Dicarboxylic acids, ketocarboxylic acids, ∝-dicarbonyls, fatty acids, and benzoic acid in urban aerosols collected during the 2006 campaign of air quality research in Beijing (CAREBeijing-2006)

Abstract

Ground-based studies of PM [sub 2.5] were conducted for determination of 30 water-soluble organic species, including dicarboxylic acids, ketocarboxylic acids and dicarbonyls, nine fatty acids, and benzoic acid, during the Campaign of Air Quality Research in Beijing 2006 (CAREBeijing-2006; 21 August to 4 September 2006) at urban (Peking University, PKU) and suburban (Yufa) sites of Beijing. Molecular distributions of dicarboxylic acids demonstrated that oxalic acid (C ₂ ) was the most abundant species, followed by phthalic acid (Ph) and succinic acid (C ₄ ) at both sites. The sum of three dicarboxylic acids accounted for 71% and 74% of total quantified water-soluble organics (327–1552 and 329–1124 ng m ⁻³ ) in PKU and Yufa, respectively. Positive correlation was found between total quantified water-soluble species and water-soluble organic compounds (WSOC). On a carbon basis, total quantified dicarboxylic acids and ketocarboxylic acids and dicarbonyls account for up to 14.2% and 30.4% of the WSOC in PKU and Yufa, respectively, suggesting that they are the major WSOC fractions in Beijing. The distributions of fatty acids are characterized by a strong even carbon number predominance with maximum at hexadecanoic acid (C [sub 16:0]). The ratio of octadecanoic acid (C [sub 18:0]) to hexadecanoic acid (C [sub 16:0]) (0.39–0.85, with an average of 0.36) suggests that in addition to vehicular emissions, an input from cooking emissions is important, as is biogenic emission. Benzoic acid that has been proposed as a primary pollutant from vehicular exhaust and a secondary product from photochemical reactions was found to be abundant: 72.2 ± 58.1 ng m ⁻³ in PKU and 78.0 ± 47.3 ng m ⁻³ in Yufa. According to the 72 hour back trajectory analysis, when the air mass passed over the southern or southeastern part of Beijing (24–25 August and 1–2 September), the highest concentrations of organic compounds were observed. On the contrary, when the clean air masses came straight from the north during 3–4 September, the lowest levels of organic compounds were recorded. This study demonstrates that pollution episodes in Beijing were strongly controlled by wind direction; that is, air quality in Beijing is good when air masses originate from the north and northwest, whereas it deteriorates when the air mass originates from the south and southeast. (See Article file for details of the abstract.)