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| Titel |
The influence of biomass burning and transport on tropospheric composition over the tropical Atlantic Ocean and Equatorial Africa during the West African monsoon in 2006 |
| VerfasserIn |
J. E. Williams, M. P. Scheele, P. F. J. Velthoven, V. Thouret, M. Saunois, C. E. Reeves, J.-P. Cammas |
| 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. 20 ; Nr. 10, no. 20 (2010-10-19), S.9797-9817 |
| Datensatznummer |
250008835
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| Publikation (Nr.) |
 copernicus.org/acp-10-9797-2010.pdf |
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| Zusammenfassung |
| Biomass burning (BB) in southern Africa is the largest emission source of
CO and O3 precursors within Africa during the West African Monsoon (WAM)
between June and August. The long range transport and chemical processing
of such emissions thus has the potential to exert a dominant influence
on the composition of the tropical troposphere over Equatorial Africa (EA) and the Tropical
Atlantic Ocean (TAO). We have performed simulations using a three-dimensional
global chemistry-transport model (CTM) to quantify the effect that continental
transport of such BB plumes has on the EA region. BB emissions from
southern Africa were found to exert a significant influence over the TAO and
EA between 10° S–20° N. The maximum concentrations
in CO and O3 occur between 0–5° S near the position
of the African Easterly Jet – South as placed by the European Centre for Medium
range Weather Forecasts (ECMWF) meteorological analysis data.
By comparing co-located model output with in-situ measurements we show that the CTM
fails to capture the tropospheric profile of CO in southern Africa near the main
source region of the BB emissions, as well as the "extreme" concentrations of both
CO and O3 seen between 600–700 hPa over EA around 6° N. For more
northerly locations the model exhibits high background concentrations in both
CO and O3 related to BB emissions from southern Africa. By altering both
the temporal resolution and the vertical distribution of BB emissions in the
model we show that changes in temporal resolution have the largest influence
on the transport of trace gases near the source regions, EA, and in the outflow
towards the west of Central Africa. Using a set of trajectory calculations we show
that the performance of the CTM is heavily constrained by the ECMWF meteorological
fields used to drive the CTM, which transport biomass burning plumes from southern
Africa into the lower troposphere of the TAO rather than up towards the middle troposphere
at 650 hPa. Similar trajectory simulations repeated using an updated meteorological
dataset, which assimilates additional measurement data taken around EA,
show markedly different origins for pollution events and highlight the current
limitations in modelling this tropical region. |
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