Probing Photochemistry in the Quasi-Liquid Layer: Laboratory Studies and Implications for OASIS Processes

Recent studies illustrate the previously overlooked importance of snow and ice as reactive chemical media in the environment. It has been shown that the Arctic snowpack plays an important role in processing atmospheric species such as mercury, nitrogen oxides, alkyl halides, ozone, carbonyl compounds and molecular halogens. Photochemical transformations of anthropogenic organic contaminants in ice also have been observed, although published information regarding these processes is scant. It has been shown that a liquid-like (quasi-liquid or disordered) layer exists on the surface of pure ice and that a quasi-liquid layer (QLL) is also found on the surface of ambient snow crystals and ice at temperatures relevant to polar conditions. It is unclear what role the QLL on the surface of snow/ice plays in potential photochemical reactions. Here we report results of recent laboratory studies of photochemistry occurring in the QLL. We used the well characterized reaction of p-nitroanisole with pyridine to probe changes in photochemistry that may occur upon freezing. We found that freezing greatly enhanced the rate of this particular reaction (the half-life of the reaction was 20 times shorter when the solution was frozen). Additionally, we could alter the half-life in predictable ways by changing variables such as ionic strength and temperature. The findings of these experiments will be discussed as well as the potential implications to ocean-air-sea ice-snow (OASIS) interactions of organic pollutants in polar climates.