40 CFR 52.21 : Protection Of Environment (§ 1.1 To Parts 1851-1899) — (§ 52.01 To §§ 52.1000-52.1018) — Environmental Protection Agency (Continued) (§ 52.01 To §§ 52.1000-52.1018) — Air Programs (Continued) (§ 52.01 To §§ 52.1000-52.1018) — Approval And Promulgation Of Implementation Plans (§ 52.01 To §§ 52.1000-52.1018) — General Provisions (§ 52.01 To § 52.39) — Prevention of significant deterioration of air quality.