Particle‐scale characterization of volcaniclastic dust sources within Iceland

Abstract

AbstractVolcaniclastic dust particles are characterized by unique physical properties, which are speculated to influence their rates of entrainment, emission and deposition within the atmospheric boundary layer. Few detailed particle‐scale measurements exist, so that natural particles often are idealized as solid glass spheres in the parameterization of dust dispersion models. This study shows that volcaniclastic dust particles from Iceland contain substantial quantities of amorphous glass, large internal voids and copious dustcoats comprised of nano‐scale flakes. Their high porosity, found to increase with particle diameter, generates particle densities that can be substantially lower than expected for a solid sphere. An abundance of volcanic glass also seems to increase particle porosity and roughness, and thereby strongly correlates with the Brunauer Emmett Teller surface area. An analysis based on Stokes' law further suggests that Icelandic dust with a standardized geometric diameter (10 μm or PM10), but with varying density, shape and origin, may have settling velocities in still air that are up to 20% lower than for a reference glass sphere. As a first approximation, neglecting complex particle interactions and wind speed, which also affect the deposition rate in the atmosphere, their low density and large surface area could increase the expected residence time by a factor of five. Model parameterization should be refined to incorporate these particle‐scale factors in order to improve on the estimation of volcaniclastic dust dispersion.