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Impacts of Traffic Reductions Associated With COVID-19 on Southern California Air Quality

Parker, H. A. and Hasheminassab, S. and Crounse, J. D. and Roehl, C. M. and Wennberg, P. O. (2020) Impacts of Traffic Reductions Associated With COVID-19 on Southern California Air Quality. Geophysical Research Letters, 47 (23). Art. No. e2020GL090164. ISSN 0094-8276. PMCID PMC7744837. doi:10.1029/2020gl090164.

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On 19 March 2020, California put in place Stay‐At‐Home orders to reduce the spread of SARS‐CoV‐2. As a result, decreases up to 50% in traffic occurred across the South Coast Air Basin (SoCAB). We report that, compared to the 19 March to 30 June period of the last 5 years, the 2020 concentrations of PM_(2.5) and NO_x showed an overall reduction across the basin. O₃ concentrations decreased in the western part of the basin and generally increased in the downwind areas. The NO_x decline in 2020 (approximately 27% basin‐wide) is in addition to ongoing declines over the last two decades (on average 4% less than the −6.8% per year afternoon NO₂ concentration decrease) and provides insight into how air quality may respond over the next few years of continued vehicular reductions. The modest changes in O₃ suggests additional mitigation will be necessary to comply with air quality standards.

Item Type:Article
Related URLs:
URLURL TypeDescription ItemCalifornia Air Resources Board Air Quality Data Query Tool ItemCalNex campaign
https://s5phub.copernicus.euRelated ItemSentinel-5P Data Hub ItemCaltrans PeMS program
http://tccon-weather.caltech.eduRelated ItemWeather data CentralArticle
Parker, H. A.0000-0002-0041-2764
Hasheminassab, S.0000-0002-4422-8547
Crounse, J. D.0000-0001-5443-729X
Roehl, C. M.0000-0001-5383-8462
Wennberg, P. O.0000-0002-6126-3854
Additional Information:© 2020 The Authors. This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial‐NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made. Issue Online: 01 December 2020; Version of Record online: 01 December 2020; Accepted manuscript online: 23 November 2020; Manuscript accepted: 10 November 2020; Manuscript revised: 05 November 2020; Manuscript received: 01 August 2020. The views expressed in this document are solely those of the authors and do not necessarily reflect those of the South Coast AQMD. The CITAQS facility was funded by Caltech's Linde Center for Global Environmental Science and the Resnick Sustainability Institute. We thank NASA via NNX17AE15G for support of retrievals of CH₂O from the Caltech TCCON station. Harrison Parker thanks the Rose Hill Foundation for initial support of his graduate fellowship. Data Availability Statement: Data from the CITAQS are available by request and will be available online to the public in the near future. All data from the AQMD sites are available through the California Air Resources Board Air Quality Data Query Tool ( Data from the CalNex campaign are available online ( TROPOMI data used in this research are available through the Sentinel‐5P Data Hub ( Traffic data used here are available through the Caltrans PeMS program ( Weather data are available online or by contacting the corresponding author (https://tccon‐
Group:Resnick Sustainability Institute, COVID-19
Funding AgencyGrant Number
Ronald And Maxine Linde Center for Global Environmental ScienceUNSPECIFIED
Resnick Sustainability InstituteUNSPECIFIED
Rose Hills FoundationUNSPECIFIED
Subject Keywords:air quality; lockdown; COVID‐19; South Coast Air Basin; ozone; nitrogen dioxide
Issue or Number:23
PubMed Central ID:PMC7744837
Record Number:CaltechAUTHORS:20201124-133212486
Persistent URL:
Official Citation:Parker, H. A., Hasheminassab, S., Crounse, J. D., Roehl, C. M., & Wennberg, P. O. (2020). Impacts of traffic reductions associated with COVID‐19 on Southern California air quality. Geophysical Research Letters, 47, e2020GL090164.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:106816
Deposited By: Tony Diaz
Deposited On:24 Nov 2020 22:00
Last Modified:16 Nov 2021 18:57

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