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WESTAR, 3 Caliente Road #8, Santa Fe, NM (505) 930-5197

WESTERN STATES AIR RESOURCES COUNCIL

May 11, 2016 

U.S. Environmental Protection Agency

EPA Docket Center (EPA/DC)

1200 Pennsylvania Avenue N. W.

Washington, D.C. 20760

Docket ID No: EPA-HQ-OAR-2016-0097

RE: Western States Responses Regarding Background Ozone and Recommendations for 

Additional Efforts in the Western U.S.

The Western States Air Resources (WESTAR) Council, an association of 15 western state air 

quality managers, appreciates the opportunity to share our input on aspects of background ozone 

(O3) that are relevant to attaining the 2015 NAAQS. WESTAR has several recommendations to 

share with EPA based on our review of the Implementation of the 2015 Primary Ozone NAAQS: 

Issues Associated with Background Ozone White Paper for Discussion (White Paper). In 

general, western states are concerned with the characterization of U.S. background (USB) O3 and 

the limited CAA regulatory relief mechanisms offered through exceptional event exclusions or 

area designations. 

WESTAR herein offers suggestions for EPA’s consideration to strengthen the assessment of 

USB O3 in the western U.S. As part of the recommendations, WESTAR offers its services in 

engaging states, EPA, and other stakeholders cooperatively in some of these activities. A 

summary of WESTAR’s recommendations is provided below. A more detailed discussion of 

these recommendations and WESTAR’s concerns is included in WESTAR’s responses to 

questions posed in the White Paper, as found in the Attachment.

• EPA, in coordination with western states, should continue its efforts to characterize USB 

O3 in the West. A supplement to the White Paper that specifically addresses high USB 

O3 concentrations at high-elevation, rural monitors across the western U.S. that don’t 

respond to regional precursor reductions, would provide a better common understanding 

of this situation. Guidance on evaluating these concentrations will be beneficial to all 

affected states, as well as to the understanding of interstate transport of O3 in general.

• To clarify the relationship between USB O3 estimates and events that quality for relief 

through the Exceptional Events Rule, western states would benefit from a clear, explicit 

statement from EPA regarding the role of models and other data in determining USB O3.
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WESTAR, 3 Caliente Road #8, Santa Fe, NM (505) 930-5197

• Further classification of the components of USB O3 should be addressed within the 

definition of USB O3 and modeling characterization of USB should identify the 

contribution of each component.

• The needs of EPA and co-regulators for estimating USB O3 for air quality planning 

purposes should be identified in order to provide tools and timely “best available” 

estimates under the CAA. Assessment and re-assessment of USB O3 in the western U.S. 

should be routine and ongoing.

• A joint EPA/co-regulator effort should be initiated that builds on existing modeling 

expertise to refine USB O3 estimates. This effort could estimate USB O3 levels as 8-hour 

averages so they are consistent with how the O3 NAAQS is characterized and 

implemented. 

• The influence on USB O3 from site elevation, long-term increases in tropospheric O3

concentrations, stratospheric intrusion/long-range transport events, and climatic 

variability (El Niño/La Niña) should be better characterized.

• Boundary conditions from global models that inform U.S. regional models used for 

estimating O3 should be further evaluated. This could include:

o Identification of the criteria for determining the “best” global model for providing 

boundary conditions to U.S. regional models.

o Determination of the potential improvements to U.S. regional model performance 

from the “most robust” and “enhanced global model(s).” This effort could 

increase confidence in modeled estimates of USB O3.

• EPA should provide guidance to support and inform Section 179B of the CAA so that 

states understand how to create a successful international transport area demonstration.

• Two alternative mechanisms to address USB O3 should be evaluated. These include: 1) 

assessing the principal contributor concept proposed by BP America; and, 2) considering 

a more robust natural events policy for USB O3.

• In its Integrated Review Plan for a future O3 NAAQS, EPA should include the questions 

raised in its White Paper, as well as those issues raised in these comments. In addition, 

the upcoming Clean Air Scientific Advisory Committee O3 NAAQS Review Panel 

should include scientists who are actively engaged in background O3 research and 

understand the policy implications of background O3 on state implementation planning.
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WESTAR, 3 Caliente Road #8, Santa Fe, NM (505) 930-5197

Thank you for considering WESTAR’s recommendations and our responses to the White Paper 

questions. We hope to continue the important conversations and working relationship with EPA 

to address USB O3 in the western U.S. We look forward to working with EPA to better 

characterize USB O3 and identify additional CAA mechanisms to address USB.

Sincerely,

Terry O’Clair, President

WESTAR Council

Attachment
1

Attachment

WESTAR Responses to Questions Proposed by EPA in the White Paper1

A. Has the EPA properly characterized the current best estimates of background O3? Are 

there additional existing data analyses or modeling simulations that need to be folded into 

the assessment?

No, EPA has acknowledged that background O3 is not currently well characterized. In the White 

Paper, EPA provided a national overview of USB O3. However, that does not imply that the 

conclusions apply equally to all states and monitors in U.S. Moreover, the western states are 

unconvinced that USB O3 will not prevent attainment everywhere in U.S., particularly in the 

inter-mountain western U.S. There is large variability in the influence of USB O3 across the U.S.

