Multiple Impacts of Aerosols on O 3 Production Are Largely Compensated: A Case Study Shenzhen, China.

Tropospheric ozone (O 3 ) is a harmful gas compound to humans and vegetation, and it also serves as a climate change forcer. O 3 is formed in the reactions of nitrogen oxides and volatile organic compounds (VOCs) with light. In this study, an O 3 pollution episode encountered in Shenzhen, South China in 2018 was investigated to illustrate the influence of aerosols on local O 3 production. We used a box model with comprehensive heterogeneous mechanisms and empirical prediction of photolysis rates to reproduce the O 3 episode. Results demonstrate that the aerosol light extinction and NO 2 heterogeneous reactions showed comparable influence but opposite signs on the O 3 production. Hence, the influence of aerosols from different processes is largely counteracted. Sensitivity tests suggest that O 3 production increases with further reduction in aerosols in this study, while the continued NO x reduction finally shifts O 3 production to an NO x -limited regime with respect to traditional O 3 -NO x -VOC sensitivity. Our results shed light on the role of NO x reduction on O 3 production and highlight further mitigation in NO x not only limiting the production of O 3 but also helping to ease particulate nitrate, as a path for cocontrol of O 3 and fine particle pollution.