During November–December 2010 aerosol scattering coefficients were monitored using a single-waved （525 nm） Nephelometer at a regional monitoring station in the central Pearl River Delta region and 24-hr fine particle （PM 2.5） samples were also collected during the period using quartz filters for the analysis of major chemical components including organic carbon （OC）,elemental carbon （EC）,sulfate,nitrate and ammonium.In average,these five components accounted for about 85% of PM 2.5 mass and contributed 42% （OC）,19% （SO 4 2 -）,12% （NO 3 -）,8.4% （NH 4＋） and 3.7% （EC）,to PM 2.5 mass.A relatively higher mass scattering efficiency of 5.3 m 2/g was obtained for fine particles based on the linear regression between scattering coefficients and PM 2.5 mass concentrations.Chemical extinction budget based on IMPROVE approach revealed that ammonium sulfate,particulate organic matter,ammonium nitrate and EC in average contributed about 32%,28%,20% and 6% to the light extinction coefficients,respectively.
Organic acids as important constituents of organic aerosols not only influence the aerosols＇ hygroscopic property, but also enhance the formation of new particles and secondary organic aerosols. This study reported organic acids including C14-C32 fatty acids, C4-C9 dicarboxylic acids and aromatic acids in PM2.5 collected during winter 2009 at six typical urban, suburban and rural sites in the Pearl River Delta region. Averaged concentrations of C14-C32 fatty acids, aromatic acids and C4- C9 dicarboxylic acids were 157, 72.5 and 50.7 ng/m3, respectively. They totally accounted for 1.7% of measured organic carbon. C20-C32 fatty acids mainly deriving from higher plant wax showed the highest concentration at the upwind rural site with more vegetation around, while Cl4-C18 fatty acids were more abundant at urban and suburban sites, and dicarboxylic acids and aromatic acids except 1,4-phthalic acid peaked at the downwind rural site. Succinic and azelaic acid were the most abundant among C4-C9 dicarboxylic acids, and 1,2-phthalic and 1,4-phthalic acid were dominant aromatic acids. Dicarboxylic acids and aromatic acids exhibited significant mutual correlations except for 1,4-phthalic acid, which was probably primarily emitted from combustion of solid wastes containing polyethylene terephthalate plastics. Spatial patterns and correlations with typical source tracers suggested that C14-C32 fatty acids were mainly primary while dicarboxylic and aromatic acids were largely secondary. Principal component analysis resolved six sources including biomass burning, natural higher plant wax, two mixed anthropogenic and two secondary sources; further multiple linear regression revealed their contributions to individual organic acids. It turned out that more than 70% of C14-C18 fatty acids were attributed to anthropogenic sources, about 50%-85% of the C20-C32 fatty acids were attributed to natural sources, 80%-95% of dicarboxylic acids and 1,2-phthalic acid were secondary in contrast with that 81% of 1,4-phthalic acid was primary.
