Preprints
https://doi.org/10.5194/acp-2021-834
https://doi.org/10.5194/acp-2021-834

  06 Oct 2021

06 Oct 2021

Review status: this preprint is currently under review for the journal ACP.

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

Kun Zhang1,2,, Zhiqiang Liu1,3,, Xiaojuan Zhang1,3, Qing Li1,2, Andrew Jensen4,5, Wen Tan6, Ling Huang1,2, Yangjun Wang1,2, Joost de Gouw4,5, and Li Li1,2 Kun Zhang et al.
  • 1School of Environmental and Chemical Engineering, Shanghai University, Shanghai, 200444, China
  • 2Key Laboratory of Organic Compound Pollution Control Engineering, Shanghai University, Shanghai, 200444, China
  • 3Changzhou Institute of Environmental Science, Changzhou, Jiangsu, 213022, China
  • 4Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, 80309, USA
  • 5Department of Chemistry, University of Colorado, Boulder, Colorado, 80309, USA
  • 6Tofwerk AG, Thun, Switzerland
  • These authors contribute equally to this work.

Abstract. The outbreak of COVID-19 promoted strict restrictions to human activities in China, which led to dramatic decrease in most air pollutant concentrations (e.g., PM2.5, PM10, NOx, SO2, and CO). However, abnormal increase of ozone (O3) concentrations was found during the lockdown period in most urban areas of China. In this study, we conducted a field measurement targeting ozone and its key precursors by utilizing a novel proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) in Changzhou, which is representative for the Yangtze River Delta (YRD) city cluster of China. We further applied the integrated methodology including machine learning, observation-based model (OBM), and sensitivity analysis to get insights into the reasons causing the abnormal increase of ozone. Major findings include: (1) By deweathered calculation, we found changes in precursor emissions contributed 5.1 ppbv to the observed O3 during the Full-lockdown period, while meteorological conditions only contributed 0.5 ppbv to the O3 changes. (2) By using an OBM model, we found that although significant reduction of O3 precursors was observed during Full-lockdown period, the photochemical formation of O3 was stronger than that during the Pre-lockdown period. (3) The NOx / VOCs ratio dropped dramatically from 1.84 during Pre-lockdown to 0.79 in Full-lockdown period, which switched O3 formation from VOCs-limited regime to the conjunction of NOx- and VOC-limited regime. Additionally, the decrease in NOx / VOCs ratio during Full-lockdown period was supposed to increase the MeanO3 by 2.4 ppbv. Results of this study investigate insights into the relationship between O3 and its precursors in urban area, demonstrating reasons causing the abnormal increase of O3 in most urban areas of China during the COVID-19 lock-down period. This study also underlines the necessity of controlling anthropogenic OVOCs, alkenes, and aromatics in the sustained campaign of reducing O3 pollution in China.

Kun Zhang et al.

Status: open (until 18 Nov 2021)

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Kun Zhang et al.

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Short summary
Abnormal increase of O3 concentrations were found during the lockdown period in COVID-19 in most areas of China. By field measurement coupled with machine learning, observation-based model (OBM), and sensitivity analysis, we found the changes in NOx / VOCs ratios was the key reason for the abnormal rise of O3. To restrain O3 pollution, more efforts should be paid on the control of anthropogenic OVOCs, alkenes, and aromatics.
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