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| Titel |
The role of bromine and chlorine chemistry for arctic ozone depletion events in Ny-Ålesund and comparison with model calculations |
| VerfasserIn |
M. Martinez, T. Arnold, D. Perner |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 17, no. 7 ; Nr. 17, no. 7, S.941-956 |
| Datensatznummer |
250013791
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| Publikation (Nr.) |
 copernicus.org/angeo-17-941-1999.pdf |
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| Zusammenfassung |
During the Arctic Tropospheric Ozone
Chemistry (ARCTOC) campaigns at Ny-Ålesund, Spitsbergen, the role of halogens
in the depletion of boundary layer ozone was investigated. In spring 1995 and
1996 up to 30 ppt bromine monoxide were found whenever ozone decreased from
normal levels of about 40 ppb. Those main trace gases and others were
specifically followed in the UV-VIS spectral region by differential optical
absorption spectroscopy (DOAS) along light paths running between 20 and 475 m
a.s.l.. The daily variation of peroxy radicals closely followed the ozone
photolysis rate J(O3(O1D)) in the absence of ozone
depletion most of the time. However, during low ozone events this close
correlation was no longer found because the measurement of radicals by chemical
amplification (CA) turned out to be sensitive to peroxy radicals and ClOx.
Large CA signals at night can sometimes definitely be assigned to ClOx
and reached up to 2 ppt. Total bromine and iodine were both stripped
quantitatively from air by active charcoal traps and measured after neutron
activation of the samples. Total bromine increased from background levels of
about 15 ppt to a maximum of 90 ppt during an event of complete ozone depletion.
For the spring season a strong source of bromine is identified in the pack ice
region according to back trajectories. Though biogenic emission sources cannot
be completely ruled out, a primary activation of halogenides by various oxidants
seems to initiate an efficient autocatalytic process, mainly driven by ozone and
light, on ice and perhaps on aerosols. Halogenides residing on pack ice surfaces
are continuously oxidised by hypohalogenous acids releasing bromine and chlorine
into the air. During transport and especially above open water this air mixes
with upper layer pristine air. As large quantities of bromine, often in the form
of BrO, have been observed at polar sunrise also around Antarctica, its release
seems to be a natural phenomenon. The source strength of bromine from halogen
activation on the pack ice, as based on the measured inorganic bromine levels,
averages about 1012 Br-atoms m-2 s-1 during
sunlit periods in Arctic spring. The total source strength of inorganic bromine
from sunlit polar regions may therefore amount to 30 kt y-1.
Key words. Atmospheric composition and structure
(troposphere · composition and chemistry; instruments and techniques) |
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