{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,5,21]],"date-time":"2026-05-21T19:10:40Z","timestamp":1779390640247,"version":"3.53.1"},"reference-count":55,"publisher":"MDPI AG","issue":"24","license":[{"start":{"date-parts":[[2020,12,16]],"date-time":"2020-12-16T00:00:00Z","timestamp":1608076800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>A lockdown was implemented in Canada mid-March 2020 to limit the spread of COVID-19. In the wake of this lockdown, declines in nitrogen dioxide (NO2) were observed from the TROPOspheric Monitoring Instrument (TROPOMI). A method is presented to quantify how much of this decrease is due to the lockdown itself as opposed to variability in meteorology and satellite sampling. The operational air quality forecast model, GEM-MACH (Global Environmental Multi-scale - Modelling Air quality and CHemistry), was used together with TROPOMI to determine expected NO2 columns that represents what TROPOMI would have observed for a non-COVID scenario. Applying this methodology to southern Ontario, decreases in NO2 emissions due to the lockdown were seen, with an average 40% (roughly 10 kt[NO2]\/yr) in Toronto and Mississauga and even larger declines in the city center. Natural and satellite sampling variability accounted for as much as 20\u201330%, which demonstrates the importance of taking meteorology into account. A model run with reduced emissions (from 65 kt[NO2]\/yr to 40 kt[NO2]\/yr in the Greater Toronto Area) based on emission activity data during the lockdown period was found to be consistent with TROPOMI NO2 columns.<\/jats:p>","DOI":"10.3390\/rs12244112","type":"journal-article","created":{"date-parts":[[2020,12,16]],"date-time":"2020-12-16T09:21:15Z","timestamp":1608110475000},"page":"4112","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":11,"title":["Assessing the Impact of Corona-Virus-19 on Nitrogen Dioxide Levels over Southern Ontario, Canada"],"prefix":"10.3390","volume":"12","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-4849-9125","authenticated-orcid":false,"given":"Debora","family":"Griffin","sequence":"first","affiliation":[{"name":"Air Quality Research Division, Environment and Climate Change Canada, Toronto, ON M3H 5T4, Canada"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5054-1380","authenticated-orcid":false,"given":"Chris Anthony","family":"McLinden","sequence":"additional","affiliation":[{"name":"Air Quality Research Division, Environment and Climate Change Canada, Toronto, ON M3H 5T4, Canada"},{"name":"Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, SK S7N 5E2, Canada"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jacinthe","family":"Racine","sequence":"additional","affiliation":[{"name":"Canadian Meteorological Centre Operations Division, Environment and Climate Change Canada, Dorval, QC H9P 1J3, Canada"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Michael David","family":"Moran","sequence":"additional","affiliation":[{"name":"Air Quality Research Division, Environment and Climate Change Canada, Toronto, ON M3H 5T4, Canada"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Vitali","family":"Fioletov","sequence":"additional","affiliation":[{"name":"Air Quality Research Division, Environment and Climate Change Canada, Toronto, ON M3H 5T4, Canada"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Radenko","family":"Pavlovic","sequence":"additional","affiliation":[{"name":"Canadian Meteorological Centre Operations Division, Environment and Climate Change Canada, Dorval, QC H9P 1J3, Canada"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Rabab","family":"Mashayekhi","sequence":"additional","affiliation":[{"name":"Canadian Meteorological Centre Operations Division, Environment and Climate Change Canada, Dorval, QC H9P 1J3, Canada"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Xiaoyi","family":"Zhao","sequence":"additional","affiliation":[{"name":"Air Quality Research Division, Environment and Climate Change Canada, Toronto, ON M3H 5T4, Canada"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8743-4455","authenticated-orcid":false,"given":"Henk","family":"Eskes","sequence":"additional","affiliation":[{"name":"Royal Netherlands Meteorological Institute (KNMI), 3731 GA De Bilt, The Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2020,12,16]]},"reference":[{"key":"ref_1","unstructured":"Statistics Canada (2020, September 29). 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