UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

REGION 8 

1595 Wynkoop Street 

DENVER, CO 80202-1129 

Phone 800-227-8917 

http://www.epa.gov/region08 

J 2011, 

Ref: 8P-AR 

Christopher E. Urbina, MD, MPH 

Executive Director and Chief Medical Officer 

Colorado Department of Public Health and Environment 

4300 Cherry Creek Drive South 

Denver, Colorado 80246-1530 

Dea'\p1 ~\J~ a 

Thank you for Colorado's recommendations on air quality designations for the revised primary National 

Ambient Air Quality Standard (NAAQS) for nitrogen dioxide (N02) throughout Colorado. This letter is 

to notify you of the U.S. Environmental Protection Agency's (EPA's) response to Colorado's 

designation recommendations, and to inform you of our 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 

N02 by setting a new I-hour N02 standard at the level of 100 parts'per billion (ppb). The EPA also 

retained with no change, the annual average N02 standard of 53 ppb. This suite of standards 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 ofN02 that occur more broadly across communities. 

In the preamble to the 2010 N02 NAAQS and in the EPA's October 2010 letter to your predecessor 

requesting designation recommendations, the agency stated that it expected to designate most areas of 

the country as "unclassifiable," indicating that there are insufficient data to determine whether or not an 

area is attaining the revised N02NAAQS. This approach took into account that 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 Colorado's recommendations and others, and intends to designate all areas of 

Colorado, as well as the rest of the country, as "unclassifiable/attainment" rather than "unclassifiable." 

Based on air quality data from 2008-2010, all monitored areas in the country meet the 2010 N02 
NAAQS. While we acknowledge that the existing N02 monitoring network does not provide adequate 

evidence to determine whether or not the new NAAQS is met in all areas, there currently is no evidence 

of violations 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 new monitoring 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 of states, the area of the 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 of Significant Deterioration (PSD) 

permitting program of having the entire state designated as a single area rather than smaller areas (e.g., 

counties, groups of counties, etc.). To ensure that the size of designated areas is consistent with your 

state's objectives for managing air quality deterioration and economic growth, we recommend that your 

permitting staff be consulted on the area boundary issues. 

If you have additio"nal information 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's preliminary 

designation decisions and supporting documentation available to the general public for review. We are 

accepting public comments on our preliminary decisions for 30 days after a notice announcing the 

public comment period is published in the Federal Register. We will review any information we receive 

from the state of Colorado 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 staff as 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 of my staff at (303) 312-6416. 

Sincerely, 

... me B. ~&L art 

gional A -ministrator 

cc:	 Martha Rudolph, Director, CDPHE 

Paul Tourangeau, Director, APCD 

Gina McCarthy, Assistant Administrator for Air and Radiation
 

Stephen D. Page, Director, Office of Air Quality Planning and Standards