UNITED STATES ENVIRONMENTAL PROTECTION AGENCY REGION 8 1595Wynkoop Street DENVER, CO 80202-1129 Phone 800-227-8917 http://www.epa.gov/region08 

# J 2011,

Ref: 8P-AR ChristopherE. Urbina, MD, MPH Executive Director and ChiefMedical Officer Colorado Department ofPublic Health and Environment 4300 Cherry Creek Drive South Denver, Colorado 80246-1530

# ~\J~ Dea'\p1a

Thank you for Colorado's recommendations on air quality designations for the revised primary National AmbientAir Quality Standard (NAAQS) for nitrogen dioxide (N02) throughout Colorado. This letter is to notify you ofthe U.S. Environmental Protection Agency's (EPA's) response to Colorado's designation recommendations, and to inform you ofour approach for completing the designations for the revised N02NAAQS.

On January 22, 2010, the EPA strengthened the health-based National Ambient Air Quality Standard for N02by setting a new I-hourN02standard at the level of 100 parts'per billion (ppb). The EPA also retained with no change, the annual average N02 standard of53 ppb. This suite ofstandards will protect public health by limiting people's exposures to short-term peak concentrations ofN02 and by limiting community-wideN02concentrations to levels belowthose that have been linked to respiratory-related emergency departmentvisits and hospital admissions in the United States. To determine compliance with the new standard, the EPA established new ambientair 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 preamble to the 2010N02 NAAQS and in the EPA's October 2010 letter to yourpredecessor requesting designation recommendations, the agency stated that it expected to designate most areas of the country as "unclassifiable,"indicating that there are insufficient datato determine whether or not an area is attaining the revised N02NAAQS.This approachtook into account that the new monitoring network requirements established with the revised N02NAAQS will not be effective until January 2013 and that air quality datafrom these new monitors would not be available to inform these initial designations.

Theagency has reviewed Colorado'srecommendations and others, and intends to designate all areas of Colorado, 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 meet the 2010 N02NAAQS. While we acknowledge that the existing N02monitoring network does not provide adequate evidence to determine whether or not the new NAAQS 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 data from the newmonitoring network are available.

We will designate Colorado unclassifiable/attainment using the boundaries Colorado recommended to the EPA or revised boundaries you may provide in response to this letter. In past designations for N02 , for the majority ofstates, the area ofthe state where the air quality could not be classified, or was 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 area rather 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 additio"nal information that you want the EPA to consider with respectto 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 announcingthe public commentperiod is published in the 

### Federal Register. We will review any information we receive from the state ofColorado 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 implement the 

### 2010 N02 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,



# ...**~&L** me B. art gional A -ministrator

cc: MarthaRudolph, Director, CDPHE Paul Tourangeau, Director, APCD
Gina McCarthy, Assistant Administrator for Air and Radiation StephenD. Page, Director, Office ofAir Quality Planning and Standards