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BACKGROUND INFORMATION DOCUMENT 

DEVELOPMENT OF HYPOTHETICAL NONATTAINMENT AREAS FOR 

ILLUSTRATING PROPOSED CLASSIFICATION THRESHOLDS FOR AREAS 

DESIGNATED NONATTAINMENT FOR THE 2008 0.075 PPM 8-HOUR OZONE 

NATIONAL AMBIENT AIR QUALITY STANDARD 

Docket ID No. EPA-HQ-OAR-2010-0885 

U.S. ENVIRONMENTAL PROTECTION AGENCY 

OFFICE OF AIR AND RADIATION 

OFFICE OF AIR QUALITY PLANNING AND STANDARDS 

RESEARCH TRIANGLE PARK, NC 

January 2012 
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INTRODUCTION 

 The EPA is proposing rules to establish classification thresholds for nonattainment areas 

under the 2008 ozone national ambient air quality standard (NAAQS). The proposed rule does 

not propose to establish attainment or nonattainment designations, nor does it address the 

principles that will be considered in the designation process. EPA has already issued guidance 

concerning designations for the 2008 ozone NAAQS and is following the CAA process for 

designating areas for the 2008 NAAQS in a separate action. 

 The Clean Air Act (CAA) specifies certain planning and emission control obligations in 

accordance with each classification and provides the maximum attainment date for each 

classification. To evaluate the potential impact of the proposed classification thresholds, EPA 

developed a set of hypothetical nonattainment areas based on the counties that have monitors 

measuring violations of the 2008 NAAQS based on a 2010 design value. There a total of 113 

counties with monitored 2010 design values that exceed the 2008 ozone NAAQS of 0.075 ppm. 

We note that some areas may certify data from 2011 early so that it can be considered in the 

designation process; thus the counties indentified in this document may not exactly match the 

counties that are considered violating the 2008 NAAQS for purposes of the designations. For 

analysis purposes, the counties were grouped into “hypothetical urban areas” based on the 

following steps below. Once a site is placed in a hypothetical nonattainment area under a step, it 

is not considered for further steps. 

(1) Monitoring sites inside an existing 8-hr ozone nonattainment area boundary designated 

for the 1997 NAAQS are assigned to that area. 

(2) Additional sites inside a county/CBSA/CSA overlapping an existing nonattainment area 

are assigned to that area (i.e. existing nonattainment area is expanded to include those 

sites). 

(3) Remaining sites inside a Combined Statistical Area (CSA) are assigned to that CSA. 

(4) Remaining sites inside a Core Based Statistical Area (CBSA) are assigned to that CBSA. 

(5) All remaining sites are assigned to the county in which they reside. 

The 2006 definitions of Combined Statistical Areas (CSAs) and Core-Based Statistical Areas 

(CBSAs) were used for CSA and CBSA boundaries. 

 

The approach proposed in the rulemaking and analyzed herein is the “Percent-Above-Standard” 

method concerning classification. The classifications for the hypothetical nonattainment areas 

are based on the following thresholds:
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Area class Classification Threshold 

Percent-Above-Standard (ppm) 

Marginal From 0.076 

up to1 0.086 

Moderate From 0.086 

up to1 0.100 

Serious From 0.100 

up to1 0.113 

Severe-15 From 0.113 

up to1 0.119 

Severe-17 From 0.119 

up to1 0.175 

Extreme equal to 

or above 0.175 

1 but not including 

It is important to note that EPA’s method for inclusion and grouping of counties into 

hypothetical nonattainment areas was done solely for the purpose of illustrating how the 

proposed classification schemes discussed might apply to areas designated nonattainment for the 

2008 NAAQS. The creation of this set of hypothetical nonattainment areas, while based on 

actual air quality data from 2008-2010, is not intended to pre-judge the designation process that 

will occur between now and the time of designation, which could be based on more recent 

quality assured air quality data if available sufficiently in advance of the designations. Thus, the 

final designations by EPA may include nonattainment areas that are not on this list. Similarly, 

states may recommend and EPA may designate as attainment some areas or portions of areas that 

are on this list. In addition, boundaries of nonattainment areas could be different than as defined 

in this list of hypothetical areas. This list should not be construed as a proposal by EPA of areas 

that should be designated nonattainment. 

