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| Titel |
Halogen speciation in volcanic plumes - Development of compact denuder sampling techniques with in-situ derivatization followed by gas chromatography-mass spectrometry and their application at Mt. Etna, Mt. Nyiragongo and Mt. Nyamulagira in 2015. |
| VerfasserIn |
Julian Rüdiger, Nicole Bobrowski, Thorsten Hoffmann |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250124726
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| Publikation (Nr.) |
 EGU/EGU2016-4204.pdf |
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| Zusammenfassung |
| Volcanoes are a large source for several reactive atmospheric trace gases including sulfur and
halogen containing species. The detailed knowledge of volcanic plume chemistry can give
insights into subsurface processes and can be considered as a useful geochemical tool for
monitoring of volcanic activity, especially halogen to sulfur ratios (e.g. Bobrowski
and Giuffrida, 2012; Donovan et al., 2014). The reactive bromine species bromine
monoxide (BrO) is of particular interest, because BrO as well as SO2 are readily
measurable by UV spectrometer at a safe distance. Furthermore it is formed in the
plume by a multiphase reaction mechanism under depletion of ozone in the plume.
The abundance of BrO changes as a function of the reaction time and therefore
distance from the vent as well as the spatial position in the plume. The precursor
substance for the formation of BrO is HBr with Br2as an intermediate product.
The reaction of HBr to BrO involves heterogeneous reactions involving aerosol
particles, while Br2 reacts directly with O3 to form BrO in a UV radiation induced
mechanism. Due to the lack of analytical approaches for the species analysis of halogens
(HBr, Br2, Br, BrCl, HOBr) there are still uncertainties about the magnitude of
volcanic halogen emissions and in particular their speciation and therefore also in
the understanding of the bromine chemistry in volcanic plumes (Bobrowski et al.,
2007).
In this study a gas diffusion denuder sampling method using a 1,3,5-trimethoxybenzene
(1,3,5-TMB) coating for the derivatization of reactive halogen species (Rüdiger et al., 2015)
was characterized by reaction chamber experiments. The coating proved to be suitable to
collect selectively gaseous bromine species with oxidation states of +1 or 0 (such as Br2,
BrCl, BrO(H) and BrONO2), while being ignorant to HBr (OS -1). The reaction of
1,3,5-TMB with reactive bromine species gives 1-bromo-2,4,6-trimethoxybenzene
(1-bromo-2,4,6-TMB) - other halogens give corresponding products. The diffusion denuder
technique allows sampling of gaseous compounds exclusively without collecting particulate
matter. Solvent elution of the derivatized analytes and subsequent analysis with gas
chromatography-mass spectrometry gives a limit of detection below 1 ng of bromine. The
method was applied in 2015 on volcanic gas plumes at Mt. Etna (Italy), Mt. Nyiragongo and
Mt. Nyamulagira (DR Congo) giving reactive bromine mixing ratios from 0.3 ppb
(Nyiragongo) up to 22 ppb (Etna, NEC). Compared with total halogen data derived by
alkaline trap sampling (Raschig-tube) and ion-chromatography analysis the reactive bromine
mixing ratios allow the investigation of the conversion of HBr into reactive species due to
plume chemistry with progressing plume age.
The new method will be described in detail and the first results on the reactive halogen to
total halogen output will be discussed (for bromine and chlorine) and compared to earlier
volcanic plume chemistry model studies.
References
Bobrowski, N. and G. Giuffrida: Bromine monoxide / sulphur dioxide ratios in relation
to volcanological observations at Mt. Etna 2006-2009. Solid Earth, 3, 433-445,
2012
Bobrowski, N., R. von Glasow, A. Aiuppa, S. Inguaggiato, I. Louban, O. W. Ibrahim and
U. Platt: Reactive halogen chemistry in volcanic plumes. J. Geophys. Res., 112,
2007
Donovan A., V. Tsanev, C. Oppenheimer and M. Edmonds: Reactive halogens (BrO and
OClO) detected in the plume of Soufrière Hills Volcano during an eruption hiatus. Geochem.
Geophys. Geosyst., 15, 3346-3363, 2014
Rüdiger, J., N. Bobrowski, T. Hoffmann (2015), Development and application
of compact denuder sampling techniques with in situ derivatization followed by
gas chromatography-mass spectrometry for halogen speciation in volcanic plumes
(EGU2015-2392-2), EGU General Assembly 2015 |
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