Elementary processes of heterogeneous ice nucleation observed by nonlinear optical spectroscopy: The role of hydroxyl groups on the surfaces of mineral aerosol particles

云通过散射阳光和吸收来自地球的热辐射来影响能量收支，因此被认为是气候系统的主要参与者。大气过程的研究，特别是冰的成核，对我们理解云动力学、降水形成以及与辐射的相互作用的机制具有根本的重要性。矿物尘埃是地球大气气溶胶的最大组成部分，在低饱和度和比均匀冻结温度高的温度下可以引发冰的形成，从而影响云的动力学、微物理学和性质。尽管有许多研究来阐明冰成核颗粒的颗粒尺寸和表面性质的影响，但我们仍然缺乏关于冰在分子水平上的非均质成核的基本知识。该项目更新提案的总体目标是使用非线性光学（NLO）光谱，主要是过冷和频发生（SFG）光谱，研究矿物气溶胶颗粒表面OH在非均质冰成核（IN）过程中的作用。在DFG项目AB 604/1-1中，在KIT的IMK-AAF奠定了新研究线（大气表面科学）的基石。该项目清楚地表明，非线性光学光谱适合于探测分子水平上的异质IN过程。这里提出的实验计划主要是基于探测水和表面羟基在非均相冻结的两个大气相关的矿物氧化物的不同IN能力（长石和石英）的表面上。我将使用过冷SFG来研究矿物表面的界面水（液体和冰），并确定表面OH在增强或阻碍非均质冻结过程中的作用。这项研究将奠定基础，更确定性的描述大气矿物气溶胶颗粒的非均匀冻结。它将对我们理解大气过程以及气候系统产生重大影响。因此，在改变当地天气（例如，播云、防雹）和减缓气候变化研究方面将特别有意义。

Clouds influence the energy budget by scattering sunlight and absorbing thermal radiation from the Earth and, hence, are considered the major player in the climate system. Investigation of atmospheric processes in general and ice nucleation in particular is of fundamental importance to our understanding of the mechanisms of cloud dynamics, precipitation formation, and interaction with radiation. Mineral dust, the largest component of the Earths atmospheric aerosols, can initiate ice formation at low saturations and temperatures warmer than homogeneous freezing and, thus, influence cloud dynamics, microphysics, and properties. Despite numerous investigations to elucidate the effect of particle size and surface properties of the ice nucleating particle, there still is a fundamental lack of our knowledge about heterogeneous nucleation of ice on the molecular level. The overall goal of this project renewal proposal is to investigate the role of surface OH of mineral aerosol particles in heterogeneous ice nucleation (IN) processes using nonlinear optical (NLO) spectroscopy, mainly supercooled sum-frequency generation (SFG) spectroscopy. In the DFG project AB 604/1-1, the cornerstone of a new research line (Atmospheric Surface Science) at IMK-AAF of KIT was laid. The project clearly demonstrated that NLO spectroscopy is suited for probing heterogeneous IN processes on the molecular level. The experimental plan proposed here is mainly based on probing water and surface hydroxyl groups during the heterogeneous freezing on the surface of two atmospherically relevant mineral oxides of different IN abilities (feldspar and quartz). I will use supercooled SFG to study the interfacial water (liquid and ice) on mineral surfaces and determine the role of surface OH in enhancing or impeding the heterogeneous freezing process. This study will lay the foundations for a more deterministic description of heterogeneous freezing on atmospheric mineral aerosol particles. It will have a significant impact on our understanding of atmospheric processes and, hence, climate system. Consequently, it will be of particular interest as regards local weather modification (e.g. cloud seeding, hail prevention) and climate mitigation studies.