Volcaniclastic 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.

中文翻译：

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冰岛火山碎屑尘埃源的粒度表征

火山碎屑尘埃颗粒具有独特的物理特性，据推测会影响其在大气边界层内的夹带，发射和沉积速率。很少有详细的粒度测量，因此，在粉尘弥散模型的参数化中，天然颗粒通常理想化为固体玻璃球。这项研究表明，来自冰岛的火山碎屑尘埃颗粒含有大量的无定形玻璃，较大的内部空隙和由纳米鳞片组成的大量尘土涂层。发现它们的高孔隙率随粒径增加而增加，产生的颗粒密度可能大大低于固体球体的预期密度。大量的火山玻璃似乎还会增加颗粒的孔隙率和粗糙度，从而与Brunauer Emmett Teller表面积紧密相关。根据斯托克斯定律进行的分析进一步表明，冰岛的尘埃具有标准化的几何直径（10μm或PM）₁₀），但密度，形状和来源不同，在静止空气中的沉降速度可能比参考玻璃球低20％。作为第一个近似值，忽略了复杂的粒子相互作用和风速，这也影响了大气中的沉积速率，它们的低密度和大表面积可能会使预期的停留时间增加五倍。为了完善火山碎屑散布的估算，应完善模型参数化以纳入这些颗粒比例因子。