Microanalysis Techniques to Study Atmospheric Ice Nucleation and Ice Crystal Growth

Atmospheric ice crystal formation impacts the hydrological cycle and climate. Ice-nucleating particles (INPs), typically consisting of sub- and supermicrometer-sized particles, initiate heterogeneous ice nucleation processes leading to ice crystal formation. Ice nucleation commences on the nanoscale at the substrate surface and depends on ambient temperature and humidity. This chapter provides an overview of microanalysis techniques that examine the heterogeneous ice nucleation process and explore the complex morphologies of ice crystals. The first section introduces the different ice nucleation pathways, provides a brief outline of the underlying nucleation theory, and describes the different ice crystal habits. The second section provides an overview of the microanalysis techniques and experiments to study INPs or ice-nucleating substrates, including multimodal instrument approaches and in situ ice nucleation studies. Examples of microanalysis techniques include Raman, atomic force, electron, and X-ray microscopy, and the techniques' unique capabilities to examine the physical and chemical properties of the ice-nucleating substrate are discussed. The third section presents electron microscopy studies of ice crystals during growth and sublimation, displaying the morphological complexities of ice crystals. Finally, the fourth section discusses experimental requirements, including sample sizes, radiation effects, and the role of standard INPs.