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Ground-based PM2.5 samples collected at four different sites in PearlRiver Delta region (PRD) during winter and summer (from 14 December 2006 to28 January 2007 in winter and from 4 July to 9 August 2007 in summer)were analyzed for 30 water-soluble organic species, including dicarboxylicacids, ketocarboxylic acids and dicarbonyls, nine fatty acids, and benzoicacid. Molecular distributions of dicarboxylic acids demonstrated that oxalicacid (C2) was the most abundant species followed by phthalic acid (Ph)in PRD region. The concentrations of total dicarboxylic acids ranged from 99to 1340 ng m−3, with an average of 438 ± 267 ng m−3 in PRD.The concentrations of total ketocarboxylic acids ranged from 0.6 to 207 ng m−3 (43 ± 48 ng m−3 on average) while the concentrations of total α-dicarbonyls, including glyoxal and methylglyoxal, rangedfrom 0.2 to 89 ng m−3, with an average of 11 ± 18 ng m−3 inPRD. The total quantified water-soluble compounds (TQWOC) (organic carbon)accounted for 3.4 ± 2.2% of OC and 14.3 ± 10.3% of water-solubleOC (WSOC). Hexadecanoic acid (C16:0), octadecanoic acid (C18:0)and oleic acid (C18:1) were the three most abundant fatty acids in PRD.The distributions of fatty acids were characterized by a strong even carbonnumber predominance with a maximum (Cmax) at hexadecanoic acid(C16:0). Ratio of C18:1 to C18:0 acts as an indicator foraerosol aging. In PRD, an average of C18:1/C18:0 ratio was0.53 ± 0.39, suggesting an enhanced photochemical degradation ofunsaturated fatty acid. Moreover, the concentrations of benzoic acid rangedfrom 84 to 306 ng m−3, (165 ± 48 ng m−3 on average), which canbe emitted as primary pollutant from motor vehicles exhaust, or formed fromphotochemical degradation of aromatic hydrocarbons. Seasonal variations ofthe organic specie concentrations were found in the four sampling cities.Higher concentrations of TQWOC were observed in winter (598 ± 321 ng m−3) than in summer (372 ± 215 ng m−3). However, the abundancesof TQWOC in OC mass were higher in summer (0.9–12.4%, 4.5 ± 2.7%on average) than in winter (1.1–5.7, 2.5 ± 1.2% on average), beingconsistent with enhanced secondary production of dicarboxylic acids inwarmer weather. Spatial variations of water-soluble dicarboxylic acids werecharacterized by higher concentrations in Hong Kong and lower concentrationsin Guangzhou (GZ)/Zhaoqing (ZQ) during winter whereas the highestconcentrations were observed in GZ/ZQ during summer. These spatial andseasonal distributions are consistent with photochemical production and thesubsequent accumulation under different meteorological conditions

atmospheric chemistry and physics

Summer and winter variations of dicarboxylic acids, fatty acids and benzoic acid in PM&amp;lt;sub&amp;gt;2.5&amp;lt;/sub&amp;gt; in Pearl Delta River Region, China