Aerosol Optical Properties and Direct Radiative Forcing in Beijing in the Recent Decade

Combined with the aerosol optical characteristic data observed by Aerosol Robotic Network (AERONET) Beijing station, the Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) radiation transmission mode was used to evaluate the radiative forcing of aerosols and black carbon (BC) aerosols in Beijing in the recent decade. The main results are as follows: The mean values of aerosol optical depth (AOD) for 440 nm and Ångström exponent are 0.61±0.56 and 1.09, respectively, while the mean value of single scattering albedo (SSA) for 440 nm is 0.888±0.045. AOD shows a slight decreasing trend in the recent decade, but SSA shows a slight increasing trend, indicating that aerosol pollution in Beijing has improved. Under clear sky conditions, the annual radiative forcing values of the aerosol at the top of the atmosphere, on the ground, and in the atmosphere are −24.91±19.80 W m⁻², −65.52±43.78 W m⁻², and 40.61±28.62 W m⁻², respectively. This indicates that the aerosol heats the atmosphere although it has a cooling effect on the top of the atmosphere and on the surface. The inter-annual variation of the absolute value of the direct radiative forcing of aerosols and BC aerosols shows a slight decreasing trend, and the seasonal variation is higher in spring and summer and lower in winter, which is consistent with the changing rule of AOD. The decreasing trend of direct radiative forcing of BC aerosols and the increasing trend of SSA show a good inverse phase relationship.