Variation Characteristics of Aerosol Optical Depth at 14 Meteorological Observatories over China during 1961-2005

A new method of retrieving aerosol optical depth (AOD) was proposed using daily global and diffuse radiative insolations. After a comparison with daily AOD products of AERONET, it shows that the correlation coefficient between the two AODs exceeded 0.95, and the mean bias error was less than 0.03. Using this retrieval method, AODs at 0.55mum were obtained at 14 meteorological observatories over China during 1961-2005. The analysis shows that, as to the average AOD for all the 14 stations of the 45 years, the mean value is 0.40 and its annual increment is 0.005. As to the seasonal average values, the AODs from high to low occur in order of spring (0.45), summer (0.43), winter (0.37) and autumn (0.34), separately. Over the 14 observatories, the stations of Chengdu in Sichuan Basin has the fastest AOD increasing speed of 0.01 per year, while AODs at Kashi and Geermu station show a slightly downward trend.