Abstract. The mechanisms behind heterogeneous ice nucleation are of fundamental importance to the prediction of the occurrence and properties of many cloud types, which influence climate and precipitation. Aerosol particles act as cloud condensation and freezing nuclei. The surface-water interaction of an ice nucleation particle plays a major, not well explored, role in its ice nucleation ability. This paper presents a real–time–molecular–level comparison of different freezing modes on the surface of an atmospherically relevant metal oxide surface (mica) under varying supersaturation conditions using second harmonic generation spectroscopy. Two sub-deposition nucleation modes were identified (one- and two-stage freezing). The nonlinear signal at water-mica interface was found to drop upon the formation of a thin film on the surface regardless of 1) the formed phase (liquid or ice) and 2) the freezing path (one- or two-step), indicating similar molecular structuring. The results also revealed a transient phase of ice at water-mica interfaces during freezing, which has a lifetime of around one minute. Such information will have a significant impact on climate change, weather modification, and tracing of water in hydrosphere studies.
Abdelmonem, A.: Direct molecular level characterization of different heterogeneous freezing modes on mica, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2017-322, in review, 2017.