Characterization of VOCs and their related atmospheric processes in a central Chinese city during severe ozone pollution periods

Abstract

Abstract. A 5-month campaign (from May to September 2017) was conducted to characterize volatile organic compounds (VOCs) for the first time at four sites in Zhengzhou, Henan Province, China, where ground level ozone (O3) concentration has shown an increasing trend in recent years. Canister samples were collected for the measurement of 57 VOCs, which, along with reactive nitrogen oxides (NOx), are the most important O3 precursors. During the same period, O3 and its precursor gases were monitored online simultaneously. The results indicated that the average mixing ratio of total quantified VOCs (ΣVOCs=28.8±22.1 ppbv) in Zhengzhou was lower than that in the other Chinese megacities, while alkyne comprised a higher proportion of ΣVOCs. The abundances, compositions and ratios of typical VOCs showed clear spatial and temporal variations. Cluster analysis indicates that air masses from the south of Zhengzhou were cleaner than from other directions. The molar ratio of VOCs to NOx indicated that, in general, O3 formation was more sensitive to VOCs than NOx formation in Zhengzhou. The source apportionment was conducted with positive matrix factorization (PMF), and it was found that vehicle exhaust, coal and biomass burning and solvent usage were the major sources for ambient VOCs at all four sites. From potential source contribution function (PSCF) analysis, the strong emissions from coal + biomass burning and solvent usage were concentrated in the southwest of Shanxi and Henan provinces. This study gathers scientific evidence on the pollution sources for Zhengzhou, benefiting the government to establish efficient environmental control measures, particularly for O3 pollution.