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中的主要参与者。大气过程特别是冰核的研究对于我们理解云动力学、降水形成和与辐射相互作用的机制具有重要意义。矿物尘埃是地球大气气溶胶的最大成分，在低饱和度和比均匀冻结更温暖的温度下可以启动冰的形成，从而影响云的动力学、微物理和性质。尽管有大量的研究来阐明冰核的颗粒大小和表面性质的影响，但在分子水平上我们对冰的非均相成核仍然缺乏基本的了解。本项目更新计划的总体目标是利用非线性光学(NLO)光谱，主要是过冷和频(SFG)光谱，研究矿物气溶胶颗粒表面羟基在非均相成冰(IN)过程中的作用。在DFG项目AB 604/1-1中，IMK-AAF的一个新的研究项目(大气表面科学)的基石已经奠定。该项目清楚地表明，非线性光学光谱学适合在分子水平上探测非均匀的IN过程。本文提出的实验方案主要基于两种不同IN能力的大气相关矿物氧化物(长石和石英)在非均相冻结过程中的水和表面羟基的探测。我将使用过冷SFG来研究矿物表面的界面水(液体和冰)，并确定表面羟基在促进或阻碍非均质冻结过程中的作用。这项研究将为更确定地描述大气矿物气溶胶颗粒的非均匀冻结奠定基础。它将对我们对大气过程的理解产生重大影响，从而对气候系统产生重大影响。因此，这将对当地的人工影响天气(如播云、防雹)和气候缓解研究产生特别的影响。

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.