Articles | Volume 17, issue 17
Research article
13 Sep 2017
Research article |  | 13 Sep 2017

Direct molecular-level characterization of different heterogeneous freezing modes on mica – Part 1

Ahmed Abdelmonem

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 mineral 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 the water–mica interface was found to drop following 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 1 min. Such information will have a significant impact on climate change, weather modification, and the tracing of water in hydrosphere studies.

Short summary
On the basis of supercooled SHG spectroscopy, I report molecular-level evidence for the existence of one- and two-step deposition freezing depending on the surface type and the supersaturation conditions. In addition, immersion freezing shows a transient ice phase with a lifetime of c. 1 min. This study provides new insights into atmospheric processes and can impact various industrial and research branches, particularly climate change, weather modification, and tracing water in the hydrosphere.
Final-revised paper