“clean air”

established air pollution control standards and gave citizens' groups the right to sue alleged violators. Most notably, it set auto emission standards and required manufacturers to drastically reduce the amount of pollutants discharged from new cars. Enforcement authority was assigned to the Environmental Protection Agency (EPA). A 1977 amendment extended certain deadlines for reaching specified auto emission levels while applying tighter restrictions on coal burning and other pollution sources; and a 1990 amendment imposed more stringent requirements on urban areas and mandated the increased use of cleaner-burning fuels.