Characterization of mineral dust emitted from an actively retreating glacier in Yukon, Canada

Airborne mineral dust emitted in Arctic regions can significantly alter the energy balance of the Northern atmosphere through scattering and absorption of radiation; dust also plays an important role in the biogeochemical cycling of metals and can have deleterious effects on air quality and public health. The impact of northern dust sources on the atmosphere and environment may change rapidly, as warming temperatures in the North can increase mineral dust production and source regions by inducing topographical changes due to rapid glacier ablation. However, at present, the impact of such changes is difficult to evaluate because there are very few scientific studies that perform direct field measurements of mineral dust emissions as well as of mineral dust chemical and microphysical properties in Arctic regions. To address this knowledge gap, we performed mineral dust measurement campaigns in June 2017 and May 2018 near the Ä’äy Chù (Slims River), within a proglacial valley in Yukon, Canada that has exhibited strong dust emissions. The Ä’äy Chù Valley has been impacted heavily by climate change, as the rapid retreat of the adjacent Kaskawulsh glacier, recently routed waters away from the river valley, leaving the riverbed exposed and thus potentially increasing its dust-producing erodible surface area. We have collected aerosol samples (PM10 and deposited mineral dust) throughout the Ä’äy Chù Valley, and have recorded weather data to establish a link between environmental factors and the emission of dust. We have also employed an efficient, quantitative method for analysis of trace metals in mineral dust via inductively coupled plasma mass spectrometry (ICP-MS) to quantify trace metals in PM10 samples, soil and in deposited mineral dust samples.  Ours is the first field campaign to provide chemical and microphysical characterization of mineral dust emitted directly from a high-latitude dust source in Canada. Analysis of data obtained by an optical particle counter (OPC) indicated dust events occurred during both daylight and non-daylight hours, while gravimetric analysis of filter samples found ambient concentrations ranging between 240 µg/m3 and 3950 µg/m3 at the dust source during the course of the dust observation campaign. Furthermore, air quality thresholds of the World Health Organization (WHO) were exceeded at sites near the dust source, including at the Thachäl Dhäl Visitor’s Center run by Parks Canada and a site next to the Alaska Highway. We were unable to successfully analyze our samples using laser ablation ICP-MS and single particle ICP-MS. Nevertheless, we successfully validated a protocol for performing ICP-MS analysis of digested samples and were thus able to apply this technique to the analysis of our samples. Analysis of elemental composition via ICP-MS has revealed enrichment of minor and trace element content in ambient air samples as compared to soils and dust deposition, generally by a factor of 1.5 to 2. Moreover, SEM/EDS analysis has demonstrated that the emitted dust primarily consists of non-spherical particles composed of aluminosilicate clay mineral aggregates. Finally, we have calculated the vertical flux of particulate mass, and have used the flux, the size distribution, and the composition of both PM10 and soil samples to evaluate several theories related to the predominant dust emission mechanism that occurs in the Ä’äy Chù Valley.

Keyphrases: Mineral dust, Canadian North, Atmospheric chemistry, Aerosols, Climate change