Simulation of aerosol influences on shortwave radiative flux under different pollution conditions

Aerosol optical properties with high spectral resolution are applied in the radiative transfer model of BCC_RAD (974 bands) to simulate direct radiative forcing (DRF) and radiative forcing efficiency (DFE) of aerosols in the surface and near-surface layer under different pollution conditions. It is found that DRF is negative in the surface but positive in near-surface layer. The DFE increases with increasing aerosol concentration, indicating that higher concentration of atmospheric aerosols cause larger DRF with unit aerosol optical depth (AOD). The shortwave band (SW) is divided into three bands:ultraviolet (UV), visible (VIS) and near-infrared (NIR). The DRF ranges under different pollution conditions in these three bands are -1.36—-13.66, -3.03—-32.41 and -2.74—-28.62 W/m² at the surface, respectively, and the corresponding DRF ranges are 0.44-4.26, 0.99-9.80 and 0.93-8.87 W/m² in the near-surface layer, respectively.The negative DRF at the surface (SUR) and in the top of the atmosphere (TOA) and the positive DRF over the entire atmospheric layer and at the near-surface caused by anthropogenic aerosols are greater than those caused by natural aerosols. The effects of aerosols from these two sources on the atmospheric radiation balance are mainly concentrated in the atmosphere higher than 800 hPa. The effects of different types of aerosols on radiation are then analyzed according to the magnitude of absolute value of the DRF. Results indicate that SF (sulfate) > OC (organic carbon) > BC (black carbon) > SS (sea salt) > SD (dust) at the surface, and BC > OC > SD > SS > SF in near-surface layer. Finally, the effects of scattering aerosol (SF) and absorbing aerosol (BC) on the radiative flux are analyzed, and the differences between the scattering and absorbing processes in the atmosphere are also compared.