© Author(s) 2007. This work is licensed under a Creative Commons License. Atmospheric Chemistry and Physics Retrieval of stratospheric and tropospheric BrO columns from

Abstract. Spectral measurements of BrO using zenith-sky and off-axis viewing geometries are combined in a lin-ear multiple regression retrieval algorithm to provide strato-spheric and tropospheric BrO vertical columns. One year of measurement data are investigated over Reunion-Island (20.9 ◦ S, 55.5 ◦ E), from August 2004 to June 2005. A com-parison between the stratospheric columns retrieved at 45◦, 80◦, 85◦, 87.5 ◦ and 92.5 ◦ solar zenith angles and photo-chemical simulations initialized by chemical fields from the 3-D-CTM SLIMCAT and further constrained by observed NO2 profiles shows a good agreement only by consider-ing a contribution from the very short-lived organic bromine substances to the stratospheric inorganic bromine budget, of 6 to 8 pptv. Furthermore, stratospheric BrO profiles re-trieved from late twilight zenith-sky observations are con