authority for 

This Regulatory Action 

B. The 2007 Exceptional Events Rule 

C. Early Experience in Implementing the 

2007 Exceptional Events Rule 

D. The EPA’s Interim Exceptional Events 

Implementation Guidance 

E. More Recent Implementation Experience 

Including EPA-Recommended Best 

Practices for the Development of 

Exceptional Events Demonstrations 

V. Proposed Rule Revisions 

A. To whom and to what pollutants does 

the Exceptional Events Rule apply? 

1. Current Situation 

2. Proposed Changes 

B. What is an exceptional event? 

1. Current Situation 

2. Proposed Changes 

C. What types of ambient concentration 

data and data uses may be affected by the 

Exceptional Events Rule? 

1. Current Situation 

2. Proposed Changes 

D. What is a natural event? 

1. Current Situation 

2. Proposed Changes 

E. Technical Criteria for the Exclusion of 

Data Affected by Events 

1. Human Activity Unlikely To Recur at a 

Particular Location or a Natural Event 

2. Not Reasonably Controllable or 

Preventable 

3. Clear Causal Relationship Supported by 

a Comparison to Historical 

Concentration Data 

F. Treatment of Certain Events Under the 

Exceptional Events Rule 

1. Exceedances Due to Transported 

Pollution 

2. Wildland Fires 

3. Stratospheric Ozone Intrusions 

4. High Wind Dust Events 

G. Other Aspects of Flagging Exceptional 

Events-Influenced Data and 

Demonstration Submittal and Review 

1. Who may submit a demonstration and 

request for data exclusion? 

2. Aggregation of Events for NAAQS With 

Periods Longer Than 24 Hours and 

Demonstrations With Respect to 

Multiple NAAQS for the Same Pollutant 

3. Exclusion of Entire 24-Hour Value 

Versus Partial Adjustment of the 24-Hour 

Value for Particulate Matter 

4. Flagging of Data 

5. Initial Notification of Potential 

Exceptional Event 

6. Submission of Demonstrations 

7. Timing of the EPA’s Review of 

Submitted Demonstrations 

8. Dispute Resolution Mechanisms 

VI. Mitigation 

A. Current Situation 

B. Proposed Changes 

1. Defining Historically Documented or 

Known Seasonal Events 

2. Mitigation Plan Components 

3. Options for Implementing Mitigation 

Plans 

VII. Draft Guidance on the Preparation of 

Exceptional Events Demonstrations for 

Wildfire Events That May Influence 

Ozone Concentrations 

A. What is this draft guidance about and 

why is it needed? 

B. What scenarios are addressed in the 

draft guidance? 

VIII. Environmental Justice Considerations 

IX. Statutory and Executive Order Reviews 

A. Executive Order 12866: Regulatory 

Planning and Review and Executive 

Order 13563: Improving Regulation and 

Regulatory 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 & 

Safety Risks 

H. Executive Order 13211: Actions 

Concerning Regulations That 

Significantly Affect Energy Supply, 

Distribution or Use 

I. National Technology Transfer and 

Advancement Act 

J. Executive Order 12898: Federal Actions 

To Address Environmental Justice in 

Minority Populations and Low-Income 

Populations 

X. Statutory Authority 

II. Glossary of Terms and Acronyms 

The following are abbreviations of 

terms used in the preamble. 

AQCR Air Quality Control Region 

AQS Air Quality System 

Be Beryllium 

BACM Best available control measures 

BLM Bureau of Land Management 

BMP Best management practice(s) 

BSMP Basic smoke management practices 

CAA Clean Air Act 

CASTNET Clean Air Status and Trends 

Network 

CBI Confidential business information 

CFR Code of Federal Regulations 

CO Carbon monoxide 

EPA Environmental Protection Agency 

FLM Federal land manager responsible for 

management of a federally owned area that 

has been designated a Class I area as 

codified in 40 CFR part 81, subpart D 

FR Federal Register 

IPV Isentropic potential vorticity 

Lidar A remote sensing technology that 

measures distance by illuminating a target 

with a laser and analyzing the reflected 

light 

mg/m3 Micrograms per cubic meter 

mph Miles per hour 

NAAQS National ambient air quality 

standard or standards 

NAM North American Mesoscale Forecast 

System 

NASA National Aeronautics and Space 

Administration 

NEPA National Environmental Policy Act 

NO2 Nitrogen dioxide 

NOAA National Oceanic and Atmospheric 

Administration 

NOV Notice of violation 

NOx Nitrogen oxides 

NPS National Park Service 

NSR New source review 

NRCS Natural Resources Conservation 

Service 

NRDC Natural Resources Defense Council 

NWCG National Wildfire Coordinating 

Group 

NWS National Weather Service 

OAQPS Office of Air Quality Planning and 

Standards, U.S. EPA 

OMB Office of Management and Budget 

Pb Lead 

PM Particulate matter 

PM10 Particulate matter with a nominal 

mean aerodynamic diameter less than or 

equal to 10 micrometers 

PM2.5 Particulate matter with a nominal 

mean aerodynamic diameter less than or 

equal to 2.5 micrometers 

ppb Parts per billion 

PSD Prevention of significant deterioration 

PT Potential temperature 

RACM Reasonably available control 

measures 

RAQMS Real-time Air Quality Modeling 

System 

RUC Rapid Update Cycle 

SIP State implementation plan 

SMP Smoke management program 

SO2 Sulfur dioxide 

TAR Tribal Authority Rule 

TIP Tribal implementation plan 

UMRA Unfunded Mandates Reform Act 

USDA U.S. Department of Agriculture 

USFS U.S. Forest Service 

VOC Volatile organic compound or 

compounds 

III. Executive Summary 

This section summarizes the purpose 

of this regulatory action, the major 

provisions of this action, and the 

development of associated guidance. 

Purpose of This Regulatory Action 

Recognizing that it may not be 

appropriate for the EPA to use certain 

monitoring data collected by the 

ambient air quality monitoring network 

and maintained in the air quality data 

system (AQS) in the EPA’s regulatory 

determinations, in 2005 Congress 

provided the statutory authority for the 

exclusion of data in specific situations 

by adding section 319(b) to the Clean 

Air Act (CAA). The EPA promulgated 

the 2007 Exceptional Events Rule 

(March 22, 2007, 72 FR 13560) to 

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implement this 2005 amendment of the 

CAA. The purpose of this action is to 

propose revisions to the 2007 

Exceptional Events Rule to address 

certain substantive issues raised by 

state, local and tribal co-regulators and 

other stakeholders since promulgation 

of the rule and to increase the 

administrative efficiency of the 

Exceptional Events Rule criteria and 

process. The EPA intends to promulgate 

these rule revisions in advance of the 

date by which states, and any tribes that 

wish to do so, are required to submit 

their initial designation 

recommendations for the revised 2015 

ozone NAAQS (expected in October of 

2016). In addition, the EPA intends to 

address a 2008 D.C. Circuit Court 

decision in which the court found that 

certain preamble language was ‘‘legally 

null’’ because there was no associated 

implementing rule language. 

Interpreting and implementing the 

2007 Exceptional Events Rule has been 

challenging in certain respects both for 

the air agencies developing exceptional 

events demonstrations and for the EPA 

Regional offices reviewing and acting on 

these demonstrations. Since 2007, air 

agencies have submitted exceptional 

event demonstrations for a variety of 

pollutant and event combinations 

ranging from volcanic activity 

influencing sulfur dioxide (SO2) and 

particulate matter (PM) concentrations 

to stratospheric ozone intrusions. Air 

agencies preparing demonstrations have 

expressed specific concerns and 

identified challenges associated with 

preparing analyses to satisfy the ‘‘but 

for’’ rule criterion, determining what 

controls constitute reasonable controls 

particularly for natural sources and for 

interstate and international transport 

and identifying how much 

documentation to include in a 

demonstration. 

As a result of both our experiences 

and feedback related to implementing 

the 2007 Exceptional Events Rule 

received from state, local and tribal coregulators and other stakeholders via 

letters and numerous conference calls 

and meetings, the EPA developed and 

released Interim Exceptional Events 

Implementation Guidance in May of 

2013. This guidance has addressed some 

of the concerns and challenges raised by 

interested parties, has helped reduce the 

burden of preparing demonstrations and 

has reduced the time needed for review. 

However, the EPA acknowledged that 

additional changes could only be 

accomplished through a notice-andcomment rulemaking. Therefore, when 

the EPA released the Interim 

Exceptional Events Implementation 

Guidance in May of 2013, we 

simultaneously announced our intent to 

pursue revisions to the Exceptional 

Events Rule. These changes are reflected 

in this proposed action. 

Concurrent with preparing this 

proposed action, the EPA held 

conference calls with some air agencies 

to discuss more recent implementation 

experiences and to better understand 

currently employed exceptional events 

implementation processes and practices. 

As a result of these discussions, the EPA 

developed a list of best practices for 

communication and collaboration 

between the EPA and air agencies. 

Agencies using these approaches have 

developed a common understanding of 

expectations, terminology and 

interpretation of the EPA’s regulations 

and policy, which, in turn, helps focus 

efforts, optimize resources and save 

time during the demonstration 

development and review process. 

Based on our experiences and the 

input we have received from our 

collaborations with interested parties 

(including state, local and tribal air 

agencies) following the promulgation of 

the 2007 Exceptional Events Rule and 

since the development of the Interim 

Exceptional Events Implementation 

Guidance and based on the previous 

legal challenge, we have determined 

those aspects of the 2007 Exceptional 

Events Rule that most need to be 

addressed in this proposed action. 

Summary of Major Provisions 

For the first time, the EPA proposes 

to interpret CAA section 319(b) as 

applying to only a specific set of 

regulatory actions (e.g., designations) 

because we believe that the criteria and 

process steps specified in the CAA were 

not clearly intended by Congress to 

apply to all types of regulatory actions 

and in some cases certain of the criteria 

and steps are not appropriate. We 

address this concept in this document 

in general terms, but we also intend to 

develop a separate guidance document 

to provide guidance on when data can 

be excluded and when they cannot for 

other specific types of regulatory 

actions. 

The EPA proposes to return to the 

core statutory elements and implicit 

concepts of CAA section 319(b): The 

event affected air quality in such a way 

that there exists a clear causal 

relationship between the specific event 

and the monitored exceedance or 

violation, the event was not reasonably 

controllable or preventable and the 

event was caused by human activity that 

is unlikely to recur at a particular 

location or was a natural event. Within 

each of these elements, we are 

proposing clarifications regarding the 

desired analyses to include in 

exceptional events demonstrations and 

we discuss the applicability of these 

clarifications to certain event types or 

categories. As part of this return to the 

core statutory elements, we are 

proposing to remove from the 

Exceptional Events Rule a paragraph 

containing what is commonly referred 

to as the ‘‘but for’’ criterion. 

The EPA is proposing to incorporate 

the statutory ‘‘affects air quality’’ 

criterion and the regulatory ‘‘historical 

fluctuations’’ criterion within the ‘‘clear 

causal relationship’’ element. We 

believe that if an air agency 

demonstrates that an event has a clear 

causal relationship to an exceedance or 

violation of a NAAQS, then the event 

has certainly affected air quality and 

that a submitting air agency does not 

need to address ‘‘affects air quality’’ as 

a distinct component. As we indicated 

in the Interim Exceptional Events 

Implementation Guidance (see section 

IV.D), we believe that a comparison of 

the claimed event-influenced 

concentration(s) to concentrations at the 

same monitoring site at other times is 

extremely useful evidence in an 

exceptional events demonstration, 

particularly as part of showing a clear 

causal relationship, and we propose to 

continue requiring this type of 

comparison. This proposed action 

details the minimum set of statistical 

analyses that the EPA expects to see in 

demonstrations. 

With respect to the ‘‘not reasonably 

controllable or preventable’’ criterion, 

many states have requested that the EPA 

automatically consider an event to be 

reasonably controlled if the EPA has 

approved a state implementation plan 

(SIP) that contains controls for 

anthropogenic sources that contribute to 

the event that are also specific to the 

pollutant of concern in the exceptional 

events demonstration. In response, the 

EPA proposes that enforceable control 

measures implemented in accordance 

with an attainment or maintenance SIP, 

approved by the EPA within 5 years of 

the date of a demonstration submittal, 

that address the event-related pollutant 

and all sources necessary to fulfill the 

requirements of the CAA for the SIP to 

be reasonable controls with respect to 

all anthropogenic sources that have or 

may have contributed to event-related 

emissions. Also for this criterion, the 

EPA clarifies that air agencies generally 

have no obligation to specifically 

address controls if the event was natural 

or if it was due to emissions originating 

outside their jurisdictional (i.e., state or 

tribal) border(s). 

With respect to the ‘‘human activity 

that is unlikely to recur at a particular 

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location or was a natural event’’ 

criterion, we propose a general 

approach to determining whether the 

recurrence frequency of an event is 

‘‘unlikely to recur at a particular 

location’’ and an approach applicable to 

prescribed fire on wildland only. We 

also clarify that natural events can 

recur, sometimes frequently, and 

reiterate our belief that we generally 

consider human activity to have played 

little or no direct role in causing 

emissions if anthropogenic emission 

sources that contribute to the event 

emissions are reasonably controlled at 

the time of the event. 

Air agencies must address all of the 

core statutory elements and implicit 

concepts of CAA section 319(b) within 

an exceptional events demonstration. In 

this proposed action, the EPA clarifies 

the content and organization of 

exceptional events submittals to include 

the core statutory elements, but we also 

propose that states be required to 

include a conceptual model, or 

narrative, describing the event(s) 

causing the exceedance or violation and 

a discussion of how emissions from the 

event(s) led to the exceedance at the 

affected monitor(s) and documentation 

that the air agency conducted a public 

comment process. We are proposing to 

require an initial notification by the 

state to the EPA of a potential 

exceptional event as a preliminary step 

before submitting a demonstration, to 

ensure the submitting air agency and the 

reviewing EPA Regional office share a 

common understanding regarding the 

potential event and are in 

communication regarding the timeline 

for the demonstration to be submitted 

and to be reviewed by the Regional 

office. 

Because affected air agencies have 

provided feedback regarding the 

difficulty associated with meeting the 

current regulatory timelines associated 

with data flagging, initial event 

descriptions and demonstration 

submittals, the EPA proposes to remove 

the specific deadlines that apply in 

situations other than initial area 

designations following promulgation of 

a new or revised NAAQS. Also 

associated with demonstration timing, 

the EPA proposes to officially terminate 

review of demonstrations that, due to 

the passage of time, will have no further 

regulatory significance specifically for 

the five types of regulatory actions 

identified in section V.C. of this 

preamble. 

Since promulgation of the 2007 

Exceptional Events Rule, stakeholders 

have raised numerous questions about 

fire-related components that were 

discussed, but not fully defined or 

clarified in the preamble to the 2007 

Exceptional Events Rule. This proposed 

action addresses fire-related definitions, 

provides more clarity regarding 

expectations for smoke management 

programs (SMPs) and basic smoke 

management practices (BSMP), and 

proposes limited scenarios under which 

FLMs and other federal agencies may 

prepare and submit exceptional events 

demonstrations and data exclusion 

requests directly to the EPA. 

Associated Guidance Documents 

In addition to proposing revisions to 

the 2007 Exceptional Events Rule, this 

proposed action simultaneously 

provides a notice of availability of a 

draft non-binding guidance document 

titled, Draft Guidance on the 

Preparation of Exceptional Events 

Demonstrations for Wildfire Events that 

May Influence Ozone Concentrations, 

which applies the proposed Exceptional 

Events Rule revisions to wildfire/ozone 

events. This guidance document is 

intended to further address specific 

stakeholder questions regarding the 

Exceptional Events Rule and further 

increase the efficiency of rule 

implementation. In addition, the EPA is 

currently developing a guidance 

document titled, Draft Guidance for 

Excluding Some Ambient Pollutant 

Concentration Data from Certain 

Calculations and Analyses for Purposes 

Other than Retrospective 

Determinations of Attainment of the 

NAAQS, which will apply to the 

exclusion of certain data for certain 

applications using a process and criteria 

outside of the Exceptional Events Rule. 

The EPA intends to make this guidance 

document available shortly after 

proposing revisions to the Exceptional 

Events Rule. The EPA expects to finalize 

these guidance documents concurrently 

with promulgating revisions to the 

Exceptional Events Rule. 

IV. Background for Proposal 

A. Purpose of and Statutory Authority 

for This Regulatory Action 

Part of the EPA’s mission is to 

preserve and improve, when needed, 

the quality of our nation’s ambient air 

to protect human health and the 

environment. As part of accomplishing 

this, the EPA develops the national 

ambient air quality standards (NAAQS) 

for criteria pollutants and oversees the 

states’ programs to improve air quality 

in areas where the current air quality is 

unacceptable and to prevent 

deterioration in areas where the air 

quality meets or exceeds the NAAQS. 

The EPA then evaluates the status of the 

ambient air as compared to these 

NAAQS by using data collected in the 

national ambient air quality monitoring 

network established under the authority 

of section 319(a) of the CAA. 

Recognizing that it may not be 

appropriate for the EPA to use certain 

monitoring data collected by the 

ambient air quality monitoring network 

and maintained in AQS in our 

regulatory determinations, in 2005 

Congress provided the statutory 

authority for the exclusion of data in 

specific situations by adding section 

319(b) to the CAA in 2005. The EPA 

promulgated the 2007 Exceptional 

Events Rule (March 22, 2007, 72 FR 

13560) to implement this 2005 

amendment of the CAA. The purpose of 

this action is to propose revisions to the 

2007 Exceptional Events Rule to address 

certain issues raised by stakeholders 

since promulgation of the rule and to 

increase the administrative efficiency of 

the Exceptional Events Rule criteria and 

process. 

In addition to proposing revisions to 

the 2007 Exceptional Events Rule, we 

are simultaneously providing a notice of 

availability of a draft non-binding 

guidance document titled, Draft 

Guidance on the Preparation of 

Exceptional Events Demonstrations for 

Wildfire Events that May Influence 

Ozone Concentrations, which applies 

the proposed Exceptional Events Rule 

revisions to wildfire/ozone events. We 

seek comment on whether the concepts 

in this guidance document should be 

finalized as rule text. We are also 

currently developing a second guidance 

document titled, Draft Guidance for 

Excluding Some Ambient Pollutant 

Concentration Data from Certain 

Calculations and Analyses for Purposes 

Other than Retrospective 

Determinations of Attainment of the 

NAAQS, which will apply to the 

exclusion of certain data for certain 

applications using a process and criteria 

outside of the Exceptional Events Rule. 

Both of these draft guidance documents 

are intended to further address specific 

stakeholder concerns regarding the 

Exceptional Events Rule and further 

increase the efficiency of rule 

implementation. 

B. The 2007 Exceptional Events Rule 

The 2007 Exceptional Events Rule 

created a regulatory process codified at 

40 CFR parts 50 and 51 (sections 50.1, 

50.14 and 51.930). These regulatory 

sections contain definitions, procedural 

requirements, requirements for air 

agency demonstrations, criteria for the 

EPA’s approval of the exclusion of 

event-affected air quality data from the 

data set used for regulatory decisions, 

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1References to ‘‘air agencies’’ are meant to 

include state, local and tribal air agencies 

responsible for implementing the Exceptional 

Events Rule. The regulatory text in the 2007 

Exceptional Events Rule often uses ‘‘State’’ to apply 

to ‘‘air agencies.’’ In the context of flagging data and 

preparing and submitting demonstrations, the role 

of and options available to air agencies would also 

apply to federal land managers of Class I areas and 

other federal agencies managing federal land. 

2Per the definition at 40 CFR 50.1(l), an 

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. 

Violations of a standard are standard-specific and 

are determined by applying the standard-specific 

procedures for air quality data handling identified 

in the appendices to 40 CFR part 50. For example, 

per the requirements in 40 CFR part 50, appendix 

N, an exceedance of the 2006 24-hour PM2.5

NAAQS of 35 mg/m3 occurs when the 24-hour 

concentration is above 35 mg/m3 on a single day. A 

violation of the 2006 24-hour PM2.5 NAAQS occurs 

when the 3-year average of the annual 98th 

percentile 24-hour concentrations is above 35 mg/

m3. 

3Previous guidance and policy documents that 

either implied or stated the need for special 

treatment of data affected by an exceptional event 

include: 

i) Guideline for the Interpretation of Air Quality 

Standards, U.S. EPA, OAQPS No. 1.2–008, Revised 

February 1977. Available at http://nepis.epa.gov/

Exe/ZyNET.exe/2000YFDB.TXT?ZyActionD=Zy

Document&Client=EPA&Index=1976+Thru+1980&

Docs=&Query=&Time=&EndTime=&Search

Method=1&TocRestrict=n&Toc=&TocEntry=&

QField=&QFieldYear=&QFieldMonth=&QField

Day=&IntQFieldOp=0&ExtQFieldOp=0&Xml

Query=&File=D%3A%5Czyfiles%5CIndex%20Data

%5C76thru80%5CTxt%5C00000007%5C2000

YFDB.txt&User=ANONYMOUS&Password=

anonymous&SortMethod=h%7C-&Maximum

Documents=1&FuzzyDegree=0&ImageQuality=

r75g8/r75g8/x150y150g16/i425&Display=p%7Cf&

DefSeekPage=x&SearchBack=ZyActionL&Back=Zy

ActionS&BackDesc=Results%20page&Maximum

Pages=1&ZyEntry=1&SeekPage=x&ZyPURL. 

ii) Guideline on the Identification and Use of Air 

Quality Data Affected by Exceptional Events (the 

Exceptional Events Policy), U.S. EPA, OAQPS, 

EPA–450/4–86–007, July 1986. 

iii) Areas Affected by PM–10 Natural Events (the 

PM10 Natural Events Policy), memorandum from 

Mary D. Nichols, Assistant Administrator for Air 

and Radiation, to EPA Regional Offices, May 30, 

1996. Available at http://www.epa.gov/ttn/caaa/t1/ 

memoranda/nepol.pdf. 

iv) Interim Air Quality Policy on Wildland and 

Prescribed Fires. U.S. EPA. April 23, 1998. 

Available at http://www.epa.gov/ttn/oarpg/t1/

memoranda/firefnl.pdf. 

v) Guideline on Data Handling Conventions for 

the PM NAAQS. U.S. EPA, OAQPS, EPA–454/R– 

98–017, December 1998. 

and requirements for air agencies 1 to 

take appropriate and reasonable actions 

to protect public health from 

exceedances or violations of the 

NAAQS.2 The 2007 Exceptional Events 

Rule superseded the EPA’s previous 

natural events guidance and those 

sections of an earlier guidance 

document that addressed the treatment 

of data affected by exceptional events.3

In general, the exceptional events 

regulatory process consists of the 

following steps. First, an air agency 

identifies a potential event-related 

exceedance or violation. After noting 

these data in AQS, the air agency 

prepares a draft demonstration package 

to support the exclusion of the 

identified event-related data and 

provides an opportunity for public 

comment. The air agency submits the 

draft demonstration and any received 

public comments to its EPA Regional 

office, which then reviews the submittal 

and concurs, nonconcurs or defers a 

decision related to the air agency’s 

request to exclude data that have been 

affected by exceptional events. If the 

EPA agrees with the air agency’s 

request, the data are excluded. If the 

EPA does not agree with the air agency 

claim, or if the EPA decides to defer a 

decision on the submittal, the data are 

used in regulatory determinations. 

The 2007 Exceptional Events Rule 

was challenged in 2008. In NRDC v. 

EPA, 559 F.3d 561 (D.C. Cir. 2009), the 

Natural Resources Defense Council 

(NRDC) brought a petition for review 

challenging the EPA’s definition of a 

natural event and seeking to vacate 

several statements in the preamble to 

the final 2007 Exceptional Events Rule 

concerning the types of events that 

could qualify as being eligible for 

exclusion under the rule provisions. In 

particular, NRDC objected to treating 

‘‘events in which human activities play 

‘little’ causal role’’ as natural events. 

Regarding the definition of a natural 

event, the D.C. Circuit Court determined 

that NRDC did not identify its objection 

during the rulemaking process and, 

therefore, did not have standing under 

CAA section 307 to challenge the 

definition. 

NRDC also challenged the preamble 

language addressing high wind events. 

In its decision, the D.C. Circuit stated, 

In one section of the preamble, EPA refers 

to its ‘‘final rule concerning high wind 

events,’’ which ‘‘states that ambient 

particulate concentrations due to dust being 

raised by unusually high winds will be 

treated as due to uncontrollable natural 

events’’ when certain conditions apply. . . . 

There is no such final rule. The final rule 

does not mention high wind events or 

anything about ‘‘ambient particulate matter 

concentrations.’’ EPA calls this a drafting 

error. In light of the error, the high wind 

events section of the preamble is a legal 

nullity. 

The EPA believes it is clear that the 

‘‘high wind events section of the 

preamble’’ to which the court referred is 

the entire section titled, ‘‘B. High Wind 

Events’’ beginning at 72 FR 13576. 

Accordingly, since 2007, the EPA has 

not relied solely on this section of the 

preamble when implementing the 2007 

Exceptional Events Rule. The EPA 

maintains that certain of the preamble 

passages determined to be ‘‘legally null’’ 

are in fact appropriate interpretations of 

the Exceptional Events Rule and are 

consistent with the CAA. For clarity and 

regulatory certainty, the EPA is 

proposing in rule text form some of the 

interpretative positions originally stated 

in the High Wind Events section of the 

preamble to the 2007 Exceptional 

Events Rule. 

Within each topical area of this 

notice, the EPA has provided more 

detailed background information on 

specific aspects of the 2007 Exceptional 

Events Rule and its implementation to 

allow readers to consider the proposed 

changes in the context of the current 

situation. 

C. Early Experience in Implementing the 

2007 Exceptional Events Rule 

Interpreting and implementing the 

2007 Exceptional Events Rule has been 

a challenging process both for the air 

agencies developing exceptional events 

demonstrations and for the EPA 

Regional offices reviewing and acting on 

these demonstrations. Shortly after the 

EPA promulgated the rule in 2007, air 

agencies asked the EPA to clarify key 

rule provisions and expectations for 

these demonstrations. Air agencies also 

asked for demonstration templates and/ 

or examples of acceptable 

demonstrations for various event and 

pollutant combinations. Although the 

EPA provided some of this information 

via the exceptional events Web site at 

http://www2.epa.gov/air-qualityanalysis/treatment-data-influencedexceptional-events, air agencies noted 

that, in their view, the information 

provided was insufficient and sought 

additional guidance to facilitate 

consistency among the EPA Regional 

offices in interpreting and implementing 

the 2007 Exceptional Events Rule. In the 

years since rule promulgation, air 

agencies continued to express concern, 

through various mechanisms including 

formal letters, informal emails, 

interaction at various meetings and 

Congressional testimony, about the 

consistent application of the 2007 

Exceptional Events Rule and the 

resources expended to prepare 

exceptional events demonstrations. 

The EPA has also faced challenges in 

reviewing submitted demonstrations. 

Because exceptional events are factspecific and thus unique and varied, 

providing templates or general guidance 

was, and still is, challenging. The EPA 

also acknowledges that the final rule 

and preamble language for the 2007 

Exceptional Events Rule provided room 

for interpretation, making it difficult for 

air agencies and the EPA to determine 

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4The EPA established Docket ID No. EPA–HQ– 

OAR–2011–0887 for the July 2012 notice of 

availability for the Draft Exceptional Events 

Implementation Guidance and has incorporated this 

docket into the record for this action. 

5Responses to Significant First-Round Comments 

on the Draft Guidance Documents on the 

Implementation of the Exceptional Events Rule, 

U.S. EPA, June 2012. Available in Docket No. EPA– 

HQ–OAR–2011–0887. 

6The Interim Exceptional Events Implementation 

Guidance includes: The Interim Guidance to 

Implement Requirements for the Treatment of Air 

Quality Monitoring Data Influenced by Exceptional 

Events, the Interim Exceptional Events Rule 

Frequently Asked Questions (the Interim Q&A 

document), and the Interim Guidance on the 

Preparation of Demonstrations in Support of 

Requests to Exclude Ambient Air Quality Data 

Affected by High Winds under the Exceptional 

Events Rule (the Interim High Winds Guidance 

document). 

how much evidence or technical 

analysis for demonstrations is needed. 

We do, however, think that providing 

additional recommendations on 

appropriate documentation would be 

helpful. Throughout this proposal, for 

example in section V.E, Technical 

Criteria for the Exclusion of Data 

Affected by Events, and in section V.F, 

Treatment of Certain Events Under the 

Exceptional Events Rule, we provide 

recommendations for language and 

analyses to include in demonstration 

packages. Additional detail regarding 

specific recommendations is available 

in the EPA’s guidance documents and 

on the EPA’s exceptional events Web 

site, which the EPA will update to 

incorporate the finalized rule changes 

concurrently with or shortly after 

promulgating the final rule. The EPA 

will also continue to maintain and 

update the exceptional events 

submissions table on its Web site with 

examples of approved submissions. 

These examples may help air agencies 

develop demonstration packages; 

however, they may not contain the 

minimum level of data or case-specific 

analyses necessary for all exceptional 

events demonstrations of the same event 

type. In addition, commenters on this 

notice may wish to provide suggestions 

on the appropriate documentation for 

specific types of exceptional events 

demonstrations. 

D. The EPA’s Interim Exceptional 

Events Implementation Guidance 

As a result of stakeholder-identified 

concerns and the EPA’s own experience 

related to implementing the 2007 

Exceptional Events Rule, in 2010 the 

EPA began developing additional 

implementation guidance. In May of 

2011, the EPA released the Draft 

Exceptional Events Implementation 

Guidance: The Draft Guidance to 

Implement Requirements for the 

Treatment of Air Quality Monitoring 

Data Influenced by Exceptional Events, 

the Draft Exceptional Events Rule 

Frequently Asked Questions document 

and the Draft Guidance on the 

Preparation of Demonstrations in 

Support of Requests to Exclude Ambient 

Air Quality Data Affected by High 

Winds under the Exceptional Events 

Rule. The EPA provided these draft 

guidance documents to interested air 

agencies, FLMs, other federal agencies 

and other parties upon request, for 

preliminary review to solicit comment 

and help ensure that the EPA’s final 

guidance provided an efficient and 

effective process to make 

determinations regarding air quality 

data affected by exceptional events. The 

EPA also placed additional examples of 

approved demonstrations on the EPA’s 

Web site. 

The EPA incorporated the 

commenters’ feedback, as appropriate, 

into revised draft guidance documents, 

which were made available for broad 

public review in a July 6, 2012, Federal 

Register Notice of Availability (77 FR 

39959) and in the associated docket 

(Docket ID No. EPA–HQ–OAR–2011– 

0887).4 This docket includes a summary 

of the comment and response process 

from the 2011 preliminary review of the 

draft guidance documents. In addition 

to identifying specific comments on the 

draft guidance documents, this 

summary clearly identifies that 

implementation challenges originated 

shortly after the EPA promulgated the 

2007 Exceptional Events Rule.5 In May 

2013, after a round of review and 

comment by the general public, the EPA 

finalized the Interim Exceptional Events 

Implementation Guidance and made 

these documents publicly available on 

the exceptional events Web site at 

http://www2.epa.gov/air-qualityanalysis/treatment-data-influencedexceptional-events.6

With the release of the Interim 

Exceptional Events Implementation 

Guidance, the EPA simultaneously 

acknowledged the need to consider 

additional changes that could only be 

accomplished through a notice-andcomment rulemaking to revise the 2007 

Exceptional Events Rule. To inform the 

development of proposed rule revisions, 

the EPA hosted exceptional events 

listening sessions in August and 

November of 2013 for interested air 

agencies, FLMs, other federal agencies, 

regional planning organizations, nongovernmental organizations and other 

members of the public. The EPA has 

considered feedback from these 

listening sessions and the previous 

public comments on the Interim 

Exceptional Events Implementation 

Guidance in the development of these 

proposed revisions to the 2007 

Exceptional Events Rule. 

E. More Recent Implementation 

Experience Including EPARecommended Best Practices for the 

Development of Exceptional Events 

Demonstrations 

Because of the passage of time since 

the 2013 exceptional events listening 

sessions, the EPA’s Office of Air Quality 

Planning and Standards (OAQPS) held 

conference calls with some air agencies 

and the EPA Regional offices between 

September 2014 and March 2015 to ask 

whether any new implementation 

concerns had arisen and to better 

understand currently employed 

exceptional events implementation 

processes and practices. 

As a result of these discussions, the 

EPA developed a list of best practices 

for communication and collaboration 

between the EPA and air agencies. 

These best practices include having 

discussions before, during and after the 

development and submission of 

exceptional events demonstration 

packages. Specifically, these best 

practices recommend that the EPA 

Regional offices and their air agencies 

discuss, on a mutually agreed upon 

frequency, those demonstrations that 

the agencies have developed and 

submitted for the EPA’s action. These 

regular discussions should focus on 

whether the demonstrations have 

regulatory significance (e.g., significance 

for any of the five types of regulatory 

actions identified in section V.C.) and, 

if not, whether the EPA can provide 

general technical or policy feedback that 

the air agency can include in future 

demonstrations. Prior to an air agency’s 

development of future demonstrations, 

the air agency and the EPA should 

identify the relevant days and monitors 

of focus, the regulatory significance of 

these monitor days, the analyses of 

particular interest for a specific event 

and pollutant combination and the 

anticipated timeframe for demonstration 

submission and response. Discussions 

should continue while the air agency is 

developing the demonstration and after 

the agency submits the demonstration 

and while the EPA is reviewing the 

demonstration, to ensure both the air 

agency and the EPA are aware of status, 

direction and progress. Finally, after the 

EPA has acted on the demonstration, the 

reviewing EPA Regional office and the 

air agency should discuss elements of 

the process that should continue and 

those that should be improved, should 

understand the information in the 

demonstration that was useful versus 

the information that was extraneous and 

should discuss the possibility of 

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7As of the signature date of this action, only one 

tribe is eligible to implement all portions of CAA 

section 319 under the TAR. Several other tribes, 

however, operate air quality monitoring networks 

that produce regulatory data that could be affected 

by emissions from exceptional events. 

8The Ambient Air Quality Surveillance 

provisions in 40 CFR part 58 include, among other 

elements, the requirements for monitoring data 

certification and data submittal and archive in AQS. 

40 CFR 58.3 provides that these data reporting 

requirements specifically apply to state air 

pollution control agencies and any local air 

pollution control agency to which the state has 

delegated authority to operate a portion of the 

state’s monitoring network. 

9For a description of one network of monitoring 

sites operated by federal agencies, see the 2014 

CASTNET (Clean Air Status and Trends Network) 

Annual Network Plan, available at http://epa.gov/

castnet/javaweb/ozone/CASTNET_Plan_2014_

Final.pdf, which applies to National Park Service 

(NPS) and Bureau of Land Management (BLM) site 

managers operating CASTNET monitors. 

10There are NAAQS for carbon monoxide (CO), 

lead (Pb), nitrogen dioxide (NO2), ozone, particle 

pollution and sulfur dioxide (SO2). This 

applicability includes the primary and secondary 

NAAQS. At present, most of the secondary NAAQS 

are identical to the primary NAAQS for the same 

pollutant, so there is no distinction in how the 

Exceptional Events Rule applies. To date, the EPA 

has not encountered an exceptional event situation 

with respect to a non-identical secondary NAAQS. 

developing a demonstration template(s) 

for future events of the same type(s). 

Agencies using this communications 

approach have developed a common 

understanding of expectations, 

terminology and interpretation of the 

EPA’s regulations and policy, which, in 

turn, helps focus efforts, optimize 

resources and save time during the 

demonstration development and review 

process. A summary of this ‘‘best 

practices’’ approach to implementation 

is available at http://www2.epa.gov/airquality-analysis/treatment-datainfluenced-exceptional-events. 

V. Proposed Rule Revisions 

A. To whom and to what pollutants 

does the Exceptional Events Rule apply? 

1. Current Situation 

Under the CAA, states are primarily 

responsible for the administration of air 

quality management programs within 

their borders, which includes 

monitoring and analyzing ambient air 

quality, submitting monitoring data to 

the EPA, which are then stored in the 

EPA’s AQS database, and identifying 

measurements that may warrant special 

treatment under the Exceptional Events 

Rule. The 2007 Exceptional Events Rule 

applies to all state air agencies and to 

local air quality agencies to whom a 

state has delegated relevant 

responsibilities for air quality 

management, including air quality 

monitoring and data analysis. 

Additionally, the 2007 Exceptional 

Events Rule applies to some tribal air 

quality agencies who have been granted 

treatment as a state for section 319 of 

the CAA. Section 301(d) of the CAA 

authorizes the EPA to recognize tribal 

authority, allowing eligible, federallyrecognized tribal governments to 

implement provisions of the CAA. 

Pursuant to section 301(d)(2), the EPA 

promulgated regulations, known as the 

Tribal Authority Rule (TAR), on 

February 12, 1999 (63 FR 7254, codified 

at 40 CFR part 49). That rule specifies 

those provisions of the CAA for which 

it is appropriate to treat tribes in a 

similar manner as states. Under the 

TAR, tribes may choose to develop and 

implement their own CAA programs, 

but are not required to do so. The TAR 

also establishes procedures and criteria 

by which tribes may request from the 

EPA a determination of eligibility to 

implement the provisions of the CAA. 

In cases where a tribal air quality agency 

is eligible to implement CAA section 

319 and has installed and operates an 

air quality monitoring network that 

produces regulatory data that is affected 

by emissions from exceptional events, 

the criteria and procedures identified in 

these proposed rule revisions may be 

used to exclude data for purposes of 

regulatory decisions. Some tribes may 

implement only portions of the relevant 

air quality monitoring program and may 

choose not to address all of the 

procedures and requirements associated 

with excluding data that have been 

influenced by exceptional events (e.g., a 

particular tribe may operate a 

monitoring network for purposes of 

gathering and identifying data 

appropriate for informational or 

educational purposes, but may choose 

not to implement relevant programs for 

the purpose of mitigating the effects of 

exceptional events). Where a tribal air 

quality agency is not eligible to 

implement CAA section 319 but 

operates an air quality monitoring 

network that produces regulatory data 

that is affected by emissions from 

exceptional events, the tribal air quality 

agency should consult with the EPA 

Regional office prior to addressing the 

procedures and requirements associated 

with excluding data that have been 

influenced by exceptional events.7 In all 

cases, the EPA will continue to work 

with tribes in implementing any 

promulgated rule revisions. 

While air agencies are responsible for 

administering air quality management 

programs within their borders, FLMs of 

Class I areas, other federal agencies and/ 

or other entities (e.g., industrial 

facilities pursuant to permit conditions) 

may also operate ambient air quality 

monitors that meet all requirements of 

40 CFR parts 50 and 58.8 The FLMs, 

other federal agencies and other entities 

operating these regulatory monitors may 

submit collected data to the EPA’s AQS 

database.9 These concentration 

measurements can be affected by 

exceptional events. The AQS software 

allows only the entity operating a 

monitor (and the EPA data system 

manager) to apply exceptional events 

flags to data from that monitor. 

Although FLMs and other entities can 

apply exceptional events flags to data 

from monitors they operate, the 

Exceptional Events Rule at 40 CFR 

50.14(b)(1) states that the EPA shall 

exclude data from use in determinations 

of exceedances and NAAQS violations 

where a state demonstrates to the EPA’s 

satisfaction that an exceptional event 

caused a specific air pollution 

concentration in excess of one or more 

NAAQS. The language, ‘‘where a State 

demonstrates’’ has resulted in an 

interpretation that only states can 

initiate the exceptional events process 

and submit demonstrations. Some 

stakeholders have asked the EPA to 

identify the process that the state air 

agency should follow if the state air 

agency does not have AQS access rights 

to place exceptional events flags on 

event-affected data from monitoring 

stations located within the state but not 

operated by the state. The EPA 

addressed this issue generally in 

Question 23 of the Interim Q&A 

document by indicating that air agencies 

should consult with their EPA Regional 

office early in the development of an 

exceptional event demonstration 

package if they believe that monitors on 

federally-owned and managed land (e.g., 

national parks within the state) have 

been affected by an event. In these 

instances, the EPA has assisted in 

facilitating cross-agency coordination 

regarding the flagging of data, where 

needed. 

The 2007 Exceptional Events Rule 

applies to all criteria pollutant 

NAAQS.10 This is appropriate given the 

language in CAA section 

319(b)(3)(B)(iv), which applies to 

exceedances or violations of ‘‘the 

national ambient air quality standards.’’ 

The EPA regulations for the 

interpretation of ambient data with 

respect to the NAAQS that were in place 

prior to the 2007 Exceptional Events 

Rule and that have not been revised do 

not contain provisions allowing for the 

special handling of air quality data 

affected by exceptional events or do so 

without explicit reference to the 

Exceptional Events Rule as governing 

such exclusion. One NAAQS without a 

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11A public comment opportunity is important 

prior to submission to the EPA because under the 

Exceptional Events Rule the EPA is not required to 

provide a public comment opportunity prior to 

concurring with an air agency’s request to exclude 

data. The EPA generally provides a public comment 

opportunity before we use air quality data, with or 

without such exclusions, in a final regulatory 

action. States typically provide an opportunity for 

public comment by posting draft demonstrations on 

a Web site. Federal agencies could do the same. 

affected data is 40 CFR part 50, 

appendix K for PM with a nominal 

mean aerodynamic diameter less than or 

equal to 10 micrometers (PM10). 

Nevertheless, the EPA has enabled in 

AQS the capability to flag all criteria 

pollutant data, including the option for 

the EPA’s concurrence, as the EPA 

maintains that the monitored 

concentrations of all NAAQS pollutants 

have the potential to be elevated by one 

or more event types and the Exceptional 

Events Rule should govern the process 

of data exclusion for certain types of 

regulatory actions (see section V.C). 

2. Proposed Changes 

As noted above, because FLMs and 

other federal agencies may operate 

regulatory monitors and submit 

collected data to the EPA’s AQS 

database and emissions from 

exceptional events could affect these 

same monitors, the EPA proposes to 

allow FLMs and other federal agencies 

to prepare and submit exceptional 

events demonstrations and data 

exclusion requests directly to the EPA. 

The EPA believes that the CAA language 

at section 319(b)(3)(B)(i), which states 

that ‘‘the occurrence of an exceptional 

event must be demonstrated by reliable, 

accurate data that is promptly produced 

and provided by Federal, State, or local 

government agencies’’ provides 

authority for FLMs to initiate and 

submit such demonstration packages 

and data exclusion requests. Further, 

the EPA believes this is appropriate 

because, in many cases, the lands 

managed and/or owned by federal 

entities are not entirely within the 

jurisdictional boundary of a single state 

or local government. Also, as we discuss 

in more detail in section V.F.2, federal 

entities may either initiate prescribed 

fires or fight wildfires on lands managed 

and/or owned by federal entities. The 

EPA could determine both of types of 

fires to be exceptional events. The EPA 

expects that allowing FLMs and other 

federal agencies to submit exclusion 

requests directly will expedite the 

exceptional events demonstration 

development and submittal process. The 

EPA solicits comment on this proposed 

addition to the rule text, which appears 

at the end of this document. Based on 

comments received, the EPA may retain, 

modify or not include this provision in 

the final promulgated rule. This 

provision would apply only to FLMs 

and other federal agencies that either 

operate a monitor that has been affected 

by an event or that manage land on 

which an exceptional event originates. 

The provision would allow such FLMs 

and other federal agencies to provide 

demonstrations directly to the EPA only 

after a discussion with the state in 

which the monitor is operated. 

Alternatively, this discussion might 

result in an agreement that the federal 

agency flag the data in AQS at the air 

agency’s request and then provide a 

draft demonstration document to the 

appropriate state air agency for adoption 

and submission by the air agency to the 

EPA, as is currently allowed. Regardless 

of who ultimately submits the 

demonstration, the EPA encourages 

collaboration between the FLMs and 

other federal agencies and the 

appropriate state air agency during the 

event identification and demonstration 

development process. If the provision 

for direct submission to the EPA is 

included in the final action, 

demonstrations prepared by FLMs or 

other federal agencies would be 

required to meet all provisions in the 

Exceptional Events Rule, including the 

requirement for a public comment 

period on a prepared demonstration 11

and the requirements related to 

schedules and procedures for 

demonstration package submittal (see 

sections V.G.4, V.G.5 and V.G.6) that 

apply to state agencies that operate 

monitors. 

B. What is an exceptional event? 

1. Current Situation 

The existing definition of an 

exceptional event at 40 CFR 50.1(j) 

repeats the CAA definition, which 

provides that an exceptional event is 

one that affects air quality, is not 

reasonably controllable or preventable, 

is caused by human activity that is 

unlikely to recur at a particular location 

or is a natural event, and is determined 

by the Administrator in accordance with 

40 CFR 50.14 to be an exceptional event. 

Also, CAA section 319(b)(3)(B)(ii) 

requires that a clear causal relationship 

must exist between the measured 

exceedances of a NAAQS and the 

exceptional event to demonstrate that 

the exceptional event caused a specific 

air pollution concentration at a 

particular air quality monitoring 

location. In addition to these defining 

elements, the 2007 Exceptional Events 

Rule at 40 CFR 50.14(c)(3)(iv) requires 

that the demonstration provide evidence 

that ‘‘the event is associated with a 

measured concentration in excess of 

normal historical fluctuations, including 

background’’ and evidence that ‘‘there 

would have been no exceedance or 

violation but for the event.’’ 

