Characterization, source apportionment, and risk assessment of ambient volatile organic compounds in urban and background regions of Hainan Island, China

The pollution characteristics of volatile organic compounds (VOCs) in urban and background regions in Hainan province, China, were determined based on field measurements of CO, NO, NO2, O3, VOCs, and meteorological parameters conducted at Haikou (HK, an urban site) and Wuzhishan (WZS, a background site) in 2019. The annual average concentration of VOCs at HK was 13.1 ppb, which was 2.2 times higher than that at WZS (6.0 ppb). VOC concentrations at HK were higher in winter, whereas there was no significant monthly variation at WZS. Diurnal variations in VOCs were characterized by two peaks at HK, attributable to emissions during morning and evening rush-hour traffic. At WZS, the diurnal variations of VOCs were characterized by one peak at 13:00-16:00, corresponding to the high temperature and intense sunlight in the afternoon. The total O3 for-mation potential of ambient VOCs was 135.1 g g-1 at HK and 80.6 g g-1 at WZS, with the O3 formation potential of alkenes accounting for 53.4% and 47.2%, respectively. The potential source region of VOCs at both sites was likely the southeastern ocean region of China (i.e., Guangdong, Guangxi, Hunan, and Jiangxi provinces) and Vietnam, Cambodia, and Thailand. Using on an empirical kinetic modeling approach, O3 formation at HK occurred under a mixed-limited region, and at WZS under a NOx-limited region. Traffic emissions were the largest contributor to VOCs at HK, accounting for 38.7%, followed by solvents (19.6%), combustion (15.2%), industrial sources (15.0%), and plant sources (11.5%). At WZS, traffic accounted for 39.6% of VOCs, similar to HK, whereas the contribution of industrial sources (22.1%) was higher. Although there are few vehicles and little industry around WZS, the long-distance transport of VOCs emitted elsewhere by these sources had a significant influence on the region's VOCs. The contribution of plant sources of VOCs was 1.5 times higher at WZS (17.0%) than at HK. None of the VOC species posed significant non-carcinogenic or carcinogenic risks at either HK or WZS.