Non-methane hydrocarbons (NMHCs) from four sampling sites in Lanzhou, a petrochemical industrialized city in northwest China, was sampled by stainless steel canisters and measured by gas chromatography–mass selective detection/ﬂame ionization detection (GC–MSD/FID) in May and June of 2017. Based on these results, the contributions of NMHCs to the ozone (O3) and secondary organic aerosols (SOA), differences in tracer ratios, and source apportionment by principal component analysis (PCA) were analyzed. The results showed that the total NMHCs concentration in Lanzhou was 48.4 ± 48.3 ppbv (parts per billion by volume) during the observation and it was higher in May (78.6 ppbv) than in June (37.8 ppbv); the highest NMHCs concentration was observed in industrial areas. Alkanes were the dominant group at all sites in Lanzhou and account for more than 60% of the NMHCs, while isopentane, n-butane n-pentane, propane and ethane were the major compounds. Additionally, the NMHCs in Lanzhou have made great contributions to O3 and SOA generation and the S1 site of the industrial area contributed the most to both of them. Propene, toluene, ethylbenzene and n-pentane were found to be more reactive with relatively high contributions to ozone formation. Aromatics and high carbon alkanes were major contributors to SOA formation potential (SOAp) (i.e., toluene, m,p-xylene, dodecane, undecane, n-tanane, benzene and ethylbenzene) in Lanzhou. Based on the speciﬁc volatile organic compounds (VOCs) ratio method and the PCA mode,the observation sites in Lanzhou were greatly affected by the surrounding industrial areas. The sources consisted of petrochemical industry, vehicle emissions, solvent usage and combustion sources, which contributed to 33.9%, 31.6%, 19.2% and 7.9% of the total monitored NMHCs, respectively. From different sites, though the influence of regional transport was not very significant on the whole, it also affected the NMHCs of nonindustrial areas based on the ratio of xylene to ethyl-benzene (X/E), especially the S4 site; vehicle emission was less important compared to sources from petrochemical industries in S1, as characterized by relatively higher toluene to benzene (T/B) ratios. However, vehicle emission has significant influence on NMHCs in S4. Overall, local emissions are the main source of NMHCs in Lanzhou and the petrochemical industry has a great influence on the distribution of NMHCs in the whole region.
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