Free Energy Prediction of Ion-Induced Nucleation of Aqueous Aerosols.

Ion-induced nucleation (IIN) is thought to be an important nucleation pathway of atmospheric aerosols. We present a combined polarizable molecular dynamics (MD) simulation and the classic ion-induced nucleation theory (IINT) approach to predict the free energy profiles of the ion-induced nucleation of aqueous aerosols in a qualitative or semiquantitative way. The dependence of both cluster structure and thermodynamic properties on cluster sizes and ion species is also systemically studied. It is confirmed the ions can significantly enhance the cluster stability, and thereby increase the nucleation rate. The ability of the common atmospheric ions to enhance the nucleation rate follows the order SO > HO > NH > NO, coinciding with the order of their solvation free energies. Therefore, the solvation energy can be employed as a rough index for evaluating the INN ability. Overall, the consistency between the present predictions and previous experimental and theoretical observations demonstrates the combination of MD simulation and the IINT appears to be a promising approach for exploring the IIN process and understanding the microscopic mechanism of atmospheric-related ions.