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| Titel |
Moonlight DOAS for nighttime studies of volcanic plumes |
| VerfasserIn |
Johannes Zielcke, Nicole Bobrowski, Leif Vogel, Christoph Kern, Ulrich Platt |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250042733
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| Zusammenfassung |
| Differential Optical Absorption Spectroscopy (DOAS) in the ultraviolet and visible
wavelength region has become a widespread tool not only to study the chemistry of trace
gases such as sulphur dioxide (SO2) and halogen oxides (e.g. BrO, ClO, OClO) in volcanic
plumes, but also for volcano monitoring by observing SO2 fluxes.
During daylight hours either direct or scattered sunlight can be used for measurements. At
night other light sources have to be used, the two main possibilities being artificial ones and
the moon. While artificial lighting has several important advantages, such as otherwise not
available wavelength regions (e.g. deep UV) and a known light path, it is limited to
measurements at the crater rim in most circumstances in volcanic environments, which is a
potentially dangerous place, and limits the investigation of plume chemistry to the nearer
source region. To study the composition of the plume further downwind at night, the moon is
the only available source of light.
Within the NOVAC (Network for Volcanic and Atmospheric Change) project, passive
scanning DOAS instruments in the UV wavelength region were developed and deployed at
several degassing volcanoes. We adapted these instruments, however, to track the moon and
thus to conduct direct light measurements.
As the speciation of bromine and other halogenic oxides relies on photodissociation of
their respective elementary molecules, a discrepancy between day and nighttime chemistry is
expected. While emissions during the day have been studied for some time now, little is
known about the reactions occuring at night.
We present direct moonlight measurements carried out at Mount Etna during
November/December 2009. SO2 slant column densities (SCD) of up to 2 -
1018 molecules-cm2
were detected and spectra are analyzed for halogen compounds. The results are compared to
direct sunlight measurements undertaken in the same period. Our maximum nighttime
BrO-SO2 ratio is significantly lower than the ones obtained during daytime in the same
period, thus further supporting the current ideas of the halogen and atmospheric chemistry in
volcanic plumes. |
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