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| Titel |
Rain-induced emission pulses of NOx and HCHO from soils in African regions after dry spells as viewed by satellite sensors |
| VerfasserIn |
Jan Zörner, Marloes Penning de Vries, Steffen Beirle, Patrick Veres, Jonathan Williams, Thomas Wagner |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250092331
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| Publikation (Nr.) |
 EGU/EGU2014-6666.pdf |
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| Zusammenfassung |
| Outside industrial areas, soil emissions of NOx (stemming from bacterial emissions of NO)
represent a considerable fraction of total NOx emissions, and may even dominate in remote
tropical and agricultural areas. NOx fluxes from soils are controlled by abiotic and
microbiological processes which depend on ambient environmental conditions. Rain-induced
spikes in NOx have been observed by in-situ measurements and also satellite observations.
However, the estimation of soil emissions over broad geographic regions remains uncertain
using bottom-up approaches. Independent, global satellite measurements can help constrain
emissions used in chemical models. Laboratory experiments on soil fluxes suggest
that significant HCHO emissions from soil can occur. However, it has not been
previously attempted to detect HCHO emissions from wetted soils by using satellite
observations.
This study investigates the evolution of tropospheric NO2 (as a proxy for NOx) and
HCHO column densities before and after the first rain fall event following a prolonged dry
period in semi-arid regions, deserts as well as tropical regions in Africa. Tropospheric NO2
and HCHO columns retrieved from OMI aboard the AURA satellite, GOME-2 aboard
METOP and SCIAMACHY aboard ENVISAT are used to study and inter-compare
the observed responses of the trace gases with multiple space-based instruments.
The observed responses are prone to be affected by other sources like lightning,
fire, influx from polluted air masses, as well measurement errors in the satellite
retrieval caused by manifold reasons such as an increased cloud contamination. Thus,
much care is taken verify that the observed spikes reflect enhancements in soil
emissions. Total column measurements of H2O from GOME-2 give further insight
into the atmospheric state and help to explain the increase in humidity before the
first precipitation event. The analysis is not only conducted for averages of distinct
geographic regions, i.e. the Sahel, but also for higher resolution grid boxes to map
the spatial pattern of absolute and relative enhancements after the wetting of dry
soils.
At the beginning of the wet season in the Sahel in April/May/June strong NO2 VCD
enhancements compared to the background levels are observed by all three satellite sensors.
A significant enhancement in HCHO VCD is also detected with GOME-2. Further analysis
shows that spatial patterns and the magnitude of such enhancements over Africa
are highly dependent on the season, prevailing temperatures and land cover types. |
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