6-4 Index of Key Air Pollutant Emissions from U.S. Transportation: 1990-2008

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Index: 1990 = 1.0

Key: R = revised, PM-10 = airborne particulates of less than 10 microns, PM-2.5 = airborne particulates of less than 2.5 microns, U = unavailable.

Notes: The indexes are calculated using data on emissions from highway vehicles only. Particulate matters include PM without condensibles. 2003 data are revised except carbon monoxide, nitrogen oxide, surfur dioxide, and ammonia. 2004 data are revised except nitrogen oxide, sufur dioxide, and ammonia. 2005 data are revised except carbon monoxide, surfur dioxide, and ammonia. 2006 data are revised except carbon monoxide, volatile organic compounds, and ammonia. 2007 data revised except carbon monoxide, surfur dioxide, and ammonia.

Source: U.S. Environmental Protection Agency, Clearinghouse for Inventories and Emissions Factors (CHIEF), Current Emission Trends Summaries, available at http://www.epa.gov/ttn/chief/trends/index.html as of September 2009.