A research flight with the NOAA WP-3D aircraft revealed evidence for stratospheric-tropospheric exchange within the Arctic through tropopause folding on the flank of the polar vortex. Observations showed descent of the tropopause and of stratospheric ozone to 700 mb along the west coast of Greenland. Measurements of condensation nuclei and analysis of high volume impactor samples documented the presence of volcanic debris probably from the 1982 El Chichon eruption, including H2SO4 droplets, within the polar vortex and associated tropopause fold.