Characterization and source apportionment of aerosol light extinction in Chengdu, southwest China

To investigate aerosol properties in the Sichuan Basin of China, field aerosol sampling was carried out in Chengdu, China during four one-month periods, each in a different season in 2011. Aerosol scattering coefficient (b_sp) at dry (RH<40%) and wet (40%<RH<90%) conditions and aerosol absorption coefficient (b_ap) were measured. Additionally, daily PM_2.5 and PM₁₀ samples were also collected. PM_2.5 samples were subject to chemical analysis for various chemical components including major water-soluble ions, organic and elemental carbon (OC and EC), trace elements, as well as anhydrosugar Levoglucosan (LG) and Mannosan (MN). A multiple linear regression analysis was applied to the measured dry b_sp against (NH₄)₂SO₄, NH₄NO₃, organic mass (OM), fine soil (FS), and coarse mass (CM, PM_2.5-10), and to the measured b_ap against EC in all the four seasons to evaluate the impact of individual chemical components of PM_2.5 and CM on aerosol light extinction (b_ext=b_sp+b_ap). Mass scattering efficiency (MSE) and mass absorption efficiency (MAE) of the individual chemical components of PM_2.5 were estimated based on seasonal regression equations and were then used for estimating b_ext. The annual b_sp, b_ap and single scattering albedo (SSA) at dry conditions were 456±237Mm^-1, 96±48Mm^-1 and 0.82±0.05, respectively. The annual average b_sp at ambient conditions estimated through hygroscopic curve of aerosol (f(RH)) was 763±415Mm^-1, which was 1.7 times of the dry b_sp. The annual average SSA at ambient conditions also increased to 0.88±0.04. The estimated dry b_ext was only 2±9% higher than the measurements and the estimated ambient b_ext from individual chemical components was only 1±10% lower, on an annual basis, than that estimated from using f(RH). Secondary inorganic aerosols, coal combustion, biomass burning, iron and steel industry, Mo-related industry, soil dust, and CM to b_ext were estimated to account for 41±19%, 18±12%, 14±13%, 13±11%, 5±4%, 5±7% and 4±3%, respectively, of the estimated ambient b_ext.