Atmospheric turbidity data from multi-wavelength sunphotometers at both oasis and desert sites in the Hexi Corridor of northwest China, from January 1991 to September 1992, have been analyzed. The aerosol optical thickness revealed a seasonal cycle with a spring maximum due to the frequent occurrence of duststorms in the Gobi Desert and its surrounding areas. The ratio of the aerosol optical thickness at 675nm to that at 500nm suggested a seasonal variation of the aerosol size distribution.Although the observation sites are located near the Gobi Desert, which is one of the major sources of dust aerosols, the aerosol optical thickness under background conditions was not high. The mean values of aerosol optical thickness at 500nm were 0.254 over the oasis and 0.327 over the desert. The aerosol optical thickness over the desert was 1.28 times larger than that over the oasis.
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