Measurements of formaldehyde, acetaldehyde, and acetone in ambient and snowpack air were conducted as a part of the SNOW99 study in northern Michigan. Vertical profiles of ambient and snowpack air illustrate large concentration gradients through the top ~10 cm of the snowpack, implying a positive flux of these species from the surface. Snow chamber experiments that involved flushing a snow-filled 34L Teflon-lined chamber with zero air at 20 slpm indicated that release from the snow followed first order kinetics, with decay constants of 0.19, 0.44, and 0.34 hr-1 for formaldehyde, acetaldehyde, and acetone, respectively. Although it is likely that temperature dependent adsorption/desorption processes play a role, the data are not inconsistent with loss from the snowpack via snow grain metamorphism. The data also imply that formaldehyde is not hydrated in the snow grain surface layer. ¿ 2000 American Geophysical Union