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| Titel |
Retrieval of stratospheric and tropospheric BrO profiles and columns using ground-based zenith-sky DOAS observations at Harestua, 60° N |
| VerfasserIn |
F. Hendrick, M. Roozendael, M. P. Chipperfield, M. Dorf, F. Goutail, X. Yang, C. Fayt, C. Hermans, K. Pfeilsticker, J.-P. Pommereau, J. A. Pyle, N. Theys, M. Mazière |
| 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. 18 ; Nr. 7, no. 18 (2007-09-21), S.4869-4885 |
| Datensatznummer |
250005200
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| Publikation (Nr.) |
 copernicus.org/acp-7-4869-2007.pdf |
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| Zusammenfassung |
| A profiling algorithm based on the optimal estimation method is applied to
ground-based zenith-sky UV-visible measurements from Harestua, Southern
Norway (60° N, 11° E) in order to retrieve BrO vertical profiles. The
sensitivity of the zenith-sky observations to the tropospheric BrO detection
is increased by using for the spectral analysis a fixed reference
spectrum corresponding to clear-sky noon summer conditions. The information
content and retrieval errors are characterized and it is shown that the
retrieved stratospheric profiles and total columns are consistent with
correlative balloon and satellite observations, respectively. Tropospheric
BrO columns are derived from profiles retrieved at 80° solar zenith
angle during sunrise and sunset for the 2000–2006 period. They show a marked
seasonality with mean column value ranging from 1.52±0.62×1013 molec/cm² in late winter/early
spring to 0.92±0.38×1013 molec/cm² in summer, which
corresponds to 1.0±0.4 and 0.6±0.2 pptv, respectively, if we assume that BrO is uniformly mixed in the
troposphere. These column values are also consistent with previous estimates
made from balloon, satellite, and other ground-based observations. Daytime
(10:30 LT) tropospheric BrO columns are compared to the p-TOMCAT 3-D
tropospheric chemical transport model (CTM) for the 2002–2003 period.
p-TOMCAT shows a good agreement with the retrieved columns except in late
winter/early spring where an underestimation by the model is obtained. This
finding could be explained by the non-inclusion of sea-ice bromine sources
in the current version of p-TOMCAT. Therefore the model cannot reproduce the
possible transport of air-masses with enhanced BrO concentration due to bromine
explosion events from the polar region to Harestua. The daytime stratospheric BrO columns are
compared to the SLIMCAT stratospheric 3-D-CTM. The model run used in this study, which assumes
21.2 pptv for the Bry loading (15 pptv for long-lived bromine species and additional
6 pptv for very short-lived species (VSLS) added by a scaling of CH3Br), significantly
underestimates the retrieved BrO columns. A sensitivity study shows that a good agreement
can only be obtained if 6 to 8 pptv accounting for VSLS are added directly (and not by
a scaling of CH3Br) to the SLIMCAT long-lived bromine species profile. This contribution
of the VSLS to the total bromine loading is also consistent with recently published studies. |
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