## Guidance on the Preparation of Ex ceptional Events Demonstrations for Wildfire Events that May In fluence Ozone Concentrations

Draft

October 2015

U.S. Environmental Protection Agency Office of Air Quality Planning and Standards Air Quality Policy Division Geographic Strategies Group Research Triangle Park, North Carolina*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

ii 

### Table of Contents

Acronyms ...................................................................................................................... ................. iii

1. Highlights .................................................................................................................... ............ 1
2. Narrative Conceptual Model and Event Summary ................................................................. 7

2.1 Overview and EER Provisions ......................................................................................... 7

2.2 Examples of Supporti ng Documentation ......................................................................... 7

3. Clear Causal Relationship Between the Specifi c Event and the Monitored Concentration ... 9

3.1 Overview and EER Provisions ......................................................................................... 9

3.2 Event-related Concentration in the Cont ext of Historical Concentrations ....................... 9

3.2.1 Examples of Supporting Documentation 10

3.3 Concept of Different Tiers of Excep tional Events Demonstrations ............................... 12

3.4 Key Factor of and Suggested Evidence to Include in Tier 1 Demonstrations ............... 12

3.4.1 Evidence the Event, Monitor(s), and Exceedance Meet the Key Factor for Tier 1
Demonstrations 12

3.4.2 Evidence the Fire’s Emissions Were Transported to the Monitor(s) 13

3.5 Key Factors of and Suggested Evidence to Include in Tier 2 Demonstrations .............. 14

3.5.1 Evidence that the Event, Monitor(s), and Exceedance Meet the Key Factors for
Tier 2 Demonstrations 15

3.5.2 Evidence that the Fire Emissions Affected the Monitor(s) 19

3.5.3 Evidence the Fire’s Emissions were Transported to the Monitor 20

3.5.4 Summary of Evidence that Could be Used to Meet the EER Elements for Tier 1
and Tier 2 Demonstrations 21

3.6 Additional Clear Causal Relationshi p Evidence for Tier 3 Events ................................ 22

3.6.1 Relationship of the Event, Monitor(s), a nd Exceedance to the Key Factors for Tier
2 demonstrations 22

3.6.2 Evidence that the Fire Emissions Affected the Monitor(s) 22

3.6.3 Evidence that the Fire Emissions were Transported to the Monitor 23

3.6.4 Additional Evidence that the Fi re Emissions Caused the O 3 Exceedance 23

3.7 Example Conclusion Statement ..................................................................................... 26

4. Caused by Human Activity that is Un likely to Recur at a Particular .................................. 27
Location or a Natural Event ................................................................................................... ....... 27
4.1 Overview and EER Provisions ....................................................................................... 27

4.2 Examples of Supporti ng Documentation ....................................................................... 27

4.3 Example Conclusion Statement ..................................................................................... 27

5. Not Reasonably Controllable or Preventable .................................................................... 28

5.1 EER Provisions .............................................................................................................. 2 8
5.2 Examples of Supporti ng Documentation ....................................................................... 28

5.3 Example Conclusion Statement ..................................................................................... 28

6. Public Comment................................................................................................................ 29
6.1 EER Provisions .............................................................................................................. 2 9
6.2 Examples of Supporti ng Documentation ....................................................................... 29

6.3 Example Conclusion Statement ..................................................................................... 29 Appendix A1. Example Conceptual Model/Event Summary ....................................................... 30 Appendix A2. Relating Fire Emi ssions and Downwind Impacts ................................................. 34 Appendix A3. Interpreti ng HYSPLIT Results .............................................................................. 50 Appendix A4. References for Guidance Document ..................................................................... 53*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

iii 

### Acronyms

AGL Above ground level
AQS Air Quality System

CAA Clean Air Act
CAMx Comprehensive Air Quality Model with Extensions

CARB California Air Resources Board
CFR Code of Federal Regulations
CM Conceptual model
CMAQ Community multiscale air quality model

CO Carbon monoxide
DDM Direct decoupled method
EER Exceptional Events Rule
EPA Environmental Protection Agency
FINN Fire inventory from the Nationa l Center for Atmospheric Research
FIPS Federal Information Processing Standards
GDAS Global data analysis system
HAURL Human activity unlikely to recur at a particular location
HYSPLIT Hybrid single particle lagra ngian integrated trajectory model

K Potassium

km Kilometers

mb Millibars
MDA8 Maximum daily 8-hour average for ozone
MODIS Moderate Resolution Imaging Spectroradiometer
nRCP not reasonably cont rollable or preventable
NAAQS National Ambient Air Quality Standard or Standards
NAM North American mesoscale forecast system
NCAR National Center for Atmospheric Research
NDAS North American mesoscale data analysis system
NEI National Emission Inventory
NO Nitrogen oxide
NOx Nitrogen oxides

NO 2 Nitrogen dioxide

NWS National Weather Service

O 3 Ozone*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

iv PM Particulate matter

PM 10 Particulate matter with a nominal mean aerodynamic diameter less than or equal
to 10 micrometers

PM 2.5 Particulate matter with a nominal mean aerodynamic diameter less than or equal
to 2.5 micrometers ppb Parts per billion

Q/D 24-hour fire emissions, in tons per day, divided by the distance of the fire to the monitor, in kilometers ROG Reactive organic gases
rVOC Reactive volatile organic compounds
SIP State implementation plan
SMARTFIRE Satellite Mapping Automated Reanalys is Tool for Fire In cident Reconciliation
TOG Total organic gases including meth ane and other reactive volatile organic compounds VOC Volatile organic compounds

WRF-CHEM Weather research and for ecasting model coupled with chemistry*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

1 

### 1. Highlights

Statutory and Regul atory Requirements The Environmental Protection Agency (EPA) pr omulgated the Exceptional Events Rule (EER)
in 2007 1 to address Clean Air Act (CAA) section 319( b), which allows for the exclusion of air quality monitoring data influenced by excepti onal events from use in determinations of
exceedances or violations of the national am bient air quality standards (NAAQS). The CAA includes four requirements that, collec tively, define an exceptional event:

1) The event affected air quality. 2) The event was not reasonably controllable or preventable. 3) The event was caused by human activity that is unlikely to recur at a particular location
or was a natural event. 4) There exists a clear causal relationship be tween the specific event and the monitored
exceedance.

The EPA has revised the 2007 EER (2016 revisions) 2 based on implementation experiences with the exceptional events data exclusion process. Th e revisions clarify the required elements that exceptional events demonstrations must addre ss. The revised EER [at 40 CFR 50.14(c)(3)(iv)] requires that demonstrations submitted to the EPA include the following elements:

1) A narrative conceptual model; 2) A demonstration that the event was both not reasonably controllable and not reasonably preventable; 3) A demonstration that the event was a human activity that is unlikely to recur at a particular location or was a natural event; and 4) A demonstration that the event a ffected air quality in such a way that there exists a clear causal relationship between the specific event and the monitored exceedance or violation.

Demonstrations prepared by air agencies 3 and submitted to the EPA must address each of these rule elements. This document recommends exampl e language and analyses that may be sufficient
to address these elements in demonstrations for wildfires that influence monitored ozone (O 3 )

1 “Treatment of Data Influenced by Exceptio nal Events; Final Rule” (72 FR 13560, March 22, 2007).

2 The EPA has prepared this draft guidance to align with the proposed EER revisions signed on XXXX and available on the EPA’s exceptional events website at http://www2.epa.gov/airquality-analysis/treatment-data-influenced-exceptional-events . The EPA will revise this guidance to reflect the relevant final promulgated EER revisions if the final revisions differ from the proposal.

3 The term “air agencies” is used throughout the document to include state, local, and tribal air agencies responsible for implementing the EER. In the context of flagging data and preparing and submitting demonstrations, the roles and opti ons available to air agencies may apply to federal land managers of Class I areas and other federal agencies that either operate monitors affected by an event or that manage federal land.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

2 concentrations. 4 The EPA may not be able to concur with an air agency’s reque st to exclude data
under the EER if a demonstration does not addre ss the identified elements. Air agencies are encouraged to contact their EPA Regional O ffice as soon as the agency identifies eventinfluenced data that potentially influence a re gulatory decision or when an agency wants the EPA’s input on whether or not to prepare a demonstration.

Purpose of this Document The EPA developed this document to assist air ag encies in the preparation of exceptional events
demonstrations for wildfire influences on O 3 concentrations that meet the requirements of CAA section 319(b) and the EER. This guidance docum ent follows the requirements of the EER and provides three different tiers of demonstrations that air agencies can use to develop evidence for exceptional events demonstrations.

The EPA recognizes the limited resources of the ai r agencies that prepare and submit exceptional
events demonstrations and of th e EPA Regional Offices that review these demonstrations. One of the EPA’s goals in developing this document is to establish clear expectations to enable affected agencies to better manage resources as they prepare the documentati on required under the EER and to avoid the preparation and submission of extraneous information. Submitters should prepare and submit the appropriate level of supporting documentati on, which will vary on a caseby-case basis depending on the nature and severity of the event, as appropriate under a weight of evidence approach. This guidance contains example analyses that may be used by air agencies in their demonstrations, however analyses not listed or explained here may also be appropriate to
include. The evidence included in a demonstrat ion should be well-documented, appropriately applied, technically sound, and should support the weight of ev idence showing that the event and/or monitored concentration meets the regulat ory criteria. Because this guidance identifies important analyses and language to include within an exception al events demonstration and promotes a common understanding of these elements between the submitting air agency and the reviewing EPA Regional Office, the EPA anticipat es an expedited review of demonstrations prepared according to this guidance.

Fire-related Defin itions and Terminology
The EPA defined wildfire in the 2016 revision of the EER as: “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 ha s been declared to be a wildfire.” The EER and this guidance document differentiate wildfires from prescribed fires in that prescribed fires are intentionally ignited by management actions in a ccordance with applicable laws, policies, and regulations to meet specific land or resource management objectives ( e.g ., ecosystem maintenance, habitat restoration, or the reduction of potential wildfire emissions by reducing fuel loadings). Fire managers may declare specific pres cribed fire projects to be wildfires if the conditions of a prescribed fire develop in a way that the project no longer meets the resource objectives ( e.g., if the fire has escaped secure containm ent lines along all or part of its boundary). If a prescribed fire project is declared to be a wildfire, it should be cons idered and treated as a

4 This draft version of the guidance addresses wildfire events only, although many technical analyses described in Section 3 ap ply to both wildfire and prescrib ed fires. Prescribed fires may be added in a later version, or may be addres sed in a future companion guidance document.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

3 wildfire from that point time forward. The 2016 EER revisions also codified the 2014 National Wildfire Coordinating Group’s 5 definition of wildland as “an area in which human activity and development is essentially non-existent, except for roads, railroads, power lines, and similar transportation facilities. Struct ures, if any, are widely sca ttered.” This guidance document
differentiates between wildfires on wildland and wildfires on other lands, particularly in the “human activity unlikely to recur at a particular location or a natural event” section of the
document.

This guidance uses the following terminology:

 Fire : While this document refers to “a fire” or “the fire,” we recogni ze that there could be multiple individual fires that, when aggregated, affect O 3 concentrations at a given monitoring site.

 Event includes the fire (or fires), the fire’s O 3 precursor emissions, and the resulting O 3 from the fire.

 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 reason ably controllable or preventable, is an event caused by human activity that is unlikel y to recur at a part icular location or a natural event, and is determined by the Ad ministrator in accordance with 40 CFR 50.14 to be an exceptional event. It does not incl ude stagnation of air masses or meteorological inversions, a meteorological ev ent involving high temperatures or lack of precipitation, or air pollution relating to source noncompliance. See definition in the proposed revisions to
the EER.

 Episode refers to the period of elevated O 3 concentrations in the affected area.

 Plume means an air mass that contains polluta nts emitted by a fire; it may be broad and mixed into the surrounding air, or the mo re conventional long narrow plume with welldefined edges.

 Evidence includes, but is not limited to, m easurements and analyses based on

measurements.

Tiered Approach for Determining the Level of Evidence Likely to be Necessary in
Demonstrations The EPA reviews all exceptional events demonstr ations using a weight of evidence approach.
This means the EPA evaluates all evidence submitted with the demonstration or otherwise known to the EPA and weighs the relevance, un certainty, and persuasiveness of the evidence with respect to each of the EER elements before acting to approve or disapprove an air agency’s request to exclude data under the EER. Each ev ent eligible for consideration under the EER will likely have unique characteristics. Therefore, th e documentation and analyses that should be included in demonstrations will vary according to the event characteristics, relationship to the monitor where the exceedance occurred, and th e complexity of the airshed. Though EPA will evaluate the evidence necessary to support the exclusion of data on a case-by-case basis, the EPA

5 Glossary of Wildland Fire Terminology, Na tional Wildfire Coordinating Group, PMS 205,
October 2014. Available at http://www.nwcg.gov/sites/def ault/files/products/pms205.pdf

.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

4 acknowledges that air agencies may need to prov ide varying levels of evidence depending on the nature and severity of an event.

This guidance outlines a tiered approach to demons trations for wildfire events, recognizing that some fire events may be more clear and/or extreme and therefor e require relatively less evidence to satisfy the rule requirements, particularly for the clear causal relationship element. Tier 1 demonstrations are the simplest and least resour ce intensive and would be appropriate for fire
events that cause clear O 3 impacts in areas or during times of year that typically experience lower

O 3 concentrations. Tier 2 demonstrations would be used when the impacts of the fire on O 3 levels are less clear and would re quire more evidence than Tier 1 demonstrations. Similarly, Tier 3 demonstrations would require more evidence than Tier 2 demonstrations and would be appropriate when the relationship between the subject fires and influenced O 3 concentrations is more complicated. Tier 1 demonstrations ar e described in detail in section 3.4, Tier 2
demonstrations are described in section 3.5, and Tier 3 demonstra tions are described in section

3.6.

The EPA intends that air agencies will look at key factors of events and re lated concentrations to determine the appropriate tier (Tier 1, 2, or 3) of demonstration before preparing and submitting
a demonstration. As indicated in the “Initial Notification of Pote ntial Exceptional Event” portion of the proposed revisions to the EER, the EPA e xpects to discuss potential event-influenced exceedances with an affected air agency prio r to the air agency preparing and submitting a
demonstration. This discussion will provide an opportunity to disc uss the appropriate tier for the
event demonstration.

