"Wood, Dana A." 

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Subject Attention Docket ID No. EPA-HQ-OAR-2011-0887

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BP Exceptional Exceptional Events Rule Guidance Guidance 2nd Draft Comments Comments - 09-04-12.pd 09-04-12.pdf

Dear EPA,

BP America (BP) appreciates the opportunity to provide written comments to the U.S. Environmental

Protection Agency (EPA) on the Draft Guidance on the Implementation of the Exceptional Events Rule

(EER) (77 Fed. Reg. 39959, July 6, 2012).

BP’s detailed comments are attached.  Thank you for your consideration of BP America’s comments.  If

you need any further information, you can contact me, Dana Wood, at dana.wood@bp.com or

281‐366‐3489.

Sincerely,

Dana Wood

Dana Wood, P.E.

Senior Environmental Technical Advisor

BP America Production Company

501 Westlake Park Blvd.

Houston, TX 77079-3092

Phone: (281) 366-3489

Cell Phone: (713) 679-1815

Fax: (281) 366-7105

Email: dana.wood@bp.com
Karen St John

Senior Director

Regulatory Affairs

September 4, 2012

Attention Docket ID No. EPA–HQ–OAR–2011–0887

U.S. Environmental Protection Agency

Mail Code: 6102T 

1200 Pennsylvania Ave. NW

Washington, DC 20460.

Subject: Comments on Draft Guidance to Implement Requirements for the Treatment of Air Quality 

Monitoring Data Influenced by Exceptional Events

Dear Beth W. Palma, 

BP America (BP) appreciates the opportunity to provide written comments to the U.S. Environmental 

Protection Agency (EPA) on the Draft Guidance on the Implementation of the Exceptional Events 

Rule (EER) (77 Fed. Reg. 39959, July 6, 2012). 

BP's comments identify and discuss the following key issues with the EER and draft guidance 

document:

1. Issues with the guidance interpretation and required data to meet the following demonstration 

requirement in 40 CFR 50.14(c)(3)(iv)(D): ‚There would have been no exceedance or violations 

but for the event”.

2. Additional requirements that guidance is adding that are not included in the EER or the Clean Air 

Act (CAA).

3. The need for getting the wildfire guidance out before the finalization of the revisions to the PM2.5

NAAQS on December 14, 2012.

4. Clearer presentation and definition of the information required for demonstration of each of the 6 

‚tests‛ that air agencies must address when requesting that EPA exclude event-related 

concentrations from regulatory determinations.

5. The need for a more streamlined process for submittal and approval of exceptional events 

demonstration packages.

6. EPA should post demonstrations that were not approved as well as those approved. 

7. The need for additional tools and protocols for identification of exceptional events.

8. Changes that are needed to the EER.

BP’s detailed comments follow this cover letter. Thank you for your consideration of BP America’s 

comments. If you need any further information, you can contact Dana Wood at dana.wood@bp.com

or 281-366-3489.

Sincerely,

Karen St. John

Sr. Director, Regulatory Affairs

BP America, Inc.

202-457-6594 (W)

202-351-1399 (cell)
Comments on the Draft Guidance to 

Implement Requirements for the 

Treatment of Air Quality Monitoring 

Data Influenced by Exceptional Events

Docket ID No. EPA-HQ-OAR-2011-0887

September 4, 2012

Prepared for:

BP America

Prepared by:

Dana Wood, PE

BP
Table of Contents

1. Introduction .....................................................................................................................................1

2. ‚But For‛ Test.................................................................................................................................2

3. Additional Requirements Not Included in the EER or CAA.............................................................7

4. Wildfire Guidance Needed Quickly .................................................................................................9

5. Demonstration Required for Various Types of Events..................................................................10

6. Approval Process for Exceptional Events .....................................................................................12

7. Posting Approved and Disapproved Packages..............................................................................14

8. Recommended Exceptional Events Tools ....................................................................................14

9. Recommended Rule Changes ......................................................................................................15

10. References ....................................................................................................................................17
1

1. INTRODUCTION

On July 6, 2012, EPA published the 2nd draft of guidance to clarify key provisions to the 2007 

Exceptional Events Rule (EER) promulgated under 40 CFR 50.1, 50.14, and 51.930 on May 22, 2007. 

These regulations contain requirements for state demonstrations and criteria for EPA approval for the 

exclusion of air quality data from regulatory decisions. The EPA requires that the following 6 

elements must be addressed by the states when requesting that EPA exclude event-related 

concentrations from regulatory determinations.

1. The event affected air quality (40 CFR 50.1(j))

2. The event was not reasonably controllable or preventable (40 CFR 50.1(j))

3. The event was caused by human activity that is unlikely to recur at a particular location, or 

was a natural event (40 CFR 50.1(j))

4. There exists a clear causal relationship between the specific event and the monitored 

concentration (40 CFR 50.14(c)(3)(iv)(B))

5. The event is associated with a measured concentration in excess of normal historical 

fluctuations including background. (40 CFR 50.14(c)(3)(iv)(C))

6. There would have been no exceedance or violation but for the event. (40 CFR 

50.14(c)(3)(iv)(D))

From the standpoint of the determining compliance with the National Ambient Air Quality Standards 

(NAAQS), the EER is extremely important because it defines the requirements for monitored 

exceedances of the standard to be excluded from non-attainment designations that are caused by 

events that are outside the control of the states and tribes including:

 Chemical spills and industrial accidents

 Structural fires

 Transported pollution

 Terrorist attacks

 Natural events including:

 Natural disasters

 Volcanic and seismic activities

 High wind events

 Wildfires and wild land fires

 Stratospheric ozone intrusions

As the NAAQS are established at concentration levels close to or below background concentrations, 

the EER rule will become more important because the number exceedances of the NAAQS will 

increase as a result of ‚exceptional events.‛ However, the requirements of the EER and this draft 

guidance pose technical and procedural problems for states, tribes, local agencies, and EPA to 

exclude exceptional events from the non-attainment designation process. 

EPA has made considerable improvement from the 1st draft by noting that natural events do not have 

to be infrequent, adding a formal dispute resolution process, and adding further examples.

