Snow and Ice Photochemistry
Recent research has shown that deposited snow is, despite initial expectations to the contrary, very photochemically active. Reactions in sunlit snowpacks both release a variety of trace gases (such as nitrogen oxides and volatile organic compounds) and act as sinks that destroy other species (such as ozone and some organic compounds). These reactions can alter the composition of the atmosphere as well as the snow grains, which might affect ice core records of past atmospheres. However, because snow photochemistry is a relatively new field, we do not understand most of the reactions that are important in sunlit snowpacks.

Our snow and ice research has both a laboratory and field component. Much of our work involves characterizing the formation and concentrations of oxidants on snow grains and examining how these oxidants interact with organic compounds. For example, in the laboratory we have quantified the formation of highly reactive hydroxyl radical (^•OH) from the photolysis of nitrate, hydrogen peroxide, nitrite, and other trace species on snow. We have also measured the rates of formation of ^•OH on sunlit snow grains at Summit, Greenland, at the top of the Greenland ice sheet. Together this information allows us to estimate how important ^•OH will be in transforming trace species in polar snows. We are also studying the formation of singlet molecular oxygen (¹O₂*) on snow grains and examining how important this oxidant might be in determining the lifetimes of organic pollutants in polar regions. In terms of reactions of organic compounds, we are currently examining the loss of PAHs (polycyclic aromatic hydrocarbons), phenols, and organic acids on illuminated ice and snow. Finally, in addition to our research on chemical reactions, we are also interested in the penetration of sunlight into snowpacks (since this light initiates much of the snowpack chemistry) and identifying the light-absorbing species on snow grains.