UPPER LIMIT OF IODINE OXIDE IN THE LOWER STRATOSPHERE

It has been suggested that iodine oxides, IOx, could play a significan t role in the ozone destruction in the lower stratosphere. To investig ate this suggestion, spectra from nine SAOZ uv-visible spectrometer ba lloon flights were examined for the IO absorption signature between 40 5 and 450 nm. IO was not detected, either at mid- or high latitude, in the morning or the evening, in summer or winter. An upper limit of 0. 2 parts per trillion by volume (pptv) at 20 km and 0.1 pptv at 15 km a t the 95% confidence level (2 sigma), was derived from the best measur ements at 90 degrees SZA at sunset and sunrise. Since a photochemical model shows that 70% of inorganic iodine should be in the form IO at t hat time, it is concluded that unless iodine chemistry is different fr om that assumed at the moment, the role of iodine in stratospheric ozo ne depletion is small.