EPA noted that modeled USB O3 estimates reviewed in the Integrated Science Assessment (ISA)

“compare reasonably,” post-ISA review of modeled USB estimates “show greater variability,”

and EPA modeling is “roughly consistent with previous estimation exercises.”

2 In the intermountain west, boundary condition contributions often exceed 50 percent.

3 EPA suggests that

“there may also be a limited number of rural areas where USB O3 is appreciable.”

4

 However, the 

White Paper5 lists seven counties in the inter-mountain western U.S. outside California with 

2012-2014 Design Values (DV) greater than 70 ppb and fractions of 2017 DVs from manmade 

U.S. sources less than or equal to 15 percent. All of these counties have fractions of 2017 DV 

from manmade in-state sources less than 10 percent and five additional counties have 

contributions from in-state sources less than or equal to 10 percent. These twelve counties with 

less than or equal to 10 percent contribution from in-state sources are located across six states 

encompassing much of the inter-mountain western U.S. 

USB O3 is enhanced by naturally occurring stratospheric intrusions (SI) and long-range transport 

(LRT) of international emissions, both natural and anthropogenic. The results of the Las Vegas 

Ozone Study6 suggest contributions resulting from these events are much more frequent than 

EPA has acknowledged, but as EPA states, models “are not capable of precise background 

estimates on a daily level.”

7

 In many cases, the high USB O3 in the western U.S. leaves little 

margin for contributions resulting from manmade U.S. sources or manmade in-state sources 

without exceeding the 2015 O3 NAAQS. The potential stigma associated with having large areas 

of the inter-mountain western U.S. designated as nonattainment will stifle potential economic 

																																																												 1

U.S.	EPA,	Implementation	of	the	2015	Primary	Ozone	NAAQS:	Issues	Associated	with	Background	Ozone	White	

Paper	for	Discussion,	referred	to	as	White	Paper	throughout	this	document 2 Ibid.	at	4	– 5. 3 Ibid.	at	24,	Table	2c. 4

Ibid.	at	7.		

5 Ibid.	at	24,	Table	2c.

6 Langford,	A.O.,	et	al,	2015.		An	overview	of	the	2013	Las	Vegas	Ozone	Study	(LVOS):	Impact	of	stratospheric	

intrusions	and	long-range	transport	on	surface	air	quality.	Atmos.	Environ,	

http//dx.doi.org/10.1016/atmosenv.2014.08.040. 7

White	Paper,	supra	note	1,	at	4.
2

growth and presents immense interstate planning challenges towards meaningful implementation 

of CAA requirements. 

States and locals will address the requirements of CAA § 110 in their 2015 O3 NAAQS

infrastructure state implementation plans (i-SIPs) due October, 2018 and attainment plans due in 

December, 2020. EPA modeling will be critical to better characterize USB O3 and inform 

planning for these SIPs. Robust model performance evaluations and identification of the 

strengths, as well as limitations of model performance will be of great value, especially in light 

of the interstate transport “good neighbor” provisions.

8

 

Since the western region is most affected by high USB O3 in ways that are not completely 

understood, WESTAR suggests additional data analyses and modeling are necessary to develop a 

more comprehensive assessment of the role of USB. WESTAR appreciates the engagement with 

EPA during the recent USB Workshop9 and requests EPA continue its efforts to address USB O3

and transport across the western U.S., similar to EPA’s long-standing efforts in the eastern U.S. 

involving the Ozone Transport Commission, NOx SIP call, and Cross-State Air Pollution Rule. 

Preparation of a white paper documenting further evaluation of USB O3 and transport in the 

inter-mountain west where monitors do not respond to regional reductions in O3 precursor 

emissions would be a good first step. 

Ozone and O3 background are at the forefront of atmospheric research activities and the level of 

scientific understanding is expanding at a rapid pace. For example, the journals Science of the 

Total Environment and Atmospheric Environment have recently published issues with sections 

dedicated to furthering the understanding of O3 in rural United States, titled “The Nevada Rural 

Ozone Initiative: A Framework for Developing an Understanding of Factors Contributing to 

Elevated Ozone Concentrations in Rural and Remote Environments” (October, 2015) and 

"Observations and source attribution of O3 in rural regions of the Western United States," (May, 

2015), respectively. NOAA conducts numerous field campaigns to investigate O3 (e.g., CalNex, 

FRAPPE / DISCOVER-AQ, CABOTS, etcetera). A Western Regional Air Partnership (WRAP) 

webpage10 provides links to presentations to Western States Air Council’s (WESTAR) Ozone 

Background Workgroup by experts in the field, presentations related to O3 by WRAP technical 

staff, and O3-related workshops or forums hosted by others. Consideration of these and other 

technical resources documenting the advancements in the state of the science may assist EPA 

with further characterizing O3 background. 

