Launched in October 2006, the GOME-2 instrument is a nadir looking UV-visible spectrometer that flies aboard the MetOp-A satellite (Munro et al., 2006). Compared to its predecessors GOME and SCIAMACHY, GOME-2 combines the advantages of a performant spectroscopic design and both good spatial resolution and coverage. Using an advanced retrieval technique further described below, we separate the stratospheric and tropospheric contributions from the total BrO seen by the satellite. These results demonstrate the potential of GOME-2 to quantify and follow the transport of BrO plumes formed in the Arctic boundary layer.

The BrO columns are derived in three steps:

• GOME-2 calibrated radiances are analyzed for BrO with the DOAS method in the wavelength interval from 336 to 352 nm.
• Stratospheric BrO columns are calculated using an innovative stratospheric BrO climatology*.
• Air mass factors are applied to account for changes in measurement vertical sensitivity due to clouds and surface reflectivity.

A cloud screening removes the measurements with a cloud fraction larger than 0.4 as determined by the FRESCO algorithm (Koelemeijer et al., 2001).


Satellite total BrO column hotspots seen by GOME-2 exhibit spatial patterns similar to model estimates of stratospheric BrO column. A closer look to the BrO columns results shows also that several BrO hotspots are observed in both stratospheric columns and tropospheric residual columns. This can not be explained by a mismatch in the stratospheric BrO correction. This interesting feature emphasizes the need, for a proper quantitative interpretation of the results, to separate the BrO total columns into their stratospheric and tropospheric contributions. These results can be used to better understand the mechanisms for BrO generation in the arctic troposphere (leading e.g. to ozone and mercury depletion episodes in the boundary layer). In the future, we intend to apply the same algorithm to measurements from other sensors with the aim to create a long-term consistent database of tropospheric measurement from space.

* The stratospheric BrO correction is based on a dynamical climatology generated from the BASCOE 3D chemical transport model. This climatology explicitly accounts for the impact of atmospheric dynamics and photochemistry on the stratospheric BrO distribution based on a parameterization using O₃ and NO₂ columns measured as an input (Theys et al., 2009).

References:
Koelemeijer, R., Stammes, P., Hovenier, P., and de Haan J.: A fast method for retrieval of cloud parameters using oxygen A-band measurements from the Global Ozone Monitoring Experiment, J. Geophys. Res., 106, 3475-3490, 2001.

Munro, R., et al., GOME-2 on MetOp, in: Proc. of The 2006 EUMETSAT Meteorological Satellite Conference, Helsinki, Finland, 12-16 June 2006, EUMETSAT P.48, ISBN 92-9110-076-5, 2006.

Theys, N., Van Roozendael, M., Errera, Q., Hendrick, F., Daerden, F., Chabrillat, S., Dorf, M., Pfeilsticker, K., Rozanov, A., Lotz, W., Burrows, J.P., Lambert, J.-C., Goutail, F., Roscoe, H.K., and De Mazière, M.: A global stratospheric bromine monoxide climatology based on the BASCOE chemical transport model, Atmos. Chem. Phys., 9, 831-848, 2009.

For more information, please contact Nicolas Theys