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https://doi.org/10.5194/acp-2020-1064
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-1064
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  03 Nov 2020

03 Nov 2020

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This preprint is currently under review for the journal ACP.

Enhancement of nanoparticle formation and growth during the COVID-19 lockdown period in urban Beijing

Xiaojing Shen1, Junying Sun1, Fangqun Yu2, Xiaoye Zhang1, Junting Zhong1,3, Yangmei Zhang1, Xinyao Hu1, Can Xia1,4, and Sinan Zhang1 Xiaojing Shen et al.
  • 1State Key Laboratory of Severe Weather & Key Laboratory of Atmospheric Chemistry of CMA, Chinese Academy of Meteorological Sciences, Beijing 100081, China
  • 2Atmospheric Sciences Research Center, State University of New York at Albany, 251 Fuller Road, Albany, New York 12203, USA
  • 3University of Chinese Academy of Sciences, Beijing 100049, China
  • 4Nanjing University of Information Science & Technology, Nanjing 210000, China

Abstract. Influenced by the spread of the global 2019 novel coronavirus (COVID-19) pandemic, primary emissions of particles and precursors associated with anthropogenic activities decreased significantly in China during the Chinese New Year of 2020 and the lockdown period (January 24–February 16, 2020), as indicated by approximately 50 % reduction of NOx emission nation-wide based on the open literature. Two-month measurements of the number size distribution of neutral particles and charged ions showed that during the lockdown (LCD) period, the number concentration of particles smaller than 100 nm decreased by approximately 40 % compared to the pre-LCD period in January. However, the accumulation mode particles increased by approximately 20 % as several polluted episodes contributed to secondary aerosol formation. In this study, new particle formation (NPF) events were found to be enhanced in the nucleation and growth processes during the LCD period, as indicated by higher formation (J2) and growth rate (GR), even as NPF occurrence frequency slightly decreased. The condensing vapors controlling the nucleation and growth process, sulfuric acid, and oxidation product of volatile organic compounds were estimated based on available information. The proxy values showed that sulfuric acid and organic oxidized vapors increased during the LCD period by approximately 35 % and 133 % on NPF days, respectively. Higher J2 and GR during the LCD period were favored by the increased concentration level of condensing vapors and decreased condensation sink. Several heavy haze episodes have been reported by other studies during the LCD period; however, the increase in nanoparticle number concentration should also be considered. Some typical NPF events produced a high number concentration of nanoparticles that intensified in the following days to create severe aerosol pollution. Our study confirms a significant enhancement of the nucleation and growth process of nanoparticles during the COVID-19 LCD in Beijing and highlights the necessity of controlling nanoparticles in current and future air quality management.

Xiaojing Shen et al.

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Short summary
In this work, we revealed the changes of PNSD and NPF events during COVID-19 lockdown period in Beijing, China, to illustrate the impact of reduced primary emission and elavated atmospheric oxidized capicity on the nucleation and growth processes. The subsequent growth of nucleated particles and their contribution to the aerosol pollution formaiton were also expolred, to highlight the necessity of controlling the nanoparticle in the future air quality management.
In this work, we revealed the changes of PNSD and NPF events during COVID-19 lockdown period in...
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