Isolating the impact of COVID-19 lockdown measures on urban air quality in Canada
Rabab Mashayekhi, Radenko Pavlovic, Jacinthe Racine, Michael D. Moran, Patrick M. Manseau, Annie Duhamel, Ali Katal, Jessica Miville, David Niemi, Si Jun Peng, Mourad Sassi, Debora Griffin, C. A. McLinden
Abstract
Abstract We have investigated the impact of reduced emissions due to COVID-19 lockdown measures in spring 2020 on air quality in Canada’s four largest cities: Toronto, Montreal, Vancouver, and Calgary. Observed daily concentrations of NO 2 , PM 2.5 , and O 3 during a “pre-lockdown” period (15 February–14 March 2020) and a “lockdown” period (22 March–2 May 2020), when lockdown measures were in full force everywhere in Canada, were compared to the same periods in the previous decade (2010–2019). Higher-than-usual seasonal declines in mean daily NO 2 were observed for the pre-lockdown to lockdown periods in 2020. For PM 2.5 , Montreal was the only city with a higher-than-usual seasonal decline, whereas for O 3 all four cities remained within the previous decadal range. In order to isolate the impact of lockdown-related emission changes from other factors such as seasonal changes in meteorology and emissions and meteorological variability, two emission scenarios were performed with the GEM-MACH air quality model. The first was a Business-As-Usual (BAU) scenario with baseline emissions and the second was a more realistic simulation with estimated COVID-19 lockdown emissions. NO 2 surface concentrations for the COVID-19 emission scenario decreased by 31 to 34% on average relative to the BAU scenario in the four metropolitan areas. Lower decreases ranging from 6 to 17% were predicted for PM 2.5 . O 3 surface concentrations, on the other hand, showed increases up to a maximum of 21% close to city centers versus slight decreases over the suburbs, but O x (odd oxygen), like NO 2 and PM 2.5 , decreased as expected over these cities.