These comments identify and discuss the following key issues with the EER and draft guidance 

document:

1. Issues with the guidance interpretation and required data to meet the following demonstration 

requirement in 40 CFR 50.14(c)(3)(iv)(D): ‚There would have been no exceedance or violations 

but for the event”.

2. Additional requirements that guidance is adding that are not included in the EER or the Clean Air 

Act (CAA).
2

3. The need for getting the wildfire guidance out before the finalization of the revisions to the PM2.5

NAAQS on December 14, 2012.

4. Clearer presentation and definition of the information required for demonstration of each of the 6 

‚tests‛ that air agencies must address when requesting that EPA exclude event-related 

concentrations from regulatory determinations.

5. The need for a more streamlined process for submittal and approval of exceptional events 

demonstration packages.

6. EPA should post demonstrations that were not approved as well as those approved. 

7. The need for additional tools and protocols for identification of exceptional events.

8. Changes that are needed to the EER.

Based on these issues we recommend that EPA revise the current EER to address these issues, 

improve this guidance, and develop readily accessible and efficient tools and protocols for 

identification and exclusion of exceptional events. 

2. “BUT FOR” TEST

The most concerning requirement for exclusion as an exceptional event is the requirement that 

‚There would have been no exceedance or violation but for the event.‛ Most air pollutant 

exceedance events, especially ozone, are not a result of a single source. Ozone events can include

contributions from US anthropogenic emissions (both local and regional), natural sources of both 

ozone and precursors, and international transport of both ozone and ozone precursors. Determining 

whether or not an exceedance would have occurred ‚but for‛ an exceptional event is extremely 

difficult if not impossible, particularly with the high standard that EPA is setting in this guidance for 

demonstration, with no tools or protocols for doing such a demonstration, and the limited time 

provided to for submittal of the exceptional events package. 

The March 22, 2007 Preamble to the EER states that ‚EPA recognized, in recently acting to retain 

PM10 as a measure of coarse particulate, that in some instances exceedances of this NAAQS ‘‘may 

be caused in whole or in part, by exceptional events, including natural events such as windstorms * * 

*. (and that) an exceedance may be treated as an exceptional event even though anthropogenic 

sources such as agricultural and mining emissions contribute to the exceedance.’’ (71 FR 

61216; October 17, 2006).‛ The examples of relevant evidence EPA provides for ‚demonstration that 

ozone exceedances would not have occurred but for the effect of a wildfire‛, are quite concerning, 

particularly the following for the reasons discussed below. The required data for “but for the 

effect of a wildfire” is excessive and difficult to acquire. EPA should not require so much 

information for “but for the effect of a wildfire” test.

“Evidence that there were no known unusual emission releases from non-fire sources at the 

time of the fire event, such as from traffic due to a sports or entertainment event or source 

non-compliance.” (See ‚Draft Exceptional Events Rule Frequently Asked Questions‛, 

Attachment 2 (‚Attachment 1‛, page 9.)

There are an infinite number of other possible sources that could contribute to ozone 

formation that the states would have to review and consider. 

“Evidence that the plume from the fire passed over the location of the monitoring site, and 

mixed down to ground level. This can include satellite images, wind data including HYSPLIT 

trajectories, visual smoke observations, and chemical analysis of PM filters showing 

elements and compounds that are markers for biomass burning.” (See Attachment 1, page 

9.)
3

Demonstrating that a fire plume has passed over a monitor is extremely difficult. All the 

methods that EPA suggested for demonstrating that a fire plume passed a monitor are 

insufficient as discussed below. This should not be an example of demonstration of an 

ozone exceedance due to a fire.

Satellites monitoring smoke plumes typically pass over a site a maximum of one time during 

daylight hours and they do not necessarily pass over all sites daily. This means that a 

satellite image will only provide a short duration snapshot of the smoke plume, but the plume 

can affect large regions as a result of changes in wind direction that will not be captured by 

the satellite. Furthermore, satellites cannot see smoke through cloud cover, so if there is any 

cloud cover, the satellite will not see the smoke plume. Also, satellites have a difficult time 

seeing smoke over snow covered or other highly reflective surfaces

The use of a model such as HYSPLIT will not show that the plume from a fire has mixed 

down to ground level to be detected by the monitor. Further, because of the large grid size 

used in HYSPLIT, it will be difficult for this model to accurately simulate 3 dimensional flow in 

complex terrain.

Visual identification of smoke requires large diameter particulate matter. In addition, the 

residence time of the particulates in smoke is much shorter than the lifetime of ozone 

precursors; therefore, particulates may be removed from the plume before the ozone 

precursors. CO is a much better tracer for fires than PM because it has a longer residence 

time (2 months). However, if CO is used as a tracer the monitoring equipment must have 

sufficient sensitivity to identify the fire plume. A standard FRM CO monitor will not work for 

this purpose

PM data is not collected at most of the locations where ozone data is collected. 

Furthermore, PM filters have specific 24 hour averaging times which may ‚smooth out: peak 

PM impacts of the fire if the fire only impacted the monitor for an hour or so. Furthermore, 

some of the monitors only take measurements every 3 days.

“Altered pollutant amounts, ratios, or patterns that indicate the affect of the event rather than 

non-event sources. This information could include the level, timing and patterns of CO and 

PM; PM size distribution or composition; indicators of precursor composition and “age”, 

such as oxygenated VOCs, radicals, sulfates, and timing and pattern of NO2 and NO; and 

pollutant ratios, such as CO/NOx, CO/PM10, Elemental Carbon (EC)/Organic Carbon (OC), 

O3/NOy and O3/CO.” (See Attachment 1, page 9.)

As discussed above, most ozone monitors are not co-located with monitors for CO or PM 

which will make this demonstration impossible. Furthermore, the residence time of the 

particulates in smoke is much shorter than the lifetime of ozone precursors; therefore, 

particulates will be removed from the plume before the ozone precursors. Also, rain will 

remove the particulates and still leave precursors which produce ozone. CO is a much better 

tracer for fires than PM because it has a longer residence time (2 months). EPA should 

consider installing CO monitors, with the appropriately low detection capabilities, along with 

ozone monitors to assist in the identification of exceptional events. 