In summary, WESTAR offers the time, expertise, and leveraged resources of its technical and 

planning committees, and working groups of topical experts, in coordination and collaboration 

with EPA, to support furthering the understanding of USB O3 through the development of a 

white paper regarding the role of ozone background specific to the western U.S. 

																																																												 8 Memorandum from Stephen D. Page to Regional Air Directors, Information on the Interstate Transport “Good 

Neighbor” Provisions for the 2008 Ozone National Ambient Air Quality Standards (NAAQS) under Clean Air Act 

(CAA) Section 110(a)(2)(D)(i)(I), 2015. 9 U.S. EPA Workshop to Advance the Collective Understanding of Technical and Policy Issues Associated with 

Background Ozone, February 24-25, 2016, Phoenix, AZ. Referred to as Workshop throughout this document. 10 http://www.wrapair2.org/WestJumpAQMS.aspx
3

B. What additional data elements and/or modeling improvements are needed to improve 

characterization of background O3 levels across the U.S.?

Although EPA has used state-of-the-art modeling to assess USB O3, large uncertainties and 

errors remain. Additional research and development are required to improve the models and 

results, as EPA acknowledged during the Workshop. WESTAR appreciates EPA’s efforts in this 

area. Clearly this is a long-term process, but the current limitations should be acknowledged. 

EPA suggests monitored concentrations are not indicative of USB O3 because of the effects of 

U.S. anthropogenic emissions.

11 WESTAR notes there are two O3 monitoring sites located on or 

near the coast of California and Oregon that should be appropriate to use for determining USB 

O3 resulting from long-range transport. These two sites are Trinidad Head, California (operated 

by NOAA) and Mt. Bachelor, Oregon (operated by the University of Washington). Data from 

these sites have been widely used in the past as indicators of Asian transport and could also be 

used for global model validation efforts. There are likely other sites along the West Coast and 

the Mexican or Canadian borders that could be utilized to evaluate USB O3 impacts.

Evaluation of the temporal variability of U.S. emissions contributions to monitored O3

concentrations could be used as part of a weight of evidence approach that integrates 

observational data, including satellite and other remote sensing information, along with modeling 

to assist EPA in identifying USB O3. It may be that for remote monitors the contributions by 

U.S. anthropogenic emissions to the observed O3 may fall below the errors and biases of model 

estimates of USB O3. 

There are several areas in which EPA might conduct additional assessments and evaluations to 

better understand the role of USB O3 in the western U.S., including: global model evaluation 

(i.e., boundary conditions); assessing the significance of increasing mid-tropospheric O3

concentrations over the last two decades; the role of site elevation and climatic variability in 

USB O3; and, development of more precise hourly and daily estimates of USB O3. 

Boundary Conditions and Global Models

WESTAR has previously provided comments12 suggesting the need of further evaluation, 

including sensitivity testing, of the global models used to inform boundary conditions for the 

CONUS modeling domain. The comments also addressed EPA’s practice of holding boundary 

conditions constant when conducting CONUS modeling exercises for projected future 

conditions. These comments remain germane to furthering the understanding of the role of 

boundary conditions in modeling USB O3. 

WESTAR appreciates the efforts EPA has made to refine estimates of background O3, especially 

its outreach to the global modeling community. A robust review of global model performance at 

rural monitors across the West would inform sensitivity analyses using a number of the best 

																																																												 11 White Paper, supra note 1, at 3. 12 WESTAR letters to Chet Wayland, OAQPS, dated April 9, 2014 and June 11, 2014 regarding the 2011/2018 

modeling platforms.
4

performing global models to inform boundary conditions for CONUS modeling, leading to better 

understanding of where CONUS modeling efforts to address USB O3 could be improved. 

The White Paper does not cite important modeling work on background in the western U.S. A 

large study sponsored by western states and the BLM, the West-wide Jumpstart Air Quality 

Modeling Study13 (WestJumpAQMS) conducted extensive and well-documented modeling 

studies for calendar year 2008, reaching very different conclusions as to the quantities of USB O3

transported to rural and urban sites across the West. The WestJumpAQMS is on par with EPA 

national modeling platform studies and has been thoroughly evaluated on its own by western 

states, federal land managers, western EPA regional offices, and other western air quality 

agencies. 

In addition, recent work by the WRAP investigated sensitivity of CONUS models to two global 

models14 and estimated USB O3 employing zero-out modeling techniques.

15 The Intermountain 

West Data Warehouse-Western Air Quality Study16 will conduct additional evaluations along 

these lines for the new 2014 base year modeling platform in the coming summer. An evaluation 

of the AM3 global model is being performed through Lamont Doherty under a separate project. 

The State of Colorado and Denver/Northern Front Range Regional Air Quality Council have also 

conducted source apportionment and sensitivity studies of USB O3 transport for the Denver 

metro O3 nonattainment area.

17 Finally, EPA OAQPS and western EPA regional offices have 

been closely involved in the biannual WRAP-EPA Modeling Workshops18 in 2011, 2013, and 

2015. 

It is hard to understand why results from western modeling studies and workshop were not 

included in EPA’s White Paper. Consideration of these resources and that of others may be of 

assistance to the EPA in their efforts to improve CONUS model performance, particularly in the 

West.

