Distributions, spatial patterns and source identification of n-alkanes in air and bulk deposition in the eastern coastal areas of China: Fluxes and removal efficiency of bulk deposition

Abstract

Normal alkanes (n-alkanes) are crucial components of organic carbon in the atmosphere. Low-carbon number n-alkanes act as precursors for secondary organic aerosols, while long-chain alkanes are difficult to degrade after deposition, posing risks to human health and garnering widespread attention. However, their environmental partitioning, chemical composition, removal efficiency by bulk deposition, and sources in the eastern coastal areas of China remain understudied. To address this, this study investigated n-alkanes (C11 to C40) in the air and bulk deposition. This investigation was conducted by applying passive sampling-gas chromatography-mass spectrometry analysis technology in Qingdao from December 2019 to October 2020. The mean concentrations of n-alkanes in the atmosphere and bulk deposition were 160 ng/m3 and 15.6 μg/m2/d, respectively, throughout the year. Deposition fluxes followed this order: background site > suburban > rural > urban, while atmospheric n-alkanes showed the reverse trend. Plant sources contributed more to n-alkanes in bulk deposition than in the atmosphere. N-alkanes with medium to high-carbon numbers (C20–C36) were more efficiently removed from the atmosphere during summer-autumn. Based on carbon preference index (CPI) and positive matrix factorization (PMF) analysis, the main contributors to n-alkanes in air and bulk deposition were fossil fuel combustion, emissions from higher plants, and motor vehicle exhaust.