Retrieval of BrO vertical profiles from SCIAMACHY limb during Arctic spring 2008

Discrepancies between satellite-derived total column amounts of BrO and in-situ measurements taken in the ARCTAS spring campaign have brought to question the interpretation of nadir BrO retrievals and how this derived BrO is distributed through the troposphere and stratosphere. To help resolve these questions, we present an algorithm for SCIAMACHY Limb BrO retrievals, which provides vertical resolution through the stratosphere, and apply it to Arctic latitudes from March 25 through April 19, 2008 to correspond with the ARCTAS spring deployment. Resulting information on stratospheric BrO is compared to selected OMI BrO total columns during this period to draw inference on the presence of BrO in the troposphere. Our retrieval process has two primary stages, (1) the calibration and fitting of backscattered, near-UV measurements for trace gas slant column amounts, and (2) the use of a nonlinear optimal estimation (OE) procedure to invert the fitted columns into vertical profiles of number density. Jacobians used within the OE framework are generated by finite differencing output from a multiple scattering vector radiative transfer model. This forward model treats the diurnal effect for several trace gases including BrO, which is especially important for Arctic springtime limb measurements due to steep gradients in the solar zenith angle along the line of sight.