Source forensics ofn-alkanes andn-fatty acids in urban aerosols using compound specific radiocarbon/stable carbon isotopic composition

Abstract

N-Alkanes and fatty acids are important molecular markers for the source apportionment of organic matter in the atmosphere. Traditional approaches to date have mostly relied upon the source-specific differences in their molecular distributions and carbon preference index. Alternatively, we demonstrate here the use of stable carbon and radiocarbon isotopic composition (delta C-13 and Delta C-14, respectively) ofn-alkanes andn-fatty acids in aerosols from two urban receptor sites (Beijing and Tianjin) in Northeast China to assess their sources in autumn. The Delta(14)C(n)(-alkanes)of C-19-C(24)and C-26-C(32)even-carbon homologs (-851 to -708 parts per thousand) indicate their dominance from fossil fuel combustion. In contrast, the Delta C-14 of most abundant palmitic acid (C-16:0) and stearic acid (C-18:0) suggest a larger contribution from nonfossil sources (similar to 91%-94%), mainly due to inputs from cooking, biomass burning and microorganisms. Compared with lower Delta C-14 of C(27)and C(31)n-alkanes (-449 parts per thousand), C(29)n-alkane (-241 parts per thousand) and C-20-C(30)n-fatty acids (-263 parts per thousand) showed more contemporary likely due to significant contribution from plant litter and biomass burning that contain more fresh biogenic material. Fossil character of C-27-C(31)n-alkanes (40%) and C-20-C(30)n-fatty acids (30%) could be from soil resuspension and/or loess deposits in upwind regions through long-range atmospheric transport.