PNNL

Abstract

Mineral dust aerosol serves as a reactive surface, and promotes the growth of ice in the atmosphere. In particular, the hydroxyl groups on aluminosilicate clay minerals are important for heterogeneous chemistry and for the nucleation of ice. These functional groups may be altered by acidic processing during atmospheric transport. In this study, we exposed kaolinite (KGa-1b) and montmorillonite (STx-1b) to aqueous sulfuric acid and then rinsed the soluble reactants and products off in order to explore changes to functional groups on the mineral surface. To quantify the changes due to acid treatment of edge hydroxyl groups, we use 19F magic angle spinning nuclear magnetic resonance spectroscopy and a probe molecule, 3,3,3-trifluoropropyldimethylchlorosilane. We find that the edge hydroxyl groups (OH) increase in both number and density with acid treatment. Using contact angle and ice nucleation measurements, we found that the interactions with water and ice are not significantly changed by this increase in OH groups. While interactions with water do not appear to be influenced by edge hydroxyl groups, other chemical reactions may still be impacted by the increase in OH at the mineral edge.