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| Titel |
Novel SO2 Spectral Evaluation Scheme Using the 360-390 nm Wavelength Range |
| VerfasserIn |
Nicole Bobrowski, Christoph Kern, Ulrich Platt, Christoph Hörmann, Thomas Wagner |
| 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 |
250042684
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| Zusammenfassung |
| Differential Optical Absorption Spectroscopy (DOAS) is a well established spectroscopic
method to determine trace gases in the atmosphere. During the last decade, passive DOAS,
which uses solar radiation scattered in the atmosphere as a light source, has become a
standard tool to determine SO2 column densities and emission fluxes from volcanoes and
other large sources by ground based as well as satellite measurements. For the determination
of SO2 column densities, the structured absorption of the molecule in the 300-330 nm region
(due to the A1B1Â -Â X1A1 transition) is used. However, there are several problems limiting
the accuracy of the technique in this particular application. Here we propose to use an
alternative wavelength region (360-390 nm) due to the spin-forbidden a3B2Â -Â X1A1
transition for the DOAS evaluation of SO2 in conditions where high SO2 column densities
prevail. The sensitivity reduction due to the rougly two orders of magnitude smaller
differential absorption cross section of the later transition is largly compensated by the
higher intensity of solar radiation and more favourable radiation transport at longer
wavelengths.
We will present example results for both wavelength regions applying the novel and the
standard evaluations to Gome-2 satellite data and groundbased MAX-DOAS measurements.
We show the novel range to have considerable advantages, in particular when the
particle content of the plume is high and when measurements are performed at large
distances from the area of interest. We will show by radiative transport modeling that
apparent differences in the derived SO2-column for the two wavelength ranges can be
explained by differences in radiation transport and briefly discuss the importance of
these results for global and local flux estimates and volcanological interpretation. |
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