Inspection and maintenance program (I/M program) – Auto inspection programs are required for some polluted areas.  These periodic inspection checks whether a car is being maintained to keep pollution down and whether emission control systems are working properly.  Vehicles which do not pass inspection must be repaired.  Under the 1990 Clean Air Act, some areas have enhanced inspection and maintenance programs, using special machines that can check for such things as how much pollution a car produces during actual driving conditions.

International Air Pollution - Pollution that moves across national borders. The 1990 Clean Air Act includes provisions for cooperative efforts to reduce pollution that originates in one North American country and affects another.

Interstate air pollution – In many areas, two or more states share the same air.  We say these states are in the same air basin defined by geography and wind patterns.  Often, air pollution moves out of the state in which it is produced into another state.  Some pollutants, such as the power plant combustion products that cause acid rain, may travel over several states before affecting health, the environment and property.  The 1990 Clean Air Act includes many provisions, such as interstate compacts, to help states work together to protect the air they share.  Reducing interstate air pollution is very important since many Americans live and work in areas where more than one state is part of a single metropolitan area.