Emerging Mineral Dust Source in ’A’ay Chù’ Valley, Yukon, Canada Poses Potential Health Risk via Exposure to Metal and Metalloids Enriched in PM ₁₀ and PM _2.5 Size Fractions

Abstract. The ’A’ą̈y Chù’ Valley in Kluane National Park, Yukon, Canada has undergone significant hydrological change in the past decade due to climate-driven glacial recession. This has reverted the ’A’ą̈y Chù’ to a major source of sediment-derived mineral dust, representing an environmental change for the region. Mineral dust influences climatic radiative forcing and impacts human health, both of which depend on its concentration, size distribution, and composition. This work discusses results from a field campaign conducted in the ’A’ą̈y Chù’ Valley in 2021 aimed at understanding and quantifying these parameters, with comparison to a previous campaign in the same location to evaluate the evolution of the dust emissions between 2018 and 2021. An optical particle counter (OPC) instrument measured a mean volume diameter of airborne dust of 4.43 µm at 3.3 m above ground, with Coulter Counter measurements being used for comparison and validation. The concentration of many metal(loid)s in the dust were also studied: Al, Ag, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Ni, Pb, Rb, Tl, U, V, and Zn. It was found that 24-hour ambient air quality criteria for exposure to several metal(loid)s were surpassed. Significant enrichment of several metal(loid)s was observed for both the PM10 and PM2.5 size fractions relative to the Total Suspended Material (TSP) fraction of the mineral dust. This suggests that the mineral dust in the ’A’ą̈y Chù’ Valley possesses compounding characteristics that are detrimental to human health due to exposure to potentially toxic metal(loid) concentrations.