Scope of This External Review Draft

Event types: This document focuses on the preparation of demonstrations for wildfires that
influence monitored O 3 concentrations. This document does not specifically address demonstration components that may be necessary for showing prescribed fire impacts on O 3 concentrations. However, many example technical analyses contained in the “clear causal relationship” section of this guidance document will also be appropriate for exceptional events demonstrations for prescribed fire impacts on O 3 concentrations. The “human activity unlikely to recur” and “not reasonably contro llable or preventable” elements require different approaches for prescribed fires than those included in this draft guidance document. The EPA is inviting comment on whether additional guidance to address prescribed fires is needed and, if so, whether this guidance should be include d in this document or in a separate guidance document.

Regulatory determinations: The EER (as revised in 2016) clar ifies the EPA’s interpretation of the types of regulatory determinations eligible for data exclusion under the EER. This guidance document applies only to the specific regulat ory determinations iden tified in the 2016 EER
revisions. These actions include determinations of historical NAAQS exceedances/violations or
non-exceedances/non-violations and determinations of the air quality “desi gn value” at particular monitoring sites when made as part of the basis for any of the following five types of regulatory
actions:

 An action to designate or rede signate an area as attainment , unclassifiable/ attainment, nonattainment, or unclassifiable for a particular NAAQS.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

5  The assignment or re-assignment of a clas sification category (marginal, moderate, serious, etc.) to a nonattainment area to the ex tent this is based on a comparison of its “design value” to the established framework for such classifications.

 A determination as to whether a nonattainme nt 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 attain ment date extension, if applicable.

 A finding of SIP inadequacy leading to a SI P call to the extent the finding hinges on a
determination that the ar ea is violating a NAAQS.

Overview of the Process for Demonstrat ion Preparation, Submission, and Review The EER (as revised in 2016) outlines the pr ocess, including communications, schedule for demonstration submission, and review timelin es for preparing, submitting, and reviewing exceptional events demonstrations. A flowchar t including recommendations on the process for preparing, submitting, and reviewing wildfire O 3 demonstrations is included as Figure 1.

Outline of this Guidance This guidance document is organized by EER-requi red elements in the recommended order for
inclusion within an exce ptional events demonstration. Sectio n 2 covers the narrative conceptual model, Sections 3-5 discuss re quired elements of an exception al events demonstration, and Section 6 addresses the public comment process. Of particular note, Sections 3.4 – 3.6 discuss the three tiers of demonstrations. Air agencies should include clear evidence and documentation
for each rule element to facil itate the EPA’s review and ac tion on a submitted demonstration.

Role of this Guidance The EER is the source of the regulatory requi rements for exceptional events and exceptional events demonstrations. This document provides gu idance and interpretation of the EER. It does not impose any new requirements and shall not be considered binding on any party. If an air agency submits a demonstration using the appro ach in this guidance and the EPA concurs with the request to exclude data, the EPA will also prepare documentation to support the decision.*** E.O. 12866 Review – Revised Version – Do No t Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Implementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

6 Figure 1: Flowchart for the recommended proce ss for preparation, submission, and review of exceptional events demonstrations for wildfire impacts on O 3 , including communications with EPA Regional Offices.

no Wildfire-influenced ozone exceedance Air agency enters AQS
Initial Event Description

The EPA reviews and acts (priority given to near-term regulatory decisions):

 If during EPA review, additional information is needed to determine if criteria are met, EPA will discuss this with the submitting air agency.

o If the information needed is minor and a natural outgrowth of previously submitted information, the EPA will not require the air agency to seek further public comment on the demonstration. However, if
the needed information is significant, the air agency may need to seek additional public comment before resubmitting to EPA.

 If the additional information is not received in 12 months,
then EPA will consider the submitted demonstration inactive, and will not continue the review. If the air agency later decides to request exclusion again, it should submit a
new demonstration. Provide the Initial Notification of Potential Exceptional Event (letter, email, meeting, or documented phone conversation) with the EPA Regional Office (generally within 12 months of event)

The EPA reviews and communicates (by email or letter and call): 1 - within 90 days (typically) 2 - with prioritization for package review based on regulatory significance The EPA and air agency continue working together to determine appropriate scope of demonstration based on regulatory significance and approvability considerations.

After agreement on scope (days and monitors) and regulatory significance of demonstration package, air agency revisits AQS to flag data requested for exclusion. Do the air agency and the EPA agree that the exceedance, monitor, and event qualify for
a Tier 1 or Tier 2
demonstration?

yes

Air agency prepares
and submits a Tier 1 or Tier 2 exceptional
events demonstration Air agency prepares and
submits a Tier 3 exceptional events
demonstration*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

7 

### 2. Narrative Conceptual Model and Event Summary

2.1 Overview and EER Provisions

The EER requires that demonstrations include a conceptual model, or narrative, describing the event causing the exceedance, a discussion of how emissions from the event led to the exceedance at the affected monitor(s), and a su mmary of the regulatory determination that has been or would be affected by the event. This na rrative for a wildfire event can be more or less detailed depending on the event and local area comp lexities, but the genera l idea is to provide near the beginning of the demonstration a descri ption of the wildfire event, interaction of emissions, meteorology, and chemistry of event and non-event O 3 formation in the area, and a description of the regulat ory significance of the pr oposed data exclusion.

The 2016 EER revisions include a requirement th at the air agency pr ovide an “Initial Notification of Potential Exceptional Event” to the EPA Regional Office after the agency identifies a potential exceptional event. This Ini tial Notification process is intended to initiate conversations between an air agency and the EP A if not already on-going, or engage in more detailed discussions if a proce ss is currently in place, regarding specific data and whether the identified data are ripe for submittal as exceptional events. As identified in the EER revisions, the Initial Notification step i nvolves the air agency submitting a description of the event, a summary of the data requested for exclusion, and a description of the regu latory significance of the data exclusion to the EPA. It is likely th at much of the information the air agency has submitted to the EPA during the initial notification of a potential exceptional event would also be useful to include in the conceptual model section of a demonstration.

2.2 Examples of Supporting Documentation

The possible types of monitored evidence and techni cal analyses that should be included in the demonstration are described in the following se ctions, but to be meaningful and clearly interpreted, they should be tied to a simple narra tive describing how em issions from a specific fire (or group of fires) resulted in elevated O 3 at a particular location and how the emissions and resulting high O 3 concentrations differ from typical high O 3 episodes in the area. This narrative description of the cause of th e exceedance and the supporting da ta and technical analyses will provide a consistent framework by which the EPA can evaluate the evidence in a demonstration. The interaction of the fire plume with non-even t emissions and meteorological conditions of the area will, in part, determin e the relevant evidence.

The conceptual model should describe the principa l features of the inter action of the event and event emissions, transport ( e.g ., wind patterns such as strength, convergence, subsidence, recirculation), and O 3 chemistry that characterize an O 3 episode. This narrative should highlight key factors in O 3 formation for the particular epis ode, and their relative importance. A description of the typical urban plume direction (if present), h our of occurrence for peak O 3 concentration, distance downwind, typical wind fl ow patterns, expected influence of major sources or emissions categor ies, relationship between O 3 concentrations to diurnal temperature and growth of mixing laye r, the importance of O 3 and precursors aloft, and multiple day carryover of pollutants are a few items that could be used to disc uss this conceptual model. See Appendix A1 for an example of an event summary and conceptual model.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

8 Finally, even if the monitored data and/or technical analyses may not unequivocally support the clear causal relationship, agenci es should submit available inform ation regarding the event and monitored concentrations. It may still be possible to explain, with a weight of evidence approach, why the majority of the data or analyses are consistent with the event’s impact on O 3 (for example, that most of the meteorological parameters would have indicated a lower O 3 day under non-fire conditions, even though the temperature was high).

Where a conceptual model that consistently explains non-event O 3 exceedances in the area already exists or can be formulated, highlighti ng the differences between the conceptual model for the event day with the non-event concep tual model can significantly strengthen a demonstration. For example, if the winds were from an urban center to the monitor of interest on
all non-event O 3 exceedance days, but the winds are not from that direction on the event day, this
difference can form a theme in the overall demonstr ation if it is clearly noted in the conceptual model discussion. Evidence substantiating the accuracy of the non-even t conceptual model would give this approach more weight in th e weight of evidence determination. Section 3 discusses this type of evidence. Much of th e evidence included in the conceptual model may have also been included in the air agency’s In itial Notification of Potential Exceptional Event.

The EPA recommends that air agencies include th e following information in their conceptual model and event summary:

 Maps and tables of the wildfire event info rmation including location, size, and extent. The maps should also include the location of the monitor(s) where data exclusion is requested. This map and table should clearly identify the fire(s) believed by the air agency to have caused the exceedance, not ju st a list of fires occurring within the jurisdiction of the s ubmitting air agency. 6

 Characteristics and description of the monito r with the request for data exclusion. Nonevent similarities and differences between this monitor and nearby monitors should be explained.

 An explanation and identification of the cause and point of origin fo r the event fire(s).

 Examples of media coverage of the even t, including special weather statements, advisories, and news reports.

 Smoke forecasts based on meteorology and burn conditions; these are often provided as part of the Wildland Air Quality Response Program.

 Description of meteorological data from or n ear the affected monito r and how this relates to the transport of the fire emissions.

 Description of the route of th e wildfire emissions to the impacted monitor, including meteorological information ( e.g ., general atmospheric circ ulation characteristics) regarding the transport of fire emissions to the monitor.

6 Burn scar areas by month, 2010-2014: http://activefiremaps.fs.fed.us/burnscar.php ; Federal Land Fires, 1980-2013, with de tails (dates, acreage): http://wildfire.cr.usgs.gov/fi rehistory/viewer/viewer.htm.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

9  Non-event O 3 formation characteristics of the ar ea normally influencing the monitor ( i.e

., the non-event conceptual model).

 Discussion of the differences observed be tween the non-event conceptual model and event related conditions causing high O 3 concentrations at a particular location.

 A summary of spatial and temporal O 3 patterns on the day of interest, and days before and after the event, relative to other, non-event days (either high O 3 days, or days with similar meteorology than the event day) including maps of affected and non-affected
monitors.

 Description of the regulatory determination an ticipated to be impacted by the exceptional event, including a table of the moni tor data requested for exclusion ( e.g ., date, hours, monitor values, and design value calculations with and without the exceptional event).

 NAAQS attainment and classifi cation information including O 3 SIP status.



### 3. Clear Causal Relationship Between the Specific Event and the
Monitored Concentration

3.1 Overview and EER Provisions

The 2016 EER revisions require that demonstrati ons address the technical element that “the event affected air quality in such a way that th ere exists a clear causal relationship between the specific event and the monitored exceedance or vi olation (supported in part by the comparison to
historical concentrations and other analyses).” This section of the demonstration provides evidence supporting the clear causa l relationship between the ev ent and the monitored NAAQS exceedance or violation and, ther efore, that the event has affected air quality. Air agencies should support the clear causal relati onship with a comparison of the O 3 data requested for
exclusion with historical concentrations at the air quality monitor. In addition to providing this
information on the historical context for the even t-influenced data, a clea r causal relationship is generally established by demonstrat ing that the fire’s emissions were transported to the monitor, the fire’s emissions affected the monitor, and in some cases, a quantification of the level of impact of the fire’s emissions on the monitored O 3 concentration.

3.2 Event-related Concentration in the Context of Historical Concentrations

Part of demonstrating a clea r causal relationship between th e event and the monitored O 3 exceedance involves a comparison w ith historical concentrations measured at the monitor or throughout the area during the same season. Air agen cies should compare the data requested for
exclusion with the historical conc entrations at the monitor, incl uding all other “high” values in
the relevant historical record. If other values in the historical record are alleged to have been affected by exceptional events, the EPA recomm ends identifying those values and including event information to support that the monitored con centrations were impacte d, such as a list of previous fire dates and locatio ns, evidence of stratospheric in trusion, or evidence supporting other event types. In addition to demonstrating how the level of the event exceedance compares with historical data, it may also be useful to demonstrate how the diurnal or seasonal pattern differs, if such a deviation occurr ed, due to the event. To be e ffective, such comparisons need
some level of robustness. Statistical summ aries used to charact erize non-event, highconcentration day historical data and the differences seen on event days would carry more weight*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

10 than anecdotal or general assertions of when non-event behavior occurs, without evidence or quantification.

The data used in the comparison of histori cal concentrations anal ysis should focus on
concentrations of O 3 at the impacted monitor and nearby monitors if appropriate. Evidence of additional impacts on air quality [carbon monoxid e (CO), particulate matter (PM), nitrogen oxides (NOx), etc.] can also be provided if they provide additional insight.

There is no pass or fail threshold for the historical concentrations data presentation. However, the comparisons may inform the additional evidence need ed to successfully esta blish the clear causal relationship element. For example, historical co mparisons conclusively showing that the eventaffected O 3 concentration was outside the range of hist orical concentrations will likely indicate less additional evidence may be needed to demonstrate the clear causal relationship. The seasonality of the event-related exceedance versus other exceedan ces may be used to determine if a Tier 1 (Section 3.4) demonstration may be an appropriate option. A dditionally, th e percentile ranking of the event-influenced data against historical da ta may also be used in one of the factors (Section 3.5) to determine if a Tier 2 demonstration may be a suitable option.

3.2.1 Examples of Supporting Documentation

 Provide a plot of the maximum daily 8-hour O 3 concentrations at the monitor(s) in question for the high O 3 seasons (April through October, or other months as appropriate) for at least 5 years. An example approach to plotting these data is shown below in Figure 2. Alternatively, including separate plots fo r each year (or season) may also be an informative approach to presenting this information.

 Timeseries plots of O 3 concentrations at nearby monitors to demonstrate spatial and/or temporal variability of O 3 in the area.

 Determine 5-year percentile of the data requ ested for exclusion on a per monitor basis.

 Determine the annual ranking of the data re quested for exclusion. This assessment may be potentially helpful to show when the non-event O 3 during the year with the exclusion request was lower than surrounding years.

 Identify the cause of other “peaks” – fires, other causes, or normal photochemical events, and provide evidence to support th e identification when possible.

 A timeseries plot covering 12 months (or the months of the high O 3 season) overlaying all 5 years of data plotted can be useful in identifying monitored concentrations that are unusually high for a time of year, and/or that coincide with fire events. An example is provided below in Figure 3.

