• aerosol radiative forcing;
  • Beijing;
  • weather conditions

[1] Direct aerosol radiative forcing (ARF) under four classic weather conditions, i.e., clear, hazy, foggy, and dusty days, over Beijing was investigated using the Santa Barbara Discrete Ordinate Radiative Transfere (SBDART) model, ground-based sunphotometer measurements, pyranometer measurements, and a back-trajectory analysis. The ratios of aerosol optical depths (AOD) under hazy, foggy, and dusty weather conditions to the AOD under clear weather condition were much greater than the ratios of surface aerosol concentrations under these conditions. The single scattering albedo and the ratio of ARF at the surface level to ARF at the top of the atmosphere suggested that more absorbing particles existed under hazy and foggy conditions than those under dusty conditions. ARF measured at both the surface level and the top of the atmosphere for dusty days was higher than that for foggy, hazy, and clear days. Therefore, significantly difference exists in ARF over Beijing due to changes in aerosol sources and weather conditions. The altitude of the aerosol transport layer for dusty days was higher than that for foggy days.