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| Titel |
Airborne DOAS limb measurements of tropospheric trace gas profiles: case studies on the profile retrieval of O4 and BrO |
| VerfasserIn |
C. Prados-Roman, A. Butz, T. Deutschmann, M. Dorf, L. Kritten, A. Minikin, U. Platt, H. Schlager, H. Sihler, N. Theys, M. Roozendael, T. Wagner, K. Pfeilsticker |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 4, no. 6 ; Nr. 4, no. 6 (2011-06-28), S.1241-1260 |
| Datensatznummer |
250002020
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| Publikation (Nr.) |
 copernicus.org/amt-4-1241-2011.pdf |
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| Zusammenfassung |
A novel limb scanning mini-DOAS spectrometer for the detection
of UV/vis absorbing radicals (e.g., O3, BrO, IO, HONO)
was deployed on the DLR-Falcon (Deutsches Zentrum für Luft-
und Raumfahrt) aircraft and tested during the ASTAR 2007
campaign (Arctic Study of Tropospheric Aerosol, Clouds and
Radiation) that took place at Svalbard (78° N) in
spring 2007. Our main objectives during this campaign were to
test the instrument, and to perform spectral and profile
retrievals of tropospheric trace gases, with particular
interest on investigating the distribution of halogen
compounds (e.g., BrO) during the so-called ozone depletion
events (ODEs). In the present work, a new method for the
retrieval of vertical profiles of tropospheric trace gases
from tropospheric DOAS limb observations is presented. Major
challenges arise from modeling the radiative transfer in an
aerosol and cloud particle loaded atmosphere, and from
overcoming the lack of a priori knowledge of the targeted
trace gas vertical distribution (e.g., unknown tropospheric
BrO vertical distribution). Here, those challenges are tackled
by a mathematical inversion of tropospheric trace gas profiles
using a regularization approach constrained by a retrieved
vertical profile of the aerosols extinction coefficient
EM. The validity and limitations of the algorithm
are tested with in situ measured EM, and with an
absorber of known vertical profile (O4). The method is
then used for retrieving vertical profiles of tropospheric
BrO. Results indicate that, for aircraft ascent/descent
observations, the limit for the BrO detection is roughly
1.5 pptv (pmol mol−1), and the BrO profiles inferred from the
boundary layer up to the upper troposphere and lower
stratosphere have around 10 degrees of freedom.
For the ASTAR 2007 deployments during ODEs, the retrieved BrO
vertical profiles consistently indicate high BrO mixing ratios
(∼15 pptv) within the boundary layer, low BrO mixing
ratios (≤1.5 pptv) in the free troposphere, occasionally
enhanced BrO mixing ratios (∼1.5 pptv) in the upper
troposphere, and increasing BrO mixing ratios with altitude in
the lowermost stratosphere. These findings agree reasonably well with
satellite and balloon-borne soundings of total and partial BrO
atmospheric column densities. |
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