Component characteristics and source apportionment of volatile organic compounds during summer and winter in downtown Chengdu, southwest China

Volatile organic compounds (VOCs) are critical precursors of secondary pollutants such as O3 and PM2.5; some VOCs are also harmful to human health directly. In recent years, O3 pollution in summer and PM2.5 pollution in winter have occurred frequently in Chengdu, a megacity in southwest China. Effective pollution control on O3 and PM2.5 require clarification of VOCs pollution characteristics. In this study, 90 VOC species were observed using the online VOC monitoring system in June 2018 and in January 2019 at an urban monitoring station in Chengdu. The positive matrix factorization (PMF) model and the potential source contribution function (PSCF) model were used to analyze the main sources and potential source regions of VOCs in summer and winter. The O3 formation potentials (OFPs) of VOCs from different species, sources, and its contribution to secondary organic aerosols (SOA) were analyzed. Additionally, the health risks of human exposure to VOCs were also assessed. The results showed that the mixing ratio of total VOCs (TVOCs) in winter (53.3 ppbv) was around twice as high as in summer (26.8 ppbv), and TVOCs were mainly composed of alkanes. From the perspective of diurnal variation, the high values of VOCs in the morning and evening were mainly affected by traffic, and the low mixing ratios of VOCs in the afternoon was mainly due to photochemical reactions. The main sources of VOCs in downtown Chengdu was LPG/NG usage, which accounted for more than 30% in both summer and winter. The main potential source regions of TVOCs were from the western and northern regions with industrial contribution. The regional transmission characteristics between the two seasons were different, pollutants diffused in short distance and moved slowly in summer, while they migrated far and spread widely in winter. The most reactive species were alkenes and aromatics which contributed most to O3 formation potentials. VOCs from solvent utilization, vehicle exhaust, and LPG/NG usage were the main precursors of O3. VOC concentration in the atmosphere is unlikely to cause evident non-carcinogenic risk to human health, but still poses potential carcinogenic risk.