Considerable amounts of chlorine dioxide, OClO, were observed from 5 January through 2 February, 1990 in the stratosphere above S¿ndre Str¿mfjord showing a highly perturbed chlorine chemistry. Photolysis and simultaneous formation of the OClO leads to a typical concentration minimum at noon. Its changes in concentration indicate the release of the OClO precursors BrO and C1O from this respective reservoir substances in the morning. Two incidences of increased OClO production occur repeatly at 92¿ and 89¿ solar zenith angle (SZA). Furthermore, in the beginning of January OClO morning values exceed those found at dusk for comparable SZA whereas towards the end of the month the morning values become depressed compared to the evening.

The twilight vertical column densities of OClO often reach about 1.6¿1013 molec cm-2 and a comparison shows an increase from 1988 to 1990. ¿American Geophysical Union 1991