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Changes in the chemistry of precipitation in the United States, 1981-1998

Water, Air, and Soil Pollution

By:
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DOI: 10.1023/A:1013889302895

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Abstract

Regulatory measures in the United States, such as Title IV of the Clean Air Act Amendments of 1990, have primarily restricted sulfur dioxide emissions as a way to control acidic deposition. These restrictions, coupled with increasing concentrations of NH4+ in wet deposition in some regions of the U.S. and continued high emissions of nitrogen oxides have generated a significant shift in the chemistry of precipitation as measured at National Atmospheric Deposition Program/National Trends Network sites. Trends in precipitation chemistry at NADP/NTN sites were evaluated for statistical significance for the period 1981-1998 using a Seasonal Mann-Kendall Test, a robust non-parametric test for detection of monotonic trends. SO42- declines were detected at 100 of the 147 sites examined while no sites exhibited increasing SO42- trends. On average, SO42- declined 35% over the period 1981-1998 with downward SO42- trends being most pronounced in the northeastern United States. In contrast, no consistent trends in NO3- concentrations were observed in precipitation in any major region of the United States. Although the majority of sites did not exhibit significant trends in NH4+ concentration, 30 sites exhibited upward trends. For Ca2+ concentration in precipitation, 64 sites exhibited a significant decreasing trend and no sites exhibited an upward trend.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Changes in the chemistry of precipitation in the United States, 1981-1998
Series title:
Water, Air, and Soil Pollution
DOI:
10.1023/A:1013889302895
Volume
130
Issue:
1-4 II
Year Published:
2001
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
409
Last page:
414
Number of Pages:
6