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| Titel |
Multi-satellite sensor study on precipitation-induced emission pulses of NOx
from soils in semi-arid ecosystems |
| VerfasserIn |
Jan Zörner, Marloes Penning de Vries, Steffen Beirle, Patrick Veres, Jonathan Williams, Thomas Wagner |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250131827
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| Publikation (Nr.) |
 EGU/EGU2016-12271.pdf |
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| Zusammenfassung |
| Soil emissions of NOx (≡ NO + NO2), stemming from biotic emissions of NO,
represent a considerable fraction of total NOx emissions, and may even dominate in
agricultural and remote areas. 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 and on short time scales remains
uncertain.
This study presents a top-down approach to estimate pulsed soil emissions of trace gases
on a global scale using tropospheric NO2 column densities (as a proxy for NOx) as observed
by OMI, GOME-2 and SCIAMACHY. We introduce an optimized algorithm that
synchronizes and averages multiple time series of atmospheric variables either from one
location only, or also from different grid pixels, by aligning them on a relative scale to each
other. This method allows investigating changes in the evolution of NO2 VCDs around the
first day of rainfall after a prolonged dry period with a temporal resolution of one day and a
spatial resolution of 0.25˚ .
We find enhancements in NO2 VCDs on the day of first rainfall in many semi-arid regions
in the world which are highly dependent on the season and land cover type. Strongest and
most clustered enhancements are found in the distinct band of the Sahel region during the
onset of the wet season in April-May-June. Absolute enhancements averaged over the Sahel
region for four seasons from 2007 to 2010 range from 0.3*1015molec cm−2 for
OMI to 0.4*1015molec cm−2 for GOME-2 and SCIAMACHY on the first day of
rainfall. A thorough analysis of other influences on the retrieved signal as well as
sensitivity studies are conducted which help to better characterize these short term
enhancements.
Translating the observed enhancements in NO2 VCDs to emission rates, leads to
estimates between 5 and 65 ng N m−2 s−1 for the first day of rainfall which is in line with
previous literature. We find that the enhancement in NO2 VCDs already starts to develop
several days before the actual first rainfall. After the initial large pulse, soil emissions
diminish rapidly the subsequent day, but stay still enhanced over the following two weeks
with 1.6 ng N m−2s−1 averaged over the Sahel region.
We also present a case study in the surroundings of Lake Chad which is based on
daily orbits of OMI and does not rely on averaging over multiple time series. A
characteristic enhancement in NO2 VCDs, in response to the first rain of the wet
season, is found which agrees well with our general findings for the Sahel region. |
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