 Trends due to emission reductions from planni ng efforts, or othe r variability due to meteorology or economics of an area can be discussed in explaini ng the distribution of data over the previous 5 years. For example, if a downward trend in O 3 concentrations over the 5-year historical da ta record obscures the uniqueness of the event-related concentration, the air agency should use appropriate plot s to explain this trend.*** E.O. 12866 Review – Revised Version – Do No t Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Implementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

11 Figure 2. Example of an O 3 time series plot from an even t-impacted monitor to include in a
demonstration.

Figure 3. Example of a seasonal O 3 plot, overlaying multiple years of data from an eventimpacted monitor to incl ude in a demonstration.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

12 3.3 Concept of Different Tiers of Ex ceptional Events Demonstrations

The nature and severity of a fire event and the characteristic s of the typical O 3 concentrations at the affected monitor will, in part, determine th e evidence that an air ag ency will need in its weight of evidence showing for the clear causa l relationship portion of an exceptional events demonstration for fire impacts on monitored O 3 concentrations. The tieri ng strategy described in this guidance contains three tiers of demonstra tions and is based on an event’s potential for O 3 formation at a given monitor a nd/or the history of non-event O 3 concentrations at the monitor. This strategy acknowledges that some fire events can be extreme or otherwise clearly stand out from normally occurring O 3 concentrations and, thus, may necessitate less evidence for the clear causal relationship analysis.

Tier 1 demonstrations are appropr iate for the clearest events, e.g. , fires located in close proximity to a monitor in an area or during a time of year with typically low O 3 concentrations. Tier 1 demonstrations would likely need the least amount of evidence. Tier 2 demonstrations would be used in situations with less clear fire impacts and would thus require more evidence than Tier 1 demonstrations. Tier 3 demonstrations, requiring more evidence than Tier 2 demonstrations, would be appropriate when the relationship between the subject fires and influenced O 3 concentrations is complex. Section 3.4 defines s ituations where a Tier 1 demonstration may be appropriate, Section 3.5 defines si tuations and evidence suggested for a Tier 2 demonstration, and Section 3.6 suggests additional evidence that may be necessary for a Tier 3 demonstration.

3.4 Key Factor of and Suggested Evidence to Include in Tier 1 Demonstrations

The EPA expects that Tier 1 exceptional events demonstrations may be appropriate for fire events that have a clear impact on O 3 concentrations when they oc cur in an area that typically experiences lower O 3 concentrations ( e.g. , few or no O 3 exceedances), are associated with an O 3 concentration that is clearly high er than non-event relate d concentrations, or occur outside of the
area’s normal O 3 season. In these situations, O 3 impacts should be accompanied by clear evidence that the fire’s emissions were transpor ted to the location of monitor. This tier of demonstration is expected to be the mo st simple and easiest to prepare.

3.4.1 Evidence the Event, Monitor(s), and Exceedance Meet the Key Factor for Tier 1
Demonstrations

Key Factor – Seasonality and/or dist inctive level of the monitored O 3 concentration : The key
factor that delineates event-related monitored O 3 concentrations for Tier 1 demonstrations is the uniqueness of the concentration when compared to the typical seasonality and/or levels of O 3 exceedances. For example, if an event-related exceedance occurs during a time of year that typically has no exceedances, then that event-rela ted exceedance may be more straightforward to attribute as having been due to the fire than event-related con centrations that occur during the same month or season as typical high O 3 concentrations. If there are other exceedances during the same time of the year as the fire-rel ated exceedance, for example during normal O 3 season, they either should also be attrib utable to fire (or other exceptiona l events) or if attributable to normal emissions and photochemistry they should be clearly lower in ma gnitude than the firerelated concentrations. The EPA recommends that event-related exceedances should be at least 5-10 ppb higher than non-event related concentrati ons for them to be clearly distinguishable.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

13 This key factor is based on the fact that if there are no similar-level non-event exceedances mixed in with the event-related exceedance, then less evidence may be n ecessary to demonstrate the clear causal relationship betw een the event and the monitored O 3 concentration. Following are two types of analyses that an air agency can provide for this section of the demonstration.

1) Provide a timeseries plot coveri ng 12 months (or the typical O 3 season months plus months with the event-related exceed ance) overlaying at least 5 years of O 3 monitoring data. An example is shown in Figure 3. 2) Provide a description of how the seasonality of the event-related exceedance differs from the typical photochemical O 3 season and how other exceedances, if any, during the time of year of the fire-re lated exceedance are not attributable to normal emissions and photochemistry, are attr ibutable to fire (or other exceptional events), or are clearly lower in magnitude than the fire-relat ed concentrations.

3.4.2 Evidence the Fire’s Emissions Were Transported to the Monitor(s)

In addition to the evidence suggest ed in Section 3.4.1, th e air agency should supply at least one piece of additional evidence to support the weight of evidence in a Tier 1 demonstration that the
emissions from the fire were tran sported to the monitor location ( i.e., the latitude and longitude). Air agencies can use either a trajectory analys is or a combination of satellite and surface measurements to show this transport. Th is evidence could be any of the following:

 Trajectory analysis. Atmospheric trajectory models use meteorological data and mathematical equations to simulate three- dimensional transport in the atmosphere. Generally, these models calculate the position of particles or parcel s of air with time based on meteorological data such as wind speed and dire ction, temperature, humidity, and pressure. Model results depend on the spatial and temporal resolution of the atmospheric data used and also on the comp lexity of the model itself. The HYSPLIT (Hybrid Single-Particle Lagrangi an Integrated Trajectory) model is frequently used to produce trajectories for assessments associ ated with air quality programs. HYSPLIT contains models for trajectory, dispersion a nd deposition. However, analyses applicable to exceptional events demonstrations typi cally use the trajectory component. The trajectory model, which uses existing meteor ological forecast fields from regional or global models to compute advection ( i.e ., the rate of change of an atmospheric property caused by the horizontal movement of air) and stability, is designed to support a wide range of simulations related to the a tmospheric transport of pollutants.

Air agencies can produce HYSPLIT trajectori es for various combinations of time, locations and plume rise. HY SPLIT back-trajectories gene rated for specific monitor locations for days of high O 3 concentrations illustrate the potential source region for the air parcel that affected the monitor on the day of the high concentration and provide a useful tool for identifying meteorologi cal patterns associated with monitored exceedances. Forward-trajectories from specific fire events to specific monitors can also
be used to indicate potential receptors. HYSPLIT trajector ies alone cannot definitively conclude that a particular regi on contributed to high pollutant concentrations, but a set of HYSPLIT trajectories that show no wind flow from a particular region on days with high concentrations might support discounting that region as contributing to the*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

14 concentrations. Appendix A3 contains a dditional information on HYSPLIT trajectory analyses.

Air agencies could use other trajectory m odels, to demonstrate expected transport. Exceptional events demonstrations using ot her trajectory models should contain enough background information and detail supporting m odel application to allow reviewers to thoroughly understand the model and to reproduce the results if necessary.

 Satellite Imagery of Plume with Evidence of the Plume Impacting the Ground . Because plume elevation is not directly available from simple imag ery, plume imagery alone does not conclusively show that fire emissions transported aloft reached a ground-level monitor. If plume arrival at a given locati on coincides with elev ation of fire plume components (such as PM 2.5 , CO or organic and elemental carbon) those two pieces of
evidence combined can show that smoke was transported to the event location.

3.5 Key Factors of and Suggested Evidence to Include in Tier 2 Demonstrations

The EPA expects that additional evidence may be required for Tier 2 demonstrations, in comparison to Tier 1 demonstrations. To delineate key factors where Tier 2 demonstrations may be appropriate, the EPA review ed approved exceptional events demonstrations, conducted a literature review of case specific fire-O 3 impacts, and completed photochemical modeling analyses.

Literature review: Fires can impact O 3 concentrations by emitting O 3 precursors including NOx and VOCs. These precursor emissions can generate O 3 within the fire plume or can mix with emissions from other sources to generate O 3 (Jaffe and Wigder, 2012). Also, in some situations, including near fires, reduced O 3 concentrations have been ob served and attributed to O 3 titration by enhanced NO concentrations and reduced sola r radiation available to drive photochemical reactions (Jaffe et al., 2008; Yoke lson et al, 2003). The magnitude and ratios of emissions from fires vary greatly depending on fire size, fuel characteristics, and me teorological conditions (Akagi et al., 2012). As a result of variable emissions and non-linear O 3 production chemistry,
the O 3 production from fires is very complex, highly variable, and often difficult to predict (Jaffe and Wigder, 2012).

Despite the complexities in predicting O 3 formation from fire emissions, several studies have
found increases in O 3 concentrations attributable to fire impacts. For example, Pfister et al. analyzed surface O 3 data during a high wildfire year in California (2007) with modeled fire impacts and found monitored 8-hour O 3 concentrations were approximately 10 ppb higher when the modeled fire impacts were high (Pfister et al., 2008). Jaffe et al. an alyzed three wildfire periods in the western U.S. during 2008 and 2012 and compared monitored surface O 3 concentrations with two different modele d estimates of fire contributions to O 3 concentrations to
find enhancements in O 3 when fire impacts were predicted to be high (Jaffe et al., 2013). Many other publications have found similar relationships between surface O 3 and fire occurrences, using a variety of technical approaches (Bytnero wicz et al., 2013). One literature study was used to evaluate the relationship between O 3 impact and fire characte ristics (Jaffe et al., 2013).*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

15 Empirical Relationships between Fire Events and O 3 Concentrations in Previous

Demonstrations: The EPA reviewed previous demonstr ations for specific fire events to determine if general relationships exist between the magnitude of the fire emissions, the distance
of the fire to O 3 monitors, and O 3 impacts at those monitors. Between 2010 and September 2015, the EPA approved two exceptional events dem onstrations for fire-related impacts on O 3 . The first was approved in 2011. In this case, the EPA concurred on three exceedances of the 1-hour

O 3 NAAQS near Sacramento, California in 2008 due to a series of lightni ng-initiated wildfires throughout northern California. The second demonstration for fire impact on O 3 was approved in 2012. In this case, the EPA concurred with th e exclusion of eight 8-hour daily maximum O 3 exceedances during April 2011 in Kansas due to imp acts from prescribed fires and wildfires.
Prescribed fires caused most of the exceedance s identified in the Kansas demonstration.

Modeling Studies of O 3 Impacts from Fires: To support the development of this guidance and to assess the relationship between fire source strengths and resultant O 3 concentrations at various distances from the fire (Appendix A2), the EPA conducted modeling analyses for fires identified in the EPA’s 2011 National Emissions Inventory (N EI). Four fires of varying strengths and locations were simulated with the Community Multiscale Air Quality Model (CMAQ) model.
The O 3 impacts of these fires were estimated us ing a source apportionment technique (Kwok et al., 2015). Consistent with previ ous literature studie s, the EPA modeling suggests that NOx and
VOC emissions can lead to significant increases in O 3 concentrations downwind of the fire. The
simulated O 3 increases are related to distance down wind from the fire emissions and the magnitude of the fire emissions. Examination of th is modeling and related st udies suggests that it is appropriate to use a simple Q/D (emissions/dis tance) metric to conduct a screening assessment of potential fire impacts. This model applica tion was evaluated agains t monitoring data and appears to capture the ambient relationships between CO and O 3 measured in the vicinity of smoke plumes. The EPA acknowledges that the sc ience continues to emerge in modeling the O 3 impacts of fires ( e.g ., plume chemistry, plume rise). The 2011 modeling includes some limited treatment of the sunlight-blo cking impacts of smoke on O 3 photochemistry.

The EPA used the general relationships between O 3 impacts and fire characteristics from the modeling study, in combination with the assessment of previously approved demonstrations and fire case-studies from the peer-reviewed literature to develop two key factors (Section 3.5.1) for a Tier 2 demonstration. These two key factors ac t together to identify event and monitor pairs that may be appropriate for a Tier 2 demonstr ation. Section 3.5.1 includes a recommended value and guidance for determining Q/D.

3.5.1 Evidence that the Event, Monitor(s), and Exceedance Meet the Key Factors for Tier 2
Demonstrations

This section details the evidence to be included in a Tier 2 demonstrat ion for the clear causal relationship rule element.

Key Factor #1 – Fire emissions an d distance of fire(s) to affect ed monitoring site location(s): At least one air quality related program ( i.e ., determining impacts at Class I areas) uses an emissions divided by distance (Q/D) relationship as a key fact or for determining the influence of emissions
on a downwind monitor. The EPA believes that it is appropriate to use a similar approach, along with key factor #2 detailed below, to determine if a Tier 2 exceptional events demonstration*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

16 provides sufficient evidence to satisfy the clear ca usal relationship criteria of the EER for fire O 3 demonstrations. To determine an appropriate and conservative value for the Q/D threshold (below which a full/Tier 3 exceptional events demonstration would be recommended), the EPA conducted a review of approved ex ceptional events demonstrations , a literature review of case specific fire-O 3 impacts, and photochemical modeling an alyses as described above. The three analyses generally s howed that larger O 3 impacts occurred at higher Q/D values. The reviews and analyses did not conc lude that particular O 3 impacts will always occur above a particular value for Q/D. For this reason, a Q/D screeni ng step alone is not sufficient to delineate
conditions where sizable O 3 impacts are likely to occur. Give n this, the EPA recommends, as the first of two key factors, that the Q/D (as described below) should be ≥ 100 tons per day/kilometers (tpd/km). The rati onale for the recommendation of ≥ 100 tpd/km as a
conservative indicator of O 3 impacts is based on the Q/D ratio for previously approved firerelated O 3 exceptional events demonstrations and the modeling results that showed the largest O 3 impacts were often associated with high Q/D values. The O 3 values within the approved demonstrations generally were associated with Q/D values above 50 tpd/km (Figure A2-1), though not all the concentra tions shown were clear decisions. The largest O 3 impacts from the modeling studies of the two largest fires (Wallow and Flint Hill fires) were associated with Q/D values above 100 tpd/km (Figure A2-5), and large O 3 impacts were not observed in the modeling of the two smaller fires (Big Hill and Waterhole fires). Based on results from these analyses and reviews, if the Q/D (as defined a nd calculated in Section 3.5.1) is ≥ 100 (tpd/km), and key factor #2 is also met, then a Tier 2 demonstration ma y be appropriate. Following is a description of how an air agency could develop a Q/D analysis.

