Figure 1 - National Transportation Emissions Trends Index: 1970-1999

Figure 1 - National Transportation Emissions Trends Index: 1970-1999

(Index: 1970 = 1.0; 1990 = 1.0 for PM-2.5 and ammonia)

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Year CO NOx VOC PM-10 PM-2.5 Lead Ammonia
1970 1.0 1.0 1.0 1.0   1.0  
1971 1.0 1.1 1.0 1.1   1.1  
1972 1.0 1.2 0.9 1.1   1.2  
1973 1.0 1.2 0.9 1.1   1.0  
1974 0.9 1.1 0.8 1.1   0.9  
1975 0.9 1.2 0.8 1.1   0.7  
1976 1.0 1.2 0.8 1.1   0.8  
1977 1.0 1.2 0.8 1.1   0.8  
1978 1.0 1.3 0.8 1.1   0.6  
1979 0.9 1.2 0.7 1.1   0.5  
1980 0.9 1.2 0.7 1.0   0.4  
1981 0.9 1.2 0.7 0.9   0.3  
1982 0.9 1.2 0.7 0.9   0.2  
1983 0.9 1.2 0.7 0.9   0.2  
1984 0.9 1.2 0.7 1.0   0.2  
1985 0.9 1.2 0.8 1.0   0.1  
1986 0.8 1.1 0.7 0.9   0.1  
1987 0.8 1.1 0.7 1.0   0.0  
1988 0.8 1.2 0.7 1.1   0.0  
1989 0.8 1.2 0.6 1.1   0.0  
1990 0.7 1.2 0.5 1.1 1.0 0.0 1.0
1991 0.7 1.2 0.6 1.1 1.0 0.0 1.1
1992 0.7 1.2 0.5 1.1 1.0 0.0 1.1
1993 0.7 1.3 0.5 1.0 0.9 0.0 1.2
1994 0.7 1.3 0.6 1.0 0.9 0.0 1.2
1995 0.7 1.3 0.5 0.9 0.8 0.0 1.3
1996 0.7 1.4 0.5 1.0 1.0 0.0 1.2
1997 0.7 1.4 0.5 1.0 0.9 0.0 1.4
1998 0.6 1.4 0.5 0.9 0.9 0.0 1.4
1999 0.6 1.4 0.5 0.9 0.8 0.0 1.4

KEY: CO = carbon monoxide; NOx = nitrogen oxides; VOC = volatile organic compounds; PM-10 = particulate matter 10 microns in diameter or smaller; PM-2.5 = particulate matter 2.5 microns in diameter or smaller.

SOURCE: U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards, "National Emission Inventory (NEI), Air Pollutant Emission Trends," available at http://www.epa.gov/ttn/chief/trends/, as of January 2001.