Source forensics of n-alkanes and n-fatty acids in urban aerosols using compound specific radiocarbon/stable carbon isotopic composition
Lujie Ren, Yiyun Wang, Kimitaka Kawamura, Srinivas Bikkina, Negar Haghipour, Lukas Wacker, Chandra Mouli Pavuluri, Zhimin Zhang, Siyao Yue, Yele Sun, Zifa Wang, Yanli Zhang, Xiaojuan Feng, Cong‐Qiang Liu, Timothy I. Eglinton, Pingqing Fu
Abstract
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 ( δ 13 C and Δ 14 C, respectively) of n -alkanes and n -fatty acids in aerosols from two urban receptor sites (Beijing and Tianjin) in Northeast China to assess their sources in autumn. The Δ 14 C n -alkanes of C 19 –C 24 and C 26 –C 32 even-carbon homologs (−851 to −708‰) indicate their dominance from fossil fuel combustion. In contrast, the Δ 14 C of most abundant palmitic acid (C 16:0 ) and stearic acid (C 18:0 ) suggest a larger contribution from nonfossil sources (∼91%–94%), mainly due to inputs from cooking, biomass burning and microorganisms. Compared with lower Δ 14 C of C 27 and C 31 n -alkanes (−449‰), C 29 n -alkane (−241‰) and C 20 –C 30 n -fatty acids (−263‰) 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.