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

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