Water Vapor Adsorption and Deposition Ice Nucleation by Soil Dusts

Deposition ice nucleation (DIN) occurs when water vapor is nucleated directly to ice on insoluble aerosol particles at low temperatures. The traditional way to represent DIN theoretically is using the classical heterogeneous nucleation theory (CHNT), which describes the interaction between the ice nucleus and the underlying aerosol surface using a single parameter, the contact angle. Unfortunately, CHNT is not able to correctly predict the critical supersaturations at which DIN is initiated when reasonable contact angle values corresponding to measurements are used (the situation is similar with heterogeneous liquid drop nucleation, where critical supersaturations are drastically over-predicted if measured contact angles are used). Therefore, if CHNT is used e.g. in a climate model, one needs to apply contact angle values that are adjusted so that the theory matches laboratory measurements of DIN. A more recent approach is to use a purely empirical description of DIN that calculates temperature-dependent nucleation site densities based on experimental nucleation rates and aerosol surface areas. Neither the CHNT nor the nucleation site density approach is very reliable in climate modelling as one cannot be certain that they work outside the range of lab experiments for a given aerosol type.

In a recent theoretical development, we have postulated that adsorption and nucleation of water vapor on hydrophobic surfaces can be described within a unified framework, and that experimental adsorption parameters can be used to predict the critical supersaturation at which nucleation of water vapor occurs on a given surface. Remarkably, the new theory does not need any adjustable parameters. In this presentation, a review of the theory is given together with experimental evidence of its success in predicting heterogeneous nucleation of water droplets on different types of surfaces, both flat substrates and nanoparticles.  Furthermore, the theory is applied to DIN occurring on clay minerals, and it is shown that the predictions correspond well to experimental results.