Both the statutory and regulatory 

definitions of an exceptional event 

include the provision that the event 

affected air quality. Many types of 

events affect air quality by causing 

emissions or increasing otherwise 

occurring emissions. Stratospheric 

ozone intrusions, one type of event, 

differ from most other event types in 

that they transport ozone already 

formed in the stratosphere to a surface 

monitor. High temperatures, air 

stagnations and meteorological 

inversions can increase the level of air 

pollution formed from a given amount 

of emissions. However, both the 

statutory and regulatory definitions of 

an exceptional event specifically 

exclude stagnation of air masses, 

meteorological inversions and 

meteorological events involving high 

temperatures or lack of precipitation, as 

well as air pollution relating to source 

noncompliance. 

While the CAA definition of an 

exceptional event excludes ‘‘a 

meteorological event involving high 

temperatures or lack of precipitation,’’ 

high temperatures and drought 

conditions can contribute to 

exceedances and violations caused by 

other exceptional events such as high 

wind dust events. If an air agency 

submits evidence showing that a severe 

drought that resulted in arid conditions 

(e.g., lower than typical soil moisture 

content, decreased vegetation) was 

combined with an event, such as a high 

wind event, that falls within the CAA 

definition of an exceptional event and 

has affected air quality data, these data 

could be considered eligible for 

exclusion under the provisions of the 

Exceptional Events Rule. Under this 

scenario, the EPA would consider the 

high wind event as the critical 

exceptional event. The high wind event 

would need to meet the provisions of 

the Exceptional Events Rule, including 

assessing whether the event is a natural 

event or an event due to human activity 

unlikely to recur at a particular location. 

As another example, if a wildfire 

exacerbated by drought conditions 

causes ozone exceedances, then the EPA 

can consider the ozone exceedances for 

exclusion under the Exceptional Events 

Rule because wildfires, unlike lack of 

precipitation itself, are not excluded 

from the CAA definition of an 

exceptional event. However, high 

temperatures alone that result in 

elevated ozone concentrations would 

not be eligible for exclusion under the 

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12The EPA considers on-going emissions from 

volcanic activity to be ‘‘events’’ even if they occur 

every day over a long period. The EPA considers 

this approach to be consistent with Congressional 

intent, but that extending the same treatment to air 

pollution due to every day biological processes or 

lightning would not be consistent with that intent. 

Exceptional Events Rule. Elevated 

temperatures and inversions can affect 

ambient air quality apart from any 

interactions with emissions, but such 

conditions alone are not exceptional 

events by the very clear provisions of 

the CAA. The EPA believes that 

Congress intended air agencies to 

compensate for the effects of high 

temperature and inversions on 

concentrations formed from 

anthropogenic emissions through the 

development of SIPs. 

To summarize, the 2007 Exceptional 

Events Rule specifies six elements that 

air agencies must address when 

requesting that the EPA exclude eventrelated concentrations from regulatory 

determinations: 

• The event affected air quality. 

• The event was not reasonably 

controllable or preventable. 

• The event was a human activity that 

is unlikely to recur at a particular 

location, or was a natural event. 

• There exists a clear causal 

relationship between the specific event 

and the monitored exceedance. 

• The event is associated with a 

measured concentration in excess of 

normal historical fluctuations including 

background. 

• There would have been no 

exceedance or violation but for the 

event. 

Section 50.14(b)(3) clearly makes the 

first three of these elements 

preconditions for the EPA to approve an 

air agency’s request to exclude data. 

However, the last three of these 

elements are listed only in § 50.14(c)(iv), 

which provides that the state ‘‘shall 

provide evidence’’ that they are true. 

Since promulgation of the 2007 

Exceptional Events Rule, the EPA has 

treated all six elements as conditions 

that air agencies must address in a 

demonstration prior to the EPA’s 

concurring with an air agency’s request 

to exclude data. In the Interim 

Exceptional Events Implementation 

Guidance, the EPA stated that for the 

fifth of these elements (e.g., the 

‘‘historical fluctuations’’ element), there 

is no bright line that defines when a 

concentration is ‘‘in excess of historical 

fluctuations.’’ With respect to the sixth 

element, referred to as the ‘‘but for’’ 

criterion, although the EPA has, in some 

cases, expected demonstrations to 

contain a quantitative estimate of the 

concentration increment caused by the 

event, more frequently the EPA has 

considered the ‘‘but for’’ criterion to be 

satisfied by a more qualitative showing 

that the measured concentration was 

much greater than the non-exceedance 

concentration that would have normally 

been expected on the day in question. 

In addition to considering whether or 

not an event is ‘‘exceptional’’ under the 

Exceptional Events Rule, an air agency 

and the EPA must also decide whether 

an ‘‘event’’ has occurred. An event, or 

anomaly, is a deviation from normal or 

expected conditions that contributes to 

air pollution. In some cases, air agencies 

or other observers can clearly see this 

‘‘deviation,’’ for example unusually high 

wind speeds transporting dust, fires 

generating PM or ozone precursors or 

volcanoes venting plumes of SO2, PM 

and PM precursors.12 In other cases, 

such as with stratospheric ozone 

intrusions, the physical effects of the 

event may not be visible and the 

occurrence of an event can only be 

inferred from seeing the effect on 

monitored air quality of emissions 

associated with the event. As described 

in section V.E.3, comparing the ambient 

pollutant concentrations in question to 

the historical distribution of 

concentrations of the same pollutant can 

help an air agency determine whether a 

deviation from normal concentrations 

occurred. However, such comparisons 

must consider that multiple factors 

often contribute to high pollutant 

concentrations. Some events, such as 

stratospheric ozone intrusions and high 

wind dust events, may last only a few 

hours at any one location. Still other 

events, such as volcanic activity, may 

occur and affect pollutant 

concentrations for a sustained period of 

time (e.g., multiple days). Some events 

may create pollutant-increasing 

conditions that persist after the original 

event process has ceased, for example 

high winds or volcanic eruptions that 

leave deposits of dust on roadways. 

2. Proposed Changes 

The EPA is proposing the following 

generally applicable changes to the 2007 

Exceptional Events Rule with respect to 

clarifying what constitutes an 

exceptional event: 

• Revising the definition of 

exceptional event by including the 

concept of considering the combined 

effects of an event and the resulting 

emissions. 

• Removing the ‘‘but for’’ element. 

• Moving the ‘‘clear causal 

relationship’’ element into the list of 

criteria that explicitly must be met for 

data to be excluded. 

• Subsuming the ‘‘affects air quality’’ 

element into the ‘‘clear causal 

relationship’’ element. 

• Removing the term ‘‘historical 

fluctuations’’ and replacing it with text 

referring to a comparison to historical 

concentrations, identifying the types of 

analyses that are necessary in a 

demonstration to address the 

comparison of the event-affected 

concentration to historical 

concentrations and clarifying that an air 

agency does not need to prove a specific 

‘‘in excess of’’ fact. 

Making these changes would result in 

returning to the following three core 

statutory elements of CAA section 

319(b) that air agencies must meet when 

requesting that the EPA exclude eventrelated concentrations from regulatory 

determinations: 

• The event affected air quality in 

such a way that there exists a clear 

causal relationship between the specific 

event and the monitored exceedance or 

violation. 

• The event was not reasonably 

controllable or preventable. 

• The event was a human activity that 

is unlikely to recur at a particular 

location or was a natural event. 

The implicit intent of CAA section 

319(b) is that when the above conditions 

are met, the data should be excluded 

from regulatory decisions so as not to 

drive SIPs to include unreasonable or 

additional measures to address the 

effects of certain events. 

a. Definition of an Event 

While an event may have a physical 

component that is purely natural in 

origin, for example high wind speeds, 

human activity either prior to or 

simultaneous with the event may 

influence air quality during the event. In 

implementing the 2007 Exceptional 

Events Rule, the EPA’s approach in 

determining whether an exceptional 

event that affected a monitored 

concentration was natural or due to 

human activity (an important 

distinction, as discussed in section V.D) 

has been to consider both whether the 

initiating physical event was natural or 

the result of human activity and 

whether human activity had any role in 

strengthening the emissions generation 

process. In contrast, some parties have 

argued that only the naturalness of the 

initiating physical event should be 

considered. To clarify that an event is 

not a ‘‘natural event’’ merely because 

natural processes initiated the emissions 

generation process, the EPA proposes to 

revise the regulatory definition of 

exceptional event to say that both the 

naturally occurring physical event and 

its associated resulting emissions are to 

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13The EPA believes that the terminology 

‘‘specific air pollution concentration’’ refers to the 

identified exceedance or violation rather than a 

specific increment in the measured concentration, 

which implies quantitative source attribution and a 

supporting quantitative analysis. 

14CAA section 319(b)(3)(B)(iv) (emphasis added). 

15The EPA stated in the preamble to the 2007 

Exceptional Events Rule that a ‘‘weight of evidence 

demonstration can present a range of possible 

concentrations, which is not as technically 

demanding as justifying a specific adjustment to a 

measured value.’’ 72 FR 13570 (March 22, 2007). 

16 72 FR 13570 (March 22, 2007). 

17The term ‘‘weight of evidence’’ means that the 

EPA will consider all relevant evidence and 

qualitatively ‘‘weigh’’ this evidence based on its 

relevance to the Exceptional Events Rule criterion 

being addressed, the degree of certainty, its 

persuasiveness, and other considerations 

appropriate to the individual pollutant and the 

nature and type of event. 

18This approach is consistent with language in 

the preamble to the 2007 Exceptional Events Rule 

that states, ‘‘The final rule permits a case-by-case 

evaluation, without prescribed threshold criteria, to 

demonstrate that an event affected air quality.’’ 72 

FR 13569 (March 22, 2007). 

be considered when applying the 

definitions and criteria for exclusion 

provided in the Exceptional Events 

Rule. For example, an exceptional event 

might consist of a high wind and the 

subsequently entrained PM that is 

transported to a monitoring site or a 

wildfire that generates ozone or ozone 

precursors, which are transported to a 

monitoring site. The EPA would not 

consider the physical event (e.g., in the 

previous example, the high wind or the 

wildfire) to be an exceptional event 

unless the resulting emissions (e.g., the 

PM or ozone) reached and elevated the 

concentration at a monitoring location 

or locations. 

b. ‘‘But For’’ Element 

The EPA proposes to rely more 

directly upon the statutory requirement 

at CAA section 319(b)(3)(B)(ii) by 

removing the regulatory requirement at 

40 CFR 50.14(c)(3)(iv)(D) that ‘‘there 

would have been no exceedance or 

violation but for the event’’ (i.e., the 

‘‘but for’’ criterion). In promulgating the 

2007 Exceptional Events Rule, the EPA 

derived the ‘‘but for’’ criterion from the 

language at section 319(b)(3)(B)(ii), 

which requires ‘‘a clear causal 

relationship. . . between the measured 

exceedances . . . and the exceptional 

event to demonstrate that the 

exceptional event caused a specific air 

pollution concentration at a particular 

air quality monitoring location.’’ 13 The 

EPA combined this language with the 

requirement that there be ‘‘criteria and 

procedures for the Governor of a State 

to petition the Administrator to exclude 

. . . data that is directly due to the 

exceptional events.’’ 14 Under the EPA’s 

interpretation of CAA section 319(b) at 

the time, these words suggested that a 

‘‘but for’’ causation standard for 

exceptional events was appropriate. 

Air agencies have expressed concern 

that the EPA has, in many cases, 

historically interpreted the ‘‘but for’’ 

criterion as implying the need for a 

strict quantitative analysis to show a 

single value, or at least an explicitly 

bounded plausible range,15 of the 

estimated air quality impact from the 

event. While a single event can in some 

cases clearly be shown to be a ‘‘but for’’ 

cause of a NAAQS exceedance or 

violation in the sense that without the 

event, the exceedance or violation 

would not have occurred, it is more 

often the case that the impact of 

emissions from events and other sources 

cannot be separately quantified and 

distinguished, and the ‘‘but for’’ role of 

a single source or event is difficult to 

determine with certainty. Even when 

the effects of events are quantifiable 

with a sufficient degree of confidence, 

air agencies have reported expending 

significant resources to quantify them. 

The EPA was aware of these concerns in 

2007 as a result of public comment on 

the proposed rule and attempted to 

alleviate them by stating in the 

preamble to the 2007 Exceptional 

Events Rule that an air agency’s ‘‘but 

for’’ analysis does not necessarily need 

to be precise and that the EPA would 

use a holistic ‘‘weight of evidence’’ 

approach in analyzing submitted 

demonstration packages.16 Without 

clear examples of what the EPA would 

accept as satisfying a weight of evidence 

approach, some air agencies began using 

burdensome approaches to provide 

quantitative ‘‘but for’’ analyses in their 

exceptional events demonstrations. The 

reviewing EPA Regional offices use 

similarly resource-intensive approaches 

to validate these quantitative analyses as 

they review demonstrations. In some 

cases, the detailed quantitative 

approaches have not produced results 

any better than what could have been 

achieved with less burdensome 

measures. Therefore, the EPA is 

proposing to remove the ‘‘but for’’ 

regulatory language and focus on the 

‘‘clear causal relationship’’ statutory 

criterion applied to the specific case, 

using a weight of evidence approach.17

In so doing, we propose that in their 

submittals, air agencies demonstrate by 

the weight of evidence in the record that 

the event caused the specific air 

pollution concentration at issue.18

Depending on the event characteristics 

and the case-by-case nature of the 

evaluation, an air agency may or may 

not need to provide quantitative 

analyses or estimates to support the 

weight of evidence approach. The EPA 

will discuss with an air agency the 

appropriate approach for a given event 

demonstration during conversations 

preceding the submittal of a 

demonstration. For example, when a 

concentration during an event is higher 

than any concentration previously 

observed in the same area and time of 

year, the air agency will generally not 

need to quantify the event impact to 

reach the conclusion that the event 

‘‘caused’’ the concentration at issue. 

However, in cases where the 

concentrations on non-event days 

during the same season come close to or 

exceed the applicable NAAQS, thus 

providing evidence that non-event 

pollution sources may produce 

exceedances of the NAAQS, the EPA 

would expect an air agency’s clear 

causal relationship showing to include 

a quantitative estimate (or range of 

estimates) of the specific event’s impact 

on air pollution concentrations, even if 

uncertain, as a part of a weight of 

evidence showing alongside other 

qualitative evidence. Section V.E.3 of 

this proposal clarifies the EPA’s 

expectations regarding analyses 

associated with the ‘‘clear causal’’ 

criterion. 

c. Clear Causal Relationship Element 

The EPA is proposing to modify the 

regulatory language in section 

50.14(c)(iv) to more clearly indicate, 

consistent with the CAA directive, the 

requirement to ‘‘demonstrate’’ versus to 

merely ‘‘provide evidence’’ that a clear 

causal relationship must exist between 

the specific event and the monitored 

exceedance. The EPA will evaluate this 

criterion on a weight of evidence basis. 

d. Affects Air Quality Element 

As explained above, the EPA has 

treated the ‘‘affects air quality’’ element 

as a distinct criterion that air agencies 

must meet for data to be excluded, and 

has expected exceptional events 

demonstrations to conclude that the 

‘‘affects air quality’’ condition has been 

satisfied. However, after carefully 

considering Congress’ intent and air 

agencies’ and the EPA’s experience in 

implementing the 2007 Exceptional 

Events Rule, we propose to integrate the 

phrase ‘‘affected air quality’’ into the 

clear causal relationship criterion. We 

believe that separately requiring an air 

agency to provide evidence to support a 

conclusion that an event ‘‘affects air 

quality’’ is unnecessary if we finalize 

this proposal to require a mandatory 

clear causal relationship showing. If an 

air agency demonstrates that an event 

has a clear causal relationship to an 

exceedance or violation of a NAAQS, 

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19 78 FR 3086 (January 15, 2013). 

20 80 FR 2206 (January 15, 2015). 

then the event has certainly affected air 

quality. This proposed approach will 

reduce the time required to prepare 

demonstrations, reduce their length, 

result in more understandable 

demonstrations for the public during the 

notice-and-comment process, and 

simplify and expedite the EPA’s review 

process. 

e. Historical Fluctuations Element 

As we indicated in the Interim 

Exceptional Events Implementation 

Guidance, we believe that a comparison 

of the claimed event-influenced 

concentration(s) to concentrations at the 

same monitoring site at other times is 

extremely useful evidence in an 

exceptional events demonstration. The 

EPA considers these comparisons as 

part of the evidence available for 

determining whether an air agency has 

satisfied the statutory and regulatory 

‘‘clear causal relationship’’ criterion. 

Because preparing this type of 

comparison is within the ability and 

resources of every air agency, the EPA 

proposes to continue to require this type 

of comparison in every demonstration. 

However, the EPA is proposing to reword the requirement to prevent 

misinterpretation that this comparison 

must show that the concentration in 

question was ‘‘in excess of normal 

historical fluctuations, including 

background.’’ This phrase is not clear 

and has caused confusion and 

regulatory uncertainty. For example, 

‘‘fluctuations in concentrations’’ can 

convey either day-to-day or hour-tohour differences in monitored 

concentrations. These concentration 

differentials cannot usefully be 

compared to an absolute concentration 

(i.e., monitored concentration at a given 

point in time) because many absolute 

concentrations will be larger than the 

differences between concentrations. The 

phrase ‘‘in excess’’ might be interpreted 

to mean that the concentration at issue 

must be higher than all historical 

concentrations, but the EPA maintains 

that Congress did not intend this, nor 

would such an interpretation be 

reasonable. Concentrations that are 

exceedances of a standard but are not 

higher than all concentrations recorded 

at a particular monitor may be causally 

connected to an event of the type that 

Congress clearly identified for treatment 

as an exceptional event. Finally, the 

language ‘‘including background’’ is 

confusing. In many cases, the monitor or 

monitors intended to represent 

‘‘background’’ concentrations are 

separated from the event-influenced 

monitoring site by some distance such 

that the event-influenced monitor and 

the ‘‘background’’ monitor reflect a 

different mixture of emissions sources, 

which could lead to misinterpretation. 

Regardless, the EPA sees no clear reason 

why such ‘‘background’’ concentrations 

are relevant for analyses associated with 

provisions in the Exceptional Events 

Rule. 

The change that the EPA is proposing 

to the text of the 2007 Exceptional 

Events Rule would require 

demonstrations to include a 

comparative analysis of the 

concentration data alleged to have been 

affected by an event and data at other 

times, and would specify certain aspects 

of the analysis. The change would also 

make clear that there is no specific ‘‘in 

excess of’’ relationship between the 

event-affected data and other data that 

must be proven, for example that the 

event-affected data be above a certain 

percentile point in the annual 

distribution of data. Section V.E.3 of 

this proposal contains additional detail 

regarding the minimum set of statistical 

analyses that the EPA expects to see in 

demonstrations. 

C. What types of ambient concentration 

data and data uses may be affected by 

the Exceptional Events Rule? 

The CAA language at section 

319(b)(3)(B)(iv) requires the 

Administrator to promulgate regulations 

that provide that there are criteria and 

procedures for the governor of a state to 

petition the Administrator to exclude air 

quality monitoring data that is 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. The implementing 

language in the 2007 Exceptional Events 

Rule states at 40 CFR 50.14(a)(1) that air 

agencies may request that the EPA 

exclude data showing exceedances or 

violations of the NAAQS that are 

directly due to an exceptional event 

from use in determinations without 

naming those determinations in that 

paragraph. The rule at 40 CFR 

50.14(b)(1) states that the EPA shall 

exclude data from use in determinations 

of exceedances and NAAQS violations 

where an air agency demonstrates to the 

EPA’s satisfaction that an exceptional 

event caused a specific air pollution 

concentration in excess of one or more 

NAAQS. Thus, both the statutory 

language and the 2007 Exceptional 

Events Rule use the phrase ‘‘in 

determinations of exceedances and 

NAAQS violations’’ with no further 

explanation. 

In this section, we consider the 

specific types of determinations by the 

Administrator that should be governed 

by CAA section 319(b). This issue was 

not specifically addressed in the 

rulemaking that promulgated the 2007 

Exceptional Events Rule and 

consequently has caused some 

confusion and regulatory uncertainty. 

1. Current Situation 

The EPA believes that Congress 

clearly intended the CAA language in 

section 319(b) to apply to exclusions of 

ambient data from determinations of 

whether a NAAQS exceedance or 

violation occurred at an ambient 

monitoring site at a particular time in 

the past. We characterize these 

exceedances or violations as occurring 

in the ‘‘past’’ because the process of 

determining whether an actual 

exceedance or violation occurred 

involves reviewing the ambient air 

monitoring data collected at monitoring 

sites over some historical timeframe. For 

example, on December 14, 2012, the 

EPA promulgated a revised primary 

annual PM2.5 NAAQS of 12.0 mg/m3, 

which is attained when the 3-year 

average of the annual arithmetic means 

does not exceed 12.0 mg/m3.19 The EPA 

Administrator made initial area 

designation decisions for the revised 

NAAQS in December 2014 based on air 

quality monitoring data for the most 

recent period 3-year period, which was 

2011 through 2013.20 Historical, or 

‘‘past,’’ data were reviewed and assessed 

to determine whether an exceedance or 

violation had occurred that would 

influence a current or future regulatory 

determination. Determinations of ‘‘past’’ 

exceedances or violations are key to the 

EPA’s actions to designate or 

redesignate an area, to initially classify 

an area for a NAAQS (where 

classifications apply), to determine if a 

nonattainment area has attained the 

NAAQS for which it has previously 

been designated nonattainment, to 

determine whether a nonattainment area 

is eligible for an attainment date 

extension (where applicable) and, in 

some cases, to find that a SIP is 

inadequate and to issue a SIP call. No 

affected stakeholders with whom the 

EPA has interacted since 2007 have 

disputed this interpretation or 

approach. 

It is not as clear whether CAA section 

319(b) also means that data should be 

excluded from determinations of 

whether a NAAQS exceedance or 

violation will or is likely to occur in the 

future. Predictions of future NAAQS 

violation(s) generally involve reviewing 

the historical ambient concentration 

data that are the evident focus of CAA 

section 319(b), estimating expected 

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21Projection of future NAAQS exceedances or 

violations do not necessarily play a role in 

reclassification of an ozone nonattainment area to 

a higher classification level. 

22 Interim Exceptional Events Rule Frequently 

Asked Questions. U.S. EPA. May 2013. Available at 

http://www2.epa.gov/sites/production/files/2015- 

05/documents/eer_qa_doc_5-10-13_r3.pdf. 

23The EPA uses design values in many regulatory 

decisions, including, but not limited to, when 

designating areas as attainment, nonattainment or 

unclassifiable for a NAAQS and when determining 

whether a nonattainment area has attained or is still 

violating a NAAQS. A design value is a statistic that 

describes the air quality status of a given location 

relative to the level of a particular NAAQS. Design 

values are computed according to the procedures 

defined in 40 CFR part 50 and published annually 

by EPA’s Office of Air Quality Planning and 

Standards. Design values are available at http://

www.epa.gov/airtrends/values.html. 

24 In some cases where the EPA has revised a 

NAAQS by strengthening it, the default AQS query 

will exclude data for the more recent, revised 

NAAQS, but may include concurred data for the 

historical NAAQS. 

25 If the EPA is the permitting authority, the EPA 

will propose permits on this basis. If the EPA is 

commenting on another permitting authority’s 

proposed action, the EPA’s comments will be 

consistent with the determinations in this guidance 

document and any applicable New Source Review 

(NSR) permitting and/or modeling guidance. 

26Transportation conformity hot spot analysis is 

applicable only to PM10 and PM2.5. ‘‘Transportation 

Conformity Guidance for Quantitative Hot-spot 

Analyses in PM2.5 and PM10 Nonattainment and 

Maintenance Areas,’’ EPA–420–B–10–040, U.S. 

EPA Office of Transportation and Air Quality, 

December 2010, page 98. 

27These data may be included in statistics 

intended to describe current status and trends in 

actual air quality in the area for public information 

purposes including reporting of the Air Quality 

Index. 

28The attainment demonstration would be 

adequate in the sense that if a similar event does 

not occur during the period on which actual 

attainment will be based, there would be no 

monitored NAAQS violation, and if a similar event 

were to occur during that period the event-affected 

data could be excluded and thus there would be no 

‘‘official’’ violation. 

future emissions, and then using both of 

these data sets as inputs to an air quality 

modeling tool or other analytical 

approach that extrapolates these data to 

predict a future outcome. While science 

supports and the EPA relies on 

predictions of future NAAQS violations 

in several parts of the clean air program, 

such as in the EPA’s approval of 

attainment demonstrations in SIPs, in 

prevention of significant deterioration 

(PSD) air permitting programs and in 

actions to reclassify a moderate PM10 or 

PM2.5 nonattainment area to serious,21

the fact that these predicted future 

values rely only in part on historical 

monitoring data implies that a different 

standard for data exclusion may be 

appropriate. 

Another interpretation question is 

whether and under what conditions 

event-affected data should be excluded 

from determinations that are based 

wholly or in part on monitoring data but 

formally are not determinations of 

exceedances or violations of the 

NAAQS. For example, under 40 CFR 

part 51, subpart H, Prevention of Air 

Pollution Emergency Episodes, the 

required content of a state’s emergency 

plan depends on whether the state has 

experienced air pollution that exceeds a 

specified threshold level that is well 

above any NAAQS. Also, under the 

EPA’s guidance, the eligibility of an area 

for a simplified maintenance plan for 

PM10 depends on the difference between 

the better-than-the-NAAQS air quality 

in an area and the NAAQS. 

To date, the EPA has not issued 

guidance that explicitly and 

comprehensively identifies the types of 

data exclusion that are authorized and 

required by CAA section 319(b) or that 

may be otherwise appropriate and 

permissible. In the 2013 Interim Q&A 

document, the EPA provided only 

limited clarification regarding the 

meaning of ‘‘exclude data.’’ 22 Question 

14a of the Interim Q&A document notes 

that when the EPA concurs based on the 

weight of evidence that an air agency 

has successfully made the 

demonstrations referred to in 40 CFR 

50.14(a)(2) and (b)(1), then the EPA 

generally excludes the affected data 

from the following types of calculations 

and activities: 

• The EPA’s AQS does not count 

these days as exceedances when 

generating user reports, and does not 

include them in design values 

estimates,23 unless the AQS user 

specifically indicates that they should 

be included, which may be appropriate 

for non-regulatory applications of 

interest to the user.24

• The EPA accepts the exclusion of 

these data for the purposes of selecting 

appropriate background concentrations 

for PSD air quality analyses 25 and for 

transportation conformity hot spot 

analyses.26

• The EPA accepts the exclusion of 

these data for the purposes of selecting 

appropriate ambient data for projecting 

future year concentrations as part of a 

modeled attainment demonstration. 

• The data continue to be publicly 

available, but the EPA’s publications 

and public information statements on 

the status of air quality in the affected 

area generally do not reflect these data 

in any summary statistic of potential 

regulatory application, unless such 

inclusion is specifically noted.27

Thus, the EPA has maintained that 

once data are excluded under the 

Exceptional Events Rule, these same 

data should be excluded from the aboveidentified calculations and activities. 

The EPA has not clearly addressed 

whether approval for exclusion under 

the Exceptional Events Rule means that 

the data may or must be excluded for 

the purpose of other types of actions 

that use monitoring data but are not 

included in the list above. The EPA has 

also not clearly addressed whether data 

that have not been approved for 

exclusion under the Exceptional Events 

Rule can nevertheless under some other 

principle or interpretation be excluded 

from any of the various types of 

calculations and activities. 

The current situation is further 

complicated by the fact that the 

conditions for data exclusion in CAA 

section 319(b) and the Exceptional 

Events Rule, while logical when applied 

to determinations of NAAQS 

exceedances or violations occurring in 

the past, may not be logical when 

applied to predictions of future 

exceedances or violations. The EPA 

recognizes, and acknowledged in 

Question 13 of the Interim Q&A 

document, that an event may have made 

a past air concentration significantly 

higher than it would have been in the 

absence of the event contribution, and 

thus elevated an exceedance for a 

NAAQS pollutant to an even greater 

degree of exceedance. This same eventinfluenced concentration may not be 

eligible for exclusion under the 2007 

Exceptional Events Rule because the 

‘‘but for’’ criterion is not satisfied 

because either (1) there would have 

been a 3-year violation with or without 

the event or (2) there would not have 

been a violation either with or without 

the event. The 2007 Exceptional Events 

Rule does not explicitly authorize the 

exclusion of data associated with such 

an event because the event fails to meet 

the clear causal relationship criterion 

and ‘‘but for’’ criterion. Retaining the 

event-influenced data could, however, 

have regulatory implications that seem 

contrary to the purpose of CAA section 

319(b). For example, retaining such data 

in the calculation of the historical 

design value for a nonattainment area 

can make it seem that the area needs 

more emissions reduction to attain the 

NAAQS than is actually the case, and 

could lead to the EPA’s disapproval of 

an attainment demonstration that is in 

fact adequate, and thus require the state 

to adopt additional emission controls.28

As another example, events can make 

past air concentrations higher without 

causing an actual NAAQS exceedance 

or violation. However, retaining such 

data in the calculation of background 

concentrations used in air quality 

analysis for a PSD permit may suggest 

that there will be a NAAQS violation 

after construction of a new source and 

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29 If a similar event were to occur after 

completion of construction, the event-affected data 

could be excluded and thus there would be no 

‘‘official’’ violation. 

30The term ‘‘current’’ denotes the determination 

at issue in the current analysis. In actual practice, 

such determinations are based on historical data 

and thus reflect a past actual condition. 

31The EPA’s initial area designations process also 

makes use of other information relevant to the CAA 

criteria for designations, such as pollution 

contributions between nearby areas. 32Reclassification of PM10 and PM2.5

nonattainment areas, by contrast, do not exclusively 

rely on area design values (and thus, past monitored 

violations) but can also result from the 

Administrator’s determination that an area cannot 

practicably attain a standard by the attainment date. 

See CAA section 188(b)(1). 

thus could prevent the permitting 

authority from issuing the permit.29

2. Proposed Changes 

To remove the ambiguities described 

in the preceding section and to provide 

greater regulatory certainty, the EPA 

proposes in regulatory language to 

interpret the CAA section 319(b) phrase 

‘‘determinations by the Administrator 

with respect to exceedances or 

violations of national ambient air 

quality standards’’ to encompass 

determinations of current 30 or historical 

NAAQS exceedances/violations or nonexceedances/non-violations and 

determinations of the air quality ‘‘design 

value’’ at particular receptor sites when 

made as part of the basis for any of the 

following five types of regulatory 

actions: 

• An action to designate or 

redesignate an area as attainment, 

unclassifiable/attainment, 

nonattainment or unclassifiable for a 

particular NAAQS. Such designations 

rely on a violation at a monitoring site 

in or near the area being designated. 

• The assignment or re-assignment of 

a classification category (marginal, 

moderate, serious, etc.) to a 

nonattainment area to the extent this is 

based on a comparison of its ‘‘design 

value’’ to the established framework for 

such classifications. 

• A determination regarding whether 

a nonattainment area has actually 

attained a NAAQS by its CAA deadline. 

• A determination that an area has 

had only one exceedance in the year 

prior to its deadline and thus qualifies 

for a 1-year attainment date extension, 

if applicable. 

• A finding of SIP inadequacy leading 

to a SIP call to the extent the finding 

hinges on a determination that the area 

is violating a NAAQS. 

For these types of actions, the EPA 

proposes to interpret the CAA to require 

that data be excluded only if the 

requirements of section 319(b) and the 

Exceptional Events Rule are satisfied. In 

addition, we propose that when one of 

these determinations is based on a 

combination of monitoring data and air 

quality modeling, the criterion requiring 

that there be a clear causal relationship 

between the event and a NAAQS 

exceedance or violation will apply to 

the combined estimate of air pollution 

levels rather than directly to the 

monitored background air quality data. 

That is, the event would not be required 

to have caused an actual exceedance or 

violation at the background ambient 

monitoring site, but rather to have made 

the critical difference in the combined 

estimate of air pollution levels 

(background plus source impact) 

resulting in a NAAQS exceedance or 

violation, because the event increased 

the background levels that are added to 

the air quality modeling output. 

When the EPA designates or 

redesignates areas as attainment or 

nonattainment for the NAAQS; initially 

classifies ozone nonattainment areas as 

marginal, moderate, serious, severe or 

extreme; grants a request for a 1-year 

NAAQS attainment date extension 

where applicable; or determines 

whether areas designated nonattainment 

for the NAAQS have attained the 

respective NAAQS by the applicable 

attainment date, it does so based on 

monitoring data (where available) or 

modeling of actual air quality, or a 

combination thereof, as the evidence of 

the occurrence or non-occurrence of a 

NAAQS exceedance or violation and, in 

the case of classification actions, the 

degree of violation.31 In the case of 

reclassifying an ozone nonattainment 

area to a higher classification, the new 

classification is based on the design 

value either at the time of the 

determination of attainment by the 

attainment deadline under CAA section 

181(b)(2), or at the time of the EPA’s 

grant of a voluntary request for 

reclassification from a state under CAA 

section 181(b)(3).32 This proposal, if 

finalized, would in effect apply the 

exceptional events process in the same 

way across these related types of 

determinations and across the NAAQS, 

which we believe is an appropriate 

interpretation of the CAA 319(b) phrase 

‘‘determinations by the Administrator 

with respect to exceedances or 

violations of national ambient air 

quality standards.’’ For these types of 

determinations, the EPA proposes to 

exclude event-affected data only if an 

air agency satisfies the procedural (e.g., 

event identification, opportunity for 

public comment, demonstration 

submission) and substantive (i.e., clear 

causal relationship, not reasonably 

controllable or preventable, and human 

activity not likely to recur or natural 

event) requirements of the exceptional 

events process. As indicated previously, 

the EPA has maintained to this point 

that once data are excluded under the 

Exceptional Events Rule, these same 

data also should be excluded from (i) 

design value estimates and AQS user 

reports (unless the AQS user 

specifically indicates that they should 

be included), (ii) selecting appropriate 

background concentrations for PSD air 

quality analyses and transportation 

conformity hot spot analyses, and (iii) 

selecting appropriate ambient data for 

projecting future year concentrations as 

part of a modeled attainment 

demonstration. As described below, we 

intend that EPA approval for exclusion 

of data under the Exceptional Events 

Rule continue to mean that the same 

data may be excluded for the three 

applications listed in the previous 

sentence, but that there should be other 

pathways for exclusion for the second 

and third of these applications (and 

others) as well. 

This action proposes to require that 

data exclusion associated with the five 

actions in the above bulleted list (i.e., 

initial area designations, classifications, 

attainment determinations, 

determinations regarding requests for 

attainment date extensions and findings 

of SIP inadequacy leading to a SIP call) 

must follow the provisions in the 

Exceptional Events Rule. It does not, 

however, mean that the EPA would 

never exclude or agree to exclude eventaffected data from other types of 

regulatory determinations. For example, 

while the EPA would exclude 

concurred-upon event-affected data 

from the five types of regulatory actions 

discussed in V.C.1, the EPA would not 

exclude these same data when setting 

priority classifications for emergency 

plans under 40 CFR 51.150 as the EPA 

believes that implementing the CAA 

principle at section 319(b)(3)(A) that 

‘‘protection of public health is the 

highest priority’’ may necessitate that an 

air agency address in its emergency plan 

the appropriate planned response for 

any elevated concentration known to be 

possible because it has already been 

observed, although the appropriate type 

of response may depend on the cause(s) 

of the elevated concentration. The 

concept that the EPA does not consider 

CAA section 319(b) and the revised 

Exceptional Events Rule to be the 

necessary or sole governing authorities 

for all data exclusions will be discussed 

further in upcoming, new draft guidance 

on excluding (or in some cases not 

excluding) data, independent of the 

Exceptional Events Rule, from several 

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33See as examples, Hawaii’s exceptional events 

demonstration for volcanic activity affecting PM2.5

concentrations in 2011–2012 and California Air 

Resources Board’s demonstration for wildfire events 

affecting PM2.5 concentrations in 2008, both 

available at http://www2.epa.gov/air-qualityanalysis/exceptional-events-submissions-table. 

34For example, if an area affected by a high wind 

dust event has adequate rules or ordinances for 

sources of windblown dust (e.g., rules that establish 

restrictions for operating vehicles on unpaved 

property, rules that control windblown dust 

emissions associated with lands disturbed by 

construction, earthwork and land development) and 

the air agency can provide evidence of 

implementation and enforcement, then the EPA 

would generally consider human activity to have 

played little or no direct causal role in causing the 

event-related emissions. 

35The EPA considers wildfires to be natural 

events even though some wildfires are initiated by 

human actions and to some degree the frequency 

and scale of wildfires may be influenced by prior 

land management practices. The EPA believes this 

interpretation best implements the Congressional 

intent and is a more appropriate approach than 

expecting air agencies to determine the initial cause 

of each wildfire of interest and classifying it as 

natural or anthropogenic based on that cause. In 

addition, land owners and managers and 

government public safety agencies are strongly 

motivated to reduce the frequency and severity of 

human-caused wildfires and the EPA believes they 

can be presumed to make reasonable efforts to avoid 

them. 36 72 FR 13565–13566 (March 22, 2007). 

types of determinations and regulatory 

actions. The EPA is currently 

developing a supplementary guidance 

document, Draft Guidance for Excluding 

Some Ambient Pollutant Concentration 

Data from Certain Calculations and 

Analyses for Purposes Other than 

Retrospective Determinations of 

Attainment of the NAAQS, which will 

describe the appropriate additional 

pathways that we intend to make 

available for data exclusion for some 

monitoring data applications (e.g., 

predicting future attainment that is the 

basis for approval of an attainment 

demonstration in the SIP for a 

nonattainment area, preparing required 

air quality analyses in an application for 

a PSD permit or preparing required air 

quality analysis for the purposes of 

transportation conformity). The EPA 

intends to post the draft guidance on the 

exceptional events Web site at http://

www2.epa.gov/air-quality-analysis/

treatment-data-influenced-exceptionalevents and expects to finalize the 

document when we finalize these rule 

revisions. We intend that this guidance 

will recommend exclusion of data for 

PSD, transportation conformity and 

certain other applications in any 

situation in which exclusion has already 

been approved under the Exceptional 

Events Rule, as well as in applications 

in which the facts would support 

exclusion under the criteria of the 

Exceptional Events Rule even if an EPA 

determination has not yet been made 

under the Exceptional Events Rule and 

in some other situations that we will 

describe in the guidance. 

D. What is a natural event? 

1. Current Situation 

The CAA definition at section 

319(b)(1)(iii) specifies that an 

exceptional event ‘‘is an event caused 

by human activity that is unlikely to 

recur at a particular location or a natural 

event.’’ Thus, the statute limits the 

expected occurrence frequency of an 

event caused by human activity as 

‘‘unlikely to recur’’ but does not limit 

the occurrence frequency of a natural 

event. Natural events may recur, even 

frequently.33 Air agencies can request, 

and the EPA can agree, to exclude data 

affected by a natural event if an air 

agency’s demonstration meets the other 

requirements of the Exceptional Events 

Rule. Thus, considering whether an 

event was a natural event or was caused 

by human activity is important to the 

content within and to the approval of a 

demonstration. 

As previously discussed, to be 

considered an exceptional event, an 

event, whether natural or anthropogenic 

in origin, must affect air quality at the 

affected monitor. 40 CFR 50.1(k) defines 

a natural event as one in which human 

activity plays little or no direct causal 

role in the generation of emissions. In 

some cases, such as stratospheric ozone 

intrusions or volcanic eruptions, the 

EPA recognizes that human activity 

plays no role in the magnitude of 

emissions or level of air pollution that 

occurs. In other cases, past or current 

human activity does influence the 

magnitude of emissions and hence the 

level of air pollution. For example, in 

high wind dust events, the pollution 

from the event may originate from a 

mixture of natural lands (e.g., 

undisturbed soil), soil that has been 

disturbed by human activity and has 

been made more prone to windgenerated dust emissions (e.g., recent 

construction activity), and materials 

accumulated and stored by human 

activity (e.g., sand and gravel facilities). 

The EPA generally considers human 

activity to have played little or no direct 

role in causing emissions if 

anthropogenic emission sources that 

contribute to the event emissions are 

reasonably controlled at the time of the 

event, regardless of the magnitude of 

emissions generated by these reasonably 

controlled anthropogenic sources and 

regardless of the relative contribution of 

these emissions and emissions arising 

from natural sources in which human 

activity has no role.34 35 Thus, the event 

could be considered a natural event. In 

such cases, the EPA applies the 

reasonable interpretation that the 

anthropogenic source had ‘‘little’’ direct 

causal role. If anthropogenic emission 

sources that contribute to the event 

emissions can be reasonably 

controllable but reasonable controls 

were not implemented at the time of the 

event, then the event would not be 

considered a natural event. The EPA 

explained this concept in the preamble 

to the 2007 Exceptional Events Rule.36

However, the rule text did not reflect 

the identified concept. This has resulted 

in some regulatory uncertainty as to 

whether the EPA’s interpretation of the 

CAA and the 2007 Exceptional Events 

Rule as described here is appropriate. 

2. Proposed Changes 

Based on the discussion above, the 

EPA proposes to revise the definition of 

natural event to clarify that 

anthropogenic emission sources that 

contribute to the event emissions that 

are reasonably controlled do not play a 

‘‘direct role’’ in causing emissions. 

Thus, an event with a mix of natural 

emissions and reasonably controlled 

human-affected emission sources may 

be considered a natural event. However, 

an event resulting from only reasonably 

controlled human affected emissions 

may not be considered a natural event. 

This proposal is consistent with 

statements made in the preamble to the 

2007 Exceptional Events Rule, and 

including it in the rule text provides 

more regulatory certainty to all parties. 

When addressing the not reasonably 

controllable or preventable criterion for 

this same event type consisting of a mix 

of natural emissions and humanaffected emission sources (e.g., a high 

wind event affecting both open desert 

areas and urbanized lands), air agencies 

must assess reasonable controls for both 

the contributing natural and 

anthropogenic sources. While air 

agencies must ‘‘assess’’ reasonable 

controls for most types of contributing 

natural sources because this statutory 

factor applies to all events, they do not 

necessarily need to implement controls 

for these same sources. Additionally, 

because the rule revisions propose a 

categorical presumption of not 

reasonably controllable for wildfires and 

large-scale, high-energy and/or sudden 

high wind dust events, ‘‘assessing’’ 

these events would involve referencing 

the appropriate regulatory citation. As 

we explain in more detail in section 

V.E.2, for natural sources, we do not 

think that air agencies need to have 

implemented any controls for 

windblown dust from never-disturbed, 

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37 Guideline on the Identification and Use of Air 

Quality Data Affected by Exceptional Events (the 

Exceptional Events Policy), U.S. EPA, OAQPS, 

EPA–450/4–86–007, July 1986. 

large-scale natural landscapes. 

Therefore, lack of controls on natural 

sources that contribute to event-related 

emissions would not disqualify the 

event from being considered as an 

exceptional event. When assessing the 

contribution from anthropogenic 

sources, similar to the analyses involved 

in determining whether these same 

sources play a ‘‘direct role’’ in causing 

event-related emissions, the air agency 

should identify the contributing 

anthropogenic sources, explain why the 

controls specified in rules or ordinances 

are reasonable, and provide evidence of 

implementation and enforcement. Also 

as explained in section V.E.2, in our 

view an event is ‘‘not reasonably 

controllable’’ if an exceedance or 

violation occurs even when reasonable 

controls were actually in place and any 

further control would have been beyond 

what was reasonable. The EPA intends 

to consider these aspects when applying 

the concept of ‘‘reasonable controls’’ on 

anthropogenic sources to determine 

whether the event can be considered a 

natural event and to evaluate the not 

reasonably controllable or preventable 

criterion. 

With respect to determining whether 

anthropogenic emission sources that 

contribute to the event emissions were 

reasonably controlled at the time of the 

event, the EPA also proposes to revise 

the definition of a natural event to 

indicate that the reasonableness of 

available controls should be assessed as 

of the date of the event. The EPA does 

not believe that information related to 

the cost and effectiveness of control 

measures, or related to the frequency of 

events, that became available to the air 

agency after the date of the event should 

affect the assessment of whether 

anthropogenic sources were reasonably 

controlled and thus the identification of 

an event as natural or caused by human 

activity. 

When addressing this criterion as part 

of an exceptional events demonstration, 

the EPA recommends that the 

submitting air agency clearly identify 

whether the event is natural or was a 

human activity that is unlikely to recur 

at a particular location. If purely natural 

(e.g., lightning-ignited wildfire, volcanic 

or seismic activity, stratospheric ozone 

intrusion), the EPA recommends that 

the submitting air agency identify the 

purely natural status in the ‘‘human 

activity/natural event’’ section of its 

demonstration; provide the type/source 

of event, the resulting emissions, and 

the documented frequency of the event; 

and affirmatively state that in 

characterizing the event, the submitting 

air agency has satisfied the human 

activity/natural event criterion. 

E. Technical Criteria for the Exclusion 

of Data Affected by Events 

As described in section V.B, the EPA 

proposes to return to the core statutory 

elements and implicit concepts of CAA 

section 319(b): That the event affected 

air quality in such a way that there 

exists a clear causal relationship 

between the specific event and the 

monitored exceedance or violation, the 

event was not reasonably controllable or 

preventable, and the event was caused 

by human activity that is unlikely to 

recur at a particular location or was a 

natural event. All exceptional events 

demonstrations, regardless of event type 

or relevant NAAQS, must address each 

of these technical criteria. This section 

describes the EPA’s proposals for rule 

revisions and guidance regarding each 

of these technical criteria. Section V.G 

discusses additional process-related 

components of exceptional events 

demonstration packages. 

