Oct 15, 1998 - in several aircraft (ER-2) and balloon-borne measure- ments [e.g. ... and on June 20, 1997 from Gap/France (44.00 N, 6.10 E). (accordingly ...
GEOPHYSICAL RESEARCH LETTERS, VOL. 25, NO. 20, PAGES 3847-3850, OCTOBER 15, 1998
StratosphericBrO profiles measured at different latitudes and seasons:Instrument description,spectral analysisand profile retrieval F. Ferlemann 1, C. Camy-Peyret 2, R. Fitzenberger 1, H. Harder1'3,T. Hawat2 H. Osterkamp 1, M. Schneider •, D. Perner3, U. Platt1, P. Vradelis1, and K. Pfeilsticker • Abstract.
Measurements of stratospheric BrO profiles specifity,but due to the weaknessof the BrO absorption (observed optical densities . . are of the order . •-0 ß1%)
are reportedusinga novelDOAS instrument(Differential Optical AbsorptionSpectrometry)operatedon the LPMA/DOAS balloongondola(LPMA/Laboratoirede Physique Mo16culaireet Applications) during three flights (Le6n, Nov.23, 1996, Kiruna, Feb.14, 1997, and Gap, June 20, 1997). BrO was detectedby its vibrational bands(4-0 at 354.7nm;5-0 at 348.8nm) of the
andbecause ofinterference w•thtrol•osphenc absorbers (warm03, NOu, CH•O, and others)and the necessary
radiative transfermodelingin remotescatteredskylight BrO measurements,the accuracyis also barely better
than +30% for the total vertical column.
Details on the measurementtechniqueare reported here, while the measuredBrO profiles are describedby A(2•r)•-X(2•r) transitionin directsunlight spectrafrom Harder et al. (this issue). balloon ascent, descentand during solar occultation at maximum(float) altitude. We showthat our accuracy is about4-18%(1 er)duringballoonascent(solarzenith 2. Measurements, Spectral Analysis Retrieval angles,SZA • 88ø), and about +25% for solar occul- and Profile tation
measurements.
For altitudes
above the balloon
Three balloonflights were conductedusinga novel osof (14.4+2.5)ppt, (15.6+2.8)ppt,and (15.3+2.8)ppt DOAS-instrument[Ferlemannet al., 1998]; (1) on above 30.6 kin, 30.0 kin, and 39.8 kin, respectively. Nov.23, 1996fromLe6n/Spain(42.60N, 5.70W), (2) on Feb. 14, 1997from Esrange/Sweden (67.90N,21.1øE), andonJune20, 1997fromGap/France(44.00N, 6.10E) 1. Introduction (accordingly denotedflight 1 2, and 3). float our observationsindicate averageBrO mixing rati-
Presently stratospheric bromine, estimated to amount
20 ppt [$chau•fieret al., 1998],contributes•-25% to the anthropogenicOa depletion. The stratospherickey in-
organicbrominespeciesis BrO at daytime[Lary e! al., 1996a,b]. Unfortunately, only few stratosphericBrO measurements were conducted so far with a quite limi-
ted coverageof latitudes and seasons- and thus more BrO measurements appear to be warrant. BrO measurements rely on two techniques:
(1) In-situ observationof BrO (and C10) by chemical conversion/resonance fluorescence previouslyemployed in severalaircraft (ER-2) and balloon-borne measurements[e.g.,Brune andAnderson,1986].While a strong point of this technique is its capability of in-situ measurements,its absolute calibration is difficult, limiting
its accuracyto •-30%. (2) DOAS spectroscopy relieson the detectionof vi-
brationalabsorption bandsof the A(2•)•-X(2•) UV transitions
of the BrO
molecule.
The
method
can be
employedby_using zenith scattered Sun light or direct moon light [Carroll e! al., 1989; Solomon e! al., 1989; and others]. A major advantageof spectroscopy is its
Thespectral retrieval of Br•) wasperformed aspre-
viouslydescribedby e.g., $tutz and Platt, [1996](Fig. 1 and Fig. 2) with a low air column "low" Sun spectrum (denotedFR) recordedat maximumaltitude as
reference. The spectral retrieval also included two referencespectra of O3 at-20øC, and-80øC and NO•. at -70øC recordedin the laboratory usingour instrument,
the 04 spectrumof Greenblattet al. [1990],the BrO spectrum(at T=223 K) of Wahneret al. [1988],and to accountfor the spectrometer'sstraylighta product of an "inversed"measuredspectrum with the spectrometer straylight spectrum. The inclusionof a calculatedRing spectrumwas also tested [Fish and Jones,1995] but the amplitude of the Ring spectrumwas found neglig
