Index: 1990 = 1.0
Key: PM-10 and PM-2.5 = airborne particulates of less than 10 microns or 2.5 microns, respectively.
Notes: Data in the previous edition include all onroad mobile sources and some nonroad mobile sources. EPA revised the emissions estimation methodology for onroad mobile sources.
Source: U.S. Environmental Protection Agency, Clearinghouse for Inventories and Emissions Factors (CHIEF), Current Emission Trends Summaries, Internet website http://www.epa.gov/ttn/chief/trends/index.html as of September 2007.