A growing body of evidence indicates that active photochemistry occurs on the surfaces of ice grains in polar and mid-latitude snowpacks. We have recently conducted field studies in Greenland, arctic Canada, and Michigan that demonstrates significant impacts on the composition of snowpack interstitial air, which is enriched in a range of trace gases relative to the overlying atmosphere. These compounds are produced by photochemical breakdown of compounds in the snow. At the same time, we have discovered that ozone is destroyed in the snowpack, also through a sunlight-driven process. Surface snow is quite porous, and air flows through the upper layers as a result of wind-driven pressure gradients. As a result, snowpack photochemistry affects the ambient atmosphere. These findings have potentially significant implications for atmospheric chemistry in remote regions and interpretation of the ice-core record of past atmospheric composition, and may affect non-remote midlatitude regions as well. This seminar will provide an overview of our recent field studies and observations of the impacts of snow photochemistry, and an introduction to current understanding of the processes responsible.