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Electronic Code of Federal Regulations

e-CFR data is current as of December 12, 2019

Title 40Chapter ISubchapter CPart 51Subpart X → §51.903


Title 40: Protection of Environment
PART 51—REQUIREMENTS FOR PREPARATION, ADOPTION, AND SUBMITTAL OF IMPLEMENTATION PLANS
Subpart X—Provisions for Implementation of 8-hour Ozone National Ambient Air Quality Standard


§51.903   How do the classification and attainment date provisions in section 181 of subpart 2 of the CAA apply to areas subject to §51.902(a)?

(a) In accordance with section 181(a)(1) of the CAA, each area subject to §51.902(a) shall be classified by operation of law at the time of designation. However, the classification shall be based on the 8-hour design value for the area, in accordance with Table 1 below, or such higher or lower classification as the State may request as provided in paragraphs (b) and (c) of this section. The 8-hour design value for the area shall be calculated using the three most recent years of air quality data. For each area classified under this section, the primary NAAQS attainment date for the 8-hour NAAQS shall be as expeditious as practicable but not later than the date provided in the following Table 1.

Table 1—Classification for 8-Hour Ozone NAAQS for Areas Subject to §51.902(a)

Area class    8-hour
design value
(ppm ozone)
Maximum period for attainment dates in state plans (years after effective date of nonattainment designation for 8-hour NAAQS)
Marginalfrom
up to1
0.085
0.092
3
Moderatefrom
up to1
0.092
0.107
6
Seriousfrom
up to1
0.107
0.120
9
Severe-15from
up to1
0.120
0.127
15
Severe-17from
up to1
0.127
0.187
17
Extremeequal to
or above
0.18720

1but not including.

(b) A State may request a higher classification for any reason in accordance with section 181(b)(3) of the CAA.

(c) A State may request a lower classification in accordance with section 181(a)(4) of the CAA.

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