Balloon-borne and ground-based instruments indicated in early February 1990 that a major type II polar stratospheric cloud event occurred above Scandinavia at temperatures as low as -90 ¿C at 30 hPa. We first report in this paper the TOVS/HIRS2 measurements during this period, which show that the polar stratospheric cloud had an area at least equivalent to similar events observed from this instrument during the formation of the Antarctic ozone hole. Then, in order to assess the amount of air chemically processed by this type II PSC, short integrations have been carried out at high resolution (1.5¿) with the ''Emeraude''GCM, initialized from the ECMWF analysis of February 4, 1990. The temperature and PSC forecasts are described and compared with the analysis and satellite observations. In particular, the horizontal and vertical extent of the cloud, given by the model after 2 days of simulation, is found to be in good agreement with the remote and in situ measurements. An idealized tracer giving the time spent inside the type II PSC has also been introduced in the simulation. It is shown that about 60% of the vortex air at 470 K has passed through the PSC after 3 1/2 days of integration. Emphasis is put on a localized area situated downstream from the PSC and believed to be the most chemically perturbed air mass: the air parcels of this region have spent, after 3 days of integration, more than 50 hours at temperature below the frost point and about 16 hours in sunlight. Since the largest discrepancy between the total ozone forecast and TOMS data is found in the same area, we discuss the possibility of a considerable chemical ozone destruction subsequent to the type II PSC formation. This localized destruction could reflect the high degree of chlorine activation and denitrification expected to occur immediately downstream of water-ice PSCs. ¿ American Geophysical Union 1992