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UP: Fachverband Umweltphysik

UP 2: Poster Session

UP 2.18: Poster

Dienstag, 9. März 2010, 16:30–18:30, Lichthof

Direct moonlight DOAS for nighttime studies of volcanic plumes — •Johannes Zielcke, Nicole Bobrowski, Leif Vogel, Christoph Kern, and Ulrich Platt — Institute of Environmental Physics, University of Heidelberg, Germany

Passive Differential Optical Absorption Spectroscopy (DOAS) utilizing scattered sunlight is a widespread tool to study the chemistry of trace gases such as sulphur dioxide (SO₂) and halogen oxides (e.g. BrO, ClO) in volcanic plumes. At night however, the moon is the only feasible light source available for passive instruments. Within the Network for Observation of Volcanic and Atmospheric Change (NOVAC), passive scanning DOAS instruments were developed and deployed at several degassing volcanoes. These instruments can be adapted to track the moon and conduct direct light measurements to study the plume composition at night.

As the speciation of bromine and other halogenic compounds 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 December 2009. SO₂ slant column densities of 2 · 10¹⁸ molec/cm² were detected and spectra are analyzed for halogen compounds in the UV and visible wavelength region. The results are compared to scattered and direct sunlight measurements during the day.