Ice formation and transformation in aerosols are critical in defining atmospheric processes and human activities. Despite efforts to study ice formation using macro- and micro-scale approaches, minimal direct evidence of nanoscale ice nucleation and transformation mechanisms has been collected due to a lack of tools for observing ice nanostructures in real space. The proposed research aims to elucidate the nucleation, phase transformation, and melting pathways of ice nanocrystals at an unprecedented resolution. Specifically, we will identify (1) the interfacial structure of ice with certain minerals and proteins that promote or inhibit heterogeneous ice nucleation, (2) the structural and facet evolution of the water-ice interface during the phase transformation, and (3) the presence and evolution of possible metastable structures at the beginning of ice crystallization and near the complete melting of ice into water. A model-experiment (ModEx) approach will be adopted to iteratively incorporate in situ electron microscopy (EM) experiments, a theoretical framework of thermodynamics and kinetics, and machine learning (ML)-assisted modeling and simulations. Taken together, the proposed study may pave the way for a new level of research on ice in earth and biological systems and shed light on environmental, surface chemical, and cryobiological technologies.