1. Human Activity Unlikely To Recur at 

a Particular Location or a Natural Event 

The concept of recurrence applies to 

human activity; the statements in this 

section are not relevant for natural 

events. Section V.D includes a detailed 

discussion of a ‘‘natural event.’’ 

a. Current Situation 

According to both the regulatory and 

statutory definitions, an exceptional 

event must be ‘‘an event caused by 

human activity that is unlikely to recur 

at a particular location or a natural 

event’’ (emphasis added). For clarity, in 

this section, the EPA focuses on the 

language ‘‘unlikely to recur at a 

particular location.’’ 

The ‘‘unlikely to recur at a particular 

location’’ requirement of CAA section 

319(b) does not define ‘‘unlikely to 

recur.’’ Thus, this language requires 

interpretation on a case-by-case or event 

type-by-event type basis. The term 

‘‘unlikely’’ implies consideration of the 

expected future frequency of events 

similar to the event that has already 

happened, but does not convey any 

particular benchmark for what 

frequency should be low enough to be 

considered ‘‘unlikely.’’ Also, the term 

‘‘at a particular location’’ requires 

interpretation, as it could refer to the 

exact area or only to the general area of 

the event, to the location of the ambient 

monitoring station or stations that were 

affected by the event or to the 

combination of both. 

The EPA’s 1986 Guideline on the 

Identification and Use of Air Quality 

Data Affected by Exceptional Events 

stated that events can be considered 

exceptional if they are not expected to 

‘‘recur routinely at a given location.’’ 37

This document did not further define or 

give specific examples of ‘‘routinely.’’ 

The preamble to the 2007 Exceptional 

Events Rule did not provide specific 

guidance on the unlikely to recur 

criterion, except to say that recurrence 

is event-specific and should be assessed 

on a case-by-case basis and that in the 

particular case of prescribed fires a 

comparison to the natural fire return 

interval is a relevant consideration for 

this criterion. 

The CAA section 319(b) and the 2007 

Exceptional Events Rule do not 

specifically address temporary, but 

multi-day or multi-year activities, such 

as construction projects. However, 

Question 16 in the Interim Q&A 

document noted that the 2007 

Exceptional Events Rule does not 

explicitly place a limit on the duration 

of a single event and that a submitting 

agency could make a showing that a 

prolonged activity (e.g., a multi-year 

road construction project) is a single 

event that is not likely to recur at the 

location in question. The Interim High 

Winds Guidance document addressed 

recurrence for high wind events, as 

summarized in section V.F.4 of this 

document. Other than this, the Interim 

Exceptional Events Implementation 

Guidance did not provide any specific 

guidance on the unlikely to recur 

criterion. 

b. Proposed Changes 

While we believe that it is appropriate 

to consider recurrence to be eventspecific and for the unlikely to recur 

criterion to be assessed on a case-bycase basis, we also believe that this 

proposed action presents an opportunity 

to clarify certain points. This section 

provides general clarifications with 

respect to the meaning of ‘‘unlikely to 

recur.’’ Section V.F.2 addresses this 

criterion for wildland fires (specifically 

prescribed fires on wildland) and 

section V.F.4 specifically addresses this 

criterion for high wind dust events. 

Also, under CAA section 319(b) and the 

2007 Exceptional Events Rule, air 

pollution related to source 

noncompliance is not an exceptional 

event regardless of its frequency. 

The EPA proposes, as guidance, to 

recommend the following boundaries on 

the interpretation of the unlikely to 

recur criterion. If an event type has not 

previously occurred within a given air 

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38Air Quality Control Regions are defined in 40 

CFR part 81, subpart B, Designation of Air Quality 

Control Regions. 

39The EPA will consider previously flagged 

exceedances within AQS with their associated 

descriptions to be ‘‘events’’ regardless of whether 

the EPA has received or acted on event 

demonstrations. The EPA also notes that a single 

event could influence concentrations on multiple 

days. 

40See footnote 27 in table 2 of Interim Guidance 

on the Preparation of Demonstrations in Support of 

Requests to Exclude Ambient Air Quality Data 

Affected by High Winds Under the Exceptional 

Events Rule. U.S. EPA. May 2013. Available at 

http://www2.epa.gov/sites/production/files/2015- 

05/documents/exceptevents_highwinds_guide_

130510.pdf. 41 72 FR 13564 (March 22, 2007). 

42For example, in section V.F.2, we propose that 

under certain circumstances a prescribed fire may 

not be reasonably preventable because of the safety 

or ecosystem benefits that would be foregone, but 

emissions and air quality impacts from the fire may 

be reasonably controllable through the application 

of basic smoke management practices. 

43The EPA has many resources to help states 

identify appropriate control technologies and 

includes links to some of these sources on the 

Control Strategies Web site available at http://

www3.epa.gov/airquality/aqmportal/management/

control_strategies.htm. 

quality control region (AQCR) 38 in the 

3 years preceding the submittal of an 

exceptional events demonstration, the 

EPA will consider this to be a ‘‘first’’ 

event and will generally consider it to 

be unlikely to recur in the same 

location. Similarly, a ‘‘second’’ event 

within the 3 years preceding the 

submittal of an exceptional events 

demonstration would also generally be 

considered unlikely to recur in the same 

location. If there have been two prior 

events of a similar type within a 3-year 

period in an AQCR, that would 

generally indicate the third event, for 

which the demonstration is being 

prepared (or would be prepared), does 

not satisfy the ‘‘human activity that is 

unlikely to recur at a particular 

location’’ criterion and, thus, would not 

qualify as an exceptional event. The 

terms ‘‘first’’ and ‘‘second’’ events refer 

to events that affect the same AQCR, 

even if they have not affected the same 

monitor.39 This proposed guidance is 

consistent with the approach taken to 

recurrence in our Interim High Winds 

Guidance document in which we 

identified non-recurring events as being 

less than one event per year in a given 

area.40 In the Interim High Winds 

Guidance, we did not define area other 

than to differentiate areas by attainment 

status or jurisdiction (i.e., intrastate 

versus interstate or international). 

The EPA solicits comment on this 

proposed guidance regarding recurrence 

at a particular location, specifically the 

use of an AQCR to define the bounds for 

an area subject to event recurrence given 

that some AQCRs may be quite large. 

The EPA also solicits comments on 

whether this benchmark of three events 

in 3 years should be incorporated into 

the rule text, rather than being provided 

only as guidance. 

The EPA proposes, as guidance, that 

to satisfy the documentation 

requirements for the ‘‘human activity 

that is unlikely to recur at a particular 

location’’ criterion, the submitting air 

agency should document and discuss, in 

a distinct ‘‘human activity/natural 

event’’ section of the demonstration, the 

type/source of event (e.g., a particular 

type of chemical spill or other industrial 

accident or a fire in a particular type of 

structure), the resulting emissions and 

the documented frequency of the event 

in the prior 3 years. The demonstration 

should affirmatively state that in 

characterizing the event, the submitting 

air agency has satisfied the ‘‘human 

activity unlikely to recur at a particular 

location or a natural event’’ criterion. 

2. Not Reasonably Controllable or 

Preventable 

The CAA section 319(b) does not 

restrict the not reasonably controllable 

or preventable criterion to apply only to 

events caused by human activity. It also 

applies to natural events. Accordingly, 

the Exceptional Events Rule applies this 

criterion to all types of events. This 

section discusses the criterion in general 

terms. We discuss the criterion’s 

applicability to fire events on wildland 

in section V.F.2 and to high wind dust 

events in section V.F.4. 

a. Current Situation 

As noted in section V.B of this 

document, the definition of an 

exceptional event at 40 CFR 50.1(j) 

repeats the CAA definition and includes 

the requirement at section 

319(b)(1)(A)(ii) that an exceptional 

event, whether natural or caused by 

human activity, is one that ‘‘is not 

reasonably controllable or preventable.’’ 

Neither the rule text of the 2007 

Exceptional Events Rule nor the 

preamble to the final rule provided 

additional clarification regarding this 

statutory element. Rather, the preamble 

to the final rule stated, ‘‘[w]e are not 

finalizing more detailed requirements 

for determining when an event is ‘not 

reasonably controllable or preventable’ 

because we believe that such 

determinations will necessarily be 

dependent on specific facts and 

circumstances that cannot be prescribed 

by rule.’’ 41 While we maintain that 

determining whether or not an event is 

not reasonably controllable or 

preventable is event-specific and 

necessarily requires judgment by the air 

agency and the EPA, we also believe 

that some concepts regarding this 

criterion are broadly applicable. 

To begin, the statutory requirement 

that an exceptional event is one that ‘‘is 

not reasonably controllable or 

preventable’’ contains two factors: 

Prevention and control. Within the 

context of the Exceptional Events Rule, 

we intend that ‘‘prevent’’ means to stop 

or avert the event, and ‘‘control’’ means 

to reduce the magnitude and impact of 

event-related emissions. We interpret 

CAA section 319(b) to mean that to 

qualify as an exceptional event, the 

event cannot be reasonably preventable 

and cannot be reasonably controllable, 

rather than that only one of the two 

elements must be satisfied. It would be 

contrary to the emphasis of section 

319(b) on protection of public health if 

there were no requirement for 

reasonable control for an event merely 

because the event could not be 

reasonably prevented from happening. It 

is possible for an event to not be 

reasonably preventable, but to be 

reasonably controllable.42 In this case, if 

emissions were reasonably controlled, 

then the event could be considered for 

concurrence as an exceptional event. It 

is also possible that an event be neither 

preventable nor its air quality impacts to 

be controllable to any degree, such as 

potential increases in SO2

concentrations associated with volcanic 

eruptions. 

The EPA considers the statutory 

requirement that an exceptional event 

be ‘‘not reasonably preventable’’ to 

mean that if a set of prevention 

measures should reasonably have been 

in place for anthropogenicallyinfluenced emission sources that 

contribute to the event emissions, then 

those measures must have been in place 

for the event to qualify as an exceptional 

event under the Exceptional Events 

Rule. Similarly, we consider the 

statutory requirement that an 

exceptional event be ‘‘not reasonably 

controllable’’ to mean that if a set of 

control measures should reasonably 

have been in place for emission sources 

that contribute to the event emissions, 

then those controls must have been in 

place for the event to qualify as an 

exceptional event under the Exceptional 

Events Rule. Satisfying the not 

reasonably controllable element 

necessitates a showing of reasonable 

controls. Whether a set of controls 

constitutes ‘‘reasonable controls’’ is 

event-, time-, and place-dependent, and 

involves judgment by the air agency 

when preparing the demonstration and 

by the EPA when reviewing the 

demonstration.43 We stated in the 

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44The CAA provides different timeframes for 

developing and implementing SIPs depending on 

the NAAQS and the nonattainment area’s 

classification (e.g., severity of the nonattainment 

problem). The EPA recognizes that within the SIP 

development and implementation process, some 

measures may be implemented relatively quickly 

(e.g., transportation conformity, new source review) 

whereas other programs, such as development or 

rules for particular source types, can take time and 

involve state legislative processes. 

45 Interim Guidance on the Preparation of 

Demonstrations in Support of Requests to Exclude 

Ambient Air Quality Data Affected by High Winds 

Under the Exceptional Events Rule. U.S. EPA. May 

2013. Available at http://www2.epa.gov/sites/

production/files/2015-05/documents/exceptevents_

highwinds_guide_130510.pdf. 

Interim Exceptional Events 

Implementation Guidance, and we 

reiterate in this action, that it may not 

be reasonable to apply any prevention 

or control efforts for some events. 

In the course of implementing the 

2007 Exceptional Events Rule, both the 

EPA and air agencies have expressed 

concern regarding the determination of 

‘‘reasonable’’ prevention or control 

efforts for particular events. When an air 

agency prepares a demonstration, it 

attempts to show that whatever efforts 

were made were all that were reasonable 

to make. When the EPA reviews a 

demonstration, we are responsible for 

determining if the demonstration is 

credible and convincing. The EPA has 

been unable to make this determination 

regarding reasonableness for some 

demonstrations because the content 

regarding the use and implementation of 

control measures is insufficient. Given 

the elasticity of the concept of 

‘‘reasonable,’’ it is not surprising that 

disagreements have arisen. We have in 

the past few years, particularly since 

issuing the Interim Exceptional Events 

Implementation Guidance, worked with 

states to reach mutual understandings of 

what efforts are reasonable and to have 

those efforts in place before events 

happen. However, situations will likely 

occur in the future, as they have in the 

past, in which an assessment of 

reasonableness must be made 

retrospectively, when it is too late for 

the air agency to have applied greater 

efforts. The EPA recognizes that our 

action on the air agency’s demonstration 

may have important regulatory 

consequences for the area in question. 

The EPA has stated that for all types 

of events, we consider reasonableness in 

light of the technical information 

available to the air agency at the time 

the event occurred. An air agency 

‘‘caught by surprise’’ by an event of a 

given type (or by an unexpected number 

of such events in a period over which 

NAAQS compliance is evaluated, 

typically 3 years) should not be 

expected to have implemented the same 

controls prior to an event as an air 

agency that has been aware that events 

of a certain type occur with regularity 

and cause NAAQS exceedances or 

violations. The EPA anticipates that 

nonattainment (or maintenance) areas 

have technical information needed to 

understand those measures that 

constitute reasonable control of 

anthropogenic sources in their 

jurisdiction for recurring events of the 

type(s) that cause or contribute to 

nonattainment (or that did previously). 

In contrast, the EPA generally does not 

expect areas identified as attainment, 

unclassifiable/attainment or 

unclassifiable for a NAAQS to have the 

same understanding or to have adopted 

the same level of event-relevant controls 

as areas that are nonattainment (or 

maintenance) for the same NAAQS. 

Also, if an area has been recently 

designated to nonattainment but is still 

developing its SIP and has not yet 

reached a deadline to implement 

controls, the EPA expects the level of 

controls that is appropriate for that 

planning stage.44 Regardless of 

attainment status or natural/

anthropogenic source contribution, each 

demonstration package should address 

the question of reasonable controls 

within the not reasonably controllable 

or preventable portion of the 

demonstration. 

The not reasonably controllable or 

preventable criterion is a source of 

particular complexity when an event 

occurs outside the jurisdiction of the 

state that is requesting that data be 

excluded. The area outside a state’s 

jurisdiction may be in an area of Indian 

country, in another state, or in a foreign 

country. For these cases, the air agency 

requesting data exclusion, and other 

government authorities in the state, 

generally do not have regulatory 

authority over those who might have 

been able to prevent or control the 

event. Therefore, the EPA believes that 

event-related emissions that originate 

outside of the boundaries of the state 

within which the concentration at issue 

was monitored are generally ‘‘not 

reasonably controllable or preventable’’ 

even if no party has made any effort to 

control or prevent them. To date, we 

have advised air agencies that an 

exceptional events demonstration for 

such a case must nevertheless explicitly 

address the question of reasonable 

efforts towards prevention and control. 

For these situations, we have suggested 

template language to the effect that 

satisfying the not reasonably 

controllable or preventable element 

could consist of an air agency stating 

that because the event occurred outside 

of its jurisdiction, the not reasonably 

controllable or preventable criterion is 

satisfied. 

Because the reasonableness of 

controls for event-related emissions is 

case-specific, the EPA has not issued 

guidance that particular controls are 

reasonable or are not reasonable. The 

Interim High Winds Guidance 

document indicates sources of 

information that identify measures that 

an air agency and the EPA should 

consider. In that guidance, we said that 

if the EPA has approved a SIP revision 

to windblown dust controls within the 

past 3 years of the event, then an air 

agency can rely on the SIP-approved 

controls to satisfy a portion of a 

‘‘prospective controls analysis.’’ 45 By 

this, we meant that we would agree with 

the air agency that for any high wind 

dust events in the next 3 years, 

implementation of the controls in the 

SIP would be sufficient to establish that 

those events are not reasonably 

controllable. In our discussions during 

the development of these proposed 

revisions of the Exceptional Events 

Rule, air agencies have urged us to give 

more deference to relevant controls in 

the EPA-approved SIPs. Some air 

agencies have recommended that we 

always accept that the controls in the 

approved SIP are all that should have 

reasonably been in place at the time of 

the event (and/or that we accept no 

controls if there are no controls in the 

approved SIP). We understand at least 

some of those recommending this 

approach to mean it to apply both to 

nonattainment and maintenance areas 

that have approved attainment or 

maintenance plans and to areas whose 

SIPs have been approved only with 

respect to less specific infrastructure SIP 

requirements. 

b. Proposed Changes 

The EPA generally plans to continue 

its past interpretations with respect to 

the ‘‘not reasonably controllable or 

preventable’’ criterion. We propose to 

codify in regulatory language key 

aspects of these past interpretations to 

reduce uncertainty for air agencies and 

other parties. Specifically, we are 

proposing changes to the text of the 

Exceptional Events Rule to indicate that: 

• The not reasonably controllable or 

preventable criterion has two prongs, 

prevention and control. An air agency 

must demonstrate that an event was 

both not reasonably preventable and not 

reasonably controllable. 

• An event is not reasonably 

preventable if reasonable measures to 

prevent the event were applied at the 

time of the event. 

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46Under the CAA, the EPA generally considers a 

state (not including areas of Indian country) to be 

a single responsible actor. Accordingly, neither the 

EPA nor the 2007 Exceptional Events Rule provides 

special considerations for intrastate scenarios when 

an event in one county affects air quality in another 

county in the same state, assuming that the event 

occurs on land subject to state authority (versus 

tribal government authority). The EPA expects 

controls appropriate for the designation status of 

the county (or portion of the county) in which the 

emissions originate. 

47An event with a significant contribution from 

anthropogenically-influenced emissions sources 

that have not themselves been reasonably 

controlled cannot be considered a natural event 

subject to this provision. 

48By ‘‘remote’’ events, we mean events that occur 

in locations where the application of control 

measures is either cost-prohibitive or presents 

unreasonable risks to worker safety because of the 

distance of the source from logistical staging areas, 

or absence of roads and/or location on rough or 

steep terrain. By ‘‘large-scale’’ we mean a regional 

event that involves a significant expanse of land 

and/or affects all/most monitors in an area. ‘‘Highenergy’’ means an event involving levels of kinetic 

energy that feasible human efforts cannot absorb or 

redirect. Example large-scale and/or high-energy 

events might include seismic events, hurricanes, 

tornadoes and ‘‘haboobs’’ in the southwest where 

sustained wind speeds can exceed 40 mph and 

generate walls of dust several miles wide and more 

than a mile high. 

49When addressing reasonable controls for the 

incineration of debris associated with the recovery 

period following a natural disaster, air agencies may 

want to consider, as appropriate, the basic smoke 

management practices discussed in more detail in 

section V.F.2.d of this proposal. 

• An event is not reasonably 

controllable if reasonable measures to 

control the impact of the event on air 

quality were applied at the time of the 

event. 

• The reasonableness of measures is 

case-specific and is to be evaluated in 

light of information available at the time 

of the event. 

• No case-specific justification is 

needed to support the ‘‘not reasonably 

controllable or preventable’’ criterion 

for emissions-generating activity that 

occurs outside of the boundaries of the 

state (or tribal lands) within which the 

concentration at issue was monitored.46

With regard to the last of these 

proposed rule text changes, the EPA 

maintains that it is not reasonable to 

expect the downwind air agency (i.e., 

the state or tribe submitting the 

demonstration) to have required or 

persuaded the upwind foreign country, 

state or tribe to have implemented 

controls on sources sufficient to limit 

event-related air concentrations in the 

downwind state or tribal lands, nor does 

the EPA believe that Congress intended 

to deny the downwind state or tribe 

relief in the form of data exclusion 

within the context of the Exceptional 

Events Rule. Submitting (downwind) air 

agencies will, however, need to assess 

potential contribution from local and 

state-wide sources and submit evidence 

and statements supporting the other 

exceptional events criteria (i.e., clear 

causal relationship and human activity 

unlikely to recur or a natural event). 

In addition to proposing to codify the 

five current interpretations listed above, 

with regard to this criterion, we are 

proposing and requesting comments on 

changes from our current interpretations 

and changes in the rule text that are 

explained below in more detail. 

Natural Events and Natural Sources. 

The not reasonably controllable or 

preventable criterion applies to natural 

events, including natural sources and 

any contributing anthropogenic sources 

and activities.47 The EPA proposes, as 

guidance, that to satisfy the not 

reasonably controllable or preventable 

criterion for natural events, air agencies 

should identify in their demonstration 

the origin and evolution of the natural 

event, describe any local efforts to 

prevent the event and explain how any 

efforts to limit the duration, intensity or 

extent (and thus the emissions) from the 

event were reasonable. 

Large-scale natural landscapes, such 

as deserts, are one type of natural source 

from which emissions can originate and 

contribute to event-related emissions. 

We propose, as guidance for these types 

of natural sources, that air agencies 

would not need to have implemented 

any controls for windblown dust from 

never-disturbed, large-scale natural 

landscapes. If such a landscape is the 

only source of wind-blown dust, the 

EPA would consider the event in this 

scenario to be not reasonably 

controllable or preventable regardless of 

the past frequency of similar events. 

Other such cases include volcanic 

releases of SO2 and stratospheric ozone 

intrusions. In these cases, the air agency 

should affirmatively state that the not 

reasonably controllable or preventable 

criterion is satisfied by the fact that the 

natural event was of a character that 

could not have been prevented or 

controlled and that there were no 

contributions of event-related emissions 

from anthropogenic sources. 

We also propose, as guidance, for 

events other than high wind dust events 

and wildfire on wildland (for which the 

proposed rule revisions take an 

equivalent approach), to consider the 

direct effects of remote, large-scale, 

high-energy and/or sudden natural 

events to generally be not reasonable to 

prevent or control.48 This concept, as it 

relates specifically to proposed rule 

changes addressing high wind dust 

events, is discussed in more detail in 

section V.F.4. Section V.F.2.c discusses 

how the same concept relates to 

proposed rule changes addressing the 

‘‘not reasonably controllable or 

preventable’’ criterion for wildfire on 

wildland. 

There may, however, be natural 

events or activities associated with the 

clean-up following a natural event 

where some type of control effort would 

be reasonable. For example, while an 

initial volcanic dust event may not be 

controllable or preventable, it may be 

reasonable to implement a street 

cleaning program to control the 

subsequent re-entrainment of dust 

deposited on roadways after the 

eruption. Also, air quality impacts 

during the active period of a weather 

disaster event generally cannot be 

prevented or controlled and it would be 

reasonable for no effort to have been 

made to do so. However, air agencies 

should apply reasonable controls, as 

applicable, in the recovery period after 

the event (e.g., during the removal or 

incineration 49 of debris following a 

hurricane or tornado). There may also 

be smaller scale natural sources and 

events for which some control actions 

would be reasonable. We request 

comment on additional general and 

event-specific recommendations that 

would be consistent with the CAA and 

the revised Exceptional Events Rule 

regarding natural events and sources 

that the EPA could include in guidance 

to provide more certainty and allow air 

agencies to efficiently prepare 

demonstrations. 

The Role of Past Occurrences. When 

assessing the controls that should 

reasonably have been in place in light 

of information available at the time of 

the event, both the air agency and the 

EPA should consider the then-known 

frequency and severity of recurring 

events of the same type as both 

characteristics should affect decisions 

regarding those measures that constitute 

reasonable controls. A measure may not 

be reasonable when the event type and 

severity was known to occur 

infrequently, but such measures may be 

reasonable if that event type and 

severity occurs frequently, because there 

are greater (more frequent) benefits to 

balance against the cost of 

implementation. If the event was the 

area’s first experienced event of this 

type, then the submitting air agency 

would note that fact. The air agency 

could then rely on measures in the SIP 

and other controls in place at the time 

of the event, if any, to satisfy the not 

reasonably controllable or preventable 

criterion because, at the time of the 

event, the air agency did not have a 

basis for understanding the possible 

need for better controls for this type of 

event. If, however, the area has 

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50Because a state is considered a single 

responsible entity for purposes of SIP development 

and implementation, there may be state 

governmental authorities whose knowledge of the 

need for an availability of controls at the time of 

the event is also relevant, particularly for in-state 

sources outside the geographic area covered by the 

air agency’s regulatory authority. 

51Marginal ozone nonattainment areas are 

exceptions because they are not required to submit 

attainment demonstrations. 

52A request for data exclusion must also show 

that the event was not a result of noncompliance 

with any existing state or local laws or rules that 

have not been incorporated into the SIP. 

previously experienced events of the 

type that are the focus of the 

demonstration, then the air agency has 

a basis for understanding the possible 

need for better controls.50

We note that this consideration of 

past recurrence when determining what 

controls would have been sufficient to 

satisfy the not reasonably controllable or 

preventable criterion is not the same as 

the consideration of the likelihood of 

future recurrence for the purposes of the 

unlikely to recur criterion. Past 

experiences are a general guide to future 

likelihood but the EPA recognizes that 

future recurrence may follow a different 

pattern and may necessitate new 

measures to prevent events of a given 

type. 

The Role of the EPA-approved SIP as 

the Benchmark for Reasonable 

Measures—In General. As already 

mentioned, some air agencies have 

urged us to defer to relevant controls in 

EPA-approved SIPs as always sufficient 

to satisfy the not reasonably controllable 

or preventable criterion. The EPA could 

conceivably give ‘‘deference’’ to several 

different types of SIPs. CAA section 

110(a)(1) and 110(a)(2) requires every 

state to develop and submit to the EPA 

an ‘‘infrastructure SIP’’ for each NAAQS 

within 3 years of the promulgation of a 

new or revised NAAQS. Infrastructure 

SIPs address a number of CAA 

requirements, including the requirement 

to contain emission limits to ensure 

attainment and maintenance of a 

NAAQS. However, under the EPA’s 

interpretation of these CAA sections, 

infrastructure SIPs are not required to 

include attainment or maintenance 

demonstrations and are not required to 

demonstrate that the controls on 

particular sources are ‘‘reasonable.’’ 

Thus, in general, EPA-approved 

infrastructure SIPs do not necessarily 

constitute a robust assessment of those 

controls that are reasonable to have in 

place to address air quality impacts 

from particular types of events that may 

become the focus of exceptional events 

demonstrations. 

In contrast, states with areas 

designated as nonattainment for a 

NAAQS must prepare attainment plan 

SIPs, which must include an attainment 

demonstration and reasonably available 

control measures (RACM), among other 

requirements.51 Attainment plans for 

serious PM10 or PM2.5 areas must also 

contain best available control measures 

(BACM). When a nonattainment area 

reaches attainment, it may be 

redesignated to maintenance area status 

if it has implemented all applicable 

nonattainment area requirements and 

obtains the EPA’s approval for a 

maintenance plan for a 10-year period. 

Thus, in both maintenance and 

nonattainment areas with approved 

attainment plan SIPs, the air agency and 

the EPA will have considered what 

controls are necessary and reasonable to 

provide for attainment, based on 

information available at the time of plan 

development and approval. 

Taken to its furthest limit, the 

deference recommended by some air 

agencies would mean that the EPA 

would always approve a state air agency 

assertion that the control measures in a 

SIP that has received full approval by 

the EPA as meeting currently applicable 

requirements related to the eventrelevant NAAQS constituted the 

reasonable set of controls for the event 

in question and thus the event was not 

reasonably controllable or preventable. 

We believe that this degree of deference 

could, in some cases, result in the 

approval for data exclusion contrary to 

CAA requirements. Deference to the 

measures in an EPA-approved SIP is not 

always appropriate because EPA 

approval at some time in the past does 

not necessarily mean that (1) the control 

measures in a current SIP address all 

event-relevant sources of current 

importance, (2) the control measures 

that were considered by the air agency 

and the EPA at the time the EPA last 

approved the SIP are the same measures 

that were known and available at the 

time of a more recent event, or (3) that 

conditions in the area have not changed 

in a way that would affect the 

approvability of the same SIP if it newly 

needed the EPA’s approval. However, 

we believe that it may be consistent 

with the CAA to revise the Exceptional 

Events Rule to identify the conditions 

under which the EPA and air agencies 

can rely upon measures in an EPAapproved SIP to satisfy the not 

reasonably controllable or preventable 

criterion. To clarify these scenarios, the 

EPA is proposing, and discusses below, 

various combinations of rule provisions 

and guidance for areas of different 

designation status. 

The best time for air agency and 

federal officials to exchange both 

technical information and views on the 

balance between costs and benefits 

related to the sufficiency of reasonable 

controls is before an event happens. To 

avoid the EPA’s retrospective second 

guessing of an air agency’s 

consideration of information available 

to it before an event occurs, we have 

identified and described below several 

proposals, which would apply when an 

affected air agency and the EPA have 

not reached a mutual understanding 

regarding reasonable controls prior to an 

event. 

The Role of the EPA-approved SIP in 

Nonattainment and Maintenance Areas. 

To satisfy the not reasonably 

controllable or preventable criterion for 

nonattainment or maintenance areas, 

the EPA proposes to establish by rule a 

non-rebuttable presumption that, during 

a 5-year window (or, alternatively 

another appropriate timeframe) 

following approval of an attainment 

plan or maintenance plan SIP during 

which no subsequent new obligation for 

the air agency to revise the SIP has 

arisen, the control measures included in 

the SIP that are specific to the relevant 

pollutant, sources and event type are 

sufficient for purposes of the not 

reasonably controllable or preventable 

criterion.52 The EPA believes that 5 

years is an appropriate timeframe upon 

which to rely for SIP deference for 

several reasons. As noted earlier, 

deference to the measures in an EPAapproved SIP is not always appropriate 

because EPA approval at some time in 

the past does not necessarily mean that 

(1) the control measures in a current SIP 

address all event-relevant sources of 

current importance, (2) the control 

measures that were considered by the 

air agency and the EPA at the time the 

EPA last approved the SIP are the same 

measures that were known and available 

at the time of a more recent event, or (3) 

that conditions in the area have not 

changed in a way that would affect the 

approvability of the same SIP if it newly 

needed the EPA’s approval. A 5-year 

window provides a reasonable 

timeframe under which to evaluate the 

above-identified potential changes. 

Additionally, as we discuss in section 

V.E.3 of this proposal, we encourage the 

use of 5 years of data when developing 

analyses to support the clear causal 

relationship criterion because we 

believe that 5 years of ambient air data 

represent the range of ‘‘normal’’ air 

quality. 

The EPA would evaluate the not 

reasonably controllable or preventable 

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53The NAAQS not mentioned here have rarely 

presented exceptional events issues. 

criterion on a case-by-case basis for 

those demonstrations involving an event 

affecting a nonattainment or 

maintenance area with a SIP last 

approved more than 5 years prior to the 

submittal of the subject demonstration. 

Because the issue of deference to a SIP 

is most often applicable for high wind 

events, section V.F.4 further illustrates 

this proposal. 

The Role of the EPA-approved SIP in 

Attainment, Unclassifiable/Attainment 

or Unclassifiable Areas. Attainment, 

unclassifiable/attainment and 

unclassifiable areas should have EPAapproved infrastructure SIPs in place 

that the EPA approved within a few 

years following the promulgation of a 

new or revised NAAQS. Infrastructure 

SIPs for the 1987 PM10 NAAQS are 

likely to be many years old, while 

infrastructure SIPs for ozone, PM2.5, 1- 

hour SO2 and 1-hour NO2 have been 

approved more recently.53 In addition to 

the EPA-approved infrastructure SIPs, 

these areas may have in place other 

relevant state or local laws and rules, a 

natural events action plan, an SMP and/ 

or other programs based on voluntary 

participation. 

Because the development and the 

EPA’s review of infrastructure SIPs 

typically do not involve a robust 

assessment of needed measures to 

prevent or control the effects of 

particular types of events and because 

even in the absence of a pending SIP 

call the SIP may not reasonably address 

events of importance, the EPA does not 

propose to establish in rule text or in 

guidance any form of general deference 

to the SIP in attainment, unclassifiable/ 

attainment or unclassifiable areas. The 

EPA will review exceptional events 

demonstrations on a case-by-case basis, 

applying the Exceptional Events Rule 

and the EPA’s guidance. A case-by-case 

review may conclude that the measures 

that were in place under the SIP, a 

natural events action plan, an SMP or 

other state or local programs were 

sufficient or insufficient to satisfy the 

not reasonably controllable or 

preventable criterion. 

If the air agency has historically 

documented recurring events, then the 

EPA would expect the submitting air 

agency to identify any anthropogenic 

emission sources that contribute to the 

event emissions and specifically 

document the controls that were in 

place for these sources at the time of the 

event. It is possible that the air agency 

may not be able to make a sufficient 

showing for the not reasonably 

controllable or preventable criterion if it 

has not implemented reasonable 

controls for anthropogenic sources that 

contribute to recurring events. In this 

case, the EPA Regional office may not be 

able to concur with an air agency’s 

request for data exclusion. If the air 

agency has no such control plans and 

has no history of recurring events, then 

the air agency would note this in the not 

reasonably controllable or preventable 

portion of its demonstration and would 

rely on the fact that at the time of the 

event, the air agency did not have a 

basis for understanding the possible 

need for better reasonable controls. 

Note that in section V.G.7 of this 

proposed action, ‘‘Timing of the EPA’s 

Review of Submitted Demonstrations,’’ 

the EPA proposes to work with air 

agencies to prioritize exceptional events 

determinations that affect near-term 

regulatory decisions. In an attainment, 

unclassifiable/attainment or 

unclassifiable areas, the only likely nondiscretionary regulatory action would be 

an initial designation under a new or 

revised NAAQS. Possible discretionary 

actions include a redesignation under a 

long-standing NAAQS or a SIP call. 

Under its planned prioritization 

approach, the EPA would not expect to 

act on demonstrations for events in an 

attainment, unclassifiable/attainment or 

unclassifiable areas unless the area 

could become nonattainment under a 

new or revised NAAQS, the area is the 

subject of a planned EPA discretionary 

redesignation for a long-standing 

NAAQS where the approval of a 

demonstration affects the basis for the 

redesignation, or the area becomes the 

subject of another EPA discretionary 

action (e.g., a SIP call at the initiative of 

the EPA or in response to a petition) 

that hinges on the approval of a 

demonstration. 

The Role of Prior Communications 

with the EPA in Case-Specific 

Assessments for Not Reasonably 

Controllable or Preventable. As already 

stated, the EPA believes that an air 

agency must include in its exceptional 

events demonstration a retrospective 

assessment of whether an event was not 

reasonably controllable or preventable. 

The air agency should base this 

assessment on information available to 

relevant authorities (e.g., the air agency 

submitting the demonstration and 

potentially other government authorities 

in the state, for example an upwind air 

quality control district where the event 

occurred) that could have implemented 

measures to prevent or control the event 

and its effects prior to and during the 

event. We are proposing to adopt the 

following approach as guidance to air 

agencies submitting demonstrations that 

will be subject to a case-specific 

assessment (i.e., in situations other than 

when deferring to a nonattainment or 

maintenance plan SIP). 

To satisfy the not reasonably 

controllable or preventable criterion in 

a case-specific assessment, the EPA 

proposes to consider communications 

between the EPA and the air agency 

when assessing ‘‘reasonableness’’ as part 

of assessing the technical information 

available to the air agency at the time 

the event occurred and what should 

reasonably have been in place at the 

time of the event for anthropogenic 

emission sources that contribute to the 

event emissions. It is not the EPA’s 

intent to retroactively apply its current 

judgments about the reasonableness of 

controls for past events. However, it 

would also be inappropriate for an air 

agency to fail to respond to the EPA’s 

recommendations prior to an event and 

then claim later in an event 

demonstration that it was unaware of a 

reasonable control issue. 

The EPA recognizes that regulations 

and an area’s planning status are often 

evolving and changing. The EPA may 

have recently promulgated new or 

revised federal rules requiring controls 

on particular sources or promulgated a 

new or revised nationally applicable 

standard that will ultimately result in an 

air agency’s adoption of new control 

measures. The planning process to 

implement these new standards (e.g., 

the SIP or maintenance plan approval 

process) can be lengthy, sometimes 

spanning several years and involving 

multiple rounds of formal and informal 

communications between the affected 

air agency and the EPA regarding the 

appropriateness and completeness of 

planning elements. In some cases, 

discussion of issues regarding 

appropriate controls, including what 

controls would constitute ‘‘reasonable’’ 

controls for exceptional events 

purposes, are part of this iterative 

communications process. The EPA 

solicits comment on what form of 

communication (short of a SIP call) 

would be most effective in conveying 

the EPA’s views to the affected air 

agency and whether this approach 

would be most appropriately addressed 

through guidance or regulatory text. 

Prospective Agreement on 

Assessments of Not Reasonably 

Controllable or Preventable. In the 

Interim High Winds Guidance, the EPA 

suggested that an air agency could 

develop an assessment showing that the 

controls in place for a particular type of 

event, or a planned enhancement of 

those controls, were sufficient to meet 

the not reasonably controllable or 

preventable criterion, and then obtain 

the EPA’s review and concurrence with 

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54The EPA generally expects evidence that the 

controls determined to be reasonable, if any, were 

effectively implemented and appropriately 

enforced. This assessment of local sources should 

include a review and description of any known 

nearby facility upsets or malfunctions that could 

have resulted in emissions of the relevant 

pollutant(s) that influenced the monitored 

measurements on the day(s) of the claimed events. 

In the case of a high wind dust event, for example, 

for the identified potentially contributing local and 

upwind sources, the analysis should explain how 

significant dust emissions occurred despite having 

reasonable controls in place (e.g., that controls were 

overwhelmed by high wind), if appropriate. 55 72 FR 13569 (March 22, 2007). 

56For purposes of summarizing example clear 

causal relationship analyses in one place, the EPA 

has included an entry for the comparison to 

historical concentrations showing in Table 1. The 

EPA notes that although the Interim High Winds 

Guidance and the Interim Q&A document discussed 

the comparison to historical concentrations 

showing, neither of these guidance documents 

presented this showing as part of the clear causal 

relationship. See specifically Interim Guidance on 

the Preparation of Demonstrations in Support of 

Requests to Exclude Ambient Air Quality Data 

Affected by High Winds Under the Exceptional 

Events Rule. U.S. EPA. May 2013. Available at 

http://www2.epa.gov/sites/production/files/2015- 

05/documents/exceptevents_highwinds_guide_

130510.pdf and Interim Exceptional Events Rule 

Frequently Asked Questions. U.S. EPA. May 2013. 

Available at http://www2.epa.gov/sites/production/ 

files/2015-05/documents/eer_qa_doc_5-10-13_

r3.pdf. 

the assessment prior to more events of 

that type occurring. This prospective 

approach would reduce disagreements 

that might otherwise occur over later 

retrospective assessments. To date, most 

air agencies that face recurring event 

issues have not pursued this option, but 

the EPA will work with any air agency 

expressing an interest in pursuing this 

approach. 

Summary of Requests for Comments 

Regarding Not Reasonably Controllable 

or Preventable. The EPA solicits 

comment on the following clarifications 

to the ‘‘not reasonably controllable or 

preventable’’ criterion: 

• The EPA solicits comment on 

recommending as guidance that when 

addressing the ‘‘not reasonably 

controllable or preventable’’ criterion 

within an exceptional events 

demonstration, air agencies should: (1) 

Identify the natural and anthropogenic 

sources of emissions causing and 

contributing to the event emissions, 

including the contribution from local 

sources, (2) identify the relevant SIP or 

other enforceable control measures in 

place for these sources and the 

implementation status of these controls, 

and (3) provide evidence of effective 

implementation and enforcement of 

reasonable controls, if applicable.54 In 

identifying natural and anthropogenic 

sources, the air agency should assess 

both potentially contributing local/instate and upwind sources. We also 

request comment on whether we should 

revise the rule text to require these 

elements in a demonstration. 

• The EPA proposes to codify rule 

language to specify that no case-specific 

justification is needed to support the 

‘‘not reasonably controllable or 

preventable’’ criterion for emissionsgenerating activity that occurs outside of 

the boundaries of the state (or tribal 

lands) within which the concentration 

at issue was monitored. 

• The EPA solicits comment on 

specific guidance or rule requirements 

regarding what constitutes reasonable 

control of particular natural events and 

sources. 

• The EPA proposes to codify in rule 

language that, provided the air agency is 

not under an obligation to revise the 

SIP, the EPA would consider (i.e., give 

deference to) enforceable control 

measures implemented in accordance 

with a state implementation plan, 

approved by the EPA within 5 years of 

the date of a demonstration submittal, 

that address the event-related pollutant 

and all sources necessary to fulfill the 

requirements of the CAA for the SIP to 

be reasonable controls with respect to 

all anthropogenic sources that have or 

may have contributed to event-related 

emissions. 

• The EPA proposes to codify in rule 

language the time period for such 

deference to be 5 years from the date of 

the SIP approval measured to the date 

of an event at issue, but is taking 

comment on whether and what other 

timeframes might be appropriate. To the 

extent an alternative timeframe might be 

appropriate, comments should explain 

how it would address the criteria 

provided above in support of the 5-year 

timeframe. 

• The EPA proposes to consider 

communications and planning status 

when assessing the status of reasonable 

controls and proposes to do this through 

guidance. The EPA solicits comment on 

methods to definitively identify the 

status of communications and planning 

efforts (e.g., formal correspondence or 

other documentation, timelines for 

responding) and whether this approach 

would be more appropriately addressed 

through rule language. 

3. Clear Causal Relationship Supported 

by a Comparison to Historical 

Concentration Data 

a. Current Situation 

The CAA at section 319(b)(3)(B)(ii) 

requires that ‘‘a clear causal relationship 

must exist between the measured 

exceedances of a national ambient air 

quality standard and the exceptional 

event to demonstrate that the 

exceptional event caused a specific air 

pollution concentration at a particular 

air quality monitoring location.’’ The 

clear causal relationship criterion 

establishes causality between the event 

and a measured exceedance or violation 

of a NAAQS. As stated in the preamble 

to the 2007 Exceptional Events Rule, 

given the directive in CAA section 

319(b)(3)(B)(ii), it would be 

unreasonable to exclude data affected by 

an exceptional event simply because of 

a trivial contribution of an event to air 

quality.55 The EPA does, however, 

recognize that distinguishing trivial 

contributions from more significant 

contributions to an exceedance may be 

difficult. As with the other exceptional 

events criteria, the EPA has used a 

weight of evidence approach when 

reviewing analyses to support a causal 

relationship between an event and a 

monitored exceedance. 

Showing that an event and elevated 

pollutant concentrations occurred 

simultaneously may not establish 

causality. The clear causal relationship 

section of an exceptional events 

demonstration should include analyses 

showing that the event occurred and 

that emissions of the pollutant of 

interest resulting from the event were 

transported to the monitor(s) recording 

the elevated concentration 

measurement(s). The example analyses 

to support the clear causal relationship 

criterion, shown in Table 1 and first 

summarized in the EPA’s Interim 

Exceptional Events Implementation 

Guidance, are generally appropriate 

analyses for most event types.56 The 

EPA does not expect air agencies to 

include all of the evidence and analyses 

identified in the table below, but rather 

to use available information to build a 

weight of evidence showing. The EPA 

may accept limited analyses (e.g., a 

comparison to historical concentrations 

in combination with one or two 

additional analyses from Table 1) for 

areas whose monitored ambient air 

concentrations are generally well below 

the NAAQS on non-event days. 

Additional analyses are beneficial if 

they establish a different facet of the 

event and/or if they are used in 

combination with other analyses with 

limited data. For example, the EPA 

expects that areas prone to frequent 

elevated ozone (or other pollutant) 

concentrations, such as nonattainment 

areas, to have more sophisticated air 

quality prediction tools. We would 

expect these areas could use these tools 

when supporting an exceptional events 

demonstration and developing analyses 

to support a clear causal relationship. 

Additionally, photochemical or 

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regression modeling analyses may be 

beneficial in situations where the 

causality between the event and a 

measured exceedance of a NAAQS is 

not clearly established with evidence 

and analyses identified in Table 1. For 

example, if a fire occurs during the 

normal high ozone season and the ozone 

level associated with the fire is in the 

range of otherwise-occurring ozone 

levels and/or only slightly above the 

ozone NAAQS, the causal relationship 

between the fire and the exceedance or 

violation may not be clear. In such a 

situation, modeling may produce a 

specific estimate of the ozone 

contribution from the fire. Air agencies 

should discuss with their EPA Regional 

office those types of analyses that may 

be adequate to satisfy the weight of 

evidence requirement in individual 

exceptional events demonstrations. 

TABLE 1—EXAMPLE CLEAR CAUSAL RELATIONSHIP EVIDENCE AND ANALYSES

Example of clear causal relationship evidence Types of analyses/information to support the evidence 

Comparison to Historical Concentrations ................................................. Analyses and statistics showing how the observed event concentration 

compares to the distribution or time series of historical concentrations of the same pollutant. 

Occurrence and geographic extent of the event ...................................... Special weather statements, advisories, news reports, nearby visibility 

readings, measurements from regulatory and non-regulatory (e.g., 

special purpose, emergency) monitoring stations throughout the affected area, satellite imagery. 

Transport of emissions related to the event in the direction of the monitor(s) where the measurements were recorded.Wind direction data showing that emissions from sources identified as 

part of the ‘‘not reasonably controllable or preventable’’ demonstration were upwind of the monitor(s) in question, satellite imagery, 

monitoring data showing elevated concentrations of other pollutants 

expected to be in the event plume. 

Spatial relationship between the event, sources, transport of emissions 

and recorded concentrations.

Map showing likely source area, wind speed/direction and pollutant 

concentrations for affected area during the time of the event, trajectory analyses. 

Temporal relationship between the event and elevated pollutant concentrations at the monitor in question.Hourly time series showing pollutant concentrations at the monitor in 

question in combination with wind speed/direction data in the area 

where the pollutant originated/was entrained or transported. 

Chemical composition and/or size distribution (for PM2.5 to PM10) of 

measured pollution that links the pollution at the monitor(s) with particular sources or phenomenon.

Chemical speciation data from the monitored exceedance(s) and 

sources, size distribution data. 

