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| Titel |
Satellite-based observations of rain-induced NOx emissions from soils around Lake Chad in the Sahel |
| VerfasserIn |
Jan Zörner, Marloes Penning de Vries, Steffen Dörner, Holger Sihler, Steffen Beirle, Thomas Wagner |
| 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 |
250144054
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| Publikation (Nr.) |
 EGU/EGU2017-7834.pdf |
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| Zusammenfassung |
| Rain-induced emission pulses of NOx (≡ NO + NO2) from soils have been observed in many
semi-arid regions over the world. They are induced by the first precipitation of the wet season
and are mainly caused by the sudden re-activation of microbes in the soil releasing reactive
nitrogen. In this study, a single intense event of pulsed NOx emissions from soils
around Lake Chad is investigated. This is achieved by analysing daily tropospheric
NO2 vertical column densities (VCDs) as observed by the satellite-based OMI
instrument together with other satellite and model data on precipitation, lightning, fire
and wind. The study region of Lake Chad and its ecosystems are indispensable to
life in the Sahel region. Climate variability and unsustainable water utilization,
however, caused a drastic decrease in the lakes’ surface area which, in turn, lead to
extensive land cover changes converting former lake area to shrub land and fertile farm
land.
The results indicate that the region of Lake Chad does not only show consistent
enhancements in average NO2 VCDs in the early months of the wet season compared to its
surrounding desert but also exhibits particularly strong NOx emissions shortly after a single
large-scale precipitation event in June 2007. NO2 VCDs measured 14 hours after this
precipitation event show strong enhancements (2.5*1015 molecules cm−2) compared to the
seasonal background VCDs and, moreover, represent the highest detected NO2 VCDs of the
entire year. Detailed analysis of potential contributors to the observed NO2 VCDs strongly
indicate that fire, lightning and retrieval artefacts cannot explain the NO2 pulse. The
estimated emission flux from the soil, calculated based on mass balance, amounts to about
32.3 ng N m−2 s−1, which corresponds to about 65 tonnes of nitrogen released to the
atmosphere within one day. |
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