Pollution characterization and source apportionment of n-alkanes during the winter in Qingdao City

To investigate mass concentrations, molecular compositions and sources of n-alkanes in PM_2.5 in Qingdao during the winter, PM_2.5 samples were collected from Laoshan District, Qingdao from January 10 to 23, 2020. Twenty-six kinds of n-alkanes (C₁₁-C₃₆) were determined through quantitative analysis by gas chromatography-mass spectrometry (GC-MS), and the pollution characteristics and sources of n-alkanes were analyzed in detail. The results showed that the concentration of total n-alkanes was （230.9±111.7）ng/m³, with the average concentration ranging from 59.2-429.2 ng/m³. C₂₄ was the monomer species with the highest concentration, which concentration was 49.63 ng/m³. According to the secondary concentration limit of PM_2.5 of the National Ambient Air Quality Standards of China (NAAQS), the sampling period was divided into 8 polluted days and 6 clean days. The concentrations of n-alkanes on polluted and clean days were (283.7±93.6) ng/m³ and (160.5±82.1) ng/m³, respectively. The carbon number distribution of n-alkanes on polluted days and clean days was similar. The main peak carbon (C_max) was C₂₂ and the secondary peak carbon was C₂₄. CPI, CPI1 and CPI2 values of n-alkanes on polluted and clean days were 0.91, 0.81, 1.19 and 0.98, 0.84, 1.38, respectively, and %WaxC_n was 6.67% and 19.31%, respectively, indicating that anthropogenic emissions were the main source of n-alkanes in Qingdao during the winter. Principal component analysis (PCA) results showed that the n-alkanes in Qingdao during the winter mainly came from anthropogenic emission sources (coal combustion, vehicle exhaust emissions), and the contribution of plant emission sources was small. The potential source analysis results showed that the potential source distributions of low carbon number n-alkanes and high carbon number n-alkanes were basically the same, mainly from the long-distance transmission in the northwest direction.