LETTER: Western Governors express concern over EPA tightening of national ozone standard

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August 11, 2016

Honorable Gina McCarthy
U.S. Environmental Protection Agency
1200 Pennsylvania Avenue, N.W. (1101A)
Washington, D.C. 20460

Dr. Howard A. Shelanski
Administrator, Office of Information and Regulatory Affairs
Office of Management and Budget
Eisenhower Executive Office Building
1650 Pennsylvania Avenue, NW
Washington, D.C. 20503

Brian C. Deese
Assistant to the President and Senior Adviser
The White House
1600 Pennsylvania Avenue, NW
Washington, D.C. 20500

Re: Background Ozone in the Western United States and the Exceptional Events Rule

Dear Administrator McCarthy, Administrator Shelanski, and Mr. Deese:

Western Governors write regarding final revisions to the Environmental Protection Agency’s (EPA) Exceptional Events Rule (EER) which is now undergoing White House Review. Western Governors are concerned that the EPA decision to lower the National Ambient Air Quality Standard (NAAQS) for ground-level ozone under the Clean Air Act (CAA) is likely to cause areas in the West to enter non-attainment status based on high levels of uncontrollable background ozone through the final EER. We strongly urge EPA to adjust criteria to properly account for events that contribute to background ozone concentrations, which are impossible for states to control.

The CAA obligates all states to develop State Implementation Plans (SIPs) to attain and maintain the NAAQS. SIPs are intended to reduce emissions only from sources over which states can exert control, not including natural or international sources. However, various events and conditions result in elevated levels of background ozone, which states cannot and are not expected to control. Such events and conditions include wildfire, lightning, biogenic emissions, stratospheric ozone intrusion, and transported ozone from international and interstate sources. These events may be discrete (such as a wildfire or stratospheric intrusion) or may present as a periodic or ongoing condition (such as transported ozone). All result in emissions over which states have no control. Comments submitted to EPA by the Western States Air Resources Council (WESTAR) artfully elaborate challenges faced by western states as a result of these background ozone contributors and are supported by Western Governors. (1)

Upon lowering the NAAQS for ground-level ozone in 2015, EPA affirmed that, “[u]nder the [CAA] states are not responsible for reducing emissions from background sources.” (2) The agency recognized that certain areas of the West are particularly susceptible to high background ozone levels and pledged to, “work directly with responsible air management agencies in these areas to ensure that all CAA provisions that would provide regulatory relief associated with background ozone are recognized.” (3)

Western Governors value the agency’s statements from late 2015. As stated in WGA Policy Resolution 2014-13, State Clean Air Act Authority and Air Quality Regulation, Western Governors believe EPA should engage states as co-regulators and should ensure state agencies and representatives have a robust voice and play a meaningful role in any EPA rule promulgated under the CAA. (4) We recognize the critical importance of maintaining air quality in the West and appreciate the opportunity to work with EPA to achieve this.

In that regard, Western Governors have significant concerns over the lack of CAA tools available to account for ozone NAAQS exceedances resulting from factors outside state control. As noted in the EPA Memorandum, the CAA contains provisions to ensure states must address only man-made sources within their jurisdiction and must impose emissions controls only to the extent they are reasonably available. (5) The existing regulatory framework, however, lacks effective tools to identify emission sources outside state control. Methods of accounting for background ozone sources identified by the EPA are insufficient.

In addition, although the proposed EER can be useful to account for ozone contribution from discrete events such as wildfires and stratospheric intrusion, the rule could be improved. Western Governors suggested several such improvements in our February 3, 2016 comments in response to EPA’s proposal. (6)

Even with our suggested improvements, however, the EER is not an adequate mechanism to account for factors such as lightning, biogenic sources and transported ozone. These sources are inherently difficult to measure and establish in a state’s exceptional event demonstration. Identifying and quantifying the role of these factors and making a judgment about their relative importance is an onerous, if not impossible, undertaking. Prior to implementation of the NAAQS for ozone and before finalization of the revised EER, it is vital that EPA recognize the inadequacy of CAA mechanisms states have at their disposal to account for ozone-contributing factors outside state control and develop a more workable framework.

Western Governors believe the states – and in turn EPA – would benefit from a more holistic approach under which states could aggregate multiple ozone-contributing factors to prove a single exceptional event exceedance demonstration. This approach would be in line with EPA’s shift to a “Clear Causal Relationship” standard outlined EPA’s proposed revisions to the EER. (7) Under such an approach, there would be no onerous requirement to differentiate and quantify contributions of various background sources or to utilize multiple CAA provisions to account for various background ozone contributors. Rather, the focus would be on showing that these sources, rather than controllable man-made emissions, are the principal contributing factor in a monitored NAAQS exceedance.

A potential path to implement this approach would be:

  • Revision to the EER so that, either individually or in the aggregate, all factors contributing to high background ozone levels could be considered as “exceptional events,” for which states are not held responsible.
  • The approach could also be incorporated into Appendix U of the CAA, which sets out the methodologies EPA uses to interpret exceedances of the ground-level ozone NAAQS and assess factors contributing to NAAQS exceedances.

Western Governors are supportive of efforts by WESTAR and EPA to collaborate to address issues posed by background ozone in the West. Western Governors would like to be helpful in the development in this process. We look forward to working with EPA and other partners. We believe development of a state-EPA collaborative workplan with defined timelines consistent with this letter, the EPA Memorandum, and WGA Policy Resolution 2014-13 would be a positive step toward state and federal partnership on the issue of background ozone in the West. Western Governors will be following up to assure that its views are considered during final review of the EER revisions.


Steve Bullock
Governor of Montana
Chair, WGA

Dennis Daugaard
Governor of South Dakota
Vice Chair, WGA

cc: Janet McCabe, Acting Assistant Administrator for Air and Radiation, EPA

(1) May 11, 2016 Comments from WESTAR to EPA, Western States Responses Regarding Background Ozone and Recommendations for Additional Efforts in the Western U.S.  Available here.
(2) October 1, 2015 Memorandum from Janet G. McCabe, Acting Assistant Administrator, EPA Office of Air and Radiation, to Regional Administrators, Region 1-10, Paragraph D of Attachment (EPA Memorandum).
(3) Id.
(4) Section B(1)(a) of WGA Policy Resolution 2014-13. Attached and incorporated by reference.
(5) Id.
(6) Attached and incorporated by reference.
(7) Section V(B)(c) of proposed EER.

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