Comparison of event-affected day(s) to specific non-event days ............ Comparison of concentration and meteorology to days preceding and 

following the event, comparison to high concentration days in the 

same season (if any) without events, comparison to other event days 

without elevated concentrations (if any), comparison of chemical speciation data. 

As explained in additional detail in 

the EPA’s Interim Exceptional Events 

Implementation Guidance, what has 

previously been called the ‘‘historical 

fluctuations’’ showing (i.e., now referred 

to as the comparison to historical 

concentrations) consists of analyses and 

statistics showing how the observed 

event-affected concentration compares 

to the distribution or time series of 

historical concentrations of the same 

pollutant. 

A demonstration may be less 

compelling if some evidence is 

inconsistent with the description of how 

the event caused the exceedance. For 

example, if an air agency describes an 

event as a regional dust storm or 

wildfire, then the EPA anticipates that 

most or all monitors within the same 

regional scale to be similarly affected by 

the event. That is, the EPA expects that 

the demonstration elements and factors 

(e.g., clear causal relationship, 

reasonable controls, meteorology, wind 

speeds) would also support the case for 

a regional event. Comparison of 

concentrations and conditions at other 

monitors could thus be very important 

for the demonstration of a clear causal 

relationship. Alternatively, eliminating 

plausible non-event causes may also 

support a causal relationship between 

the event and the elevated 

concentration. 

The EPA has been recommending that 

the clear causal relationship section of 

the demonstration should conclude 

with this type of statement: ‘‘On [day/ 

time] an [event type] occurred which 

generated pollutant X or its precursors 

resulting in elevated concentrations at 

[monitoring location(s)]. The monitored 

[pollutant] concentrations of [ZZ] were 

[describe the comparison to historical 

concentrations including the percentile 

rank over an annual (seasonal) basis]. 

Meteorological conditions were not 

consistent with historically high 

concentrations, etc.’’ and ‘‘Analyses X, 

Y and Z support Agency A’s position 

that the event affected air quality in 

such a way that there exists a clear 

causal relationship between the specific 

event and the monitored exceedance or 

violation and thus satisfies the clear 

causal relationship criterion.’’ 

b. Proposed Changes 

As previously noted, the EPA is 

proposing to revise the 2007 

Exceptional Events Rule text as follows: 

• To move the ‘‘clear causal 

relationship’’ element into the list of 

criteria that explicitly must be met for 

data to be excluded 

• To subsume the ‘‘affects air quality’’ 

element into the ‘‘clear causal 

relationship’’ element 

• To remove the term ‘‘historical 

fluctuations’’ and replace it with text 

referring to a comparison to historical 

concentrations 

• To clarify that the comparison to 

historical concentrations is not a fact 

that must be proven 

• To clearly identify the types of 

analyses that are necessary and 

sufficient in a demonstration to 

address the comparison to historical 

concentrations 

• To remove the ‘‘but for’’ element (as 

discussed in section V.B.2) 

Additionally, the EPA proposes to 

reiterate in guidance the example 

analyses to support the clear causal 

relationship criterion, shown in Table 1 

above, and first summarized in the 

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EPA’s Interim Exceptional Events 

Implementation Guidance. As noted 

previously, the EPA does not expect air 

agencies to include all of the evidence 

and analyses identified in Table 2 

below, but rather to use available 

information to build a weight of 

evidence showing. 

The EPA’s rationale for proposing the 

previously identified changes to the 

clear causal relationship criterion is 

presented in section V.B. The remainder 

of this section focuses on the types of 

analyses that an air agency must provide 

in its demonstration to make the 

comparison to historical concentrations. 

As noted in the Current Situation 

section, the EPA has included an entry 

in Table 1 for the comparison to 

historical concentrations showing. 

The comparison to historical 

concentrations, referred to as the 

‘‘historical fluctuations’’ showing in the 

2007 Exceptional Events Rule and the 

Interim Exceptional Events 

Implementation Guidance, is a 

requirement in the 2007 Exceptional 

Events Rule but it is not a statutory 

requirement. The EPA’s intent with this 

regulatory element was to require air 

agencies to present event-influenced 

concentration data along with historical 

data and to quantify the difference, if 

any, between the event and the nonevent concentrations. Comparing eventinfluenced concentrations to historical 

concentrations bolsters the weight of 

evidence within the clear causal 

relationship determination. The EPA 

proposes to re-phrase and incorporate 

the current regulatory requirement at 40 

CFR 50.14(c)(3)(iv)(C), which requires 

that a demonstration to justify data 

exclusion provide evidence that ‘‘[t]he 

event is associated with a measured 

concentration in excess of normal 

historical fluctuations, including 

background,’’ within the ‘‘clear causal 

relationship’’ criterion. In using this 

approach, we propose to remove from 

the regulatory text the ‘‘in excess of 

normal historical fluctuations, including 

background’’ phrase and to subsume the 

concept of historical comparisons into 

what will effectively be a 

‘‘completeness’’ requirement within the 

‘‘clear causal relationship’’ criterion. As 

noted above, we specifically propose to 

remove the phrase ‘‘in excess of normal 

historical fluctuations, including 

background’’ as we believe this language 

is vague and provides no additional 

value to historical concentration 

comparisons. 

To aid the EPA’s review, reduce our 

need to request additional information 

from air agencies and facilitate our 

understanding of the air agency’s 

position, we are proposing rule text 

changes to indicate that an air agency 

submitting a demonstration must 

provide the following types of statistics, 

graphics and explanatory text regarding 

comparisons to past data. The rule 

change would also indicate that this 

information is sufficient to satisfy the 

rule’s requirement regarding the 

comparison to historical concentration 

data. Table 2 below identifies 

appropriate analyses and examples for 

comparing event-related concentrations 

to historical concentrations within the 

clear causal relationship criterion. 

TABLE 2—EVIDENCE AND ANALYSES FOR THE COMPARISON TO HISTORICAL CONCENTRATIONS

Historical concentration 

evidence Types of analyses/supporting information Required or optional? 

1. Comparison of concentrations on the 

claimed event day with 

past historical data.

Seasonal (appropriate if exceedances occur primarily in one season, but 

not in others).

Required seasonal and/or annual 

analysis (depending on which is 

more appropriate). 

• Use all available seasonal data over the previous 5 years (or more, if 

available).

• Discuss the seasonal nature of pollution for the location being evaluated.

• Present monthly maximums of the NAAQS relevant metric (e.g., maximum daily 8-hour average ozone or 1-hr SO2) vs monthly or other averaged daily data as this masks high values.

Annual (appropriate if exceedances are likely throughout the year).

• Use all available data over the previous 5 years (or more, if available).

Seasonal and Annual Analyses 

• Provide the data in the form relevant to the standard being considered for 

data exclusion.

• Label ‘‘high’’ data points as being associated with concurred exceptional 

events, suspected exceptional events, other unusual occurrences, or high 

pollution days due to normal emissions.

• Describe how emission control strategies have decreased pollutant concentrations over the 5-year window, if applicable.

• Include comparisons omitting known or suspected exceptional events 

points, if applicable.

• See examples at http://www.epa.gov/ttn/analysis/docs/IdeasforShowingEE

Evidence.ppt and Question 3 in the Interim Q&A document provides additional detail. a

2. Comparison of concentrations on the 

claimed event day with 

a narrower set of similar days.

• Include neighboring days at the same location (e.g., a time series of two 

to three weeks) and/or other days with similar meteorological conditions 

(possibly from other years) at the same or nearby locations with similar 

historical air quality along with a discussion of the meteorological conditions during the same timeframe. b

Optional analysis. 

• Use this comparison to demonstrate that the event caused higher concentrations than would be expected for given meteorological and/or local 

emissions conditions.

3. Percentile rank of concentration when compared to annual data. c• Provide the percentile rank of the event-day concentration relative to all 

measurement days over the previous 5 years to ensure statistical 

robustness and capture non-event variability over the appropriate seasons or number of years. d

Required analysis when comparison 

is made on an annual basis (see 

item #1). 

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57A malfunction at an industrial facility could be 

considered to be an exceptional event if it has not 

resulted in source noncompliance, which is 

statutorily excluded from consideration as an 

exceptional event, see CAA 319(b)(1)(b)(iii), and if 

it otherwise meets the requirements of the 

Exceptional Events Rule. 

58Of these noted event types, only fireworks are 

currently identified in the regulatory language at 40 

CFR 50.14. We are not proposing any revisions to 

the exclusion at 40 CFR 50.14(b)(2) for fireworks 

that are demonstrated to be significantly integral to 

traditional national, ethnic, or other cultural events. 

TABLE 2—EVIDENCE AND ANALYSES FOR THE COMPARISON TO HISTORICAL CONCENTRATIONS—Continued 

Historical concentration 

evidence Types of analyses/supporting information Required or optional? 

• Use the daily statistic (e.g., 24-hour average, maximum daily 8-hour average, or maximum 1-hour) appropriate for the form of the standard being 

considered for data exclusion.

4. Percentile rank of concentration relative to 

seasonal data. c

• Provide the percentile rank of the event-day concentration relative to all 

measurement days for the season (or appropriate alternative 3-month period) of the event over the previous 5 years.

Required analysis when comparison 

is made on a seasonal basis (see 

item #1). 

• Use the same time horizon as used for the percentile rank calculated relative to annual data, if appropriate.

a Interim Exceptional Events Rule Frequently Asked Questions. U.S. EPA. May 2013. Available at http://www2.epa.gov/sites/production/files/

2015-05/documents/eer_qa_doc_5-10-13_r3.pdf. b If an air agency compares the concentration on the claimed event day with days with similar meteorological conditions from other years, the 

agency should also verify and provide evidence that the area has not experienced significant changes in wind patterns, and that no significant 

sources in the area have had significant changes in their emissions of the pollutant of concern. cThe EPA does not intend to identify a particular historical percentile rank point in the seasonal or annual historical data that plays a critical 

role in the analysis or conclusion regarding the clear causal relationship. dSection 8.4.2.e of appendix W (proposed revisions at 80 FR 45374, July 29, 2015) recommends using 5 years of adequately representative 

meteorology data from the National Weather Service to ensure that worst-case meteorological conditions are represented. Similarly, for exceptional events purposes, the EPA believes that 5 years of ambient air data, whether seasonal or annual, better represent the range of ‘‘normal’’ air 

quality than do shorter periods. 

As with other evidence in an 

exceptional events demonstration 

submittal, the EPA will use a holistic 

weight of evidence approach in 

reviewing submitted demonstration 

packages and will consider the ‘‘clear 

causal relationship’’ information, 

including the comparison to historical 

concentrations showing, along with 

evidence supporting the other 

Exceptional Events Rule criteria. 

F. Treatment of Certain Events Under 

the Exceptional Events Rule 

As we stated in the preamble to the 

2007 Exceptional Events Rule, we 

maintain that air quality data affected by 

the following event types are among 

those that could meet the definition of 

an exceptional event and qualify for 

data exclusion provided all 

requirements of the rule are met: (1) 

Chemical spills and industrial 

accidents,57 (2) structural fires, (3) 

terrorist attacks, (4) volcanic and 

seismic activities, (5) natural disasters 

and associated cleanup and (6) 

fireworks.58 We are not proposing any 

changes to the definition or discussion 

of these event types. The AQS database 

contains a more detailed list of other 

similar events that may be identified for 

special consideration. The EPA will 

consider other types of events on a caseby-case basis. 

Based on our implementation 

experience, the following other 

potential exceptional events categories 

warrant additional discussion: 

Exceedances due to transported 

pollution, wildland fires including 

wildfires and prescribed fires, 

stratospheric ozone intrusions and high 

wind dust events. We discuss each of 

these event categories in the following 

sections. 

1. Exceedances Due to Transported 

Pollution 

a. Current Situation 

The 2007 Exceptional Events Rule 

implements one important CAA 

provision related to transported 

pollution. Certain events, national or 

international in origin and from natural 

or anthropogenic sources, may cause 

exceedances that are eligible for 

exclusion under the 2007 Exceptional 

Events Rule if an air agency satisfies the 

rule criteria. We discuss in this section 

our position regarding exceedances due 

to event-related transported pollution. 

We also clarify in part c of this section 

how the Exceptional Events Rule 

provisions currently relate to other CAA 

mechanisms that address or involve 

transported pollution. We are not 

proposing any changes to these 

relationships. 

The EPA believes that the Exceptional 

Events Rule will often be the most 

appropriate mechanism to use when 

addressing transported emissions from 

out-of-state natural events and/or events 

due to human activity that is unlikely to 

recur at a particular location, because 

the Exceptional Events Rule may be 

used during the initial area designations 

process and may make a difference 

between an attainment versus a 

nonattainment designation. It is 

important to note, however, that the 

transported natural emissions must be 

event-related (e.g., wildfires or 

stratospheric ozone intrusion) versus 

ongoing on a daily basis. 

b. Proposed Changes 

If an air agency determines that the 

Exceptional Events Rule is the most 

suitable approach to address 

contributions from transported 

emissions, then the air agency must 

consider the point of origin and the 

sources contributing to the exceedance 

or violation to determine how to address 

individual Exceptional Events Rule 

criteria, specifically the not reasonably 

controllable or preventable criterion and 

the human activity unlikely to recur or 

a natural event criterion. The analyses 

to satisfy the clear causal relationship 

criterion (which would subsume the 

CAA’s affects air quality criterion, if 

promulgated as proposed and discussed 

in section V.B) are largely independent 

of whether the point of origin and 

contributing sources are within the air 

agency’s jurisdiction. The EPA first 

addressed these concepts in its Interim 

Q&A document and now proposes to 

clarify these intrastate and interstate 

scenarios. 

Under the CAA, the EPA generally 

considers a state (not including areas of 

Indian country) to be a single 

responsible actor. Accordingly, neither 

the EPA nor the 2007 Exceptional 

Events Rule provides special 

considerations for intrastate scenarios 

when an event in one part of a state, 

such as a county or air district, affects 

air quality in another part of the same 

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state, assuming that the event occurs on 

land subject to state authority (versus 

tribal government authority). For cases 

involving intrastate transport, the state 

or local air agency should evaluate 

whether contributing event emissions 

from all parts of the state were not 

reasonably controllable or preventable. 

Section V.E.2 discusses the assessment 

of the not reasonably controllable or 

preventable criterion. Because there 

may be special considerations regarding 

air agencies’ authority to regulate 

activity on federally-owned and 

managed lands (e.g., national parks 

within the state), states and tribes 

should consult with the appropriate 

FLM or other federal agency and their 

EPA Regional office early in the 

development of an exceptional events 

demonstration package if they believe 

that sources on federally-owned and 

managed land contributed event-related 

emissions to a degree that raises issues 

of reasonable control. 

Interstate and international transport 

events are different than intrastate 

events. As noted in section V.E.2, the 

EPA maintains that it is not reasonable 

to expect the downwind air agency (i.e., 

the state or tribe submitting the 

demonstration) to have required or 

persuaded the upwind foreign country, 

state or tribe to have implemented 

controls on sources sufficient to limit 

event-related air concentrations in the 

downwind state nor does the EPA 

believe that Congress intended to deny 

the downwind state or tribe of relief in 

the form of data exclusion. As with any 

demonstration submittal, the submitting 

(downwind) state should identify all 

natural and anthropogenic contributing 

sources of emissions (both local/in-state 

and out-of-state) to show the causal 

connection between an event and the 

affected air concentration values. A 

submitting state may provide a less 

detailed characterization of sources in 

the upwind state or foreign country than 

of sources within its jurisdiction. After 

completing the source characterization, 

the submitting state should assess 

whether emissions from sources within 

its state were not reasonably 

controllable or preventable (see section 

V.E.2 of this proposal). Although the 

downwind state must still assess 

potential contribution from in-state 

sources, we propose that the eventrelated emissions that were transported 

in the downwind state are ‘‘not 

reasonably controllable or preventable’’ 

for purposes of data exclusion. The EPA 

does not expect air agencies to submit 

analyses to satisfy the not reasonably 

controllable or preventable criterion for 

those upwind, out-of-state sources that 

contribute to the exceedance as part of 

a submitted demonstration. Rather, with 

respect to this element for such sources, 

an air agency would merely point to the 

relevant provision we propose to add to 

the Exceptional Events Rule. Submitting 

states are, however, still required to 

assess the contribution and potential 

controls from local/in-state sources and 

submit evidence/statements supporting 

the other exceptional events criteria 

(i.e., clear causal relationship, human 

activity unlikely to recur or a natural 

event). If the event-related emissions are 

international in origin and affect 

monitors in multiple states or regions, 

the EPA may assist affected agencies in 

identifying approaches for evaluating 

the potential impacts of international 

transport and determining the most 

appropriate information and analytical 

methods for each area’s unique 

situation. 

The EPA proposes a similar approach 

to significant out-of-state anthropogenic 

sources in the case of a mixed natural/ 

anthropogenic event that the submitting 

state wishes to have treated as a natural 

event on the grounds that all significant 

anthropogenic sources were reasonably 

controlled. That is, if a mixture of 

natural and anthropogenic sources in an 

upwind state contributed to an event, 

the downwind state is not required to 

demonstrate that the anthropogenic 

sources in the upwind state were 

reasonably controlled for those sources 

to be considered to not have directly 

caused the event. The submitting state 

could consider the event to be a natural 

event based on the situation within the 

state requesting the data exclusion (that 

is, the contributing sources within the 

jurisdiction of the submitting state were 

either natural or reasonably controlled 

anthropogenic sources). 

As with all exceptional events 

demonstrations, the EPA will evaluate 

the information on a case-by-case basis 

based on the facts of a particular 

exceptional event including any 

information and arguments presented in 

public comments received by the state 

in its public comment process or by the 

EPA in a notice-and-comment 

regulatory action that depends on the 

data exclusion. 

c. Relationship Between Exceptional 

Events Rule Provisions and Other CAA 

Transport Mechanisms 

Two provisions of the CAA other than 

section 319(b) also provide regulatory 

relief for transported pollution, for 

different circumstances than those 

addressed by the 2007 Exceptional 

Events Rule. These provisions are 

briefly described here as context for 

understanding the role of the 

Exceptional Events Rule itself. 

• CAA section 179B, International 

Transport—CAA section 179B allows 

states to consider in their attainment 

demonstrations whether a 

nonattainment area might have met the 

NAAQS by the attainment date ‘‘but 

for’’ emissions contributing to the area 

originating outside the U.S. This 

provision addresses sources of 

emissions originating outside of the U.S. 

and provides qualifying nonattainment 

areas some regulatory relief from 

otherwise-applicable additional 

planning and control requirements 

should the area fail to reach attainment 

by its deadline. It does not provide a 

pathway for regulatory relief from 

designation as a nonattainment area. 

• CAA section 182(h), Rural 

Transport Areas—CAA section 182(h) 

authorizes the EPA Administrator to 

determine that an ozone nonattainment 

area can be treated as a rural transport 

area, which provides relief from more 

stringent requirements associated with 

higher nonattainment area 

classifications (i.e., classifications above 

Marginal). Under CAA section 182(h), a 

nonattainment area may qualify as a 

Rural Transport Area if it does not 

contain emissions sources that make a 

significant contribution to monitored 

ozone concentrations in the area or in 

other areas, and if the area does not 

include and is not adjacent to a 

Metropolitan Statistical Area. Generally, 

an area qualifies as a Rural Transport 

Area because it does not contribute to 

its own or another area’s nonattainment 

problem; rather, ozone exceedances are 

due to transported emissions, which 

could be international, interstate or 

intrastate in origin. The Rural Transport 

Area determination can be made during 

or after the initial area designations and 

classifications process. 

Two additional provisions of the CAA 

specifically address and appropriately 

regulate transported pollution that does 

not qualify for data exclusion under the 

Exceptional Events Rule or for 

regulatory relief under CAA section 

179B or CAA section 182(h). These 

provisions are briefly described here as 

context for understanding the role of the 

Exceptional Events Rule itself. 

• CAA section 110(a)(2)(D)(i)(I), 

Interstate Transport—CAA section 

110(a)(2)(D)(i)(I) requires states to 

develop and implement SIPs to address 

the interstate transport of emissions. 

Specifically, this provision requires 

each state’s SIP to prohibit ‘‘any source 

or other type of emissions activity 

within the State from emitting any air 

pollutant in amounts which will 

significantly contribute to 

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59The text of section 126 codified in the United 

States Code cross references section 110(a)(2)(D)(ii) 

instead of section 110(a)(2)(D)(i). The courts have 

confirmed that this is a scrivener’s error and the 

correct cross reference is to section 110(a)(2)(D)(i), 

See Appalachian Power Co. v. EPA, 249 F.3d 1032, 

1040–44 (D.C. Cir. 2001). 

60Forestland is land on which the vegetation is 

dominated by trees or, if trees are lacking, the land 

shows historic evidence of former forest and has not 

been converted to other uses. Definition available 

at https://globalrangelands.org/rangelandswest/

glossary. 

61Shrubland is land on which the vegetation is 

dominated by shrubs. Definition available at 

https://globalrangelands.org/rangelandswest/

glossary. 

62 Grassland is land on which the vegetation is 

dominated by grasses, grass like plants, and/or 

forbs. Definition available at https://globalrange

lands.org/rangelandswest/glossary. 

63Wetlands, as defined in 40 CFR 230.3(t), means 

those areas that are inundated or saturated by 

surface or ground water at a frequency and duration 

sufficient to support, and that under normal 

circumstances do support, a prevalence of 

vegetation typically adapted for life in saturated soil 

conditions. Wetlands generally include swamps, 

marshes, bogs and similar areas. 

64The Administrator’s finding on the adverse 

effects of greenhouse gases included the observation 

that wildfires have increased, and that there are 

potential serious adverse impacts from further 

wildfire occurrence. 74 FR 66530 (December 15, 

2009). 

65Climate Change in the United States: Benefits 

of Global Action, U.S. EPA, EPA–430–R–15–001, 

June 2015. Available at http://www2.epa.gov/cira. 

66The National Strategy: The Final Phase in the 

Development of the National Cohesive Wildland 

Fire Management Strategy, Report to Congress 

developed by the U.S. Department of Agriculture 

and the U.S. Department of the Interior, April 2014. 

Available at http://www.forestsandrangelands.gov/

strategy/thestrategy.shtml. 

67 Indeed, ‘‘fire policy that focuses on [wildfire] 

suppression only, delays the inevitable, promising 

more dangerous and destructive future . . . fires.’’ 

Stephens, SL; Agee, JK; Fule, PZ; North, MP; 

Romme, WH; Swetnam, TW. (2013). Managing 

Forests and Fire in Changing Climates. Science 342: 

41–42. 

nonattainment’’ of any NAAQS in 

another state, or which will ‘‘interfere 

with maintenance’’ of any NAAQS in 

another state. When the EPA 

promulgates or revises a NAAQS, each 

state is required to submit a SIP 

addressing this interstate transport 

provision as to that NAAQS within 3 

years. The EPA interprets this interstate 

transport provision to address 

anthropogenic sources of emissions 

from other states; we believe that is not 

intended to address natural sources of 

emissions. 

• CAA section 126, Interstate 

Transport—CAA section 126 provides 

states and political subdivisions with a 

mechanism to petition the 

Administrator for a finding that ‘‘any 

major source or group of stationary 

sources emits or would emit any air 

pollution in violation of the prohibition 

of CAA 110(a)(2)(D)(i).’’ 59 Where the 

EPA grants such a petition, an existing 

source may operate beyond a 3-month 

period only if the EPA establishes 

emissions limitations and compliance 

schedules to bring about compliance 

with CAA section 110(a)(2)(D)(i) as 

expeditiously as practicable, but no later 

than 3 years after such finding. Similar 

to our interpretation above for CAA 

section 110(a)(2)(D)(i), the EPA 

interprets the reference to ‘‘major source 

or group of stationary sources’’ in 

section 126 to refer to anthropogenic 

sources of emissions from other states. 

The EPA’s interpretation is that this 

provision is not intended to address 

natural sources of emissions. This 

mechanism is available to all downwind 

states, and political subdivisions, 

regardless of area designations, that may 

be affected by anthropogenic sources of 

emissions from upwind states in 

violation of the prohibition in CAA 

section 110(a)(2)(D)(i). 

As noted previously, in most cases, 

the mechanisms in the Exceptional 

Events Rule often provide the most 

regulatory flexibility in that air agencies 

can use these provisions to seek relief 

from designation of an area as 

nonattainment. The CAA section 179B 

(International Transport) and section 

182(h) (Rural Transport Areas) apply 

following, or concurrent with, the initial 

area designations process. 

2. Wildland Fires 

Fires on wildland play an important 

ecological role across the globe, 

benefiting those plant and animal 

species that depend upon natural fires 

for propagation, habitat restoration and 

reproduction. Wildland can include 

forestland,60 shrubland,61 grassland 62

and wetlands.63 Fires on wildland can 

be of two types: wildfire (unplanned) 

and prescribed fire (intentionally 

ignited for management purposes). 

Since promulgation of the 2007 

Exceptional Events Rule, the EPA has 

received and acted upon exceptional 

events demonstrations for both wildfires 

and prescribed fires. The EPA 

anticipates receiving increasing 

numbers of fire-related demonstrations 

in the future due to the natural 

accumulation of fuels in the absence of 

fire, due to climate change that is 

leading to increased incidence of 

wildfire,64 which may necessitate land 

managers employing prescribed fire 

more frequently to manage fuel loads 

and achieve other benefits as described 

below,65 66 and due to the potential for 

fire-related demonstrations to affect 

near-term regulatory decisions such as 

the initial area designations decisions 

associated with a revised 8-hour ozone 

NAAQS. Consequently, the EPA is 

proposing revisions to the 2007 

Exceptional Events Rule and developing 

additional guidance to make the 

preparation and review of 

demonstrations for wildland fire events 

more efficient and predictable for all 

parties. 

Wildfire emissions account for a large 

portion of direct PM2.5 emissions 

nationally and can contribute to 

periodic high PM2.5 and PM10 levels. 

Wildfires also emit volatile organic 

compounds (VOC) and nitrogen oxides 

(NOX), which are precursors to PM2.5, 

PM10 and ozone. Besides their effect on 

air quality, wildfires pose a direct threat 

to public safety. Changes in wildfire risk 

and occurrence are closely associated 

with the lack of periodic fire in firedependent ecosystems, demographic 

changes and associated infrastructure 

investment at the margins of wildland 

and, as already noted, climate change 

and climate variability. The threat from 

wildfires can be mitigated through 

management of wildland vegetation. 

Attempts to suppress wildfires have 

resulted in unintended consequences, 

especially the buildup of fuel loads, 

which can create a lingering fire liability 

that will eventually find resolution, 

unplanned or planned. Unplanned fires 

in areas with high fuel loads present 

high risks to both humans and 

ecosystems.67 Planned prescribed fires 

and letting some wildfires proceed 

naturally (typically those with lower fire 

intensity and severity) are tools that 

land managers can use to reduce fuel 

load, unnatural understory and tree 

density, thus helping to reduce the risk 

of catastrophic wildfires. Allowing some 

wildfires to continue to burn even 

though they could be suppressed and 

the thoughtful use of prescribed fire can 

influence the occurrence, size and 

severity of catastrophic wildfires, which 

may lead to improved public safety, 

improved protection of property and an 

overall reduction in fire-induced smoke 

impacts and subsequent health effects. 

Thus, appropriate use of prescribed fire 

may help manage the contribution of 

wildfires to both background and peak 

PM and ozone air pollution. However, 

prescribed fires themselves can affect 

monitored air quality at some times and 

places affecting public health, and thus 

give rise to exceptional events issues. 

This action proposes a workable 

approach to addressing these prescribed 

fire exceptional events issues. 

In addition to reducing wildfire risks 

to humans and ecosystems and wildfire 

contributions to air pollution, 

prescribed fires can have benefits to 

those plant and animal species that 

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68 Interim Exceptional Events Rule Frequently 

Asked Questions. U.S. EPA. May 2013. Available at 

http://www2.epa.gov/sites/production/files/2015- 

05/documents/eer_qa_doc_5-10-13_r3.pdf. See 

question 20b. 

69Prevention/control efforts could include 

posting High Fire Danger signs to make people more 

careful and prevent accidental fires, and/or taking 

reasonable action to contain a fire once it has 

started. 

70Example language to limit the duration and 

extent of the wildfire might include, ‘‘During 

wildfires, fire management resources were deployed 

to the fire event giving first priority to protecting 

life and property.’’ 

71 Interim Exceptional Events Rule Frequently 

Asked Questions. U.S. EPA. May 2013. Available at 

http://www2.epa.gov/sites/production/files/2015- 

05/documents/eer_qa_doc_5-10-13_r3.pdf. 

72 Interim Air Quality Policy on Wildland and 

Prescribed Fires. U.S. EPA. April 23, 1998. 

Available at http://www.epa.gov/ttn/oarpg/t1/

memoranda/firefnl.pdf. 

depend upon natural fires for 

propagation, habitat restoration and 

reproduction, as well as benefits to a 

myriad of ecosystem functions (e.g., 

carbon sequestration, maintenance of 

water supply systems and endangered 

species habitat maintenance). The EPA 

understands the importance of 

prescribed fire, which mimics a natural 

process necessary to manage and 

maintain fire-adapted ecosystems and 

climate change adaptation, while 

reducing risk to public safety and the 

risk of uncontrolled emissions and 

ecosystem damage from catastrophic 

wildfires. The EPA is committed to 

working with federal land managers, 

other federal agencies, tribes, states and 

private landowners to effectively 

manage prescribed fire use to reduce the 

impact of catastrophic wildfire-related 

emissions on ozone, PM10 and PM2.5. 

a. Current Situation 

When the EPA promulgated the 2007 

Exceptional Events Rule, we included 

definitions for fire-related terms (e.g., 

wildfire, prescribed fire and wildland) 

in the preamble and attributed these 

definitions to the National Wildland 

Fire Coordinating Group (now the 

National Wildfire Coordinating Group 

or NWCG) Glossary of Wildland Fire 

Terminology, 2003. The EPA did not, 

however, codify these definitions in 

regulatory text. Since promulgation of 

the 2007 Exceptional Events Rule, the 

NWCG has modified some of its 

recommended definitions and the EPA 

used slightly different definitions in its 

Interim Exceptional Events 

Implementation Guidance, creating 

some confusion for air agencies and 

other entities working with air agencies 

who have tried to use fire-related 

definitions and concepts when 

preparing and submitting exceptional 

events demonstrations for fires. 

The preamble to the 2007 Exceptional 

Events Rule discussed how the EPA 

expected to apply the rule to wildfires 

and prescribed fires. The EPA stated 

that wildfires would be considered 

natural events, while prescribed fires 

would be considered events caused by 

human activity. As events caused by 

human activity, prescribed fires are 

subject to the ‘‘not likely to recur’’ 

criterion, and the preamble to the rule 

discussed the considerations that would 

apply for this criterion. Section V.F.2.d 

provides a more detailed summary of 

the current situation and planned 

changes for this criterion. 

Demonstrations for wildfires and 

those prescribed fires claimed to be 

exceptional events must also address 

the ‘‘not reasonably controllable or 

preventable’’ criterion. Neither the 2007 

Exceptional Events Rule nor its 

preamble addressed this criterion in any 

depth for wildfires. Since promulgating 

the rule in 2007, the EPA has concluded 

that short, general statements in 

demonstrations for fire events satisfy 

this criterion. The EPA has been 

advising air agencies that when 

documenting the ‘‘not reasonably 

controllable or preventable’’ criterion in 

a wildfire exceptional events 

demonstration submittal, air agencies 

should identify the origin and evolution 

of the wildfire, describe local efforts to 

prevent fires due to unauthorized 

activity or accidental human-caused 

actions (if relevant given the origin of 

the fire) and explain any efforts to limit 

the duration or extent (and thus the 

emissions) of the wildfire.68 69 70 We 

have also advised air agencies that if the 

wildfire originated outside of the 

jurisdiction of the air agency submitting 

the exceptional events demonstration, 

then the submitting air agency should 

identify this fact in its demonstration.71

The 2007 Exceptional Events Rule 

and its preamble gave more extensive 

treatment to the not reasonably 

controllable or preventable criterion for 

prescribed fires. The rule text tied the 

eligibility of prescribed fires as 

approved exceptional events to the air 

agency having a ‘‘certified’’ SMP in 

place or, in the alternative, to using 

BSMP for the prescribed fire(s) in 

question. In the preamble, the EPA did 

not provide detailed guidance on SMPs 

or BSMP, but committed to defining and 

developing these concepts when we 

updated the guidance contained in the 

1998 Interim Air Quality Policy on 

Wildland and Prescribed Fires.72

However, the EPA has not revised this 

guidance document. Although some 

states have developed demonstrations 

that incorporate BSMP employed for a 

specific prescribed fire and/or have 

referenced BSMP in their SMPs, the 

EPA has not in any other more recent 

guidance clarified what it means for an 

air agency or burner to have a certified 

SMP in place and/or to implement 

BSMP. Like the inconsistency that has 

developed since 2007 in fire-related 

definitions, the absence of further 

clarifying guidance on SMPs and BSMP 

has created confusion for air agencies 

trying to develop these plans and/or 

apply these practices for purposes of 

developing and submitting exceptional 

events demonstrations for prescribed 

fires. 

b. Proposed Changes 

In this action, the EPA proposes to 

codify in regulatory language certain 

fire-related definitions and SMP/BSMP 

factors necessary for exceptional events 

demonstration and program 

implementation purposes. Codifying 

these definitions in 40 CFR 50.1 will 

promote understanding and standardize 

terminology for the purposes of 

characterizing an event for exceptional 

events demonstration purposes. 

Finalizing these proposed changes 

will also decouple implementation of 

the exceptional events process from 

potential future revisions to the Interim 

Policy on Wildland and Prescribed 

Fires. Although the EPA solicits 

comment on the regulatory process 

associated with developing exceptional 

events demonstrations for fire-related 

events, the EPA does not intend to take 

comment on any aspects of the 1998 

Interim Policy on Wildland and 

Prescribed Fires as part of this effort to 

revise the Exceptional Events Rule. 

The proposed new definitions, along 

with other proposed changes, are 

described in detail in the separate 

sections on wildfires (section V.F.2.c) 

and prescribed fire (section V.F.2.d) that 

follow immediately below this section. 

c. Wildfires 

Current Situation. The preamble to 

the 2007 Exceptional Events Rule 

defined a wildfire as ‘‘an unplanned, 

unwanted wildland fire (such as a fire 

caused by lightning), [to] include 

unauthorized human-caused fires (such 

as arson or acts of carelessness by 

humans), escaped prescribed fire 

projects (escaped control due to 

unforeseen circumstances), where the 

appropriate management response 

includes the objective to suppress the 

fire.’’ The 2007 Exceptional Events Rule 

preamble also defined a ‘‘wildland fire 

use’’ as ‘‘the application of the 

appropriate management response to a 

naturally-ignited (e.g., as the result of 

lightning) wildland fire to accomplish 

specific resource management objectives 

in predefined and designated areas 

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73 Interim Exceptional Events Rule Frequently 

Asked Questions. U.S. EPA. May 2013. Available at 

http://www2.epa.gov/sites/production/files/2015- 

05/documents/eer_qa_doc_5-10-13_r3.pdf. 

74 Guidance for Implementation of Federal 

Wildland Fire Management Policy, developed 

cooperatively by the Fire Executive Council, 

February 13, 2009. Available at http://wildfiretoday.

com/documents/Federal%20Wildland%20Fire%20

Management%20Policy%2002-13–2009.pdf. 

75National Wildfire Coordinating Group. 

Glossary of Wildland Fire Terminology, PMS 205. 

October 2014. Available at http://www.nwcg.gov/

sites/default/files/products/pms205.pdf. 

76See submitted exceptional events 

demonstrations available on the EPA’s Web site at 

http://www2.epa.gov/air-quality-analysis/

exceptional-events-submissions-table. 

77The wildland-urban interface is the line, area 

or zone where structures and other human 

development meet or intermingle with undeveloped 

wildland or vegetative fuels. The term describes an 

area within or adjacent to private and public 

property where mitigation actions can prevent 

damage or loss from wildfire. See, Glossary of 

Wildland Fire Terminology, PMS 205. October 

2014. Available at http://www.nwcg.gov/sites/

default/files/products/pms205.pdf. 

78We would generally treat a large prescribed fire 

in a wildland-urban interface area as a prescribed 

fire on wildland, subject to the prescribed fire 

provisions described in this proposal. We do not 

expect a small prescribed fire in an interface area 

(e.g., a prescribed burn ignited by a single 

landowner on his/her personal property) to generate 

emissions that would raise exceptional events 

issues. 

where fire is necessary and outlined in 

fire management or land management 

plans.’’ The 2007 Exceptional Events 

Rule preamble further clarified that the 

EPA believed that both wildfires and 

wildland fire use fires fall within the 

meaning of ‘‘natural events’’ as that term 

is used in CAA section 319(b). 

In the 2013 Interim Q&A Document, 

after consulting with other federal 

agencies that manage wildfires and 

prescribed fires, the EPA defined a 

wildfire as ‘‘[a]ny fire started by an 

unplanned ignition caused by lightning; 

volcanoes; unauthorized activity; 

accidental, human-caused actions; and 

escaped prescribed fires.’’ 73

Building off of the principles in the 

February 2009 Guidance for 

Implementation of Federal Wildland 

Fire Management Policy,74 the NWCG 

defines ‘‘wildland’’ as ‘‘an area in which 

development is essentially non-existent, 

except for roads, railroads, power lines, 

and similar transportation facilities. 

Structures, if any, are widely 

scattered.’’ 75

Proposed Changes. Although the EPA 

has previously approved exceptional 

events demonstrations for wildfires,76

the EPA recognizes air agencies 

preparing exceptional events 

demonstrations for future wildfires will 

benefit from additional clarification and 

guidance related to wildfire 

terminology. This section discusses the 

EPA’s proposed changes. 

(i) Definition of wildland and wildfire. 

For purposes of this action, the EPA 

proposes to codify in regulatory 

language the definition of ‘‘wildland’’ 

by using the October 2014 NWCG 

Glossary definition that a wildland is 

‘‘an area in which human activity and 

development is essentially non-existent, 

except for roads, railroads, power lines, 

and similar transportation facilities. 

Structures, if any, are widely scattered.’’ 

As previously noted, wildland can 

include forestland, shrubland, grassland 

and wetlands. This proposed definition 

of wildland would include lands that 

are predominantly wildland, such as 

land in the wildland-urban 

interface.77 78

In proposing this definition for 

wildland, the EPA considered the types 

of human intervention that could affect 

whether a land is considered a 

‘‘wildland.’’ In our view and the view of 

other federal agencies with which we 

have consulted in the development of 

this proposed action, the presence of 

fences to limit the movement of grazing 

animals, or of infrastructure to provide 

water to grazing animals, does not 

prevent a land area from being 

wildland. Cultivated cropland (i.e., a 

field that is plowed or disked or from 

which crops are removed on an annual 

or more frequent basis) is not wildland. 

Land areas on which nursery stock is 

grown to marketable size (e.g., 

Christmas tree farms) are generally not 

wildland unless they are ‘‘wild’’ in 

terms of a having only limited human 

entrance and intervention for 

management or removal purposes 

thereby resulting in a complex 

ecosystem. Generally, managed timber 

lands may be considered wildland if 

they have a complex ecosystem affected 

by only limited human entrance and 

intervention. The EPA invites comment 

on whether it would be appropriate to 

incorporate these examples of land use 

types that can be considered to be (or 

not to be) wildland into the regulatory 

definition of wildland or whether or it 

is adequate to discuss them in the 

preamble only. 

Also for purposes of this action, the 

EPA proposes to codify in regulatory 

language the following definition of 

‘‘wildfire,’’ which slightly modifies the 

definition of ‘‘wildfire’’ with respect to 

prescribed fires that appeared in the 

Interim Q&A document. 

A wildfire is any fire started by an 

unplanned ignition caused by lightning; 

volcanoes; other acts of nature; unauthorized 

activity; or accidental, human-caused 

actions; or a prescribed fire that has been 

declared to be a wildfire. A wildfire that 

predominantly occurs on wildland is a 

natural event. 

This proposed definition of wildfire 

does not require that the objective be to 

put out a fire for the fire to be 

categorized as a wildfire. When an 

unplanned fire on wildland does not 

threaten catastrophic consequences, it 

may be very appropriate to allow it to 

continue. The proposed definition 

therefore encompasses the type of 

activity previously referred to as a 

wildland fire use (i.e., a situation in 

which a fire manager deliberately allows 

a wildfire to continue to burn over a 

certain land area rather than 

immediately extinguish it or block its 

progress into that area). This inclusion 

is consistent with the approach taken in 

2007 that all types of wildfire were 

considered to be natural. We note here, 

as guidance, that the part of the 

proposed definition referring to a 

prescribed fire that has been declared to 

be a wildfire refers to specific instances 

in which the conditions of a particular 

prescribed fire have developed in a way 

that leads the fire manager to decide 

that the fire should be treated as a 

wildfire, for example if it has escaped 

secure containment lines and requires 

suppression along all or part of its 

boundary or no longer meets the 

resource objectives (e.g., smoke impact, 

flame height). It is not the intention that 

land managers may categorically redefine some types of prescribed fire to 

be wildfires. 

Because the EPA is proposing in rule 

text that all wildfires on wildland are 

always considered natural events, the 

proposed definition of wildland will in 

turn determine which fires are 

considered to be natural events. This is 

consistent with the approach in the 

2007 Exceptional Events Rule. The EPA 

realizes that some wildfires are initiated 

by human actions (e.g., careless use of 

campfires or leaf and brush pile fires). 

The EPA also realizes that past human 

activity in the form of decades of 

suppressing wildfires has influenced the 

size and emissions of wildfires that do 

occur. However, wildfire is mostly 

dominated by natural factors, and the 

EPA believes that treating all wildfires 

on wildland as natural events is in 

keeping with Congressional intent and 

not contradictory to any plain meaning 

of CAA section 319(b). Therefore, 

because a wildfire on wildland is a 

natural event and because natural 

events can recur, an air agency would 

not need to address event recurrence in 

the ‘‘human activity unlikely to recur at 

a particular location or a natural event’’ 

portion of its exceptional events 

demonstration. 

(ii) Not reasonably controllable or 

preventable. Although a wildfire is 

unplanned, the ‘‘not reasonably 

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79While we are proposing special provisions only 

for fires that occur predominantly on wildland, we 

do not intend to restrict fires on other types of land 

from receiving similar treatment. In addressing the 

not reasonably controllable or preventable criterion 

in a demonstration for a wildfire that is not on 

wildland, air agencies should state that available 

resources were reasonably aimed at suppression 

and avoidance of loss of life and property and that 

no further efforts to control air emissions from the 

fire would have been reasonable. 

80 72 FR 13575 (March 22, 2007). 

81One example of this collaborative approach is 

the evolving interagency Wildland Fire Air Quality 

Response Program, which has developed resources 

to help address and predict smoke impacts from 

wildfires to reduce public exposure to wildfire 

smoke. Additional information is available at 

http://www.westar.org/Docs/Business%20Meetings/

Spring14/Boise/12.3%20Lahm_WFAQRP_5_28_

14.pdf. 

82See, for example, National Ambient Air Quality 

Standards for Ozone; Proposed Rule (79 FR 75234, 

December 17, 2014) and Implementation of the 

2008 National Ambient Air Quality Standards for 

Ozone: State Implementation Plan Requirements; 

Final Rule (80 FR 12264, March 6, 2015). 

controllable or preventable’’ criterion 

still applies. Another function of the 

definition of wildland is that the EPA is 

proposing that the treatments of 

wildfires and prescribed fires on 

wildland with regard to the not 

reasonably controllable or preventable 

criterion have a number of common 

aspects, as described here and below in 

the section on prescribed fires, because 

a wildland situation presents particular 

considerations applicable to both fire 

types with respect to what prevention or 

control measures may be reasonable. 

The EPA is not proposing any general 

approach for wildfires or prescribed 

fires that are not on wildland.79

Because wildfires on wildland are 

unplanned, fire management agencies 

generally have either no advanced 

notice or limited and uncertain notice, 

of wildfire ignition and location. In 

addition, many areas of wildland are 

very remote and rugged, and thus not 

easily reached and traversed. These 

factors generally limit preparation time 

and on-site resources to prevent or 

control the initiation, duration or extent 

of a wildfire. Also, by their nature, 

catastrophic wildfires typically present 

some risk of property damage, 

ecosystem damage and/or loss of life (of 

the public or firefighters), which is a 

strong motivation for appropriate 

suppression and control efforts. The 

EPA believes that land managers and 

other fire management entities have the 

motivation and the best information for 

taking action to reasonably prevent and 

limit the extent of wildfires on 

wildland, thus also controlling the 

resulting emissions. Therefore, the EPA 

believes that it is not useful to require 

air agencies to include in their 

individual wildfire exceptional events 

demonstrations descriptions of 

prevention and control efforts employed 

by burn managers to support a position 

that such efforts were reasonable. To 

increase the efficiency of the 

exceptional events process, the EPA 

proposes a new approach for wildfires 

on wildland, under which there would 

be a rebuttable presumption that every 

wildfire on wildland satisfies the ‘‘not 

reasonably controllable or preventable’’ 

criterion, unless evidence in the record 

demonstrates otherwise. Applying this 

categorical presumption of not 

reasonably controllable for wildfires 

would involve referencing the 

appropriate regulatory citation in the 

demonstration. 