“A prediction that the “normal” ozone concentration would have been below the level of the 

NAAQS. “Normal” ozone concentrations can be predicted using statistical methods based on 

previous-day ozone and same-day weather variables (like methods used for air quality 

advisories in some areas) or using air quality models. If either type of prediction is included in 

a demonstration, EPA will likely give it consideration only if the demonstration package also 
4

includes information on the uncertainty of the prediction methods, i.e., information on its past 

success in predicting normal ozone levels. The demonstration should also explain the 

predictive method in terms that are understandable enough to allow informed public 

comment.” (See Attachment 1, page 9.)

And

“A prediction based on air quality/photochemical modeling of the incremental ozone 

concentration due to the emissions from the fire, from comparing modeling results with and 

without the emissions from the fire. A demonstration that includes such evidence should 

address the uncertainties in the emission estimates for the fire including the speciation of the 

VOC and NOx emissions, and the uncertainties due to other aspects of the modeling 

platform such as grid cell size, etc.” (See Attachment 1, pages 9 and 10.)

Developing an air quality model to determine if the ozone concentration would have been 

below the level of the NAAQs ‚but for‛ the event takes a great deal of time, money, and 

resources. Models for such an evaluation will need area and time specific (paired in time and 

space) meteorological data, emissions data, and fire data. Furthermore, the models have to 

be calibrated to actual monitoring data. The effort for just developing and gathering the 

needed information for such a model could take over a year to do. The EPA needs to 

consider that the states are very limited in both the staff and funding for doing each 

exceptional event demonstration. Furthermore, they are limited in the amount of time they 

have to develop a demonstration for consideration to ‚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‛.

Figures 1 and 2, taken from the Four Corners Air Quality Task Force Modeling Analysis

(Stoeckenius, 2009 and 2010), show modeled contributions from various sources to ozone 

concentrations at two locations, Navajo Lake and Mesa Verde, prepared using ozone source

apportionment technology (OSAT). In OSAT, precursor emissions are stratified by source 

category and by source region; tracers are used to tag emissions from each category-region 

pair and track transport, chemical evolution, and removal. NOX and VOC tracers are run to 

apportion total ozone throughout the grid to NOX and VOC precursor source categories and 

regions. Figures 1 and 2 indicate that during the spring in the intermountain West, boundary 

conditions dominate predicted (and presumably measured) ozone concentrations with very 

little enhancement from US anthropogenic sources. Also, during the summer, as shown in 

Figures 1 and 2, boundary conditions still dominate predicted concentrations. The boundary 

conditions for these simulations represent monthly average concentrations at the edge of the 

12 km modeling domain shown in Figure 3, which is essentially international transport. 

Figures 1 and 2 show that no one source contributes solely to each ozone event. There are 

cases where there are spikes with higher contributions from a particular source than seen 

historically such as the spikes from fires and biogenic sources shown in Figure 2; however, 

they are still dominated by boundary conditions and have contributions from other sources as 

well. Please note that this modeling exercise took approximately 2 years to perform and cost 

approximately $200,000 to $300,000. It could not be done for determining exceptional 

events as suggested in the answer to Question 6 in the 12 month timeframe provided for the 

states to do such analysis.
5

Figure 1: Source Apportionment Results for 8-Hour Average Ozone at Mesa Verde and Navajo Lake 

in April (Stoeckenius, 2010)

2018 OSAT Navajo Lake ozone contributions April

0

10

20

30

40

50

60

70

80

4/01 4/02 4/03 4/04 4/05 4/06 4/07 4/08 4/09 4/10 4/11 4/12 4/13 4/14 4/15 4/16 4/17 4/18 4/19 4/20 4/21 4/22 4/23 4/24 4/25 4/26 4/27 4/28 4/29 4/30 Date 1-hour Ozone (ppb)

fires nonEGUs 12km anthro

12km bio

4km bio

other area mobile EGUs O+G

BCs

ICs

2018 OSAT Mesa Verde ozone contributions April

0

10

20

30

40

50

60

70

80

4/01 4/02 4/03 4/04 4/05 4/06 4/07 4/08 4/09 4/10 4/11 4/12 4/13 4/14 4/15 4/16 4/17 4/18 4/19 4/20 4/21 4/22 4/23 4/24 4/25 4/26 4/27 4/28 4/29 4/30 Date 1-hour Ozone (ppb)

fires nonEGUs 12km anthro

12km bio

4km bio

other area mobile EGUs O+G

BCs

ICs

Oil and 

Gas

12 km US 

Anthropogenic

Boundary Conditions -

International 

Transport

12 km US 

Anthropogenic

Boundary Conditions -

International 

Transport

AT Navajo Lake ozone contributions

July

15 7/16 7/17 7/18 7/19 7/20 7/21 7/22 7/23 7/24 7/25 7/26 7/27 7/28 7/29 7/30 7/31

Date

fires

nonEGUs

12km anthro

12km bio

4km bio

other area

mobile

EGUs

O+G

BCs

ICs
6

Figure 2: Source Apportionment Results for 8-Hour Average Ozone at Mesa Verde and Navajo Lake 

in July (Stoeckenius, 2010)

