A modeling approach to dynamically estimating local photochemistry process and its contribution to surface O₃...

Ozone (O₃) pollution in city level is a complex issue that arises not only from local photochemistry process but also involves mid- or long-range O₃ transport. In this study, we developed a modeling approach to dynamically quantifying local photochemical process (indicated as Chem_O₃) and estimating its role in surface O₃ pollution in city level. The work was conducted on North BTH of China for summer of 2022 and mainly focused on the urban areas, in which surface O₃ usually as the most dominant air pollutants to harm population health. The method was constructed via establishing the hourly response of locally-formed O₃ to locally-released NOx (R_O3-NO2, ppb·ppb^-1) based on ISAM simulations and then combining R_O3-NO2 and ambient NO₂ levels to quantify time-varying Chem_O₃. The results showed that the monthly mean of Chem_O₃ and its proportion to actual O₃ (Chem%) was 17.9-26.0 ppb and 46.7%-62.6% in major urban areas of North BTH, following the order of mega-city > industrialized city > normal city > forest city. Moreover, daily Chem% presented the different trend with daily O₃ in these study areas, slight-positive for mega-cities, but moderate or strong-negative for most other cities. Specially, our developed method could additionally disentangling O₃ physical transport among the studied cities, and we found the inflow of O₃ was much lower than the outflow of O₃ for two mega-cities, while it was opposite in other cities. We think this method could clearly point out the role of local photochemistry control in O₃ reduction, which could help city environment managers to develop scientific and effective policy strategies to cope with ozone-related problems.