NOTE: In estimating criteria and related pollutant emissions for 1997, the Environmental Protection Agency (EPA) made adjustments to prior years. For onroad mobile sources, EPA revised 1996 data. For nonroad mobile sources, EPA revised some estimates back to 1970. The figure reflects those changes and supercedes the similar figure 4-8 in Transportation Statistics Annual Report 1998.
SOURCE: U.S. Environmental Protection Agency, Office of Air and Radiation, Air Quality Planning and Standards, National Air Pollution Emission Trends, 1900-1997 , available on the EPA website at www.epa.gov/ttn/chief/trends97/emtrnd.html.