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| Titel |
Chemistry of rain events in West Africa: evidence of dust and biogenic influence in convective systems |
| VerfasserIn |
K. Desboeufs, E. Journet, J.-L. Rajot, S. Chevaillier, S. Triquet, P. Formenti, A. Zakou |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 10, no. 19 ; Nr. 10, no. 19 (2010-10-01), S.9283-9293 |
| Datensatznummer |
250008801
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| Publikation (Nr.) |
 copernicus.org/acp-10-9283-2010.pdf |
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| Zusammenfassung |
| This paper documents the chemical composition of 7 rain events associated
with mesoscale convective systems sampled at the supersite of Banizoumbou,
Niger, during the first special observation periods (June–July 2006) of the
African Monsoon Multidisciplinary Analyses (AMMA) experiment. Time-resolved
rain sampling was performed in order to discriminate the local dust
scavenged at the beginning of rain event from the aerosol particles
incorporated in the cloud at the end of the rain. The total elemental
composition is dominated by Al, Si, Fe and Ca, indicating a high influence
of dust and limited marine or anthropogenic contribution. After the aerosol
wash-out, the elemental concentrations normalized to Al and the microscopic
observations of diatoms, a tracer of the Bodélé depression, both
indicate that the total elemental composition of rainwater is controlled by
dust originating from North-eastern Saharan sources and probably
incorporated in the convective cloud from the Harmattan layer. The low
variability of the rain composition over the measurement period indicates a
regional and temporal homogeneity of dust composition in the Harmattan
layer. In the dissolved phase, the dominant anions are nitrate
(NO3−), sulphate (SO42−) and chloride (Cl−).
However, between June and July we observe an increasing contribution of the
organic anions (formate, acetate, oxalate) associated with biogenic
emissions to the total ion composition. These results confirm the large
influence of biogenic emissions on the rain composition over Sahel during
the wet season. The paper concludes on the capacity of mesoscale convective
systems to carry simultaneously dust and biogenic compounds originating from
different locations and depose them jointly. It also discusses the potential
biogeochemical impact of such a phenomenon. |
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