Calculate Q/D for the event and monitor pairs:

Determine fire emissions (Q): For the pur poses of exceptional events tiering, fire emissions (Q in the Q/D expression) is defi ned as the daily sum of the NOx and reactiveVOC emissions (in units of tons per day) from specific fire events impacting the O 3 monitor on the day of the O 3 exceedance. Air agencies should describe and characterize in the conceptual model/event summary section of the demonstration all fires included in the calculation of Q/D. Since a fire even t can span several days and because fire emissions may not impact a monitor on the da y that they are generated, this guidance suggests the following approach for assessing a range of days to determine the maximum Q/D value to use for the screening test:

1) Determine the date of the 1 st hour in the period of the 8-hour (or 1-hour) O 3 average that is the subj ect of the demonstration. Example : August 15, 2014.

2) Determine the date of the 8 th hour of that 8-hour period, which may be the same as the first date or the following date. Example : August 16, 2014.

3) Identify fires generating emissions on these one or two dates and identify the date prior to the date of the 1 st hour. Including the latter date allows for the possibility that fire emissions on one day affected ozone on the next day. These are the two*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

17 or three dates that will be included in assessing the clea r causal relationship. Example : August 14, 15, and 16.

The EPA recommends generating 24-hour b ack trajectories from the affected O 3 monitoring site(s) beginning at each hour of these two or three dates. Identify fires that are close to any of these back trajectories. Example : the air agency identifies three fires: Fire A, Fire B and Fire C.

4) Identify the latitude/longit ude of each fire for each day. Determine “D,” the

distance in kilometers between the fire’s latitude/longitude and the affected O 3 monitor for each fire for each day.

5) For each fire and each day, identify the sum of NOx and reactive VOC (rVOC) emissions in tons/day. If only TOG em issions (versus rVOC) are available, multiply the TOG emissions by 0.6 to repr esent the reactive fraction that can

contribute to O 3 formation ( see Appendix A2). Alternatively, sum the specific rVOC emissions or use a multiplier other than 0.6 with appropriate justification. This step is designed to acc ount for the fact that some of the gases included in the

TOG emissions estimates to not contribute to ozone formation.

Day-specific emissions estimates should be readily available for wildfire (and prescribed fire events) that occur duri ng NEI years using the EPA methods. In

addition to the actual emissions estimates (NOx, VOC, CO, SO 2 , PM tons/day), the NEI methods also result in many other da ta fields that will be made available (date of fire occurrence, fire event na me, state/county FIPS, latitude, longitude, quality assurance flag, fire type, acres burned). Detailed information about how the EPA develops inventories for fires on wildlands is part of the latest NEI

documentation available on CHIEF ( http://www3.epa.gov/ttn/c hief/eiinformation.html ). In general, the EPA’s approach for estimating fire emissions relies on a combination of satellite detection of fires merged with on-the- ground observational data (especially with activity data submitted by local air regulatory and forestry agencies) and where

available combined with m odels that specify fuel loading, fuel consumption, and emission patterns/factors. These emissions are based on the latest version of the Satellite Mapping Automated Reanalysis To ol for Fire Incide nt Reconciliation (SMARTFIRE) system ( http://www.airfire.org/smartfire/ ). Air agencies can provide fire event emissions and activity da ta as part of an exceptional events

demonstration that the state believes more accurately characterize the event than the information contained in the NEI, pr ovided those emissions and activity data are well-documented and supported.

To estimate fire-related emissions in non- NEI years, air agencies may use other techniques to represent fire emissions, es pecially methods that have been agreed*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

18 upon by multiple public agencies ( e.g. , http://www.airfire.org/data/playground/ )

or emission estimates that reside in the published literature. The fire activity data and emissions estimation techniques used should be well-documented and supported. However, the EPA encourages the use of ground-based observations and local fuel information whenever possible as these factors can significantly improve the resulting estimates of fire emi ssions. As resources allow, to assist air agencies in locating fire-related emissions in non-NEI years, the EPA anticipates providing year and day-speci fic fire event emissions summaries using similar methodologies to that used in the NEI.

6) Check the fires individually to see whet her any one of them had Q/D >100 for any of the days. If yes, evaluate key factor #2.

7) If no, determine whether the fires satisfy the Q/D test when aggregated. For each day of fire, weight the distances be tween the fire locations and the O 3 monitor by the NOx+rVOC emissions for that day to get an emissions-weighted D. Sum the NOx+rVOC emissions of all three fires ( e.g ., Fire A, Fire B and Fire C from the above example) from the day, and calcul ate Q/D using the emissions sum and the

distance.

8) If Q/D ≥ 100 for the day, evaluate key fact or #2. Apply the same aggregated approach for the other identified days. If Q/D is < 100, then the Tier 2 approach is not appropriate. Show all calculations and values. The demonstration should clearly describe the result of the calculation, and the em issions, distance, and any assumptions that the air agency ma de in developing the Q/D ratio.

Key Factor #2 – Comparison of the event related O 3 concentration with non-event related high

O 3 concentrations: The second key factor for a Tier 2 dem onstration considers the characteristics
of the event-related concentr ation versus the non-event O 3 concentration distribution at the monitor. Addressing key factor #2 involves show ing that the exceedance due to the exceptional

event:

 is in the 99 th or higher percentile of th e 5-year distribution of O 3 monitoring data, OR

 is one of the four highest O 3 concentrations within 1 year (among those concentrations that have not already been excluded under the EER, if any).

Applying this key factor recognizes that an air ag ency will likely need more detailed information
to establish a clear causal rela tionship between the event and th e monitored exceedance in an
area or season with elev ated non-event related O 3 concentrations. Therefore, limiting the Tier 2
demonstration to events in the 99 th or higher percentile of 5 years of monitoring data will generally ensure the event-impacted data are high compared to other data at the monitoring site.
If event-related concentrations ha ve already been excluded for this year, then those values should not be included when determining th e ranking. However, if the non-event O 3 concentrations at a monitor in the year (or seas on) when the event-related O 3 exceedance occurred are low when compared with other surrounding years in the 5 year record, an exceedance in this “low” O 3 year*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

19 could still affect design value calculations a nd determinations within the scope of the EER. Therefore, if the data requested for exclusion ar e one of the fourth high est within 1 year (among
those concentrations that have not already been excluded under th e EER, if any), the key factor would be met. If both key factors (#1 and #2) are met, then a Tier 2 demonstration may be
sufficient.

Compare the event-related O 3 concentration with non-event related high O 3 concentrations:

1) Provide the percentile ranking of the data requested for exclusion when compared with the most recent 5 years of monitoring data . Include the plot showing this result or reference the generated plot in anot her section of the demonstration.

2) If data are in the 99 th (or higher) percentile OR are one of the top four O 3 maximums within 1 year AND key factor #1 is satis fied AND the EPA Regional Office and the affected air agency have di scussed the potential event THEN the air agency should prepare a Tier 2 demonstration.

3.5.2 Evidence that the Fire Emissions Affected the Monitor(s)

In addition to the evidence sugge sted in Section 3.5.1, the air agency shou ld supply at least one piece of additional evidence to support the weight of evidence that the emissions from the fire
affected the monitored O 3 concentration. The example evidence explained below can be used by air agencies to demonstrate the fire emissions we re present at the altit ude of the monitor(s).

This evidence could include any of the following:

1) Photographic evidence of ground-level smoke at the monitor

2) Concentrations of supporting measurements [CO, PM (mass or speciation), VOCs, or altered pollutant ratios]

3) Evidence of changes in spatial/temporal patterns of O 3 and/or NOx.

While fires generate emissions of CO, NO, NO 2 , VOCs, PM 10 , and PM 2.5 , anthropogenic sources, such as from industrial and vehicular co mbustion, also emit these pollutants. Therefore, the air agency should distinguish the differe nce in the non-event po llutant behavior ( e.g ., concentration, timing, ratios, and/or spatial patterns) from the be havior during the event impact to more clearly show that the emissions from th e fire(s) affected the monitor(s). Evidence from regulatory and non-regulatory ( e.g. , special purpose, emergency) monitors may be used to support these analyses.

Specific analyses to support the above- identified evidence include the following:

 Photographic evidence of ground-level smoke at the monitor.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

20  Satellite evidence of smoke or precur sors (NOx) at the monitoring site. http://ofmpub.epa.gov/rsig/ rsigserver?index.html and http://arset.gsfc.nasa.gov/airquality/applications/fires-and-smoke may be helpful

resources.

 Plots of co-located or nearby CO, PM 2.5 , PM 10 , or O 3 and PM 2.5 precursor concentrations in the same airshed (or nona ttainment/near nonattainment area ) that have increases or differences in typical behavior that indicate the fire’s emi ssions impacted the monitor. Elevated levels of CO or PM (inclu ding pre-cursors) at an affected O 3 monitor upwind of urban centers or occurring at non-commute tim es at a monitor within an urban area despite the lack of a surface inversion would be consistent with fire plume impact. Include an explanation of the plots.

 Elevated light extinction measurements at or near the O 3 monitoring site that cannot be explained by emissions from other sources and are consistent with fire impact.

 The timing and spatial distribution of NO, NO 2 , and O 3 , shown with data from multiple monitoring sites. These pollutant concentra tions may vary when influenced by a fire plume. Elevated levels that are widespr ead throughout a region, or are upwind of the urban area, may be due to impact of a fire plume. Peaks at locations and times different than those normally seen in an O 3 episode can indicate fire plume impact.

 Differences in CO:NOx ratios: The ratio of CO and NOx emissions depends on their source; for agricultural burning it is about 10-20, for wildfire and prescribe wildland burning about 100 (Dennis et al., 2002), wh ereas for high-temperature fossil fuel combustion sources it is more like 4 (Chin et al., 1994). Thus, an unusually high CO/NOx ratio is consistent with fire impact. Similarly, the CO/PM 10 emission ratio is 8-16 in fires, but 200-2000 for vehicles (Phuleria et al., 2005). Changes in CO and CO ratios might be difficult to discern in an area dominated by ve hicular CO, however, as the fire signal may be small in comparison.

 PM speciation data: PM 2.5 emissions from forest fires often contain elevated levels of organic carbon (OC) and occasionally are en riched in water soluble potassium (K) (Watson et al., 2001). Levoglucosan, a tracer molecule, is a constituent of smoke from biomass burning that can serve as an indicator for fire; PM 10 from wood smoke is 14% or higher levoglucosan by mass (Jordan et al., 2006; Dennis et al., 2002). Co-located or nearby particle speciation data (OC, K, and/or levoglucosan) can be used to indicate fire impacts.

3.5.3 Evidence the Fire’s Emissions were Transported to the Monitor

In addition to the evidence s uggested in Sections 3.5.1 and 3.5.2, an air agency should provide evidence showing the emissions from the fire were transported to the monitor location ( i.e., the latitude and longitude). Air agencies can use e ither a trajectory analysis or a combination of
satellite and surface measurements to show this transport. (These recommendations are the same as for Tier 1 demonstrations in Section 3.4.2, but are explained here ag ain for completeness).*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

21  Trajectory analysis. Atmospheric trajectory models use meteorological data and mathematical equations to simulate three- dimensional transport in the atmosphere. Generally, these models calculate the position of particles or parcel s of air with time based on meteorological data such as wind speed and dire ction, temperature, humidity, and pressure. Model results depend on the spatial and temporal resolution of the atmospheric data used and also on the comp lexity of the model itself. The HYSPLIT (Hybrid Single-Particle Lagrangi an Integrated Trajectory) model is frequently used to produce trajectories for assessments associ ated with air quality programs. HYSPLIT contains models for trajectory, dispersion a nd deposition. However, analyses applicable to exceptional events demonstrations typi cally use the trajectory component. The trajectory model, which uses existing meteor ological forecast fields from regional or global models to compute advection ( i.e ., the rate of change of an atmospheric property caused by the horizontal movement of air) and stability, is designed to support a wide range of simulations related to the a tmospheric transport of pollutants.

Air agencies can produce HYSPLIT trajectori es for various combinations of time, locations and plume rise. HY SPLIT back-trajectories gene rated for specific monitor locations for days of high O 3 concentrations illustrate the potential source region for the air parcel that affected the monitor on the day of the high concentration and provide a useful tool for identifying meteorologi cal patterns associated with monitored exceedances. HYSPLIT trajectories alone cannot definitively conclude that a particular region contributed to high pollutant concen trations, but a set of HYSPLIT trajectories that show no wind flow from a particular re gion on days with high concentrations might support discounting that region as contributing to the concentrations. Appendix A3 contains additional information on HYSPLIT trajectory analyses.

Air agencies could use other trajectory m odels to demonstrate expected transport. Exceptional events demonstrations using ot her trajectory models should contain enough background information and detail supporting m odel application to allow reviewers to thoroughly understand the model and to reproduce the results if necessary.

 Satellite Imagery of Plume with Evidence of the Plume Impacting the Ground . Because plume elevation is not directly available from simple imag ery, plume imagery alone does not conclusively show that fire emissions transported aloft reached a ground-level monitor. If plume arrival at a given locati on coincides with elev ation of fire plume components (such as PM 2.5 , CO or organic and elemental carbon) those two pieces of
evidence combined can show that smoke was transported to the event location.

3.5.4 Summary of Evidence that Could be Used to Meet the EER Elements for Tier 1 and Tier
2 Demonstrations

Table 2 summarizes the technical support that ai r agencies can use to support the clear causal relationship in a Tier 2 demonstration, co mpared with a Tier 1 demonstration.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

22 Table 2. Clear Causal Relationship Technical Demonstration Components Recommended
for Tier 1 and Tier 2 Demonstrations

Tier 1 Demonstration Should Include Tier 2 Demonstration Should Include Comparison of the fire-influenced
exceedance with historical concentrations Comparison of the fire-influenced
exceedance with historical concentrations Evidence that the fire and monitor(s) meet the key factor Evidence that the fire and monitor(s) meet the key factors (#1 and #2) Evidence of transport of fire emissions from fire to the monitor ( one of these):

 Trajectories linking fire with the monitor (forward and backward), considering height of trajectories

 Satellite evidence in combination
with surface measurements Evidence of transport of fire emissions from fire to the monitor ( one of these):

 Trajectories linking fire with the monitor (forward and backward), considering height of trajectories

 Satellite evidence in combination
with surface measurements

Evidence that the fire emissions affected the monitor ( one of these):

 Visibility impacts (satellite or photo)

 Changes in supporting

measurements

 Satellite NOx enhancements

 Differences in spatial/temporal
patterns

3.6 Additional Clear Causal Relati onship Evidence for Tier 3 Events

As discussed in Section 3.3, air agencies may need additional de tail to satisfy the clear causal relationship element for events not meeting the Tier 1 or Tier 2 key factors. This section describes the additional evidence that may be appropriate for inclusion in Tier 3 event demonstrations. The appropriate level of evid ence should be discussed between the submitting air agency and the EPA regional office duri ng the Initial Notifi cation discussions.

