| 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. |
| Genre: | Article |
| ProdID: | 70023032 |
| Citation Author: | Nilles, M. A.; Conley, B. E. |
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| Citation End Page: | 414 |
| Citation Issue: | 1-4 II |
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| Citation Language: | English |
| Citation Larger Work Title: | Water, Air, and Soil Pollution |
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| Citation Number Of Pages: | 6 |
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| Citation Search Results Text: | Changes in the chemistry of precipitation in the United States, 1981-1998; 2001; Article; Journal; Water, Air, and Soil Pollution; Nilles, M. A.; Conley, B. E. |
| Citation Start Page: | 409 |
| Citation Volume: | 130 |
| Citation Year: | 2001 |
| Type: | citation/reference |
| Text: | Changes in the chemistry of precipitation in the United States, 1981-1998; 2001; Article; Journal; Water, Air, and Soil Pollution; Nilles, M. A.; Conley, B. E. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| URL (DIGITAL OBJECT IDENTIFIER): | http://dx.doi.org/10.1023/A:1013889302895 |
| Date Other: | Mon, 1 Jan 2001 00:00 -0600 |
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