The Acidity of the Quasi-Liquid Layers of Ice and Snow

点击翻译按钮获取中文摘要

The intent of this project is to measure the acidity of frozen electrolyte solutions of environmental relevance by means of spectroscopic in situ pH probes. Nuclear magnetic resonance (NMR) will be used to distinguish the properties of the fluid and solid regions. Solid-state magic angle spinning NMR spectroscopic measurements will be used to monitor the local acidity of the microscopic fluids embedded in frozen electrolyte solutions of environmental relevance. The spatial distribution of acidity in these materials will be obtained by freezing aqueous electrolytes and using magnetic resonance imaging (MRI) in conjunction with the pH probes. The alternative use of sensitive fluorescent pH probes will also be explored. This work will provide information on the chemical environment in microfluids wetting polycrystalline ices, such as those found in ice and snow. These fluids have drastically different ionic composition than the ice itself, and may have very different acidities. Local acidity determines whether weak volatile acids or bases can be exchanged between ice and the gas phase, or whether reactions between dopants are inhibited or catalyzed in frozen media. As an example, the dissimilar evolution of nitrous acid from sunlit snow packs in Antarctica and Greenland points to the need for a better understanding of the factors controlling ice acidity. This project will provide fundamental understanding that will lead to insights on very important environmental questions regarding the chemical properties and photochemical processes that occur at the interfaces of ice and snow. Because of the fundamental nature of these studies, applications in other areas of science and engineering may be possible. The project will provide opportunities for education and training from the K-12 through graduate level.