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.
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
Received: 19 Nov 2020 – Accepted for review: 26 Dec 2020 – Discussion started: 29 Dec 2020
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.
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.
We use the COVID-19 pandemic as a unique natural experiment to obtain a more robust...
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