Advancing Understanding of Super-Coarse and Giant Dust Particles via Novel Measurements of Emission and Transport

沙尘暴在地球大气中无处不在，由直径大小不一的小矿物颗粒组成。理论表明，对于长距离传播的尘埃，这些颗粒的直径应该限制在大约10微米或更小，因为向下的引力作用于将较大的颗粒从大气中移除。然而，在距离沙漠数千公里远的地方，已经测量到直径为数十微米甚至数百微米的尘埃颗粒，这些尘埃颗粒就是在那里被送入大气的。迄今为止，对于所谓的“巨大尘埃粒子难题”还没有公认的解释，这凸显了对大气和气溶胶过程的物理理解上的差距。由于沙尘暴对天气和气候的影响程度，从吸收阳光到成为海洋生物活动的催化剂，取决于灰尘的物理特性，包括颗粒大小，因此有必要解决这个难题。该项目旨在提高对直径大于10微米的尘埃颗粒（超粗和巨型颗粒，或SCG尘埃）在大气中的运动的理解，并在解决巨型尘埃颗粒难题方面取得进展。在垂直扩散和水平平流输送过程中，SCG粉尘浓度的大小变化将被测量。此外，还将测量SCG粉尘在发射点的尺寸分辨垂直通量。这些测量结果将被用来检验两个可以解释这一难题的假设：(i)目前的理论严重高估了这些大颗粒在垂直湍流扩散和水平平流输送期间的干沉积；（ii） SCG尘埃在发射时的通量比理论预测的要大一个到几个数量级。这些数据将提供一个独特的机会来评估控制这些粒子的排放和大气输送的理论，并产生在天气和气候模式中表示这些过程的新方法。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Dust storms are ubiquitous in Earth’s atmosphere and are composed of small mineral particles having diameters of varying sizes. Theory suggests that for dust transported long distances, the diameters of these particles should be limited to approximately 10 microns or smaller, due to the downward gravitational force acting to remove larger particles from the atmosphere. However, dust particles with diameters of tens to even hundreds of microns in size have been measured thousands of kilometers away from the deserts where they were lofted into the atmosphere. To-date, there is no accepted explanation for this so-called “giant dust particle conundrum”, highlighting a gap in physical understanding of atmospheric and aerosol processes. Since the magnitudes of dust storm effects on weather and climate, ranging from the absorption of sunlight to being a catalyst for biological activity in the oceans, depend on the physical characteristics of dust, including the particle sizes, there is a need to solve this conundrum. This project aims to improve understanding of the movement of dust particles having diameters greater than 10 microns (super coarse and giant particles, or SCG dust) in the atmosphere, and make progress towards solving the giant dust particle conundrum. Size-resolved changes in the concentrations of SCG dust during vertical diffusive and horizontal advective transport will be measured. Additionally, the size-resolved vertical flux of SCG dust at the point of emission will also be measured. These measurements will then be used to test two hypotheses that could explain the conundrum: (i) that current theory grossly overestimates dry deposition of these large particles during both vertical turbulent diffusive and horizontal advective transport and (ii) that the flux of SCG dust at emission is one to several orders of magnitude greater than that predicted by theory. These data will provide a unique opportunity to evaluate the theory governing the emission and atmospheric transport of these particles, and to generate new methods to represent these processes in weather and climate models.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.