Compositions and sources of organic acids in fine particles (PM2.5) over the Pearl River Delta region, south China

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 PM_2.5 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 C₁₄-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.