Much is known about the characteristics of bulk snow and ice but there is a lack of knowledge about what occurs in the microscopic environment of the surface. Reactions occur between the atmosphere and the surfaces of the snow which can alter the composition of the atmosphere. Some of these reactions are believed to be acid catalyzed and the surface of snow may have enhanced acidity compared to the bulk. We report the change in pH with freezing and annealing solutions of water and acetic acid. These solutions were frozen on the ZnS crystal of an attenuated total reflection infrared spectrometer. The ice-ZnS combination results in a penetration depth of about 1.4 mm so this technique is sensitive to the near-surface region of the ice. The temperature of the frozen solutions was varied between -20 and 0 degrees Celsius and spectra were taken at the different temperatures. The pH was then determined by comparing the ratios of absorbance between acetic acid at 1290 cm-1 and its conjugate base acetate at 1414 cm-1. In addition, solutions of nitric acid with acetic acid were studied because of nitrate’s prevalence in ice and the role that it plays in snow chemistry. The effects of the presence HNO3 on the pH of the near-surface region of ice will be discussed.

Determining the pH of frozen and annealed solutions using infrared spectroscopy

2019 Spring National Meeting

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