A computationally cheap, and easily initialized photochemical model utilizing UARS MLS measurements of ClO to calculate ozone destruction rates within the polar vortices due to the ClO+ClO, ClO+BrO, and ClO+O catalytic cycles is developed. The method involves calculating local reactive chlorine concentrations from individual ClO retrievals, and then inferring the diurnal cycle of ClO from a quadratic expression using the relevant kinetic parameters. In test integrations this simple treatment is shown to give good agreement with more detailed model calculations. Analysis of the late Arctic and Antarctic winters of 1993 yields similar vortex-averaged ozone loss rates at 465 K of ~1% per day in both hemispheres, while the reactive chlorine remains enhanced. Net ozone destruction in the north is less, largely because the elevated ClO and Cl2O2 concentrations are less persistent. The estimated chemical destruction on isentropic surfaces in the lower stratosphere is broadly similar to the observed change in ozone distribution, implying that the change is dominated by chemical destruction. ¿ American Geophysical Union 1996