Atmospheric deposition of chromophoric dissolved organic matter in the Athabasca Oil Sands Region, Canada, is strongly influenced by industrial sources during the winter months

There is growing interest in the atmospheric deposition of chromophoric dissolved organic matter (CDOM) owing to its impact on aquatic processes and surface albedo. Industrial operations in the Athabasca Oil Sands Region (AOSR), Canada, are a major source of emissions of organic gases and particulate matter, which likely contribute to regional CDOM deposition. Here we investigated the composition and spatiotemporal variation of CDOM within regional snowpack (45 sites, collected March of 2023) and weekly precipitation samples (three monitoring stations between January 2021-December 2021) using ultraviolet-visible and fluorescence spectroscopy. Spectroscopic analysis identified three distinct fluorescent compounds (fluorophores) in both snowpack and precipitation. Elevated absorbance and fluorescence intensity among near-field samples demonstrated that industrial emissions influenced CDOM deposition in the AOSR. Fluorescent compounds linked to wildfire emissions (indicated by positive associations with pyrogenic indicators) were the dominant source of fluorescence during the summer while an industrial-sourced fluorophore (indicated by high near-field emission intensity and positive associations with continuous air quality monitoring data) was most prominent (absolute and relative emission intensity) during the cold season, possibly due to enhanced atmospheric stability and lower photolysis rates favouring fluorophore formation. Our results suggested that elevated wintertime CDOM deposition associated with oil sands operations will potentially alter snowpack albedo throughout the region.