Abstract. Mineral aerosol particles nucleate ice, and many insights have been obtained
on water freezing as a function of mineral surface properties such as charge
or morphology. Previous studies have mainly focused on pristine samples
despite the fact that aerosol particles age under natural atmospheric
conditions. For example, an aerosol-containing cloud droplet can go through
freeze–melt or evaporation–condensation cycles that change the surface
structure, the ionic strength, and pH. Variations in the surface properties
of ice-nucleating particles in the atmosphere have been largely overlooked.
Here, we use an environmental cell in conjunction with nonlinear
spectroscopy (second-harmonic generation) to study the effect of freeze–melt
processes on the aqueous chemistry at silica surfaces at low pH. We found
that successive freeze–melt cycles disrupt the dissolution equilibrium,
substantially changing the surface properties and giving rise to marked
variations in the interfacial water structure and the ice nucleation ability
of the surface. The degree of order of water molecules, next to the surface,
at any temperature during cooling decreases and then increases again with
sample aging. Along the aging process, the water ordering–cooling
dependence and ice nucleation ability improve continuously.
Hyaluronan orders water molecules in its nanoscale extended hydration shells
