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Title IV of the Clean Air Act Amendments of 1990 has produced a significant reduction in
nationwide sulfur dioxide (802) emissions over the last 10 years, with an especially
significant drop from 1994 to 1995. During the same period, emissions of oxides of nitrogen
have stayed fairly constant. Measurements from the U.S. Environmental Protection Agency`s
Clean Air Status and Trends Network (CASTNet) of ambient concentrations, and
concentrations in precipitation of various sulfur and nitrogen species, provide information on
trends in wet and dry deposition of these species. Data collected over the period 1990
through 1999 show a significant reduction in SC>2 concentrations and total (wet plus dry)
sulfur depositions averaged over 34 monitoring sites in the eastern United States. The trends
in concentrations and depositions of sulfur were similar to trends in SO2 emissions over the
same period. No trends were found for nitrogen species. CASTNet measurements of ozone
concentrations show an extensive region with fourth highest daily maximum 8-hour values
above 85 parts per billion. PlS/^.s measurements from eight sites show ammonium sulfate is
the principal contributor to fine particle mass. Organic carbon and ammonium nitrate are
also significant contributors. Cloud chemistry measurements at three sites indicate cloud
deposition is an important pathway at high elevations.
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CNumber:
ACE 2001 ORLANDO, FLORIDA
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Publication Type:
Proceedings
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Publication Date:
June 2001
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