Summertime measurements of NO2 vertical column amounts over a 5 year period from May 1990 until February 1995 from Faraday Base, Antarctica, show a marked reduction following the arrival of the Mount Pinatubo volcanic aerosol in December 1991. Model calculations show that this reduction can be explained by BrONO2 and N2O5 hydrolysis on the volcanically enhanced aerosol, with the former dominating. Given the measurement and model uncertainties and lack of any treatment the effects of the quasi-biennial oscillation, the reduction in NO2 is consistent with a BrONO2 sticking coefficient gamma of 0.4. However, the best agreement 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 are dominated by the HOx cycle between 12 and 18 km and by the NOx cycle 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.¿ 1997 American Geophysical Union