19 Understanding global model performance will aid understanding of CONUS model 

performance and increase confidence in model results by all users. 

Increasing USB Ozone Trends

EPA has noted the increase in mid-troposphere O3 concentrations in remote areas over the last 

two decades, which could result in USB O3 increases of up to 7 ppb by 2025.

20 Owen Cooper, 

NOAA, suggested during the Workshop that this trend is likely to persist for another 10 to 20 

years, the result of long-lived atmospheric processes, in spite of any reductions in international 

emissions. The White Paper’s discussion of future O3 levels in 2025 suggests most areas in the 

U.S. will have design values less than the current NAAQS of 70 ppb based on modeling 

																																																												 13 Available from: http://www.wrapair2.org/WestJumpAQMS.aspx 14 Available from: http://vibe.cira.colostate.edu/wiki/wiki/1043/bc-sensitivity-modeling-results 15 Available from: http://vibe.cira.colostate.edu/wiki/wiki/1020/background-air-quality-modeling-results 16 Link: http://views.cira.colostate.edu/tsdw/ 17 Noted in Summary at: https://www.epa.gov/sites/production/files/2016-03/documents/bgo3-high-levelsummary.pdf

18 Available from: http://www.wrapair2.org/ozone.aspx 19 See: Feb 19, 2007: Multi-Scale Modeling of the Effects of Global Change upon Regional Air Quality 20 White Paper, supra note 1, at 8.
5

projections using current boundary conditions.

21 However, the current O3 NAAQS is at the high 

end of CASAC’s recommended range, the O3 NAAQS will be subject to another periodic review 

prior to 2025, and EPA’s assessment is based on holding global model boundary conditions 

constant which is inconsistent with current measured trends. 

Further evaluation of the role of increasing concentration trends and the influence of projected 

future boundary conditions on USB O3 will be critical for the preparation of i-SIPs and 

informing O3 nonattainment planning, especially with the potential for a lower future O3

NAAQS. International emission inventories have a high degree of uncertainty. An evaluation of 

international emissions would identify where the inventories are most uncertain, and additional 

sensitivity analyses would determine the significance of how changes in the international 

emissions influence CONUS model results. Border states are particularly concerned with proper 

characterization of emissions from Canada and Mexico. Since future international emissions are 

extremely difficult to project, sensitivity analysis is one method to bracket O3 impacts under 

differing growth and economic assumptions. 

Assessing Site Elevation and Climatic Conditions

Ozone concentrations in the inter-mountain western U.S. are strongly influenced by high site 

elevations and high mixing heights that enhance O3 concentrations through natural stratospherictropospheric exchange and downward mixing. EPA acknowledges natural atmospheric 

exchange processes can transport high-O3 stratospheric air into the troposphere and under certain 

meteorological conditions can displace discreet plumes of stratospheric air into the troposphere22

(i.e., SI). Recent work in Nevada23 documents that high elevation O3 monitored values do not 

show the daily variation of O3 concentrations typically recorded by other monitors, suggesting a 

very limited contribution from local emissions sources. It is unclear what the role of natural 

atmospheric exchange processes are on high elevation monitors without the enhancements 

resulting from SI and LRT events. A better understanding of these processes is important for 

implementation planning in the inter-mountain western U.S. 

The White Paper does not discuss the contributions of LRT of Asian pollution via the subtropical 

jet stream to USB O3 identified by researchers. Several researchers have noted the frequency 

with which SI and LRT events contribute to USB O3 at high elevation western sites. Recent 

NOAA research24 suggests these processes are frequent contributors to USB O3 at high elevation 

sites. It is critical to both EPA and states for EPA to further the understanding of these processes 

and quantify the resulting contributions to USB O3. 

 

Lin et al 201525 documented the variations in background O3 resulting from climate variability. 

Evaluating changes in boundary conditions generated by global models for La Niña and El Niño 

years while holding global emissions constant would provide valuable information regarding the 

																																																												 21 Ibid. at 9. 22 Ibid. at 3. 23 Gustin, M.S., Fine, R., Miller, M., Jaffe, D., Burley, J., 2015, The Nevada Rural Ozone Initiative (NVROI): 

Insight to understanding air pollution in complex terrain, Science of the Total Environment, 530-531, 455-470. 24 Overview of 2013 LVOS, supra note 6. 25 Lin, M. et al. Climate variability modulates western US ozone air quality in spring via deep stratospheric 

intrusions. Nat. Commun, 6:7105 soi: 10.1038/ncomms8105 (2015)
6

influence of climate variations on USB O3 at high elevation sites in the western U.S. and further 

inform attainment and maintenance planning. 

Hourly and Daily Estimates of USB Ozone

EPA suggests that there is general consistency between zero out and source apportionment 

modeling approaches and thus an increased confidence in the model findings.

26 Since the two 

approaches used the same boundary conditions and meteorology, this is not surprising and only 

supports the idea that the internal algorithms in the two models are performing similarly and/or 

the contributions of boundary conditions are so large. However, this does not confirm the 

models are producing the “right” USB O3 estimates. 

