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| Titel |
Volcanic plumes: BrO formation during the first 100 minutes after emission |
| VerfasserIn |
L. Vogel, N. Bobrowski, M. Fickel, C. Hoermann, C. Kern, R. von Glasow, U. Platt |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250067133
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| Zusammenfassung |
| The main volatile species emitted by volcanoes are H2O, CO2 and SO2 in order of
magnitude. Significant amounts of HCl are also emitted along with a minor fraction of other
hydrogen halides (HX, X = F , Cl, Br, I). Halogen radicals can be formed in the plume
from HX. E.g., BrO is produced in the volcanic plume from the emitted HBr in an
auto-catalytic reaction cycle similar to the “Bromine-Explosion” known from the Arctic and
Antarctic tropospheric chemistry. Reactive bromine species (and probably analogous chlorine
species) are known to have a strong influence on the oxidation capacity of the atmosphere.
The chemical abundance of BrO in volcanic plumes is commonly described by the
BrO-SO2 ratio, as SO2 is chemically inert on time scales of hours, and can therefore be
used as a tracer for dilution of volcanic gas. Based on measured BrO-SO2 ratios, improved
numerical models of the chemical plume evolution could be used to estimate the total amount
of bromine emitted by the volcano as well as the impact of volcanic emissions on the
atmosphere.
BrO-SO2 ratios will be presented which were measured at Mt. Etna during July 2008 and
July 2009 with differential optical absorption spectroscopy (DOAS). These measurements
were performed simultaneously with 1-3 stationary Multi-Axis DOAS instruments
(MAX-DOAS) and car based traverses. They constitute the first capture of the evolution of
BrO-SO2 ratios in a volcanic plume in the first two hours after emission, and are the
hitherto most comprehensive data set of BrO-SO2 ratios from any single volcano. Different
evolutions of ratios for both measurement campaigns are observed. During the July 2008
measurements, a small but consistent increase in BrO-SO2 with increasing plume age was
observed in the first hour, with a maximum value of BrO-SO2 = 1.2 -
10-4 found after
60 minutes. In contrast, measurements during July 2009 generally show smaller BrO-SO2
ratios. After an initial increase from 0 to 0.65 -
10-4 during the first 5 minutes, a
decrease of the ratio appears to occur. Previously published chemical model runs do
not adequately represent the encountered boundary conditions and measurements,
and overestimate the observed evolution of BrO-SO2 ratio at plume ages greater
than 5 minutes by a factor of 3. Thus additional chemical model runs are presented
which are based on the new data set. The impact of the new insights is discussed. |
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