Chemical interactions at the air-ice interface are of great importance to the local atmospheric chemistry but also to the concentrations of pollutants deposited onto natural snow and ice. However, the study of such processes has been hampered by the lack of general, surface-specific probes. Even seemingly basic chemical questions, such as the local concentration of chemical compounds, or the pH at the interface, have required the application of assumptions about solute distributions in frozen media. We have used glancing-angle laser spectroscopy to interrogate the air-ice interface. This has yielded several insights into the chemical interactions there. The environment at the interface between air and freshwater ice surfaces is distinct from that at the interface between air and liquid water. Acids such as HCl that adsorb to ice surfaces from the gas phase result in significantly different pH responses than at liquid water surfaces. Further, the solvation of aromatic species is suppressed at freshwater ice surfaces compared to at liquid water surfaces, leading to extensive self-association of aromatics at ice surfaces. Photolysis kinetics of these species are much faster than at liquid water surfaces; this can sometimes (but not always) be explained by red-shifts in the absorption spectra of self-associated aromatics increasing the extent to which solar radiation is absorbed. By contrast, the extent of hydrogen bonding and the solvation of adsorbed species are similar at liquid water surfaces and at frozen saltwater surfaces. Adsorbed acids and bases evoke similar pH responses at frozen saltwater ice surfaces and liquid water surfaces, and photochemical kinetics of at least some aromatic compounds at frozen saltwater ice surfaces are well-described by kinetics in liquid water.

A pinch of salt is all it takes: Chemistry at the frozen water surface

248th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.