Spectroscopy of Atmospheric Aerosol Particles

气溶胶是悬浮在气体中的液体或固体颗粒，是地球上许多大气过程的关键组成部分。无论气溶胶来自自然还是人为来源，它们在全球气候中发挥着重要作用，因为它们极大地影响地球的辐射平衡，充当云凝结核，并作为化学反应的场所。然而，在许多这样的过程中，人们对气溶胶的确切影响知之甚少。光学镊子是高精度单一气溶胶颗粒测量前沿的分析仪器，因为它们允许对微和飞图液体和固体进行无表面控制，跨越相态和时间尺度，这是通过批量测量无法获得的。有了这个工具，我们的团队已经能够询问许多重要的微物理性质，如吸湿生长、表面张力、粘度、液-液平衡和大气多相化学。我们研究项目的双重目标是：(i)开发单微米和纳米颗粒的光谱测量实验平台（例如，腔增强拉曼散射），这些实验平台可以在广泛的学科范围内找到应用；（ii）利用这些平台解决大气气溶胶科学中的突出科学问题。在即将到来的拨款期内，我们将以2014年以来的进展为基础，开发下一代光捕获平台和光谱技术，以研究凝聚态化学在地球大气中的作用。使用我们的光学陷阱将研究的现象示例包括过饱和液滴的多步相变化，高粘度有机气溶胶（如半固体，玻璃状和凝胶状形成）的相状态及其对多组分质量传输的影响，表面张力在气溶胶活化成云滴中的作用，以及测量强吸收颗粒（如棕色碳）的光学性质。除了将设计和建造用于研究这些系统的新陷阱外，我们还将同时继续发展在单粒子实验中模拟光散射、辐射压力、多组分质量输运和气溶胶热力学所需的理论框架。这些工具不仅对于从光谱测量中准确检索气溶胶物理特性很重要，而且它们也有助于我们详细了解空气中颗粒的总体目标。总之，我们的项目将继续开发最先进的分析仪器和模型，同时研究与地球大气相关的系统。这一切都是为了提高我们对大气气溶胶粒子物理化学的基本知识。

Aerosols are liquid or solid particles suspended in a gas and are a key component in many atmospheric processes on Earth. Whether aerosols originate from natural or anthropogenic sources, they play an important role in the global climate as they greatly impact the Earth's radiation balance, act as cloud condensation nuclei, and serve as sites for chemical reactions. In many of these processes, however, the exact influence of aerosols is poorly understood. Optical tweezers are an analytical instrument at the frontier of high-precision single aerosol particle measurements as they allow for surface-free control of pico- and femtogram liquids and solids across phase states and timescales which are inaccessible via bulk measurements. With this tool, our group has been able to interrogate many important microphysical properties such as hygroscopic growth, surface tension, viscosity, liquid-liquid equilibrium, and atmospheric multiphase chemistry. The dual objectives of our research program are (i) the development of experimental platforms for spectroscopic measurements (e.g. cavity-enhanced Raman scattering) of single micron- and nanosized particles that can find application across a broad spectrum of disciplines and (ii) utilizing these platforms to address outstanding scientific questions within atmospheric aerosol science. In the coming grant period, we will build on our progress since 2014 and develop the next generation of optical trapping platforms and spectroscopic techniques to investigate the role that condensed-phase chemistry plays in Earth's atmosphere. Examples of phenomena that will be studied using our optical traps include multistep phase changes in supersaturated droplets, phase states of high viscosity organic aerosols (e.g. semisolid, glassy, and gel formation) and their effect on multicomponent mass transport, the role of surface tension in aerosol activation into cloud droplets, and measuring the optical properties of strongly absorbing particles (e.g. brown carbon). In addition to the new traps that will be designed and constructed to study these systems, we will simultaneously continue our development of the theoretical framework that is required to model light scattering, radiation pressure, multicomponent mass transport, and aerosol thermodynamics in our single particle experiments. These tools are important not only for the accurate retrieval of aerosol physical properties from spectroscopic measurements, but they also serve our overall goal of a detailed understanding of airborne particles. In summary, our program will continue to develop both state-of-the-art analytical instrumentation and models while studying systems of relevance to Earth's atmosphere. This is all in pursuit of improving our fundamental knowledge of the physical chemistry of atmospheric aerosol particles.