Relationships between chemical elements of PM2.5 and O3 in Shanghai atmosphere based on the 1-year monitoring observation

Mass level of fine particles (PM_2.5) in main cities in China has decreased significantly in recent years due to implementation of Chinese Clean Air Action Plan since 2013, however, O₃ pollution is getting worse than before, especially in megacities such as in Shanghai. In this work, O₃ and PM_2.5 were continuously monitored from May 27, 2018 to March 31, 2019. Our data showed that the annual average concentration of PM_2.5 and O₃ (O₃-8 hr, maximum 8-hour moving average of ozone days) was 39.35 ± 35.74 and 86.49 ± 41.65 µg/m³, respectively. The concentrations of PM_2.5 showed clear seasonal trends, with higher concentrations in winter (83.36 ± 18.66 µg/m³) and lower concentrations in summer (19.85 ± 7.23 µg/m³), however, the seasonal trends of O₃ were different with 103.75 ± 41.77 µg/m³ in summer and 58.59 ± 21.40 µg/m³ in winter. Air mass backward trajectory, analyzing results of potential source contribution function model and concentration weighted trajectory model implied that pollutants from northwestern China contributed significantly to the mass concentration of Shanghai PM_2.5, while pollutants from areas of eastern coastal provinces and South China Sea contributed significantly to the mass level of ozone in Shanghai atmosphere. Mass concentration of twenty-one elements in the PM_2.5 were investigated, and their relationships with O₃ were analyzed. Mass level of ozone had good correlation with that of Ba (r = 0.64, p < 0.05) and V (r = 0.30, p > 0.05), suggesting vehicle emission pollutants contribute to the increasing concentration of ozone in Shanghai atmosphere.