Environmental & Climate Sciences Department Seminar

Atmospheric ice crystal formation is recognized as one of the grand challenges in the atmospheric sciences. Aerosol particles that can serve as ice nucleating particles (INPs) initiate the freezing process by various ice nucleation pathways. Those depend on the particle types and ambient conditions such as temperature and humidity which define the supersaturation with respect to ice. For temperatures above -38 °C, ice nucleation commences, in most cases, on the particle surface. Measurements of INPs are challenging and typically do not provide the size, morphological, and compositional information of the particles that acted as INPs. Studying ice nucleation by a particles-on-substrate approach allows for the application of single-particle micro-spectroscopic analytical tools that resolve particle morphology and composition in the order of 10s of nanometers. In recent years computer-controlled scanning electron microscopy with energy-dispersive X-ray analysis and scanning transmission X-ray microscopy with near-edge X-ray absorption fine structure spectroscopy have been employed to study ice nucleation. These techniques allow us to determine the aerosol population and associated INPs in terms of size, composition, and mixing state. This capability enables us to characterize the physicochemical nature of INPs and their relationship with the aerosol population. This in turn, has implications for the interpretation and description of ice nucleation in experiments and cloud-resolving models. Application of a simplified large eddy simulation informed 1D aerosol-cloud model of a long-lived stratus mixed-phase cloud demonstrates how different interpretations of freezing by aerosol particles impact the ice crystal number concentrations