Chapter 7

Measurements from the GOME/ERS-2 and GOME-2/MetOp-A satellite nadir UV-visible instruments have been analyzed for tropospheric BrO using a new retrieval technique that combines measured BrO slant columns and estimates of the stratospheric BrO content using the climatology presented in chapter 6. Air mass factors calculated using a radiative transfer model, are applied to account for the impact of observation geometry, clouds, surface albedo and BrO profile shape on the measurements. It is shown that this method enables to better isolate and quantify the polar BrO surface emissions. Moreover, the separation of stratospheric and tropospheric fractions of the observed total BrO columns allows studying the transport of BrO plumes in both stratosphere and troposphere in more detail. Supported by correlative ground-based data and a comprehensive error budget, evidences are provided for a global free-tropospheric BrO background with columns of 1-3 x 10 molec/cm2. No sign of significant seasonal or latitudinal variation of this tropospheric BrO background could be found.