The contributions to USB O3, which can be enhanced by specific events, have not been assessed 

by U.S EPA on an hourly or 8-hour timeframe. EPA has only considered the values of USB O3

on possible O3 NAAQS exceedance days in detail via a re-analysis of zero-out modeling.

27 

Zero-out modeling perturbs the complex atmospheric chemistry of O3 formation and may not be 

an appropriate tool to estimate USB. The significant contributions of boundary conditions may 

suppress perturbations of the complex atmospheric chemistry resulting from zeroing out U.S. 

emissions (i.e., one possibility is that the contributions from transported pollutants is far greater 

than the contributions of U.S. anthropogenic pollutants so the system remains relatively stable 

even in the absence of U.S. anthropogenic emissions). 

The form of the 2015 O3 standard is the annual fourth-highest daily maximum 8-hour 

concentration averaged over three years. EPA has acknowledged the uncertainty in regional 

modeled estimates of USB O3, the difficulties with temporal resolution experienced by the global 

models, and the reported seasonal average estimates of USB O3. If the available modeling tools 

are not analyzing USB O3 consistent with the current form of the NAAQS, then EPA should 

either make the modeling consistent with the 8-hour form of the standard or consider 

implementation of the NAAQS on a seasonal basis. Consistency between the modeling and the 

form of the standard allows for more accurate estimates of state contributions and the sources of 

controllable emissions. Successful planning requires that states clearly understand the 

contributions from controllable emissions from sources they can control. Thus, the modeling 

should be informed by a complete year of meteorological data along with improved temporal 

resolution. States should not be held to implementation of the “good neighbor” provisions when 

the contributions are based on seasonal averages with limited temporal resolution, especially 

given the uncertainties in the estimates of USB O3. In addition, the form of the O3 NAAQS 

suggests modeling assessments should be multi-year to account for the inter-annual variability of 

the processes that influence USB O3, as well as the influence of transported O3. 

In summary, WESTAR has suggested several data elements and model improvements in an 

effort to improve USB O3 characterization. WESTAR offers its assistance through its technical 

and planning committees, as well as working groups of topical experts, in coordination and 

collaboration with EPA to support further characterization of USB O3, as follows: 

																																																												 26 White Paper, supra note 1, at 5. 27 Ibid. at 4.
7

• Development of consensus, well-documented, and reproducible inputs and assumptions for 

key western U.S. natural uncontrollable sources, regulated anthropogenic sources, and 

international sources; as well as addressing these same inputs and assumption with respect to 

global modeling platforms for base year and ranges of future projections. 

• Development of forecasting tools for regional and jurisdiction-specific use in warning the 

public about poor air quality, for international transport, wildfire impacts, of both PM and O3, 

and stratospheric intrusions of O3, building on the tools used by states and other agencies.

• Continuation of the biannual series of Western Modeling Workshops as a forum to discuss 

comparisons of model performance and needed improvement for various models used by 

EPA, western U.S. air agencies, and others.

• Continuation of the development of a modeling approach based on regional consensus and 

refined inventories, linking the work products to planning requirement timelines for both O3

and regional haze, while providing frequent updates to background assessments. 

• The efforts should be guided by a consensus process involving western U.S. air agencies, 

EPA OAQPS and EPA Regional Offices with reports out to biannual Western Modeling 

Workshops. 

C. EPA has focused on USB in this white paper. Are there other definitions of background 

ozone that concern stakeholders?

Yes. From a pragmatic point of view, the current definition works well. The definition of USB 

serves the purpose of providing a consistent framework for analyses and modeling. However, 

from the point of view of an agency that needs to assess what is causing violations of the 

NAAQS, the current definition presents several issues and is of limited utility for air quality 

planning. In particular, the current estimate of USB includes all contributions except those of 

U.S. anthropogenic emissions. It would be helpful to states if the USB estimates distinguished 

the contributions of different sources. For instance, it is confusing to include wildfire and SI in 

USB, when these events are allowed to be excluded from the calculation of design values with 

appropriate demonstrations under the Exceptional Events Rule (EER). Contributions from 

international biogenic and geogenic emissions should also be estimated separately. 

Characterization of the contributions from both international anthropogenic emissions, as well as 

interstate transport of anthropogenic emissions would facilitate the identification of long-range 

transport events which may qualify for EER relief under certain meteorological conditions.

Model estimates of USB O3 are not well characterized on a local scale or at temporal resolutions 

consistent with the form of the NAAQS. In addition, the models do not robustly address 

episodic SI, LRT, and large fire events - events that may qualify under the EER. Western states 

would benefit from a clear, explicit statement from EPA regarding the role of models and other 

data in determining USB O3. Such a statement would clarify the relationship between USB O3

estimates and events that quality for relief through the EER. This statement could provide the 

basis for formulation of guidance for the estimation of the contribution to USB O3 from events 

falling under the umbrella of the EER that are not well captured by model estimates, as well as 

estimation of the contribution from local emission sources to observed concentrations. Guidance 

of this sort would assist states and locals with implementation planning and identifying 

meaningful emission reductions that could contribute to attaining the NAAQS. 
8

D. Does the EPA preliminary conceptual model of O3 attainment planning align with 

stakeholder perspectives on the O3 planning process?

