5 YEARS OF NO2 VERTICAL COLUMN MEASUREMENTS AT FARADAY (65-DEGREES-S)- EVIDENCE FOR THE HYDROLYSIS OF BRONO2 ON PINATUBO AEROSOLS

Summertime measurements of NO2 vertical column amounts over a 5 year p eriod from May 1990 until February 1995 from Faraday Base, Antarctica, show a marked reduction following the arrival of the Mount Pinatubo v olcanic aerosol in December 1991. Model calculations show that this re duction can be explained by BrONO2 and N2O5 hydrolysis on the volcanic ally enhanced aerosol, with the former dominating, Given the measureme nt and model uncertainties and lack of any treatment the effects of th e quasi-biennial oscillation, the reduction in NO2 is consistent with a BrONO2 sticking coefficient gamma of 0.4. However, the best agreemen t between the model and the measurements occurs using a gamma of 0.2. Over the time span of the measurements the known increases in chlorine and bromine loadings have an effect of less than 2% on midsummer NO2 columns. With background aerosols, summertime ozone catalytic losses a re dominated by the HOx cycle between 12 and 18 km and by the NOx cycl e at greater altitudes. With heavy aerosol loading, HOx is the primary loss cycle from 12 to 22 km. The total ozone loss increases by 38% at 16 km as a result of heavy aerosol loading.