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成分。无论气溶胶来自自然来源还是人为来源，它们都在全球气候中发挥着重要作用，因为它们极大地影响了地球的辐射平衡，充当了云的凝结核，并充当了化学反应的场所。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粒子测量的前沿分析仪器，因为它们允许跨相态和时间尺度对微米级和飞秒级液体和固体进行无表面控制，而通过整体测量无法获得这些控制。利用这一工具，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。我们研究计划的双重目标是(I)开发用于单微米和纳米颗粒光谱测量(例如，腔增强拉曼散射)的实验平台，该平台可应用于广泛的学科和(Ii)利用这些平台来解决大气气溶胶科学中的悬而未决的科学问题。在即将到来的赠款期间，我们将在2014年以来取得的进展的基础上，开发下一代光学捕获平台和光谱技术，以研究凝聚相化学在地球大气中所起的作用。将使用我们的光学陷阱研究的现象示例包括过饱和液滴的多步相变、高粘度有机气溶胶(如半固态、玻璃态和凝胶形成)的相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粒子(如棕色碳)的光学性质。除了将设计和建造的用于研究这些系统的新陷阱外，我们还将同时继续发展理论框架，这是在我们的单粒子实验中模拟光散射、辐射压力、多组分质量传输和气溶胶热力学所需的。这些工具不仅对从光谱测量中准确地恢复气溶胶物理性质很重要，而且还为我们详细了解空气中颗粒物的总体目标服务。总而言之，我们的计划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.