Variations in summertime ozone in Nanjing between 2015 and 2020: roles of meteorology, radical chain length and ozone production efficiency

Highlights

● Temperature, relative humidity and wind field are influential meteorological factors.

● OH radical chain length and OPE are dominated by the NO _x decline.

● The O₃ formation is controlled by VOCs and NO _x in 2020 summertime.

Abstract

Changes in ozone (O₃) can be evaluated to inform policy effectiveness and develop reasonable emissions reduction measures. This study investigated the causes of summertime maximum daily 8-h average (MDA8) O₃ variation between 2015 and 2020 in Nanjing, China, a megacity in the Yangtze River Delta (YRD) region, from the perspective of meteorological conditions and anthropogenic emissions of O₃ precursors (VOCs and NO_x). Compared with 2015, the observed MDA8 O₃ decreased by 19.1 μg/m³ in August 2020. The indirect and indirect impacts of meteorological conditions contributed 44% of the decline, with temperature, relative humidity, and wind playing important roles in the O₃ variation. The O₃ drop by 10.7 μg/m³ (56% of the total decrease) may have been due to the decreases in anthropogenic emissions of VOCs and NO_x by 7.8% and 11.7%, respectively. The longer hydroxyl (OH) radical chain length and higher ozone production efficiency (OPE) indicated that the reduction of anthropogenic emissions accelerated the RO_x (RO_x = OH + HO₂ + RO₂) and NO_x cycles in O₃ production, making O₃ more sensitive to NO_x. This corresponded to the O₃ formation shifting from a VOC-limited regime in 2015 to a transition regime in 2020 and O₃ decrease with anthropogenic emission reduction. Hence, the joint control of O₃ precursor emissions can effectively mitigate O₃ pollution in Nanjing.

Graphical abstract

Keywords

Ozone / Meteorological condition / Anthropogenic emission / OH radical chain length / OPE

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Acknowledgements

This research was financially supported by the National Natural Science Foundation of China (Grant Nos. 42277095, 42021004).

Conflict of Interests

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Electronic Supplementary Material

is available in the online version of this article at https://doi.org/10.1007/s11783-024-1897-z and is accessible for authorized users.

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