Satellite Observations of Tropospheric BrO

Abstract

We present an algorithm to retrieve tropospheric BrO columns from satellite nadir UV/visible observations based on an innovative stratospheric BrO correction that makes use of a recently developed dynamical climatology of stratospheric BrO (Theys et al., Atmos. Chem. Phys., 2009). This climatology has been generated using output from the BASCOE three-dimensional chemical transport model, which includes a contribution to the stratospheric inorganic bromine budget from very short-lived brominated sources gases. Model simulations have been extensively validated through comparison with several independent correlative data sets of stratospheric BrO observations, including ground-based, balloon-borne and space-limb techniques. We describe results from global tropospheric BrO column retrievals obtained from the ERS-2 GOME and METOP GOME-2 instruments. Our new approach to correct for the stratospheric BrO absorption allows separating the large-scale stratospheric BrO structures from those of tropospheric origin in the total BrO column field measured from space. This results in a refined and more quantitative interpretation of the nadir BrO observations and allows e.g. to study with reduced ambiguity the transport of BrO plumes emitted in the polar boundary layer. We also use our retrieved tropospheric BrO columns above cloudy scenes to derive information on the vertical distribution of BrO in the free-troposphere, based on a cloud-slicing approach.