As previously stated, there will be 

situations in which a fire manager could 

have suppressed or contained a wildfire 

but has allowed the fire to continue 

burning through an area with a current, 

in-place land management plan calling 

for restoration through natural fire or 

mimicking the natural role of fire. The 

EPA recognizes that this scenario could 

occur when a fire manager has a plan for 

acquiring personnel and equipment to 

address the wildfire (either 

coincidentally or because the wildfire 

was originally a prescribed fire) but the 

manager determines that allowing the 

wildfire to continue burning is safe and 

will conserve overall fire management 

resources compared to suppressing or 

containing the current wildfire and then 

conducting a separate prescribed burn at 

a later time. In such a scenario, even 

though the fire would meet the 

definition of a wildfire and even though 

we are proposing that in general 

wildfires will not need to be reviewed 

individually against the not reasonably 

controllable or preventable criterion, we 

would expect the fire manager to 

employ appropriate BSMP as described 

in section V.F.2.d when possible. 

(iii) Coordinated communications. 

Regardless of the above considerations 

for wildfires, the EPA urges land 

managers and air agencies to coordinate, 

as appropriate, in developing plans and 

appropriate public communications 

regarding public safety and reducing 

exposure in instances where wildfires 

are potential exceptional events and 

contribute to exceedances of the 

NAAQS. Coordinated efforts can help 

air agencies satisfy the Exceptional 

Events Rule obligation at 40 CFR 51.930 

that air agencies must provide public 

notice and public education and must 

provide for implementation of 

reasonable measures to protect public 

health when an event occurs.80 Also, 

when wildfire impacts are frequent and 

significant in a particular area, land 

managers, land owners, air agencies and 

communities may be able to lessen the 

impacts of wildfires by working 

collaboratively to take steps to minimize 

fuel loading in areas vulnerable to fire.81

Fuel load minimization steps can 

consist of both prescribed fire and 

mechanical treatments, such as using 

mechanical equipment to reduce 

accumulated understory. 

d. Prescribed Fires 

As noted previously, the EPA 

recognizes and acknowledges the 

potential significant impact on air 

quality posed by catastrophic wildfires. 

The use of prescribed fire on wildland 

can influence the occurrence, severity, 

behavior and effects of catastrophic 

wildfires, which may help manage the 

contribution of wildfires to measured 

ambient pollutant levels (particularly 

ozone and PM concentrations). 

Additionally, prescribed fires can 

benefit the plant and animal species that 

depend upon natural fires for 

propagation, habitat restoration and 

reproduction, as well as a myriad of 

ecosystem functions (e.g., carbon 

sequestration, maintenance of water 

supply systems and endangered species 

habitat maintenance). The EPA formally 

recognized in the 1998 Interim Air 

Quality Policy on Wildland and 

Prescribed Fires that federal, tribal and 

state owners and land managers use 

prescribed fire on wildland to achieve 

some of these resource benefits, to 

correct the undesirable conditions 

created by past wildfire suppression 

management strategies and to reduce the 

risk of wildfires to the public. Although 

the 1998 Interim Air Quality Policy on 

Wildland and Prescribed Fires focused 

on the role of federal, tribal and state 

owners/land managers, it also 

recognized that prescribed fires on 

private lands achieve some of the same 

goals. These concepts, also noted in the 

preamble to the 2007 Exceptional 

Events Rule, are summarized in more 

detail immediately below. In recent 

regulatory actions,82 the EPA has 

continued to express an understanding 

of the importance of prescribed fire, 

noting that it can be used to mimic the 

natural process necessary to manage and 

maintain existing fire-adapted 

ecosystems and/or return an area to its 

historical ecosystem (or another natural 

ecosystem if the historical ecosystem is 

no longer attainable) while reducing the 

risk to public safety and the risk of 

uncontrolled emissions from 

catastrophic wildfires. 

Current Situation. The 2007 

Exceptional Events Rule recognized the 

benefits of prescribed fire as 

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83The October 2014 NWCG definition of 

‘‘prescribed fire’’ is similar but includes the concept 

that the fire is not illegal: ‘‘[a]ny fire intentionally 

ignited by management actions in accordance with 

applicable laws, policies, and regulations to meet 

specific objectives.’’ 

84The natural fire return interval is the typical 

number of years between two successive naturallyoccurring fires in a specified area or ecosystem. The 

historical rate of return of these fires resulted in 

plant communities that evolved with recurring fire 

and therefore became dependent on fire for 

maintenance. 

85The discussion of the 1998 Interim Air Quality 

Policy on Wildland and Prescribed Fires 

recommendations regarding SMPs appears in the 

preamble to the 2007 Exceptional Events Rule at 72 

FR 13567 (March 22, 2007). 

86The language associated with the six basic 

components of a certifiable SMP was taken directly 

from the 1998 Interim Air Quality Policy on 

Wildland and Prescribed Fires. For context, the EPA 

notes that the identified components of a certifiable 

SMP apply to managing smoke from prescribed fires 

managed for resource benefits. The EPA would 

expect burn managers to consider actions and 

approaches where applicable or where appropriate 

rather than in all prescribed fire scenarios. 

87 In specifying the basic components of 

certifiable SMPs that would include the 

requirement for agency approval of prescribed fire 

plans, the 1998 Interim Air Quality Policy on 

Wildland and Prescribed Fires noted that SMPs can 

mitigate the nuisance and public safety hazards 

associated with smoke from prescribed fires 

intruding into populated areas, prevent 

deterioration of air quality and NAAQS violations 

and address visibility impacts in mandatory Class 

I Federal areas. Since the EPA issued the Interim 

Policy in 1998, some federal agencies have reported 

to us their assessment that some states and/or local 

air agencies have managed their SMP (or other 

regulatory programs) in such a way as to exclude 

the use of prescribed fires in areas to such an extent 

that fuels have continued to accumulate to levels 

that increase the likelihood of catastrophic 

wildfires. 

summarized earlier in this section and 

included provisions for these event 

types in both the preamble to the final 

rule and in regulatory language. The 

preamble to the 2007 Exceptional 

Events Rule defined a prescribed fire as 

‘‘a fire ignited by management 

objectives to meet specific resource 

management needs.’’ This was 

consistent with the definition of 

prescribed fire in general use by the fire 

management community at the time.83

Also in the preamble language, the EPA 

explained that prescribed fire cannot be 

classified as natural given the extent of 

the direct human causal connection. 

However, the preamble explained that a 

prescribed fire that causes or contributes 

to an exceedance or violation of an 

ambient air quality standard could still 

be considered an exceptional event if it 

satisfies all core statutory elements of 

CAA section 319(b), including the 

‘‘human activity that is unlikely to recur 

at a particular location’’ and the ‘‘not 

reasonably controllable or preventable’’ 

criteria. 

The 2007 Exceptional Events Rule 

preamble further explained that air 

agencies should take into account the 

natural fire return interval 84 as part of 

the basis for establishing that the human 

activity (i.e., the prescribed fire) is 

‘‘unlikely to recur at a particular 

location.’’ The preamble acknowledged 

that the natural fire return interval can 

vary widely and range from once every 

year to less frequently than once every 

200 years. 

When addressing the ‘‘not reasonably 

controllable or preventable’’ criterion, 

the 2007 Exceptional Events Rule 

preamble instructed agencies to 

examine whether there are ‘‘reasonable 

alternatives,’’ such as mechanical or 

other (e.g., chemical) treatments to the 

use of prescribed fire. The preamble 

language recognized that, although caseand area-specific, any number of 

conditions could exist that would favor 

the use of prescribed fire rather than 

alternate treatments. Such scenarios 

identified in the preamble included: 

significant build-up of forest fuels in a 

particular area that if left unaddressed 

would pose an unacceptable risk of 

catastrophic wildfire; pest or disease 

outbreak; natural species composition 

dependent on a specific fire return 

interval; and legal requirements 

precluding the use of mechanical fuel 

reduction methods. 

The 2007 Exceptional Events Rule 

also indicated, in both preamble 

discussion and rule text, that to further 

satisfy the ‘‘not reasonably controllable 

or preventable’’ criterion for prescribed 

fires and to address the principle at 

section 319(b)(3)(A) of the CAA that the 

protection of public health is the highest 

priority, a prescribed fire would be 

considered to be an exceptional event 

only if the state has certified to the EPA 

that it has adopted and is implementing 

a SMP or the state has ensured that the 

burner has employed BSMP. While the 

EPA did not identify in the 2007 

Exceptional Events Rule the necessary 

components of an SMP or what SMP 

certification entails, the preamble cited 

the 1998 Interim Air Quality Policy on 

Wildland and Prescribed Fires.85 This 

policy identified the following basic 

components of a certifiable SMP: 86

• Authorization to Burn—includes a 

process for authorizing or granting 

approval to manage fires for resource 

benefits within a region, state or on 

Indian lands and identify a central 

authority responsible for implementing 

the program. The authorization process 

could include burn plans that consider 

air quality and the ability of the airshed 

to disperse emissions from all burning 

activities on the day of the burn. 

• Minimizing Air Pollutant 

Emissions—encourages wildland 

owners/managers to consider and 

evaluate alternative treatments to fire, 

but if fire is the selected approach to 

follow emission reduction techniques. 

• Smoke Management Components of 

Burn Plans—identifies the following 

components if the SMP requires burn 

plans: Actions to minimize fire 

emissions, evaluate smoke dispersion, 

public notification and exposure 

reduction procedures and air quality 

monitoring. 

• Public Education and Awareness— 

establishes the criteria for issuing health 

advisories when necessary and 

procedures for notifying potentially 

affected populations. 

• Surveillance and Enforcement— 

includes procedures to ensure that 

wildland owners/managers comply with 

the SMP. 

• Program Evaluation—provides for 

periodic review by all stakeholders of 

the SMP effectiveness and program 

revision as necessary. 

The 1998 Interim Air Quality Policy 

on Wildland and Prescribed Fires also 

noted, regarding the certification 

process for SMPs, that to receive special 

consideration for air quality data whose 

concentrations were influenced by 

prescribed fires, ‘‘[t]he State/tribal air 

quality manager must certify in a letter 

to the Administrator of EPA that at least 

a basic [smoke management] program 

has been adopted and 

implemented . . . .’’ The 1998 Interim 

Air Quality Policy on Wildland and 

Prescribed Fires further identified that 

federal agencies intending to use 

prescribed fire should operate under an 

approved prescribed fire plan and meet 

the National Environmental Policy Act 

(NEPA) requirements, where applicable, 

prior to ignition.87

The EPA did not use the preamble to 

the 2007 Exceptional Events Rule to 

expand on the concept of using BSMP 

in lieu of an SMP. Rather, the EPA only 

noted that burners could use BSMP to 

minimize emissions and control the 

impacts of fire. Although the EPA 

identified several example BSMP in a 

footnote in the preamble (footnote 12 at 

72 FR 13567), we also committed to 

developing the concept when we 

updated the guidance in the 1998 

Interim Air Quality Policy on Wildland 

and Prescribed Fires. The EPA has not 

revised this guidance and does not 

currently plan to do so. Although some 

states have developed demonstrations 

that incorporate BSMP employed for a 

specific prescribed fire and/or 

referenced BSMP in their SMPs, the 

EPA has not in any other more recent 

guidance clarified what it means for an 

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88Treatment of Data Influenced by Exceptional 

Events: Exceptional Events Submissions Table. U.S. 

Environmental Protection Agency, Research 

Triangle Park, NC. See links associated with ‘‘April 

2011 Fires’’ in the ozone section of the table 

available at http://www2.epa.gov/air-qualityanalysis/exceptional-events-submissions-table. 

89The benchmarks for the expected frequency of 

prescribed fires not on wildland would be assessed 

on a case-by-case basis. 

air agency or burner to have a certified 

SMP in place and/or to implement 

BSMP. 

In addition to conditioning the 

approval of a prescribed fire as an 

exceptional event on the existence and 

implementation of a certified SMP or 

the actual use of BSMP, as described 

above, the 2007 Exceptional Events Rule 

also requires that ‘‘[i]f an exceptional 

event occurs using the basic smoke 

management practices approach, the 

State must undertake a review of its 

approach to ensure public health is 

being protected and must include 

consideration of development of a 

SMP.’’ To date, air agencies have 

submitted few exceptional events 

demonstrations for prescribed fires. One 

recent submission came from Kansas, a 

state already operating an SMP.88

The 2007 Exceptional Events Rule at 

40 CFR 50.14(b)(3) allows for the 

exclusion of data where a state 

demonstrates to the EPA’s satisfaction 

that emissions from prescribed fires 

caused a specific air pollution 

concentration in excess of one or more 

NAAQS at a particular air quality 

monitoring location and otherwise 

satisfies the requirements in the 

Exceptional Event Rule. The regulatory 

language also requires that the subject 

prescribed fire meets the definition in 

40 CFR 50.1(j) and requires that the state 

has certified to EPA that it has adopted 

and is implementing a Smoke 

Management Program or the state has 

ensured that the burner employed basic 

smoke management practices. The 

definition of an exceptional event at 40 

CFR 50.1(j) includes the requirement 

that an event ‘‘is not reasonably 

controllable or preventable.’’ Thus, the 

EPA has interpreted that a 

demonstration for a prescribed fire 

independently address both the SMP/

BSMP element and the not reasonably 

controllable or preventable criterion. We 

have not indicated that meeting the 

SMP/BSMP condition is sufficient to 

satisfy the not reasonably controllable or 

preventable criterion. 

Proposed Changes. As previously 

noted, the EPA has not to date clarified 

fire-related definitions or its 

expectations regarding SMPs or BSMP 

in rule or preamble form. This 

uncertainty has created confusion for air 

and fire management agencies trying to 

develop fire-related plans and/or apply 

fire management practices for 

prescribed fires. It has also created 

confusion for air agencies when 

developing and submitting exceptional 

events demonstrations for both wildfires 

and prescribed fires. 

To assist air agencies in documenting 

an exceptional events package for a 

prescribed fire on wildland, the EPA 

proposes to clarify its expectations for a 

satisfactory demonstration, as follows. 

(i) Definition of a prescribed fire. We 

are proposing to adopt in rule language 

the current NWCG-recommended 

definition of a prescribed fire: ‘‘[a]ny 

fire intentionally ignited by 

management actions in accordance with 

applicable laws, policies and 

regulations to meet specific objectives.’’ 

In this definition, ‘‘management’’ refers 

to the owner or manager of the land area 

to which prescribed fire is applied, and 

‘‘specific objectives’’ refers to specific 

land or resource management objectives. 

(ii) Events caused by human activity. 

We are proposing to say in rule form 

that prescribed fires are events caused 

by human activity. Thus, to be 

considered an exceptional event, every 

prescribed fire demonstration must 

address the ‘‘human activity unlikely to 

recur at a particular location’’ criterion. 

(iii) Unlikely to recur at a particular 

location. As discussed in more detail in 

section V.E.1 of this proposal, this 

requirement of CAA section 319(b) is 

not specific and requires interpretation 

on a case-by-case or event type-by-event 

type basis. The term ‘‘unlikely’’ implies 

consideration of the expected future 

frequency of events similar to the event 

that has already happened, but does not 

convey any particular benchmark for 

what frequency should be low enough 

to be considered ‘‘unlikely.’’ Also, the 

term ‘‘at a particular location’’ requires 

interpretation, as it could refer to the 

exact area or only to the general area of 

the event, to the location of the ambient 

monitoring station or stations that were 

affected by the event or to the 

combination of both. 

As was our position in 2007, we 

continue to believe that the natural fire 

return interval is a useful and 

appropriate benchmark for a satisfactory 

demonstration that a prescribed fire is 

unlikely to recur at a particular location, 

in the sense that if a planned program 

of prescribed fire calls for the 

application of prescribed fire at a 

similar interval to the natural fire return 

interval at given locations then each 

prescribed fire conducted in that 

program can be considered not likely to 

recur at its particular location. However, 

we now believe based on experience 

and further consideration that the 

natural fire return interval is not the 

only appropriate benchmark. It can be 

difficult in some cases to determine 

what fire return interval prevailed under 

natural conditions, which may not have 

existed for decades or even hundreds of 

years in a particular area. Also, in some 

cases environmental conditions may 

have changed, for example due to 

climate change, such that the original 

natural ecosystem cannot realistically be 

restored and the well-considered land 

management goal instead may be the 

development and maintenance of a 

sustainable and resilient ecosystem that 

is different than what historically 

existed and that will likely reduce the 

risk of catastrophic wildfire. In such a 

case, the frequency of prescribed fire 

needed to establish or restore such an 

ecosystem during a transitional period 

and/or the frequency needed to sustain 

the resilient ecosystem may be different 

than the natural fire return interval that 

once prevailed. It is also important to 

consider issues of fire personnel and 

public safety and protection of nearby 

property. Land managers may need to 

apply prescribed fire at a frequency that 

maintains the accumulation of fuel 

loading between prescribed fires at a 

level that does not create the risk of a 

dangerous wildfire. 

Accordingly, the first proposed 

change for prescribed fires on wildland 

is to include in the rule text two 

benchmarks for the expected future 

frequency of prescribed fires on 

wildland to meet the not likely to recur 

criterion: (1) The natural fire return 

interval as articulated in the 2007 

preamble and (2) the prescribed fire 

frequency needed to establish, restore 

and/or maintain a sustainable and 

resilient wildland ecosystem. If 

finalized, an air agency could include 

information provided by the land 

manager with respect to the appropriate 

benchmark for a prescribed fire on 

wildland as the basis for satisfying the 

human activity unlikely to recur at a 

particular location criterion in its 

exceptional events demonstration.89

Successfully implementing one of 

these benchmarks for prescribed fire 

frequency necessitates that the air 

agency and the land manager 

collaborate to establish and document 

the appropriate fire return interval or 

frequency in a submitted demonstration. 

Federal agencies that use prescribed fire 

to manage lands for which they are 

responsible generally prepare multi-year 

plans for the use of prescribed fire in a 

given national park, national forest, 

armed forces base or other land area. 

Many of these plans include an 

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90An example of a federal land management plan 

that considers the need for the use of prescribed fire 

is the Land and Resource Management Plan for the 

Kaibab National Forest, Coconino, Yavapai, and 

Mojave Counties, Arizona, USDA Forest Service 

Southwestern Region, MB–R3–07–17, February 

2014, available at http://www.fs.usda.gov/Internet/

FSE_DOCUMENTS/stelprd3791580.pdf. 

91These plans could also include fire 

management plans, prescribed fire on wildland 

management plans, landscape management plans or 

equivalent public planning documents. 

92The EPA anticipates that any person within an 

air agency responsible for submitting exceptional 

events demonstrations or SIP revisions could also 

be responsible for certifying a Smoke Management 

Program. 

93USDA Forest Service and Natural Resources 

Conservation Service, Basic Smoke Management 

Practices Tech Note, October 2011, http://

www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/

stelprdb1046311.pdf. 

94The EPA also addressed how federal agencies 

may use basic smoke management practices to 

establish a presumption of conformity in the 

preamble to the EPA’s General Conformity Rule at 

40 CFR 93.153(g)–(i) (75 FR 17264, April 5, 2010). 

The six practices identified in Table 3 are not a 

presumed to conform action for purposes of a 

federal agency satisfying their General Conformity 

responsibilities. For basic smoke management 

practices to provide a presumption of conformity, 

the identified basic smoke management practices 

must be publicly and state reviewed as part of a 

presumed to conform action under 40 CFR 

93.153(g) or (f) of the General Conformity Rule. 

objective to establish, restore and/or 

maintain a sustainable and resilient 

wildland ecosystem and incorporate the 

best science available to determine what 

prescribed fire cycle will accomplish 

this.90 Some tribes, private landowners 

(and federal, state and local agencies 

working with private landowners) and 

state agencies that manage state-owned 

lands (e.g., state parks) also prepare 

multi-year management plans. While 

plans developed by public agencies (i.e., 

state and federal agencies) often 

undergo public comment prior to being 

finalized, the plans developed by tribes 

and private landowners may not follow 

a public comment process. However, 

public agencies often work with tribes 

and private owners to develop these 

plans, which are based on conservation 

practices and standards that have often 

undergone public comment as part of 

the state or federal agency process. 

The EPA understands that multi-year 

plans incorporate factors relevant to 

identifying and selecting the areas and 

times under which management will 

initiate a specific prescribed fire. The 

EPA also recognizes that evaluating the 

behavior and results of prior prescribed 

fires aids in determining the frequency 

and need for future prescribed fire in a 

given area. In addition, personnel and 

equipment must be available on site, 

which cannot be specifically planned 

far in advance. Thus, it is typical for 

multi-year plans to identify somewhat 

general targets for the frequency of 

prescribed fire use and for specific burn 

plans. Even then, unexpected 

differences between planned and actual 

fire behavior, landscape or ecosystem 

characteristics, fuel loading patterns and 

weather patterns may cause 

management to deviate from the general 

plan and/or the specific burn plan. 

Therefore, when the EPA reviews an 

exceptional events demonstration for a 

prescribed fire conducted under a 

wildland management plan, we intend 

to compare the actual time pattern of 

prescribed fires on the land with the 

pattern described in the applicable 

multi-year plan in a general way, rather 

than treating the multi-year plan as 

containing a specific schedule to which 

management must adhere. For example, 

if the wildland management plan 

identified an approximate 5-year burn 

interval, the EPA would not disapprove 

a demonstration if the burn occurred on 

a 4-year or a 6-year interval. 

Therefore, we are proposing in rule 

text that we will consider a 

demonstration’s referencing of a multiyear land or resource management 

plan 91 (and including either a copy or 

an internet link to the plan) with a 

stated objective to establish, restore and/ 

or maintain a sustainable and resilient 

wildland ecosystem and/or to preserve 

endangered or threatened species that 

also identifies the subject area as a 

candidate for prescribed fire to be 

dispositive evidence that a particular 

fire conducted in accordance with such 

a plan satisfies the ‘‘unlikely to recur at 

a particular location’’ criterion. We 

would also consider a demonstration’s 

referencing of a fire management plan 

for tribal or private lands that has been 

reviewed and certified by the 

appropriate fire and/or resource 

management professionals and agreed to 

and followed by the land owner/

manager to be sufficient evidence 

satisfying the ‘‘unlikely to recur at a 

particular location’’ criterion. 

(iv) Not reasonably controllable or 

preventable. Consistent with current 

practice and 2007 preamble/rule 

language, the EPA considers it 

appropriate to allow air agencies to rely 

on an in-place and implemented statecertified SMP to satisfy the 

controllability prong of the ‘‘not 

reasonably controllable or preventable’’ 

criterion. The EPA proposes to 

incorporate the six elements of SMPs 

discussed in the 1998 Interim Air 

Quality Policy on Wildland and 

Prescribed Fires and referenced in the 

preamble to the 2007 Exceptional 

Events Rule into the preamble of the 

final rule for this proposal, where it 

would serve as guidance. That is, at a 

minimum, a state-certified SMP would 

include provisions for (i) authorization 

to burn, (ii) minimizing air pollutant 

emissions, (iii) smoke management 

components of burn plans, (iv) public 

education and awareness, (v) 

surveillance and enforcement, and (vi) 

program evaluation. Certification would 

require that the air agency certify in a 

letter to the Administrator of the EPA, 

or a Regional Administrator, that it has 

adopted and is implementing a SMP.92

Alternatively, the EPA solicits comment 

on incorporating these SMP elements 

into rule text language. The EPA 

proposes to accept as sufficient the 

testimony of the air agency submitting 

an exceptional events demonstration 

that the SMP is being implemented, 

provided that prior to the EPA’s acting 

on a demonstration, the record contains 

no clear evidence to the contrary. 

Consistent with current practice and 

2007 preamble and rule language, the 

EPA also considers it appropriate to 

allow air agencies to rely on a burn 

manager’s use of BSMP that minimize 

emissions and control impacts, in lieu 

of a state-certified SMP, to satisfy the 

controllability prong of the ‘‘not 

reasonably controllable or preventable’’ 

criterion. To provide clarity and reduce 

uncertainty for air agencies and burn 

managers, the EPA proposes to identify 

in the rule text six BSMP practices as 

being generally applicable for 

exceptional events purposes for 

prescribed fires on wildland as well as 

other prescribed fires. The six BSMP, 

listed and described in more detail in 

Table 3, come from guidance on BSMP 

for prescribed burns provided by the 

U.S. Department of Agriculture (USDA) 

Forest Service (USFS) and USDA 

Natural Resources Conservation Service 

(NRCS).93 Land managers of other 

federal, state and local agencies and 

private land owners generally endorse 

and follow this BSMP guidance.94 While 

the listed practices are broadly stated, 

fire managers use site-specific 

considerations to select the exact 

actions of each type and apply them to 

specific burn projects. There may be 

situations in which one or more of the 

six BSMP is clearly not applicable for a 

particular prescribed burn—for 

example, if a prescribed fire is so remote 

that there are no neighbors to be 

notified. The EPA generally does not 

intend to challenge a burn manager’s 

selection of the intensity or specific 

measure within the BSMP categories 

when we review a particular 

exceptional events demonstration. As 

part of the on-going assessment of our 

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regulatory programs, we intend to 

generally review those practices 

commonly employed by federal 

agencies and other users of prescribed 

fire. 

As another component of the 

approach for prescribed fires on 

wildland, the EPA is proposing to 

accept as evidence of the actual use of 

BSMP the fire manager’s statement that 

he or she employed applicable BSMP 

for a prescribed fire. Documentation of 

such statement for an exceptional events 

demonstration could consist of a copy of 

the routine post-burn report or a letter 

prepared by the fire manager (see 

example content of a burn report in 

Table 4). The EPA and other federal 

agencies will work collaboratively to 

provide access to such post-burn reports 

by air agencies that need them. We 

encourage land managers and other 

organizations that employ prescribed 

fires to work with states and tribes to 

develop an efficient process to provide 

air agencies with documentation that 

BSMP were employed for particular 

prescribed fires. 

TABLE 3—SUMMARY OF BASIC SMOKE MANAGEMENT PRACTICES, BENEFIT ACHIEVED WITH THE BSMP, AND WHEN IT IS

APPLIED

[before, during or after ignition of the burn] a

Basic smoke management practice Benefit achieved with the BSMP When the BSMP is applied—before/during/

after the burn 

Evaluate Smoke Dispersion Conditions ............. Minimize smoke impacts .................................. Before, During, After.

Monitor Effects on Air Quality ............................ Be aware of where the smoke is going and 

degree it impacts air quality.

Before, During, After. 

Record-Keeping/Maintain a Burn/Smoke Journal.Retain information about the weather, burn 

and smoke. If air quality problems occur, 

documentation helps analyze and address 

air regulatory issues.

Before, During, After. 

Communication—Public Notification .................. Notify neighbors and those potentially impacted by smoke, especially sensitive receptors.Before, During. 

Consider Emission Reduction Techniques ........ Reducing emissions through mechanisms 

such as reducing fuel loading can reduce 

downwind impacts.

Before, During, After. 

Share the Airshed—Coordination of Area Burning.Coordinate multiple burns in the area to manage exposure of the public to smoke.Before, During, After. 

aThe EPA believes that elements of these BSMP could also be practical and beneficial to apply to wildfires for areas likely to experience recurring wildfires. 

TABLE 4—ELEMENTS THAT MAY BE INCLUDED IN BURN PLANS AND POST-BURN REPORTS FOR PRESCRIBED FIRES

SUBMITTED AS EXCEPTIONAL EVENTS

Element Burn plan Post-burn report 

Fire Name a ......................................................... X ....................................................................... X. 

Permit number (if appropriate) ........................... X ....................................................................... X. 

Latitude/longitude and physical description ....... X ....................................................................... X. 

Date of burn, ignition time and completion time 

(duration of burn).

X ....................................................................... X. 

AQI status on burn day, if available (both in the 

vicinity of the fire and in the affected upwind 

area).

Predicted .......................................................... Actual. 

Acres burned ...................................................... Planned ............................................................ Actual (blackened). 

Description of fuel loading .................................. Estimated ......................................................... Actual (tons consumed). 

Meteorological data (weather conditions, wind 

speed and direction, dispersion).

Predicted conditions (including predicted dispersion).Actual conditions (including actual dispersion). 

Smoke Impacts ................................................... Anticipated smoke impacts .............................. Observed or reported smoke impacts (include 

nature, duration, spatial extent and copies 

of received complaints). 

BSMP actions to reduce impacts ....................... Expected BSMP actions .................................. Actual BSMP actions. 

Recommendations for future burns in similar 

areas.

.......................................................................... X. 

Analytics (modeled/actual fire spread, satellite 

imagery and analysis, webcam/video, PM/

ozone concentrations over the course of the 

fire).

.......................................................................... X. 

aThe ‘‘Fire Name’’ should be unique and referenced, to the greatest extent possible, in all exceptional events-related documentation, including 

the event name in AQS. The fire name could simply consist of the county and state in which the burn occurred (e.g., County X, State Y Prescribed Burn on Date Z) if no other name has been assigned. 

States with certified SMPs typically 

have robust communications between 

officials concerned with air quality 

impacts and officials and members of 

the public who use prescribed fire. 

These groups communicate during the 

development of the SMP, during the 

day-to-day burn authorization process 

and in the periodic review and potential 

revision of the SMP. States that instead 

rely on fire managers employing BSMP 

on a more individual basis may not have 

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95See additional information on prescribed fire 

councils on the Coalition of Prescribed Fire 

Councils, Inc. Web site at http://www.prescribed

fire.net/membership/state-councils. 

96Many multi-year plans developed by state and 

federal agencies are available electronically online 

or can be requested directly from the preparing 

agency. Interested parties can also request 

electronic versions of project level plans, if they are 

not available online. 

97On a case-by-case basis, in the absence of a 

multi-year plan, the EPA would also consider a 

prescribed fire on wildland conducted on a fire 

return interval established according to scientific 

literature to satisfy the not reasonably controllable 

or preventable criterion provided the prescribed fire 

was also conducted with the objective to establish, 

restore and/or maintain a sustainable and resilient 

wildland ecosystem and conducted in compliance 

with either a state-certified SMP or BSMP. This 

case-by-case approach is similar to the approach 

currently used under the 2007 Exceptional Events 

Rule. 

98With respect only to the not reasonably 

controllable prong, we also believe that the SMP 

and BSMP approach each is sufficient for 

prescribed fires that are not on wildland. 

such regularly occurring 

communications processes, particularly 

in states in which state legislation gives 

the leadership of fire management to a 

forestry or public safety agency rather 

than to an air agency. We encourage all 

agencies and managers/owners involved 

in land, air quality and fire management 

to develop good communications about 

both fire use practices in general and 

plans for specific prescribed fires with 

use of BSMP. This will, among other 

benefits, allow them to better coordinate 

on public air quality notice efforts and, 

if necessary, public health advisories 

should smoke enter an inhabited area. 

Additionally, the EPA encourages the 

development of ‘‘prescribed fire 

councils,’’ comprised of federal, state, 

tribal, private and other stakeholders to 

coordinate activities involving fire 

planning issues and, thus, minimize or 

prevent smoke impacts while using 

prescribed fire to accomplish land 

management objectives.95 However, we 

are not proposing that notifications 

between prescribed fire users and 

specific types of state agencies be a 

condition for approval of a prescribed 

fire as an exceptional event. 

As previously stated, to date we have 

considered the existence and 

implementation of a SMP or the use of 

BSMP to be a necessary part of the 

supporting evidence needed to satisfy 

the not reasonably controllable or 

preventable criterion, but we have not 

clearly addressed what conditions are 

minimally sufficient to satisfy the 

criterion. The remainder of this section 

focuses on that issue. 

Because prescribed fires are 

intentionally initiated, clarifying the 

minimal conditions for the not 

reasonably preventable prong is 

particularly relevant. The detailed 

USFS/NRCS guidance on the fifth listed 

BSMP, Consider Emission Reduction 

Techniques, includes the potential to 

reduce the fuel loading. It does not 

suggest that it may be reasonable to not 

ignite a particular prescribed fire (i.e., 

that the fire be prevented), because this 

guidance is aimed at those fires that are 

already planned to happen. Similarly, 

SMPs address coordination of 

previously planned prescribed fires and 

typically do not ask SMP participants to 

consider whether particular prescribed 

fires are reasonably preventable. 

Therefore, we do not believe that the 

existence of an SMP or the use of BSMP 

is a sufficient basis for concluding that 

a prescribed fire is not reasonably 

preventable. A prescribed fire should be 

concluded to be not reasonably 

preventable on the basis of the benefits 

that would be foregone if it were not 

conducted, as described below. 

For federal agencies, the planning of 

prescribed fire programs typically 

happens through the development of 

multi-year plans that focus on specific 

land or resource management objectives. 

This planning process, and the resulting 

multi-year plan, typically considers the 

importance of a prescribed fire program 

to achieving land management goals, 

which may include an objective to 

establish, restore and/or maintain a 

sustainable and resilient wildland 

ecosystem, in light of the availability, 

cost and effectiveness of other 

approaches to fuel management. The 

final multi-year plans thus generally 

identify the level of prescribed fire use 

necessary to achieve those goals. As 

noted previously, some tribes, private 

landowners (and federal, state and local 

agencies working with private 

landowners) and state agencies that 

manage state-owned lands (e.g., state 

parks) also prepare multi-year 

management plans. While plans 

developed by public agencies (i.e., state 

and federal agencies) often undergo 

public comment prior to being 

finalized,96 the plans developed by 

tribes and private landowners may not 

follow a public comment process. 

However, public agencies often work 

with tribes and private owners to 

develop these plans, which are based on 

conservation practices and standards 

that have often undergone public 

comment as part of the state or federal 

agency process. Not conducting the 

prescribed fire programs described in 

such plans could mean forgoing 

important ecosystem services and other 

benefits. Accordingly, the EPA is 

proposing in rule text form to consider 

a prescribed fire on wildland conducted 

in accordance with a multi-year fire 

management plan that has an objective 

to establish, restore and/or maintain a 

sustainable and resilient wildland 

ecosystem to be not reasonably 

preventable, provided there is no 

compelling evidence to the contrary in 

the record when the EPA approves the 

associated exceptional events 

demonstration.97

We also propose in rule text that 

compliance with either a state-certified 

SMP or BSMP is sufficient to establish 

that a prescribed fire was not reasonably 

controllable, provided there is no 

compelling evidence to the contrary in 

the record when the EPA concurs with 

the associated exceptional events 

demonstration. This is an appropriate 

approach to implementing CAA section 

319(b), because SMPs and BSMP aim to 

reasonably control the air quality 

impacts of prescribed fires.98

This two-part categorical approach 

would reduce the length of exceptional 

events demonstrations for prescribed 

fires on wildland and make the 

demonstration preparation and review 

process more resource efficient. In 

summary, to satisfy the not reasonably 

controllable or preventable criterion for 

a prescribed fire on wildland, a 

demonstration would need to identify 

that the prescribed burn was conducted 

in accordance with a multi-year plan 

that has an objective of the 

establishment, restoration and/or 

maintenance of a sustainable and 

resilient wildland ecosystem and was 

conducted in compliance with either a 

state-certified SMP or BSMP. 

Finally, we are proposing to remove 

the phrase ‘‘and must include 

consideration of development of a SMP’’ 

from the sentence of the existing text of 

40 CFR 50.14(b)(3) that reads, ‘‘If an 

exceptional event occurs using the basic 

smoke management practices approach, 

the State must undertake a review of its 

approach to ensure public health is 

being protected and must include 

consideration of development of a 

SMP.’’ While the EPA supports states 

considering the development of a SMP 

in the situation described in this 

sentence, we believe states have had 

ample opportunity to develop such a 

program since 2007. This rule language 

effectively requires an ongoing 

consideration to develop an SMP every 

time a prescribed fire causes a NAAQS 

exceedance or violation that merits 

exclusion as an exceptional event. We 

do not believe Congress intended this 

ongoing consideration to be a 

requirement flowing from CAA section 

319(b). In addition, we believe that an 

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99The height of the tropopause varies with 

latitude and season but the average height at midlatitudes is about 11 kilometers (km) (7 miles or 

36,000 feet). The stratosphere, the second layer of 

the Earth’s atmosphere, is located above the 

tropopause at 13 to 50 km (8–31 miles or 43,000 to 

160,000 feet) above the Earth’s surface. 

100Pan, L. L., et al. (2014), ‘‘Thunderstorms 

enhance tropospheric ozone by wrapping and 

shedding stratospheric air.’’ Geophys. Res. Lett., 41, 

7785–7790, doi:10.1002/2014GL061921. 

101A. O. Langford, K. C. Aikin, C. S. Eubank and 

E. J. Williams. Stratospheric Contribution to High 

Surface Ozone in Colorado During Springtime, 

Geophysical Research Letters, Vol. 36, Issue 12, 

June 2009. 

102Other mechanisms by which stratospheric 

ozone is transported into the troposphere include 

cutoff cyclones, streamers (long filamentary 

structures that often roll into vortices), and clear air 

turbulence (see http://www.atmos.umd.edu/∼dkuhl/ 

documents/Kuhl_Tropopause_Folding.ppt). 

103 Integrated Science Assessment of Ozone and 

Related Photochemical Oxidants (Final Report). 

U.S. EPA.Washington, DC EPA/600/R–10/076F. 

Available at: http://www3.epa.gov/ttn/naaqs/

standards/ozone/s_o3_2008_isa.html. 

104Cristofanelli, P. A 6-year analysis of 

stratospheric intrusions and their influence on 

ozone at Mt. Cimone (2165 m above sea level). 

Journal of Geophysical Research, Vol. 111, D03306, 

doi:10.1029/2005JD006553, 2006. 

105A recent review of AQS data revealed 216 sites 

in the United States with collocated ozone and 

carbon monoxide monitors in operation after 

January 1, 2014. Most of these sites are located in 

either urban or suburban locations. In these 

settings, local emissions would likely hide the 

stratospheric CO suppression. 

106Lidar, which stands for Light Detection and 

Ranging, is a remote sensing method that uses light 

in the form of a pulsed laser to measure ranges 

(variable distances) to the Earth. These light pulses, 

combined with other data recorded by the airborne 

system, generate precise, three-dimensional 

information about the shape of the Earth and its 

surface characteristics. See, NOAA definition at 

http://oceanservice.noaa.gov/facts/lidar.html. 

107See NOAA data available at ftp://

aftp.cmdl.noaa.gov/data/ozwv/Ozonesonde. On 

April 30, 2015, NOAA’s site identified the 

following five sites in the U.S. that conduct biweekly ozone sonde launchings: Hilo, HI; 

Huntsville, AL; Narragansett, RI; Trinidad Head, 

CA; and Boulder, CO. Additional launchings occur 

in Pago Pago, American Samoa, and outside of the 

U.S. in Greenland, Antarctica and Fiji. 

SMP is most appropriate when multiple 

parties wish to employ prescribed fire at 

about the same time in the same 

airshed, which is a more narrow 

situation than specified in this sentence. 

We also do not want our rules to be 

open to an inference that development 

of a SMP should only be considered 

following a NAAQS exceedance or 

violation, because the impacts from fires 

may affect public health in areas 

without NAAQS-compliance air 

monitoring stations. Also, we believe 

that when air agencies observe NAAQS 

exceedances or violations attributed to a 

prescribed fire, air agencies should 

consider a wide range of alternatives 

including, but not limited to, the 

development of a SMP. For example, 

agencies might also consider the more 

frequent or intensive use of BSMP to 

limit the fuel available to burn in each 

fire. 

The EPA solicits comment on all 

aspects of the identified fire-related 

approaches. 

3. Stratospheric Ozone Intrusions 

a. Current Situation 

Stratospheric ozone intrusions are 

natural events that occur when a parcel 

of air originating in the stratosphere is 

re-entrained into the troposphere, and 

in some cases mixes directly to the 

surface of the earth. These relatively 

rare events can create elevated ozone 

concentrations that affect areas ranging 

from a single monitoring site to a wider 

area as the air mass with a high ozone 

concentration moves across the 

landscape. 

Normally, the tropopause, the 

temperature inversion layer of air that 

separates the troposphere from the 

stratosphere, limits the transport of 

stratospheric air into the troposphere, 

the lowest layer of the Earth’s 

atmosphere.99 In some cases, however, 

parcels or ribbons of ozone-rich air from 

the stratosphere can be transported 

rapidly to the surface during deep 

mixing events, such as thunderstorms or 

strong frontal passages, by a process 

known as tropopause folding. Although 

this ‘‘folding’’ process can occur 

throughout the year, it is typically 

associated with frontal passages and 

upper level low pressure systems during 

the spring season.100 101 The ozone 

transported through these ‘‘folds,’’ or 

through other less significant 

mechanisms, may disperse within and 

be destroyed in the upper troposphere 

or it may mix down to the surface.102

The ‘‘intrusion’’ of stratospheric ozone 

is identified most frequently at high 

elevation sites where upper 

tropospheric air is more likely to reach 

the surface than at lower elevation sites 

where more downward movement 

would be needed for a monitoring site 

to be affected. At these high elevation 

sites in particular, stratospheric ozone 

intrusion has been estimated to 

contribute about 20 to 25 percent of the 

total tropospheric ozone budget and can 

cause relatively short-term (i.e., ranging 

from several hours to 2–3 days in 

duration) increases of surface ozone of 

10 to 50 ppb above normal background 

levels.103 Stratospheric intrusions with 

short-lived surface ozone concentrations 

of several hundred ppb have also been 

observed, although these events are 

extremely rare. 

Because stratospheric intrusion events 

are relatively infrequent and because 

identifying and monitoring these events 

are challenging, there have been few 

direct measurements showing that a 

given parcel of surface air contains 

stratospheric ozone (versus ozone 

generated by local natural or 

anthropogenic sources). Interpreting 

these direct measurements is also 

challenging. One approach to confirm 

the presence of stratospheric ozone in 

surface air is through the use of the 

beryllium tracers, beryllium isotopes 

Be-7 and Be-10, which are produced 

primarily in the stratosphere by cosmic 

ray collisions with atmospheric gas 

atoms.104 Beryllium isotope 

measurements are, however, rare and 

expensive, and, consequently not 

normally available. 

More common approaches to identify 

stratospheric ozone in surface air can 

include evaluating measurements at the 

potentially influenced ozone monitoring 

site for very low concentrations of CO 

and/or relative humidity. Both can be 

strong indicators of stratospheric air 

because, relative to tropospheric air, 

stratospheric air has very low relative 

humidity and very low concentrations 

of other air pollutants such as CO, NOX

and PM. The concurrent impacts on CO 

and relative humidity can be subtle, 

however, when stratospheric air has 

mixed with tropospheric air as the 

mixing process dilutes the ozone 

enhancement and increases CO and 

water vapor concentrations relative to 

stratospheric conditions. Typical CO 

monitors used for ambient air 

monitoring have operational ranges of 

500 to 50,000 ppb (0.5 to 50 ppm) and 

are not sufficiently sensitive to reliably 

measure the very low CO levels found 

in stratospheric air (50 to 150 ppb). 

Additionally, few rural high altitude 

monitoring sites have both ozone and 

CO monitors.105 The EPA urges air 

agencies to provide concurrent readings 

of ozone and CO and/or relative 

humidity in their exceptional events 

demonstrations if they have these data. 

The EPA will evaluate these data as a 

part of a weight of evidence showing 

alongside other qualitative evidence in 

a clear causal relationship showing. 

A third measurement-based approach 

to identifying stratospheric ozone could 

include measurements of ozone above 

ground level (i.e., measurements in the 

troposphere). This approach is also 

uncommon. Currently, five sites in the 

U.S. conduct ozone sonde (balloon) 

launches two or more times per week 

and an additional few research locations 

operate ozone lidars to vertically 

measure ozone profiles.106 107

In the absence of direct measurements 

of stratospheric tracers at ground level, 

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108See http://raqms-ops.ssec.wisc.edu/. 

109Wyoming Department of Environmental 

Quality, Air Quality Division. Big Piney and 

Boulder, Wyoming Ozone Standard Exceedance, 

June 14, 2012. Available at http://www2.epa.gov/

air-quality-analysis/exceptional-eventssubmissions-table. 

110 Interim Guidance on the Preparation of 

Demonstrations in Support of Requests to Exclude 

Ambient Air Quality Data Affected by High Winds 

Under the Exceptional Events Rule. U.S. EPA. May 

2013. Available at http://www2.epa.gov/sites/

production/files/2015-05/documents/exceptevents_

highwinds_guide_130510.pdf. 

meteorological models can indicate 

conditions under which stratospheric 

air parcels may reach the surface. 

Meteorological models such as the 

National Oceanic and Atmospheric 

Administration (NOAA)/National 

Weather Service (NWS) North American 

Mesoscale Forecast System (NAM) or 

the NOAA Rapid Update Cycle (RUC) 

models simulate parameters 

characteristic of stratospheric air such 

as isentropic potential vorticity (IPV) 

and potential temperature (PT) that can 

be used to identify tropopause folding. 

Visualization tools using the model 

output can show spatially where 

stratospheric air is located in proximity 

to or in contact with the surface. 

Similarly, atmospheric chemistry 

models, such as the National 

Aeronautics and Space Administration 

(NASA)/NOAA Real-time Air Quality 

Modeling System (RAQMS) 108 can 

provide both real time intrusion 

forecasting and retrospective analysis of 

ozone from intrusions. Finally, satellite 

observation of atmospheric ozone and 

CO can be used to validate predictions 

based on atmospheric modeling. 

