Much of the emphasis in the sphere of environmental law is on the federal statutes and regulations. However, as the Jennings text points out (2018, pp. 351-352), the states also play a vital role. For instance, there are areas of environmental "cooperation" (whether voluntary or imposed) between the federal and state governments. A primary example of this, mentioned in both texts (Jennings, 2018, p. 333; Emerson, 2015, p. 555), are the state implementation plan programs required under the Clean Air Act, as amended.

Rather than have you delve into the myriad of state regulations themselves, you may search the Code of Federal Regulations to find the state implementation plan for a state air implementation plan of your choice. When you have found it, please provide the initial citation, including the Subpart, for where that state's implementation plan begins in the Code of Federal Regulations, and then the date and Federal Register citation for when initial (some, as with the District of Columbia, which follows as an example, have more than one citation) approval status was granted for that plan. For example, using the District of Columbia, it would be 40 C.F.R., Part 52, Subpart J, 52.470, with initial status approval on Dec. 6, 1973, 52.472.