Changes in the chemistry of precipitation in the United States, 1981-1998
Water, Air, & Soil Pollution
By: M.A. Nilles and B.E. Conley
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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.
Suggested Citation
Nilles, M., and Conley, B., 2001, Changes in the chemistry of precipitation in the United States, 1981-1998: Water, Air, & Soil Pollution, v. 130, no. 1-4 II, p. 409-414, https://doi.org/10.1023/A:1013889302895.
ISSN: 1573-2932 (online)
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Changes in the chemistry of precipitation in the United States, 1981-1998 |
| Series title | Water, Air, & 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 |
| Larger Work Title | Water, Air, and Soil Pollution |
| First page | 409 |
| Last page | 414 |