Although as of the date of this 

proposal the EPA has concurred with 

only one stratospheric ozone intrusion 

exceptional events demonstration 

prepared under the provisions of the 

2007 Exceptional Events Rule (and 

disapproved none),109 the EPA has been 

communicating that we consider it 

appropriate to use the previously 

mentioned stratospheric ozone tools 

with other event/pollutant exceptional 

events analyses (e.g., seasonal analysis 

of ozone data, comparison of event days 

with non-event days, trajectory analysis, 

ozone measurement time series and 

spatial distribution analysis, 

meteorological analysis to show the 

presence of weather systems associated 

with typical intrusions and balloon 

soundings of the NWS Upper Air 

Observation Program to detect parcels of 

dry air aloft) to successfully 

demonstrate stratospheric ozone 

exceptional events. 

b. Proposed Changes 

As is true for all exceptional events 

and pollutant combinations, when 

submitting a demonstration for 

stratospheric ozone intrusion events, air 

agencies must address all of the 

Exceptional Events Rule criteria. As 

noted in this action, the EPA proposes 

to return to the core statutory elements 

and implicit concepts of CAA section 

319(b): That the event affected air 

quality in such a way that there exists 

a clear causal relationship between the 

specific event and the monitored 

exceedance or violation, the event was 

not reasonably controllable or 

preventable and the event was a human 

activity that is unlikely to recur at a 

particular location or was a natural 

event. The EPA suggests the following 

approach when addressing these 

technical criteria for an ozone 

exceedance or violation caused by a 

stratospheric intrusion. 

An air agency should begin by 

showing the geographic extent of 

elevated or exceedance-level ozone 

concentrations associated with the 

intrusion event in conjunction with an 

evaluation of the historical measured 

surface ozone levels for the same season 

(see section V.E.3 of this proposal for 

example analyses of how to present the 

comparison to historical concentrations 

within the clear causal relationship 

criterion). If the intrusion happened at 

a time of year when local or transported 

photochemical ozone is generally low, 

evidence that the intrusion affected 

ground level air quality may be 

relatively brief and still be sufficient, 

compared to an intrusion occurring at 

the height of the historical ozone 

season. 

If intrusion claims coincide with 

historically high photochemistry 

seasons, then the air agency may need 

additional evidence to support the clear 

causal relationship criterion by showing 

the relative contribution estimates to the 

exceedance from local and transported 

anthropogenic pollutants compared to 

the intrusion contribution. An air 

agency can provide additional analyses 

supporting the clear causal relationship 

by showing that an intrusion occurred at 

or near the location of an identified 

monitor by using atmospheric models 

such at RAQMS, NAM or RUC, with 

additional data from satellite 

observations of total column ozone and 

CO. 

The EPA intends to accept a short 

statement in a demonstration that 

because stratospheric ozone intrusions 

are purely natural events and are large 

in scale, they are not reasonably 

controllable or preventable. 

4. High Wind Dust Events 

a. Current Situation 

The 2007 Exceptional Events Rule 

preamble noted that ‘‘[t]he EPA’s final 

rule concerning high wind events states 

that ambient particulate matter 

concentrations due to dust being raised 

by unusually high winds will be treated 

as due to uncontrollable natural events 

where (1) The dust originated from 

nonanthropogenic sources, or (2) the 

dust originated from anthropogenic 

sources within the State, that are 

determined to have been reasonably 

well-controlled at the time that the 

event occurred, or from anthropogenic 

sources outside the State.’’ As noted in 

section IV.B of this document, although 

this language still reflects the EPA’s 

interpretation of what might be 

appropriate under the Exceptional 

Events Rule, the D.C. Circuit determined 

the language to be a legal nullity 

because the EPA did not specifically 

address high winds or ambient 

particulate matter concentrations in the 

promulgated regulatory language in 40 

CFR 50.14. 

The preamble to the 2007 Exceptional 

Events Rule also noted that because 

‘‘. . . the conditions that cause or 

contribute to high wind events vary 

from area to area with soil type, 

precipitation, and the speed of wind 

gusts, [air agencies] should provide 

appropriate documentation which 

indicates what types of circumstances 

contributed to the exceedances or 

violation at the monitoring site in 

question.’’ The EPA declined to identify 

a specific high wind threshold to qualify 

as being an exceptional event and 

instead relied on air agencies to submit 

appropriate documentation supporting 

their position. 

Because of the uncertainty associated 

with these high wind statements and 

stakeholder feedback asking the EPA to 

interpret this language and provide 

examples of applying the provisions in 

the 2007 Exceptional Events Rule to 

high wind dust events, the EPA clarified 

many concepts related to high wind 

dust events in its May 2013 Interim 

Exceptional Events Implementation 

Guidance, specifically the Interim High 

Winds Guidance document.110 In this 

guidance, the EPA defined a high wind 

dust event as including the high wind 

and the dust that the wind entrains and 

transports to a monitoring site, clarified 

our expectations regarding ‘‘reasonable 

controls’’ for high wind events with 

contribution from both natural and 

anthropogenic sources and introduced 

the concept of establishing a value for 

a high wind threshold, up to which 

reasonable windblown dust controls are 

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111We use ‘‘Western U.S.’’ to refer to states in the 

Great Plains (North Dakota, South Dakota, 

Nebraska, Kansas, Oklahoma and Texas) and those 

farther west including Arizona, California, 

Colorado, Nevada, New Mexico, Utah, and 

Wyoming. 

112As identified in section V.D of this proposal, 

the EPA will generally consider human activity to 

have played little or no direct role in causing 

emissions of the dust generated by high wind for 

purposes of the regulatory definition of ‘‘natural 

event’’ if contributing anthropogenic sources of the 

dust are reasonably controlled, regardless of the 

amount of dust coming from these reasonably 

controlled anthropogenic sources, and thus the 

event could be considered a natural event. In such 

cases, the EPA believes that it would generally be 

a reasonable interpretation to find that the 

anthropogenic source had ‘‘little’’ direct causal role. 

If anthropogenic sources of windblown dust that are 

reasonably controllable but that did not have those 

reasonable controls applied at the time of the high 

wind event have contributed significantly to a 

measured concentration, the event would not be 

considered a natural event. 

113Areas Affected by PM–10 Natural Events (the 

PM10 Natural Events Policy), memorandum from 

Mary D. Nichols, Assistant Administrator for Air 

and Radiation, to EPA Regional Offices, May 30, 

1996. 

114See Appendix A1 of the Interim Guidance on 

the Preparation of Demonstrations in Support of 

Requests to Exclude Ambient Air Quality Data 

Affected by High Winds Under the Exceptional 

Events Rule. U.S. EPA. May 2013. Available at 

http://www2.epa.gov/sites/production/files/2015- 

05/documents/exceptevents_highwinds_guide_

130510.pdf. 

115See Appendices A2 and A3 in the Interim 

Guidance on the Preparation of Demonstrations in 

Support of Requests to Exclude Ambient Air 

Quality Data Affected by High Winds Under the 

Exceptional Events Rule. U.S. EPA. May 2013. 

Available at http://www2.epa.gov/sites/production/ 

files/2015-05/documents/exceptevents_highwinds_

guide_130510.pdf for additional information on the 

development of a high wind threshold. 

116Section 6.3.2.2 in the Interim Guidance on the 

Preparation of Demonstrations in Support of 

Requests to Exclude Ambient Air Quality Data 

Affected by High Winds Under the Exceptional 

Events Rule. U.S. EPA. May 2013. Available at 

http://www2.epa.gov/sites/production/files/2015- 

05/documents/exceptevents_highwinds_guide_

130510.pdf for details on the calculation of 

sustained wind speed. Generally, the EPA will 

accept that high winds could be the cause of a high 

24-hour average PM10 or PM2.5 concentration if 

there was at least one full hour in which the hourly 

average wind speed was above the area-specific 

high wind threshold. 

117The 25 mph threshold is based on studies 

conducted on natural surfaces. See additional 

information relevant to establishing this threshold 

in Appendix A1 in the Interim Guidance on the 

Preparation of Demonstrations in Support of 

Requests to Exclude Ambient Air Quality Data 

Affected by High Winds Under the Exceptional 

Events Rule. U.S. EPA. May 2013. Available at 

http://www2.epa.gov/sites/production/files/2015- 

05/documents/exceptevents_highwinds_guide_

130510.pdf. 

expected to be effective in the absence 

of site specific data or analyses. 

As identified in the Interim High 

Winds Guidance document, dust 

phenomena are experienced primarily 

in the western U.S. where rainfall is 

seasonal, creating dry and dusty 

landscapes.111 In high wind dust events, 

the meteorological phenomenon (i.e., 

wind) is purely natural, but the 

pollution from the event may be a 

mixture of natural sources (e.g., 

undisturbed soil) and anthropogenic 

sources (e.g., soil disturbed by human 

activity, emissions from sand and gravel 

facilities, etc.). The EPA generally 

classifies high wind dust events as 

‘‘natural events’’ in cases where 

windblown dust is entirely from natural 

sources or where all significant 

anthropogenic sources of windblown 

dust have been reasonably controlled.112

This long-standing policy was first 

established in the PM10 Natural Events 

Policy, which provided that: 

Ambient PM–10 concentrations due to dust 

raised by unusually high winds will be 

treated as due to uncontrollable natural 

events under the following conditions: (1) 

The dust originated from nonanthropogenic 

sources, or (2) the dust originated from 

anthropogenic sources controlled with best 

available control measures (BACM).113

Also integral to definition of a high 

wind dust event is that the wind speed 

be ‘‘high,’’ or, as indicated in the PM10

Natural Events Policy, ‘‘unusually 

high.’’ Only ‘‘high wind’’ dust events 

are exceptional events and ‘‘high’’ is 

area-specific. 

Typically, undisturbed desert 

landscapes in the western U.S. have a 

natural crust that protects the surface 

and tends to limit emissions of 

windblown dust. The wind speed 

capable of causing emissions from these 

natural undisturbed areas varies by 

location, depending on characteristics of 

the local landscape (e.g., soil type and 

characteristics, vegetation). Numerous 

studies have been conducted to 

determine the minimum wind speed 

capable of causing emissions from 

natural undisturbed areas and/or 

overwhelming reasonable controls on 

anthropogenic sources.114 In the Interim 

High Winds Guidance, the EPA called 

the minimum threshold wind speed 

capable of causing emissions from 

natural undisturbed areas or 

overwhelming reasonable controls on 

anthropogenic sources the ‘‘high wind 

threshold.’’ 

In the Interim High Winds Guidance, 

the EPA articulated its expectations 

regarding the development and 

application of high wind thresholds. In 

this guidance, the EPA encouraged air 

agencies to identify an appropriate high 

wind threshold for each area 

experiencing high wind dust events 

within their exceptional events 

submissions for high wind dust 

events.115 The guidance recommended 

that these thresholds should consider 

local conditions and specify a minimum 

wind speed capable of causing 

emissions from those natural 

undisturbed areas or overwhelming 

reasonable controls on contributing 

anthropogenic sources (see section V.E.2 

for additional discussion regarding 

reasonable controls). This approach was 

consistent with the PM10 Natural Events 

Policy in which the EPA recommended 

that air agencies define the conditions 

in which BACM level controls were 

overwhelmed. The area-specific high 

wind threshold should be representative 

of conditions (i.e., sustained wind 

speeds 116) that are capable of 

overwhelming reasonable controls 

(whether RACM, BACM or other) on 

anthropogenic sources and/or causing 

emissions from natural undisturbed 

areas. The threshold was not intended 

to represent the minimum wind speed 

at which any level of emissions could 

occur (e.g., aerodynamic entrainment), 

but rather when significant emissions 

begin due to reasonable controls or 

natural undisturbed areas becoming 

overwhelmed. We have stated that if an 

agency is unable to develop an areaspecific high wind threshold, we 

generally will accept a threshold of a 

sustained wind of 25 mph for areas in 

the western U.S. provided the agencies 

support this as the level at which they 

expect stable surfaces (i.e., controlled 

anthropogenic and undisturbed natural 

surfaces) to be overwhelmed.117 We did 

not indicate what form such support 

could take. We also have said that if we 

receive specific information based on 

relevant studies to choose an alternative 

high wind threshold for an identified 

area, we will notify the affected air 

agency. 

Also as noted in the Interim High 

Winds Guidance document, the EPA has 

expected air agencies to provide 

relevant wind data (e.g., wind speed and 

direction) as part of an exceptional 

events submission for high wind dust 

events. Wind speed data consist of 

analyses and statistics showing how the 

observed high wind dust event wind 

speed compares to the distribution of 

historical wind speeds and the 

established high wind threshold. The 

EPA has recommended that air agencies 

show these historical comparisons on an 

annual and/or seasonal basis, depending 

on which is more appropriate, using a 

format similar to the recommended 

format of the comparison to historical 

concentrations showing as part of the 

clear causal relationship criterion 

discussed in section V.E.3 of this 

proposal. The EPA has encouraged air 

agencies to discuss wind direction in 

the narrative and to present wind 

direction information graphically in 

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118Reference Guide for Cropping Systems and 

General Land Management. USDA, NRCS and U.S. 

EPA. October 2012. Available at http://

www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/

stelprdb1049502.pdf. 

maps/plots in the clear causal 

relationship section of the high wind 

dust exceptional events demonstration. 

In considering past high wind dust 

event demonstrations, the EPA has 

found that the ‘‘not reasonably 

controllable or preventable’’ and the 

‘‘clear causal relationship’’ (to include 

the comparison to historical 

concentrations showing) criteria play 

significant roles in the supporting 

exceptional events documentation. The 

EPA has generally found that for high 

wind dust events, air agencies can meet 

the ‘‘human activity or natural event’’ 

criterion by satisfying the requirements 

for not reasonably controllable or 

preventable and clear causal 

relationship as well as addressing the 

additional components of exceptional 

events demonstration packages as 

discussed in section V.G. 

As is the case with all demonstration 

packages, air agencies with agricultural 

sources that potentially contribute to 

high wind event-related emissions 

should address the question of source 

contribution and associated reasonable 

controls on these sources within the not 

reasonably controllable or preventable 

portion of the demonstration. The EPA 

has noted in previous guidance that 

when considering the anthropogenic 

sources that contribute to event-related 

emissions and the appropriate 

‘‘reasonable controls’’ on these sources, 

air agencies should be aware of USDA/ 

NRCS-approved Best Management 

Practices (BMPs) (also referred to as 

conservation management practices) 

that are designed to effectively reduce 

fugitive dust air emissions and prevent 

soil loss in agricultural applications.118

We have stated that these BMPs could 

be included in the collection of controls 

determined to constitute reasonable 

controls for wind-blown dust events in 

areas in which they have been 

implemented. 

b. Proposed Changes 

The EPA proposes to include in the 

preamble to the final rule for this action 

a modified version of some of the 

language that first appeared in the 

Interim High Winds Guidance 

document and to incorporate into the 

rule text the revisions proposed in this 

section. We also intend to revise the 

Interim High Winds Guidance to be 

consistent following promulgation of 

final Exceptional Events Rule revisions. 

Definition of an Event. Consistent 

with the EPA’s proposal to revise the 

regulatory definition of an exceptional 

event to include both the event and its 

associated resulting emissions, the EPA 

proposes to define a high wind dust 

event as an event that includes the highspeed wind and the dust that the wind 

entrains and transports to a monitoring 

site. Consistent with the nullified 

language in the 2007 Exceptional Events 

Rule preamble, the PM10 Natural Events 

Policy and the Interim High Winds 

Guidance, the EPA proposes to define 

high wind dust events in the rule text 

as ‘‘natural events’’ in cases where 

windblown dust is entirely from natural 

sources or where all significant 

anthropogenic sources of windblown 

dust have been reasonably controlled. 

High Wind Threshold. To facilitate 

clearer expectations regarding the 

evidence needed to demonstrate which 

controls constitute ‘‘reasonable 

controls,’’ the EPA proposes to codify in 

rule language the definition of ‘‘high 

wind threshold’’ as the minimum 

threshold wind speed capable of 

causing particulate matter emissions 

from natural undisturbed lands in the 

area affected by a high wind dust event. 

The EPA proposes to accept a threshold 

of a sustained wind of 25 mph for areas 

in the western U.S. provided this value 

is not contradicted by evidence in the 

record when we review a 

demonstration. If the EPA receives 

specific information based on relevant 

studies that suggest a different high 

wind threshold for an identified area, 

the EPA will notify the affected air 

agency so that the agency may consider 

basing its demonstration on that 

threshold value. The EPA would 

consider such information as part of the 

weight of evidence analysis for a 

submitted demonstration. In lieu of 

using the default 25 mph high wind 

threshold, air agencies would have the 

option to identify an area-specific high 

wind threshold that is more 

representative of local/regional 

conditions. 

The high wind threshold concept will 

continue to apply to the review of 

demonstrations for events in a 

nonattainment or maintenance area for 

which the dust controls in a recently 

approved SIP are generally accepted as 

sufficient to satisfy the not reasonably 

controllable criterion. For such a 

demonstration, the controls specified in 

the SIP should be considered 

reasonable, while acknowledging the 

possibility that the controls are not 

being complied with and that 

uncontrolled anthropogenic sources of 

PM could be the contributing to the 

exceedance. For events with sustained 

wind speeds above the high wind 

threshold, it is very plausible that SIP 

controls were being implemented and 

the high PM concentrations are due to 

emissions generated from sources in the 

area despite implementation of the SIP 

measures. Conversely, for events with 

sustained wind speeds below the high 

wind threshold, it becomes more 

plausible that there may be 

noncompliance with control measures 

or that uncontrolled anthropogenic 

sources are contributing to the 

exceedance. Therefore, the comparison 

of sustained wind speeds during an 

event to the high wind threshold will 

help the EPA Regional offices determine 

what evidence is required to be 

included in a demonstration regarding 

reasonable controls, the possibility of 

non-compliance, or non-event sources. 

Large-Scale or High-Energy High 

Wind Dust Events. The EPA proposes to 

codify in rule language to apply a casespecific approach when considering 

reasonableness of controls for remote, 

large-scale, high-energy and/or sudden 

high wind dust events, such as 

‘‘haboobs’’ in the southwest where 

sustained wind speeds can exceed 40 

mph and generate walls of dust several 

miles wide and more than a mile high. 

The proposed rule text provides that in 

these situations, the event will be 

considered not reasonably preventable 

or controllable. Therefore, a 

demonstration limited to such event(s) 

will not need to substantively address 

this criteria. The EPA solicits comment 

on this proposed, case-specific approach 

when considering reasonableness of 

controls for remote, large-scale, highenergy and/or sudden high wind dust 

events. 

Other Types of High Wind Dust 

Events. Any demonstration for a nonhigh-energy event would be evaluated 

on a case-by-case basis. In doing so, the 

EPA would consider what controls are 

reasonable in light of an area’s 

attainment status and associated CAA 

control requirements, the frequency, 

and range of non-high energy wind 

events known (at the time of the 

particular event that is the subject of the 

demonstration) to occur in the area. 

The Role of the EPA-approved SIP in 

Nonattainment and Maintenance Areas. 

As stated in section V.E.2, the EPA 

proposes to establish by rule a nonrebuttable presumption that, during a 5- 

year window (or, alternatively another 

appropriate timeframe) following 

approval of an attainment plan or 

maintenance plan SIP during which no 

subsequent new obligation for the air 

agency to revise the SIP has arisen, the 

control measures included in the SIP 

that are specific to the relevant 

pollutant, sources and event type satisfy 

the not reasonably controllable or 

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119A request for data exclusion must also show 

that the event was not a result of noncompliance 

with any existing state or local laws or rules that 

have not been incorporated into the SIP. 

120Other possible reasons for an area to be in a 

Scenario 2 situation would be if it has been 

designated nonattainment for a revised NAAQS for 

the relevant pollutant or is subject to a SIP call for 

the relevant pollutant following the EPA’s 

determination that the SIP is inadequate for some 

other reason. 

preventable criterion.119 Otherwise, the 

air agency and the EPA would evaluate 

the not reasonably controllable or 

preventable criterion on a case-by-case 

basis. 

We describe below one potential 

scenario in which deference to the SIP 

for purposes of ‘‘reasonable controls’’ 

(versus a case-by-case analysis) satisfies 

the not reasonably controllable or 

preventable criterion. We also provide 

two other scenarios needing a case-bycase analysis for purposes of satisfying 

the not reasonably controllable or 

preventable criterion. We identify these 

scenarios below and then discuss them 

in more detail in sequence. 

• Nonattainment Area Scenario 1— 

The EPA approved the SIP with the 

enforceable control measures as meeting 

attainment or maintenance planning 

requirements within 5 years of the date 

of submittal of the event AND the air 

agency is not under an obligation to 

revise the SIP for the reason listed in 

Scenario 2 or any other reason. 

Additionally, the sustained winds 

during the event are above the high 

wind threshold. The SIP includes 

enforceable control measures that 

address the event-related pollutant and 

all sources necessary to fulfill the 

requirements of the CAA for the SIP that 

have or may have contributed to eventrelated emissions. This indicates that in 

the development and approval of the 

SIP, both the EPA and the state 

considered what event-related controls 

were sufficient to meet the attainment or 

maintenance plan requirements of the 

CAA. 

• Nonattainment Area Scenario 2— 

The air agency is under an obligation to 

revise the SIP as a result of a SIP call 

based on failing to provide for 

attainment and maintenance of the 

relevant NAAQS as evidenced by 

current violations.120

• Maintenance Area Scenario 3—The 

EPA approved the SIP more than 5 years 

prior to the date of submittal of a 

demonstration. 

Details for Nonattainment Area 

Scenario 1 

In this scenario, where the sustained 

winds during the event are above the 

high wind threshold, the EPA would 

apply a non-rebuttable presumption that 

the controls in the existing SIP represent 

reasonable measures to prevent or 

control any event of the given type that 

occurs in the 5-year window. To satisfy 

the not reasonably controllable or 

preventable criterion, the EPA would 

expect the submitting air agency to 

identify the emission sources that 

contribute to the event emissions and 

exceedance and identify the associated 

SIP controls plus any other enforceable 

control measures required by state laws 

or rules. The air agency would also 

identify the implementation status of 

these controls and provide evidence of 

effective implementation and 

enforcement. 

Example: An air agency submits a 

demonstration for a high wind dust 

event in a PM10 nonattainment area that 

occurred in October 2015. The air 

agency has an EPA-approved attainment 

plan SIP for the affected area that was 

approved in October 2010 and that SIP 

includes enforceable controls 

implemented in accordance with the 

SIP that address the event-related 

pollutant (i.e., PM) and all sources 

necessary to fulfill the requirements of 

the CAA. The sustained winds during 

the event were above the high wind 

threshold. In the not reasonably 

controllable or preventable portion of its 

high wind dust demonstration, the air 

agency would describe the event-related 

wind characteristics and identify the 

natural and anthropogenic emission 

sources that contributed to the event 

emissions and the associated SIP and 

other control measures. The air agency 

would then describe the 

implementation status of these controls 

and provide evidence of effective 

implementation and enforcement. The 

air agency would conclude the ‘‘not 

reasonable controllable or preventable’’ 

portion of the demonstration by 

affirmatively stating that because the 

EPA had approved the SIP within 5 

years of the event and because the SIP 

measures and other measures specific to 

the pollutant and at least some 

anthropogenic emission sources that 

contributed to the event emissions were 

implemented, the agency has satisfied 

the not reasonably controllable or 

preventable criterion. 

In reviewing the demonstration in this 

scenario, the EPA would generally 

concur that the air agency met the not 

reasonably controllable or preventable 

criterion during the 5-year period 

provided the SIP was implemented and 

the event was not attributable to 

noncompliance. Thus, assuming the 

demonstration also satisfied the 

remaining technical and procedural 

elements in the Exceptional Events 

Rule, the EPA would concur with the air 

agency’s request to exclude data for 

purposes of regulatory actions within 

the scope of the final revised 

Exceptional Events Rule. If, however, 

the air agency experienced an 

exceedance or violation during the 5- 

year period for reasons other than those 

attributable to the successful 

exceptional events demonstration (e.g., 

industrial source noncompliance or 

another type of event), the EPA may 

take one of these actions. In addition, 

the EPA may issue a SIP call because 

the SIP is inadequate with regard to a 

requirement of the CAA that is not tied 

to the occurrence of NAAQS violations 

related to exceptional events. If the EPA 

issues a SIP call during the 5-year 

window, the situation would switch to 

Scenario 2. 

Details for Nonattainment Area 

Scenario 2 

In this scenario (where the SIP is 

being revised to respond to a SIP call 

involving the PM10 or PM2.5 NAAQS), 

the existing SIP controls should not be 

presumed to satisfy the not reasonably 

controllable or preventable criterion 

regardless of whether the event-related 

wind speeds are above or below the 

high wind threshold. The EPA 

recommends that as the first step in 

preparing an exceptional events 

demonstration, the air agency should 

assess the case-specific effectiveness of 

the controls that were in place at the 

time of the event and consider potential 

controls that are more comprehensive 

and effective than those in the SIP that 

the agency could have implemented 

before or during the event. This casespecific assessment should apply the 

concept that if a set of control measures 

should reasonably have been in place 

for emission sources that contribute to 

the event emissions in light of the 

information in the record of the EPA 

action that has created the obligation to 

revise the SIP, then those controls must 

have been in place for the event to 

satisfy the not reasonably controllable or 

preventable criterion. 

The submitting air agency preparing a 

case-specific assessment should first 

identify the natural and anthropogenic 

emission sources that significantly 

contribute to the event emissions and 

exceedance. The air agency should 

categorize sources as those that are 

addressed through SIP or other state or 

local laws or rules and those sources 

that are not addressed by SIP measures 

or other measures. Where the 

contributing source has SIP or other 

controls, the air agency would identify 

the implementation status of these 

controls and provide evidence of 

effective implementation and 

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enforcement. The air agency should also 

consider whether those SIP controls 

should have been made more stringent 

and effective prior to the event. For 

emission sources that contribute to the 

event emissions but are not specifically 

addressed in the SIP or other laws or 

rules, the air agency should identify and 

document why it was reasonable to have 

not implemented controls. 

We invite comment on whether there 

should be a grace or grandfathering 

period before a SIP call involving a 

relevant NAAQS has the effect of ending 

the deference that applied prior to the 

SIP call, such that for an event occurring 

during the grace period the SIP would 

be given the deference described for the 

first scenario. We believe that such a 

grace period should not extend beyond 

the due date for the required SIP 

revision in response to the SIP call. 

Example: An air agency has an EPAapproved attainment plan SIP for a PM10

nonattainment area that was approved 

in 1994 and includes controls for some 

of the anthropogenic emission sources 

that contribute fugitive dust during high 

wind events. The nonattainment area 

did not include fugitive dust controls 

for gravel operations in its 1994 SIP and 

has not required any controls of these 

operations in the years since SIP 

approval. The area does not have an 

approved maintenance plan, in part 

because it has been experiencing 

unresolved exceedances since 1994. The 

air agency alerts the reviewing EPA 

Regional office that it wishes to submit 

an exceptional events demonstration for 

a high wind dust event that occurred in 

2015 and affected several of the area’s 

monitoring sites. This is the second high 

wind dust event associated with an 

exceedance in the past 3 years. After the 

first event, the EPA issued a SIP call for 

the air agency to revise its PM10 SIP, but 

the air agency has not yet submitted a 

new SIP. Because the EPA issued a SIP 

call, the air agency is required to show 

on a case-specific basis that the not 

reasonably controllable or presentable 

criterion has been met. Applying the 

concept that if a set of control measures 

should reasonably have been in place 

for emission sources that contribute to 

the event emissions to the information 

in the record supporting the SIP call 

would likely result in a determination 

that those controls must have been in 

place for the event to satisfy the not 

reasonably controllable or preventable 

criterion. Because the gravel operations 

are not controlled and because the high 

wind dust event was the second in 3 

years, the air agency had a basis for 

understanding the possible need for 

better controls. Given the air agency’s 

knowledge of recurring events, the air 

agency may not be able to make a 

sufficient showing for the not 

reasonably controllable or preventable 

criterion and the reviewing EPA 

Regional office may not be able to 

concur with the air agency’s request to 

exclude data. If, however, the air agency 

can show that the gravel operations did 

not contribute to the event-related 

emissions, the reviewing EPA Regional 

office might be able to concur with the 

air agency’s request to exclude data. 

Details for Maintenance Area Scenario 3 

In this scenario (where the SIP was 

approved more than 5 years prior to the 

date of submittal of a demonstration and 

the air agency is not under an obligation 

to revise the SIP), because of the passage 

of time the SIP controls should not be 

presumed to satisfy the not reasonably 

controllable or preventable criterion 

regardless of whether the event-related 

wind speeds are above or below the 

high wind threshold. In this case, the air 

agency should complete a case-specific 

assessment of the reasonableness of 

controls to satisfy the not reasonably 

controllable or preventable criterion. 

The assessment should consider 

controls beyond those required by the 

existing SIP and other state or local laws 

and rules. The case-specific assessment 

should apply the concept that if a set of 

control measures should reasonably 

have been in place for emission sources 

that contribute to the event emissions, 

then those controls must have been in 

place for the event to satisfy the not 

reasonably controllable or preventable 

criterion. The submitting air agency 

should first identify the natural and 

anthropogenic emission sources that 

contribute to the event emissions and 

exceedance. The air agency should 

categorize sources as those that are 

addressed through SIP or other state or 

local laws or rules and those sources 

that are not addressed by SIP measures 

or other measures. Where the 

contributing source has SIP or other 

controls, the air agency would identify 

the implementation status of these 

controls and provide evidence of 

effective implementation and 

enforcement. The air agency should also 

consider whether those SIP controls 

should have been made more stringent 

and effective prior to the event. For 

emission sources that contribute to the 

event emissions but are not specifically 

addressed in the SIP or other laws or 

rules, the air agency should identify and 

document why it was reasonable to have 

not implemented controls. 

Example: An air agency has an EPAapproved attainment plan SIP for a PM10

former nonattainment area that was 

approved in 2008 and includes controls 

for anthropogenic emission sources that 

contribute fugitive dust during high 

wind events. The area has an approved 

maintenance plan. Between 2008 and 

2014 it has not been experiencing 

exceedances related to high winds. In 

2014 there is a single high wind dust 

event with sustained wind speeds above 

the high wind threshold that results in 

two exceedance days, sufficient to 

constitute a 3-year NAAQS violation. 

The air agency submits a demonstration 

covering both exceedances. In the not 

reasonably controllable or preventable 

portion of its demonstration, the air 

agency would identify all sources 

contributing to the event emissions, 

including natural sources, sources 

identified and controlled in the SIP, and 

any sources not controlled by the SIP. 

The air agency would then identify the 

applicable controls, the implementation 

status of these controls and evidence of 

enforcement. The air agency should also 

consider whether those SIP controls 

should have been made more stringent 

and effective prior to the event. Given 

the area’s past history of not having 

events and the fact that the sustained 

wind speed during the event was above 

the high wind threshold, it is likely that 

the air agency could make a sufficient 

showing for the not reasonably 

controllable or preventable criterion. In 

this case, provided the air agency 

satisfies the other rule criteria, the EPA 

Regional office would likely concur 

with an air agency’s request for data 

exclusion. 

However, in this maintenance area 

scenario, another possible outcome of 

an event that causes an exceedance or 

violation is that the EPA determines that 

the not reasonably controllable or 

preventable criterion is not met and the 

event-affected data are retained for 

regulatory actions within the scope of 

the Exceptional Events Rule. This may 

lead to the EPA taking an action that 

places the air agency under an 

obligation to revise the SIP, in which 

case the situation would change into the 

second scenario for any later events of 

the same type. 

Best Management Practices. The EPA 

solicits comment on whether or not, as 

part of the assessment of local sources 

and reasonable controls, USDA/NRCSapproved BMPs constitute sufficient 

reasonable controls in any or in all high 

wind event-affected areas and whether 

these measures should therefore be 

specifically and categorically identified 

in preamble or rule language as 

constituting reasonable controls. As 

discussed in the ‘‘Current Situation’’ 

section, the EPA has noted in previous 

guidance that USDA/NRCS-approved 

BMPs designed to effectively reduce 

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121 Interim Guidance on the Preparation of 

Demonstrations in Support of Requests to Exclude 

Ambient Air Quality Data Affected by High Winds 

Under the Exceptional Events Rule. U.S. EPA. May 

2013. Available at http://www2.epa.gov/sites/

production/files/2015-05/documents/exceptevents_

highwinds_guide_130510.pdf and Interim Guidance 

to Implement Requirements for the Treatment of Air 

Quality Monitoring Data Influenced by Exceptional 

Events. U.S. EPA. May 2013. Available at http://

www2.epa.gov/sites/production/files/2015-05/

documents/exceptevents_guidememo_130510.pdf. 

122A public comment opportunity is important 

prior to submission to the EPA because under the 

Exceptional Events Rule the EPA is not required to 

provide a public comment opportunity prior to 

concurring with an air agency’s request to exclude 

data. The EPA generally provides a public comment 

opportunity before we use air quality data, with or 

without such exclusions, in a final regulatory 

action. States typically provide an opportunity for 

public comment by posting draft demonstrations on 

a Web site. Federal agencies could do the same. 

fugitive dust air emissions and prevent 

soil loss in agricultural applications 

could be included in the collection of 

controls determined to constitute 

reasonable controls for wind-blown dust 

events in areas in which they have been 

implemented.121 Although the EPA has 

addressed the sufficiency of BMPs in 

decisions on individual exceptional 

events demonstrations when the BMPs 

were part of a SIP-approved BACM 

determination, we have not previously 

addressed whether or not BMPs 

individually or in some combination 

with each other constitute sufficient 

reasonable controls nationally or in any 

particular types of areas. We recognize 

that this question may be difficult to 

answer because BMPs often describe 

general types of practices (e.g., installing 

wind breaks) rather than specifying the 

penetration, scale or intensity of use of 

these practices by the landowners who 

adopt them. Therefore we also solicit 

comment on the evidence for degree of 

penetration, scale and intensity that 

would be appropriate in demonstrations 

to consider BMPs individually or in 

some combination with each other to be 

reasonable controls. 

G. Other Aspects of Flagging 

Exceptional Events-Influenced Data and 

Demonstration Submittal and Review 

1. Who may submit a demonstration and 

request for data exclusion? 

a. Current Situation 

Before addressing the schedule and 

mechanics of flagging event-influenced 

data and preparing demonstrations, the 

EPA believes it is necessary to first 

clarify which parties can submit an 

exceptional events demonstration 

package to the EPA. The CAA language 

at section 319(b)(3)(B)(i) states that ‘‘the 

occurrence of an exceptional event must 

be demonstrated by reliable, accurate 

data that is promptly produced and 

provided by Federal, State, or local 

government agencies.’’ As noted in 

section V.A of this proposal, state, local 

and some tribal agencies administer air 

quality management programs within 

their jurisdiction, which includes 

monitoring and analyzing ambient air 

quality and submitting monitoring data 

to the EPA, which are then stored in the 

EPA’s AQS database. Also, FLMs and 

other federal agencies operate air quality 

monitoring stations on some lands they 

manage, and some of these monitors 

meet the technical specifications and 

quality assurance requirements for their 

data to be used in regulatory 

determinations. As operators of 

regulatory monitors, each of these 

agencies can flag their own data within 

AQS for consideration as an exceptional 

event. 

As discussed in section V.F.1 of this 

proposed action, however, the EPA 

generally considers a state, exclusive of 

tribal lands, to be a single responsible 

actor, and, as the state is the entity 

primarily responsible for administering 

air quality planning and management 

activities, the state has been ultimately 

responsible for submitting exceptional 

events demonstrations for exceedances 

that occur at all regulatory monitoring 

sites within the boundary of the state, 

including exceedances occurring at 

monitoring sites operated by local air 

quality agencies to whom a state has 

delegated relevant responsibilities or at 

regulatory monitoring sites operated by 

any other entity within the state, such 

as FLMs of Class I areas, other federal 

agencies and/or industrial facilities. 

Although the state is responsible, a local 

agency, an FLM, another federal agency 

or another entity operating a regulatory 

monitor with an event-influenced 

exceedance can develop a 

demonstration for submittal by the state. 

If a state disagrees with the local 

agency’s, FLM’s, other federal agency’s 

or other entity’s exceptional events 

claim, the state can decide not to act on 

or forward that submittal to the EPA. A 

state can request that operators of other 

regulatory monitors experiencing eventinfluenced exceedances prepare or 

assist in the preparation of 

demonstration analyses for ultimate 

submittal by the state. 

Because some tribal air quality 

agencies also operate regulatory ambient 

air quality monitoring sites and submit 

these data to the EPA’s AQS database, 

as appropriate, these tribal agencies may 

also submit exceptional events 

demonstrations for exceedances that 

occur at their monitoring sites. 

b. Proposed Changes 

As indicated in section V.A of this 

proposal, because FLMs and other 

federal agencies may operate regulatory 

monitors and submit collected data to 

the EPA’s AQS database and these same 

monitors could be affected by emissions 

from exceptional events, the EPA 

proposes to allow FLMs and other 

federal agencies to prepare and submit 

exceptional events demonstrations and 

data exclusion requests directly to the 

EPA. The EPA solicits comment on this 

proposed addition to the rule text, 

which appears at the end of this 

document. Based on comments 

received, the EPA may retain, modify or 

not include this provision in the final 

promulgated rule. This provision would 

apply only to FLMs and other federal 

agencies that manage land on which an 

exceptional event originates or that 

operate a monitor that has been affected 

by an event. The provision would allow 

such FLMs and other federal agencies to 

provide demonstrations directly to the 

EPA only after a discussion with the 

state in which the monitor is operated. 

This discussion might instead result in 

an agreement that the federal agency (or 

another party) will provide a draft 

demonstration document to the 

appropriate state air agency for adoption 

and submission by the state air agency 

to the EPA, as is currently allowed. 

Regardless of who ultimately submits 

the demonstration, the EPA encourages 

collaboration between the FLMs and 

other federal agencies and the 

appropriate state air agency during the 

event identification and demonstration 

development process. If the provision 

for direct submission to the EPA is 

included in the final action, 

demonstrations prepared by FLMs or 

other federal agencies would be 

required to meet all provisions in the 

Exceptional Events Rule, including the 

requirement for a public comment 

period on a prepared demonstration 122

and the requirements related to 

schedules and procedures for 

demonstration package submittal (see 

sections V.G.4, V.G.5 and V.G.6) that 

apply to state agencies that operate 

monitors. 

2. Aggregation of Events for NAAQS 

With Periods Longer Than 24 Hours and 

Demonstrations With Respect to 

Multiple NAAQS for the Same Pollutant 

a. Current Situation 

The EPA’s AQS database houses 

ambient air quality monitoring and 

related data. The data in AQS are 

maintained as individual reported 

measurements, which can range from 5- 

minute maximum concentrations per 

hour for SO2, to hourly data for ozone, 

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123 Interim Exceptional Events Rule Frequently 

Asked Questions. U.S. EPA. May 2013. Available at 

http://www2.epa.gov/sites/production/files/2015- 

05/documents/eer_qa_doc_5-10-13_r3.pdf. 

CO, NO2, SO2 and some PM 

measurements to 24-hour measurements 

for lead and other particulate matter 

measurements. Air agencies identify 

and the EPA concurs with exceptional 

event-related data in AQS that are 

reported as individual measurements. 

Some NAAQS have long averaging 

periods, such that multiple independent 

events may affect the period-average 

concentration of the NAAQS pollutant. 

In the aggregate, a clear causal 

relationship may exist between the 

events and an exceedance or violation, 

but no single event satisfies the clear 

causal relationship criterion because 

each event has too small of an effect on 

the longer-period metric to do so by 

itself. CAA section 319(b) and the 2007 

Exceptional Events Rule do not clearly 

allow the aggregation of events for 

purposes of the clear causal relationship 

criterion, yet aggregation seems 

consistent with the intent of section 

319(b). The EPA has not to date 

indicated that actual aggregation of 

events is permitted. However, Question 

30 in the Interim Q&A document 

provided guidance that can be of some 

help in this situation. This guidance 

was that 24-hour concentrations of Pb, 

NO2, or SO2 can be individually 

compared to the NAAQS level defined 

for a longer period, for purposes of 

meeting ‘‘but for’’ with respect to both 

the 24-hour NAAQS, if applicable, and 

for purposes of meeting ‘‘but for’’ with 

respect to the NAAQS with the longer 

averaging period. This guidance focused 

on the intention of a passage in the 

preamble to the 2007 Exceptional 

Events Rule addressing the PM2.5

NAAQS in particular, and extended the 

approach of the 2007 preamble to other 

cases of NAAQS for the same pollutant 

that have different averaging periods. 

The practical effect of this approach is 

that several events that individually 

have effects too small to have a causal 

connection to a longer-period 

exceedance or violation might be 

excluded one-by-one, and the net effect 

of the exclusions may make a difference 

to compliance with the longer-period 

NAAQS. As guidance, however, the 

Interim Q&A document does not 

provide full certainty that an air agency 

may rely on the recommended 

approach. 

As noted in section IV.B of this 

proposal, the 2007 Exceptional Events 

Rule requires that for data exclusion, 

among other requirements, an air agency 

must demonstrate that there would have 

been no exceedance or violation of the 

NAAQS ‘‘but for’’ the event. The ‘‘but 

for’’ criterion necessarily requires 

comparing the individual measurements 

in AQS to the averaging period of the 

relevant NAAQS to determine whether 

an exceedance or violation occurred. 

When the averaging period for the 

NAAQS is the same as the measurement 

duration period, this comparison is 

relatively straightforward. For example, 

air agencies and the EPA can directly 

compare 1-hour ozone, 1-hour CO, 1- 

hour SO2, and 1-hour NO2

measurements to the respective 1-hour 

NAAQS. This comparison becomes 

more complicated, however, when there 

is a difference between the pollutant 

measurement duration and the 

averaging time of the NAAQS, which is 

the case when comparing a 1-hour 

measurement to an 8-hour, 24-hour, 3- 

month or annual NAAQS (or in the case 

of 1-hour ozone the previously existing 

NAAQS). In fact, the EPA devoted 

Questions 29–31 in the Interim Q&A 

document to explaining how to make 

these complicated comparisons.123 The 

Interim Q&A document also explained 

that because these comparisons are 

NAAQS-specific, air agencies should 

request and support the exclusion of a 

measured air concentration separately 

for each NAAQS that applies to the 

pollutant and the EPA will similarly 

provide separate concurrences. Under 

the 2007 Exceptional Events Rule 

provisions, this means, for example, that 

an air agency with several 24-hour 

measurements of event-influenced PM2.5

data measuring 75 micrograms per cubic 

meter (mg/m3) would need to separately 

flag the data within AQS on a NAAQSspecific basis, and submit separate 

requests, analyses and demonstration 

components to support exclusion of the 

identified event-influenced data for the 

1997 annual secondary PM2.5 NAAQS of 

15 mg/m3, the 2012 annual primary 

PM2.5 NAAQS of 12 mg/m3 and the 2006 

primary and secondary 24-hour PM2.5

NAAQS of 35 mg/m3. Depending on the 

outcome of the ‘‘but for’’ criterion with 

respect to each PM2.5 NAAQS, it could 

be that the data would be excluded for 

purposes of determinations with respect 

to only some of these NAAQS. 

This current situation can result in 

complicated demonstrations for air 

agencies seeking data exclusion from 

determinations with respect to multiple 

NAAQS for the same pollutant. This 

complexity may make it more difficult 

for the public to comment, and requires 

time for the EPA to review such a 

demonstration. 

b. Proposed Changes 

The EPA is taking comment on 

proposed rule text allowing 24-hour 

concentrations of any NAAQS pollutant 

to be compared to a NAAQS level 

defined for a longer period as part of a 

weight of evidence showing for the clear 

causal relationship with respect to the 

NAAQS with the longer period. This 

approach would be more amenable to 

less quantified weight of evidence 

demonstrations, since only one day 

would be examined at a time. 

The EPA is also proposing that for 

NAAQS with averaging or cumulative 

periods longer than 24 hours, events 

occurring on different days may be 

aggregated for the purpose of 

determining whether their collective 

effect has caused an exceedance or 

violation, without regard to whether the 

events are of the same type (e.g., 

stratospheric ozone intrusion followed 

by a wildfire). The EPA notes that such 

aggregation may be very difficult if the 

effects of the individual events on their 

individual days are not fully quantified. 

Proposed rule text for this change is 

provided for comment. 

Finally, to simplify some 

demonstrations, the EPA is also taking 

comment on whether a successful 

demonstration with respect to any 

NAAQS for a given pollutant would 

suffice to qualify the data in question for 

exclusion with respect to all NAAQS for 

that pollutant. The EPA believes it is 

useful to invite public comment on this 

‘‘approved for one NAAQS approved for 

all NAAQS for the same pollutant’’ 

concept. 

The EPA will carefully consider the 

comments it receives on these concepts 

and may finalize all, some or none of 

the three proposals described in this 

section. 

3. Exclusion of Entire 24-Hour Value 

Versus Partial Adjustment of the 24- 

Hour Value for Particulate Matter 

a. Current Situation 

As indicated in Question 29 of the 

Interim Q&A document, we have 

advised air agencies preparing 

demonstrations to support requests to 

exclude PM2.5 and PM10 data obtained 

via monitor instruments that provide 1- 

hour measurements that they should 

flag all 24 1-hour values within a given 

event-affected day, even if the event did 

not last all these hours. If concurred 

upon, flagging all 1-hour values will 

ultimately result in the same available 

remaining data for regulatory analysis 

and calculation as would be the case 

had the 24-hour PM2.5 or PM10

measurement data been collected from 

filter-based (24-hour) monitoring 

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124Filter based instruments typically record a 

single value within a 24-hour period while 

continuous monitors typically collect 24 1-hour 

measurements. Because AQS can calculate a valid 

24-hour average concentration with as few as 18 

hours, it may be necessary to exclude hours not 

actually affected by the event to ensure the same 

data exclusion outcome as if the measurement had 

been made with a 24-hour filter. 

