40 C.F.R. § 52.1172
With the exceptions set forth in this subpart, the Administrator approves Michigan's plan for the attainment and maintenance of the National Ambient Air Quality Standards under section 110 of the Clean Air Act. Furthermore, the Administrator finds the plan satisfies all requirements of Part D, Title I of the Clean Air Act as amended in 1977, except as noted below. In addition, continued satisfaction of the requirements of Part D for the ozone portion of the SIP depends on the adoption and submittal of RACT requirements by July 1, 1980 for the sources covered by CTGs between January 1978 and January 1979 and adoption and submittal by each subsequent January of additional RACT requirements for sources covered by CTGs issued by the previous January.
40 C.F.R. §52.1172