Nitrate concentrations have decreased across the state since 1983 by an average of 16.6 percent. At most sites, ammonium concentrations were generally within the range reported since 1982. Because ammonium concentrations in precipitation result largely from agricultural activities, the concentrations were highest near large-scale farm operations. The 1998 statewide annual and dormant season mean calcium and magnesium concentrations were well within the range reported since 1982. Continued monitoring of precipitation chemistry will help to evaluate the effectiveness of emission control programs mandated under the 1990 Clean Air Act Amendments and identify the impacts of atmospheric deposition on Pennsylvania's terrestrial, aquatic, cultural, and material resources.
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