Adsorption and Deposition Freezing on Silver Iodide Surface: A Computer Simulation Study
- 1Finnish Meteorological Institute, Helsinki, Finland (golnaz.roudsari@fmi.fi)
- 2Laboratory of Atmospheric Processes and their Impacts, ENAC, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland
Pure liquid water can remain liquid at temperatures as low as -38 oC in the atmosphere. However, ice nucleation can occur at temperatures even higher than -3 oC in the presence atmospheric particles. Cloud ice usually forms as a result of heterogeneous ice nucleation (HIN), where insoluble airborne particles catalyze the freezing process. The current models of HIN are based either on empirical fits to laboratory or field data, or on classical nucleation theory (CNT), which assumes that ice formation occurs in a single step. However, the results of these models can deviate significantly from experimental observations. Molecular simulations can provide an atomistic-level insight into the study of the mechanisms of HIN on different ice nucleating particles.
In this study, a combination of molecular dynamics and grand canonical Monte Carlo simulations is used to study the deposition freezing on silver iodide surfaces at various saturation vapor pressures. Silver iodide (AgI) is known for excellent ice nucleating properties and has long been used in rain-seeding applications. The surfaces of ice nucleating particles first adsorb water molecules, forming liquid droplets that fluctuate stochastically until they freeze.
Our results reveal atomistic level mechanisms of deposition freezing and further characterize the effects of ice nucleating particles on HIN phenomenon. Based on the simulation trajectories, we found that water molecules adsorb dropletwise on the AgI surfaces in hexagonal arrangements. We also observed simultaneous adsorption of the first and second layers of water molecules and a slightly delayed adsorption of the third layer. Afterward, the multilayer droplets merge into bigger droplets. In addition, our simulation results suggest that ice nucleation initiates after the adsorption of at least four layers of water.
Acknowledgment:
This work was supported by the Academy of Finland Flagship ACCC (grant no. 337552) and
MEDICEN project (grant no. 345125).
How to cite: Roudsari, G., Lbadaoui-Darvas, M., Nenes, A., and Laaksonen, A.: Adsorption and Deposition Freezing on Silver Iodide Surface: A Computer Simulation Study, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-9736, https://doi.org/10.5194/egusphere-egu23-9736, 2023.
