A requirement in the federal Clean Air Act that places responsibility on individual states to develop programs that will ensure compliance with standards prescribed in the act.
To comply with provisions of the act, a state environmental agency begins by establishing geographical divisions within its jurisdiction: divisions referred to as Air Quality Control Regions (AQCRs). For each AQCR, the agency is then required to develop a specific plan, outlining the pollution control requirements for that region. In a metropolitan AQCR, for example, Stage II gasoline vapor control might be required. In a rural AQCR, it would not be.
These regional programs, adopted by a state, are referred to in the Clean Air Act as state implementation plans–SIPs.