Isolating the impact of COVID-19 lockdown measures on urban air quality in Canada.

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 NO2, PM2.5, and O3 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 NO2 were observed for the pre-lockdown to lockdown periods in 2020. For PM2.5, Montreal was the only city with a higher-than-usual seasonal decline, whereas for O3 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. NO2 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 PM2.5. O3 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 Ox (odd oxygen), like NO2 and PM2.5, decreased as expected over these cities. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s11869-021-01039-1.

Health impact analysis of PM2.5 from wildfire smoke in Canada (2013-2015, 2017-2018).

Smoke from wildfires contains many air pollutants of concern and epidemiological studies have identified associations between exposure to wildfire smoke PM2.5 and mortality and respiratory morbidity, and a possible association with cardiovascular morbidity. For this study, a retrospective analysis of air quality modelling was performed to quantify the exposure to wildfire-PM2.5 across the Canadian population. The model included wildfire emissions from across North America for a 5-month period from May to September (i.e. wildfire season), between 2013 and 2015 and 2017-2018. Large variations in wildfire-PM2.5 were noted year-to-year, geospatially, and within fire season. The model results were then used to estimate the national population health impacts attributable to wildfire-PM2.5 and the associated economic valuation. The analysis estimated annual premature mortalities ranging from 54-240 premature mortalities attributable to short-term exposure and 570-2500 premature mortalities attributable to long-term exposure, as well as many non-fatal cardiorespiratory health outcomes. The economic valuation of the population health impacts was estimated per year at $410M-$1.8B for acute health impacts and $4.3B-$19B for chronic health impacts for the study period. The health impacts were greatest in the provinces with populations in close proximity to wildfire activity, though health impacts were also noted across many provinces indicating the long-range transport of wildfire-PM2.5. Understanding the population health impacts of wildfire smoke is important as climate change is anticipated to increase wildfire activity in Canada and abroad.

Atmospheric deposition of persistent organic pollutants and chemicals of emerging concern at two sites in northern Sweden.

Bimonthly bulk atmospheric deposition samples (precipitation + dry particle) were taken for one year at an arctic (Abisko, 68°20' N, 19°03' E) and a sub-arctic (Krycklan 64°14' N, 19°46' E) location in northern Sweden using Amberlite IRA-743 as an absorbent for hydrophobic pollutants. The samples were analyzed by gas chromatography-high resolution mass spectrometry (GC-HRMS) for polychlorinated biphenyls (PCBs), legacy organochlorine pesticides (OCPs = hexachlorocyclohexanes and chlordane-related compounds), polybrominated diphenyl ethers (PBDEs) and emerging chemicals. Higher deposition rates of most compounds were observed at the more northern site despite its receiving less precipitation and being more remote. HCHs and PCBs made up the bulk of the total deposition at both sites. Five emerging chemicals were detected: the current-use pesticides trifluralin and chlorothalonil; and non-BDE flame retardants 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane (TBECH), 1,2-bis(2,4,6-tribromophenoxy) ethane (BTBPE), and Dechlorane Plus (DP). A decrease in the fraction of the anti isomer of DP was observed at the arctic site, indicating isomer-selective degradation or isomerization during long range transport. Air parcel back trajectories revealed a greater influence from air originating over the ocean at the more northern site. The differences in these air sources were reflected in higher ∑HCH to ∑PCB ratios compared to the more southern site, as HCHs are related to volatilization from the ocean and Abisko is located <100 km from the Norwegian coast, while PCBs are emitted from continental sources.