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

• Applicant: Dr. Ahmed Abdelmonem, Ph.D.
• Subject Area: Atmospheric Science ; Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: from 2014 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 261509307

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.

• DFG Programme: Research Grants