In the frame of the preparation of the use of ENVISAT data, the EEC is supporting the MSDOL project: Monitoring of the Stratospheric Depletion of the Ozone Layer. The purpose is to assimilate the 400 vertical profiles of Ozone recorded each day by the experiment GOMOS (on the future ESA ENVISAT spacecraft ) in a 3-D chemistry-transport model, where the winds are the ECMWF analysis. The sequentially assimilated model will better represent the reality since all single measurements are extrapolated in space and time through chemistry and transport. The assimilated model will serve at least two purposes : the comparison with other data sets, and the estimate of the evolution of ozone as a function of time and space. The 3-D model is derived from the stratospheric chemistry-transport Rose model, in which the internally generated dynamics is replaced by the actual wind field.