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BROMINE MONOXIDE IN THE ATMOSPHERE


Bromine monoxide is a trace gas that has both anthropogenic and natural sources, although its most important sources as far as the chemistry of the troposphere is concerned, are of natural origin. The sources in general are found in very remote regions where local measurements take place only sporadically.

Therefore it is very important to study these important and interesting regions continuously via satellite. This remote sensing technique give insight in a variety of questions. So the evolution of BrO events can be studied in time and space over a long period of time and compared to patterns found in distinct regions.


BrO-CHEMISTRY

BrO is an important trace gas species, because of its potential to destroy ozone via catalytic reactions both in the stratosphere and in the troposphere. The role of BrO in stratospheric ozone destruction cycle is well established [Sander89]. It is also important for the formation of OClO which in turn is an indicator for chlorine activation [Schiller96].

An important stratospheric source is the anthropogenic emission of halones, which is recently increasing [ZITAT]. The stratospheric BrO concentrations follows a strong yearly cycle that shows only little inter annual variation. This cycle is phase shifted to the NO2 cycle [Wenig03]. During summer reservoir species like BrONO2 are formed so that the stratospheric BrO mixing ratios show a minimum.

In polar spring the tropospheric BrO mixing ratios can reach much higher values than in the stratosphere. They vary strongly in time and space. These polar spring time events are the most pronounced. They start as soon as sunlight is available with the photolysis of Br2 and the catalytic ozone destruction yielding BrO. Then HOBr is formed that can liberate more Br2 by heterogenous reactions on the surfaces of halogen rich aerosols, especially over the one year old sea ice [ZITAT] or frost flowers [Rankin02].

This auto catalytic mechanism is known as the bromine explosion [Lehrer97] leading to the total destruction of ozone [Frieß03] possibly within about a day, commonly referred to as the tropospheric ozone hole; also atmospheric mercury is depleted during such events [Ebinghaus02].



BrOchemie (49K)

This figure sketches the tropospheric BrO chemistry with the catalytic ozone destruction (air) and the explosion mechanism (air liquid interface, auto catalytic release).


So these high BrO concentrations are due to the bromine explosion mechanism, that leads to an (quasi) exponential release of BrO from its reservoirs namely the sea-ice surface or frost flowers via heterogeneous reactions. Other tropospheric sources of BrO in mid-latitudes are the release of BrO by volcanoes [Bobrowski03], from salt seas [Hebestreit99, Hönninger03] or from sea salt aerosols and algae [Leser03].


BrO-RETRIEVAL

The BrO-data is derived from observations made by the GOME, the first instrument to measure trace gas species on a global scale with a daily coverage pole wards from 70° latitude on. The algorithms developed at the IUP allow the extraction of vertical column densities (VCDs) of BrO by using the DOAS [Platt94] technique in the fitting window from 344nm to 359nm and by applying air mass factors (AMFs) to account for the radiative transfer [Marquard00].

The AMFs used are derived for a purely stratospheric background profile. The solar zenith angle (SZA) is restricted to be less or equal 90°. The VCDs are then normalized to the equatorial region to remove artificial spectral structures introduced by the diffuser plate according to [Richter02].


SUGGESTED READING

Further details (and references, too) can be found in selected publications of our group:
J. Hollwedel, M. Wenig, S. Beirle, S. Kraus, S. Kühl, W. Wilms-Grabe, U. Platt, and T. Wagner: "Year-to-Year Variations of Polar Tropospheric BrO as seen by GOME" , accepted for publication in Adv. Space Res., 2003 T. Wagner, C. Leue, M. Wenig, K. Pfeilsticker, U. Platt: "Spatial and temporal distribution of enhanced boundary layer BrO concentrations measured by the GOME instrument aboard ERS-2", J. Geophys. Res., 106, 2001, 24225-24236

T. Wagner, and U. Platt: "Satellite mapping of enhanced BrO concentrations in the troposphere", Nature, 395, 1999, 486-490

You can also have a look at papers listed at BIRA-IASB or at our links and our publications.


OTHER BrO DATA PRODUCTS DERIVED FROM GOME

BIRA-IASB BrO level-3 data product.
IUP Bremen BrO level-3 data product.
IUP Bremen daily (level-2) BrO NRT data-product.


REFERENCES

[Bobrowski03]
N. Bobrowski, G. Hönninger, B. Galle, and U. Platt: "Detection of bromine monoxide in a volcanic plume", nature, 423, 2003, 273-276

[Ebinghaus02]
R. Ebinghaus, H.H. Kock, C. Temme, J.W. Einax, A.G. Löwe, A. Richter, J.P. Burrows, and W.H. Schroeder: "Antarctic Springtime Depletion of Atmospheric Mercury", Environ. Sci. Technol., 36(6), 1238-1244, 2002

[Frieß03]
U. Frieß, J. Hollwedel, G. König-Langlo, T. Wagner, and U. Platt: "Tropospheric Bromine Monoxide in the Antarctic Coastal Region", submitted to J. Geophys. Res., 2003

[Hebestreit99]
K. Hebestreit, et al.: "DOAS Measurements of Tropospheric Bromine Oxide in Mid-Latitudes." Science, 283, 1999, 55-57

[Hönninger03]
G. Hönninger, N. Bobrowski, E.R. Palenque, R. Torrez, and U. Platt: "Reactive Bromine and Sulfur Emissions at Salar de Uyuni, Bolivia", submitted to Geophys. Res. Lett., 2003

[Lehrer97]
U. Platt, and E. Lehrer, ARCTOC final report, Eur. Union, Brussels, 1997

[Leser03]
H. Leser, G. Hönninger, and U. Platt: "MAX-DOAS measurements of BrO and NO2 in the marine boundary layer", Geophys. Res. Lett., 30(10), 1537, doi:10.1029/2002GL015811, 2003

[Marquard00]
L.C. Marquard, T. Wagner, and U. Platt: "Improved air mass factor concepts for scattered radiation differential optical absorption spectroscopy of atmospheric Species", J. Geophys. Res., 105, 1315-1327, 2000

[Platt94]
U. Platt, "Differential optical absorption spectroscopy (DOAS)", in Air Monitoring by Spectroscopic Techniques, Chem. Anal. Ser., 127, M.W. Sigrist (Ed.), pp. 27-84, John Wiley, New York, 1994

[Rankin02]
A.M. Rankin, E.W. Wolff, and S. Martin: "Frost flowers: Implications for tropospheric chemistry and ice core interpretation", J. Geophys. Res., 107(D23), 4683, doi:10.1029/2002JD002492, 2002

[Richter02]
A. Richter, F. Wittrock, A. Ladstätter-Weißenmayer, and J.P. Burrows: "GOME measurements of stratospheric and tropospheric BrO", Adv. Space Res., 29(11), 1667-1672, 2002

[Sander89]
S.P. Sander and R.R. Friedl: "Kinetics and Product Studies of the Reaction ClO + BrO Using Flash Photolysis-Ultraviolet Absorption", J. Phys. Chem., 93, 1989, 4764-4771

[Schiller96]
C. Schiller, and A. Wahner: Comment on "Stratospheric OClO Measurements as a poor quantitative indicator of chlorine activation" by J. Sessler, M.P. Chipperfield, J.A. Pyle, and R. Toumi, Geophys. Res. Lett., 23, 1053-1054, 1996

[Wenig03]
M. Wenig, et al.: "Retrieval and Analysis of Stratospheric NO2 from GOME", accepted for publication in J. Geophys. Res.