With a simpli ed radiation balance model, study is performed of aerosol direct radiation forcing in relation to its optical properties and surface reflectance, indicating that with the thickened aerosol layer the earth-atmosphere system may increase or weaken the solar radiation albedo, depending upon different combinations of aerosol single scattering albedo (SSA,ω~0), asymmetry factor (g), and surface albedo (αg) rather than relying directly on the aerosol optical depth (σ), which has its value just in proportion to the changed range of albedo alone.
As indicated by the model results, systematic observations of aerosol radiative properties are required to make quantitative study of aerosol direct radiative forcing. Observational research of the properties has been undertaken based on ground and space measurements over China, including ground-based sunphotometer aerosol optical depth (AOD), nephelometer-aerosol scattering coefficients, aethalometer-aerosol absorption coefficients, and MODIS products??retrieved AOD. The satellite retrieved AOD is validated against in situ sun photometer measured AOD, indicating that for eastern China remote sensing given AODs are acceptable
owing mainly to lower surface reflectance there whereas for poor vegetation in the north of China the surface reflectance may be underestimated in AOD retrieval. However, appropriate modi cation of the scheme of aerosol remote sensing is likely to improve the retrieval accuracy. The aerosol single scattering albedo in dry condition is around 0.80 from surface-measured scattering and absorption coe cients. It requires further studies based on more observations to improve our understanding of the issue.