Iceland contains some of the largest and most active dust sources in the Arctic, with the frequency of major emission events increasing in the wake of catastrophic volcanic eruptions, such as the 2010 Eyjafjallajökull eruption. Relatively juvenile Icelandic volcaniclastic dust particles are porous and highly angular, and they frequently bear ultrafine nanoscale dustcoats. Their low density is speculated to affect deposition rates in the atmosphere, while substantial amounts of water adsorbed onto their expansive surface area may affect nucleation, aggregation, and settling. Using a 2‐D laser Doppler anemometer, the present paper reports on a set of highly controlled fall column experiments designed to evaluate the dependency of the settling velocity upon particle morphology (e.g., size, shape, density, and surface area) and relative humidity (RH). Measurements for samples obtained from four Icelandic field sites are compared to those for solid glass spheres of similar diameter. The results confirm that the amount of adsorbed water increases with RH and the particle specific surface area. Higher dust concentrations are found to favor particle interaction and the formation of aggregates, especially at higher RH. Under dry conditions (20 % < RH < 30 % ), the horizontal drift velocity measured for the angular, porous Icelandic particles exceeds that observed for solid glass spheres, although these measurements are an order of magnitude smaller than the vertical velocity. As compared to particle diameter, shape does not appear to influence either the settling rate or drag coefficient at Reynolds numbers ≤10⁻², owing to the dominance of viscous effects over form drag.

中文翻译：

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影响火山碎屑沉降速度的颗粒尺度因素的室内研究

冰岛拥有北极中最大，最活跃的一些尘埃源，随着灾难性火山爆发（例如2010年的埃雅菲亚德拉冰峰爆发）之后，主要排放事件的频率增加。相对较幼小的冰岛火山碎屑颗粒是多孔的，且具有很大的棱角，它们经常带有超细的纳米级粉尘。据推测它们的低密度会影响大气中的沉积速率，而大量吸附在其膨胀表面积上的水可能会影响成核，聚集和沉降。本文使用二维激光多普勒风速仪报告了一组高度受控的下降柱实验，旨在评估沉降速度对颗粒形态（例如大小，形状，密度和表面积）和相对湿度的依赖性。 （RH）。将来自四个冰岛现场的样品的测量结果与类似直径的实心玻璃球的测量结果进行比较。结果证实，吸附水的量随RH和颗粒比表面积而增加。发现较高的粉尘浓度有利于颗粒相互作用和聚集体的形成，尤其是在较高RH下。在干燥条件下（20％<RH <30％）时，对角形多孔冰岛粒子测得的水平漂移速度超过了对实心玻璃球的观测，尽管这些测量值比垂直速度小一个数量级。相比于粒径，形状不会出现在雷诺数以影响任一沉降速率或阻力系数≤ 10 ^-2，由于超过形状阻力粘滞效应的主导地位。