| Variation and distribution characteristics of aerosol optical depth (AOD) and solar radiation in China, and the AOD retrieval method from broadband solar radiation were main goals in this paper. Due to be short of long term data of AOD, the temporal and spatial variations of AOD were still unclear in China. Base on the above problems, some works were carried out in this paper.A method of accuracy estimation for GSR (Global solar radiation) measurements was proposed for Chinese meteorological observatories firstly. Then it was applied to evaluating accuracies of GSR data at seven observatories in China, which were Shenyang, Ejinaqi, Beijing, Wulumuqi, Geermu, Shanghai and Guangzhou. The results showed that the uncertainty of GSR data in these observatories was usually better than 5% in clear days withμ0≥0.7.The variation characteristics of solar radiations at 50 meteorological observatories in China during 1961～2000 were analyzed, the results showed that the yearly insolations of global and direct solar radiations appeared obviously descend trends with annual decreases of -24.81 and -21.67MJ·m-2, respectively, but the diffuse radiation had no remarkable trend. The descending of global and direct solar radiations was distinct in eastern part and western part of China, while that in northeastern and southwestern part was not. Diffuse radiations for most stations in eastern part showed an increasing trend, while most stations in western part decreasing. Compared with 1980s, the averaged GSR insolation in 1990s increased about 105. 6 MJ·m-2. We calculated the solar radiations under clear sky using a clear index based on cloud cover, the results showed that direct radiation reduced more quickly than GSR, but diffuse radiation showed a remarkable increasing trend.Based on the sensibility of horizontal direct solar radiation to aerosol, a new retrieval method for aerosol optical depth (AOD) was developed using daily insolations of global and diffuse solar radiations. With a error analysis using radiative transfer models, the results showed that the mean value of AOD retrieving errors due to instability of the "equivalent" model of instantaneous solar zenith angle was 3.66%; errors of AOD diurnal variation had little influence on the mean value for a relatively long period; the AOD retrieving error was less than 4 % when the error of diffuse solar radiation revision was less than 20%. A comparison between AODs retrieved from this method and the AERONET showed a good agreement with correlation coefficient of 0.95 and mean bias error of 0.02 in clear days. The seasonal and yearly mean values of AOD showed a good consistent with those from AERONET.Using the above retrieval method, the data of tropospheric AOD at 0.75μm wavelength were retrieved for 50 meteorological stations within the period of 1961-1990. The results showed that the distribution of AOD influenced mostly by topography in China. There are two high value regions of Sichuan Basin and South-Xinjiang Basin and a low value region of Qinhai-Tibet plateau. The decennary increment of AOD averaged from all stations was 0.05. As to mean values, the maximum was in Sichuan Basin of 0.649, and the second maximum in South-Xinjiang Basin of 0.411, while the minimum was in Qinhai-Tibet plateau of 0.125. As to seasonal mean, AOD in spring had the highest value, and then in summer, while the minimum was in winter. The distribution of surface visibility, which was consistent with that of AOD, showed a decreasing trend in the East and a increasing tend in the West of China.The variation characteristics of tropospheric AOD and aerosol scaling heights (ASH) for 14 first-grade radiation stations were analyzed detailedly. The results showed that the increasing trends of AOD were found in 11 stations whose annual increments were between 0.001 and 0.082 and of ASH were found in 12 stations whose annual increments were between 0.004 and 0.049km. As to average values from all 14 stations, the annual increment of AOD and ASH was 0.0029 and 0.018km, respectively.
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