6-4,,,,,,,
Index of Key Air Pollutant Emissions from U.S. Transportation: 1990–2007,,,,,,,
Index: 1990 = 1.0,,,,,,,
Year,Carbon monoxide,Nitrogen oxide,Volatile organic compounds,PM-10; PM-2.5,,Surfur dioxide,Ammonia
1990,1.00,1.00,1.00,1.00,1.00,1.00,1.00
1991,0.95,0.99,0.94,0.96,0.95,0.93,1.09
1992,0.90,0.97,0.89,0.91,0.90,0.87,1.17
1993,0.86,0.96,0.83,0.87,0.85,0.80,1.26
1994,0.81,0.94,0.78,0.83,0.81,0.73,1.35
1995,0.76,0.93,0.72,0.79,0.76,0.67,1.43
1996,0.71,0.91,0.66,0.74,0.71,0.60,1.52
1997,0.69,0.92,0.64,0.71,0.67,0.60,1.71
1998,0.66,0.90,0.62,0.66,0.62,0.60,1.65
1999,0.62,0.87,0.61,0.62,0.57,0.60,1.72
2000,0.62,0.88,0.57,0.59,0.54,0.52,1.77
2001,0.58,0.81,0.53,0.55,0.49,0.49,1.79
R2002,0.55,0.82,0.52,0.52,0.46,0.49,1.90
R2003,0.51,0.77,0.49,0.51,0.44,0.42,1.92
R2004,0.47,0.72,0.46,0.49,0.41,0.36,1.95
R2005,0.44,0.67,0.43,0.47,0.39,0.29,1.98
R2006,0.41,0.62,0.41,0.41,0.33,0.23,1.97
2007,0.38,0.58,0.38,0.39,0.31,0.18,1.98
"Key: R = revised, PM-10 = airborne particulates of less than 10 microns, PM-2.5 = airborne particulates of less than 2.5 microns.",,,,,,,
Notes: The indexes are calculated using data on emissions from highway vehicles only. Particle matters include PM without condensibles.,,,,,,,
"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 October 2008.",,,,,,,