![]() ![]() ![]() 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.Ī novel coronavirus disease 2019 (COVID-19) was initially reported in the city of Wuhan, China, on 31 December 2019 and then began to spread around the world. Lower decreases ranging from 6 to 17% were predicted for PM 2.5. 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. 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. 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. 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. ![]() Higher-than-usual seasonal declines in mean daily NO 2 were observed for the pre-lockdown to lockdown periods in 2020. 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–), when lockdown measures were in full force everywhere in Canada, were compared to the same periods in the previous decade (2010–2019). 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. ![]()
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