Office of Air & Radiation

Proposed Rule: Ozone Nonattainment 

Area Classifications Approach, 

Attainment Deadlines, and Revocation 

of the 1997 Standards for 

Transportation Conformity Purposes

Summary for NACAA

February 21, 2012
Office of Air & Radiation 

Overview 

• Proposed rule published in the Federal Register Feb.14, 2012 

(77 FR 8197). Docket ID No. EPA-HQ-OAR-2010-0885.

• Public comment period closes March 15, 2012. 

• EPA intends to finalize this rule no later than May 31, 2012. 

• What the proposed rule covers: 

– Classification thresholds for designated nonattainment areas 

– Reclassification of areas that have voluntarily requested higher 

classifications 

– Attainment deadlines for nonattainment areas 

– Revocation of the 1997 ozone NAAQS for purposes of 

Transportation Conformity 

• All other implementation rule and guidance issues will be 

addressed in separate rulemaking that is targeted for proposal 

this spring, and final by end of 2012. 2 
Office of Air & Radiation

CAA Classification Scheme

• Table 1 in CAA section 181 

specifies ozone design values 

associated with each 

classification, based on the 

standard that existed in 1990 

(0.120 ppm 1-hour exceedancebased NAAQS).

• Each classification has a 

specified attainment date tied to 

a number of years after the CAA 

amendments were enacted.

• For subsequent 8-hr standards, 

the Table 1 design values and 

attainment dates are outdated, 

but the same basic classification 

structure applies.

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Table 1 from CAA Section 181(a)(1)

Area 

classification

Design value

(ppm)

Primary 

standard 

attainment date

Marginal 0.121 up to 0.138 3 years after Nov 

15, 1990

Moderate 0.138 up to 0.160 6 years after Nov 

15, 1990

Serious 0.160 up to 0.180 9 years after Nov 

15, 1990

Severe 0.180 up to 0.280 15 years after

Nov 15, 1990

Extreme 0.280 and above 20 years after

Nov 15, 1990
Office of Air & Radiation

Classification Thresholds of NAAs 

• EPA is proposing thresholds based on the “PercentAbove-the-Standard” method for translating the design 

values in CAA section 181, Table 1 (1-hour thresholds) 

into 8-hour thresholds for the 2008 8-hour NAAQS.

• The same methodology was used for classifying areas 

for the 1997 8-hour NAAQS.

• Upper thresholds for each classification are based on 

calculated percentages above the level of the NAAQS:

• 15% for Marginal (0.138-0.120)/0.120

• 33.33% for Moderate (0.160-0.120)/0.120

• 50% for Serious (0.180-0.120)/0.120

• 133.33% for Severe (0.280-0.120)/0.120

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Office of Air & Radiation

Calculation of Thresholds Using 

Percent-Above-the-Standard Method

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Classification Range (ppm)

# Hypo. 

NAAs*

Marginal 0.076 up to 0.086 43

Moderate 0.086 up to 0.100 6

Serious 0.100 up to 0.113 3

Severe 0.113 up to 0.175 0

Extreme 0.175 and up 0

• The level of the 2008 NAAQS 

is multiplied by the percent 

above the standard for each 

classification threshold in 

Table 1 of the CAA.

• The result is added to the 

level of the 2008 NAAQS to 

obtain the new threshold.

• For example, to calculate the 

upper threshold for the 

Moderate classification using 

0.075 ppm:

 (0.075 ppm x 33.3%) + 

0.075 ppm = 0.100 ppm

* Estimated with 2010 Design Values
Office of Air & Radiation

Reclassification of areas that voluntarily 

requested higher classifications

• Under the 1997 ozone 

NAAQS, 7 areas requested 

a voluntary reclassification. 

• EPA is proposing to apply 

these voluntary 

reclassifications to the 2008 

ozone NAAQS unless the 

state requests otherwise.

• Texas has already indicated 

they do not wish to apply the 

previous reclassification to 

the Houston NAA.

