Abstract
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 modem, 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.
Highlights
Tropospheric photochemical pollution and haze pollution are principal environmental issues which pose great challenges to the development of many cities and regions in China
Though the influence of regional transport was not very significant on the whole, it affected the Non-methane hydrocarbons (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
A total of 56 NMHCs data sets were in order to analyze their compositions and concentration distributions, illustrate overall characteristics collected in order to analyze their compositions and concentration distributions, illustrate overall of different classes of NMHCs, and evaluate the ozone formation potentials (OFP) and SOA formation potential (SOAp), and source apportionment of NMHCs characteristics of different classes of NMHCs, and evaluate the OFPs and SOAp, and source using diagnostic ratios and principal component analysis (PCA) model
Summary
Volatile organic compounds (VOCs) play a vital role in formation of ground level ozone (O3 ) and secondary organic aerosols (SOA) associated with urban air quality [1,2,3]. Non-methane hydrocarbons (NMHCs) are an important part of VOCs. As significant air pollutants in the urban atmosphere, NMHCs have become severe environmental problems in China, causing negative impacts on human health, air quality, climate change, as well as natural ecosystems [4,5]. The reaction of NMHCs with OH, O3 , and nitrogen oxides (NOx) generates SOA and aggravates ground level O3 pollution in the presence of sunlight, linked to severe photochemical pollution and haze pollution events in China [3,7,8]. Estimation of the O3 and SOA formation potential of anthropogenic NMHC emissions, and implementation of effective
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