UV-Vis spectrometry measurements at zenith were carried out at Keflavik (64 N, 23 W) during the EASOE Campaign in the winter of 1991/92. During the middle of January, a situation of low ozone was observed associated to a very low temperature field in the lower stratosphere. Ozonesounding on day 15 January 1992 exhibits two different patterns, up and down 70 hPa. From the potential vorticity fields and backward trajectories analysis, the different origin of the air masses at the two layers are shown. While at the lower levels the ozone deficiency is the result of low latitudes advection, at the upper levels a more structured profile of 30% less than 10 days before is found to be air from inside the vortex presumably processed by PSC. The partial chemical depletion is supported by the very low NO2 content measured at the same period at the station.
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