40 CFR §51.1400

The following definitions apply for purposes of this subpart. Any term not defined herein shall have the meaning as defined in § 51.100. Attainment year means the calendar year in which the attainment year ozone season occurs. Attainment year ozone season means the full ozone season immediately preceding a nonattainment area's maximum attainment date. CAA means the Clean Air Act as codified at 42 U.S.C. 7401-7671q (2010). Former attainment date means any attainment date associated with the classification under subpart 2 of part D of title I of the CAA preceding reclassification from a lower classification to a higher classification. Former classification means any classification under subpart 2 of part D of title I of the CAA preceding reclassification from a lower classification to a higher classification. Higher classification/lower classification means for purposes of determining which classifications are higher or lower, the classifications are ranked from lowest to highest as follows: Marginal; Moderate; Serious; Severe-15; Severe-17; and Extreme. I/M refers to the inspection and maintenance programs for in-use vehicles required under the 1990 CAA Amendments and defined by subpart S of 40 CFR part 51. Initially classified means the first nonattainment classification that becomes effective for an area for a specific ozone NAAQS and does not include reclassification to another classification for that specific NAAQS. Initially designated means the first designation to nonattainment that becomes effective for an area for a specific ozone NAAQS. Ozone season means for each state (or portion of a state), the ozone monitoring season as defined in 40 CFR part 58, appendix D, section 4.1(i) for that state (or portion of a state).