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Transported Mineral Dust Deposition Case Study at a Hydrologically Sensitive Mountain Site: Size and Composition Shifts in Ambient Aerosol and Snowpack

Category: Regional Air Pollution

Volume: 16 | Issue: 3 | Pages: 555-567
DOI: 10.4209/aaqr.2015.05.0346
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Jessica L. Axson1, Hongru Shen1, Amy L. Bondy2, Christopher C. Landry3, Jason Welz3, Jessie M. Creamean 4,5, Andrew P. Ault 1,2

  • 1 Department of Environmental Health Sciences, University of Michigan, Ann Arbor, MI, USA
  • 2 Department of Chemistry, University of Michigan, Ann Arbor, MI, USA
  • 3 Center for Snow & Avalanche Studies, Silverton, CO, USA
  • 4 Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA
  • 5 Physical Sciences Division, NOAA Earth System Research Laboratory, Boulder, CO, USA

Highlights

Fraction of absorbing Fe-enriched ambient aerosol dust increased during dust event.
Increased number concentration and size of deposited dust in snow during dust event.
Fe-enriched has greatest absorption and larger climate impact by accelerating snowmelt.
Dust composition traced to shifts in the mineral dust source region of the Colorado Plateau.
Melted snow samples were stable when stored for up to two weeks at 4°C.


Abstract

Transported mineral dust deposition to remote mountain snow decreases snow albedo and increases absorption of solar radiation, which accelerates snowpack melt and alters water supply. Mineralogy and chemical composition determine dust particle optical properties, which vary by source region. While impacts of dust deposition at remote mountain sites have been established, few studies have connected the chemical composition of ambient particles during deposition events with the properties of those deposited on the snowpack. Ambient particles and surface snow were sampled in the San Juan Mountains of southwestern Colorado, which frequently experiences dust deposition in the spring and has evidence of dust-enhanced snow melt. Individual particles were analyzed using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX). The number concentration and size distribution of insoluble residues in the top level of snow were determined with nanoparticle tracking analysis (NTA). During a minor dust event (April 2–3, 2015), the fraction of absorbing iron-enriched dust in the ambient aerosol, the number concentration, and size of insoluble residues in snow all increased. This can be traced to shifts in mineral dust source region within the Colorado Plateau, during which, there were higher wind speeds leading to increased transport. The shift in chemical composition and mineralogy of the transported dust has the potential to impact snowpack radiative forcing during dry deposition. In addition, it can also modify the snowpack through scavenging of particles during wet deposition, as well as alter the properties of clouds and orographic precipitation. Understanding these impacts is crucial to understanding the hydrological cycle at remote mountain sites.

Keywords

Mineral dust Atmospheric aerosols Atmospheric chemistry Climate change Long-range transport Radiative effects


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