The official title of our project:
Impact of snow photochemistry on atmospheric radical concentrations at Summit, Greenland

What does this mean and why are we doing it?
In the past few years there has been an explosion of scientific interest in the chemical reactions that happen in sunlit snow. Rather than simply acting as the final resting place for pollutants that deposit from the air, snow turns out be one of the most photoreactive regions on earth! These sunlight-driven reactions in snow release a number of important pollutants to the lower atmosphere, including formaldehyde, nitrous acid, and reactive halogens. In turn, these pollutants alter the composition and chemistry in the lower atmosphere. One of the major effects of snow emissions is that they alter concentrations of atmospheric radicals, highly reactive chemicals that clean the atmosphere. Our goal is to explore snow reactions and describe how they change the amount of pollutants and radicals in the Arctic atmosphere. Although we're doing this work in Greenland, the results will help us understand atmospheric chemistry in other places with snow, such as the northern U.S.

In addition to changing the composition of the atmosphere, these sunlight-initiated reactions also change the make-up of the snow itself and the ice that eventually forms from the snow. Understanding how photochemical reactions influence ice composition will help others use ice cores to reconstruct what the atmosphere used to be like.

How are we studying the snow chemistry?
There are five major parts of our project…

• Measuring radicals. Using a variety of techniques, we are measuring hydroxyl radical (OH, the "vacuum cleaner" of the atmosphere), hydroperoxyl radical (HO2), and nitric oxide (NO). Some of these species will be measured in the snow, while others will be measured in the air above the snowpack.

• Measuring chemicals that form radicals, including hydrogen peroxide (HOOH), formaldehyde (HCHO), nitrous acid (HONO), and nitric acid (HNO3). These radical precursors are being measured on snow grains, in the air between the snow grains (firn air), and in the air that comes out of the snow. Since these chemicals form radicals in sunlight, understanding their concentrations and formation will help us understand the radical budgets at Summit.

• Characterizing sunlight in the snowpack. As mentioned above, many of the species we are measuring are formed or destroyed by sunlight. So in order to understand their rates of formation or destruction, we have to understand the amounts, and wavelengths, of light that get into the snowpack and how this varies as a function of depth.

• Determining the physical structure of the snowpack. Diffusion and winds blowing into and out of the snowpack play key roles in the release of chemicals from snow. In order to understand how fast these processes are, we are measuring the physical nature of the snow, including the sizes of snow grains, how tightly packed the snow is, and how temperature varies throughout the snowpack.

• Putting it all together. Our ultimate goal is to use our experimental observations of chemical and physical processes to create a model of photochemistry in the snowpack. This model would allow us to predict the impacts of snow reactions on the composition of the atmosphere, the snowpack, and resulting ice.