[1] The column-integrated optical properties of aerosol in the central eastern region of Asia and midtropical Pacific were investigated based on Sun/sky radiometer measurements made at Aerosol Robotic Network (AERONET) sites in these regions. Characterization of aerosol properties in the Asian region is important due to the rapid growth of both population and economic activity, with associated increases in fossil fuel combustion, and the possible regional and global climatic impacts of related aerosol emissions. Multiyear monitoring over the complete annual cycle at sites in China, Mongolia, South Korea, and Japan suggest spring and/or summer maximum in aerosol optical depth (t a ) and a winter minimum; however, more monitoring is needed to establish accurate climatologies. The annual cycle of Angstrom wavelength exponent (a) showed a springtime minimum associated with dust storm activity; however, the monthly mean a 440 -870 was >0.8 even for the peak dust season at eastern Asian sites suggesting that fine mode pollution aerosol emitted from population centers in eastern Asia dominates the monthly aerosol optical influence even in spring as pollution aerosol mixes with coarse mode dust originating in western source regions. Aerosol optical depth peaks in spring in the tropical mid-Pacific Ocean associated with seasonal shifts in atmospheric transport from Asia, and $35% of the springtime t a500 enhancement occurs at altitudes above 3.4 km. For predominately fine mode aerosol pollution cases, the average midvisible ($550 nm) single scattering albedo (w 0 ) at two continental urban sites in China averaged $0.89, while it was significantly higher, $0.93, at two relatively rural coastal sites in South Korea and Japan. Differences in fine mode absorption between these regions may result from a combination of factors including aerosol aging during transport, relative humidity differences, sea salt at coastal sites, and fuel type and combustion differences in the two regions. For cases where t a was predominately coarse mode dust aerosol in the spring of 2001, the absorption was greater in eastern Asia compared to the source regions, with w 0 at Dunhuang, China (near to the major Taklamakan dust source), $0.04 higher than at Beijing at all wavelengths, and Anmyon, South Korea, showing an intermediate level of absorption. Possible reasons for differences in dust absorption magnitude include interactions between dust and fine mode pollution aerosol and also variability of dust optical properties from different source regions in China and Mongolia.

[1] Thirty-three months of aerosol data in Beijing are presented in this paper. Aerosol optical thickness (AOT) increases from January to June and then decreases gradually. However, airborne particulate matter with diameter less than 10 mm (PM 10 ) concentration exhibits higher values in winter and spring and lower concentration in summer. For the same PM 10 concentration, AOT in summer is approximately two, three, and four times that in autumn, winter, and spring, respectively. AOT increases persistently during daytime, and the diurnal variation varies from about 15% in summer to about 45% in winter. The seasonal and diurnal variation of AOT is quite different from that of surface particle concentration. This is partly attributed to the variation of atmospheric mixing layer height. Aerosol volume concentrations increase with AOT by nearly identical magnitude for fine and coarse mode except in spring. The volume concentration of coarse mode in spring increases by a magnitude of more than two times that derived in remaining seasons. Aerosol fine mode radius increases with AOT, whereas coarse mode radius keeps relatively invariable with AOT. Mean aerosol single-scattering albedo at 440 nm is about 0.90 and decreases slightly with wavelength. Aerosol single-scattering albedos increase and their spectral dependence reverses during dust periods. Aerosol size and absorption in Beijing are close to results derived in Mexico City and Kanpur, but they are quite different from those in Maryland and Paris. Therefore different urban aerosol models should be created and used in satellite remote sensing in different urban regions.

[1] Solar radiation reaching the surface in China was analyzed on the basis of four data sets. National Centers for Environment Prediction (NCEP) reanalysis solar radiation data exceeded surface observations by 40 W/m 2 to more than 100 W/m 2 . Satellite data sets produced by Goddard Institute for Space Studies (GISS) and University of Maryland (UMD) were correlated significantly with surface observations, but satellite estimates exceeded surface observations over much of China. The largest difference occurred in the middle reach of Yangze river and coast regions where satellite algorithms occasionally overestimated solar radiation by more than 40 W/m 2 . The mean bias of satellite estimates ranged from about 8 W/m 2 to about 36 W/m 2 in regional scale. The root-mean-square error varied from about 20 to 36 W/m 2 . The effects of differences in space-time sampling between satellite and surface data might account partly for the random uncertainties of satellite estimates. The systematic overestimation by satellite algorithms in China was most likely associated with aerosols and their complex interactions with clouds. Surface data indicated a significant decline in solar radiation from 1961 to 1990, but the decline trend did not persist into the 1990s. Instead, a pronounced increase trend has been observed from 1984 to 2000, ranging from 1.7% to 7.7% per decade. The decrease would not be expected given that the cloud amount decreased significantly during the same period, but this was in accordance with the increasing aerosol loading that was indicated by the visibility deterioration. NCEP data and satellite estimates indicated quite different trends in solar radiation. The marginal increase trends were derived on the basis of NCEP data from 1961 to 2000 in three regions except in south China. The trends derived from satellite estimates since the middle 1980s were much less than that of surface observations. Moreover, both satellite estimates showed decline trends over much of China from 1984 to 2000. These differences suggested that representation of aerosols and clouds should be improved in order to make satellite estimates more robust over regions with high aerosol loading.