40 C.F.R. § 51.1303

Application of classification and attainment date provisions in CAA section 181 to areas subject to § 51.1302

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(a) In accordance with CAA section 181(a)(1), each area designated nonattainment for the 2015 ozone NAAQS shall be classified by operation of law at the time of designation. The classification shall be based on the 8-hour design value for the area at the time of designation, in accordance with Table 1 of this paragraph (a). A state may request a higher or lower classification as provided in paragraphs (b) and (c) of this section. For each area classified under this section, the attainment date for the 2015 NAAQS shall be as expeditious as practicable, but not later than the date provided in Table 1 as follows:

Table 1 to Paragraph (a)—Classifications and Attainment Dates for 2015 8-Hour Ozone NAAQS (0.070 ppm) for Areas Subject to § 51.1302
Area class		8-hour ozone design value (ppm)	Primary standard attainment date (years after the effective date of designation for 2015 primary NAAQS)
Marginal	from up to *	0.071 0.081	3
Moderate	from up to *	0.081 0.093	6
Serious	from up to *	0.093 0.105	9
Severe-15	from up to *	0.105 0.111	15
Severe-17	from up to *	0.111 0.163	17
Extreme	equal to or above	0.163	20
* But not including.

(b) A state may request, and the Administrator must approve, a higher classification for an area for any reason in accordance with CAA section 181(b)(3).

(c) A state may request, and the Administrator may in the Administrator's discretion approve, a higher or lower classification for an area in accordance with CAA section 181(a)(4).

Notes of Decisions

Cited in 4 cases (3 in the last 5 years), 2020–2025 · leading case: State of TX v. EPA, 983 F.3d 826 (5th Cir. 2020).

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State of TX v. EPA, 983 F.3d 826 (5th Cir. 2020). “See 40 C.F.R. § 51.1303 (2018). The higher a county’s nonattainment classification, the more stringent the air planning requirements are to bring the county back into compliance.”

Bd. of Cnty. Commissioners of Weld Cnty., CO v. EPA, 72 F.4th 284 (D.C. Cir. 2023). “See 40 C.F.R. § 51.1303 (a). C In Clean Wisconsin, this Court held that EPA had acted arbitrarily in designating northern Weld County and El Paso County as attainment areas.”

Bd. of Cnty. Commissioners of Weld Cnty., CO v. EPA (D.C. Cir. 2023). “See 40 C.F.R. § 51.1303 (a). C In Clean Wisconsin, this Court held that EPA had acted arbitrarily in designating northern Weld County and El Paso County as attainment areas.”

Zeldin (N.D. Cal. 2025). “; 40 C.F.R. § 51.1303 . The 14 CAA requires EPA to determine whether a nonattainment area attained the relevant NAAQS 15 within 6 months of the attainment date.”

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