Pollution characteristics and source apportionment of ozone and its precursors during typical autumn periods in urban and background regions of Hainan Province

Based on the volatile organic compounds(VOCs) online monitoring data, automatic ambient air monitoring data and meteorological observation data of the Wuzhishan background site and Sanya in November 2019, the pollution characteristics of ozone and its precursors, transport routes and potential sources of ozone pollution, as well as the chemical reactivity, source apportionment and human health risk assessment of VOCs during the month of high ozone concentrations(November) were investigated. The results showed that the ozone concentrations were relatively high at both the Wuzhishan background site and Sanya in November due to the inland pollution transport when the dominant wind direction was northeast. The cluster analysis of backward trajectories indicated that the air mass transport pathways at both sites were from the northeast. The potential sources analysis revealed that the Pearl River Delta was a significant potential source of ozone pollution. During periods of high ozone concentrations, the volume fractions of VOCs[φ(VOCs)] at the Wuzhishan background site and Sanya increased significantly. The φ(VOCs) and the mass concentration of NO2[ρ(NO2)] were higher in Sanya compared with the Wuzhishan background site; However, the mass concentration of O3[ρ(O3)] showed an opposite trend. The φ(VOCs) and ρ(NO2) in Sanya showed diurnal variations of bimodal peaks in the morning and evening, whereas no obvious diurnal variation was observed at the Wuzhishan background site. The diurnal variation of ozone in Sanya was consistent with that of temperature, exhibiting unimodal diurnal variation with a peak at noon, while the ozone peak at the Wuzhishan background site occurred at 7:00 am. The average φ(VOCs) of Sanya and the Wuzhishan background site were 11.7×10−9 and 4.2×10−9, respectively, with alkanes accounting for the highest percentage. The average ozone formation potentials (OFP) were 62.7 μg·m−3 and 19.3 μg·m−3, and the average ·OH radical loss rates (L·OH) were 2.9 s−1 and 0.7 s−1, respectively, with alkenes accounting for the highest percentage at both sites. For the secondary organic aerosol formation potential (SOAp), the mean values were 0.19 μg·m−3 and 0.07 μg·m−3, respectively, with aromatic hydrocarbons as the primary contributing component. According to the source apportionment of positive matrix factorization (PMF), the main source of VOCs at the Wuzhishan background site was traffic sources (39.1%), followed by solvent use sources (22.9%), industrial sources (18.0%), combustion sources (12.8%) and plant sources (7.2%). Traffic sources accounted for 48.9% of VOCs in Sanya, followed by solvent use sources(26.9%), combustion sources (9.6%), plant sources (8.9%) and industrial sources(6.1%). Reducing emissions from motor vehicles and solvent use is crucial for controlling ozone pollution in Sanya. None of the VOC species posed significant non-carcinogenic or carcinogenic risks at either the Sanya monitoring site or the Wuzhishan background site.