We analyzed aerosol optical

physical properties in Beijing city in January of 2013 based on ground-based remote sensing data

and used radiative transfer model to estimate aerosol radiative forcing. The results show that water-soluble Aerosol Optical Depth （ AOD） increases rapidly in haze days

and contributes most to the total AOD （ > 70% ）

black carbon aerosol AOD increases also in haze days

which is about eight times larger than clear days. The direct radiative forcing caused by aerosol is significant

but different aerosol compositions have different effects. Black carbon dominatesforcing in the atmosphere （ > 57% ）

while water-soluble dominates in surface forcing（ > 60% ） .