40 C.F.R. § 51.903 : Protection of Environment — ENVIRONMENTAL PROTECTION AGENCY — AIR PROGRAMS — REQUIREMENTS FOR PREPARATION, ADOPTION, AND SUBMITTAL OF IMPLEMENTATION PLANS — PROVISIONS FOR IMPLEMENTATION OF 8-HOUR OZONE NATIONAL AMBIENT AIR QUALITY STANDARD — How do the classification and attainment date provisions in section 181 of subpart 2 of the CAA apply to areas subject to section 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)
Marginal from up to 1 0.085 0.092 3
Moderate from up to 1 0.092 0.107 6
Serious from up to 1 0.107 0.120 9
Severe-15 from up to 1 0.120 0.127 15
Severe-17 from up to 1 0.127 0.187 17
Extreme equal to or above 0.187 20

1 but 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.

40 C.F.R. §51.903