Wildfires are becoming more prevalent and emissions from wildfires can have an impact on public health and atmospheric chemistry, with emissions often travelling long distances from the source. Biomass burning produces carbon monoxide (CO), formaldehyde (HCHO), and nitrogen dioxide (NO 2 ), among other species. Understanding how these emissions evolve downwind is important to understanding these impacts. Enhancement rates of these molecules were calculated using single-overpass TROPOspheric Monitoring Instrument (TROPOMI) measurements, MODerate resolution Imaging Spectroradiometer (MODIS) fire radiative power (FRP), a 1-D advection model, and the Gaussian-flux method for sixteen plumes as they aged downwind from nine boreal forest wildfires in Western Canada during summer 2023. Rates were also analysed and compared to data provided for three fires measured during the summer 2019 Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) campaign. Calculated rates were generally within but slightly lower than provided FIREX-AQ ranges due to diurnal differences between satellite and in-situ measurements. Spatiotemporal variation across all summer 2023 plumes confirm CO emission primarily from the fire centre, with HCHO and NO 2 showing primarily secondary formation potentially due to mixing with atmospheric oxidants. Enhancement ratios (EnhR) of calculated vertical column density enhancements for HCHO/CO, NO 2 /CO, and HCHO/NO 2 showed moderate to low average correlation (R 2 = 0.40, 0.23, 0.49, respectively), with average slopes consistent with in-situ and satellite literature values, within uncertainty, for HCHO/CO and NO 2 /CO. Our results demonstrate the effectiveness of TROPOMI and the Gaussian-flux method for analysing downwind evolution of wildfire emissions.
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