OClO, NO₂ and O₃ total column observations over Iceland during the winter 1993/94

Ground‐based observation of OClO, NO 2 , and O 3 columns by differential UV‐Visible spectroscopy at twilight during the fall 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 NO 2 abundances were at the annual minimum. NO 2 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 NO 2 was low.