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Unexpected air pollution with marked emission reductions during the COVID-19 outbreak in China

Le, Tianhao and Wang, Yuan and Liu, Lang and Yang, Jiani and Yung, Yuk L. and Li, Guohui and Seinfeld, John H. (2020) Unexpected air pollution with marked emission reductions during the COVID-19 outbreak in China. Science, 369 (6504). pp. 702-706. ISSN 0036-8075. doi:10.1126/science.abb7431.

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The absence of motor vehicle traffic and suspended manufacturing during the coronavirus disease 2019 (COVID-19) pandemic in China enabled assessment of the efficiency of air pollution mitigation. Up to 90% reduction of certain emissions during the city-lockdown period can be identified from satellite and ground-based observations. Unexpectedly, extreme particulate matter levels simultaneously occurred in northern China. Our synergistic observation analyses and model simulations show that anomalously high humidity promoted aerosol heterogeneous chemistry, along with stagnant airflow and uninterrupted emissions from power plants and petrochemical facilities, contributing to severe haze formation. Also, because of nonlinear production chemistry and titration of ozone in winter, reduced nitrogen oxides resulted in ozone enhancement in urban areas, further increasing the atmospheric oxidizing capacity and facilitating secondary aerosol formation.

Item Type:Article
Related URLs:
URLURL TypeDescription Information
Le, Tianhao0000-0002-6600-8270
Wang, Yuan0000-0001-6657-8401
Liu, Lang0000-0002-1092-0615
Yung, Yuk L.0000-0002-4263-2562
Seinfeld, John H.0000-0003-1344-4068
Additional Information:© 2020 The Authors. This work is licensed under a Creative Commons Attribution 4.0 International (CC BY 4.0) license, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. To view a copy of this license, visit This license does not apply to figures/photos/artwork or other content included in the article that is credited to a third party; obtain authorization from the rights holder before using such material. Received for publication March 16, 2020. Accepted for publication June 9, 2020. We are grateful to Chao Liu and Alexei Lyapustin for helpful discussions on the satellite products, and Yuxuan Wang and Yuanlong Huang for chemistry analysis. Y.W. and Y.L.Y. acknowledge the support of the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. Additional support was provided by the NSF AGS-1700727 grant. G.L. and L.L. acknowledge the National Key R&D Plan Grant 2017YFC0210000 and the Strategic Priority Research Program of Chinese Academy of Sciences Grant XDB40030203. Author contributions: Y.W. conceived and designed the research. T.L., Y.W., and Y.L.Y. performed the data analyses and produced the figures. L.L, Y.W., and G.L. performed and analyzed the WRF-Chem simulations. J.Y. and L.L. obtained the ground-based pollution data. Y.W. and J.H.S wrote the paper. All authors contributed to the scientific discussions and preparation of the manuscript. The authors declare no competing interests. Data and materials availability: All data are available in the manuscript or the supplementary materials.
Group:Astronomy Department, COVID-19
Funding AgencyGrant Number
National Key Research and Development Program of China2017YFC0210000
Chinese Academy of SciencesXDB40030203
Issue or Number:6504
Record Number:CaltechAUTHORS:20200622-104138262
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Official Citation:Unexpected air pollution with marked emission reductions during the COVID-19 outbreak in China. BY TIANHAO LE, YUAN WANG, LANG LIU, JIANI YANG, YUK L. YUNG, GUOHUI LI, JOHN H. SEINFELD. SCIENCE 07 AUG 2020: 702-706; DOI: 10.1126/science.abb7431
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:103957
Deposited By: George Porter
Deposited On:22 Jun 2020 18:14
Last Modified:16 Nov 2021 18:26

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