Aerosol single scattering albedo estimated across China from a combination of ground and satellite measurements

Single scattering albedo (SSA) governs the strength of aerosols in absorbing solar radiation, but few methods are available to directly measure this important quantity. There currently exist many ground-based measurements of spectral transmittance from which aerosol optical thickness (AOT) are retrieved under clear sky conditions. Reflected radiances at the top of the atmosphere as measured by a spaceborne spectroradiometer are sensitive to both AOT and SSA. On the basis of extensive radiative transfer simulations, it is demonstrated that the combined use of the two measurements allows for the retrieval of SSA at a reasonable, accuracy under moderate to heavy aerosol loadings. Retrieval of SSA is most sensitive to AOT and surface reflectance. The accuracy of SSA retrievals increases with aerosol loading. The uncertainties in SSA retrievals are 0.02-0.03 for AOT = 1.0 and 0.03-0.05 for AOT = 0.5 at 0.47 μm. The proposed retrieval method is applied to 1 a worth of Moderate Resolution Imaging Spectroradiometer (MODIS) Level-1 calibrated reflected radiances matched with surface spectral transmittances acquired at 24 stations of the Chinese Sun Hazemeter Network established under the auspices of the East Asian Study of Tropospheric Aerosols: An International Regional Experiment (EAST-AIRE). Measurements made under high-turbidity conditions (AOT > 0.4) were used. All the stations are located in relatively remote and thus spatially representative locations. From the retrieved values, the first gross map of SSA across China is generated. The retrieved SSA values were compared with those retrieved independently from AERONET sites in China. The root-mean-square deviation (RMSD) is on the order of 0.03, and the mean difference is ∼0.02. The nationwide means of AOT, Ångström exponent, and SSA (at 0.5 μm) in 2005 are 0.69 ± 0.17, 1.06 ± 0.26, and 0.89 ± 0.04, respectively.