Multi-scale analysis of the chemical and physical pollution evolution process from pre-co-pollution day to PM_2.5 and...

PM_2.5 and O₃ are two of the main air pollutants that have adverse impacts on climate and human health. The evolution process of PM_2.5 and O₃ co-pollution are of concern because of the increased frequency of PM_2.5 and O₃ co-pollution days. Here, we examined the chemical coupling and revealed the driving factors of the PM_2.5 and O₃ co-pollution evolution process from cleaning day, PM_2.5 pollution day, or O₃ pollution day, applied by theoretical analysis and model calculation methods. The results demonstrate that PM_2.5 and O₃ co-pollution day frequently occurred with high concentrations of gaseous precursors and higher sulfur oxidation ratio (SOR) and nitrogen oxidation ratio (NOR), which we attribute to the enhancement of atmospheric oxidation capacity (AOC). The AOC is positively correlated with O₃ and weakly correlated with PM_2.5. In addition, we found that the correlation coefficients of PM_2.5-NO₂ (0.62) were higher than that of PM_2.5-SO₂ (0.32), highlighting the priority of NO_x controlling to mitigate PM_2.5 pollution. Overall, our discovery can provide scientific evidence to design feasible solutions for the controlling PM_2.5 and O₃ co-pollution process.