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| Titel |
Enhanced tropospheric BrO over Antarctic sea ice in mid winter observed by MAX-DOAS on board the research vessel Polarstern |
| VerfasserIn |
T. Wagner, O. Ibrahim, R. Sinreich, U. Frieß, R. Glasow, U. Platt |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 7, no. 12 ; Nr. 7, no. 12 (2007-06-19), S.3129-3142 |
| Datensatznummer |
250005084
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| Publikation (Nr.) |
 copernicus.org/acp-7-3129-2007.pdf |
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| Zusammenfassung |
| We present Multi AXis-Differential Optical Absorption
Spectroscopy (MAX-DOAS) observations of tropospheric BrO carried out on
board the German research vessel Polarstern during the Antarctic winter
2006. Polarstern entered the area of first year sea ice around Antarctica on
24 June 2006 and stayed within this area until 15 August 2006. For the period when
the ship cruised inside the first year sea ice belt, enhanced BrO
concentrations were almost continuously observed. Outside the first year sea
ice belt, typically low BrO concentrations were found. Based on back
trajectory calculations we find a positive correlation between the observed
BrO differential slant column densities (ΔSCDs) and the duration for
which the air masses had been in contact with the sea ice surface prior to
the measurement. While we can not completely rule out that in several cases
the highest BrO concentrations might be located close to the ground, our
observations indicate that the maximum BrO concentrations might typically
exist in a (possibly extended) layer around the upper edge of the boundary
layer. Besides the effect of a decreasing pH of sea salt aerosol with
altitude and therefore an increase of BrO with height, this finding might be
also related to vertical mixing of air from the free troposphere with the
boundary layer, probably caused by convection over the warm ocean surface at
polynyas and cracks in the ice. Strong vertical gradients of BrO and O3
could also explain why we found enhanced BrO levels almost continuously for
the observations within the sea ice. Based on our estimated BrO profiles we
derive BrO mixing ratios of several ten ppt, which is slightly higher than
many existing observations. Our observations indicate that enhanced BrO
concentrations around Antarctica exist about one month earlier than observed
by satellite instruments. From detailed radiative transfer simulations we
find that MAX-DOAS observations are up to about one order of magnitude more
sensitive to near-surface BrO than satellite observations. In contrast to
satellite observations the MAX-DOAS sensitivity hardly decreases for large
solar zenith angles and is almost independent from the ground albedo. Thus
this technique is very well suited for observations in polar regions close
to the solar terminator. For large periods of our measurements the solar
elevation was very low or even below the horizon. For such conditions, most
reactive Br-compounds might exist as Br2 molecules and ozone
destruction and the removal of reactive bromine compounds might be
substantially reduced. |
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