Impacts of aerosol compositions on visibility impairment in Xi'an, China

Daily particle light scattering coefficient. PM2.5 mass and chemical composition were measured in Xi'an from February to December 2009. Visibility was strongly affected by anthropogenic air pollution sources, resulting in an average visual range (VR) of 6.4 +/- 4.5 km. The threshold PM2.5 mass concentration, corresponding to VR <10 km, was similar to 88 mu g m(-3). The revised IMPROVE equation was applied to estimate chemical extinction (b(ext)), which on average was similar to 15% lower than measured b(ext) PM2.5 ammonium sulfate was the largest contributor, accounting for similar to 40% of b(ext). followed by organic matter (similar to 24%), ammonium nitrate (similar to 23%), and elemental carbon (similar to 9%), with minor contributions from soil dust (similar to 3%), and NO2 (similar to 1%). High secondary inorganic aerosol contributions (i.e., SO42- and NO3- were the main contributors for VR <5 km. A Positive Matrix Factorization (PMF) solution to the Chemical Mass Balance (CMB) receptor model showed that coal combustion was the dominant factor, accounting for similar to 52% of the dry particle light scattering coefficient, followed by the engine exhaust factor (similar to 31%). Other factors included biomass burning (similar to 12%) and fugitive dust (similar to 5%). (C) 2012 Elsevier Ltd. All rights reserved.