Mobile Sources

Since the earliest days of the Clean Air Act (CAA), mobile sources have been recognized as one of the most important sources of air pollution and, as a result, have been a prime target for emission control. The 1970 CAA required automobile manufacturers to reduce by 90% the pollutant emissions from new vehicles by 1975. Specific limits were set for emissions of carbon monoxide, hydrocarbons, and oxides of nitrogen from automobiles. This forced the automobile industry to develop new technologies for emission control. Currently, a wide variety of mobile sources are subjected to control under the CAA. Strategies used to control mobile-source emissions include the new-source certification programs that specify emission standards applicable to new vehicles and motors; in-use technological measures and controls that include specification for fuel properties, vehicle inspections, maintenance programs, and retrofits to existing vehicles; and non-technological measures to control usage or activity.