The 2002/2003 Arctic stratospheric vortex reached temperatures low enough for PSC existence already in the middle of November. Restricted by tropospheric cloud coverage, stratospheric aerosol lidar measurements in Ny-Ålesund [78.9ºN, 12.0ºE] have been performed from December 7 onwards. Since then, PSC signals have been detected almost throughout the whole December, vanishing with the stratospheric warming in January and not showing up again even when the recovering cold pool reached the Spitsbergen region again in late January and February. During these weeks of almost constant PSC occurrence, changes both in the altitude range and particle characteristics were observed. While in the beginning of December strong type I a PSCs were found from 22 to 27 km, cloud layers with very small backscatter ratio and a shifted color ratio were observed from 16 to 22 km at the end of December. The steady descent of the clouds and the described change in backscatter characteristics suggest particle growth and sedimentation with consequent denitrification during December 2002. Here we present the PSC lidar observations in combination with results of the DLAPSE denitrification model (Univ. Leeds) which confirms the suggested NAT-rock sized particles and denitrification above Ny-Ålesund.