Brown haze types due to aerosol pollution at Hefei in the summer and fall

Abstract

Brown haze episodes were evaluated at Hefei in the summer (June–August) and fall (September–November) seasons, and typical haze types were identified by air-mass back-trajectories and fire spot maps. Compared with clear weather conditions, larger median single scattering albedo values of 0.82 and 0.78 at 550nm were obtained for the summer and fall haze episodes, respectively. Further, the observed lower scattering Angstrom exponents imply that more large particles than small particles dominated the haze plumes, which is in agreement with the profiles of size distribution. Particles during a haze episode in Hefei grow to a size such that the 0.10 limit for the backscattering ratio is reached, which may indicate that the aged aerosols promote the formation of haze episodes. Three typical haze types were identified: biomass burning, anthropogenic industrial and traffic emissions, and brown carbon. Less negative aerosol radiative forcing efficiencies of −12.7 and −10.9Wm−2 in summer and fall were estimated, respectively, for haze impacted by biomass burning, which emphasizes an enhanced significance of biomass burning aerosols on climate forcing.