Section 51.902 - Which classification and nonattainment area planning provisions of the CAA shall apply to areas designated nonattainment for the 1997 8-hour NAAQS?(a) An area designated nonattainment for the 1997 8-hour NAAQS will be classified in accordance with section 181 of the CAA, as interpreted in § 51.903(a) , for purposes of the 1997 8-hour NAAQS, and will be subject to the requirements of subpart 2 that apply for that classification. 77 FR 28841 , May 14, 2012