2008 Ozone NAAQS Hypothetical Nonattainment Areas and Classifications Under the 

Percent-Above-Standard Method 

 This section presents the hypothetical nonattainment areas, their 8-hour ozone design 

values for 2010, and the classifications under the Percent-Above-Standard proposal for 

classification of nonattainment areas under the 2008 8-hour standard of 0.075 ppm. Under this 

proposed classification method, all areas would be classified under subpart 2 of part D, Title I of 

the Clean Air Act, according to 8-hour ozone levels. The 2008 NAAQS classification thresholds 

would apply to all areas designated nonattainment and would be set at the same percentage 

above the level of the 2008 NAAQS as the 1-hour classification thresholds were above the 1-

hour standard level as established in the Clean Air Act’s Table 1 (section 181). As a result, all 

nonattainment areas would be classified as Marginal, Moderate, Serious, Severe or Extreme 

under a revised classification table that is based on a 0.075 ppm 8-hour ozone NAAQS. The 

table of the classifications and the 8-hour ozone thresholds appear in the proposal. 
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Table 1: 2008 Ozone NAAQS Hypothetical Nonattainment Areas and Classifications Under 

the Percent-Above-Standard Method 

Hypothetical Nonattainment Area Design Value 

2008-2010 (ppm) 

Prospective 

Classification 

Los Angeles South Coast Air Basin, CA 0.112 Serious 

San Joaquin Valley, CA 0.104 Serious 

Sacramento Metro, CA 0.102 Serious 

Los Angeles-San Bernardino Cos (W Mojave), CA 0.099 Moderate 

Riverside Co, (Coachella Valley), CA 0.095 Moderate 

Baltimore, MD 0.089 Moderate 

San Diego, CA 0.088 Moderate 

Dallas-Fort Worth, TX 0.086 Moderate 

Ventura Co, CA 0.086 Moderate 

Houston-Galveston-Brazoria, TX 0.084 Marginal 

Nevada Co. (Western Part), CA 0.084 Marginal 

New York-N. New Jersey-Long Island,NY-NJ-CT 0.084 Marginal 

San Luis Obispo-Paso Robles, CA 0.084 Marginal 

Amador and Calaveras Cos (Central Mtn), CA 0.083 Marginal 

Kern Co (Eastern Kern), CA 0.083 Marginal 

Mariposa and Tuolumne Cos (Southern Mtn), CA 0.083 Marginal 

Philadelphia-Wilmington-Atl. City, PA-NJ-MD-DE 0.083 Marginal 

Charlotte-Gastonia-Rock Hill, NC-SC 0.082 Marginal 

Pittsburgh-Beaver Valley, PA 0.081 Marginal 

Washington, DC-MD-VA 0.081 Marginal 

Atlanta, GA 0.080 Marginal 

San Francisco Bay Area, CA 0.080 Marginal 

Red Bluff, CA 0.080 Marginal 

Chico, CA 0.079 Marginal 

Greater Connecticut, CT 0.079 Marginal 

Cincinnati-Hamilton, OH-KY-IN 0.079 Marginal 

Reading, PA 0.079 Marginal 

Baton Rouge, LA 0.078 Marginal 

Boston-Lawrence-Worcester (E. Mass), MA 0.078 Marginal 

Denver-Boulder-Greeley-Ft Collins-Love., CO 0.078 Marginal 

Imperial Co, CA 0.078 Marginal 

Sheboygan, WI 0.078 Marginal 

Sublette County, WY – COUNTY 0.078 Marginal 

Jamestown, NY 0.077 Marginal 

Phoenix-Mesa, AZ 0.077 Marginal 

Springfield (Western MA), MA 0.077 Marginal 

St. Louis, MO-IL 0.077 Marginal 

Cleveland-Akron-Lorain, OH 0.077 Marginal 

Columbus, OH 0.077 Marginal 

Knoxville, TN 0.077 Marginal 

Lancaster, PA 0.077 Marginal 

Las Vegas, NV 0.076 Marginal 

Providence (All RI), RI 0.076 Marginal 
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Hypothetical Nonattainment Area Design Value 

2008-2010 (ppm) 

Prospective 

Classification 

Sutter Co (Sutter Buttes), CA 0.076 Marginal 

Allentown-Bethlehem-Easton, PA 0.076 Marginal 

Memphis, TN-AR 0.076 Marginal 

Richmond-Petersburg, VA 0.076 Marginal 

Greensboro--Winston-Salem--High Point, NC 0.076 Marginal 

Greenville-Spartanburg-Anderson, SC 0.076 Marginal 

Gulfport-Biloxi-Pascagoula, MS 0.076 Marginal 

Nashville-Davidson-Murfreesboro-Columbia, TN 0.076 Marginal 

Santa Barbara-Santa Maria-Goleta, CA 0.076 Marginal