Effect of Surface Pollution on Homogeneous Ice Nucleation: A Molecular Dynamics Study

Homogeneous ice nucleation in neat and surface contaminated water has been studied by means of molecular dynamics simulations. In neat water, nucleation preferentially starts in the subsurface region, which accommodates better than the bulk the volume increase associated with freezing. As models of the adsorbates, we have assumed pentanol and pentanoic acid. Homogeneous ice nucleation is affected more by alcohol than by acid. Water slabs covered by a disordered layer of pentanol exhibit negligible preference for subsurface nucleation and longer nucleation times in comparison with neat water, while nucleation times are almost unaffected by the presence of pentanoic acid and the subsurface preference is only slightly decreased. The effect of adsorbates has important implications for the microphysics of formation of high altitude clouds upon conditions when a wide range of high molecular weight compounds are emitted to the atmosphere during biomass burning.