In 1999, we discovered that photochemistry in snow leads to the release of nitrogen oxides to the atmosphere, and it is now apparent that photochemistry in surface snow is the dominant source of nitrogen oxides to the atmosphere in remote snow-covered regions like Greenland and Antarctica. This paper provides the first quantitative measurements of the magnitude of snowpack emissions of nitrogen oxides in central Greenland. These measurements have provided a useful baseline for several other large field studies working to better understand the mechanisms and impacts of snowpack photochemistry on the atmosphere.

  Does it describe a new discovery or a new methodology that's useful to others?

I have been interested in the Arctic and in atmospheric nitrogen oxides since I was a beginning graduate student, and took the opportunity to participate in a study of the atmosphere over the Greenland ice sheet...

It applies existing methods for measurement of vertical fluxes of gases to a new situation, and develops the first estimates of the regional and global impact of snowpack photochemistry on atmospheric reactive nitrogen.

  Could you summarize the significance of your paper in layman's terms?

Nitrogen oxides are fundamental drivers of atmospheric chemistry. It is important to understand the processes controlling their current atmospheric levels, and desirable to learn about past atmospheric levels. This paper is significant in relation to both of these issues. The effluxes of active nitrogen oxides (NO, NO2, and HONO) were large enough to dominate the budget of these compounds in the lower atmosphere over the Greenland ice cap, indicating that snowpack photochemistry drives atmospheric photochemistry in that environment. The paper also addresses the interpretation of the ice-core nitrate record. Nitrate in glacial ice, from deposited nitric acid (HNO3), has been used to derive information about past atmospheric composition. This paper suggests that processes affecting snowpack photochemistry (such as solar intensity) may alter the relationship between atmospheric nitrogen oxides and the nitrate ultimately preserved in glacial ice.

I have been interested in the Arctic and in atmospheric nitrogen oxides since I was a beginning graduate student, and took the opportunity to participate in a study of the atmosphere over the Greenland ice sheet when I was asked several years ago by Jack Dibb (Univ. New Hampshire) and Paul Shepson (Purdue Univ.). At that time, we had no expectation that photochemistry in the snowpack was important. However, our initial observations of nitrogen oxides levels were higher than expected, and we discovered NOx release from the snowpack as a result of trying to determine the cause.