2018 OSAT Navajo Lake ozone contributions

July

0

10

20

30

40

50

60

70

80

90

100

7/01 7/02 7/03 7/04 7/05 7/06 7/07 7/08 7/09 7/10 7/11 7/12 7/13 7/14 7/15 7/16 7/17 7/18 7/19 7/20 7/21 7/22 7/23 7/24 7/25 7/26 7/27 7/28 7/29 7/30 7/31 Date Ozone (ppb)

fires

nonEGUs

12km anthro

12km bio

4km bio

other area mobile EGUs O+G

BCs

ICs

2018 OSAT Mesa Verde ozone contributions

July

0

10

20

30

40

50

60

70

80

90

100

7/01 7/02 7/03 7/04 7/05 7/06 7/07 7/08 7/09 7/10 7/11 7/12 7/13 7/14 7/15 7/16 7/17 7/18 7/19 7/20 7/21 7/22 7/23 7/24 7/25 7/26 7/27 7/28 7/29 7/30 7/31 Date 1-hour Ozone (ppb)

fires

nonEGUs

12km anthro

12km bio

4km bio

other area mobile EGUs O+G

BCs

ICs

Oil and Gas

Electric 

Generating Units Fire

4 km Biogenic

T Navajo Lake ozone contributions

July

7/16 7/17 7/18 7/19 7/20 7/21 7/22 7/23 7/24 7/25 7/26 7/27 7/28 7/29 7/30 7/31

Date

fires

nonEGUs

12km anthro

12km bio

4km bio

other area

mobile

EGUs

O+G

BCs

ICs

Boundary Conditions -

International 

Transport

12 km US 

Anthropogenic

Boundary Conditions -

International 

Transport
7

Figure 3: Four Corners Interagency Air Quality Task Force Modeling Domain (Stoeckenius, 2009)

3. ADDITIONAL REQUIREMENTS NOT INCLUDED IN THE EER OR 

CAA

Although EPA states that their intention is to ‚help air agencies comply with the Exceptional Events 

Rule by clarifying the rule requirements‛1there are some instances in the guidance document where 

the required demonstrations appear to go beyond the EER and the CAA. The requirements posed in 

the guidance are in essence regulation since if they are not followed the exceptional events package 

will not be approved. Requirements in the guidance package discussed below need further 

justification for why they are necessary based on the EER or should be removed from the guidance 

since they attempt to regulate through guidance. 

At the bottom of page 3 of the ‚Draft Guidance to Implement Requirements for the Treatment of Air 

Quality Monitoring Data Influenced by Exceptional Events‛ under the Treatment of Technical Criteria 

for Exclusion of Data Affected by Events EPA states:

‚Note that if an event is natural, then the second element is not considered in a 

demonstration review. In the case of an event that is initiated by a natural process, such as a 

volcano or high wind dust event, the event would be considered a natural event if sources 

are entirely natural or contributing anthropogenic sources are reasonably controlled10. 

This concept is explained in more detail in Attachment 2, the draft High Winds Guidance 

document.” 

“10 Human activity would be considered to have played little or no direct causal role in 

causing the entrainment of the dust by high wind if contributing anthropogenic 

sources of dust are reasonably controlled, and thus the event would be considered a 

natural event. If anthropogenic sources contributed significantly to a measured 

 

1 U.S. Environmental Protection Agency, ‚Responses to Significant First-Round Comments on the 

Draft Guidance Documents on the Implementation of the Exceptional Events Rule‛, 6.1.1, June 

2012.
8

concentration (or if emissions from anthropogenic sources alone would have resulted 

in an exceedance or violation of the NAAQS) and these same emissions from 

anthropogenic sources are affected by an event and are reasonably controllable but 

did not have those reasonable controls applied at the time of the event, then the 

event would not be considered a natural event..‛

An exceptional event is defined in 40 CFR 50.1(j) as ‚an event that affects air quality, is not 

reasonably controllable or preventable, is an event caused by human activity that is unlikely to 

recur at a particular location or a natural event, and is determined by the Administrator in accordance 

with 40 CFR 50.14 to be an exceptional event. It does not include stagnation of air masses or 

meteorological inversions, a meteorological event involving high temperatures or lack of precipitation, 

or air pollution relating to source noncompliance.‛ Furthermore, demonstration of an exceptional 

event under 40 CFR 50.14 (c)(3)(iv) states:

‚The demonstration to justify data exclusion shall provide evidence that: 

(A) The event satisfies the criteria set forth in 40 CFR 50.1(j); 

(B) There is a clear causal relationship between the measurement under consideration and 

the event that is claimed to have affected the air quality in the area; 

(C) The event is associated with a measured concentration in excess of normal historical 

fluctuations, including background; and 

(D) There would have been no exceedance or violation but for the event.

Nowhere in the Exceptional Events Rule does it state that anthropogenic contributions must 

be reasonably controlled or preventable, it only states that the event “not be reasonably 

controllable or preventable” and that “there would have been no excedance or violation but 

for the event”. ‛ EPA defines natural event as ‚an event in which human activity plays little or no 

direct causal role. (40 CFR 50.1 (k))‛ The rule does not define event nor state that the exceptional 

event be the only cause of the exceedance. This seems to be an extreme interpretation that every 

contributor be reasonably controlled, particularly if without the ‚event‛ there would not have been an 

exceedance. Emissions levels are never zero for any pollutant. There are always multiple 

contributors from international and interstate transport, biogenic sources, anthropogenic sources 

locally, mobile, etc. However, if the typical level of emissions does not violate the standard and 

adding the event causes and exceedance it should be allowed to be an exceptional event per the 

regulation, regardless of the other sources. As stated before, the March 22, 2007 Preamble to the 

EER even stated that ‚EPA recognized, in recently acting to retain PM10 as a measure of coarse 

particulate, that in some instances exceedances of this NAAQS ‘‘may be caused in whole or in part, 

by exceptional events, including natural events such as windstorms * * *. (and that) an exceedance 

may be treated as an exceptional event even though anthropogenic sources such as 

agricultural and mining emissions contribute to the exceedance.’’ (71 FR 61216; October 17, 

2006).‛

Specifically, EPA through its draft guidance interprets the term ‚natural event‛ as defined in 40 CFR 

50.1(k) in a manner that could not have been contemplated by the public during the 2007 rulemaking. 

EPA guidance rewrites the definition of ‚natural event‛ to read ‚an event in which human activity 

plays little or no direct role and emissions from anthropogenic sources that contribute to the event 

are reasonably controlled‛. EPA must revise its regulations through proper rulemaking before it can 

lawfully require states to use such an interpretation of the term ‚natural event‚ when documenting 

exceptional events. Otherwise it would violate the Administrative Procedures Act.