No, the conceptual models for O3 attainment planning do not align with states’ needs for 

regulatory relief from nonattainment designations resulting from emission sources beyond their 

control. As noted previously, monitors in six states have contributions to DVs from in-state 

manmade sources of less than or equal to 10 percent. Western states are boxed-in by the policy 

relief and conceptual models for O3 attainment proposed in the White Paper. Preparation of 

exceptional event (EE) demonstrations is an onerous, resource-intensive task that may or may 

not be sufficient for approval by EPA. Moreover, if a state does develop and submit an EE 

demonstration, there is no guarantee that EPA will review much less approve such a 

demonstration. The provisions under CAA § 182(h) for rural transport areas and CAA § 179B 

for international transport are only applicable to nonattainment areas, complete with all the 

consequences of such designations. These conceptual models do not provide relief for many 

inter-mountain western states where in-state contributions to DVs are less than 10 percent. 

E. Has the EPA identified all of the CAA mechanisms available to address areas influenced 

by background O3?

No, stakeholders and agencies are exploring other potential CAA approaches to account for USB 

O3 that might provide some degree of regulatory relief. Some of these avenues would require 

policy changes. This effort might be similar to previous collaborative efforts between WESTAR 

and EPA in the development of the 1996 Natural Events Policy. Discussion of these 

mechanisms is provided under the next question (F). 

WESTAR disagrees that even in areas with the highest seasonal mean background 

concentrations “anthropogenic sources within the U.S. are largely responsible for the 4th highest 

8-hour MDA8 concentrations.”

28 Western air agencies have pursued EE demonstrations to 

eliminate high MDA8 values resulting from nature events to lower design values. The 2015 O3

NAAQS became effective in December, 2015 and agencies are just now evaluating the tradeoff 

between preparing EE demonstrations and the resulting regulatory relief, and in many cases are 

finding the level of effort to prepare an EE demonstration is too onerous. It is important for the 

EPA to evaluate whether the EER is a realistic mechanism to address areas influenced by high 

USB O3 by excluding data influenced by wildfire, SI, and LRT events from regulatory 

consideration, given the frequency of events and difficulty of demonstrating their roles, 

especially as the O3 NAAQS approaches USB at rural western sites and even small contributions 

from these events may interfere with attainment. 

WESTAR notes 40 CFR Part 50.1 allows for exclusion of data affected “by human activity that 

is unlikely to recur at a particular location,” including both interstate and international transport 

events of anthropogenic emissions occurring under unique meteorological conditions. The 

unique meteorological conditions being the “event” that qualifies for exclusion. This concept is 

discussed in the preamble of the recently proposed draft EER revisions29 under section V.F.1.b 

																																																												 28 Ibid. at 6. 29 Treatment of Data Influenced by Exceptional Events; Proposed Rule. 80 FR 72840, 20 November 2016.
9

and warrants more refined interpretation and evaluation as one of the regulatory relief policies 

identified by the White Paper. Exclusion of contributions from these types of events in the 

monitoring data over the inter-mountain West has the potential to allow areas primarily impacted 

by USB O3 and interstate transport with little contribution from in-state emissions to remain in 

attainment of the NAAQS. 

Additional EPA EE guidance will help reduce this level of effort and streamline the process. 

Agencies are concerned that EPA’s policy to not review EE demonstrations without regulatory 

significance may skew the historical record higher, making future demonstrations more difficult 

to approve. Furthermore, additional EE demonstration guidance should facilitate weight of 

evidence tools incorporating easily accessible observational data for successful demonstrations. 

F. What other approaches (consistent with CAA provisions) should be considered to deal with 

background O3 in implementing the 2015 O3 NAAQS?

The White Paper identified three additional mechanisms for accounting for background O3: 1) 

revising data handling procedures to exclude exceedances attributable to background O3; 2) 

deferring designations in locations impacted by background O3; and/or, 3) designating area 

influenced by background O3 as unclassifiable.

30 These mechanisms were not included in the 

overview of policy tools due to legal or other deficiencies. A more thoughtful discussion of 

these deficiencies and possible solutions from the EPA might spur identification of alternative 

proposals that overcome these deficiencies. 

WESTAR would like to continue dialogue with EPA and investigate other CAA mechanisms to 

account for background O3. Below are two additional concepts or policies for further discussion,

1) principal contributor concept and, 2) natural events policy. WESTAR looks to EPA to initiate 

a process to collaborate and further explore these concepts and policies. 

Stakeholders have proposed a mechanism31 to address areas with high USB O3 through the 

concept of principal contributor32 where all background contributions, regardless of origin, are 

excluded by either a change in the form of the standard or via the EER from 

attainment/nonattainment designation following a demonstration that background is the principal 

contributor to monitored exceedances. This would require revisions to Appendix U of 40 C.F.R. 

Part 50 or as part of the revisions to the EER. This concept should be further explored. 

