Ground-level ozone (O) pollution is a major air quality issue in densely populated urban areas. Despite a significant decline in human activities in the megacity Shanghai from March 28 to May 31, 2022, ground-level measurements indicate a rise in maximum daily average 8-h (MDA8) O concentrations in comparison to the corresponding period in 2021. There is a need for quantitative analysis to identify the reasons behind this increasing O concentration. We analyzed ground measurements of O and its precursors and meteorological parameters made in Shanghai, using random-forest (RF) model and chemical box model to elucidate the roles of meteorological and chemical factors in influencing O concentrations. Across urban, suburban, semi-rural, and coastal sites, the urban center of Shanghai experienced the largest decreases in the concentrations of nitrogen oxides (NO; 53%) and volatile organic compounds (VOCs; 52%), with the most notable rise in MDA8 O concentrations (16%). RF modeling indicates that meteorological factors reduced MDA8 O concentrations by a marginal 3%, whereas a decline in anthropogenic emissions resulted in a 17% increase in MDA8 O concentrations. Chemical box modeling at the Pudong urban site indicates that while the decline in VOCs reduced O production by 42%, this was negated by a reduction in NO from traffic emissions, which enhanced O production by 51%, resulting in an increase in O production overall. Despite a halving in precursor levels, Shanghai's urban centre remains predominately under VOC-limited conditions throughout the study period, with high NO levels from the petrochemical industry and traffic emissions. Joint control of anthropogenic VOCs (AVOCs) and NO, with a ratio greater than 1.29, could help avoid exacerbation of O pollution and reduce NO pollution. Our findings emphasize the necessity of reducing industrial emissions along with ongoing green transportation strategies for alleviating O pollution in megacities like Shanghai.

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2022年封城期间上海臭氧污染加剧的定量分析及调控政策启示

地面臭氧 (O) 污染是人口稠密城市地区的一个主要空气质量问题。尽管 2022 年 3 月 28 日至 5 月 31 日期间，上海这座大城市的人类活动显着下降，但地面测量结果显示，与 2021 年同期相比，8 小时日均最大 (MDA8) O 浓度有所上升。需要进行定量分析以确定 O 浓度增加背后的原因。我们利用随机森林（RF）模型和化学盒模型分析了上海进行的O及其前体物的地面测量和气象参数，以阐明气象和化学因素对O浓度的影响。在城市、郊区、半农村和沿海地区，上海市中心的氮氧化物（NO；53%）和挥发性有机化合物（VOC；52%）浓度下降幅度最大，上升最为显着MDA8 O 浓度 (16%)。 RF 模型表明，气象因素使 MDA8 O 浓度降低了 3%，而人为排放量的下降导致 MDA8 O 浓度增加了 17%。浦东城区的化学箱模型表明，虽然 VOC 的减少使 O 产量减少了 42%，但交通排放中 NO 的减少却抵消了这一点，从而使 O 产量增加了 51%，从而导致整体 O 产量增加。尽管前体物水平减半，但在整个研究期间，上海市中心仍然主要处于挥发性有机化合物有限的条件下，石化工业和交通排放的二氧化氮水平很高。人为VOCs（AVOCs）和NO的联合控制，其比例大于1.29，有助于避免O污染加剧，减少NO污染。我们的研究结果强调了减少工业排放以及持续实施绿色交通战略以减轻上海等大城市的氧气污染的必要性。