Ground-based observation of OClO, NO2, and O3 columns by differential UV-Visible spectroscopy at twilight during the full winter of 1993/94 at the sub-Arctic station of Reykjavik (64 ¿N, 23 ¿W) are presented. Results show no direct evidence of ozone depletion during the period but significant amounts of OClO were observed in December and January when NO2 abundances were at the annual minimum. NO2 columns are found to be controlled by the hours of light available but highly modulated by the lower stratosphere temperature OClO was observed outside the vortex as well, but only at times when NO2 was low. ¿ American Geophysical Union 1996