In the 1990’s WESTAR worked in conjunction with EPA to develop a natural events policy for 

PM10 (see http://www.westar.org/Docs/NEPolicy.pdf). This effort resulted in a more black and 

white policy as an alternative to excluding monitor data through EER demonstrations and allows 

agencies to note the occurrence of natural events and subsequently remove their influence on 

design values without further identification of the source of the event. WESTAR would like to 

																																																												 30 White Paper, supra note 1, at 12, footnote 41. 31 BP American Production Company, August 20, 2015 presentation to WESTAR Planning Committee, available 

from http://www.wrapair2.org/pdf/Backgroundpresentation%2008192015.pdf and briefing paper available from 

http://www.wrapair2.org/pdf/High%20Ozone%20Levels%20%207_8_15.pdf 32 Also referred to as the “total background” framework, see Comment submitted by Robert L. Stout, Jr., Vice 

President and Head of Regulatory Affairs, BP America, available from: 

https://www.regulations.gov/#!documentDetail;D=EPA-HQ-OAR-2016-0097-0027
10

build on its experience with the Natural Events Policy, collaborating with EPA to identify 

needed policy changes or options and determine the level of effort for the analysis supporting 

natural events policy for O3. Both of these mechanisms would assist states by preventing 

nonattainment designation resulting from emissions beyond their control. 

G. Are sufficient technical tools, data, and EPA guidance available to make the 

demonstrations necessary to invoke relevant CAA provisions?

No, EPA must continue to identify tools, methods, and data sources to inform agencies’ EE 

demonstration packages so states can streamline the process of developing an approvable 

demonstration. WESTAR appreciates EPA’s efforts regarding O3 implementation with the 

release of designation guidance, release of a mapping tool, and guidance for wildfire EE. 

Contributions to monitored O3 from fires, SI, and LRT events may be excluded by 

demonstrations under the EER, which is one of the policy relief mechanisms identified by EPA. 

However, it’s not clear the technical tools to inform EE demonstrations for these events are 

commonly agreed upon or available,

33 in spite of the recent release of draft guidance for wildfire 

event demonstrations34.

Distinguishing contributions between SI and LRT is difficult to ascertain at the best instrumented 

sites and very difficult at CASTNET sites with limited instrumentation, which includes many of 

the impacted sites. WESTAR requests EPA devote resources to assessing contributions by SI 

and LRT to USB. It would be of great assistance to states for EPA to develop a toolbox of 

criteria, methods, and data resources to identify and prepare EE demonstrations for both SI and 

LRT events. 

The tools and data sources should be publically available and of the appropriate technical 

sophistication to address the event. EPA staff should lead and focus efforts to identify, apply, 

and document the appropriate tools to meet the requirements of EE demonstrations for SI and 

LRT events, building on the state-lead efforts of the Stratospheric Intrusion Workgroup 

coordinated by EPA Region 8. WESTAR appreciates EPA efforts to release guidance for 

developing demonstrations for SI EE with proposed release for external review in late summer 

2016. 

WESTAR also strongly supports development of comprehensive guidance relevant to 

international transport demonstrations under CAA section 179B, which is critical, based on 

discussions during the Workshop. These provisions appear to be one of the primary ways under 

the CAA for regulatory relief and as such needs immediate attention. Approvals for the use of 

the 179B provisions to date have involved direct international border areas and have taken years 

to finalize. In contrast, the inter-mountain west states do not necessarily adjoin an international 

border, but are impacted by international emissions based on monitoring studies, source 

apportionment modeling, and zero-out modeling. Another concern for western states relates to 

																																																												 33 WESTAR comments on U.S. EPA Exceptional Events Proposed Rule and the Draft Guidance on the Preparation 

of Exceptional Events Demonstrations for Wildfire Events that May Influence Ozone Concentrations. February, 

2016

34 U.S. EPA, Draft Guidance on the Preparation of Exceptional Events Demonstrations for Wildfire Events that May 

Influence Ozone Concentrations. November 2015
11

the treatment of transport of emissions from other states located upwind and how interstate 

transport is characterized independent of international transport. Appropriate and comprehensive 

guidance is needed to provide states with the information EPA will need for approval 

determinations to ensure the 179B provisions can be utilized in a timely manner. 

One point of particular interest is how states can leverage EPA modeling, both existing and 

future, to support 179B demonstrations. This would relieve the burden on states and allow 

agencies without photochemical modeling capability the opportunity for regulatory relief under 

this CAA mechanism. It is known that international emissions vary over time and impacts 

change, even on a daily basis. The same can be said for emissions from states upwind of the 

inter-mountain west region. In general, states do not have the resources to conduct regional 

modeling on a daily basis to determine impacts from long-range interstate and international 

transport and look to EPA to assist or provide this critical information.

In summary, EPA cannot say, without much further and sustained, coordinated analysis with 

western air agencies, that the current understandings of background O3 described in the White 

Paper are sufficient. Analyses cited in this document convey the scope, scale, and complexity of 

the background O3 issue in the West. EPA must apply expertise and provide resources for 

western air agencies to be involved in developing an understanding of background O3 for air 

quality analyses and planning required under the CAA. WESTAR offers the time, expertise, and 

leveraged resources of its technical and planning committees, and working groups of topical 

experts, in coordination and collaboration with EPA, to support furthering our understanding of 

USB O3 on an ongoing basis related to above EPA questions C, D, E, F, and G. 

