Multiple Impacts of Aerosols on O₃ Production Are Largely Compensated: A Case Study Shenzhen, China

Abstract

Tropospheric ozone (O₃) is a harmful gas compound to humans and vegetation, and it also serves as a climate change forcer. O₃ is formed in the reactions of nitrogen oxides and volatile organic compounds (VOCs) with light. In this study, an O₃ pollution episode encountered in Shenzhen, South China in 2018 was investigated to illustrate the influence of aerosols on local O₃ production. We used a box model with comprehensive heterogeneous mechanisms and empirical prediction of photolysis rates to reproduce the O₃ episode. Results demonstrate that the aerosol light extinction and NO₂ heterogeneous reactions showed comparable influence but opposite signs on the O₃ production. Hence, the influence of aerosols from different processes is largely counteracted. Sensitivity tests suggest that O₃ production increases with further reduction in aerosols in this study, while the continued NO_<i>x</i> reduction finally shifts O₃ production to an NO_<i>x</i>-limited regime with respect to traditional O₃-NO_<i>x</i>-VOC sensitivity. Our results shed light on the role of NO_<i>x</i> reduction on O₃ production and highlight further mitigation in NO_<i>x</i> not only limiting the production of O₃ but also helping to ease particulate nitrate, as a path for cocontrol of O₃ and fine particle pollution.