Molecular distributions and compound-specific stable carbon isotopic compositions of lipids in wintertime aerosols from Beijing

Abstract

Molecular distributions and stable carbon isotopic compositions (delta C-13) of n-alkanes, fatty acids and n-alcohols were investigated in urban aerosols from Beijing, northern China to better understand the sources and long-range atmospheric transport of terrestrial organic matter during polluted and clear days in winter. n-Alkanes (C-19-C-36), fatty acids (C-8-C-32) and n-alcohols (C-16-C-32) detected in Beijing aerosols are characterized by the predominance of C-23, C-16 and C-28, respectively. Carbon preference index (CPI) values of n-alkanes, the ratios of the sum of odd-numbered n-alkanes to the sum of even-numbered n-alkanes, are close to 1, indicating a heavy influence of fossil fuel combustion. Relatively higher ratios of C(18:0+16:0)/C(18:n+16:1) (fatty acids) on clear days than polluted days indicate that long-distance transport and/or photochemical aging are more significant during clear days. delta C-13 values of n-alkanes and low molecular weight fatty acids (C-16:0, C-18:0) ranged from -34.1 to -24.7% and -26.9 to -24.6%, respectively, which are generally heavier on polluted days than those on clear days. Such a wide range suggests that atmospheric lipids in Beijing aerosols originate from multiple sources and encounter complicated atmospheric processes during long-range transport in North China