Long-term trend of ozone in southern China reveals future mitigation strategy for air pollution

The 14-year trends of surface ozone were examined using observations from 12 urban sites and 4 regional sites over the Pearl River Delta (PRD) region in China over the 2006-2019 period. Surface ozone exhibits upward trends in the range of 0.28-1.02 ppb yr(-1) at urban sites and mixed trends in the range of-0.29 - 0.21 ppb yr(-1) at regional sites. Meanwhile, surface O-x (O-x = O-3+NO2) mixing ratios exhibit downward trends at 9 urban sites and 3 regional sites in the range of-0.01 to-0.54 ppb yr(-1), revealing that the ozone rise at urban sites is predominantly attributed to the reduced titration effect by nitric oxide (NO). The further decline of surface NO2 mixing ratios could drive the decreases in O(x )mixing ratios and the increases in ozone mixing ratios at urban sites. In addition, surface O-x concentrations show a good correlation with aerosol concentrations, implying the dominant contributions of secondary production to aerosol and the consistent control strategies of ozone and aerosol pollution in PRD. For the abatement of ozone pollution, our results highlight the synergistic control of key precursors including nitrogen oxides and volatile organic compounds to counteract the reduced NO titration effect by inhibiting the photochemical production of ozone. At last, we also highlight the importance of establishing more regional sites in comprehensively assessing spatiotemporal changes in surface air pollutants in China.

Automated summary

This study examines the trends of surface ozone in the Pearl River Delta region in China from 2006 to 2019. The results show an upward trend in urban areas and mixed trends in regional areas. The rise in urban ozone is mainly attributed to the reduction in nitric oxide, while the decline in surface NO2 could drive the decrease in O(x) mixing ratios and the increase in ozone mixing ratios at urban sites. The study also highlights the importance of controlling key precursors to counteract the reduced NO titration effect. Furthermore, the correlation between surface O-x concentrations and aerosol concentrations suggests the consistent control strategies of ozone and aerosol pollution in the region. Establishing more regional sites is also emphasized to comprehensively assess spatiotemporal changes in surface air pollutants in China.