6-4 Index of Key Air Pollutant Emissions from U.S. Transportation: 1990-2006

6-4 Index of Key Air Pollutant Emissions from U.S. Transportation: 1990-2006

Index: 1990 = 1.0

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Year Carbon monoxide
CO
Nitrogen oxide
NOx
Volatile organic compounds
VOC
Particle matters Surfur dioxide
SO2
Ammonia
NH3
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
2002 0.57 0.85 0.50 0.52 0.46 0.51 1.87
2003 0.55 0.81 0.47 0.51 0.44 0.48 1.91
2004 0.53 0.77 0.45 0.50 0.42 0.44 1.95
2005 0.51 0.73 0.43 0.48 0.40 0.41 2.00
2006 0.49 0.69 0.41 0.47 0.38 0.37 2.05

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.