ABSTRACT

Aerosol samples were collected at Mangshan in the north of Beijing, China in autumn 2007 and analyzed for α,ω-dicarboxylic acids (C₂-C₁₂), ketoacids (ωC₂-ωC₄, ωC₉, pyruvic acid) and α-dicarbonyls (glyoxal and methylglyoxal). Oxalic (C₂) acid was found as the most abundant species, followed by succinic (C₄) and malonic (C₃) acids. Concentrations of most compounds, except for C₂ and some other species, were higher in daytime than nighttime, indicating that diacids are produced by photochemical oxidation of organic precursors emitted from anthropogenic sources such as fossil-fuel combustion in Beijing, and are transported to Mangshan area by the northerly wind in daytime. Phthalic acid (Ph) was detected as the 4th most abundant diacid both in daytime and nighttime samples, indicating that anthropogenic sources significantly contribute to the organic aerosols. However, lower adipic (C₆)/azelaic (C₉) acid ratios in nighttime than daytime suggest that biogenic source makes more contribution to the aerosols in nighttime. Higher ratios of C₂/total diacids in nighttime than daytime suggest the aging of aerosols proceed more in nighttime, probably due to the aqueous phase oxidation of biogenic precursors. This study demonstrates that water-soluble organic aerosols are secondarily produced in the vicinity of Beijing by the oxidation of both anthropogenic and biogenic precursors.