125The form of the 24-hour PM2.5 NAAQS of 35 

mg/m3 is 98th percentile averaged over 3 years. The 

form of the primary annual PM2.5 NAAQS of 12 mg/ 

m3 is an annual mean averaged over 3 years. The 

form of the 24-hour PM10 NAAQS of 150 mg/m3 is 

not to be exceeded more than once per year on 

average over 3 years. Biased concentrations can 

potentially skew the determination of the 98th 

percentile and/or the annual mean for PM2.5 and the 

averages for PM2.5 or PM10 calculated to determine 

compliance with the relevant NAAQS. 

126 ‘‘Flag’’ is the common terminology for a data 

qualifier code in the EPA’s AQS. Unless explicitly 

noted, the process of ‘‘flagging’’ data refers to 

adding Request Exclusion (R) data qualifier codes 

to selected data in AQS. R flags are the only AQS 

flags that satisfy the 2007 Exceptional Events Rule 

requirement for initial data flagging. The current 

design of the AQS software is such that EPA can 

act/concur only on an R flag. 

127Responses to Significant First-Round 

Comments on the Draft Guidance Documents on the 

Implementation of the Exceptional Events Rule, 

U.S. EPA, June 2012. Available in Docket No. EPA– 

HQ–OAR–2011–0887. 

128Responses to Significant First-Round 

Comments on the Draft Guidance Documents on the 

Implementation of the Exceptional Events Rule, 

U.S. EPA, June 2012. Available in Docket No. EPA– 

HQ–OAR–2011–0887. 

instruments.124 Another reason we have 

taken the position that flagging all 24 

1-hour values is appropriate is because 

flagging only peak or selected hours 

could result in the remaining 1-hour 

values still meeting the data 

completeness requirements because 

flagged and excluded data do not count 

against completeness even though they 

cannot be used in calculating an average 

concentration for a 24-hour period. 

Under the rules for data interpretation, 

exclusion of only the event-affected 1- 

hour concentrations could result in AQS 

calculating a seemingly valid 24-hour 

concentration that is actually highly 

uncertain because it is based on only a 

few hours and thus may be biased.125

b. Proposed Changes 

The EPA solicits comment on 

codifying its current approach in the 

rule text to eliminate any regulatory 

uncertainty. If finalized, this 

modification to the data handling 

procedures will be made to occur 

automatically within AQS. 

4. Flagging of Data 

While neither the preamble to nor the 

rule text contained within the 2007 

Exceptional Events Rule discuss data 

handling within AQS, explaining 

certain AQS processes and functions 

will be useful to an understanding of the 

data flagging situation that has 

developed in implementing the 

requirements in 40 CFR 50.14(c)(2) and 

why we are proposing changes. 

a. Current Situation 

Within AQS, monitoring agencies can 

use two types of data validation, or data 

qualifier, codes related to exceptional 

events: The Request Exclusion flags (R) 

and the Informational Only flags (I).126

The EPA has advised air agencies to use 

the I series flags when identifying 

informational data and the R series flags 

to identify data points for which the 

agency intends to request an exceptional 

events exclusion and the EPA’s 

concurrence. As an example, air 

agencies may currently use an I series 

flag to initially identify values they 

believe were affected by an event. Once 

the air agency collects additional 

supporting data, it may change the flag 

to an R series flag and submit an initial 

event description. Or, the air agency 

may find that additional information 

does not support flagging the data as an 

exceptional event, and the air agency 

may, therefore, delete the flag or retain 

the I series flag. Air agencies may also 

use the I series flags simply to note 

activities or conditions occurring on the 

data collection day that are unrelated to 

exceptional events or that do not result 

in an exceedance or violation of a 

NAAQS. Air agencies have previously 

indicated that they generally see little 

value in the use of I series flags.127

Flagging of event-influenced data has 

traditionally also involved associating a 

one- or two-character code with a 

monitored value within AQS indicating 

that the data have potentially been 

influenced by a particular type of 

exceptional event (e.g., ‘‘RT’’ is the 

character code used to request exclusion 

for data that have been influenced by 

wildfires in the U.S.). The 2007 

Exceptional Events rule added a 

requirement to include a more detailed 

initial description of the particular 

event associated with such a character 

code. This description consists of text of 

variable length. 

The EPA does not review or concur 

on the I series flags. Rather, an air 

agency must use an R flag to request 

data exclusion. The language at 40 CFR 

50.14(c)(2), Flagging of Data, requires 

that an air agency notify the EPA of its 

intent to exclude one or more measured 

exceedances of an applicable NAAQS as 

being due to an exceptional event by 

placing a flag and an initial event 

description in the appropriate fields in 

AQS for the data record(s) of concern no 

later than July 1 of the calendar year 

following the year in which the flagged 

measurement occurred. Only R flags 

fulfill this requirement. This ‘‘general’’ 

schedule date of July 1 applies unless 

the data are associated with the initial 

area designations process for a new or 

revised NAAQS in which case the 

specific schedule in § 50.14(c)(2)(vi) 

applies. 

Air agencies have previously 

expressed concern that the timelines for 

event flagging and demonstration 

submittal are not always appropriate.128

While the EPA has historically 

promulgated revised flagging and 

demonstration submittal schedules in 

the regulatory actions for new and 

revised NAAQS for those data years that 

might be used in the initial area 

designations process for those NAAQS, 

the EPA does not promulgate revised 

schedules for other regulatory actions 

such as clean data or attainment 

determinations. Rather, the EPA has 

relied upon the ‘‘general’’ flagging and 

demonstration submittal schedules in 

40 CFR 50.14(c)(2) and (c)(3)(i). Meeting 

the requirement at 40 CFR 

50.14(c)(2)(iii) to submit R flags and an 

initial description of the event ‘‘not later 

than July 1st of the calendar year 

following the year in which the flagged 

measurement occurred’’ can be difficult 

in the case of an annual standard where 

an air agency needs all 12 months of 

data to calculate an annual average and 

then needs 3 years of annual averages to 

identify whether or not the eventinfluenced data results in a violation of 

a 3-year design values. An air agency 

may not know that data influenced by 

an exceptional event caused the design 

value to become a NAAQS violation 

until 3 years after the event occurred. 

Some air agencies have used and 

applied I and R flags in AQS 

inconsistently with this intended 

scheme, by including applying 

numerous R flags in AQS with no real 

intention to submit an exceptional 

events demonstration. Also, R flags may 

be set immediately before a 

demonstration is submitted or even as 

late as when the EPA needs to indicate 

in AQS our approval of a request for 

data exclusion. As a result, neither the 

presence nor the absence of these flags 

provide the EPA with an indication of 

anticipated exceptional events 

demonstrations. 

b. Proposed Changes 

As part of this action, the EPA 

proposes to revise the ‘‘general’’ 

schedule language contained within 40 

CFR 50.14(c)(2) by removing the 

timelines associated with initial event 

flagging. The EPA also proposes to 

modify the associated data flagging 

process within AQS to correspond with 

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129The EPA is proposing that air agencies select 

the ‘‘type of event’’ from a pre-set list of event 

types, which would likely consist of those event 

types currently identified by existing Informational 

and Request Exclusion flags within AQS. 130 80 FR 65292 (October 26, 2015). 

131 Interim Guidance to Implement Requirements 

for the Treatment of Air Quality Monitoring Data 

Influenced by Exceptional Events. Memorandum 

from Stephen D. Page, U.S. EPA Office of Air 

Quality Planning and Standards, to Regional Air 

Directors, Regions I–X. May 10, 2013. Available at 

http://www2.epa.gov/sites/production/files/2015- 

05/documents/exceptevents_guidememo_

130510.pdf. 

these proposed regulatory changes. 

These proposed changes would include 

eliminating the use of the current 

exceptional events data validation/data 

qualifier codes: The Request Exclusion 

flags (R) and the Informational Only 

flags (I). The one- or two-character event 

type codes would be retained. The EPA 

solicits comment on the approach that 

is discussed below in additional detail. 

The EPA is proposing to change the 

definition and process for flagging 

exceptional event data. Flagging would 

in effect become the application of the 

one- or two-character event type and 

event description text as described 

below, along with a concurrent or 

subsequent request for data exclusion 

communicated to the EPA through other 

channels. 

Because the flagging of data 

necessarily begins with the 

identification of an event, the EPA 

proposes to retain, with modifications, 

the AQS free-form text field for an 

initial event description. As is currently 

the practice, we request that air agencies 

use the ‘‘initial event description’’ to 

identify a unique, real-world event. We 

propose that this ‘‘initial event 

description’’ be expanded to contain a 

unique event name; the type of the 

event (e.g., high wind dust, volcanic 

eruption, other); a brief description of 

the event; and, to the extent known, the 

scope of the event in terms of geography 

and time (e.g., likely affected area using 

latitude and longitude and a radius of 

influence and beginning day/time and 

ending day/time).129 AQS would also be 

modified to allow the air agency to 

associate specific AQS sites and 

potentially affected monitors and 

specific data points with a given event 

as so described. This will enable air 

agencies and the EPA to ‘‘flag’’ or add 

qualifier codes to selected data in a 

single step rather than adding this 

information or the necessary codes on a 

per entry basis. Historically, when 

events have influenced the 

concentrations at multiple monitors for 

multiple days, the air agency has added 

initial event descriptions and set flags 

on each monitored concentration, 

sometimes resulting in hundreds of 

identical individual entries. 

‘‘Associating’’ monitors with an event 

defined in time and space will save 

resources. 

Once an air agency has identified an 

event and created the initial event 

description within AQS, the agency 

should begin the process of requesting 

exclusion for identified data, which will 

consist of two discrete operations: (1) 

Indicating in a separate communication 

to the EPA that specific ambient air 

quality measurements are affected by a 

defined event (see section V.G.5 related 

to Initial Notification of Potential 

Exceptional Event), and (2) requesting 

that these identified ambient air quality 

measurements be excluded from 

regulatory actions according to the 

terms of the revised Exceptional Events 

Rule and EPA guidance for other 

applications of air quality data. AQS 

would retain a field to allow the EPA to 

concur or not concur with a given 

request for exclusion for one or more of 

the data points associated with a 

described event, once review of the air 

agency’s request and demonstration is 

completed. 

In addition to the proposed AQS 

modifications described above, the EPA 

is proposing to remove the ‘‘general’’ 

flagging schedule in 40 CFR 

50.14(c)(2)(iii). This regulatory language 

currently requires that air agencies 

submit [R] flags and an initial 

description of the event by July 1 of the 

calendar year following the year in 

which the flagged measurement 

occurred or by the other deadlines 

identified with individual NAAQS. As 

noted earlier in this section, an air 

agency may not know that data 

influenced by an exceptional event 

caused a violation of a NAAQS until 

after the initial event flagging deadline 

has passed. The EPA proposes to 

remove and reserve the current language 

at 40 CFR 50.14(c)(2)(iii). Additional 

changes to the regulatory language in 40 

CFR 50.14(c)(2) will be discussed in the 

next section. 

The EPA notes that the recent ozone 

NAAQS action 130 also removed and 

reserved the subsequent sections at 40 

CFR 50.14(c)(2)(iv) and (v), which 

addressed the submittal of exceptional 

events demonstrations that could affect 

regulatory determinations associated 

with initial area designations for the 

2006 24-hour PM2.5 NAAQS and the 

2010 Lead NAAQS and were made 

obsolete by the passage of time. The 

EPA will retain these removed and 

reserved sections as promulgated in the 

ozone NAAQS and proposes no 

additional changes to these sections. 

5. Initial Notification of Potential 

Exceptional Event 

a. Current Situation 

As the EPA acknowledged in the 

Interim Exceptional Events 

Implementation Guidance and in 

discussions with stakeholders, the EPA 

understands that the initial 

identification of data affected by 

exceptional events and the subsequent 

preparation, submittal and review of 

demonstration packages is a resource 

intensive process both for the preparing 

air agency and the reviewing EPA 

Regional office.131 Delays in processing 

and making decisions on submitted 

packages create regulatory uncertainty 

and potentially increase the workload 

for both the submitting air agency and 

the EPA. In addition, the backlog of 

pending actions makes selection of the 

best information to support new 

submittals potentially more uncertain. 

Further, air agencies and the EPA often 

face timelines by which they must make 

regulatory decisions that can be affected 

by the inclusion or exclusion of eventaffected data. In the Interim Exceptional 

Events Implementation Guidance and 

through the EPA’s best practices 

discussions identified in section IV.E, 

the EPA committed to work with air 

agencies as they prepare complete 

demonstration packages and we 

developed some guidelines to increase 

the efficiency of the process. 

One of the efficiency-increasing 

measures we suggested in the Interim 

Exceptional Events Implementation 

Guidance was the Letter of Intent. The 

guidance explained that the Letter of 

Intent was a voluntary process by which 

the submitting air agency notifies the 

reviewing EPA Regional office of the air 

agency’s intent to submit a 

demonstration for an identified 

exceptional event. The purpose of the 

letter was to promote early 

communication between the submitting 

air agency and the reviewing EPA 

Regional office. In the time since issuing 

the Interim Exceptional Events 

Implementation Guidance, several air 

agencies and the EPA Regional offices 

have successfully used this voluntary 

process to discuss expectations 

regarding specific exceptional events 

demonstrations. 

b. Proposed Changes 

As part of the best practices for 

communications during the exceptional 

events process and to aid all agencies in 

resource planning and prioritization, the 

EPA proposes that air agencies and the 

EPA engage in regular communications 

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132The EPA recognizes that air agencies can 

immediately identify those events that result in an 

exceedance of a NAAQS with a short averaging time 

(e.g., 1-hour, 8-hour or 24-hour standards) but may 

need additional time for an annual average 

standard. An air agency could also submit an 

annual Initial Notification if annual submittal 

makes sense for resource planning or for recurring 

seasonal events. 

to identify those data that have been 

potentially influenced by an exceptional 

event, to determine whether the 

identified data affect a regulatory 

determination, and to discuss whether 

an air agency should develop and 

submit an exceptional events 

demonstration. In most instances, these 

discussions will be between individual 

air agencies and the reviewing EPA 

Regional office. In other cases, the EPA 

regional office, or an individual air 

agency within the purview of the EPA 

Regional office, may initiate and/or host 

a general discussion with all air 

agencies in the region followed by 

individual discussions, as needed. In 

still other cases, such as where large 

events cross state lines and when two or 

more states are pursuing exclusion for 

the same event(s), the EPA region or 

regions may initiate discussions will all 

potentially affected states/agencies to 

assist in coordinating states affected by 

regional events. 

For purposes of this proposed action, 

the EPA is referring to these 

communications as the ‘‘Initial 

Notification of Potential Exceptional 

Event’’ (Initial Notification) process. 

The EPA has changed the name of this 

process from the Letter of Intent in 

recognition of the fact that effective 

communication may have multiple 

formats and does not necessarily consist 

of a formal, written letter to convey 

important information. As with the 

voluntary Letter of Intent, the ultimate 

purpose of the Initial Notification 

process is to initiate conversations 

between an air agency and the EPA if 

not already on-going, or engage in more 

detailed discussions if a process is 

currently in place, regarding specific 

data and whether the identified data are 

ripe for submittal as exceptional events. 

As stakeholders have repeatedly 

expressed and as the EPA 

acknowledges, the identification of data 

affected by exceptional events and the 

subsequent preparation, submittal and 

review of demonstration packages is a 

resource intensive process both for the 

preparing air agency and the reviewing 

EPA Regional office. 

However, in considering the 

exceptional events process, it is 

important to note that if these data do 

not have regulatory significance, then 

engaging in the development and review 

of an exceptional events demonstration 

is generally not an efficient use of an air 

agency’s or the EPA’s limited resources. 

The Initial Notification process will 

focus efforts on the relevant data and 

provide the EPA with the opportunity to 

convey to the affected air agency our 

initial thoughts regarding the identified 

event and analyses that may or may not 

be appropriate for inclusion in a 

demonstration, and, with respect to 

regulatory significance, which 

demonstrations the EPA will consider 

for review. We believe that this 

approach will help air agencies make 

the best use of their available resources. 

As noted earlier, the Initial 

Notification could include any form of 

communication (e.g., letter, email, inperson meeting with an attendees’ list 

and discussion summary or phone 

conversation with follow-up email) that 

ultimately identifies the potential need 

to develop an exceptional events 

demonstration and communicates key 

information related to the data 

identified for potential exclusion. 

Where an air agency independently 

identifies event-affected data and the 

need to submit an exceptional events 

demonstration outside of its regular, ongoing communications with the EPA 

Regional office, the air agency could 

prepare a letter or email communicating 

its Initial Notification. Generally, the 

EPA anticipates that air agencies would 

develop and provide an Initial 

Notification as soon as the agency 

identifies event-influenced data that 

potentially influence a regulatory 

decision or when an agency wants the 

EPA’s input on whether or not to 

prepare a demonstration.132 The EPA 

further proposes that each Initial 

Notification would include the 

following components: 

• Unique event name (field in AQS)— 

facilitates future communication and 

understanding between the submitting 

air agency and the reviewing EPA 

Regional office, particularly if an air 

agency has submitted multiple 

exceptional events demonstration 

packages. 

• Initial event description (field in 

AQS)—provides a brief narrative of the 

event that could also include maps or 

graphs similar to what an air agency 

might include in the proposed 

conceptual model discussed in section 

V.G.6 of this proposed action; the event 

description would include a qualitative 

description of the event and, at a 

minimum, briefly describe the agency’s 

current understanding of interaction of 

emissions with the event, transport and 

meteorology (e.g., wind patterns such as 

strength, convergence, subsidence, 

recirculation) and pollutant formation 

in the area. 

• Affected regulatory decision— 

provides a description of the regulatory 

action or actions potentially affected by 

the claimed event-influenced data and 

the anticipated timing of this action. 

• Proposed target date for 

demonstration submittal—identifies the 

proposed target date by which the air 

agency would submit a demonstration 

package to the reviewing EPA Regional 

office. 

• Most recent design value including 

and excluding the event-affected data 

(optional)—the air agency’s assessment 

of the most recent design value both 

with and without the identified event(s) 

is helpful when assessing regulatory 

significance. The EPA cannot calculate 

this value (and therefore may not be 

able to determine significance) if the air 

agency has flagged more data than it 

intends to include in an exceptional 

events demonstration. 

• Information specific to each 

monitored day—see Table 5, which 

would be developed by the submitting 

air agency and generated from the initial 

event description in AQS (see 

discussion in section V.G.4). 

TABLE 5—INITIAL NOTIFICATION INFORMATION SPECIFIC TO EACH MONITORED DAY

Agency/planning area State County 

Event 

name in 

AQS 

Type of 

event NAAQS 

Monitor 

AQS ID 

and site 

name 

Date(s) of 

event 

Monitor exceedance 

concentration 

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72886 Federal Register / Vol. 80, No. 224 / Friday, November 20, 2015 / Proposed Rules 

133 ‘‘Regulatory decisions’’ include findings as to 

whether the area has met the applicable NAAQS, 

classification determinations, attainment 

demonstrations, the development of Limited 

Maintenance Plans and clean data findings. 

134 Interim Guidance to Implement Requirements 

for the Treatment of Air Quality Monitoring Data 

Influenced by Exceptional Events. Memorandum 

from Stephen D. Page, U.S. EPA Office of Air 

Quality Planning and Standards, to Regional Air 

Directors, Regions I–X. May 10, 2013. Available at 

http://www2.epa.gov/sites/production/files/2015- 

05/documents/exceptevents_guidememo_

130510.pdf. 

135Responses to Significant First-Round 

Comments on the Draft Guidance Documents on the 

Implementation of the Exceptional Events Rule, 

U.S. EPA, June 2012. Available in Docket No. EPA– 

HQ–OAR–2011–0887. 

The EPA anticipates promptly 

acknowledging an air agency’s Initial 

Notification and then formally 

responding within 90 days of receipt via 

letter, email or in-person meeting with 

an attendees’ list and discussion 

summary. We also anticipate having 

informal phone conversations with the 

air agency prior to this formal response. 

As previously discussed, the EPA will 

generally prioritize exceptional events 

determinations that affect near-term 

regulatory decisions.133 Where the data 

are to be used in initial area 

designations, the EPA proposes to rely 

on the promulgated documentation 

submission schedule in Table 1 at 

§ 50.14(c)(2)(vi). Where the data will 

influence another near-term regulatory 

decision, the EPA proposes to rely on 

the case-by-case timelines by which the 

air agency should submit the 

demonstration. For case-by-case 

demonstrations, the EPA’s 

recommended date for demonstration 

submittal would consider the nature of 

the event, the anticipated timing of the 

regulatory decision, and would allow 

time for both an air agency’s preparation 

of the demonstration and the EPA’s 

review. The EPA may not be able to 

review and act on demonstrations 

submitted after the recommended 

submittal date. Additionally, the EPA 

will request in its response that, if the 

submitting air agency has not already 

identified the affected data within AQS, 

that it undertake this effort according to 

the process described in section V.G.4. 

If the data identified in the Initial 

Notification do not have regulatory 

significance (and there is no compelling 

reason for excluding data), then the EPA 

will indicate this in its correspondence 

back to the air agency and will 

discourage the air agency from devoting 

resources to developing a demonstration 

because the EPA will likely not review 

or act upon the submittal. 

If after discussing the content of a 

submitted Initial Notification and/or 

receiving the EPA’s response to the 

Initial Notification, the EPA 

acknowledges that identified data have 

regulatory significance (or some other 

compelling reason for excluding data), 

then the air agency should proceed with 

the development of a technical 

demonstration package that satisfies the 

requirements in 40 CFR 50.14 and 

accounts for any case-specific advice 

from the EPA and additional 

information in the EPA’s guidance 

documents.134 Although air agencies 

can submit demonstrations for events 

that do not affect a regulatory action, the 

EPA will likely not review or act on 

such submittals. 

For these reasons described in this 

section and in section V.G.4, the EPA 

proposes to revise the language in 40 

CFR 50.14(c)(2)(i) as follows: ‘‘A State 

shall notify EPA of its intent to request 

exclusion of one or more measured 

exceedances of an applicable ambient 

air quality standard as being due to an 

exceptional event by creating an initial 

event description and flagging the 

associated data that have been 

submitted to the AQS database and by 

engaging in the Initial Notification of 

Potential Exceptional Event process.’’ 

Specific steps in the Initial Notification 

process are identified in rule text at the 

end of this document. The EPA solicits 

comment on the proposed rule text 

revision (in 40 CFR 50.14(c)(2)) to 

require an Initial Notification of 

Potential Exceptional Event, with a 

provision that the EPA can waive the 

Initial Notification requirement on a 

case-by-case basis. Alternatively, the 

EPA solicits comment on making the 

Initial Notification of Potential 

Exceptional Event a voluntary process. 

Additional proposed revisions would 

continue at (ii): ‘‘The data shall not be 

excluded from determinations with 

respect to exceedances or violations of 

the national ambient air quality 

standards unless and until, following 

the State’s submittal of its 

demonstration pursuant to paragraph 

(c)(3) of this section and EPA review, 

EPA notifies the State of its concurrence 

by placing a concurrence flag in the 

appropriate field for the data record in 

the AQS database.’’ 

As noted in section V.G.4, the EPA is 

proposing to remove the ‘‘general’’ 

flagging schedule in 40 CFR 

50.14(c)(2)(iii). The EPA seeks 

comments on these proposed changes to 

the language at 40 CFR 50.14(c)(2), 

which more clearly identify the process 

for flagging data in AQS and requesting 

exclusion of one or more measured 

exceedances of an applicable ambient 

air quality standard. 

The EPA notes that the recent final 

rule to revise the ozone NAAQS also 

removed and reserved the subsequent 

sections at 40 CFR 50.14(c)(2)(iv) and 

(v), which addressed the submittal of 

exceptional events demonstrations that 

could affect regulatory determinations 

associated with initial area designations 

for the 2006 24-hour PM2.5 NAAQS and 

the 2010 Lead NAAQS and were made 

obsolete by the passage of time. The 

EPA will retain these removed and 

reserved sections as promulgated in the 

ozone NAAQS and proposes no 

additional changes to these sections. 

6. Submission of Demonstrations 

a. Current Situation 

With the recent ozone NAAQS, the 

EPA proposed and promulgated changes 

to the current exceptional events 

regulatory language at 40 CFR 

50.14(c)(2) and (3) to include finalizing 

exceptional events flagging and 

demonstration submittal schedules 

related to implementing the revised 

ozone standards and future revised 

NAAQS and removing obsolete 

regulatory language for expired 

exceptional events deadlines. Sections 

V.G.4 and V.G.5 discuss the current 

situation and additional proposed 

changes to 40 CFR 50.14(c)(2). This 

section discusses the current situation 

and proposed revisions to 40 CFR 

50.14(c)(3). 

As part of the recent final rule to 

revise the ozone NAAQS, the regulatory 

language at 40 CFR 50.14(c)(3)(i) now 

refers to a revised exceptional events 

flagging and demonstration submittal 

schedule for data that could be used in 

initial area designation decisions 

following promulgation of any future 

revised NAAQS. However, the language 

at 40 CFR 50.14(c)(3)(i) still requires air 

agencies to ‘‘. . . submit a 

demonstration to justify data exclusion 

to EPA not later than the lesser of, 3 

years following the end of the calendar 

quarter in which the flagged 

concentration was recorded or, 12 

months prior to the date that a 

regulatory decision must be made by 

EPA.’’ 

As identified in section V.G.4 of this 

proposal, air agencies have previously 

expressed concern that the timelines for 

event flagging and demonstration 

submittal are not always appropriate 

because an air agency may not know 

that data influenced by an exceptional 

event caused the design value 

exceedance until 3 years after the event 

occurred.135 The EPA acknowledges 

that this scenario can occur. 

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136The EPA expects that air agencies could use 

some of the same information and tables in both the 

conceptual model and the Initial Notification of 

Potential Exceptional Event, which is discussed in 

section V.G.5 of this proposal. 

In addition to establishing a general 

schedule for demonstration submittal, 

the regulatory language at 40 CFR 

50.14(c)(3)(i) requires that ‘‘A State must 

submit the public comments it received 

along with its demonstration to EPA.’’ 

Although this language is included in 

40 CFR 50.14(c)(3)(i), it refers to the 

regulatory language at 40 CFR 

50.14(c)(3)(v), which requires the air 

agency to document, and submit with 

its demonstration, evidence that it 

followed the public comment process. 

Regarding this requirement to 

‘‘document that the public comment 

process was followed,’’ neither the 

Exceptional Events Rule language in 40 

CFR 50.14 nor the preamble to the 

promulgated 2007 Exceptional Events 

Rule specifies a minimum timeframe for 

public comment. Many air agencies 

have been posting draft demonstrations 

for public review on their Web sites. 

The EPA has reviewed several of these 

postings and identified 30-days as an 

often cited timeframe for public 

comment on a draft exceptional events 

demonstration submittal. 

The current rule also provides at 40 

CFR 50.14(c)(3)(iv) that the 

demonstration to justify data exclusion 

shall provide evidence that the event 

satisfies the definition of an exceptional 

event provided at 40 CFR 50.1(j); that 

there is a clear causal relationship 

between the monitored exceedance and 

the event that is claimed to have 

affected the air quality in the area; that 

the event is associated with a measured 

concentration in excess of normal 

historical fluctuations, including 

background; and that there would have 

been no exceedance or violation but for 

the event. Air agencies have found this 

section of the 2007 Exceptional Events 

Rule to be confusing because it contains 

a mix of statutory requirements and 

regulatory language without clearly 

identifying the components that the 

EPA expects to see in an exceptional 

events demonstration. As the EPA 

expressed in the Interim Exceptional 

Events Implementation Guidance, all 

parties would benefit from clear 

expectations regarding demonstration 

components. 

The EPA further believes, and 

recommended in the Interim High 

Winds Guidance document, that each 

demonstration begin with a conceptual 

model, or narrative, describing the 

event(s) causing the exceedance or 

violation and a discussion of how 

emissions from the event(s) led to the 

exceedance at the affected monitor(s). 

As described in the Interim High Winds 

Guidance document, the narrative 

conceptual model could include varying 

levels of detail depending on the event 

complexity, but in all cases would 

provide a qualitative description of the 

event, interaction of the event-generated 

emissions with transport and 

meteorology (e.g., wind patterns such as 

strength, convergence, subsidence, 

recirculation) and pollutant formation 

in the area with the exceeding monitor. 

Because, in some cases, monitored data 

or technical analyses may seem to 

contradict the event claim, particularly 

the clear causal relationship, an air 

agency can use the conceptual model to 

explain, with a weight of evidence 

approach, why the majority of the data 

or analyses are consistent with the 

event’s impact on a measured 

exceedance or violation (for example, 

for a wildfire, why most of the 

meteorology would have indicated a 

lower ozone day without the fire 

emissions, even if the temperature were 

high). A useful conceptual model also 

includes (1) a description of the 

regulatory decision impacted by the 

exceptional event, (2) a summary table 

of the data requested for exclusion and 

(3) maps and/or summary tables of 

event-related information including 

location; size and extent; point and 

explanation of origin. A conceptual 

model can additionally include 

examples of media coverage of the 

event.136 Since releasing the Interim 

High Winds Guidance document in 

2013, the EPA has received several 

demonstrations that included a 

conceptual model. The EPA has found 

it very helpful to understand the event 

formation and the event’s influence on 

monitored pollutant concentrations 

before beginning to review the 

individual technical evidence to 

support the requested data exclusion. 

b. Proposed Changes 

For the previously mentioned reasons, 

the EPA is proposing and soliciting 

comment on the following changes to 

the regulatory language in 40 CFR 

50.14(c)(3) regarding the submission of 

demonstrations: 

• Removing the general schedule 

provisions in 40 CFR 50.14(c)(3)(i) for 

submitting demonstrations. 

• Moving the language requiring a 

state to include the comments it 

received during the public comment 

period for the subject demonstration 

from 40 CFR 50.14(c)(3)(i) to 40 CFR 

50.14(c)(3)(v). 

• Modifying the language at 40 CFR 

50.14(c)(3)(iv) to more clearly identify 

the required elements of an exceptional 

events demonstration to include (1) a 

narrative conceptual model and (2) 

demonstrations and analysis that 

address the core statutory technical 

criteria [the event affected air quality in 

such a way that there exists a clear 

causal relationship between the specific 

event and the monitored exceedance or 

violation (as indicated by the 

comparison to historical concentrations 

showing and other analyses), the event 

was a human activity that is unlikely to 

recur at a particular location or was a 

natural event, the event was not 

reasonably controllable or preventable]. 

• Modifying the language at 40 CFR 

50.14(c)(3)(v) to identify that a 

demonstration submittal must include 

(1) documentation that the air agency 

conducted a public comment process on 

its draft exceptional events 

demonstration that was a minimum of 

30 days, which could be concurrent 

with the EPA’s review, (2) any public 

comments received during the public 

comment period and (3) an explanation 

of how the air agency addressed the 

public comments. 

To elaborate on removing the general 

schedule provisions in 40 CFR 

50.14(c)(3)(i), the EPA proposes to 

remove the provision in 40 CFR 

50.14(c)(3)(i) that requires air agencies 

to submit a demonstration ‘‘not later 

than the lesser of 3 years following the 

end of the calendar quarter in which the 

flagged concentration was recorded or 

12 months prior to the date that a 

regulatory decision must be made by 

EPA.’’ In place of this language, the EPA 

proposes to rely on the promulgated 

documentation submission schedule in 

Table 1 at 50.14(c)(2)(vi) in those cases 

where the data are to be used in initial 

area designations. If the data could 

influence a regulatory determination 

other than initial area designations, the 

EPA proposes to rely on the case-bycase timelines established by the 

reviewing EPA Regional office as part of 

the Initial Notification of Potential 

Exceptional Event process. 

With respect to the public comment 

provisions for a developed 

demonstration, for the reasons stated 

previously, the EPA proposes to move 

the language requiring an air agency to 

include the comments it received during 

the public comment period for the 

subject demonstration from 40 CFR 

50.14(c)(3)(i) to 40 CFR 50.14(c)(3)(v) to 

consolidate the required elements of the 

public comment process for exceptional 

events demonstrations within a single 

regulatory provision. The EPA also 

proposes to specify a minimum 30-day 

public comment process, which 

provides sufficient time for exchange 

between the reviewing public and the 

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72888 Federal Register / Vol. 80, No. 224 / Friday, November 20, 2015 / Proposed Rules 

137See comment letters in Docket ID No. EPA– 

HQ–OAR–2011–0887 for the July 2012 notice of 

availability for the Draft Exceptional Events 

Implementation Guidance, which the EPA has 

incorporated into the record for this action. 

air agency. Shorter comment periods 

may not provide necessary time for the 

public to research the identified event 

and associated supporting data while 

longer timeframes may not be possible 

where a near-term regulatory decision 

relies on an exceptional events decision. 

The EPA notes that in very limited cases 

where the air agency is relying on 

exceptional events claims as part of a 

near-term regulatory action, such as a 

demonstration for events in the third 

year of a 3-year design value that will 

be used in initial area designations for 

a new or revised NAAQS under a 2-year 

designation schedule, the public 

comment period could be concurrent 

with the EPA’s review provided the 

submitting air agency sends any public 

comments and responses to the EPA by 

a specified date should comments be 

submitted. If an air agency receives 

public comment disputing the technical 

elements of a demonstration during a 

comment period that runs concurrent 

with the EPA’s review and these 

comments result in the air agency’s 

need to reanalyze or reassess the 

validity of a claimed event, a second 

public comment period may be 

necessary. 

The EPA also proposes to revise the 

language at 40 CFR 50.14(c)(3)(iv) so 

that it more clearly identifies the 

required elements of an exceptional 

events demonstration. As previously 

described, the EPA proposes that each 

demonstration begin with a narrative 

conceptual model, which summarizes 

the event in question and provides 

context for required statutory technical 

criteria analyses. The EPA further 

proposes, consistent with other 

proposed changes in this action, that an 

air agency include in its demonstration 

to justify data exclusion evidence that 

the following statutory technical criteria 

are satisfied: 

• The event was a human activity that 

is unlikely to recur at a particular 

location or was a natural event. 

• The event was not reasonably 

controllable or preventable. 

• The event affected air quality in 

such a way that there exists a clear 

causal relationship between the specific 

event and the monitored exceedance or 

violation (supported in part by the 

comparison to historical concentrations 

and other analyses). 

The EPA seeks comments on the 

identified proposed changes to the 

language at 40 CFR 50.14(c)(3)(i), (iv) 

and (v), which more clearly identify the 

required elements of an exceptional 

events demonstration. 

The EPA notes that the recent final 

rule to revise the ozone NAAQS also 

removed and reserved the subsequent 

sections at 40 CFR 50.14(c)(3)(ii) and 

(iii), which addressed the submittal of 

exceptional events demonstrations that 

could affect regulatory determinations 

associated with initial area designations 

for the 2006 24-hour PM2.5 NAAQS and 

the 2010 Lead NAAQS and were made 

obsolete by the passage of time. The 

EPA will retain these removed and 

reserved sections as promulgated in the 

ozone NAAQS and proposes no 

additional changes to this language. 

7. Timing of the EPA’s Review of 

Submitted Demonstrations 

a. Current Situation 

Since promulgation of the Exceptional 

Events Rule in 2007, stakeholders have 

questioned the process by which the 

EPA reviews submitted 

demonstrations.137 Specifically, 

stakeholders have expressed concern 

that the EPA has a backlog of submittals 

but acts only on EPA-prioritized 

packages. Stakeholders have stated that 

because the EPA has not acted on all 

submissions, the air quality values used 

for planning and regulatory purposes 

are higher than they would be if the 

effects of non-controllable emissions 

were removed from the data set. Air 

agencies have also noted that without 

feedback, they do not know the EPA’s 

expectations regarding future 

submittals. 

The EPA addressed these questions 

and comments in the Interim 

Exceptional Events Implementation 

Guidance. In Question 27 of the Interim 

Q&A document, the EPA identified the 

general process and timing for 

demonstration reviews. In this 

document, the EPA clarified the process 

by which it prioritizes submittals and 

indicated that we may not act on 

submittals with no regulatory 

significance. The guidance also 

presented the voluntary Letter of Intent 

concept as a mechanism to aid in 

planning and prioritization. 

Additionally, we stated that we intend 

to make a decision regarding 

concurrence with an air agency’s 

request to exclude data as expeditiously 

as necessary following submittal of a 

complete package if required by a nearterm regulatory action. We also 

indicated our intent to communicate 

with the submitting agency, as needed, 

during the demonstration review period. 

b. Proposed Changes 

In this proposal, the EPA is clarifying 

some of our previous statements 

regarding the prioritization and 

submittal of demonstrations. As noted 

in several subsections within section 

V.G of this proposal, we also propose to 

codify in regulatory language 

approaches to increase the efficiency of 

preparing, submitting and reviewing 

exceptional events demonstrations. 

Although the EPA is not proposing to 

codify in regulatory language any 

changes pertaining to the timing of the 

EPA review process, the EPA offers the 

following discussion to clarify 

expectations and facilitate 

communications, which are at the 

center of timing-related issues. 

As noted in the Interim Exceptional 

Events Implementation Guidance and in 

the EPA’s best practices discussions 

described in section IV.E, the EPA is 

committed to working with air agencies 

as they prepare complete demonstration 

packages. The EPA encourages ongoing 

discussions between the reviewing EPA 

Regional office and the submitting air 

agency from the onset of the Initial 

Notification of Potential Exceptional 

Event process through official package 

submittal. Since renewing our focus on 

improved communications, the EPA has 

received positive feedback from engaged 

agencies that have used this approach. 

Additionally, these communications 

have resulted in decreased instances of 

submissions containing insufficient or 

unnecessary information. 

In reviewing submitted demonstration 

packages, the EPA will generally give 

priority to exceptional events 

determinations that may affect nearterm regulatory decisions, such as EPA 

action on SIP submittals, NAAQS 

designations and clean data 

determinations. The EPA intends to 

make a decision regarding event status 

expeditiously following submittal of a 

complete package if required by a nearterm regulatory action. If during the 

review process the EPA identifies the 

need for additional information to 

determine whether the exceptional 

events criteria are met, the EPA will 

notify the submitting air agency and 

encourage the agency to provide the 

supplemental information. If the 

information needed is minor and a 

natural outgrowth of what was 

previously submitted, the EPA will not 

require the air agency to undergo an 

additional public notice-and-comment 

process. However, if the needed 

information is significant, the EPA may 

request that the air agency re-notice the 

demonstration before resubmitting it to 

the EPA, thus requiring an additional 

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138The EPA anticipates a reduced number of 

deferrals and/or nonconcurrences for 

demonstrations associated with the Initial 

Notification of Potential Exceptional Event process 

as discussed in section V.G.5 because the EPA and 

the affected air agency would have discussed 

issues/concerns prior to the EPA’s decision on a 

submitted demonstration. 

139Routine status calls between the reviewing 

EPA Regional office and air agencies could include 

an agenda item to review the status of all submitted 

demonstrations, including those that the EPA has 

deferred. 

EPA review following resubmittal. The 

EPA will work with air agencies on 

supplemental timeframes; however, the 

mandatory timing of the EPA actions 

may limit the response time the EPA 

allows. The EPA proposes to include as 

rule text a requirement for the air 

agency to submit additional information 

within 12 months. If additional 

information is not received in 12 

months, then the EPA will consider the 

submitted demonstration inactive, and 

will not continue the review or take 

action. In effect, an air agency’s lack of 

response within a 12-month period will 

‘‘void’’ the submittal. In these cases, the 

EPA does not intend to issue a formal 

notice of deferral. If the air agency later 

decides to pursue the exceptional events 

claim after a 12-month period of 

inactivity, it may re-initiate the 

exceptional events process by 

submitting a new Initial Notification of 

Potential Exceptional Event followed by 

a new demonstration, which could 

simply be revising the original submittal 

to include the additional information 

previously requested by the EPA. 

At the conclusion of the EPA’s 

review, the EPA will make a 

determination regarding the status of a 

submitted exceptional events 

demonstration. The EPA’s decision 

could result in concurrence, 

nonconcurrence or deferral.138 In acting 

on a submitted demonstration covering 

multiple event days and/or multiple 

flags, the EPA could concur with part of 

a demonstration and nonconcur or defer 

other flagged values. If the EPA 

determines that the events addressed in 

an exceptional events demonstration are 

not anticipated to affect any future 

regulatory decision, the EPA could defer 

review of these events and notify the 

submitting agency if a subsequent 

review results in a determination that 

the events do affect a regulatory 

decision.139 Formal mechanisms for 

deferral could include the EPA’s 

indicating this decision by letter, by 

email to a responsible official or during 

a high-level meeting with an attendees’ 

list and discussion summary. 

8. Dispute Resolution Mechanisms 

Since promulgation of the 2007 

Exceptional Events Rule and through 

the development of the Interim 

Exceptional Events Implementation 

Guidance, some interested parties have 

asked the EPA to identify a process by 

which submitting air agencies can 

formally dispute the EPA’s decision 

regarding requests for additional 

information to support submitted 

demonstration packages and/or 

decisions regarding concurrence, 

nonconcurrence or deferral of submitted 

demonstration packages. While the EPA 

acknowledges the expressed concerns 

and desire for a formally identified 

dispute resolution process, the EPA also 

believes that several mechanisms 

currently exist that air agencies can use 

at various points in the exceptional 

events process. These mechanisms 

include engaging in early dialogue with 

the reviewing EPA Regional office, 

submitting requests for reconsideration 

to the official who made the 

determination if a request identifies a 

clear error or if the reviewing EPA 

regional office overlooked information 

submitted by the affected air agency, 

and/or elevating the concern within the 

EPA’s chain of command. Additionally, 

air agencies can raise any unresolved 

event-related issues during the 

regulatory process that relies upon the 

claimed event-influenced data by 

participating in related public noticeand-comment processes and/or 

challenging in an appropriate court the 

regulatory decision subsequently made 

based in part on the EPA’s exceptional 

events determination. These currently 

available dispute resolution approaches 

to address exceptional events decisions 

are consistent with the mechanisms 

available for other EPA actions. With 

exceptional events decisions, however, 

the air agency has opportunities to 

elevate concerns during two processes: 

the exceptional events determination 

and the subsequent regulatory action 

that relies on the exceptional events 

decision. 

The EPA believes that the existing 

mechanisms identified above combined 

with the EPA’s commitment to focus on 

communication and collaboration with 

the submitting air agency through the 

exceptional events demonstration 

process, and the clarifications that 

would be in effect with these proposed 

revisions to the 2007 Exceptional Events 

Rule and associated guidance, will 

avoid the need for a formal dispute 

resolution mechanism for exceptional 

events. Therefore, the EPA does not 

intend to address dispute resolution 

within these proposed rule revisions 

and does not intend to respond to 

comments on this issue. 

VI. Mitigation 

A. Current Situation 

Section 319(b)(3)(A) of the CAA 

identifies five principles for the EPA to 

follow in developing implementing 

regulations for exceptional events: 

(i) Protection of public health is the 

highest priority; 

(ii) Timely information should be 

provided to the public in any case in 

which the air quality is unhealthy; 

(iii) All ambient air quality data 

should be included in a timely manner 

in an appropriate federal air quality 

database that is accessible to the public; 

(iv) Each state must take necessary 

measures to safeguard public health 

regardless of the source of the air 

pollution; and 

(v) Air quality data should be 

carefully screened to ensure that events 

not likely to recur are represented 

accurately in all monitoring data and 

analyses. 

The regulatory requirements 

implementing (iii) and (v) of this part of 

the statute are found only in 40 CFR 

50.14 while the regulatory requirements 

implementing (i) and (iv) are found only 

in 40 CFR 51.930, Mitigation of 

Exceptional Events. Both §§ 50.14(c)(1) 

and 51.930(a)(1) require states to 

provide notice of events to the public 

(the second of the five principles). 

The language at 40 CFR 51.930 

requires air agencies requesting data 

exclusion to ‘‘take appropriate and 

reasonable actions to protect public 

health from exceedances or violations of 

the NAAQS’’ and at a minimum do each 

of the following: 

• Provide for prompt public 

notification whenever air quality 

concentrations exceed or are expected to 

exceed the NAAQS. 

• 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. 

• Provide for the implementation of 

appropriate measures to protect public 

health from exceedances or violations of 

ambient air quality standards caused by 

exceptional events. 

The EPA promulgated the existing 

requirements in 2007 after considering 

and proposing several approaches to 

implementing CAA section 319(b)(3)(A). 

Some of the proposed approaches 

would have established a more formal 

structure by which air agencies 

prepared and submitted to the EPA 

mitigation plans to protect public health 

during events. These plans would have 

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140The Treatment of Data Influenced by 

Exceptional Events; Proposed Rule, 71 FR 12592 

(March 10, 2006). 

141See Comments and Responses related to 

‘‘Requirements for States To Provide Public 

Notification, Public Education, and Appropriate 

and Reasonable Measures To Protect Public Health’’ 

in Treatment of Data influenced by Exceptional 

Events; Final Rule, 72 FR 13574–13576 (March 22, 

2007). 

142The term ‘‘mitigation’’ does not appear in CAA 

section 319(b). It appears in the title but not the text 

of 40 CFR 51.930. 

143 72 FR 13574 (March 22, 2007). 

144A 3-year period is determined based on the 

submittal date of an exceptional events 

demonstration. 

145Because the form of the NAAQS varies by 

pollutant, it is possible that multiple events in a 3- 

year period may not cause a NAAQS violation. An 

air agency that identifies multiple events of the 

same type (e.g., wildfire/ozone) in AQS, but 

prepares and submits a demonstration for only one 

of these events, would trigger the proposed 

requirement to develop a mitigation plan. 