On page 23 of Attachment 1, Draft Exceptional Events Rule Frequently Asked Questions, EPA states 

that:

‚Although the language at 40 CFR §51.930 does not require the preparation or submittal of a 

mitigation plan, it does require that the air agency develop and implement processes and 
9

measures that could easily become the elements of a formal, written plan. The mitigation 

criteria focus on specific measures and actions to protect public health, rather than on 

measures that control or prevent emissions associated with a specific event. So, a mitigation 

plan may include measures that apply to emissions sources in general (e.g., dust suppression 

or covering techniques for mineral processing) rather than those measures or controls that 

might be discussed in the “not reasonably controllable or preventable” portion of an event 

demonstration (e.g., controls/measures X, Y, and Z were in place on sources A, B, and C 

during the time of the event). A mitigation plan may also include procedures and 

responsibilities for public alerts and sheltering advisories. Because having a mitigation plan in 

place will help air agencies meet the EER requirements at 40 CFR §50.14(c)(1)(i) related to 

public notification more systematically, the EPA encourages the development and submittal 

of a mitigation plan with the demonstration package if one has not already been adopted.‛

Since a mitigation plan is not required under 40 CFR 51.930, EPA should remove this 

recommendation from the guidance. This is adding un-necessary work to the states. This will 

duplicate the regulations and efforts that the states make through rule making and the SIP process 

for particulate matter. Furthermore, a mitigation plan would be quite difficult to make for the entire 

state since mitigation would be very area specific. 

4. WILDFIRE GUIDANCE NEEDED QUICKLY

In the PM2.5 NAAQS Proposal published June 29, 2012, EPA is only giving states less than one year 

from the publication of the final rule to provide documentation for 2010-2012 of Exceptional Events. 

Several wild fires have occurred between 2010 and2012 according to NOAA’s National Climatic Data 

Center State of Climate Wildfires data (http://www.ncdc.noaa.gov/sotc/fire/) as shown in Table 1 due 

to the reduction in controlled burns which have allowed for forest to become full of brush. Figure 4

shows that the maximum number of wildfires and acres burned in the past 10 year occurred in 2006 

when the number of wildfires reached 96,326 and 9,871,863 acres. This is a significant amount of 

wildfires and areas that would need to analyze PM2.5 monitoring data to determine if the annual 

exceedance was due to wildfires. 

The wildfire guidance document is needed by December 14, 2012 when the PM2.5 NAAQS will 

be finalized in order to give states adequate time to create an exceptional events package for 

the revised annual PM2.5 NAAQS. The entire years’ worth of data would have to be reviewed on a 

per hour basis to see if removing it would impact the annual average according to Table Q30-2. Each 

hour measured could have an impact on the annual average. With the wildfire guidance, EPA should 

post additional links to tools for identifying locations of wildfires such as NOAA’s National Climatic 

Data Center’s State of Climate Wildfires data, the USDA Forest Service Active Fire Maps 

(http://activefiremaps.fs.fed.us/), the Department of the Interior Federal Fire Occurrence Website 

(http://wildfire.cr.usgs.gov/firehistory/data.html), and others. 

Table 1. Number of Wildfires and Acres Burned Per Year 2010-2012 YTD (NOAA) 

Year Number of Wildfires Acres Burned

2010 71,839 3,422,823

2011 73,484 8,706,852

2012 YTD 37,576 4,088,349
10

Figure 4. US Wildfire Activity (NOAA)

5. DEMONSTRATION REQUIRED FOR VARIOUS TYPES OF EVENTS

Item 1 of EPA’s Attachment 3, Request for Comment on the Draft Guidance Documents on the 

Implementation of the Exceptional Events Rule, EPA asked for ‚comment regarding other specific, 

broadly applicable, streamlining mechanisms that the EPA could incorporate into the exceptional 

event implementation process.‛ Recommending specific types of information that EPA may want to 

see for various types of events for demonstration of meeting each of the tests would be helpful 

along with examples of the demonstration as was included in Section 3 of the ‚Draft Guidance on 

Preparation of Demonstrations in Support of Requests to Exclude Ambient Air Quality Data Affected 

by High Winds under the Exceptional Events Rule‛. The following types of events would be good to 

include:

 Wildfires

 Stratospheric-tropospheric exchange 

 International Transport

 Lightning

EPA should place this information in the main document as opposed to the question and answer 

attachment or in separate attachments. EPA could have a table or something that shows the 

elements and types of supporting information with further explanation following the table such as 

shown below on Table 2.
11

Table 2. Example of Demonstration Requirements Table

40 CFR Part 50 

Element High Winds Wildfires

StratosphericTropospheric 

Exchange

International 

Transport Lightning

Affects Air Quality Demonstrated using the 

historical fluctuations data 

and clear and causal 

relationship data below.

Demonstrated 

using the 

historical 

fluctuations 

data and clear 

and causal 

relationship 

data below.

Demonstrated 

using the 

historical 

fluctuations 

data and clear 

and causal 

relationship 

data below.

Demonstrated 

using the 

historical 

fluctuations 

data and clear 

and causal 

relationship 

data below.

Demonstrated 

using the 

historical 

fluctuations 

data and clear 

and causal 

relationship 

data below.

Not Reasonably 

controllable or 

preventable

Control analysis of the 

anthropogenic sources, 

control analysis of the 

natural sources, 

reasonableness of controls, 

explanation emissions 

despite controls, back 

trajectories of source area, 

emissions inventory 

Caused by human 

activity unlikely to 

reoccur at a particular 

location or natural event

High wind is a natural 

event, thus no necessary

Clear causal relationship 

between measurement 

and event

See Table 1 below

No exceedance or 

violation but for the 

event

Data analysis based on 

Table Q30-1 and Q30-2 

Data analysis 

based on Table 

Q30-1 and 

Q30-2 

Data analysis 

based on Table 

Q30-1 and 

Q30-2 

Data analysis 

based on Table 

Q30-1 and 

Q30-2 

Data analysis 

based on Table 

Q30-1 and 

Q30-2 

The event is associated 

with measured 

concentration in excess 

of normal historical 

fluctuations, including 

background

Statistical analysis 

comparison discussed 

below

Statistical 

analysis 

comparison 

discussed 

below

Statistical 

analysis 

comparison 

discussed 

below

Statistical 

analysis 

comparison 

discussed 

below

Statistical 

analysis 

comparison 

discussed 

below

Table 1 – Use Table 4. Example Evidence and Analysis for CCR Demonstration from the ‚Draft Guidance on Preparation of 

