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 NOx reduction finally shifts O3 production to an NOx-limited regime with respect to traditional O3-NOx-VOC sensitivity. Our results shed light on the role of NOx reduction on O3 production and highlight further mitigation in NOx 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.