Ozone Pollution and Its Response to Nitrogen Dioxide Change from a Dense Ground-Based Network in the Yangtze River Delta: Implications for Ozone Abatement in Urban Agglomeration

Understanding the response of tropospheric ozone (O-3) to nitrogen dioxide (NO2) change is important for local O-3 control. The relationship between O-3 and NO2 at county scale in China has been extensively studied using models, but there is a lack of results from direct measurements. In this study, we used measurements of O-3, NO2 and meteorological conditions from a dense network in the Yangtze River Delta (YRD), and satellite observed formaldehyde (HCHO) and NO2 column densities for the analysis of O-3 variabilities and its relationship to NO2. As a result, severe O-3 pollution occurred mainly in Shanghai city, southern Jiangsu and northern Zhejiang provinces in YRD during April-September. In addition, meteorological conditions could explain 54% the diurnal O-3 variation over YRD. During April-September 2015-2021, O-3 showed a significant positive relationship (r = 0.61 +/- 0.10) with NO2 after removing the impact from meteorological conditions. However, the relationship could be reversed with NO2 concentration change. Our result suggested that the controllable O-3 related to NO2 change is up to 100 mu g center dot m(-3) in megacities over Shanghai and northern Zhejiang province. The O-3 is much more sensitive to the NO2 reduction in megacities than surrounding areas. Our results evaluate the different impacts of NO2 changes on O-3 formation, which provides explanation for the simultaneously alleviated O-3 pollution and reduced NO2 in 2020 in Shanghai and northern Zhejiang, as well as the increased O-3 in most counties before 2019 with reduced NO2 during October-March. The driving mechanism as revealed from this study for O-3 and NO2 will be valuable for the O-3 abatement through NO2 reduction at sub-county scale over YRD in China.

Automated summary

This study analyzed the relationship between ozone (O-3) and nitrogen dioxide (NO2) in the Yangtze River Delta region in China using direct measurements and satellite observations. The results showed a significant positive correlation between O-3 and NO2, and identified the controllable O-3 related to NO2 change in megacities. These findings provide valuable insight into understanding and controlling ozone pollution.