Demonstrations in Support of Requests to Exclude Ambient Air Quality Data Affected by High Winds under the Exceptional 

Events Rule‛

Statistical Analysis Comparison:

 Comparison of concentrations on the claimed event day with a narrower set of similar days: Similar days could 

include neighboring days (e.g., a time series of two weeks) and other days with similar meteorological conditions 

(possibly from other years). The objective of such a comparison would be to demonstrate that the event caused 

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

 Percentile of concentration relative to annual data. The percentile of the event-day concentration should be provided 

for the event day relative to all measurement days over the previous 3-5 years. To ensure statistical robustness, the 

EPA expects a minimum of 300 data points to be included in this calculation. The daily statistic should be appropriate 

for the form of the standard being considered for data exclusion (see Question 30).

 Percentile of concentration relative to seasonal data. The percentile of the event-day concentration should be 

provided for the event day relative to all measurement days for the season (or appropriate alternative 3-month 

period) of the event over the previous 3-5 years. It is appropriate to use the same time horizon as used for the 

percentile calculated relative to annual data.

Making a simple list of information that the agencies should include for each type event would 

stream-line the process and reduce requests for additional data from EPA. 
12

6. APPROVAL PROCESS FOR EXCEPTIONAL EVENTS 

As EPA continues to lower the NAAQS the number of exceptional events will continue to increase. 

Each exceedance of the NAAQS will need to be evaluated by the state to ensure the event was not 

caused by an exceptional event. The lower the NAAQS, the more likely an exceptional event caused 

it. For instance, as shown in Figure 5, there were in excess of 600 cumulative days during the spring 

and summer of 2006 at 12 Western CASTNET rural monitoring sites or national parks when 8-hour 

ozone concentrations were above 60 ppb, which is an average of 50 days per monitoring site. In 

addition, EPA will need to analyze and rule on the information compiled and submitted to EPA by the 

states. Figure 5 also indicates that the elevated concentrations occurred almost as frequently in the 

spring as the summer. Researchers are just beginning to understand spring ozone events and many 

of the spring events have been predominantly attributed to both natural and international emission 

sources. At the present time it is not possible to definitely conclude that all of the spring ozone 

events identified in Figure 5 are related to an exceptional event, however, based on analysis of 

surface ozone monitoring data and ozone sonde data there is evidence of a strong correlation 

between high-altitude ozone (3-6 km) measurements and the number of days in excess of 60, 65, or 

70 ppb at Western sites (Figure 6). This strong correlation between elevated ozone concentrations in 

the upper troposphere and rural Western ozone events suggests trans-boundary transport as a 

predominant cause of the high surface events and further suggests that classical local ozone control 

strategies for urban areas will not result in reduction in monitored ozone levels at Western CASTNET 

sites. 

Figure 5. Cumulative number of days in the spring and summer that ozone concentrations were 

above 60, 65 and 70 ppb at 12 CASTNET monitoring sites in the West during 2006.

Events such as stratospheric-tropospheric exchange (STE) (refers to the transport of material across 

the tropopause) could be considered an exceptional event. STE is also known as stratosphere-totroposphere transport (STT) or stratospheric intrusion. STE has direct implications on the distribution 

of atmospheric ozone, in particular, the decrease of lower stratospheric ozone and the increase of 

tropospheric ozone‛ (Cordero et al). Langford et al examined STE along Colorado’s Front Range 

during the spring of 1999 (Langford, 2009) using lidar and surface measurements. ‚A deep 

tropopause fold brought ~215 ppbv of O3 to within 1 km of the highest peaks in the Rocky Mountains 

Average of 50 

days/yr per 

site > 60 ppb!

CASTNET Sites

• Centennial, WY

• Gothic, CO

• Rocky Mountain N.P., 

CO

• Yellowstone N.P., WY

• Pinedale, WY

• Mesa Verde N.P., CO

• Grand Canyon N.P., 

AZ

• Great Basin N.P., NV

• Canyonlands N.P., UT

• Petrified Forest, AZ

• Big Bend N.P., TX 

• Mount Rainier NP, WA
13

on 6 May 1999. One-minute average O3 mixing ratios exceeding 100 ppbv were subsequently 

measured at a surface site in Boulder, and daily maximum 8-hour O3 concentrations greater or equal 

to the 2008 NAAQS O3 standard of 0.075 ppmv were recorded at 3 of 9 Front Range monitoring 

stations.‛ This study shows that the stratospheric contribution to surface ozone is significant and 

can lead to exceedances of the ozone NAAQS for a large area.

Figure 6. Time series plots of ozone sonde free tropospheric ozone (3-6 km) concentration and 

number of exceedance days at a proposed standard between 65 and 75 ppb for spring (top) and 

summer (bottom) for 10 CASTNET sites. Notice the strong correlation between fire NOx emissions 

and exceedance days in summer. Figure from Jaffe (2010). 

With no tools or protocols available for identifying exceptional events, it will take the states a great 

deal of time and work per event to develop an exceptional events package, especially since EPA’s 

guidance is requiring ‚a case-by-case demonstration and evaluation‛ for each event. The current 

regulatory framework for dealing with exceptional events is not sufficient to deal with the anticipated 

very large increase in the number of events that will need to be analyzed as a result of further 

lowering of the NAAQS. Neither the states, tribes, nor EPA has the resources available to continue 
14

with such a case-by-case basis approach. A more streamlined and automated approach must be 

developed to ensure that both the states and EPA can efficiently evaluate exceptional events. 

