Within the European Arctic Stratospheric Ozone Experiment (EASOE) aerosols from the volcanic eruption of Mt. Pinatubo have been observed during 6 balloonborne backscatter soundings in January and February 1992 under different polar vortex conditions from Thule, Greenland. The vortex boundary seemed to retard stratospheric aerosol mixing into the inner parts of the vortex from lower latitudes; however, when Thule was outside the vortex large aerosol loadings were measured. The aerosols were simultaneously observed by ground based lidar, whereby aerosol backscatter measurements in three different wavelengths made it possible to obtain information about the particle sizes. Parameters of lognormal distributions have been derived, using a least square approach between observed and calculated backscatter coefficients from Mie theory. The aerosol surface area density was increased by factors 10--50, compared to the background levels at pre-volcanic conditions. ¿ American Geophysical Union 1994