Abstract:

Horizontal visibility and extinction coefficients could reflect the aerosol changes in the atmosphere. By using the data of visibility, relative humidity, precipitation and other weather phenomena observed at 147 sites in Sichuan Province during 1961-2010, the dry visibility (DV) and dry extinction coefficient (DEC) were calculated through the correction of relative humidity, the temporal and spatial DVvariations were characterized and the trends in the DEC and annual number of days with haze were analyzed over recent 50years in Sichuan Province. Climatologically, the poor DV of 12-20 km distributed in the Sichuan Basin and its rim region, and the good DV of 40-50 km was concentrated in the high altitude region in western Sichuan Plateau, especially in the border region to the Tibetan Plateau with the best DV (>50 km). From the 1970s to the end of last century, the Sichuan Basin and western Sichuan Plateau respectively experienced the significant decreasing and increasing trends in DV. The decreasing DVtrends in Sichuan have ceased in this century. In the Sichuan Province, there were 544% sites with the decreasing DVtrends centering in the Sichuan Basin and Panzhihua area, and 456% sites mostly in the western Sichuan Plateau with the increasing DVtrends over the 50years. The variation patterns of DEC and haze day were similar with rapid increases before 1996 and slight increases after 1996. The trend rates over the 50years were 003/10 a for DEC and 104 d/10 a for haze occurrences. The deteriorating DV, increasing DEC and frequent haze were closely related with the energy consumption and anthropogenic pollutant emissions