Furthermore, as noted in the comments by the various states for the first draft of the guidance, EPA 

is behind on reviewing the exceptional events packages. EPA has approved very few exceptional 

events packages. EPA even stated in the First External Review Draft of the Health Risk and 

Exposure Assessment for Ozone (Updated August 2012) that ‚However, concurred exceptional 

events were rare, accounting for less than 0.01% of the total observations. All concurred exceptional 

events in 2006-2010 were related to wildfires in California in 2008. There were no concurrences of 

exceptional event data for stratospheric intrusions in 2006-2010 in the data extracted on June 27, 

2011.‛ 

EPA must develop a more streamlined process for the information to be submitted by the 

states and the approval process. Otherwise, many areas will be nonattainment for the 

NAAQS due to exceptional events and unable to come into compliance. 

7. POSTING APPROVED AND DISAPPROVED PACKAGES

It is helpful to the states that EPA is posting some of the approved package. If approved by the 

states, posting all the approved packages would assist in ensuring consistency across the regions 

and providing examples of the needed information. EPA should also post packages that were not 

approved and why to help states know what is not acceptable.

8. RECOMMENDED EXCEPTIONAL EVENTS TOOLS

More technical tools need to be developed and provided for states, tribes, and location agencies to 

help identify exceptional events. As discussed already, as the NAAQS Standards are lowered, more 

and more exceedances of the NAAQS will require evaluation to determine if exceptional events 

caused the exceedance. Exceedances of the ozone NAAQS may be caused by stratospherictropospheric exchange (STE), lightning, wildfires, or long-range transport of international emissions

and combinations of these uncontrollable sources. Limited tools are available for identifying such 

events as shown on the EPA Exceptional Events Rule webpage and may not work. There are some 

tools that EPA has identified for wildfires, but identification for STE, lightning, and international 

transport or combinations of these things have not been developed or identified.

STE and international transport events are the hardest to identify and the tools are currently not 

available for identification. Global Chemical Transport Models (CTMs) cannot accurately simulate the 

highest ozone events, which are the target of the NAAQS standard. Monitoring data cannot be used 

if multiple trace gas measurements are not simultaneously recorded at each site since it is difficult to 

determine without them the source of the ozone. Satellite remote sensing of trace gases is an 

appealing avenue for application to screening events. Based on currently released NASA, European 

and Japanese products, the most reliable measurements in the troposphere are NO2, CO, and 

HCHO. Monitoring tropospheric ozone from space has proved difficult due to the blanket of ozone in 

the stratosphere, making retrievals highly uncertain. The tropospheric emission spectrometer (TES) 

is specifically designed for measuring ozone in the troposphere, but the signal to noise ratio makes it 

primarily useful for ozone in a monthly mean sense. Comparisons of TES retrievals in the troposphere 

with free tropospheric air at Mt. Bachelor, WA showed no significant correlation between 

observations and TES data (Wigder and Jaffe, 2011). The Ozone Monitoring Instrument (OMI) has 

the advantage of better spatial and temporal coverage, but again, no significant correlation between 

free tropospheric air at Mt. Bachelor and OMI were observed (Wigder and Jaffe, 2011). Additionally, 

all of the United States space-borne ozone monitors are operating beyond their design lifetime, and
15

no immediate replacements are scheduled for launch. Clearly, in the context of the 2013 ozone 

standard, satellite retrievals of ozone will not provide a reliable resource for ozone sources in the 

troposphere. 

According to Murray et. al. 2012 (in press), ‚Nitrogen oxides (NOx≡ NO + NO2) produced by lightning 

make a major contribution to the global production of tropospheric ozone and OH.‛ ‚The resulting 

global lightning NOx source in GEOS-Chem is 6.0 ± 0.5 Tg N a-1, compared to 5.5 ± 0.8 Tg N a-1 for 

the biomass burning source.‛ Fang et. al. 2010 states that ‚Lightning is a major natural source of 

NOx in the free troposphere, but its magnitude is poorly constrained with a best estimate of 5 Tg N 

yr−1 and an uncertainty range of 1–20 Tg N yr−1 [Schumann and Huntrieser, 2007, and references 

therein].‛ Identifying and quantifying emissions from lightning is challenging. EPA states in the Third 

External Review Draft of the Integrated Science Assessment for Ozone and Related Photochemical 

Oxidants on page 3-62 that ‚While progress is being made in obtaining day specific data for lightning 

strikes and area burned in wildfires, the emission factors for precursors from these episodic sources 

such as lightning and wildfires are still uncertain.‛ Specific data can be obtained on locations of 

lightning strikes from sources such as NASA’s U.S. National Lightning Detection Network Database 

(NLDN) (http://gcmd.nasa.gov/records/GCMD_NLDN.html) and other such sources; however, 

estimating the contribution is difficult. Fang et al 2010 states that ‚For example, by simulating 

several midlatitude and subtropical thunderstorms during four field projects, Ott et al. [2007, 2010] 

recommend a mean NOx production of approximately 500 moles per flash for both intracloud and 

cloud‐to‐ground flashes. Ott et al. [2010], Kaynak et al. [2008], and Pickering et al. [2006] suggest 

that a larger percentage of the total lightning NOx source is located in the free troposphere (FT) than 

proposed in an earlier work [Pickering et al., 1998].‛ The concentration increase has not been 

estimated. Further work is needed to help states, tribes and local agencies identify and estimate the 

impact from lightning. 

9. RECOMMENDED RULE CHANGES

As requested by many of the states, BP also requests that the Exceptional Events Rule needs to be 

revised. EPA even stated in their presentation the Exceptional Events Implementation Guidance 

Notice of Availability on July 31, 2012 that implementing the rule is challenging including that:

 ‚EER is relatively young

 Exceptional events are unique and varied

 Difficult to provide guidance that is both concrete and generally applicable

 Difficult to pre-determine how much evidence/technical analysis for demonstrations is 

enough

 Final rule text and preamble left room for interpretation‛ 

The Exceptional Events Rule could be revised to address these issues through a rule proposal and 

comment period. BP recommends that the following changes are needed to the Exceptional Events 

Rule based on the comments on the first draft and the current draft guidance. 

