According to the EPA, cars, buses, trucks, and off-highway mobile sources such as construction vehicles and boats produce a substantial amount of air pollution. Even though nationally air pollutants are created from a great variety of industrial and combustion processes, the personal automobile is the single greatest polluter.
Although air pollution emissions from each individual car are generally small, America's population of automobiles & drivers are increasing. The emissions from the millions of vehicles on our nation’s roads each day contribute substantially to our air pollution problems.
Driving a private car is probably a typical citizen's most "polluting" daily activity, with pollution resulting from both the combustion process and from evaporation of the fuel itself. Reducing your driving is a great way to cut down on air pollution.