(Index: 1975= 1.0, 1990 = 1.0 for PM-2.5 and ammonia)
Note: Transportation emissions include all onroad mobile sources and the following nonroad mobile sources: recreational vehicles and boats, airport service equipment, aircraft, commercial marine vessels, and railroads. Other nonroad sources, e.g., farming equipment, are not included. Lead estimates include onroad mobile sources only.
Source: U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards, National Air Pollutant Trends, available at http://www.epa.gov/ttn/chief/trends/index.html, as of September 2002.