关键词：水质；损害；空气污染；大气沉降
摘 要：Atmospheric deposition, a process that transfers pollutants, including NOx, SO2, and mercury, from the air to the earth's surface, can significantly impair the quality of the nation's waters. EPA can potentially address atmospheric deposition through the CWA and the CAA, but concerns have been raised about its ability to do so. GAO was asked to examine EPA's efforts to address atmospheric deposition of pollutants that impair waterbodies. This report examines (1) the extent to which atmospheric deposition of NOx, SO2, and mercury contributes to the impairment of the nation's waters and identify the key sources of these pollutants; (2) the regulatory tools that EPA uses under the CWA to address the effects of atmospheric deposition, and the challenges, if any, that it faces in doing so; and (3) the regulatory tools that EPA uses under the CAA to address the effects of atmospheric deposition, and the challenges, if any, that it faces in doing so. To conduct this work, GAO reviewed EPA data, reports, and activities and interviewed agency officials and other experts.