DLESE description of Trends in Precipitation Chemistry in the United States, 1983-94: An Analysis of the Effects in 1995 of Phase I of the Clean Air Act Amendments of 1990, Title IV.

Title IV of the Clean Air Act Amendments of 1990 (CAAA-90) (Public Law 101-549) seeks to reduce acidic deposition in the United States through phased reductions in sulfur dioxide and nitrogen oxide emissions. One of the first steps in assessing the effectiveness of such emissions reductions is to evaluate spatial and temporal trends in sulfate, nitrate, and hydrogen ion concentrations in precipitation. Filed as USGS Report 96-0346, this document details a study to evaluate the effects of Public Law 101-549 on such emission levels as monitored at National Atmospheric Deposition program/National Trends Network (NADP/NTN) sites in 1995. The assessment was based on a comparison of observed 1995 sulfate, nitrate, and hydrogen ion concentrations at these NADP/NTN sites with estimates obtained from linear least-squares trend models of precipitation chemistry data collected from 1983 through 1994. After a review of various reports detailing temporal trends in precipitation chemistry in North America and in the Netherlands, the report details the deposition monitoring of NAPD/NFN sites with datasets included either as tables in html or as figures in GIF formats. The research was funded by the U.S. Geological Survey as a contribution to the National Acid Precipitation Assessment Program.