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## Initial Conditions

1. The background atmosphere is approximated using the ECMWF analysis for both presssure and temperature. The profiles are interpolated to the median location o fthe OSIRIS scan.
2. The initial estmate of NO2 is derived from interpolation of the the Pratmo climatology.
3. The initial aerosol estimate is a typical log normal sulphate  profile provided by Deschler.
4. The initial ozone is derived from an interpolation of the Labow climatology.