Figure 9
Index of Key Air Pollutant Emissions from U.S.
Transportation: 1970-98
Index: 1970 = 1.0, 1990 = 1.0 for PM-2.5

Key: NOx = oxides of nitrogen; PM-10 and PM-2.5 = airborne
particulates of less than 10 microns or 2.5 microns, respectively; CO =
carbon monoxide; VOC = volatile organic compounds.
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, such as lawnmowers and farming equipment, are not included.
Lead estimates include onroad mobile sources only.
Source: U.S. Environmental Protection Agency, Office of Air
and Radiation, Air Quality Planning and Standards, National Air Quality
and Emission Trends, 1900-1998, available at www.epa.gov/ttn/chief/trends98/emtrnd/html,
as of December 2000.
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