83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01

1983-02: 14% decrease 1993-02: 4% increase

FIGURE 4-8. Ozone air quality from 1983 to 2002 based on 1-hour averages. (From EPA, Latest Findings on National Air Quality 2002 Status and Trends, Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, U.S. Government Printing Office, Washington, D.C., August 2003.)

Sulfur Dioxide (SO2)

Nationally, average SO2 ambient concentrations have decreased 54% from 1983 to 2002 and 39% over the last 10 years, as shown in Figure 4-9 [62]. SO2 emissions decreased 33% from 1983 to 2002 and 31% from 1993 to 2002. Reductions in SO2 concentrations and emissions since 1990 are due to controls implemented under the EPA's Acid Rain Program beginning in 1995. As shown in Figure 4-10, fuel combustion, primarily coal and oil, accounts for most of the total SO2 emissions. Coal combustion accounts for approximately 11 of the 15 million short tons of SO2 emitted in 2002.

Particulate Matter

Between 1993 and 2002, PM10 concentrations decreased 13%, while PM10 emissions decreased 22% [62], as illustrated in Figures 4-11 and 4-12, respectively. Fuel combustion accounts for about one-third of total particulate emissions (see Figure 4-12), while electric utilities account for approximately 5% of the total particulate matter emitted [4]. Figure 4-13 shows that direct PM2.5 emissions from anthropogenic sources decreased 17% nationally between 1993 and 2002 [62]. Figure 4-13 tracks only directly emitted particles and does not account for secondary particles, which are primarily sulfates and nitrates formed when emissions of NOx, SO2, ammonia, and other gases react in the atmosphere.

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