The vertical distribution of ClO at Ny-Alesund during March 1997

Results of the Karlsruhe Simulation Model of the Middle Atmosphere (KASIMA) are compared with vertical ClO profiles measured by the ground-based Milli meter Wave Radiometer MIRA2 inside the vortex during March 1997 at Ny-Alesu nd. The influence of the OH + ClO and HO2 + C1O reaction branching Patio an d of the absorption cross section of Cl-2 O-2 on the calculated mixing rati os of ClO and ozone has been investigated. In the upper stratosphere the Cl O mixing ratio is reduced by 90% by using a minor channel of the OH + ClO r eaction with a branching ratio of 0.07. A temperature dependent minor chann el of the HO2 + ClO reaction reduces the upper stratospheric ClO mixing rat io by 22%. Different absorption spectra of Cl-2 O-2 alter the ClO mixing ra tios up to l2% at noon at 20 km. This causes differences of l5% in the ozon e loss during winter.