6-4 Index of Key Air Pollutant Emissions from U.S. Transportation: 1990-2007

6-4 Index of Key Air Pollutant Emissions from U.S. Transportation: 1990-2007

Index: 1990 = 1.0

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Year Carbon monoxide Nitrogen oxides Volatile organic compounds PM-10; PM-2.5 Surfur dioxide Ammonia  
      PM-10 PM-2.5    
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.