A modeling approach to dynamically estimating local photochemistry process and its contribution to surface O 3 pollution

Ozone (O ) pollution in city level is a complex issue that arises not only from local photochemistry process but also involves mid- or long-range O transport. In this study, we developed a modeling approach to dynamically quantifying local photochemical process (indicated as Chem_O ) and estimating its role in surface O 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 O usually as the most dominant air pollutants to harm population health. The method was constructed via establishing the hourly response of locally-formed O to locally-released NOx (R , ppb·ppb ) based on ISAM simulations and then combining R and ambient NO levels to quantify time-varying Chem_O . The results showed that the monthly mean of Chem_O and its proportion to actual O (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 O 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 O physical transport among the studied cities, and we found the inflow of O was much lower than the outflow of O 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 O reduction, which could help city environment managers to develop scientific and effective policy strategies to cope with ozone-related problems.