CASTNet Sulfur Dioxide and Nitrogen Oxide Ambient Concentration Trends and the Title IV Acid Rain Provisions

摘要

Title IV of the Clean Air Act Amendments of 1990 (CAAA) implemented strict controls on sulfur and nitrogen oxide emissions from electric utilities. The CAAA also required the establishment of a national monitoring network to 1) monitor the status and trends of air emissions, pollutant deposition, and air quality, 2) determine the effects of emissions on water quality, forests and other sensitive ecosystems and 3) assess the effectiveness of emission reduction requirements through operation of a long-term monitoring network. In order to satisfy these requirements, the U.S. Environmental Protection Agency (EPA) established the Clean Air Status and Trends Network (CASTNet) with two primary goals: 1) to operate an effective monitoring and assessment network to determine the status and trends of air pollution levels and their environmental effects, and 2) to develop a scientific database to improve understanding of sources and effects for policy considerations. Prior to the establishment of CASTNet, EPA operated the National Dry Deposition Network (NDDN). NDDN started in 1986 and was incorporated into CASTNet in 1991. Thus, a long-term data set of sulfur and nitrogen oxide measurements now exists. This paper examines the long-term trends in ambient levels of sulfur and nitrogen oxides measured as part of NDDN and CASTNet and compares those trends to trends in emissions. The effects of the Title IV emission reductions are evaluated and compared with the ambient monitoring trends.