Insights into the significant increase in ozone during COVID-19 in a typical urban city of China

[摘要] The outbreak of COVID-19 promoted strict restrictions to human activities inChina, which led to a dramatic decrease in most air pollutant concentrations(e.g., PM 2.5 , PM 10 , NO x , SO 2 and CO). However, an obviousincrease in ozone (O 3 ) concentrations was found during the lockdownperiod in most urban areas of China. In this study, we conducted fieldmeasurements targeting ozone and its key precursors by utilizing a novelproton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) inChangzhou, which is representative of the Yangtze River Delta (YRD) citycluster of China. We further applied the integrated methodology includingmachine learning, an observation-based model (OBM) and sensitivity analysis toobtain insights into the reasons causing the obvious increase in ozone. Majorfindings include the following: (1) by deweathered calculation, we found changes inprecursor emissions contributed 1.46 ppbv to the increase in the observedO 3 during the full-lockdown period in 2020, while meteorologyconstrained 3.0 ppbv of O 3 in the full-lockdown period of 2019. (2) Byusing an OBM, we found that although a significant reduction in O 3 precursors was observed during the full-lockdown period, the photochemicalformation of O 3 was stronger than that during the pre-lockdown period.(3) The NO x / VOC ratio dropped dramatically from 1.84 duringthe pre-lockdown to 0.79 in the full-lockdown period, which switched O 3 formation from a VOC-limited regime to the boundary of a NO x - andVOC-limited regime. Additionally, box model results suggested that thedecrease in the NO x / VOC ratio during the full-lockdown period could increasethe mean O 3 by 2.4 ppbv. Results of this study give insights into therelationship between O 3 and its precursors in urban area anddemonstrate reasons for the obvious increase in O 3 in most urbanareas of China during the COVID-19 lockdown period. This study alsounderlines the necessity of controlling anthropogenic oxygenated volatile organic compounds (OVOCs), alkenes andaromatics in the sustained campaign of reducing O 3 pollution in China.

[学科分类] 医学（综合）