Figure 5-8 Index of Key Air Pollutant Emissions from U.S. Transportation: 1990–2012
KEY: PM-10 = airborne particulates of less than 10 microns; PM-2.5 = airborne particulates of less than 2.5 microns.
NOTES: Not all graph scales are comparable. The indices are calculated using data on emissions from highway vehicles only.Particulate matters include PM without condensibles.
SOURCES: U.S. Environmental Protection Agency, Clearinghouse for Inventories and Emissions Factors, 1970 - 2012 Average annual emissions (all criteria pollutants), available at http://www.epa.gov/ttn/chief/trends/index.html as of January 2013.