NIRT: Nanoscale Processes in the Environment: Atmospheric Nanoparticles

这项建议是为了响应纳米科学和工程倡议，NSF 02-148，NIRT(纳米科学跨学科研究团队)类别。该奖项支持Scot Martin教授(哈佛大学)、Peter Buseck教授(亚利桑那州立大学)和Lynn Russell教授(普林斯顿大学)的合作。讨论了纳米尺度对大气纳米粒子热力学和动力学性质的影响。直径在1到100纳米之间的颗粒是强烈影响全球气候的更大颗粒的无处不在和丰富的前体。大气颗粒物的一个主要性质是它们与水蒸气的相互作用，这决定了颗粒物是结晶的还是水的。在纳米尺度范围内，物理状态也以一种未知的方式依赖于颗粒直径，这意味着对于纳米尺度体系，体相系统的相图以不确定的方式移动。这个跨学科的项目将把观测和第一原理热力学研究结合起来。将讨论以下主题：(1)将确定纳米颗粒的潮解相对湿度(DRH)，并将其建模为尺寸的函数。(2)已知水合物的相对稳定性的变化将被测量和模拟。具有较低表面张力的水合物在较小尺寸时变得更有利，这种影响的幅度可能足以使体相尺寸的亚稳水合物转变为纳米尺寸的稳定水合物。(3)将研究纳米尺度下的结晶速率和结晶机理。对于块体体系，结晶速率与颗粒体积呈线性关系。进入纳米大小的领域，一个悬而未决的问题是，这种线性关系在哪里以及为什么会动摇。假设的原因是液滴可能变得比临界细菌小，或者液滴/空气界面上的成核等并行过程可能开始与体积成核竞争。目前，对这些课题的实验研究仅限于技术层面。将为该项目开发和改进两种最先进的仪器，一台环境透射式电子显微镜和一台扫描偏振力显微镜。这项工作将对大气中颗粒物的形成、生长和稳定性提供重要的见解，所有这些都对这些颗粒物的辐射、健康和能见度影响具有重要影响。纳米地球科学暑期本科生计划将把研究、教育和多样性整合到该项目中。

This proposal was received in response to Nanoscale Science and Engineering initiative, NSF 02-148, category NIRT (Nanoscience Interdisciplinary Research Teams). This award supports a collaboration of Prof. Scot Martin (Harvard University), Prof. Peter Buseck (Arizona State University), and Prof. Lynn Russell (Princeton University). It addresses the effects of the nano-size regime on thermodynamic and kinetic properties of atmospheric nanoparticles. Particles having diameters between 1 and 100 nm are the ubiquitous and abundant precursors to the larger particles that strongly influence global climate. A governing property of atmospheric particles is their interaction with water vapor, which determines whether the particles are crystalline or aqueous. In the nano-size regime, physical state also depends in an unknown manner on particle diameter, which implies that phase diagrams for bulk systems are shifted in uncertain ways for nano-size systems. This interdisciplinary project will integrate observational and first-principle thermodynamic investigations. The following topics will be addressed:(1) The deliquescence relative humidity (DRH) of nanoparticles will be determined and modeled as a function of size. (2) Shifts in the relative stabilities of known hydrates will be measured and modeled. Hydrates having lower surface tensions become more favorable at smaller sizes, and the magnitude of this effect may be enough that a metastable hydrate at bulk dimensions transitions into the stable hydrate at nano-sizes. (3) Rates and mechanisms will be investigated for crystallization in the nano-size regime. Crystallization rates depend linearly on particle volume for bulk systems. Entering the nano-size regime, an open question is where and why this linear relationship falters. Hypothesized reasons are that the droplet may become smaller than the critical germ or that parallel processes such as nucleation at the droplet/air interface may begin to compete with volume nucleation. Experimental investigations of these topics are currently technique limited. Two state-of-the-art instruments will be developed and refined for this project, an environmental transmission electron microscope and a scanning polarization force microscope. This work will provide significant insights into the formation, growth, and stability of particles in the atmosphere, all of which have important implications for radiative, health, and visibility impacts of those particles. A nanogeosciences summer undergraduate program will integrate research, education, and diversity into the project.