Spatiotemporal variation, source and secondary transformation potential of volatile organic compounds (VOCs) during the winter days in Shanghai, China

The spatiotemporal concentration variations, sources, and secondary transformation potential of volatile organic compounds (VOCs) were analyzed at three sampling sites, including the rural (DSL), urban (PD) and industrial (JS) sites, in December 2019, in Shanghai, China. The VOC concentrations in the DSL, PD and JS sites were 13.32 ± 3.33 ppb, 24.72 ± 4.31 ppb and 30.66 ± 5.83 ppb, respectively. The observed “weekend effects” showed the importance of traffic levels and human activities at weekend. By the PMF model, vehicle emission was identified as the largest source of VOCs, accounting for 34.29% in the DSL site, 35.38% in the PD site and 30.07% in the JS site, respectively. During the observation period, in addition to the local sources, regional transport from the provinces nearby was an essential source for VOCs. Although alkanes were the most abundant VOC species in Shanghai, alkenes were the species with the highest chemical activity according to the measurements of OH radical loss rate (LOH) and ozone formation potential (OFP), which played the dominant roles in ozone formation. Haze pollution was largely driven by secondary aerosol formation. The SOA yields from VOCs were 11.29 ± 7.21 μg/m3 and 18.91 ± 8.36 μg/m3 in the clean and haze days, respectively, with aromatics, especially toluene, being the most abundant precursor. The SOA yields in the JS site were much higher than those at the other two sites during the measurement. The VOCs in the DSL site held the highest sensitivity to PM2.5, followed by the JS and PD sites, and aromatics were more sensitive to PM2.5 than other VOC species. Thus, the critical way to reduce PM2.5 formation in Shanghai, especially in the industrial sites, is controlling the concentration of aromatics. This study highlights the vehicle-related source and the secondary transformation from VOCs, which can provide references for local governments regarding controlling strategies of VOCs.