3.6.1 Relationship of the Event, Monitor(s), a nd Exceedance to the Key Factors for Tier 2
demonstrations

As part of the weight of evid ence showing for the clear causal re lationship rule element, explain how the events, monitor and exceedance compare with the key factors outlined in Section 3.5.1. The relationship of the event to the Tier 2 key factors may help inform the amount of additional
information that will be needed in a Tier 3 demonstration.

3.6.2 Evidence that the Fire Emissions Affected the Monitor(s)*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

23 Because the relationship between the fire-related emissions and the monitored exceedance or violation cannot clearly be shown using the Tier 1 or Tier 2 appr oach, air agencies will need
additional evidence to show that the fire emi ssions affected the monitor. The clear causal relationship approach for Tier 3 demonstrations could include multiple analyses from those examples listed in Section 3.6.4. The example ev idence suggested in Section 3.6.4 can be used by air agencies to demonstrate the fire emissions were present at the alt itude of the monitor(s). Each additional piece of information that suppo rts the event’s influence will strengthen the air agency’s position.

3.6.3 Evidence that the Fire Emissions were Transported to the Monitor

To demonstrate a clear causal relationship betw een the event’s emissions and the monitored O 3 exceedance, air agencies should provide evidence s howing that the emissions from the fire were clearly transported to the monitor. This will likel y require a trajectory analysis similar to that
described in Section 3.1.1 or the sate llite plume analysis of Section 3.5.3.

Because the uncertainty of trajecto ry analyses increases with transport distance, frontal passages, and complex wind/terrain issues, additional inform ation, such as analyses of surface meteorology (wind speed and direction), will further support the clear causal relationship rule element.

3.6.4 Additional Evidence that the Fire Emissions Caused the O 3 Exceedance

Depending on evidence supplied in ot her sections of the demonstrat ion, an air agency may need
some of the additional evidence listed here to de monstrate that the fire emissions caused the O 3 exceedance. Matching day analyses, statistical re gression models, or photochemical models may help support the position that the emissions from the fire caused the O 3 exceedance.

 Comparison of O 3 Concentrations on Meteorologi cally Similar Days (Matching Day Analysis)

O 3 formation and transport are highly dependent upon meteorology, therefore a comparison between O 3 on meteorologically similar days with and without fire impacts could support a clear caus al relationship between th e fire and the monitored
concentration. Both O 3 concentrations and diurnal be haviors on days with similar meteorological conditions can be useful to compare with days believed to have been impacted by fire. Since similar meteorologi cal days are likely to have similar O 3 concentrations, significant differences in O 3 concentrations among days with similar meteorology may indicate influences from non-typical sources.

Meteorological variables to include in a sim ilar day (or “matching day”) analysis should be based on the parameters that are known to strongly affect O 3 concentrations in the vicinity of the monitor location. These variab les could include: dail y high temperature, hourly temperature, surface wind speed and di rection, upper air temper ature and pressure [such as 850 or 500 millibar (mb) height], re lative or absolute humidity, atmospheric stability, cloud cover, solar irradiance, and others as a ppropriate (Anderson and Davis, 2004; Camalier et al, 2007; Eder et al, 1993; Eder et al, 1994). These parameters should be matched within an appropr iate tolerance. Since high O 3 days may be relatively rare, air agencies should examine several years of da ta for similar meteorology versus restricting*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

24 the analysis to high O 3 days only. The complete range of normal expected O 3 on similar meteorology days will have value in the dem onstration. A similar day analysis of this type, when combined with a comparison of the qualitative description of the synoptic scale weather pattern ( e.g ., cold front location, high pressu re system location), can show
that the fire contributed to the elevated O 3 concentrations. Air agen cies may also want to consider non-meteorological factors such as choosing days with similar, non-event emissions (possibly avoiding holidays and special public events , weekend versus weekend mismatches, and other days with unusual emissions). In a recently submitted demonstration, 7 the state of Kansas included an analysis showing the synoptic-scale weather pattern typing along with an evalua tion of basic meteorological parameters similar to the “Matching Days ” analysis described here.

 Statistical Regression Modeling Air agencies can use O 3 predictions from regression equations to assess fire’s
contribution to O 3 concentrations. Regression is a statistical method for describing relationships among variables. For estimati ng air quality concentrations, regression equations are developed to describe the re lationship between pollutant concentrations (referred to as the predicti on, what is being predicted) and primarily meteorological variables (referred to as the predictors). B ecause regression equations are developed with several years of data, they represent the relationship betw een air quality and meteorology under typical emission patterns; even if some historical exceptional events data are included in the development, the influence of those days will likely be small on the developed model provided there are far more typical days than event-related days. Therefore, the difference between the pr edictions and observations can provide a reasonable estimate of the air pollution caused by event-related emissions ( e.g ., emissions from fires) provided the analysis accounts fo r the typical remaining variance of typical days (variability in monitored data not predicted by the model).

Air agencies can develop the regression equation using the O 3 data for the monitor(s) under investigation and meteorology data fr om the closest nearby National Weather
Service station. A small subset of the data s hould be reserved for testing the regression equation. Once a regression equation has been properly developed and tested, it can be used to predict the daily maximum O 3 values. The differences between the predicted values and the measured values are analyzed, and the 95 th percentile of those positive differences (observed O 3 is greater than predicted) is recorded. This 95 percent error
bound is added to the O 3 value predicted by the regressi on equation for the flagged days, and any difference between this sum and the observed O 3 for the flagged day may be
considered an estimate of the O 3 contribution from the fire if evaluation of the top 5 th percentile shows similar O 3 days in the absence of smoke are rare or not observed.

Users of regression models should consider the uncertainties in the model’s prediction abilities, specifically at high concentrati ons, before making conclusions based on the modeled results. A key question when consid ering model uncertainty is whether the model predicts O 3 both higher and lower than monitore d values at high concentrations

7 Available at: http://www2.epa.gov/sites /production/files/2015- 05/documents/kdhe_exevents_final_042011.pdf

.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

25 (above 65 or 70 ppb) or whether the model displays systematic bias on these high monitored days?

The limitations of the regression equation itsel f defines the limitations of this method. This approach is more rigorous than a compar ison to similar meteorological days in that it considers the relationship between meteor ological parameters, but regression is less rigorous than air quality modeling, which em ploys more parameters and more physical processes in its calculations. While sta tistical modeling does not resolve all the complexities of the atmosphere, carefully crafted regression models can provide an
estimate of contribution to s upport the clear causal relationshi p portion of an exceptional
events demonstration. There are several methods for developing a regression equation to
estimate O 3 concentrations from meteorological variables (Camalier et al., 2007; STI, 2014). 8

 Photochemical modeling
This section describes the ai r quality modeling tools best suited for estimating fire emissions impacts in demonstrations needi ng a more refined assessment. Secondary pollutant impacts such as O 3 and PM 2.5 need to be assessed at various spatial scales (nearsource and long-range transport) for a variet y of regulatory programs. Modeling systems used for these assessments should be appropriate for this purpose and should be evaluated for skill in replicating meteorology and atmospheric chemical and physical processes that result in secondary pollutant formation and deposition. Photochemical grid models treat emissions, atmospheric chemistry, and physic al processes such as deposition and transport. These types of models are appropria te for assessment of near-field and regional scale reactive pollutant impacts from specific industrial so urces (Baker and Foley, 2011; Bergin et al., 2008; Kelly et al., 2015; Zhou et al., 2012), specific fire events (Kansas Department of Health and Environment, 2012) or all sources (Chen et al., 2014; Russell, 2008; Tesche et al., 2006). Photochemical transp ort models have been used extensively to support State Implementation Plans and explor e relationships between inputs and air quality impacts in the United States and beyond (Cai et al ., 2011; Hogrefe et al., 2011; Russell, 2008; Tesche et al., 2006). Several state of the science photochemical grid
models could be used to estimate fire im pacts including (but not limited to) the CAMx ( www.camx.com ), CMAQ ( https://www.cmascenter.org/cmaq/ ), and WRF-CHEM ( https://www2.acd.ucar.edu/wrf-chem ) models. These models have been used to estimate
fire contribution to O 3 in the past (Fann et al., 20 13; Jiang et al., 2012; Kansas Department of Health and Environment, 2012; Kwok et al., 2015; U.S. Environmental Protection Agency, 2014). Predictions of fire impacts on air quality are complex due to uncertainties in emissions, height of emissi ons, plume temperature, and plume chemistry (including radiative impacts on chemistry). Ho wever, with proper se t-up, application, and evaluation, air quality models can be used to indicate fire impacts on O 3 concentrations. Model evaluation of predictive skill on both event days, both for concentration and spatial extent of impacts, and for typical days with little or no exceptional precursor levels is key to using the mode l results in a demonstration.

8 Camalier et al., 2007, Atmos. Environ. a nd STI Technical Report STI-910507-6062, 9/5/14.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

26 Where set up appropriately, photochemical grid models could be used with a variety of approaches to estimate and assess the cont ribution of single sources to primary and secondarily formed pollutants. These appro aches generally fall in to the category of source sensitivity (how air quality changes due to changes in emissions) and source apportionment (what air quality impacts are re lated to certain emissions). The simplest source sensitivity approach (brute-force change to emissions) is to simulate two sets of conditions, one with all emissions and one with the source of interest removed from the simulation (Cohan and Napelenok, 2011). The difference between these simulations provides an estimate of the air quality change related to the change in emissions from the fire event (Kansas Department of Hea lth and Environment, 2012). Another source sensitivity approach to differentiate the im pacts of fire events on changes in model predicted air quality is the di rect decoupled method (DDM), which tracks the sensitivity of an emissions source through all chemical and physical processes in the modeling system (Dunker et al., 2002). Sensitivity coefficients rela ting source emissions to air quality are estimated during the model simula tion and output at the resolution of the host
model.

Some photochemical models have been instru mented with source apportionment, which tracks emissions from specific sources thr ough chemical transformation, transport, and deposition processes to estimate a contribu tion to predicted air quality at downwind receptors (Kwok et al., 2015; Kwok et al., 2013). Source apportionment has been used to
differentiate the contribution from specific sources on model predicted O 3 and PM 2.5 (Baker and Foley, 2011; Baker and Kelly, 2014). The DDM has also been used to
estimate O 3 and PM 2.5 impacts from specific sources (Bak er and Kelly, 2014; Bergin et al., 2008; Kelly et al., 2015) as well as th e simpler brute-force sensitivity approach (Baker and Kelly, 2014; Bergin et al., 2008; Kelly et al., 2015; Zhou et al., 2012). Limited comparison of specific source impacts between models and approaches to differentiate single source impacts (Baker and Kelly, 2014; Kelly et al., 2015) show generally similar downwind spat ial gradients and impacts.

Air agencies should verify the modeled estima tes of fire events with other sources of
information such as satel lite products and ground based m easurements and not use the model as the sole evidence supporting the fire event contribution. Signi ficant variation in
the modeled result from other information sources may indicate that the photochemical model predictions are unreliab le for demonstration purposes.

3.7 Example Conclusion Statement

Air agencies should provide the supporting evidence and analyses identified in Sections 3.1-3.6 of this guidance to document the clear causal relationship between the fire event and the
monitored O 3 exceedance or violation and conclude the analysis with a stat ement similar to the language below:

“Based on the evidence, including comparisons a nd analyses, provided in [section X] of this demonstration, the fire events, which occurred on [dates] in [location] and the monitored O 3 exceedance on [dates/time of data requested for exclusion, or reference to summary table in*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

27 demonstration] were established to have a clear causal relationship. The clear causal relationship
evidence also demonstrates that the event affected air quality at the monitor.



### 4. Caused by Human Activity that is Unlikely to Recur at a Particular
Location or a Natural Event

4.1 Overview and EER Provisions

According to both the CAA and the EER, an exceptional event must be “an event caused by human activity that is unlikely to recur at a particular location or a natural event.” The definition of wildfire in the EER revisions is: “any fi re started by an unplanned ignition caused by lightning; volcanoes; other acts of nature; una uthorized activity; or accidental, human-caused actions; or a prescribed fire that has been declared to be a wild fire.” Fire managers may declare specific prescribed fire projects to be wildfires if the conditions of a prescribed fire develop in a way that the project no longer meets the resource objectives ( e.g., if the fire has escaped secure containment lines along all or part of its boundary).

Natural factors are principally responsible for wi ldfires on wildland (defined as “an area in which development is essentially non-existent, except for roads, railroads, powerlines, and similar transportation facilities. Structur es, if any, are widely scattered.”). Land within national parks, national forests, wilderness area s, state forests, state parks, and state wilderness areas are generally considered wildland. Therefore, the EP A believes that treating all wildfires on wildland
as natural events is consistent with the C AA and the EER. It is expected that minimal documentation will be required to meet the human activ ity that is unlikely to recur at a particular
location or a natural event element for wildfires on wildland.

The EPA will address wildfires on othe r lands on a case-by-case basis.

4.2 Examples of Supporting Documentation

To support this rule element, the air agency shou ld clearly identify the or igin and evolution of
the wildfire event and describe how the bur ned area is a wildland according to the EER
definition.

4.3 Example Conclusion Statement

In addition to the supporting information suggested in Section 4.2, the air agency should include a conclusion statement similar to the language belo w to demonstrate that the wildfire on wildland

was a natural event.

“Based on the documentation provided in [section X] of this submittal, the event qualifies as a wildfire because [lightning, ars on, accidental cam pfire escape, etc. ] caused the unplanned wildfire event. The EPA generally considers the emissions of O 3 precursors from wildfires on wildland to meet the regulatory definition of a natural event at 40 CFR 50.1(k), defined as one “in which human activity plays little or no direct causal role.” This wildfire event occurred on*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

28 wildland and accordingly, [Air Agency Name] has shown that the event is a natural event and may be considered for treatment as an excepti onal event.” [Note: if a prescribed fire was declared to be a wildfire, then the air agen cy should supplement the language above with

additional detail as to the conditi ons of the prescribed fire that led to the fire manager’s decision

that the fire should be treated as a wildfire, for example if the prescribed fire escaped secure containment lines and required suppression along all or part of its boundary or if the prescribed fire escaped as a result of quickly changing w eather and no longer meets the resource objectives ( e.g. , smoke impact, flame height)].



