Are the Effects of the COVID-19 Lockdown on Canadian Anthropogenic Emissions Still Felt in 2021 and What Are the Implications for the Ambient Air Pollutants Concentrations?

Canada anthropogenic emissions diminished during the COVID-19 lockdown. This study will investigate whether 2021 Canadian anthropogenic emissions and air pollutant concentration’s are back to pre-pandemic levels. Two annual simulations, 2019 and 2021, over North America at 10 km horizontal resolution with the Canadian air quality operational model GEM-MACH (Global Environmental Multi-scale — Modelling Air quality and Chemistry), from Environment and Climate Change Canada (ECCC), were used for this evaluation. The GEM-MACH model is an off-line multi-phase, multi-pollutant chemical transport model (CTM) with full description of atmospheric chemistry and meteorological processes. It considers the interactions of gas-, aqueous-, and particle-phase chemical components. To model gas-phase chemistry, it employs an updated version of the Acid Deposition and Oxidant Model (ADOM-2) gas-phase chemical mechanism. Anthropogenic emissions of gas-phase species and two size-bin-specific particulate matter (PM) chemical components are required by the model. Plume-rise and plume-spread calculations are performed at each model time step for large stationary point sources to determine the model vertical layers into which point-source emissions are injected. Canada’s Air Pollutant Emissions Inventory (APEI) was prepared and published by ECCC in 2023 which includes the emissions for 2019 and 2021. For the United States and Mexico, the 2016 emissions inventory was obtained from the US Environmental Protection Agency’s (US EPA) National Emission Inventory (NEI). These emissions were temporally and spatially distributed, as well as speciated, using the emission processor SMOKE (Sparse Matrix Operator Kernel Emissions). Some parameters remain constant between the two simulations, i.e. meteorological year 2019, biogenic emissions, US and Mexican emissions. Wildfire emissions are not included. The hourly outputs of the simulations, annual average concentrations of nitrogen dioxide (NO₂), particulate matters smaller than 2.5 µm (PM_2.5) and annual average of daily maximum 8-hour concentrations of ozone (O₃) over Canada will be presented and compared.