OBSERVATION STUDY OF AEROSOL RADIATIVE PROPERTIES OVER CHINA

A simple radiation balance model was used to simulate the variation of the aerosol direct radiative forcing with aerosol optical properties and surface reflectance. The results indicate when an aerosol layer is added into the original simple earth-atmosphere system, the apparent solar reflectance of the system may increase or decrease depending on the different combinations of aerosol single scattering albedo (SSA,ω0), asymmetry factor (g) and surface reflectance (αg), but not directly related with aerosol optical depth (τ). The aerosol optical depth is proportional to the absolute value of the change of the apparent reflectance. The results also demonstrate that comprehensive observation data about aerosol radiative properties are very essential to quantitatively research on aerosol direct radiative forcing. In the recent years, we have investigated the aerosol radiative properties over China from space and in situ methods. The works include in situ measurements of aerosol optical depth by ground sun-photometers, measurements of aerosol scattering coefficient by nephelometers, measurements of aerosol absorption coefficient by aethalometers, and retrieval of aerosol optical properties by MODIS data. The results from sun-photometer observations are used to validate the MODIS standard products. For the region in Eastern China, the satellite remote sensing results can be acceptable mostly due to existing of the dark reflectance in this region. However, for the region without dense vegetation the surface reflectance results are possibly underestimated. Appropriate modification to the surface reflectance estimation may improve the accuracy of aerosol products. The value of SSA calculated from direct surface measurements of aerosol scattering and absorption in heating instruments is about 0.8. More observation is needed to further comprehensively investigate the question.