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Updated: Aug 5, 2026

Determining the Ice-binding Planes of Antifreeze Proteins by Fluorescence-based Ice Plane Affinity
Published on: January 15, 2014
Short-term exposure to ammonium sulfate modifies ice nucleation by alpha-alumina but not organic monolayers or
Lian Pharoah1, Teresa M Seifried1, Gren N Patey1
1Department of Chemistry, University of British Columbia Vancouver British Columbia Canada V6T 1Z1 bertram@chem.ubc.ca.
Abstract:
Accurate predictions of ice cloud formation require understanding how ammonium sulfate affects the freezing behavior of ice-nucleating substances (INSs). This knowledge is also essential for evaluating the reliability of a freezing assay used to identify ice-nucleating mineral dusts in atmospheric samples. Here, we used a droplet freezing technique to investigate the effects of short-term exposure (minutes) to ammonium sulfate on six INSs: two α-alumina samples (submicrometer, < 1 µm, and supermicrometer, > 1 µm), two alcohol monolayers (C22H45OH and C30H61OH), and two microplastics (polyethylene terephthalate and low-density polyethylene). Exposure to ammonium sulfate did not change the ice-nucleating properties of the alcohol monolayers or microplastics. In contrast, submicrometer α-alumina exhibited enhanced ice-nucleating ability following ammonium sulfate exposure, while the supermicrometer α-alumina showed no change, despite similar bulk composition. This size-dependent response is consistent with differences in surface hydroxy protonation states. More deprotonated, negatively charged surface hydroxy groups can attract ammonium cations, modifying interfacial hydrogen-bonding networks and stabilizing nascent ice clusters. These findings should be considered when evaluating submicrometer α-alumina for stratospheric aerosol injection as a solar management strategy. In addition, our results support the use of ammonium sulfate-based freezing assays for identifying ice-nucleating mineral components in atmospheric samples.
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