Retrieval of BrO Columns from SCIAMACHY and their Validation Using Ground-based DOAS Measurements
Nicolas Theys(1), Michel Van Roozendael(1), François Hendrick(1), Isabelle De Smedt(1) and Caroline Fayt(1)
(1) BIRA-IASB, 3, Avenue Circulaire, 1180 Bruxelles, Belgium
Bromine monoxide (BrO) is an important component responsible for stratospheric ozone depletion at the global scale. Several evidences have been reported from satellites, ground-based and balloon platforms suggesting the existence of substantial amounts of BrO also in the global free-troposphere. In particular, nadir observations from satellite platforms offer the opportunity to monitor the global distribution of total BrO columns in a long-term perspective, thereby allowing to address some important current issues regarding the inorganic bromine budget in both the stratosphere and the troposphere.
Building on the experience acquired with ERS-2/GOME , a scientific algorithm has been developed at BIRA-IASB for the retrieval of total BrO columns from SCIAMACHY nadir measurements. In order to overcome problems related to anomalies in the polarization response of the the SCIAMACHY instrument, specific BrO retrieval settings have been introduced, different from those used for the retrieval of GOME data.
In the present study, we focus first on an assessment of the accuracy of the SCIAMACHY slant column retrieval, through various sensitivity tests and comparisons with coincident measurements from GOME. Second, SCIAMACHY nadir BrO results are compared with independent correlative measurements of BrO columns resolved into their stratospheric and tropospheric contributions and photochemically matched to satellite observations. Correlative data are derived from DOAS observations performed by IASB-BIRA at three locations (Harestua 60°N, OHP 44°N, and Reunion Island 22°S), complemented by balloon-borne and SCIAMACHY limb stratospheric BrO profiles available from the literature. From the combined analysis of GOME, SCIAMACHY, ground-based and balloon-borne DOAS observations the overall consistency of the remote-sensing BrO observing system is evaluated and discussed in light of recent findings published in the literature. In particular our results strengthen the existence of a worldwide background of BrO located in the free-troposphere with mixing-ratios in the range from 1-2 pptv.
Keywords: ESA European
Space Agency - Agence spatiale europeenne,
observation de la terre, earth observation,
satellite remote sensing,
teledetection, geophysique, altimetrie, radar,
chimique atmospherique, geophysics, altimetry, radar,