### 5. Not Reasonably Controllable or Preventable

5.1 EER Provisions

According to the CAA and the EER, an exceptional event must be “not reasonably controllable or preventable.” The preamble to the proposed 2016 EER revisions cl arifies that the EPA interprets this requirement to contain two f actors: the event must be both not reasonably controllable and not reasonably preventable at the time the event occurred. This requirement applies to both natural events and events caused by human activities, however it is presumptively
assumed that wildfires on wildla nd will satisfy both factors of the “not reasonably controllable or preventable” element unless evidence in the r ecord clearly demonstrat es otherwise. If a prescribed fire has been declared to be a wildfire, some of the basic smoke management practices that were planned for use for the prescribed fire may continue to be re asonable to apply during the wildfire period.

5.2 Examples of Supporting Documentation

The EER (as revised in 2016) accepts that wi ldfire events on wildland are not generally reasonable to control or prevent. Therefore, a statement that the wildfire event was caused by [lightning], and thus by the term s of the EER, was not reasonably controllable or preventable, should satisfy this rule element.

5.3 Example Conclusion Statement

In addition to the supporting information suggested in Section 5.2, the air agency should include a conclusion statement similar to the language be low to demonstrate why the wildfire event was not reasonably controllab le or preventable.

“Based on the documentation provided in [section X] of this submittal, [lightning] caused the wildfire event on wildland. The [air agency] is no t aware of any evidence clearly demonstrating that prevention or control efforts beyond those actually made would ha ve been reasonable. Therefore, emissions from this wildfire were not reasonably controllab le or preventable.”*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

29 

### 6. Public Comment

6.1 EER Provisions

In addition to providing a conceptual model and evidence to support the EER elements, air agencies “must document [in their exceptional ev ents demonstration] that the public comment process was followed” accord ing to 40 CFR §50.14(c)(3)(v).

6.2 Examples of Supporting Documentation

Air agencies should include in their exceptional events demonstration the details of the public comment process including newspa per listings, website postings, a nd/or places (library, agency office) where the hardcopy was available. The agency should also include comments received and the agency’s responses to comments.

6.3 Example Conclusion Statement

“The [air agency] posted notice of this exceptiona l events demonstration on [date posted] in the following counties/locations: [list counties affect ed and locations poste d]. [Number] public

comments were received and have been included in [Section x] of the demonstration, along with [air agency’s] responses to these comments.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

30 

### Appendix A1. Example Con ceptual Model/Event Summary

The following example of a conceptual mode l/event summary is based on a demonstration prepared by the California Air Resources B oard (CARB) to demonstrate wildfire-influence O 3 exceedances. The EPA has modified the narrative to provide a clear example of the suggested content of a conceptual model.

A. Area Description

The Sacramento federal 1-hour ozone nonattainment area (Sacramento region) consists of Sacramento County, Yolo County, the eastern por tion of Solano County, the western portion of Placer County, the western portion of El Dora do County, and the southern portion of Sutter County ( see Figure 1). The region covers over 5,600 s quare miles, and has a population of over
1.8 million.

The Sacramento region is located in the Cent ral Valley of northern Ca lifornia. The Central Valley is a 500-mile long northwest-southeast oriented valley that is composed of the Sacramento Valley and the San Joaquin Valley ai r basins. Elevations in the Central Valley extend from a few feet above sea level to almost 500 feet ( see Figure 2). This long valley is surrounded by the Coast Range Mountains on the we st, the Cascade Range on the northeast, the Sierra Nevada Mountains on the east, and th e Tehachapi Mountains on the south. The San Francisco Bay Area separates the Coast Range Mount ains into northern and southern ranges. The Coast Range Mountains generally form a topogra phic barrier to air flow between the Pacific Ocean and the Central Valley, with occasional breaks created by low elevation passes and the small gap between the northern and southern rang es in the San Francisco Bay area known as the Carquinez Strait.

The Sacramento Valley’s usual summer daytime circulation pattern is characterized by onshore flow through the Carquinez Strait (which flows from the Bay Area to Sacramento and is known as the sea breeze). Once through the Strait, the wi nd flow divides. A portion of the wind flow turns south, blowing into the San Joaquin Va lley, a portion continues eastward, across the southern Sacramento Valley, and a portion turn s north, blowing into the upper Sacramento Valley. At night, the sea breeze weakens, and th e wind direction in the Sacramento Valley changes. Typical downslope flow, known as nocturn al drainage, brings air from the Coast Range
and Sierra Nevada Mountains into the Sacramen to Valley. With the weakened sea breeze, an eddy circulation pattern forms in the southwest portion of the Sacramento Valley which serves as
a mechanism to recirculate and trap air within the region.

Because of its inland location, the climate of the S acramento region is more extreme than that of more coastal regions, such as the San Francisc o Bay Area. The winters are generally cool and wet, while the summers are hot and dry. Both se asons can experience periods of high pressure and stagnation which are conducive to pollutant buildup. These climate conditions result in seasonal patterns where ozone concentrations are highest during the summer, while PM2.5 concentrations are highest during the winter. The lack of summer time precipitation, coupled with the extent of forested regions which surround the Central Valley, also creates conditions conducive to wildfires during the summer months.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

31 B. Characteristics of Non-Event Ozone Formation

Anthropogenic emissions contributing to ozone fo rmation in the Sacramento Region comprise reactive organic gases (ROG) and oxides of nitrogen (NOx). The main sources of these emissions include mobile sources (cars, trucks , locomotives, off-road equipment) along with stationary and area sources which include i ndustrial processes, consumer products, and pesticides. Mobile source emissions dominate th e anthropogenic emissions, accounting for more than 85 percent of the total NOx inventor y. ROG and NOx emissions have decreased significantly over the past several decades. This reduction directly translates into fewer days
above the former federal 1-hour ozone standa rd. In 1990, ROG and NOx precursor emissions were estimated at 262 and 242 tons per day (t pd), respectively. In 2008, these emissions had decreased almost 50 percent, to 136 tpd of ROG and 167 tpd of NOx. These significant improvements occurred despite increases in population, vehicle activity, and economic development.

The ozone season in the Sacramento region occurs from May through October. Although
exceedances of the 1-hour federal ozone standard are infrequent, they are most likely to occur under certain meteorological condi tions. By evaluating high ozone c oncentrations and associated meteorological conditions in the Sacramento region we developed several rules of thumb to predict when ozone concentrations will be elev ated in Sacramento County (see Appendix Y for details). In general, the synop tic (large-scale) weather conditi ons leading to elevated ozone concentrations occur in the Sacramento region when a ridge of high pr essure is located over California, causing the air to subside, or sink. As the air sinks, it warms, which forms a temperature inversion that stabilizes and dries the atmosphere. This process limits the vertical mixing of boundary layer air, which traps pollu tants near the ground. The process also limits cloud production, which increases ozone photochemi stry. In addition, surface wind flow patterns conducive to high ozone concentrations occur when the thermal surface low is over or just west
of Sacramento. This results in a sea breeze whic h weakens or occurs late in the day. This prevents the dispersion of pollutants a nd leads to high ozone concentrations.

Nighttime drainage flows can bring biogenic emissi ons from the Coast Range and Sierra Nevada Mountains into the Sacramento Valley. During daytime wind flow patterns, anthropogenic precursor emissions in the Bay Area and Sacr amento combine with biogenic emissions to undergo photochemical reactions generating ozone. Due to the general daytime flow pattern from west to east, as well as the time needed for photochemical reactions to occur, the highest concentrations in the Sacramento region gene rally occur in the af ternoon in the downwind, eastern portion of the region, such as Folsom.

C. Wildfire Description

From June 20 to June 22, 2008, over 6000 light ning strikes from a seri es of thunderstorms ignited numerous wildfires througho ut northern and central Californi a. At its peak, what became known as the Northern California Lightning Sieg e (or the Lightning Complex Fires) comprised
thousands of wildfires in 26 counties and sent smoke throughout the western United States. California firefighters were assisted in their efforts to control these blazes by units from throughout the U.S., as well as Australia, Ca nada, Greece, Mexico, and New Zealand. With thousands of individual fires (s ubsequently grouped into fire complexes) in 26 counties, the*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

32 summer of 2008 was one of the most severe wildfi re seasons in California history. Most of these fires were not contained until late-July or earl y-August, with some continuing to burn through October. Vast areas experienced smoke impacts, especially areas in north ern California. Table 3 summarizes the number of wildfires and acreage burned by county from mid-June to mid-July 2008, in the counties surrounding Sacramento. Figur e 3, provides a map of fire locations. A detailed table listing the fires, distance from Folsom, and acreage burned is included in Appendix A. A summary report on these wildfires was prepared by an interagency team of investigators at the request of California Department of Forestry and Fire Protection (CAL Fire), the U.S. Forest Service, Office of Emergency Servi ces, and the National Park Service. 9 The following is an excerpt from that report , “The 2008 Fire Siege”: On June 20th and 21st a series of severe, dry thunderstorms carpeted the state from Big Sur to Yreka with more than 5,000 lightning strikes, and igniting over 2,000 fires. During the following m onths, thirteen firefighters were killed and many others were injured on fires in this si ege. Over 350 structures were destroyed and hundreds of millions of dollars of property and natural resources were damaged. Thousands of people were evacuated and smoke adversely effected air quality over much of the state for weeks. Communications, power delivery, and transporta tion systems were disrupted. Despite the intensive firefighting effort, some fires in remote areas continued to burn throughout the summer. By fall, over 1,200,000 acres had burned.

Air quality in northern California deteriorated because of the smoke. From June 23 through much of July, the Sacramento region was covere d in a thick blanket of smoke. Many of the air monitors recorded extremely high ozone concentra tions, along with hazardous concentrations of particulate matter. The hazardous air quality levels prompted air pollution control and air quality management districts in the Sacramento region to issue air quality advisories and warnings. The wildfires and smoke spread throughout the Sacr amento region and were widely recognized by residents in the region and the public media. Figures 4, 5, and 6 provide satellite maps illustrating the extent of the smoke impacts on June 23, June 27, and July 10, 2008.

2. Conceptual Model of Ozone Formation from 2008 Wildfires

Substantial amounts of NOx and VOCs were gene rated from the 2008 wildfires during late June and early July across a broad area surrounding the Sacramento Valley, corresponding to the 1- hour ozone exceedances at Folsom on June 23, June 27, and July 10, 2008. Surface wind flow conditions on these days were typical for the summertime, including nighttime drainage flow from the Coast Range and Sierra Nevada Mountai ns, coupled with an eddy circulation in the southern Sacramento Valley, followed by the daytime sea breeze. Thes e wind flow patterns transported, and subsequently trapped within the Sacramento regi on, wildfire precursor emissions coming from multiple upwind locations. In addition to surface transport, due to the buoyancy of fire plumes, substantial amounts of precursors were emitted aloft by the wildfires. An increase in the mixed laye r during the morning and early afternoon on each day allowed additional wildfire precursors aloft to reach the surface.

9 California Department of Forestry and Fire Protection, “2008 Fire Si ege” (retrieved April 1, 2011) available at http://www.fire.ca.gov/fire_protection/downl oads/siege/2008/2008FireSiege_full-book_r6.pdf (Multiagency Fire Investigation Report).*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

33 Under typical daytime photochemistry, the incr eased levels of wildfire-related precursor emissions in the Sacramento region resulted in enhanced levels of ozone throughout the region, including Folsom. Although these surface windflo w patterns would also have transported anthropogenic emissions to Folsom, the meteor ological conditions that existed on the three exceedance days were not sufficient to have caused a 1-hour ozone exceedance without the
added burden of the additional wildfire-related precursor em issions. In addition, given the lengthy duration of the fires, by June 27 and Ju ly 10 there were also substantial amounts of
wildfire-related ozone carried over from the da y before the exceedance, further increasing ozone
concentrations.

Although, NO from fires can result in ozone titration very close to the source of a fire, Folsom was sufficiently far enough downwind that a redu ction in ozone concentrations due to this phenomena was unlikely. In addition, while th e increased smoke from the fires may have
reduced the amount of solar inso lation, thereby potentially reduci ng photochemical activity, this was compensated for by the substantially increase d levels of ozone precursors generated by the fires, resulting in a net ozone enhancement.

During this period, there were 15 monitoring si tes operating in the Sacramento nonattainment area, as shown in Figure 7, below. Ozone was dramatically elevated throughout the
nonattainment area and much of northern and cent ral California during the fire period. In the Sacramento nonattainment area, five monitoring s ites recorded ozone con centrations above the
1-hour standard. More detailed information about the exceedances at these sites is shown in Table 4. Section 3 provides a more detailed di scussion of the day-spec ific meteorological conditions that existed on each of the three 1-hour ozone exceedance days included in this request to support the clear causa l connection between the wildfires and the ozone exceedances. In addition, Section 4 provides information to de monstrate that the excee dances of the 1-hour ozone NAAQS at Folsom on each of these days were directly due to the impacts of the wildfire
emissions.

The following figures and tables were included:

*Figure 1. Map of Sacramento Metropol itan non-Attainment Area *Figure 2. Topographic map of Northern California
Table 3. Summary, by county, of wildfires that contributed to the exceedance *Figure 3. Map of wildfires, colored and sized by geographic extent Figure 4. MODIS image of June 23 Figure 5. MODIS image of June 27 Figure 6. MODIS image of July 10 *Figure 7. Map of air quality monitors in the Sacramento area
Table 4. 2008 Sacramento 1-hour ozone non-atta inment days and concentrations *These maps could be combined into one.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

34 

### Appendix A2. Relating Fire Emissions and Downwind Impacts

Kirk Baker, US EP A, OAQPS, AQAD Melinda Beaver, US EPA, OAQPS, AQPD Pat Dolwick, US EPA, OAQPS, AQAD

Summary

To understand general relationships between th e magnitude of fire emissions and potential
downwind O 3 impacts, the EPA conducted an assessment of fire case studies. These case studies were drawn from peer-reviewed literature, EPA- approved exceptional events demonstrations for
fires that influenced O 3 concentrations, and EPA-performe d photochemical modeling studies. The dependence of O 3 impacts on fire emissions and distan ce from the fire across these case studies has been compared to determine fire ch aracteristics that are expected to lead to meaningful O 3 impacts.

