The Mod¿le Isentropique de transport M¿so¿chelle de l'Ozone Stratosph¿rique par Advection avec CHIMie (MIMOSA-CHIM) three-dimensional high-resolution chemical transport model has been developed to estimate the contribution of polar ozone destruction to the lower stratosphere ozone budget at midlatitudes. The ability of the model to reproduce the evolution of polar and midlatitude ozone during the 1999/2000 winter is first evaluated by comparisons against lidar and sonde measurements. The modeled potential vorticity (PV) fields are also compared with PV fields derived from ECMWF analyses and the chemical fields of the model are compared with the output of a large-scale chemical transport model in order to highlight the interest of a high-resolution model for resolving fine-scale structures such as polar filaments. A PV-based analysis is performed to estimate the area covered by polar air, vortex, and filaments in the 45¿N--55¿N latitude band at 475K and their contribution to ozone loss. The polar air contribution was found to represent usually between 20% and 40% of the total ozone loss in this latitude band but can reach 50% during large vortex intrusions. At 475K, the total chemical ozone loss in nonpolar air between 45¿N and 55¿N increases from 1% in mid-December to 15% at the end of March. Several chemical ozone tracers are considered to investigate the origin of the ozone loss in nonpolar air. These tracers allow us to quantify the amount of chemical ozone destruction that occurred in the vortex, in the polar filamentary structures, and in the nonpolar air. Until February, the main contributor to the nonpolar ozone loss is in situ destruction at midlatitudes, but the contribution from the ozone destruction in the polar vortex increases steadily during the winter and represents about 50% of the total midlatitude ozone loss in April, after the vortex breakup. The contribution from the ozone destruction within filamentary structures is found to be quasi-negligible as a result of the limited number of filaments.