EAGER: A Vertical Wind Tunnel for Determination of Scavenging Efficacy and Hydrometeor Physics

雨滴在云下的清除作用对于从大气中清除导致气候变化的自然和人为气溶胶起着关键作用。然而，降雨事件对气溶胶的清除仍然是气候模式中最不确定的组成部分，这主要是由于目前的实验限制，无法提供雨滴对气溶胶收集的直接证据。该项目将建造一个垂直风洞，能够使水滴悬浮起来，同时使水滴暴露在各种气溶胶中。集成到风洞中的将是现代气溶胶产生和表征设备，可以将气溶胶精确地输送到液滴上。实验装置将具有测量气溶胶收集量的能力，通过规定尺寸的液滴来测量大范围的气溶胶大小，而液滴驻留在隧道中。实验设备将通过控制温度和湿度，向液滴传递与大气相关的流动条件，并在平静和湍流条件下使液滴悬浮。高速摄像机将捕捉到模拟自由落体过程中水滴的形状和振荡，如水滴收集粒子、生长和蒸发。建立这样一个设施将促进美国大气科学家与国际社会之间的更大合作，促进未来的学生交流，并成为向当地高中生推广STEM的平台。建立一个能够直接清除测量的z型垂直风洞将改变大气科学家在雨滴和清除物理方面的基本实验工作。很少有像气溶胶清除这样对大气科学如此重要而又缺乏约束的问题。该项目旨在建立一个设施，解决长期存在的撞击清除问题，特别是格林菲尔德间隙内的颗粒。单分散和多分散气溶胶将被输送到由上游层压器产生的悬浮在护套流中的液滴中。在水滴的上游放置小物体会引起湍流。液滴内部和外部的流动将通过激光照射粒子和高速摄像机进行可视化。液滴物理的验证实验将与项目开始时在美因茨垂直风洞进行的实验进行比较，并将验证数据与从现有文献中获得的有限数据进行比较。垂直风洞提供了研究与落体有关的许多其他大气问题的能力，如自由落体中化学物质的吸收，雪花和霰的融化，边缘，以及落体的合并和破裂。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。

Below-cloud scavenging by raindrops plays a critical role in removing natural and anthropogenic aerosols, those which contribute to climate change, from the atmosphere. However, scavenging of aerosols by rainfall events remains the most uncertain constituent in climate models, largely due to current experimental limitations to provide direct evidence of aerosol collection by falling raindrops. This project will construct a vertical wind tunnel capable of levitating water drops while exposing the drops to a wide range of aerosol types. Integrated into the wind tunnel will be modern aerosol generation and characterization equipment that permits the precise delivery of aerosols to the drop. The experimental facility will have the ability of measuring aerosol collection by a drop of prescribed size for a large range of aerosol sizes, while the drop resides in the tunnel. The experimental facility will deliver atmospherically relevant flow conditions to the drop by controlling temperature and humidity, and levitate drops in calm and turbulent wind conditions. High-speed cameras will capture the shape and oscillation of drops in simulated free fall as drops collect particles, grow, and evaporate. The establishment of such a facility will foster greater cooperation between US-based atmospheric scientists and the international community, the future exchange of students, and be a platform for STEM outreach to local high school students. Building a Z-type vertical wind tunnel capable of direct scavenging measurements will transform how atmospheric scientists approach fundamental experimental efforts in raindrop and scavenging physics. There are very few problems of the importance to atmospheric science and as poorly constrained as aerosol scavenging. This project is an effort to create a facility that can unravel longstanding questions in impaction scavenging, particularly for particles within the Greenfield Gap. Mono- and polydisperse aerosols will be delivered to drops levitating in sheath flow, created by upstream laminarizers. Turbulence will be introduced by placing small bodies upstream of the drop. Flow internal and external to the drop will be visualized by laser illumination of particles and high-speed cameras. Validation experiments of drop physics will be compared with those performed at the Mainz vertical wind tunnel at project inception, and scavenging validation data compared to measurements garnered from existing, limited data in literature. A vertical wind tunnel provides the ability to study a number of other atmospheric problems dealing with falling objects such as chemical species absorption in free fall, melting of snowflakes and graupels, riming, and drop coalescence and breakup.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.