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This paper evaluates the spatial and temporal trends in wet and dry deposition using data
from the National Atmospheric Deposition Program National Trends Network (NTN) and
the U.S. Environmental Protection Agency’s (U.S. EPA) Clean Air Status and Trends
Network (CASTNET). Data from 19 NTN-CASTNET sites collocated within 10 km
were considered from 1990 to 2002. Seasonal mean concentrations of sulfur and nitrogen
species were evaluated using the Seasonal Kendall Trend (SKT) test to determine trend
direction, statistical significance (p = 0.10). Trend magnitudes were determined by the
Sen’s median estimator.
For NTN sulfate concentrations, all 19 sites showed decreasing trends, with 12 of these
trends (63%) being statistically significant. For CASTNET gas phase sulfur dioxide
concentrations, all but one site showed decreasing trends, with these decreasing trends
being statistically significant. Only one increasing trend in sulfur dioxide was noted in
Wyoming, but this trend was not statistically significant.
For NTN nitrate concentrations, eight sites showed an increasing trend (42%), but none
of these trends were statistically significant. Eleven sites showed a decreasing trend; four
of these sites (36%) were statistically significant. For CASTNET total nitrate
concentrations, 10 sites showed an increasing trend (53%); six of these trends (60%) were
statistically significant. Nitrate decreased at 9 sites (47%); only five of these trends (56%)
were statistically significant.
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CNumber:
A&WMA 98th Annual Conference and Exhibition: 06/21/2005
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Publication Type:
Proceedings
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Publication Date:
June 2005
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