An Investigation of the Impact of Canadian wildfires on US Air Quality using Satellite, Model and Ground Measurements

Abstract. Canadian wildfires transport large concentrations of particulate matter into the United States, leading to various impacts on surface temperature, radiation balance, visibility, and exacerbating pollution-related respiratory conditions. Using a combination of surface, satellite and numerical models, this study quantifies the increase in surface fine particulate matter (PM2.5) in the Continental United States due to long-range transported smoke from Canadian wildfires during a wildfire episode from August 9th to 25th, 2018. As a widely used indicator of surface pollution levels, satellite-retrieved AOD can provide crucial information on columnar pollution mass. However, the daily spatial coverage of satellite AOD is restricted due to cloud cover. In order to quantify the daily changes of surface pollution, we fill in the AOD gaps by utilizing simulated 10-m spatial resolution AOD from a chemistry transport model (CTM). In addition, different processes affecting smoke vertical and horizontal transport are examined using two CTM simulations. Meteorological variables associated with these processes are then selected along with the gap-filled AOD product to assess the surface pollution using geographically weighted regression (GWR) and random forest (RF) models. It is found that synoptic pressure systems dominate the horizontal transport of Canadian smoke, and the ascending air and robust winds from a low-pressure system contributes to the long distances of the transport path. Other processes affecting the vertical distribution of pollutants, including boundary layer entrainment, precipitation and terrain-induced vertical mixing are also analyzed in this paper. Our results show that Canadian fires caused a substantial increase in total PM2.5, reaching up to 13 % (62 μgm⁻³) across different US EPA regions during 2018 August wildfire event.