Total slant column densities (SCD) of NO2 and BrO from the GOME ERS-2 satellite nadir measurements have been split into stratospheric and tropospheric loadings. In order to obtain tropospheric vertical column densities (VCD) two key challenges arise: the quantification of the stratospheric column and the calculation of the tropospheric air mass factor (AMF). Stratospheric NO2 and BrO columns are derived at the instrument's overpass time by means of a stratospheric chemistry transport model, i.e. FinROSE-etm, to take into account the stratospheric variability of these trace gases. In order to gain the trace gas tropospheric column the stratospheric slant column is subtracted from the DOAS slant column retrieval.