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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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We use the COVID-19 pandemic as a unique natural experiment to obtain a more robust understanding of the effectiveness of emission reductions on air quality improvement, by combining chemical transport simulations and observations. Our findings imply a shift from current control policies in California: a strengthened control on primary PM2.5 emissions and a well-balanced control on NOx and volatile organic compounds are needed to effectively and sustainably alleviate PM2.5 and O3 pollution.
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https://doi.org/10.5194/acp-2020-1197
https://doi.org/10.5194/acp-2020-1197

  29 Dec 2020

29 Dec 2020

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

Modeling the Impact of COVID-19 on Air Quality in Southern California: Implications for Future Control Policies

Zhe Jiang1,, Hongrong Shi1,, Bin Zhao2, Yu Gu3, Yifang Zhu4, Kazuyuki Miyazaki5, Yuqiang Zhang6, Kevin W. Bowman3,5, Takashi Sekiya7, and Kuo-Nan Liou3 Zhe Jiang et al.
  • 1Key Laboratory of Middle Atmosphere and Global Environment Observation, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
  • 2Pacific Northwest National Laboratory, Richland, WA, USA
  • 3Joint Institute for Regional Earth System Science and Engineering and Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, CA, USA
  • 4Institute of Environment and Sustainability, University of California, Los Angeles, CA, USA
  • 5Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
  • 6Nicholas School of the Environment, Duke University, Durham, NC, USA
  • 7Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan
  • These authors contributed equally to this work.

Abstract. In response to the Coronavirus Disease 2019 (COVID-19), California issued statewide stay-at-home orders, bringing about abrupt and dramatic reductions in air pollutant emissions. This crisis offers us an unprecedented opportunity to evaluate the effectiveness of emission reductions on air quality. Here we use the Weather Research and Forecasting model with Chemistry (WRF-Chem) in combination with surface observations to study the impact of the COVID-19 lockdown measures on air quality in southern California. Based on activity level statistics and satellite observations, we estimate the sectoral emission changes during the lockdown. Due to the reduced emissions, the population-weighted concentrations of fine particulate matter (PM2.5) decrease by 15 % in southern California. The emission reductions contribute 68 % of the PM2.5 concentration decrease before and after the lockdown, while meteorology variations contribute the remaining 32 %. Among all chemical compositions, the PM2.5 concentration decrease due to emission reductions is dominated by nitrate and primary components. For O3 concentrations, the emission reductions cause a decrease in rural areas but an increase in urban areas; the increase can be offset by a 70 % emission reduction in anthropogenic volatile organic compounds (VOC). These findings suggest that a strengthened control on primary PM2.5 emissions and a well-balanced control on nitrogen oxides and VOC emissions are needed to effectively and sustainably alleviate PM2.5 and O3 pollution in southern California.

Zhe Jiang et al.

 
Status: open (until 23 Feb 2021)
Status: open (until 23 Feb 2021)
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Zhe Jiang et al.

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Short summary
We use the COVID-19 pandemic as a unique natural experiment to obtain a more robust understanding of the effectiveness of emission reductions on air quality improvement, by combining chemical transport simulations and observations. Our findings imply a shift from current control policies in California: a strengthened control on primary PM2.5 emissions and a well-balanced control on NOx and volatile organic compounds are needed to effectively and sustainably alleviate PM2.5 and O3 pollution.
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