UNITED STATES ENVIRONMENTAL PROTECTION AGENCY REGION 8 1595 Wynkoop Street



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# 201 DENVER, CO 80202-1129 Phone 800-227-8917 http://www.epa.gov/region08

Ref: 8P-AR

The Honorable Matthew H. Mead Governor ofWyoming State Capitol Cheyenne, Wyoming 82002

Dear Governor Mead:

Thankyou for Wyoming's recommendations on air quality designations for the revised primary National Ambient Air Quality Standard (NAAQS) for nitrogen dioxide (N02) throughout Wyoming. This letter is to notify youofthe U.S. Environmental Protection Agency's (EPA's) response to Wyoming's designation recommendations, and to inform you ofour approach for completingthe designations for the revised N02NAAQS.

On January 22, 20I0, the EPA strengthened the health-based National Ambient Air Quality Standard for N02 by setting a new l-hourN02standard at the level oflOO parts per billion (Ppb). The EPA also retained with no change, the annual averageN02standard of53 ppb. This suite ofstandards will protect public health by limiting people's exposures to short-term peak concentrations ofN02 and by limiting community-wide N02 concentrations to levels below those that have been linked to respiratory-related emergency department visits and hospital admissions in the United States. To determine compliance with the new standard, the EPA established new ambient air monitoring and reporting requirements for N02

.In urban areas, monitors are required near major roads as well as in other locations where maximum concentrations are expected. Additional monitors will be required in some large urban areas to measure the highest concentrations ofN02that occur more broadly across communities.

In the preambleto the 2010 N02NAAQS and in the EPA's October 2010 letterto your predecessor requesting designationrecommendations, the agency stated that it expected to designate most areas of the country as "unclassifiable," indicating that there are insufficient datato determine whether ornot an area is attaining the revised N02NAAQS.This approach took into accountthat the new monitoring network requirements established with the revised N02NAAQS will not be effective until January 2013 and that air quality data from these new monitors would not be available to inform these initial designations.
The agency has reviewed Wyoming's recommendations and others, and intends to designate all areas of Wyoming, as well as the rest ofthe country, as "unclassifiable/attainment" ratherthan "unclassifiable." Based on air quality data from 2008-2010, all monitored areas in the country meetthe 2010 N02 NAAQS. While we acknowledge that the existingN02monitoring network does not provide adequateevidence to determine whether ornot the newNAAQS is met in all areas, there currently is no evidence ofviolations anywhere in the country. The "unclassifiable/attainment"designation better reflects the current air quality conditions. We plan to redesignate areas, as appropriate, after sufficient air quality datafrom the new monitoring network are available.

We will designate Wyoming unclassifiable/attainment using the boundaries Wyoming recommended to the EPA or revised boundaries you may provide in response to this letter. In pastdesignations for NOl , for the majority ofstates, the area ofthe state where the air quality could not be classified, orwas better than the national standards, was. given a statewide, or rest-of-state designation. However, we recommend that you carefully consider the implications for the Prevention ofSignificant Deterioration (PSD) permitting program ofhaving the entire state designated as a single arearather than smaller areas (e.g., counties, groups ofcounties, etc.). To ensure that the size ofdesignated areas is consistent with your state's objectives for managing air quality deterioration and economic growth, we recommend that your permitting staffbe consulted on the area boundary issues.

Ifyou have additional infOlmation that you want the EPA to consider with respect to the EPA's designation, please submit it to us by August 29,2011. We are also making the EPA'spreliminary designation decisions and supporting documentation available to the general public for review. We are acceptingpublic comments on our preliminary decisions for 30 days after a notice announcing the public conunentperiod is published in the FederalRegister. We will review any information we receive from the state ofWyoming and the general public by this date, and we plan to promulgate the final designations by October 31, 2011.
We look forward to a continued dialogue with you and your staffas we work together to implementthe 2010 NOl NAAQS. Should you have any questions, please do not hesitate to call me, or have your staff contact Carl Daly ofmy staffat (303) 312-6416.

Sincerely,

cc: John Corra, Director, DEQ Steven A. Dietrich, Administrator, AQD
GinaMcCarthy, AssistantAdministrator for Air and Radiation Stephen D. Page, Director, Office ofAir Quality Planning and Standards