【精选】00Haze trends over the United States, 1980–1995.pdf

Atmospheric Environment 35 (2001) 5205–5210 Haze trends over the United States, 1980–1995 a, b b c Bret A. Schichtel *, Rudolf B. Husar , Stefan R. Falke , William E. Wilson a Co-operative Institute for Research in the Atmosphere (CIRA), Colorado State University, Fort Collins, Colorado 80523, USA b Center for Air Pollution Impact and Trend Analysis, Washington University, St. Louis, Missouri, USA c National Center for Environmental Assessment/U.S. EPA, Research Triangle Park, North Carolina, USA Received 15 September 2000; received in revised form 30 April 2001; accepted 4 May 2001 Abstract The patterns and trends of haze over the United States for the period of 1980–1995 are presented. Haze measurements are based on human visual range observations at 298 synoptic meteorological stations operated by the United States Weather Service. There was a significant ( B10%) decline in haziness over the 15-yr period. The reductions were evident throughout the eastern United States as well as over the hazy air basins of California. During the same period, in the eastern United States sulfur emissions also declined by about 10%. However, a causality for the reductions has not been established. This report is an update of an earlier survey of haze patterns and trends from 1950 to 1980. r 2001 Elsevier Science Ltd. All rights reserved. Keywords: Visibility; Light extinction; Trends; Eastern United States; SO2 emissions 1. Introduction 2. Haze trend data and processing The spatial and temporal trends, as well as the man- The data set used for the vis