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| Titel |
Unidentified atmospheric absorption structure observed by DOAS near Hamburg harbour, Germany |
| VerfasserIn |
Stefan Schmitt, Andreas Weigelt, Barbara Mathieu-Üffing, André Seyler, Folkard Wittrock, Johannes Lampel, Denis Pöhler, Ulrich Platt |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250143548
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| Publikation (Nr.) |
 EGU/EGU2017-7279.pdf |
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| Zusammenfassung |
| Within a six week campaign in July and August 2016, Long Path (LP)-DOAS measurements
were performed near the harbour of Hamburg to monitor ship emissions of NO2 and SO2.
LP-DOAS instruments retrieve information about the composition of ambient air
using active spectroscopy. Therefore, an absorption light path was set up between
the northern and the southern riverside of the river Elbe with a total length of ca.
5.7 km. The light of a laser driven Xenon arc lamp was sent to a retro reflector
mounted on a light house on the opposite riverside. By comparing the spectrum of the
Xenon lamp before and after being sent through the atmosphere, spectral absorption
structures of several molecules can be identified and their mixing ratios can be
quantified.
Besides the well-known trace gas species such as NO2, SO2, O3 and HCHO, a so far
unidentified, strong absorption structure could be observed regularly throughout the
measurement period. The structure is similar to other known absorption structures in the
UV-vis range and can be most likely associated with a molecular absorption cross
section. The absorber features a progression of absorption bands in the range of 280
nm to 330 nm with an average band distance of 3 nm to 4 nm. These bands were
observed with optical densities of up to 2 per cent along the absorption path. The
absorber predominantly occurs during daylight indicating that photolytic processes are
most likely to play an important role. Further, direct emission from ships could
be excluded by the comparison with NO2 peaks, which serve as a proxy for ship
plumes.
The respective LP-DOAS instrument was deployed at multiple other measurement sites at
the past including rural, urban and remote areas. However, the discussed absorption structure
has never been detected before and instrumental errors can be excluded. Currently,
MAX-DOAS measurements performed at the same site are evaluated. We will present the
spectral features of the putative absorber as well as an overview of the time series and
correlations to other known trace gases. |
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