1. Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control, Collaborative Innovation Center of Atmospheric Environment and Equipment Technology, Nanjing University of Information Science & Technology, Nanjing 210044, China 2. Environment Research Institute, Shandong University, Qingdao 266237, China
● 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.
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 NOx). 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 NOx 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 ROx (ROx = OH + HO2 + RO2) and NOx cycles in O3 production, making O3 more sensitive to NOx. 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.
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