Background

Fires can impact O 3 concentrations by emitting known O 3 precursors including NO X and VOCs. These precursor emissions can generate O 3 within the fire plume or can mix with emissions from other sources to generate O 3 (Jaffe and Wigder, 2012). Also, in some situations, including near fires, reduced O 3 concentrations have been observed and attributed to O 3 titration by enhanced
NO concentrations and reduced solar radiation av ailable to drive photochemical reactions (Jaffe et al., 2008; Yokelson et al, 2003). The magnitude and ratios of emissions from fires vary greatly depending on fire size, fuel ch aracteristics, and meteorological conditions (Akagi et al., 2012). As a result of variable emissions, radiative impacts, and non-linear O 3 production chemistry, the

O 3 production from fires is very complex, highly va riable, and often difficult to predict (Jaffe and Wigder, 2012). Understa nding and predicting O 3 formation from fires remains an active area
of research.

Despite the complexities in predicting O 3 formation from fire emissions, several studies have
found enhancements in O 3 concentrations attributable to fire impacts. For example, Pfister et al. analyzed surface O 3 data during a high fire year in Calif ornia (2007) with modeled fire impacts
and found 8-hour O 3 concentrations were approximat ely 10 ppb higher when the modeled impacts were high (Pfister et al., 2008). Jaffe et al. analyzed thr ee specific fire periods in the western US during 2008 and 2012, and compared surface O 3 concentrations with two different
modeled estimates of fire contributions to O 3 concentrations to find enhancements in O 3 when fire impacts were predicted to be high (Jaffe et al., 2013).

Previously Approved Fire-Impacted O 3 Exceptional Events Demonstrations

The EPA’s EER (CFR parts 50 and 51 codified at 50.1, 50.14 and 51.930) allows air agencies to exclude air quality data that has been influen ced by an exceptional event, once the agency has submitted and the EPA has approved a demonstration satisfying the EER elements. Many events, including fires, qualify for consideration under the EER.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

35 Between 2010 and August 2015, the EPA approved two exceptional events demonstrations that
linked monitored O 3 exceedances to fire impacts. The fi rst was approved in 2011. In this case,
the EPA concurred on three exceedances of the 1-hour O 3 NAAQS near Sacramento, California in 2008 due to a series of lightning-initiated wi ldfires throughout norther n California. The second demonstration for fire impact on O 3 was approved in 2012. In this case, the EPA concurred with the exclusion of eight MDA8 exceedances durin g April 2011 in Kansas due to impacts from prescribed fires and wildfires. Both of these demonstrations are available at http://www2.epa.gov/air-quality-analysis/ exceptional-events-submissions-table

.

Assessments of Q/D Relationsh ips from Previously Approved Demonstrations and Relevant
Peer-Reviewed Literature

At least one air quali ty related program ( i.e ., determining impacts at Class I areas) uses an emissions divided by distance (Q/D) key factor as a screening tool . The EPA believes that it is appropriate to use a similar appr oach, along with additional informa tion about the fire event, to determine whether a simpler and less resour ce-consuming exceptional events demonstration provides sufficient evidence to satisfy the clear ca usal relationship criteria of the EER for fire O 3 demonstrations.

To determine whether a relationship existed be tween approved demonstrations and Q/D values, the EPA estimated Q/D values from previously approved, fire-related O 3 exceptional events
demonstrations. The EPA also included in this comparison, the results from one peer-reviewed publication, which included sufficient detail for a similar analysis (Jaffe et al., 2013). The EPA used daily fire emissions estimates from the 2008 ( ftp://ftp.epa.gov/EmisInventory/fires/ ) and 2011 ( http://www3.epa.gov/ttnchie 1/net/2011inventory.html ) NEIs to estimate Q from fires impacting the O 3 monitors. For consistency, the EPA also used NEI-based estimates for the Jaffe et al. fires. In determining the appropriate emi ssions to use in this assessment, the EPA summed

NO X and rVOC because both are precursors for O 3 formation. The NEI reports total organic gas (TOG) so the reactive fraction of these emissi ons (rVOC) was estimated by applying the fraction of reactive gas to total orga nic gas based on speciation prof iles for fires provided by the
SPECIATE database. A factor of 0.6 was selected based on the SPECIATE database profile used by CMAQ for fires (speciation profile number 5560). 10

Fire events included in the estimated Q values were based on the sum of emissions from only some of the events listed by the relevant air agencies in the demons trations because the demonstrations included fires that may not di rectly impact the monitor. The CARB exceptional
events demonstration identified all wildfires bur ning in California during the time period of the

O 3 exceedances, and a subset of those (within state of CA, with latitude no rth of 37N (~north of Santa Cruz) and longitude west of -119W (~west of Mono Lake) were used. The Jaffe et al., article assessed the impact of the 2008 Nort hern California fires in Reno, NV (versus at California monitors). The same fire subset was us ed for the Jaffe et al. analysis as for the CARB demonstration. For the Kansas Department of Health and Environment demonstration, the EPA
included all fire events labeled as “Flint Hills” in the NEI emissions file. Emissions totals within these bounds on the day of the O 3 exceedances were used to calc ulate emissions totals, Q. The

10 SPECIATE is the EPA’s repository of volatile organic gas and particulate matter speciation profiles of air pollution sources. Available at http://www3.epa.gov/ttnch ie1/software/speciate/

.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

36 uncertainty in Q was taken to be approximate ly ±25% and was taken from the differences
between the NO X estimates from the NEI and the NOx es timates from the Fire Inventory from NCAR (FINN) emissions inventories of all fires (Wiedinmyer et al., 2011).

O 3 impacts were determined differently by th e CARB demonstration, the KDHE demonstration,
and the Jaffe et al. article. The CARB demonstr ation used a statistical regression model to
estimate fire contributions to O 3 concentrations. The KDHE demonstration used both a matching day analysis and photochemical modeling to estimate O 3 impacts. The Jaffe et al. paper used both photochemical and statistical residual modeling to estimate O 3 impacts.

A summary of the fire impacts on O 3 compared with Q/D for the approved demonstrations and the Jaffe et al. article is shown in Figure A2 -1. Distance (km) between the fire and the O 3 monitors was calculated based on an average fi re location determined with an emissionsweighted fire center. The uncertainty range in D was determined by using the maximum distance
between the monitor and a fire event (within the subset gi ven above) on the day of the exceedance. The range shown for the CARB O 3 impacts reflects the uncertainty analysis included in the demonstration. The ranges included for O 3 impacts estimated by the KDHE demonstration and the Jaffe et al. paper represent the range in estimates of O 3 impacts determined by the two different methods used in each case.

Modeling Studies of Wildfire Impacts on O 3

Some uncertainty exists in the magnit ude of emissions estimates, VOC and PM 2.5 speciation of emissions, downwind transport, chemical reacti ons in fire plumes, and representation of important physical processes like reduced photolys is due to smoke. However, the emissions used as input to air quality models can be paired with estimated downwind O 3 contribution to assess screening level relationships between precursor emissions a nd downwind impact. Constructing these relationships is useful for planning purposes and making preliminary determinations about
whether fires with emissions of a certain amount and distance away ma y impact a monitor and warrant further investigation for fire contribu tion using additional corr oborative information.

The entire year of 2011 was applie d using the CMAQ version 5.0.2 model ( www.cmascenter.org ). Meteorological input was genera ted using version 3.4.1 of the WRF prognostic meteorological model (Skamarock et al., 2008). Both modeling systems were applied using the same grid projection and model domain covering the continental United States with 12 km sized grid cells. Contributions from four sp ecific fire events were tracked using source apportionment approaches. Source apportionmen t tracks primarily emitted and precursor emissions from specific fire events through the m odel’s chemical and physic al processes to track contribution to primary and secondarily formed pollutants. The integrated source apportionment approach has been implemented in CMAQ for O 3 (Kwok et al., 2015) and PM 2.5 (Kwok et al., 2013) and was used in this analysis to track th e contribution from each fire event. CMAQ with source apportionment was applied for four diffe rent multi-day fire events in 2011: Wallow, Waterhole, Big Hill, and Flint Hills. The days in cluded in each model simulation for each fire event and the daily total fire event emission estimates are shown in Table A2-1. Emissionsweighted fire event locations are shown in Ta ble A2-2. All the emissions from each multi-day fire were tracked as a single source, so it is not possible to determine from the results how a single day of a particular multi-day fire event emissions affects a single day of O 3 concentrations.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

37 For example, O 3 effects on the third day of a fire may be a contribution of direct effects from a same day plume and effects from recirculated VOC, NOx and O 3 from earlier days.

Wildfire and prescribed fire emissions were included when and where these emissions occur within the modeling domain. These emissions are based on the latest version of the SMARTFIRE system ( http://www.airfire.org/smartfire/ ). Detailed information about how the EPA develops wildland fire inventories can be found in the 2011 NEI Technical Support Document (U.S. Environmental Protection Agency, 2014). This approach relies on a
combination of satellite detection of fires me rged with on-the-ground observational data where
available. Ground-based observations and local fuel information are used whenever possible as these factors can have a large impact on th e emissions. CMAQ currently uses one single speciation profile (5560; Table A2 -3) to speciate TOG fire em issions into specific compounds ( e.g ., toluene, benzene, etc.) that are subsequen tly used in the gas phase chemical mechanism within CMAQ. Similarly, a single profile is used to map total PM 2.5 emissions from fires to specific compounds ( e.g ., elemental carbon, organic carbon, et c.). Daily total emissions for each
fire event tracked for O 3 contribution are shown in Tabl e A2-1. The EPA also conducted a sensitivity analysis including reducing each fire ’s emissions to half the original emissions.

Figure A2-2 shows maximum hourly (across all modeled days of the event) source apportionment based O 3 impacts from the fire events tr acked in this assessment. Fire NO X emissions tend to contribute more to O 3 formation than fire VOC emissions, on a per fire comparison basis, for the fire events in the we stern United States where biogenic VOC is often abundant (especially near these pa rticular fire events). The str onger effect from NOx emissions compared to VOC emissions on a per ton basis (not shown) is even more pronounced, given the tonnage values in Table A2-1. The NO X contribution could be favored in the model if O 3 formation was NO X limited even when the contributing VOC was also from the same fire event.
The fire event modeled in Kansas illustrates that VOC emissions from fires can also be important, especially when other VOC sources are less abundant.

Figure A2-3 depicts downwind O 3 and CO impacts. This figure also shows Q/D for these events and forward HYSPLIT trajectory endpoints (fro m each day included in Table A2-1) from release out to 48 hours. This figure clearly shows th e importance of pairing information about the trajectory of fire emissions in combination with simple metrics of impact such as Q/D. The Wallow fire event had the most consistent trajecto ries across the days of the event. For the other fire events, wind direct ions on different days differed considerably.

Maximum hourly fire impacts on O 3 (that were greater than 1.0 ppb) and the corresponding distance of the grid cell where the maximum impact occurred from the emissions-weighted average location of the fire ev ent are shown in Figure A2-4. Th e colored box represents the 25 th

75 th percentiles of th e distribution of O 3 impacts larger than 1.0 ppb, and the solid line within the
colored box indicates the median of the distribution. Impacts onl y up to 1000 km (for Wallow, Flint Hills, and Waterhole) a nd 550 km (for Waterhole and Big Hill) are shown since the magnitude of the O 3 impacts decrease at increa sed distances. The maximum O 3 impacts tend to be highest in closer proximity to the event a nd decrease as distance from the event increases (Figure A2-4). When these impacts are normaliz ed by the sum of NOx+rVOC emissions for the event day with the highest emissions during the period modeled (Figure A2-5), the magnitude of

O 3 impacts varies over the range of Q/D values, with larger O 3 impacts occurring at higher Q/D*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

38 values. The truncation of distances used in Figure A2-4 leads to the absence of O 3 impacts at low Q/D values ( e.g., ~20 for the Wallow Fire) in Figure A2-5.

The results shown in Figure A2-5 help determine the appropriateness of using the Q/D approach as one key factor in a simpler and less resour ce-consuming exceptional events demonstrations for certain fire events ( i.e. , Tier 2). In the figure for each mo deled fire event, modeled maximum

O 3 impacts are shown for the first two days, excep t for the Big Hill Fire where the entire, three day event is shown. Each data point represents the maximum, hourly O 3 impact (over 1 ppb) that occurred in a grid cell during the first 48 hours of the event. In general, higher O 3 impacts are predicted at larger Q/D values. Comparisons across the four fire events modeled here indicate more and larger O 3 impacts at high Q/D values from the fires with the highest emissions (Wallow and Flint Hills) versus the smaller, lowe r emissions fires (Big Hill and Waterhole). When Q/D values from a fire event are paired with both elevated monitored O 3 concentrations ( i.e ., Tier 2 key factor #2) and evidence (e.g., HYSPL IT trajectory or other analyses identified in sections 3.5.2 and 3.5.3) linking the a ffected monitor to the location(s) of the subject fire(s), the EPA believes that the Q/D relationship can be used to indicate when large O 3 impacts are expected to occur.

To examine the utility of the Q/D metric, Q/D was calculated for all fires in the National Emission Inventory for the years 2008 through 2013 to provide an aggregate context for areas and times where fires may be large contributors to elevated air quality. Figures A2-6 through A2- 8 show the count of days with NO X +rVOC Q/D values greater than 50, 100, and 200 for 2008 through 2013. These figures illustrate how the fire events modeled for this assessment from 2011 compare to other fires that year and to fires fr om other recent years where data are available.
These results can be used to i nvestigate how many days and areas would meet various thresholds for the Q/D key factor.

Conclusions

The fire event impacts estimated with the photochemical model CMAQ suggest both NO X and
VOC emissions from fire events can lead to downwind O 3 formation and the importance of these precursors varies among fires, most likely due to the surrounding environm ent’s availability of

NO X and VOC emissions. Since information about the surrounding environment may not always be practically available, the approach for estima ting fire impacts should be inclusive of both NO X and reactive VOC emissions.

The downwind O 3 contribution from these fire events is gr eatest in the proximity of the fire and tends to gradually decrease as distance from th e source increases. The sp atial plots of downwind

O 3 impacts show that the impacts occur in the dir ection of air mass movement from the fire event to specific places downwind. As indicated abov e, tiering approaches that do not explicitly account for pollutant transport ( e.g ., Q/D) should be accompanied with information about pollutant transport from another source such as HYSPLIT trajectories to better spatially represent the downwind impacts.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

39 Acknowledgements

This Appendix was in part supported by contri bution from Venkatesh Rao, Alison Eyth, Alexis Zubrow, Allan Beidler, James Beidler, Chris Allen, Lara Reynolds, and Chris Misenis.