H. Do states want or need additional assistance from the EPA to develop the demonstrations 

necessary to invoke relevant CAA provisions?

Yes, states look to EPA to characterize USB O3, not only the amounts but also the mechanisms 

of the contribution of USB O3 to observed concentrations. This characterization is a high 

priority for western states, preferably on an hourly basis. WESTAR recognizes the challenges 

facing EPA and that the issues noted here and by others will not be resolved quickly. However, 

in the interim states must continue planning and implementation of the 2015 O3 NAAQS. State 

programs are struggling to meet the CAA nonattainment requirements without knowledge of 

whether reductions of local emissions will actually lower monitored concentrations and without 

having the benefit of a full understanding of the role of USB O3 and its planning implications. 

Based on recent monitoring data, (2013-2015, or 2014-2016) few areas would be designated 

non-attainment because USB O3 is causing or will cause exceedances of the standard based on 

EPA projection modeling using relative response factors to the 2025 timeframe. However, there 

is a possibility that future monitoring data will record higher concentrations, just as air agencies

are preparing their i-SIPs and developing approaches to address the CAA requirements for any 

potential nonattainment areas. To effectively manage implementation of the 2015 O3 NAAQS, 

timely and improved analyses are needed from EPA:

• By all states to robustly evaluate interstate/inter-jurisdictional transport that includes USB 

O3;
12

• By states and other upwind jurisdictions contributing to nonattainment and/or interfering 

with maintenance at downwind sites; and,

• To help states and other jurisdictions manage day-to-day exposures at urban and 

rural/Class I sites to high O3, regardless of which source is the principal cause –

“background as defined by models,” wildfire, stratospheric intrusion, contributions from 

sources in Mexico and Canada, and even U.S. anthropogenic. Any of these days could be 

“Ozone Alert Days.”

WESTAR requests better tools and guidance for demonstrating EEs including large wildland 

fires, SI, and LRT events, and especially interstate transport. The regional nature of these events 

suggests a regional approach spanning multiple jurisdictions and EPA regions, perhaps led by 

RPOs. WESTAR supports this idea and is actively exploring this option, including identification 

of potential sources of funding. Regional EE demonstrations would provide consistent 

demonstration packages and streamline regional office approvals, a clear benefit for both states 

and EPA. 

EPA can play another important role in advancing the understanding of the role of USB O3 in the 

western U.S. Current federal research efforts appear to lack a coordinated effort to reach shared 

research goals with individual agencies pursuing important work without the benefit of a more 

holistic view. Such coordination might engage EPA’s federal partners, the federal land 

managers, as well as federal research partners such as NOAA and NASA. Identification of 

common research goals would assist coordination of research efforts, optimize funding, and fast 

track a better understanding of USB O3. 

Building further on the idea of coordinated efforts, some strategically located monitors might be 

designated as “sentinel” monitors, providing real-time data to inform health advisories resulting 

from O3 events that exceed the NAAQS or alert agencies to collect additional information to 

inform EE demonstrations for SI or LRT events. For example, the CASTNET monitor located at 

Great Basin National Park might act as a sentinel for SI/LRT events while the CASTNET 

monitor at Rocky Mountain National Park might act as a sentinel for health-threatening O3

events impacting the greater Denver metro area. 

Federally operated CASTNET monitors are often located far from state offices and only provide 

basic measurements. Sentinel monitors might be equipped with the more sophisticated 

monitoring instrumentation required to support EE demonstration packages, such as water vapor 

and research-grade CO instrumentation. Identification of sentinel monitors might be 

incorporated in EPA’s efforts to coordinate with its Federal research partners. EPA could also 

facilitate USB O3 research efforts by coordinating state access to lidar and other sophisticated 

monitoring equipment on a temporary “loaner” basis for limited periods as agencies develop 

better conceptual understanding of the important sources of O3 at its monitors.

I. What are stakeholders’ perspectives on existing programs and cooperative agreements to 

reduce levels of background O3 entering the U.S.?

The White Paper only devoted one paragraph to the subject of controlling international emission 

sources and provided scant details of EPA’s engagement on this front or the results thereof. 
13

Therefore, WESTAR has not assessed existing programs and international agreements to reduce 

O3 entering the U.S. from international emission sources. During the Workshop, one California 

agency noted its engagement with international entities in its effort to curtail the impacts 

resulting from long-range transport of anthropogenic emissions. WESTAR supports this peer-to 

-peer engagement and suggests the EPA provide all support possible to allow agencies to engage 

the international community and facilitate reduction of anthropogenic O3 precursor emissions. 

However, as noted above by Owen Cooper at the Workshop, despite reductions in international 

emission and due to long-lived atmospheric processes, the trend of increasing global O3 entering 

the U.S. he has documented will persist for the foreseeable future.