Chemistry of atmospheric fine particles during the COVID-19 pandemic in a megacity of eastern China

Research output: Contribution to journalLetterpeer-review


  • Lei Liu
  • Jian Zhang
  • Rongguang Du
  • Xiaomi Teng
  • Rui Hu
  • Qi Yuan
  • Shanshan Tang
  • Chuanhua Ren
  • Xin Huang
  • Liang Xu
  • Yinxiao Zhang
  • Xiaoye Zhang
  • Gongda Lu
  • Weijun Li

External organisations

  • Zhejiang University
  • Hangzhou Meteorological Bureau
  • Chinese Academy of Sciences
  • Nanjing University


Air pollution in megacities represents one of the greatest environmental challenges. Our observed results show that the dramatic NOx decrease (77%) led to significant O3 increases (a factor of 2) during the COVID-19 lockdown in megacity Hangzhou, China. Model simulations further demonstrate large increases of daytime OH and HO2 radicals and nighttime NO3 radical, which can promote the gas-phase reaction and nocturnal multiphase chemistry. Therefore, enhanced NO3 and SO42− formation was observed during the COVID-19 lockdown because of the enhanced oxidizing capacity. The PM2.5 decrease was only partially offset by enhanced aerosol formation with its reduction reaching 50%. In particular, NO3 decreased largely by 68%. PM2.5 chemical analysis reveals that vehicular emissions mainly contributed to PM2.5 under normal conditions in Hangzhou. Whereas, stationary sources dominated the residual PM2.5 during the COVID-19 lockdown. This study provides evidence that large reductions in vehicular emissions can effectively mitigate air pollution in megacities.

Bibliographic note

Funding Information: This work was funded by the National Natural Science Foundation of China (42075096 and 91844301), the National Key R&D Program of China (2017YFC0212700), Zhejiang Provincial Natural Science Foundation of China (LZ19D050001), Zhejiang Meteorological Science and Technology Program (2019YB11), LAC/CMA (2020B02), and China Postdoctoral Science Foundation (2020M681823). Gongda Lu thanks the PhD studentship funded by China Scholarship Council. Publisher Copyright: © 2020. The Authors.


Original languageEnglish
Article number2020GL091611
Number of pages10
JournalGeophysical Research Letters
Issue number2
Early online date17 Dec 2020
Publication statusPublished - 28 Jan 2021


  • air pollution, chemical composition, COVID-19, fine particles, megacity