Deposition freezing on mineral dust particles: a case against classical nucleation theory with the assumption of a single contact angle

Abstract

Abstract. Deposition freezing on two mineral species, kaolinite and illite, was studied using a flow cell coupled to an optical microscope at ∼240 K. The results show that the onset Sice (defined as the Sice conditions when ice first nucleated) is a strong function of the surface area available for nucleation, varying from 100 % to 125 %. The surface area dependent data could not be described accurately using classical nucleation theory and the assumption of a single contact angle (defined here as the single-α model). These results suggest that caution should be applied when using contact angles determined from onset Sice data and the single-α model. In contrast to the single-α model, the active site model, the deterministic model, and a model with a normal distribution of contact angles fit the data within experimental uncertainties. Parameters from the fits to the data are presented.