146Air Quality Control Regions are defined in 40 

CFR part 81, subpart B, Designation of Air Quality 

Control Regions. 

been subject to the EPA’s approval and/ 

or the approval of the exclusion of 

event-affected data would have been 

contingent on the approval of such a 

plan. Comments on these proposed 

options varied widely.140 141

In the final 2007 Exceptional Events 

Rule, ‘‘mitigation’’ measures 142 became 

part of the 2007 Exceptional Events 

Rule, but they were not incorporated 

into the criteria and processes by which 

data are excluded from use in regulatory 

determinations. There is no requirement 

to submit such measures to the EPA for 

either prospective or retrospective 

review and approval as a condition for 

approval for exclusion of event-affected 

data. Neither are air agencies required to 

notify the EPA of the measures an air 

agency plans to take or has taken. In the 

preamble to the 2007 Exceptional 

Events Rule, we stated that states should 

take ‘‘reasonable and appropriate 

measures’’ to protect public health 

related to the occurrence of an event 

and that states should determine what 

measures constitute those that are 

‘‘reasonable and appropriate.’’ 143 We 

did not clarify how measures should be 

determined to be ‘‘appropriate’’ 

measures. 

The mitigation measures that the EPA 

sees states most commonly practicing 

are ones related to the requirement that 

air agencies ‘‘provide for prompt public 

notification whenever air quality 

concentrations exceed or are expected to 

exceed the NAAQS.’’ Often, these 

public notifications include public 

health alerts for high wind dust events 

or wildfires. We believe that other 

aspects of mitigation, including 

implementing appropriate measures to 

protect public health beyond 

notification, are also important in 

implementing the CAA guiding 

principle that ‘‘each State must take 

necessary measures to safeguard public 

health regardless of the source of the air 

pollution.’’ 

B. Proposed Changes 

Given the EPA’s and the states’ 

experience implementing the 2007 

Exceptional Events Rule as indicated 

above, we consider it appropriate to 

consider possible changes to the 

mitigation-related rule components with 

the benefit of additional public input. 

We are seeking comment on approaches 

ranging from retaining the existing rule 

requirements at 40 CFR 51.930 to the 

various possible new components 

described in this section. We invite 

comment on these alternatives and on 

other concepts. We may make no 

change; we may adopt all of the 

described new components; or we may 

adopt only some features or variations 

of the described options. Note that we 

are not considering requiring all states 

to develop formal mitigation plans. We 

are seeking comment on the concept of 

only some states being required to 

develop mitigation plans for their 

particular ‘‘historically documented’’ or 

‘‘known seasonal’’ exceptional events, 

defined below in section VI.B.1; on 

recommended elements for such 

mitigation plans described below in 

section VI.B.2; and on options for 

implementing mitigation plans 

described in section VI.B.3. Section 

VI.B.4 summarizes the EPA’s potential 

options for mitigation elements for 

exceptional events purposes. 

1. Defining Historically Documented or 

Known Seasonal Events 

The EPA seeks comment on whether 

an air agency should develop a 

mitigation plan for its particular type of 

‘‘historically documented’’ or ‘‘known 

seasonal’’ exceptional events, if any. 

The EPA would consider ‘‘historically 

documented’’ or ‘‘known seasonal’’ 

exceptional events to include events of 

the same type and pollutant (e.g., high 

wind dust/PM or wildfire/ozone) that 

meet any of the following criteria: an 

event for which an air agency has 

previously submitted exceptional events 

demonstrations; an event that an air 

agency has previously flagged for 

concurrence in AQS (regardless of 

whether the air agency submitted a 

demonstration); or an event that has 

been the subject of local news articles, 

public health alerts or published 

scientific journal articles. The EPA 

would not require an air agency to 

develop a mitigation plan for the first 

event of a given type (e.g., if an area is 

prone to wildfires but has never 

experienced a high wind dust event, 

then it would not be expected to 

develop a mitigation plan for its first 

high wind dust event, but it would be 

expected to develop a mitigation plan 

for wildfires). A second event of a given 

type within a 3-year period would 

subject the area to ‘‘having a history’’ 

and, therefore, needing a mitigation 

plan.144 This option avoids plan 

development for a one-of-a-kind 

occurrence.145 In defining ‘‘first’’ and 

‘‘second’’ events, the EPA could 

consider events that affect the same 

AQCR, but not necessarily the same 

monitor.146 For example, high wind 

dust events occur seasonally in the 

Phoenix, Arizona metropolitan area, 

which is part of the Maricopa Intrastate 

Air Quality Control Region (see 40 CFR 

81.36). These events have influenced 

particulate matter concentrations at 

multiple monitors within the Maricopa 

Intrastate AQCR. Under this proposal, 

high wind dust events in Phoenix (i.e., 

the Maricopa Intrastate AQCR) are 

known events requiring a mitigation 

plan. On the other hand, a high wind 

dust event in Sedona, Arizona, part of 

the Northern Arizona Intrastate Air 

Quality Control Region (see 40 CFR 

81.270), would be a first event and not 

subject to the development of a 

mitigation plan. As a variation of this 

concept on which we also seek 

comment, the EPA could consider a first 

season of events as one of three required 

seasons of events, so that a mitigation 

plan would be required only when an 

event type persists across several years. 

For example, an area may not have 

previously experienced wildfires in the 

past 10 years, but then experiences 

multiple wildfires and multiple 

exceedances in a single wildfire season. 

If these multiple wildfires affect the 

same general geographic area and 

monitors in a relatively short period of 

time (e.g. 2–3 months), then they could 

be considered a single event for 

purposes of developing a mitigation 

plan and would not trigger the 

requirement for a mitigation plan. 

2. Mitigation Plan Components 

The EPA solicits comment on the 

following three plan components that 

could be recommended or required in 

order to implement the mitigation 

principles found in section 319(b)(3)(A) 

of the CAA: Public notification and 

education; steps to identify, study and 

implement mitigating measures and 

provision for periodic revision of the 

mitigation plan (to include public 

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review of plan elements). This section 

discusses these elements in more detail. 

A mitigation plan should address 

actions that would be taken within a 

state’s own territory for events that 

happen within its own territory or that 

of another jurisdiction. 

a. Public notification to and education 

programs for affected or potentially 

affected communities. Air agencies 

could be required or encouraged to 

include in their mitigation plans steps 

to activate public notification and 

education systems whenever air quality 

concentrations exceed or are expected to 

exceed an applicable national ambient 

air quality standard. If possible, air 

agencies would notify the public of the 

actual or anticipated event at least 48 

hours in advance of the event using 

methods appropriate to the community 

being served. Outreach mechanisms 

could include Web site alerts, National 

Weather Service alerts, telephone or text 

bulletins, television or radio campaigns 

or other messaging campaigns. Public 

notification and education programs 

could be encouraged or required to 

include some or all of the following 

actions to support the outreach system: 

adoption of methods for forecasting/

detection, consultation with appropriate 

health department personnel regarding 

issuing health advisories and suggested 

actions for exposure minimization for 

sensitive populations (e.g., remain 

indoors, avoid vigorous outdoor 

activity, avoid exposure to tobacco 

smoke and other respiratory irritants 

and, in extreme cases, evacuation or 

public sheltering procedures). 

b. Steps to identify, study and 

implement mitigating measures, 

including approaches to address each of 

the following: 

(i) Mandatory or voluntary measures 

to abate or minimize contributing 

controllable sources of identified 

pollutants. A state could be required to 

include or encouraged to consider fulltime or contingent controls on eventrelated sources as well as non-event 

related sources. For example, these 

measures might include continuously 

operating control measures during an 

extreme event for identified sources that 

normally operate these same controls on 

an intermittent basis. It could also 

involve including work practices (e.g., 

water spray for dust suppression) or 

contingent limits during extreme events 

on emissions from non-event related 

sources that, under non-event periods, 

have no or less stringent emissions 

limits or work practices. 

(ii) Methods to minimize public 

exposure to high concentrations of 

identified pollutants. 

(iii) Processes to collect and maintain 

data pertinent to the event (e.g., to 

identify the data to be collected, the 

party responsible for collecting and 

maintaining the data and when, how 

and to whom the data will be reported). 

(iv) Mechanisms to consult with other 

air quality managers in the affected area 

regarding the appropriate responses to 

abate and minimize impacts. 

Consultation could include 

collaboration between potentially 

affected local, state, tribal and federal 

air quality managers and/or emergency 

response personnel. 

c. Provision for periodic review and 

evaluation of the mitigation plan and its 

implementation and effectiveness by the 

air agency and all interested 

stakeholders (e.g., public and private 

land owners/managers, air quality, 

agriculture and forestry agencies, the 

public). For example, air agencies could 

be required to use this review process 

and to revise, if appropriate, and certify 

the mitigation plan every 3 years or 

every three events, whichever is longer. 

The air agency could be required to 

submit a summary and response to the 

comments received during the public 

plan review process to the EPA along 

with the recertification statement and/or 

revised mitigation plan. If the 

historically documented or known 

seasonal exceptional events continue to 

result in elevated pollutant 

concentrations above the relevant 

NAAQS, thus showing that the 

combination of the existing SIP and the 

existing mitigation plan does not 

effectively safeguard public health, the 

mitigation plan might need to be 

strengthened during this review. 

If the EPA adopts requirements like 

those described above, it would not 

necessarily mean that all affected air 

agencies would have to prepare new 

plans. If an air agency has developed 

and implemented a contingency plan 

under 40 CFR part 51, subpart H, 

Prevention of Air Pollution Emergency 

Episodes, that meets the requirements of 

40 CFR 51.152, and that includes 

provisions for events that could be 

considered ‘‘exceptional events’’ under 

the provisions in 40 CFR 50.14, then the 

subpart H contingency plan would 

likely satisfy the mitigation 

requirements described above. If the 

identified basic elements are included 

and addressed, including the element 

for public comment, then other types of 

existing mitigation or contingency plans 

may satisfy the possible mitigation plan 

requirement described above. For 

example, if an area has developed a 

natural events action plan or a high 

wind action plan covering high wind 

dust events, this plan likely would 

satisfy mitigation elements for high 

wind dust events. Smoke management 

plans and/or forest management plans 

might also satisfy the mitigation 

elements for prescribed fires and 

wildfires. Most air agencies generally 

have sufficient, established processes 

that meet the public notification and 

education element, which can be easily 

adapted or modified to meet the 

mitigation elements proposed in this 

action. The EPA is requesting comment 

on how much time air agencies should 

be allowed to develop a plan. 

3. Options for Implementing Mitigation 

Plans 

The EPA is seeking comment on two 

options for tying the proposed 

mitigation plan components discussed 

in section VI.B.2 to the EPA review of 

exceptional events demonstrations. 

Option 1 includes the EPA’s review for 

completeness but not substantive 

approval or disapproval, while Option 2 

includes the EPA’s approval of the 

substance of the mitigation plan. These 

options are discussed below in more 

detail, but neither option would require 

a mitigation plan to be included in a SIP 

or to be otherwise federally-enforceable. 

Under both options, air agencies with 

historically documented or known 

seasonal exceptional events could 

submit the mitigation plan to the EPA 

in advance of an event, or submit a 

mitigation plan along with an 

exceptional events demonstration. The 

EPA would concur with a 

demonstration for the relevant event 

type only if a mitigation plan has passed 

the type of EPA review described in the 

option. Given that the air agency would 

have advance notification of the need to 

develop a plan, the air agency could 

develop and submit the mitigation plan 

in advance of any exceptional events 

demonstration so that the EPA could 

pre-review the mitigation plan and take 

faster action on an exceptional events 

submittal once one is submitted. 

Option 1: Under this option, the EPA 

would review for inclusion of required 

elements as described above and to 

ensure that the development of the 

mitigation plan included a public 

comment process. We would not 

formally review the substance of the 

plan in the sense of approving the 

details of the specific measures and 

commitments in the plan. 

Option 2: Under this option, EPA 

approval of the substance of the 

mitigation plan would be a precondition 

for EPA concurrence on an exceptional 

events demonstration. Because the EPA 

would approve the content, 

completeness and sufficiency of a 

mitigation plan, the EPA’s disapproval 

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of the plan could result in the EPA’s 

nonconcurrence on a current or future 

exceptional events demonstration. 

VII. Draft Guidance on the Preparation 

of Exceptional Events Demonstrations 

for Wildfire Events That May Influence 

Ozone Concentrations 

A. What is this draft guidance about and 

why is it needed? 

The Exceptional Events Rule contains 

the regulatory requirements and criteria 

necessary for the EPA’s approval of the 

exclusion of air quality data from 

regulatory determinations related to 

NAAQS exceedances or violations. 

During the implementation of the 2007 

Exceptional Events Rule, the EPA and 

stakeholders have identified a need for 

implementation guidance that provides 

an interpretation of and examples for 

addressing the regulatory requirements 

specific to the most common event 

types. One event type that has been 

identified by the EPA and stakeholders 

is wildfire influence on ozone 

concentrations. In 2013, the EPA 

finalized the Interim Exceptional Events 

Implementation Guidance documents 

(see section IV.D), which included the 

Interim High Winds Guidance 

document and an Interim Overview 

document that also committed to the 

preparation of a Draft Wildfire Ozone 

Guidance document. The EPA intends 

to address this need and commitment 

via the Draft Guidance on the 

Preparation of Exceptional Events 

Demonstrations for Wildfire Events that 

May Influence Ozone Concentrations 

(‘‘Draft Wildfire Ozone Guidance 

document’’), which accompanies this 

proposed rule and is also available for 

comment. 

This Draft Wildfire Ozone Guidance 

document includes example analyses, 

conclusion statements and technical 

tools that air agencies can use to provide 

evidence that the wildfire event 

influenced the monitored ozone 

concentration. The Draft Wildfire Ozone 

Guidance document also identifies fire 

and monitor-based characteristics that 

might allow for a simpler and less 

resource-consuming demonstration 

package. The EPA has developed the 

Draft Wildfire Ozone Guidance 

document concurrently with the 

proposed Exceptional Events Rule 

revisions so that the Draft Wildfire 

Ozone Guidance reflects the proposed 

rule changes. Once finalized, this 

guidance will provide the EPA regional 

offices and air agencies with guidance 

on how to prepare and submit evidence 

to meet the Exceptional Events Rule 

requirements for monitored ozone 

exceedances caused by wildfires. The 

guidance, when finalized, will not be an 

EPA rule, and in specific cases the EPA 

may depart from the guidance for 

reasons that the EPA will explain at the 

time of the action. 

B. What scenarios are addressed in the 

draft guidance? 

The EPA has prepared the Draft 

Wildfire Ozone Guidance document to 

provide assistance and example 

analyses for wildfire events that may 

influence ozone concentrations. Though 

many of the technical analyses included 

in the draft document may also be 

applied to prescribed fire events, the 

draft guidance document available for 

comment at this time does not provide 

guidance specific on how prescribed fire 

events can address all proposed rule 

requirements. Limiting the scope to 

wildfire events is intended to make the 

document easier to use for wildfire 

events. With this notice, the EPA invites 

comment on the content of this 

guidance document and whether it is 

appropriate to expand the scope of the 

guidance to include prescribed fire 

events. If commenters believe it is 

necessary to expand the scope of the 

EPA’s final new guidance beyond the 

scope of the Draft Wildfire Ozone 

Guidance document, the EPA seeks 

comment on whether wildfire and 

prescribed fire events should be 

addressed in a single fire ozone 

guidance document or in separate 

guidance documents. 

VIII. Environmental Justice 

Considerations 

The Exceptional Events Rule provides 

the criteria by which state, local and 

tribal air agencies identify air quality 

data they believe have been influenced 

by exceptional events, which by 

statutory definition are not reasonably 

controllable or preventable. Because 

these events are not reasonable to 

prevent or control, they can affect all 

downwind populations including 

minority and low-income populations. 

For this reason, in adding section 319(b) 

to the CAA, Congress identified as a 

guiding principle in developing 

regulations, ‘‘the principle that 

protection of public health is the highest 

priority.’’ The 2007 Exceptional Events 

Rule at 40 CFR 50.14 requires air 

agencies to seek public comment on 

prepared exceptional events 

demonstrations prior to submitting them 

to the reviewing EPA regional office. 

The public can also comment on 

rulemakings that include decisions 

related to the exclusion of eventinfluenced data. The mitigation of 

exceptional events language at 40 CFR 

51.930 also requires that air agencies 

provide public notification and 

education programs related to events. 

To protect all people and communities, 

notably minority and low-income 

populations, air agencies should ensure 

that notifications and education 

programs are communicated using the 

language (e.g., English and Spanish) and 

media (e.g., radio and postings in local 

community centers) best suited to the 

target audience(s). Additionally, these 

proposed revisions are part of a public 

notice-and-comment rulemaking effort, 

which will include a public hearing. 

These opportunities for public input 

and education ensure that all those 

residing, working, attending school or 

otherwise present in areas affected by 

exceptional events, regardless of 

minority and economic status, are 

protected. 

IX. Statutory and Executive Order 

Reviews 

A. Executive Order 12866: Regulatory 

Planning and Review and Executive 

Order 13563: Improving Regulation and 

Regulatory Review 

This action is a significant regulatory 

action that was submitted to the Office 

of Management and Budget (OMB) for 

review because it raises novel policy 

issues. Any changes made in response 

to OMB recommendations have been 

documented in the docket. 

B. Paperwork Reduction Act 

This action does not impose any new 

information collection burden under the 

PRA. The information being requested 

under these proposed rule revisions is 

consistent with current requirements 

related to information needed to verify 

the authenticity of monitoring data 

submitted to the EPA’s AQS database, 

and to justify exclusion of data that have 

been flagged as being affected by 

exceptional events. OMB has previously 

approved the information collection 

activities for ambient air monitoring 

data and other supporting 

measurements reporting and 

recordkeeping activities associated with 

the 40 CFR part 58 Ambient Air Quality 

Surveillance rule and has assigned OMB 

control number 2060–0084. 

C. Regulatory Flexibility Act (RFA) 

I certify that this action will not have 

a significant economic impact on a 

substantial number of small entities 

under the RFA. This action will not 

impose any requirements on small 

entities. Instead, the proposed rule 

revisions provide the criteria and 

increase the efficiency of the process by 

which state, local and tribal air agencies 

identify air quality data they believe 

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have been influenced by an exceptional 

event. The proposed rule revisions also 

clarify those actions that state, local and 

tribal air agencies should take to protect 

public health during and following an 

exceptional event. Because affected air 

agencies would have discretion to 

implement controls on sources that may 

need to be regulated due to 

anthropogenic contribution in the area 

determined to be influenced by an 

exceptional event, the EPA cannot 

predict the indirect effect of the rule on 

sources that may be small entities. 

D. Unfunded Mandates Reform Act 

(UMRA) 

This action does not contain an 

unfunded mandate of $100 million or 

more as described in UMRA, 2 U.S.C. 

1531–1538, and does not significantly or 

uniquely affect small governments. The 

action imposes no enforceable duty on 

any state, local or tribal governments or 

the private sector. 

E. Executive Order 13132: Federalism 

This action does not have federalism 

implications. The EPA believes, 

however, that this action may be of 

significant interest to states and to local 

air quality agencies to whom a state has 

delegated relevant responsibilities for 

air quality management. Consistent with 

the EPA’s policy to promote 

communications between the EPA and 

state and local governments, the EPA 

consulted with representatives of state 

and local governments early in the 

process of developing this action to 

permit them to have meaningful and 

timely input into its development. A 

summary of the concerns raised during 

that consultation is provided in section 

IV of this preamble. 

F. Executive Order 13175: Consultation 

and Coordination With Indian Tribal 

Governments 

This action does not have tribal 

implications as specified in Executive 

Order 13175. It would not have a 

substantial direct effect on one or more 

Indian tribes. Furthermore, these 

proposed regulation revisions do 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 characterizing air quality 

and developing plans to attain the 

NAAQS, and these revisions to the 

regulations do nothing to modify that 

relationship. Thus, Executive Order 

13175 does not apply to this action. 

Although Executive Order 13175 does 

not apply to this action, the EPA held 

public meetings attended by tribal 

representatives and separate meetings 

with tribal representatives to discuss the 

revisions proposed in this action. The 

EPA also provided an opportunity for 

all interested parties to provide oral or 

written comments on potential concepts 

for the EPA to address during the rule 

revision process. Summaries of these 

meetings are included in the docket for 

this proposed rule. The EPA specifically 

solicits additional comment on this 

proposed action from tribal officials. 

G. Executive Order 13045: Protection of 

Children From Environmental Health & 

Safety Risks 

The EPA interprets Executive Order 

13045 as applying only to those 

regulatory actions that concern 

environmental health or safety risks that 

the EPA has reason to believe may 

disproportionately affect children, per 

the definition of ‘‘covered regulatory 

action’’ in section 2–202 of the 

Executive Order. This action is not 

subject to Executive Order 13045 

because it does not concern an 

environmental health risk or safety risk. 

H. Executive Order 13211: Actions 

Concerning Regulations That 

Significantly Affect Energy Supply, 

Distribution or Use 

This action is not a ‘‘significant 

energy action’’ because it is not likely to 

have a significant adverse effect on the 

supply, distribution or use of energy. 

The purpose of this proposed rule is to 

provide the criteria, and increase the 

efficiency of the process, by which state, 

local and tribal air agencies may 

identify air quality data they believe 

have been influenced by an exceptional 

event. The EPA does not expect these 

activities to affect energy suppliers, 

distributors or users. 

I. National Technology Transfer and 

Advancement Act 

This rulemaking does not involve 

technical standards. 

J. Executive Order 12898: Federal 

Actions To Address Environmental 

Justice in Minority Populations and 

Low-Income Populations 

The EPA believes the human health or 

environmental risk addressed by this 

action will not have potential 

disproportionately high and adverse 

human health or environmental effects 

on minority, low-income or indigenous 

populations. The results of this 

evaluation are contained in the section 

of the preamble titled ‘‘Environmental 

Justice Considerations.’’ This proposed 

action provides the criteria and 

increases the efficiency of the process 

by which state, local and tribal air 

agencies identify air quality data they 

believe have been influenced by 

exceptional events, which, by statutory 

definition, are not reasonably 

controllable or preventable. These 

proposed regulatory provisions do, 

however, provide information 

concerning actions that state, local or 

tribal air agencies might take to 

uniformly protect public health once the 

EPA has concurred with an air agency’s 

request to exclude data influenced by an 

exceptional event. The mitigation 

component of the proposed rule could 

ultimately provide additional protection 

for minority, low income and other 

populations located in areas affected by 

exceptional events. Therefore, the EPA 

finds that this proposed action would 

not adversely affect the health or safety 

of minority or low-income populations, 

and that it is designed to protect and 

enhance the health and safety of these 

and other populations. 

X. Statutory Authority 

The statutory authority for this action 

is provided by 42 U.S.C. 7401, et seq. 

List of Subjects in 40 CFR Part 50 

Environmental protection, Air 

pollution control, National parks, 

Wilderness areas. 

Dated: November 10, 2015. 

Gina McCarthy, 

Administrator. 

For the reasons set forth in the 

preamble, it is proposed that 40 CFR 

part 50 be amended as follows: 

PART 50—NATIONAL PRIMARY AND 

SECONDARY AMBIENT AIR QUALITY 

STANDARDS 

■ 1. The authority citation for part 50 

continues to read as follows: 

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

■ 2. Amend § 50.1 by: 

■ a. Revising paragraphs (j) and (k). 

■ b. Adding paragraphs (m), (n), (o), (p), 

(q) and (r). 

The revisions and additions read as 

follows: 

§ 50.1 Definitions. 

* * * * * 

(j) Exceptional event means an event 

and its resulting emissions that affect air 

quality in such a way that there exists 

a clear causal relationship between the 

specific event and the monitored 

exceedance or violation, is not 

reasonably controllable or preventable, 

is an event caused by human activity 

that is unlikely to recur at a particular 

location or a natural event, and is 

determined by the Administrator in 

accordance with 40 CFR 50.14 to be an 

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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 and 

its resulting emissions, which may 

recur, in which human activity plays 

little or no direct causal role. 

Anthropogenic sources that are 

reasonably controlled shall be 

considered to not play a direct role in 

causing emissions. 

* * * * * 

(m) Prescribed fire is any fire 

intentionally ignited by management 

actions in accordance with applicable 

laws, policies, and regulations to meet 

specific land or resource management 

objectives. 

(n) Wildfire is any fire started by an 

unplanned ignition caused by lightning; 

volcanoes; other acts of nature; 

unauthorized activity; or accidental, 

human-caused actions, or a prescribed 

fire that has been declared to be a 

wildfire. A wildfire that predominantly 

occurs on wildland is a natural event. 

(o) Wildland means an area in which 

human activity and development is 

essentially non-existent, except for 

roads, railroads, power lines, and 

similar transportation facilities. 

Structures, if any, are widely scattered. 

(p) High wind dust event is an event 

that includes the high-speed wind and 

the dust that the wind entrains and 

transports to a monitoring site. 

(q) High wind threshold is the 

minimum wind speed capable of 

causing particulate matter emissions 

from natural undisturbed lands in the 

area affected by a high wind dust event. 

(r) Federal land manager means, 

consistent with the definition in 40 CFR 

51.301, the Secretary of the department 

with authority over the Federal Class I 

area (or the Secretary’s designee) or, 

with respect to Roosevelt-Campobello 

International Park, the Chairman of the 

Roosevelt-Campobello International 

Park Commission. 

■ 3. Amend § 50.14, as amended on 

October 26, 2015, at 80 FR 65452, 

effective December 28, 2015, as follows: 

■ a. Revise paragraphs (a) and (b); 

■ b. Revise paragraphs (c)(1), (c)(2)(i) 

through (v), and (c)(3). 

The revisions read as follows: 

§ 50.14 Treatment of air quality monitoring 

data influenced by exceptional events. 

(a) Requirements—(1) Scope. (i) This 

section applies to the treatment of data 

showing exceedances or violations of 

any national ambient air quality 

standard for purposes of the following 

types of regulatory determinations by 

the Administrator: 

(A) An action to designate an area, 

pursuant to Clean Air Act section 

107(d)(1), or redesignate an area, 

pursuant to Clean Air Act section 

107(d)(3), for a particular national 

ambient air quality standard; 

(B) The assignment or re-assignment 

of a classification category to a 

nonattainment area where such 

classification is based on a comparison 

of pollutant design values, calculated 

according to the specific data handling 

procedures in 40 CFR part 50 for each 

national ambient air quality standard, to 

the level of the relevant national 

ambient air quality standard; 

(C) A determination regarding 

whether a nonattainment area has 

attained the level of the appropriate 

national ambient air quality standard by 

its specified deadline; 

(D) A determination that an area has 

had only one exceedance in the year 

prior to its attainment deadline and thus 

qualifies for a 1-year attainment date 

extension, if applicable; and 

(E) A determination under Clean Air 

Act section 110(k)(5), if based on an area 

violating a national ambient air quality 

standard, that the state implementation 

plan is inadequate to the requirements 

of Clean Air Act section 110. 

(ii) A State, federal land manager or 

other federal agency may request the 

Administrator to exclude data showing 

exceedances or violations of any 

national ambient air quality standard 

that are directly due to an exceptional 

event from use in determinations by 

demonstrating to the Administrator’s 

satisfaction that such event caused a 

specific air pollution concentration at a 

particular air quality monitoring 

location. 

(A) For a federal land manager or 

other federal agency to be eligible to 

initiate such a request for data 

exclusion, the federal land manager or 

other federal agency must: 

(1) Either operate a regulatory monitor 

that has been affected by an exceptional 

event or manage land on which an 

exceptional event occurred that 

influenced a monitored concentration at 

a regulatory monitor; and 

(2) Initiate such a request only after 

discussing such submittal with the State 

in which the affected monitor is located; 

and 

(B) When initiating such a request, all 

provisions in this section that are 

expressed as requirements applying to a 

State shall, except as noted, be 

requirements applying to the federal 

land manager or other federal agency. 

(2) A demonstration to justify data 

exclusion may include any reliable and 

accurate data, but must specifically 

address the elements in paragraphs 

(c)(3)(iv) and (v) of this section. 

(b) Determinations by the 

Administrator—(1) Generally. The 

Administrator shall exclude data from 

use in determinations of exceedances 

and violations where a State 

demonstrates to the Administrator’s 

satisfaction that an exceptional event 

caused a specific air pollution 

concentration in excess of one or more 

national ambient air quality standards at 

a particular air quality monitoring 

location and otherwise satisfies the 

requirements of this section. 

(2) Fireworks displays. The 

Administrator shall exclude data from 

use in determinations of exceedances 

and violations where a State 

demonstrates to the Administrator’s 

satisfaction that emissions from 

fireworks displays caused a specific air 

pollution concentration in excess of one 

or more national ambient air quality 

standards at a particular air quality 

monitoring location and otherwise 

satisfies the requirements of this 

section. Such data will be treated in the 

same manner as exceptional events 

under this rule, provided a State 

demonstrates that such use of fireworks 

is significantly integral to traditional 

national, ethnic, or other cultural events 

including, but not limited to, July 

Fourth celebrations that satisfy the 

requirements of this section. 

(3) Prescribed fires. (i) The 

Administrator shall exclude data from 

use in determinations of exceedances 

and violations, where a State 

demonstrates to the Administrator’s 

satisfaction that emissions from 

prescribed fires caused a specific air 

pollution concentration in excess of one 

or more national ambient air quality 

standards at a particular air quality 

monitoring location and otherwise 

satisfies the requirements of this 

section. 

(ii) In addressing the requirements set 

forth in paragraph (c)(3)(iv)(D) of this 

section regarding the not reasonably 

controllable or preventable criterion: 

(A) With respect to the requirement 

that a prescribed fire be not reasonably 

controllable, the State must either 

certify to the Administrator that it has 

adopted and is implementing a smoke 

management plan or the State must 

demonstrate that the burn manager 

employed the generally applicable basic 

smoke management practices identified 

in Table 2 to § 50.14. To make the latter 

demonstration, the State may rely on a 

statement or other documentation 

provided by the burn manager that he or 

she employed those practices. If an 

exceptional event occurs using the basic 

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smoke management practices approach, 

the State must undertake a review of its 

approach to ensure public health is 

being protected. 

(B) With respect to the requirement 

that a prescribed fire be not reasonably 

preventable, provided the Administrator 

determines that there is no compelling 

evidence to the contrary in the record, 

the State may rely upon and reference 

a multi-year land or resource 

management plan for a wildland area 

with a stated objective to establish, 

restore and/or maintain a sustainable 

and resilient wildland ecosystem and/or 

to preserve endangered or threatened 

species through a program of prescribed 

fire, but also provided that the use of 

prescribed fire in the area has not 

exceeded the frequency indicated in 

that plan. 

(iii) Provided the Administrator 

determines that there is no compelling 

evidence to the contrary in the record, 

in addressing the requirements set forth 

in paragraph (c)(3)(iv)(E) of this section 

regarding the human activity unlikely to 

recur at a particular location criterion 

for demonstrations involving prescribed 

fires on wildland, the State must 

describe the actual frequency with 

which a burn was conducted, but may 

rely upon and reference an assessment 

of the natural fire return interval or the 

prescribed fire frequency needed to 

establish, restore, and/or maintain a 

sustainable and resilient wildland 

ecosystem contained in a multi-year 

land or resource management plan with 

a stated objective to establish, restore, 

and/or maintain a sustainable and 

resilient wildland ecosystem and/or to 

preserve endangered or threatened 

species through a program of prescribed 

fire. 

TABLE 2 TO § 50.14—SUMMARY OF BASIC SMOKE MANAGEMENT PRACTICES, BENEFIT ACHIEVED WITH THE BSMP, AND

WHEN IT IS APPLIED BEFORE, DURING OR AFTER IGNITION OF THE BURN a

Basic smoke management practice Benefit achieved with the BSMP 

When the BSMP is 

applied—before/during/after 

the burn 

Evaluate Smoke Dispersion Conditions.Minimize smoke impacts ............................................................................... Before, During, After. 

Monitor Effects on Air Quality ........... Be aware of where the smoke is going and degree it impacts air quality ... Before, During, After. 

Record-Keeping/Maintain a Burn/

Smoke Journal.

Retain information about the weather, burn and smoke. If air quality problems occur, documentation helps analyze and address air regulatory 

issues.

Before, During, After. 

Communication—Public Notification Notify neighbors and those potentially impacted by smoke, especially sensitive receptors.Before, During. 

Consider Emission Reduction Techniques.Reducing emissions through mechanisms such as reducing fuel loading 

can reduce downwind impacts.

Before, During, After. 

Share the Airshed—Coordination of 

Area Burning.

Coordinate multiple burns in the area to manage exposure of the public to 

smoke.

Before, During, After. 

aElements of these BSMP could also be practical and beneficial to apply to wildfires for areas likely to experience recurring wildfires. 

(4) Wildfires. The Administrator shall 

exclude data from use in determinations 

of exceedances and violations where a 

State demonstrates to the 

Administrator’s satisfaction that 

emissions from wildfires caused a 

specific air pollution concentration in 

excess of one or more national ambient 

air quality standard at a particular air 

quality monitoring location and 

otherwise satisfies the requirements of 

this section. Provided the Administrator 

determines that there is no compelling 

evidence to the contrary in the record, 

the Administrator will determine every 

wildfire occurring predominantly on 

wildland to have met the requirements 

identified in paragraph (c)(3)(iv)(D) of 

this section regarding the not reasonably 

controllable or preventable criterion. 

(5) High wind dust events. (i) The 

Administrator shall exclude data from 

use in determinations of exceedances 

and violations, where a State 

demonstrates to the Administrator’s 

satisfaction that emissions from a high 

wind dust event caused a specific air 

pollution concentration in excess of one 

or more national ambient air quality 

standards at a particular air quality 

monitoring location and otherwise 

satisfies the requirements of this section 

provided that such emissions are from 

high wind dust events. 

(ii) The Administrator will consider 

high wind dust events to be natural 

events in cases where windblown dust 

is entirely from undisturbed natural 

lands or where all anthropogenic 

sources are reasonably controlled as 

determined in accordance with 

paragraph (b)(7) of this section. 

(iii) The Administrator will accept a 

high wind threshold of a sustained wind 

of 25 mph for areas in the States of 

Arizona, California, Colorado, Kansas, 

Nebraska, Nevada, New Mexico, North 

Dakota, Oklahoma, South Dakota, Texas, 

Utah, and Wyoming provided this value 

is not contradicted by evidence in the 

record at the time the State submits a 

demonstration. 

(iv) In addressing the requirements set 

forth in paragraph (c)(3)(iv)(D) of this 

section regarding the not reasonably 

preventable criterion, the State shall not 

be required to provide a case-specific 

justification for a high wind dust event. 

(v) With respect to the not reasonably 

controllable criterion of paragraph 

(c)(3)(iv)(D) of this section, dust controls 

on an anthropogenic source shall be 

considered reasonable in any case in 

which the controls render the 

anthropogenic source as resistant to 

high winds as a natural undisturbed 

land area. The Administrator may 

determine lesser controls reasonable on 

a case-by-case basis. 

(vi) For remote, large-scale, highenergy and/or sudden high wind dust 

events, such as ‘‘haboobs’’ in the 

southwest, the Administrator will 

generally consider a demonstration 

documenting the nature and extent of 

the event to be sufficient with respect to 

the not reasonable controllable criterion 

of paragraph (c)(3)(iv)(D) of this section. 

(6) Determinations with respect to 

event aggregation and multiple national 

ambient air quality standards for the 

same pollutant. (i) Where a State 

demonstrates to the Administrator’s 

satisfaction that for national ambient air 

quality standards with averaging or 

cumulative periods longer than 24- 

hours the aggregate effect of events 

occurring on different days has caused 

an exceedance or violation, the 

Administrator shall determine such 

collective data to satisfy the 

requirements in paragraph (c)(3)(iv)(B) 

of this section regarding the clear causal 

relationship criterion and otherwise 

satisfies the requirements of this 

section. 

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(ii) The Administrator shall accept as 

part of a demonstration for the clear 

causal relationship in paragraph 

(c)(3)(iv)(B) of this section, a State’s 

comparison of a 24-hour concentration 

of any national ambient air quality 

standard pollutant to the level of a 

national ambient air quality standard for 

the same pollutant with a longer 

averaging period. 

(7) Determinations with respect to the 

not reasonably controllable or 

preventable criterion. (i) The 

Administrator shall determine that an 

event is not reasonably preventable if 

the State shows that reasonable 

measures to prevent the event were 

applied at the time of the event. 

(ii) The Administrator shall determine 

that an event is not reasonably 

controllable if the State shows that 

reasonable measures to control the 

impact of the event on air quality were 

applied at the time of the event. 

(iii) The Administrator shall assess 

the reasonableness of available controls 

for anthropogenic sources based on 

information available as of the date of 

the event. 

(iv) Except where a State is obligated 

to revise its state implementation plan, 

the Administrator shall consider 

enforceable control measures 

implemented in accordance with a state 

implementation plan, approved by the 

EPA within 5 years of the date of a 

demonstration submittal, that address 

the event-related pollutant and all 

sources necessary to fulfill the 

requirements of the Clean Air Act for 

the state implementation plan to be 

reasonable controls with respect to all 

anthropogenic sources that have or may 

have contributed to event-related 

emissions. 

(v) The Administrator shall not 

require a State to provide case-specific 

justification to support the not 

reasonably controllable or preventable 

criterion for emissions-generating 

activity that occurs outside of the State’s 

jurisdictional boundaries within which 

the concentration at issue was 

monitored. In the case of a tribe with 

treatment as a state status with respect 

to exceptional events requirements, the 

tribe’s jurisdictional boundaries for 

purposes of requiring or directly 

implementing emission controls apply. 

In the case of a federal land manager or 

other federal agency submitting a 

demonstration under the requirements 

of this section, the jurisdictional 

boundaries that apply are those of the 

State or the tribe depending on which 

has jurisdiction over the area where the 

event has occurred. 

(c) Schedules and procedures—(1) 

Public notification. (i) All States and, 

where applicable, their political 

subdivisions must notify the public 

promptly whenever an event occurs or 

is reasonably anticipated to occur which 

may result in the exceedance of an 

applicable air quality standard. 

(ii) [Reserved] 

(2) Initial notification of potential 

exceptional event. (i) A State shall 

notify the Administrator of its intent to 

request exclusion of one or more 

measured exceedances of an applicable 

national ambient air quality standard as 

being due to an exceptional event by 

creating an initial event description and 

flagging the associated data that have 

been submitted to the AQS database and 

by engaging in the Initial Notification of 

Potential Exceptional Event process as 

follows: 

(A) The State and the appropriate EPA 

regional office shall engage in regular 

communications to identify those data 

that have been potentially influenced by 

an exceptional event, to determine 

whether the identified data may affect a 

regulatory determination and to discuss 

whether the State should develop and 

submit an exceptional events 

demonstration according to the 

requirements in this section; 

(B) For data that may affect an 

anticipated regulatory determination or 

where circumstances otherwise compel 

the Administrator to prioritize the 

resulting demonstration, the 

Administrator shall respond to a State’s 

Initial Notification of Potential 

Exceptional Event with a due date for 

demonstration submittal that considers 

the nature of the event and the 

anticipated timing of the associated 

regulatory decision; 

(C) The Administrator may waive the 

Initial Notification of Potential 

Exceptional Event process on a case-bycase basis. 

(ii) The data shall not be excluded 

from determinations with respect to 

exceedances or violations of the 

national ambient air quality standards 

unless and until, following the State’s 

submittal of its demonstration pursuant 

to paragraph (c)(3) of this section and 

the Administrator’s review, the 

Administrator notifies the State of its 

concurrence by placing a concurrence 

flag in the appropriate field for the data 

record in the AQS database. 

(iii) [Reserved] 

(iv) [Reserved] 

(v) [Reserved] 

* * * * * 

(3) Submission of demonstrations. (i) 

Except as allowed under paragraph 

(c)(2)(vi) of this section, a State that has 

flagged data as being due to an 

exceptional event and is requesting 

exclusion of the affected measurement 

data shall, after notice and opportunity 

for public comment, submit a 

demonstration to justify data exclusion 

to the Administrator according to the 

schedule established under paragraph 

(c)(2)(i)(B). 

(ii) [Reserved] 

(iii) [Reserved] 

(iv) The demonstration to justify data 

exclusion must include: 

(A) A narrative conceptual model that 

describes the event(s) causing the 

exceedance or violation and a 

discussion of how emissions from the 

event(s) led to the exceedance or 

violation at the affected monitor(s); 

(B) A demonstration that the event 

affected air quality in such a way that 

there exists a clear causal relationship 

between the specific event and the 

monitored exceedance or violation; 

(C) Analyses identified in Table 3 to 

§ 50.14 comparing the claimed eventinfluenced concentration(s) to 

concentrations at the same monitoring 

site at other times consistent with Table 

3 to § 50.14 to support the requirement 

at paragraph (c)(3)(iv)(B) of this section. 

The Administrator shall not require a 

State to prove a specific percentile point 

in the distribution of data; 

(D) A demonstration that the event 

was both not reasonably controllable 

and not reasonably preventable; and 

(E) A demonstration that the event 

was a human activity that is unlikely to 

recur at a particular location or was a 

natural event. 

(v) With the submission of the 

demonstration containing the elements 

in paragraph (c)(3)(iv) of this section, 

the State must: 

(A) Document that the public 

comment process was followed and that 

the comment period was open for a 

minimum of 30 days, which could be 

concurrent with the Administrator’s 

review of the associated demonstration 

provided the State can meet all 

requirements in this paragraph; 

(B) Submit the public comments it 

received along with its demonstration to 

the Administrator; and 

(C) Address in the submission to the 

Administrator those comments 

disputing or contradicting factual 

evidence provided in the 

demonstration. 

(vi) Where the State has submitted a 

demonstration according to the 

requirements of this section and the 

Administrator has reviewed such 

demonstration and requested additional 

evidence to support one of the elements 

in paragraph (c)(3)(iv) of this section, 

the State shall have 12 months from the 

date of the Administrator’s request to 

submit such evidence. At the 

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conclusion of this time, if the State has 

not submitted the requested additional 

evidence, the Administrator will 

consider the demonstration to be 

inactive and will not pursue additional 

review of the demonstration. After a 12- 

month period of inactivity, if a State 

desires to pursue the inactive 

demonstration, it must reinitiate its 

request to exclude associated data by 

following the process beginning with 

paragraph (c)(2)(i) of this section. 

TABLE 3 TO § 50.14. EVIDENCE AND ANALYSES FOR THE COMPARISON TO HISTORICAL CONCENTRATIONS

Historical concentration evidence Types of analyses/supporting information Required or optional? 

1. Comparison of concentrations on the 

claimed event day with past historical 

data.

Seasonal (appropriate if exceedances occur primarily in one season, but not in others).

• Use all available seasonal data over the previous 5 years (or 

more, if available).

Required seasonal and/or annual analysis (depending on 

which is more appropriate). 

• Discuss the seasonal nature of pollution for the location being 

evaluated.

• Present monthly maximums of the NAAQS relevant metric 

(e.g., maximum daily 8-hour average ozone or 1-hr SO2) vs 

monthly or other averaged daily data as this masks high values.

Annual (appropriate if exceedances are likely throughout the year).

• Use all available data over the previous 5 years (or more, if 

available).

Seasonal and Annual Analyses.

• Provide the data in the form relevant to the standard being considered for data exclusion.

• Label ‘‘high’’ data points as being associated with concurred 

exceptional events, suspected exceptional events, other unusual occurrences, or high pollution days due to normal emissions.

• Describe how emission control strategies have decreased pollutant concentrations over the 5-year window, if applicable.

• Include comparisons omitting known or suspected exceptional 

events points, if applicable.

2. Comparison of concentrations on the 

claimed event day with a narrower set 

of similar days.

• Include neighboring days at the same location (e.g., a time series of two to three weeks) and/or other days with similar meteorological conditions (possibly from other years) at the same or 

nearby locations with similar historical air quality along with a 

discussion of the meteorological conditions during the same 

timeframe. a

Optional analysis. 

• Use this comparison to demonstrate that the event caused 

higher concentrations than would be expected for given meteorological and/or local emissions conditions.

3. Percentile rank of concentration when 

compared to annual data. b

• Provide the percentile rank of the event-day concentration relative to all measurement days over the previous 5 years to ensure statistical robustness and capture non-event variability 

over the appropriate seasons or number of years.c

Required analysis when comparison is made on an annual 

basis (see item #1). 

• Use the daily statistic (e.g., 24-hour average, maximum daily 8- 

hour average, or maximum 1-hour) appropriate for the form of 

the standard being considered for data exclusion.

4. Percentile rank of concentration relative to seasonal data. b• Provide the percentile rank of the event-day concentration relative to all measurement days for the season (or appropriate alternative 3-month period) of the event over the previous 5 

years.

Required analysis when comparison is made on a seasonal 

basis (see item #1). 

• Use the same time horizon as used for the percentile rank calculated relative to annual data, if appropriate.

a If an air agency compares the concentration on the claimed event day with days with similar meteorological conditions from other years, the 

agency should also verify and provide evidence that the area has not experienced significant changes in wind patterns, and that no significant 

sources in the area have had significant changes in their emissions of the pollutant of concern. bThe EPA does not intend to identify a particular historical percentile rank point in the seasonal or annual historical data that plays a critical 

role in the analysis or conclusion regarding the clear causal relationship. cSection 8.4.2.e of appendix W (proposed revisions at 80 FR 45374, July 29, 2015) recommends using 5 years of adequately representative 

meteorology data from the National Weather Service to ensure that worst-case meteorological conditions are represented. Similarly, for exceptional events purposes, the EPA believes that 5 years of ambient air data, whether seasonal or annual, better represent the range of ‘‘normal’’ air 

quality than do shorter periods. 

[FR Doc. 2015–29350 Filed 11–19–15; 8:45 am] 

BILLING CODE 6560–50–P 

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