Measurement of Ice Nuclei in the Contact Mode

为了充分解决气溶胶颗粒对地球气候的间接影响，必须了解这些颗粒催化冰冻的过程。粒子可以以四种方式中的任何一种作为非均相原子核--沉积、浸泡、凝结或接触。其中，最不为人所知的是接触成核，这是一种由气溶胶粒子与过冷水滴表面接触而引发的冻结过程。在这项研究中，我们将通过开发和使用两种测量接触核的仪器来提高我们对接触模式下冰核的认识，这两种仪器将使用两种独立但互补的技术。第一种是基于静电沉淀的，适合于实验室工作，对气溶胶-液滴相互作用更敏感。第二种是利用过冷水滴的声学悬浮，可以在现场部署，温度范围更广。要回答的问题包括：1)接触成核的机制是什么？2)接触模式比浸入/冷凝有效多少？3)接触模式下的非均相成核率如何取决于颗粒的大小和类型？4)接触模式下的成核率如何取决于表面上的颗粒数量？(或给定大小和类型的粒子作为接触核的比例)5)粒子撞击和成核之间需要多长时间？6)大气中接触核的浓度是多少？更广泛的影响。这些仪器提供的关于接触成核的知识将减少我们对冰和混合相云对地球辐射预算和水文循环影响的不确定性，从而有助于更好地了解地球的气候系统。该项目中仪器的开发还将加强国家的科学基础设施。据我们所知，目前还没有现有的工具可以像这个项目所做的那样量化接触成核。研究生还将参与该项目，包括仪器的设计和建造，以及使用仪器回答上述科学问题。这些领域的研究生培训和教育将加强国家的智力基础设施。此外，本科生将在整个项目的三年中参与暑期实验设计和测量，提供独特的教育体验。

To fully address the indirect effect of aerosol particles on Earth's climate must include an understanding of the processes by which those particles catalyze freezing. Particles may act as heterogeneous nuclei in any of four modes - deposition, immersion, condensation, or contact. Of the four, the least understood is contact nucleation, which is a freezing process initiated by contact of an aerosol particle with the surface of a supercooled droplet of water.Intellectual merits. In this study, we will improve our knowledge concerning ice nucleation in the contact mode by developing and using two instruments, which will measure contact nuclei, using two separate, but complementary techniques. The first, based on electrostatic precipitation, is suitable for laboratory work and is more sensitive to aerosol-droplet interactions. The second, which employs acoustic levitation of the supercooled water droplets, will be amenable to deployment in the field and will have a wider temperature range. The questions to be answered include:1) What is the mechanism of contact nucleation?2) How much more effective is the contact mode than immersion/condensation?3) How does the heterogeneous nucleation rate in the contact mode depend upon the particle size and type?4) How does the nucleation rate in the contact mode depend upon the number of particles on the surface? (Or what fraction of particles of a given size and type act as contact nuclei)5) How much time elapses between particle impact and nucleation?6) What is the concentration of contact nuclei in the atmosphere?Broader Impacts. The knowledge about contact nucleation provided by these instruments will reduce our uncertainty of the effect of ice and mixed phase clouds on Earth's radiative budget and hydrological cycle, thus contributing to an improved understanding of Earth's climate system. Development of the instruments in this project would also enhance the nation's scientific infrastructure. To our knowledge, no currently existing instrument can quantify contact nucleation in the way that this project will do. Graduate students will also be involved with the project, both in the design and construction of the instruments and in their use to answer the scientific questions posed above. Graduate training and education in these areas will enhance the nation's intellectual infrastructure. In addition, undergraduate students will participate in the experimental design and measurements during the summer for all the three years of the project, providing a unique educational experience.