ABSTRACT
As seen in Chapter 2, transportation in the United States is the major emission source of three primary pollutants: hydrocarbons (HCs), carbon monoxide (CO), and nitrogen oxides (NOx). Most of these emissions are associated with light-duty cars and trucks. Heavy-duty trucks, motorcycles, and off-road vehicles are also signicant sources. In urban areas, motor vehicles are estimated to be responsible for 40% to 50% of HC, 50% of NOx, and 80% to 90% of CO emissions. Similar patterns have been reported in Europe and Japan.