References for Appendix A2

Akagi, S., Craven, J., Taylor, J., McMeeking, G., Yokelson, R., Burling, I., Urbanski, S., Wold, C., Seinfeld, J., Coe, H., 2012. Evolutio n of trace gases and particles emitted by a chaparral fire in California. Atmospheric Chemistry and Physics 12, 1397-1421.

Jaffe, D.A., Wigder, N., Downey, N., Pfister, G., Boyn ard, A., Reid, S.B., 2013. Impact of wildfires on ozone exceptional events in the western US. Envi ronmental science & technology 47, 11065-11072.

Jaffe, D.A., Wigder, N.L., 2012. Ozone production fr om wildfires: A critical review. Atmospheric Environment 51, 1-10.

Kwok, R., Baker, K., Napelenok, S., Tonnesen, G., 2 015. Photochemical grid model implementation of VOC, NO x, and O 3 source apportionment. Ge oscientific Model Development 8, 99-114.

Kwok, R., Napelenok, S., Baker, K., 2013. Implementation and evaluation of PM 2.5 source contribution analysis in a photochemical model. Atmospheric Environment 80, 398-407.

Pfister, G., Wiedinmyer, C., Emmons, L., 2008. Im pacts of the fall 2007 California wildfires on surface ozone: Integrating local observations with global m odel simulations. Geophysical Research Letters 35.

Skamarock, W.C., Klemp, J.B., Dudhia, J., Gill, D. O., Barker, D.M., Duda, M.G., Huang, X., Wang, W., Powers, J.G., 2008. A description of the Advanced Reserch WRF version 3. NCAR Technical Note
NCAR/TN-475+STR.

U.S. Environmental Protection Agency, 2014. 2011 Na tional Emissions Inventor y, version 1 Technical Support Document. http://www3.epa.gov/ttn/chief/net/2011 nei/2011_nei_tsdv1_dr aft2_june2014.pdf.

Wiedinmyer, C., Akagi, S., Yokelson, R.J., Emmons, L., Al-Saadi, J., Orlando, J., Soja, A., 2011. The Fire INventory from NCAR (FINN): A high resolution global model to estimate the emissions from open burning. Geoscientific Model Development 4, 625.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

40 Table A2-1. Daily and emissions for each trac ked fire event in 2011. rVOC is the sum of all VOC excluding methane and non-reactive species.

Fire Event Month-Day CO NOX rVOC NOX+rVOC
Waterhole 822 9,441 96 1,331 1,427 Waterhole 823 17,652 171 2,487 2,658 Waterhole 824 38,086 408 5,373 5,780

Waterhole 825 637 6 90 96

Waterhole 826 34 1 5 6

Big Hill 814 243 7 35 42 Big Hill 815 3,248 92 468 560 Big Hill 816 189 5 27 33

Flint Hills 401 30,675 867 4,417 5,285 Flint Hills 402 51,555 1,413 7,417 8,830 Flint Hills 403 14,526 383 2,087 2,470 Flint Hills 404 3,744 106 539 646 Flint Hills 405 20,233 564 2,912 3,477 Flint Hills 406 78,622 2,218 11,321 13,539 Flint Hills 407 9,719 263 1,398 1,661 Flint Hills 408 59,020 1,584 8,485 10,070 Flint Hills 409 60,294 1,656 8,675 10,331 Flint Hills 410 9,194 257 1,324 1,580 Flint Hills 411 57,428 1,540 8,256 9,796 Flint Hills 412 105,636 2,950 15,206 18,157 Flint Hills 413 60,484 1,670 8,704 10,373 Flint Hills 414 7,874 215 1,133 1,348

Flint Hills 415 95 3 14 16

Wallow 604 115,438 1,516 16,331 17,847 Wallow 605 49,951 697 7,074 7,771 Wallow 606 113,160 1,509 16,013 17,522 Wallow 607 53,030 705 7,504 8,209 Wallow 608 131,675 1,774 18,636 20,409 Wallow 609 59,155 839 8,379 9,218 Wallow 610 52,127 736 7,383 8,119*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

41 Table A2-2. Emissions weighted fire event locations.

Fire Event Latitude Longitude

Waterhole 45.6141 -106.7889 Big Hill 42.5673 -115.8093

Flint Hills 37.9466 -96.3543

Wallow 33.8174 -109.3272

Table A2-3. Speciation profile (5560) used to map TOG emissions to specific lumped compound groups for photochem ical model application.

Profile Inventory Model Fraction

5560 TOG UNR 0.22

5560 TOG PAR 0.18

5560 TOG CH4 0.18

5560 TOG FORM 0.08

5560 TOG MEOH 0.08

5560 TOG OLE 0.07

5560 TOG ALD2 0.05

5560 TOG ETH 0.04

5560 TOG TOL 0.03

5560 TOG ALDX 0.02

5560 TOG ETHA 0.02

5560 TOG BENZENE 0.02

5560 TOG TERP 0.01

5560 TOG XYL 0.01

5560 TOG IOLE 0.00

5560 TOG ISOP 0.00

5560 TOG ETOH 0.00*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

42 Figure A2-1. Summary of O 3 impacts versus Q/D rel ationships for approved demonstrations (CARB_Folsom_2008 and KD HE_FlintHills_2011) and impacts reported by Jaffe and Wigder (2012). No results from the EPA’s photochemical modeling are shown in this Figure.

0 10 20 30 40 50 60 70 80 90

0 50 100 150 200 250 300 350 400 450deltaO3(ppb)

Q (NOx+rVOC, tpd) / D (km) CARB_Folsom_2008 KDHE_FlintHills_2011 Jaffe_Reno_2008*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

43 Figure A2-2. Event maximum 1-hour O 3 (ppb) impacts (left panels). The percent
contribution from fire event NO X emissions to event maximum 1-hour O 3 impacts shown at right. The percent contribution plots show that both NO X and VOC emissions from fires
can contribute to downwind O 3 formation.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

44 Figure A2-3. Event maximum 1-hour CO (left panels), O 3 (second to left panels), Q/D (second to right panels), and forward trajectories (right panels) shown for multiple fire events. Q/D is based on daily maximum NOX+ rVOC emissions from the fire event during the period modeled. Forward trajectories are shaded by hours from release with warm colors (red and orange) representing hours du ring the first day and cooler colors the 2 nd day (24 to 48 hours) from release.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

45 Figure A2-4. Distribution of hourly O 3 impacts from fire events by distance from the
location of the fire event.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

46 Figure A2-5. Hourly maximum O 3 impacts from the first two d ays of each fire event (Table A2-1) shown by Q/D. O 3 impacts only up to 1000 km from the fire have been included in this analysis.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

47 Figure A2-6. Count of days with NO X +rVOC Q/D > 50 for 2008 th rough 2013. Note scale has been capped at 10 to more easily distin guish the values below 10. Red may actually indicate 10 or greater than 10.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

48 Figure A2-7. Count of days with NO X +rVOC Q/D > 100 for 2008 through 2013. Note scale has been capped at 10 to more easily distin guish the values below 10. Red may actually indicate 10 or greater than 10.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

49 Figure A2-8. Count of days with NO X +rVOC Q/D > 200 for 2008 through 2013. Note scale has been capped at 10 to more easily distin guish the values below 10. Red may actually indicate 10 or greater than 10.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

50 

### Appendix A3. Interpreting HYSPLIT Results

A HYSPLIT backward trajectory, the most comm on trajectory used in assessments associated with determining source areas, is usually depicted on a standard map as a single line extending in two dimensional (x,y) space from a starting point , regressing backward in time as the line extends from the starting point. An individual trajectory can have onl y one starting height; HYSPLIT can plot trajectories of different starting hei ghts at the same latitude/longitude starting point on the same map, automatically using differe nt colors for the different starting heights.
HYSPLIT will also include a vertical plot of the trajectories in time, with colors corresponding to the same trajectory in the (x,y) plot. Diurnal mixing height da ta on flagged days should be considered in setting up the star ting point matrix. Caution is need ed, because this display can be easily misinterpreted as having finer accu racy than the underlying model and data.

It is important to observe the overall size of th e plot, its width and lengt h in kilometers, while considering the size of an individu al grid cell in the input meteor ological data set. These input grid cells are usually 40 km in width and lengt h, so the total area of a trajectory plot may sometimes represent only a few meteorological grid cells. It is also im portant to understand the trajectory line itself. The line thickness is predet ermined as a user option, so it does not imply coverage other than to represent the centerline of an air parcel’s motion calculated to arrive at the starting location at the starting time. The range of the width and the height of plume can vary significantly and are not normally part of the information output but clearly can lead to uncertainty in source strength at the centerline. Un certainties are clearly present in these results, and these uncertainties can be thought to be a ra nge on either side of th e center line in which the air parcel may be found. Further back in time along the trajectory path, that range may be assumed to increase. In other words, one s hould avoid concluding a region is not along a trajectory’s path if that trajectory missed the region by a relatively small distance.

Operating HYSPLIT

Detailed information for downloading, installi ng, and operating HYSPLIT can be found at these
websites: http://ready.arl.noaa.gov/HYSPLIT.php http://www.arl.noaa.gov/documents/reports/hysplit_user_guide.pdf http://www.arl.noaa.gov/docum ents/reports/arl-224.pdf

HYSPLIT’s many setup options allow great flexibili ty and versatility. However, careful selection and recording of these options is recommended to provide reviewers the ability to reproduce the model results. The following paragraphs describe the options that should be recorded, at a minimum, to reproduce a HYSPLIT model run.

Backward Versus Forward Trajectories . Forward and backward HYSPLIT trajectories use the same scientific treatment and processing. These tr ajectories only differ in the location of the discrete point of origin (forward) or destination (backward). For an alyses to assess the potential impact of a source area such as a wildfire on a disc rete point of destination such as an air quality monitor, a backward trajectory is more easily interpretable.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

51 Model Version. If the HYSPLIT trajector y is produced via the NOAA Air Resources Laboratory (ARL) website ( http://ready.arl.noaa .gov/HYSPLIT_traj.php ), note the “Modified:” date in the lower-left corner of the webpage, as well as the date th e trajectory was produced. If the trajectory is produced using a stand-al one version of HYSPLIT, note the release date , which will be displayed after exiting the main GUI screen.

Basic Trajectory Information. Note the starting time (YY MM DD HR), the duration of the trajectory in hours, and whethe r the trajectory is backward or forward. Note the latitude and longitude , as well as the starting height , for each starting location . Starting hei ght is given by default in meters above ground le vel (AGL) unless another option is selected. Star ting heights are typically no less than 100 meters AGL to avoid direct interference of terrain, and are typically no greater than 1500 meters AGL to confine the air parcel within the mixed layer. Some trajectories can escape the mixed layer, and this result would be considered in the interpretation. Starting height and starting location will identify the three-dimensional location of the trajectory’s latest endpoint in time if a backward trajectory is selected ( i.e ., the start of a trajectory going backward in time).

Input Meteorological Data Set . Note the input meteorological data set used in the HYSPLIT
model run. The original file name provides sufficient information to identify the data set. Meteorological data fields to run the mode l are already available for access through the HYSPLIT menu system, or by direct FTP from ARL. The ARL web server contains several meteorological model data sets already converted into a HYSPLIT compatible format in the public directories. Direct access via FTP to thes e data files is built into HYSPLIT’s graphical
user interface. The data files are automatica lly updated on the server with each new forecast cycle. Only an email address is required for th e password to access the server. The ARL analysis data archive consists of output from the Gl obal Data Analysis System (GDAS) and the NAM Data Analysis System (NDAS - previously ca lled EDAS) covering much of North America.
Both data archives are available from 1997 in semi-monthly files (SM). The EDAS was saved at 80 km resolution every 3-hours through 2003, and th en at 40 km resolution starting in 2004. Detailed information on all meteorological data available for use in HYSPLIT can be found in
the HYSPLIT4 Users Guide ( http://www.arl.noaa.gov/documents /reports/hysplit_user_guide.pdf ).

If trajectories are used in areas of highly complex terrain and source-receptor relationships are relatively close (10’s – 100 km), the resolution of some of the routinely used meteorological databases for HYSPLIT may not adequately captu re the meteorological conditions that govern source-receptor relationships for a particular event. Careful cons ideration should be used when selecting meteorological databases, as these will largely determine the accuracy of the trajectory for a given event. More information on meteor ological databases and their applicability to
HYSPLIT can be found at https://ready.arl.noaa.gov/archives.php

.

Vertical Motion Options. HYSPLIT can employ one of 5 different methods for computing
vertical motion . A sixth method is to accept the vertical motion values contained within the input meteorological data set, effectively using the vertical motion method used by the meteorological
model that created the data set. Note which meth od was selected as well as the value chosen for the top of the model , in meters AGL.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

52 Trajectory Display Options. The HYSPLIT trajectory model genera tes a text output file of endpoint positions. The end-point pos ition file is processed by an other HYSPLIT module to produce a Postscript display file or output files in other display form ats. Some parameters, such as map projection and size, can be automatically comp uted based on the location and length of the trajectory, or they can be manually set by the us er. While these display options do not directly affect the trajectory information itself, noting these options will eliminate possible misinterpretation of identical trajectories becau se of differing display options. An important display option is the choice of vertical coordinate, usually set to meters AGL for these

assessments.*** E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review *** EO12866_Supplemental Exceptional Events Im plementation Guidance_2060-ZA21_Draft Wildfire/Ozone Guidance_20151028

53 

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Bytnerowicz, A., Burley, J., Cisneros, R., Preisler, H., Schilling, S., Schweizer, D., Ray, J., Dulen, D., Beck, C., Auble, B., 2013. Surface ozone at the Dev ils Postpile National Monument receptor site during low and high wildland fire years. Atmospheric Environment, 65, 129-141.

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54 Fann, N., Fulcher, C.M., Baker, K., 2013. The R ecent and Future Health Burden of Air Pollution Apportioned Across US Sectors. Environmental Science & Technology, 47, 3580-3589.

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55 Watson, J., Chow, J., Houck, J., 2001. PM 2.5 chemical source profiles for vehicle exhaust, vegetative burning, geological material, and coal burning in Northwestern Colorado during 1995. Chemosphere, 43,

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