Clarity or revision to the wording is needed for the criteria that ‚There would have been no 

exceedance or violation but for the event‛ to clarify that the event does not have to be the only 

source of the pollutant. As discussed in Section 4, most air pollutant exceedance events, especially 

ozone, are not a result of a single source. EPA is setting in this guidance document an extremely 

high standard for the ‚but for‛ test beyond the intent of the rule as discussed in the March 22, 2007 

Preamble to the EER which states that ‚EPA recognized, in recently acting to retain PM10 as a 

measure of coarse particulate, that in some instances exceedances of this NAAQS ‘‘may be caused 

in whole or in part, by exceptional events, including natural events such as windstorms * * *. (and 

that) an exceedance may be treated as an exceptional event even though anthropogenic 

sources such as agricultural and mining emissions contribute to the exceedance.’’ (71 FR 

61216; October 17, 2006).‛ Perhaps the wording should be changed to state that ‚the exceedance 

was caused in whole or in part because of the exceptional event.‛
16

EPA should revise the Exceptional Events Rule to allow for the exclusion of ozone 

exceedances resulting for Policy Relevant Background or US Background based the answer to 

Question 16a of Attachment 1, Draft Exceptional Events Rule Frequently Asked Questions since EPA 

is claiming background ozone can be addressed in the implementation phase of the standard. The 

response to Question 16a makes it clear that not all background ozone can be excluded as an 

exceptional event. Background ozone is ozone that cannot be controlled by the states, tribes, or local 

agencies. Therefore, it should be excludable under the Exceptional Events Rule from the attainment 

demonstration process. EPA states:

‚16a. Question: Are policy relevant background ozone concentrations and exceptional events 

related?

Answer: Policy relevant background ozone concentrations and exceptional events can include 

partially overlapping concepts. The 2007 Staff Paper defines policy relevant background 

ozone ‚as the distribution of [ozone] concentrations that would be observed in the U.S. in the 

absence of anthropogenic (man-made) emissions of precursor emissions (e.g., VOC, NOx, 

and CO) in the U.S., Canada, and Mexico.‛ An exceptional event is a natural event (excluding 

stagnations, inversions, high temperatures, or precipitation) or an anthropogenic event that is 

unlikely to recur in the same location. Both exceptional events and policy relevant 

background include emissions from natural events like forest wildfires or stratospheric ozone 

intrusions. However, exceedances due to natural emissions that occur every day and 

contribute to policy relevant background, such as biogenic emissions, do not meet the 

definition of an exceptional event and are thus not eligible for exclusion under the EER. 

Routine anthropogenic emissions outside of the U.S. contribute to policy relevant 

background, but are not exceptional events. Air agency preparation of a demonstration 

package and the EPA’s subsequent review of the demonstration package is case-by-case 

based on a weight-of-evidence approach and does not explicitly consider whether the event 

type might contribute to policy relevant background. However, if a natural event that 

contributes to policy relevant background causes an observed concentration that meets the 

statutory definition of an exceptional event and fulfills all of the exceptional event criteria, the 

EPA would consider the event to be an exceptional event.‛ 

The exceptional events regulation specifically precludes the exclusion of ‘routine’ exceedances 

caused by natural sources and ozone transport from international sources. However, the Clean Air 

Act (CAA) does not preclude exclusion of ‘routine’ exceedances. The CAA defines an exceptional 

event under 319 (b) (42 USC § 7619 (b)). 

‚(1) Definition of exceptional event 

In this section: 

(A) In general 

The term ‚exceptional event‛ means an event that—

(i) affects air quality; 

(ii) is not reasonably controllable or preventable; 

(iii) is an event caused by human activity that is unlikely to recur at a particular 

location or a natural event; and 

(iv) is determined by the Administrator through the process established in the 

regulations promulgated under paragraph (2) to be an exceptional event. 

(B) Exclusions 

In this subsection, the term ‚exceptional event‛ does not include—

(i) stagnation of air masses or meteorological inversions; 

(ii) a meteorological event involving high temperatures or lack of precipitation; or 

(iii) air pollution relating to source noncompliance.‛

Therefore, the CAA leaves room for revising the Exceptional Events Rule for allowing routine 

events to be excluded. 
17

Also, Perhaps the rule could include clearer criteria for specific types of events to be declared an 

exceptional event. The types of events the rule might address include wildfires, high winds, 

stratospheric-tropospheric exchange, lightning, etc. Perhaps specific tests versus the generic tests 

could be put in place for various types of events. 

10. REFERENCES

Cordero, Eugene, Newman, Paul A., Weaver, Clark, and Fleming, Eric, Stratospheric Ozone, 

electronic textbook, Chapter 6, Section 5, http://www.ccpo.odu.edu/SEES/ozone/oz_class.htm

Fang, Y; Fiore, AM; Horowitz, LW; Levy II, H; Hu, Y; Russell, AG. (2010). Sensitivity of the NOy 

budget over the United States to anthropogenic and lightning NOx in summer. J Geophys Res 115: 

D18312. http://dx.doi.org/10.1029/2010JD014079

Langford, A. O., K. C. Aikin, C. S. Eubank, and E. J. Williams (2009), Stratospheric contribution to high 

surface ozone in Colorado during springtime, Geophys. Res. Lett., 36, L12801, 

doi:10.1029/2009GL038367.

Murray, L.T., D.J. Jacob, J.A. Logan, R.C. Hudman, and W.J. Koshak, Optimized regional and 

interannual variability of lightning in a global chemical transport model constrained by 

LIS/OTD satellite data, J. Geophys. Res., in press, 2012. [PDF]

Stoeckenius, T.E., C.A. Emery, T.P. Shah, J.R. Johnson, L.K. Parker and A.K. Pollack, 2009 and 2010. 

Air Quality Modeling Study For the Four Corners Region and Addendum. ENVIRON International 

Corp., Revised Report, August 2009 and January 2010. 

(http://www.nmenv.state.nm.us/aqb/4C/Modeling.html)

Widger, N, D.A. Jaffe, M. Lin, A. Fiore, A.M. Macdonald, and S. Gong. Interannual Variation in 

Baseline Ozone on the Western Coast of North America and Its Influence on Urban Air Quality. 

Presented at AGU Fall Meeting, December 9, 2011.