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.

To control the spread of COVID-19, Shijiazhuang implemented two lockdowns of different magnitudes in 2020 (lockdown I) and 2021 (lockdown II). We analyzed the changes in air quality index (AQI), PM2.5, O3, and VOCs during the two lockdowns and the same period in 2019 and quantified the effects of anthropogenic sources during the lockdowns. The results show that AQI decreased by 13.2% and 32.4%, and PM2.5 concentrations decreased by 12.9% and 42.4% during lockdown I and lockdown II, respectively, due to the decrease in urban traffic mobility and industrial activity levels. However, the sudden and unreasonable emission reductions led to an increase in O3 concentrations by 160.6% and 108.4%, respectively, during the lockdown period. To explore the causes of the O3 surge, the major precursors NOx and VOCs were studied separately, and the main VOCs species affecting ozone formation during the lockdown period and the source variation of VOCs were identified, and it is important to note that the relationship between diurnal variation characteristics of VOCs and cooking became apparent during the lockdown period. These findings suggest that regional air quality can be improved by limiting production, but attention should be paid to the surge of O3 caused by unreasonable emission reductions, clarifying the control priorities for urban O3 management.

Studies have shown that ozone (O₃) has adverse impacts on human health. In China, O₃ levels have continued to increase since 2010. When compared to the large number of studies concerning the health effects of PM2.5 in China, there have been limited explorations of the effects of O₃. The Beijing region has one of the highest O₃ concentrations in the country, but there appear to be no published studies regarding the health effects of O₃ in Beijing. In this study, we applied a time-stratified case-crossover design to explore the effects of O₃ on cause-specific mortality for a rural location near Beijing over the period 2005⁻2013. For year-round effects, we found that for all-causes mortality, with a 10-unit increase in O₃ concentration, the odds ratios (ORs) were in the range of 1.009⁻1.020 for different lag days. The ORs for cardiovascular mortality with a 10-unit increase in O₃ concentration were in the range of 1.011⁻1.017 for different lag days. For warm season effects, the ORs with a 10-unit increase in O₃ concentration for all-cause mortality were in the range of 1.025⁻1.031 for different lag days. The ORs for cardiovascular mortality with a 10-unit increase of O₃ concentration were in the range of 1.020⁻1.024 for different lag days. Our findings fill a knowledge gap that has hitherto existed in studies regarding O₃ health impacts, and our results will strengthen the rationale for O₃ control in China.