Characteristics of Aerosol Optical Properties and Their Chemical Apportionments during CAREBeijing 2006

Abstract

Field campaigns monitoring the aerosol optical properties and chemical components of PM_(10) were carried out in Beijing in 2006 summer. The average light extinction coefficient b_(ext), dry aerosol scattering coefficient b_(sp) and aerosol absorption coefficient b_(ap) were 895.0 ± 820.8 Mm^(-1), 364.0 ± 324.3 Mm^(-1) and 57.8 ± 31.1 Mm^(-1), respectively. b_(ext), b_(sp) and bap had the similar increasing trend during the formation process of haze. Pronounced diurnal cycles were observed for ω_(550) (aerosol single scattering albedo at 550 nm), b_(sp), b_(ap) and b_(ext). The dry b_(sp) was elevated during the daytime with a maximum mean value of 475.8 Mm^(-1) (LST 06:00). b_(ext), PM_(2.5) mass concentration and PM_(2.5)/PM_(10) ratio increased at night due to continuous emissions of pollutants to the lower nocturnal boundary layer, and decreased during the daytime due to convective mixing. b_(ap) increased at night, and decreased during the daytime and reached the minimum (37 Mm^(-1)) at LST 16:00. The single scattering albedo reached its maximum (0.87) at LST 11:00. This trend was consistent with the SNA (sulfate, nitrate, and ammonium)/PM_(10) ratio and was contrary to the BC (black carbon)/PM_(10) ratio, which demonstrated that secondary pollution largely influenced the scattering ability of aerosols. Ammonium sulfate, ammonium nitrate, organic mass, elemental carbon and coarse mass contributed 26.5%, 15.2%, 21.8%, 16.1% and 20.4% to the total extinction coefficient during clean days, and 44.6%, 22.3%, 13.6%, 10.8% and 8.7% during hazy days. The fractional contributions of ammonium sulfate and ammonium nitrate were significantly higher during the hazy time than those during the clean days. While the fractional contributions of organic mass, elemental carbon and coarse mass were lower during the haze time than those during the clean days.