Research on Optical Properties and Radiative Effects of Aerosols in a Typical City in Southwest China

Using aerosol scattering and absorption coefficient observations in Chengdu city from March 2021 to February 2022， combined with EAC-4， MERRA-2 reanalysis data， and the libRadtran radiative transfer model， the aerosol optical parameters in different seasons and the radiative effects of total aerosols and absorbing carbonaceous aerosols were investigated.The results showed significant seasonal variations in aerosol optical parameters： the single scattering albedo （SSA） at 550 nm reached its maximum value in winter （0.91±0.02）， while it was the lowest in spring （0.84±0.04）.The asymmetry factor （ASY） at 550 nm followed the order of summer > winter > spring > autumn.The mean total aerosol optical thickness （AOD） was higher in spring and winter （about 0.77）， but lower in summer and autumn （about 0.50~0.53）.Further analysis of the optical depth of light-absorbing carbonaceous aerosols revealed that black carbon （BC） contributed the most in winter， whereas the brown carbon （BrC） reached its peak in spring.The radiative transfer model calculation indicated that the annual average shortwave radiative forcing induced by total aerosols at the surface （BOA）， top of the atmosphere （TOA）， and within the atmosphere （ATM） was -107.21±42.49 W·m-2， -32.10±20.40 W·m-2， and 75.10±40.16 W·m-2， respectively.These indicated there were an overall cooling effect at the surface but a warming effect within the atmosphere for aerosol.Notably， BC exhibited distinct seasonal variations in radiative forcing： TOA forcing of BC was the highest in winter （7.18±1.59 W·m-2） and lowest in autumn （4.48±1.49 W·m-2）.Additionally， BC contributed 31.3% of the annual mean atmospheric radiative forcing， highlighting its significant warming effect.In contrast， the radiative forcing of BrC and its proportion relative to total aerosols were higher in spring and lower in winter.