Measurements in central Greenland demonstrate that ozone is rapidly destroyed through a photochemical process in the surface snowpack. The rate of destruction is too high to result from reaction with NOx or HOx, but could result from catalytic destruction by bromine if its release from snowpack bromide is highly efficient. The pristine nature of the Greenland snowpack implies that ozone destruction may be widespread in illuminated snowpacks and thus influence the budget of boundary-layer ozone. Similar destruction on tropospheric cloud ice crystals may explain observations of very low ozone levels associated with cirrus clouds. ¿ 2001 American Geophysical Union