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 (δ13C and Δ14C, 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 Δ14Cn-alkanes of C19–C24 and C26–C32 even-carbon homologs (−851 to −708‰) indicate their dominance from fossil fuel combustion. In contrast, the Δ14C of most abundant palmitic acid (C16:0) and stearic acid (C18:0) suggest a larger contribution from nonfossil sources (∼91%–94%), mainly due to inputs from cooking, biomass burning and microorganisms. Compared with lower Δ14C of C27 and C31 n-alkanes (−449‰), C29 n-alkane (−241‰) and C20–C30 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 C27–C31 n-alkanes (40%) and C20–C30 n-fatty acids (30%) could be from soil resuspension and/or loess deposits in upwind regions through long-range atmospheric transport.

Highlights

  • 22 June 2020Abstract n-Alkanes and fatty acids are important molecular markers for the source apportionment of organic matter in the atmosphere

  • Airborne particle deposition is an important pathway for much of the terrestrial carbon transported to remote ocean setting

  • Plant wax is characterized by odd-over-even carbon number preference for high molecular weight (HMW) n-alkanes (⩾25), and an even-over-odd carbon number preference for HMW n-fatty acids (⩾20), whereas low molecular weight (LMW) homologues are mainly produced by aquatic organisms (Makou et al 2018) and anthropogenic emissions (Rogge et al 1993a, 1994, Ballentine et al 1996, 1998, Zhao et al 2007b, Harvey et al 2012)

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Summary

22 June 2020

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. We demonstrate here the use of stable carbon and radiocarbon isotopic composition (δ13C and ∆14C, 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. Compared with lower ∆14C of C27 and C31 n-alkanes (−449‰), C29 n-alkane (−241‰) and C20–C30 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 C27–C31 n-alkanes (40%) and C20–C30 n-fatty acids (30%) could be from soil resuspension and/or loess deposits in upwind regions through long-range atmospheric transport

Introduction
Materials and methods
Results and discussions
Findings
Implications
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