Hygroscopic characteristics of salt particles based on molecular dynamics simulations

Molecular dynamics simulations are performed to investigate the hygroscopic growth of typical salt particles and their mixtures in supersaturated water vapor. Nucleation and condensational growth are analyzed. The results showed the dominant factors controlling the growth of the salt particle are condensation and collisions thereafter. The salt particles help to the hygroscopic growth. MgCl₂ possesses the highest tendency of hygroscopicity. The self-diffusivity of water in the MgCl₂ case (1.54 × 10⁻⁶ m²/s) is much smaller than that of the homogeneous case (2.23 × 10⁻⁶ m²/s). Radial distribution analysis (RDF) confirms the dissociation of ionic bonds and the formation of the hydration shell. Particle number concentration (PNC) and particle mass concentration (PMC) have different influence mechanisms on nucleation and growth. Moreover, the supersaturation degree is modified by changing the vapor pressure and temperature. Homogeneous nucleation is found to be more susceptible to changes in supersaturation than heterogeneous nucleation.