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Areas for which the State Requested a Voluntary Reclassification 

Under the 1997 NAAQS

Nonattainment 

Area

St.

Original 1997 

NAAQS 

Classification

Voluntary 

Reclassification

Request

2008 

NAAQS 

Potential 

Classification

Los AngelesSouth Coast Air 

Basin

CA Severe Extreme Serious

San Joaquin 

Valley

CA Serious Extreme Serious

HoustonGalvestonBrazoria

TX Moderate Severe Marginal

Riverside

County 

(Coachella 

Valley)

CA Serious Severe Moderate

Sacramento 

Metro

CA Serious Severe Serious

Ventura County CA Moderate Serious Moderate

Western Mojave

(pending)

CA Moderate Severe Moderate
Office of Air & Radiation

Proposed Attainment Deadlines

• CAA section 181 establishes 

attainment dates based on 

area classification.

• EPA is requesting comment on 

2 proposed options for 

establishing attainment dates 

for the 2008 NAAQS that are 

consistent with the intent of the 

CAA.

• If designations are completed 

in 2012, attainment dates 

would range from 2015 to 

2032.

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Area 

classification

Attainment 

deadline

Attainment 

Year

Marginal 3 years 2015

Moderate 6 years 2018

Serious 9 years 2021

Severe 15 years 2027

Extreme 20 years 2032
Office of Air & Radiation

Proposed Attainment Deadlines – Option 1:

X years after Effective Date of Designations

• Under this option, EPA is proposing that the deadlines in the 

regulatory table would be established in terms of a specified number 

of years from the effective date of designation for the 2008 standard.

• This is the same approach used for the 1997 NAAQS.

• Under Option 1, the term “years” in CAA Table 1 is interpreted to 

mean “rolling 365-day periods” and the words “after the effective 

date of designation” would be substituted for the CAA’s “after 

November 15, 1990” language.

• For example, if designations are effective on August 15, 2012, the 

attainment date for Moderate areas would be August 15, 2018. 

– Under Option 1, the evaluation of attainment for Moderate areas in this example 

would be based on the 2017 design value (2015-2017 air quality data). Air 

quality data from 2018 would not be considered.

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Office of Air & Radiation

Proposed Attainment Deadlines – Option 2:

End of Calendar Year

• Under this option, EPA is proposing that the deadlines in the regulatory 

table would be established as the number of CAA-specified years from the 

end of the calendar year in which an area’s nonattainment designation is 

effective. This is EPA’s preferred option.

• This option assures each nonattainment area will be afforded 3, 6, 9, 15, or 

20 full ozone seasons (per classification) after designation to attain.

• For example, if designations are effective on August 15, 2012, the 

attainment date for Moderate areas would be December 31, 2018. 

• Under Option 2, the evaluation of attainment for Moderate areas in this 

example would be based on the 2018 design value (2016-2018 air quality 

data). This would allow air quality improvements due to emissions 

reductions occurring in the 2018 ozone season to inform attainment 

determinations.

• EPA believes this is consistent with the near end-of-year outcome (i.e., 

November 15) associated with the 1990 CAA amendments.

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Office of Air & Radiation

Revocation of the 1997 NAAQS for 

Transportation Conformity Purposes

• A conformity demonstration is intended to show that implementation 

of the metropolitan transportation plan, TIP, or project falls within an 

area’s mobile source emissions budget.

• Newly designated areas have a 1-year grace period for transportation 

conformity. A conformity “lapse” occurs if a conformity determination 

has not been made by the end of the grace period.

• EPA is proposing to revoke the 1997 ozone NAAQS 1 year after the 

effective date of designation for the 2008 ozone NAAQS for purposes 

of transportation conformity only.

– This provides certainty for planning operations, and prevents areas from having to 

implement the transportation conformity program for two different NAAQS 

concurrently.

– Backsliding is prevented through the use of approved motor vehicle emissions 

budgets for a prior ozone NAAQS until new budgets are established for the 2008 

ozone NAAQS.

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