Tropospheric ozone over Equatorial Africa: regional aspects from the MOZAIC data B. Sauvage, V. Thouret, J.-P. Cammas, F. Gheusi, G. Athier, and P. Nédélec Laboratoire d’Aérologie, OMP, UMR 5560, Toulouse, France
Abstract. We analyze ozone observations recorded over Equatorial Africa between
April 1997 and March 2003 by the MOZAIC programme, providing the first
ozone climatology deriving from continental in-situ data over this region.
Three-dimensional streamlines strongly suggests
connections between the characteristics of the ozone monthly mean vertical profiles,
the most persistent circulation patterns in the troposphere over Equatorial Africa
(on a monthly basis) such as the Harmattan, the African Easterly Jet, the Trades
and the regions of ozone precursors emissions by biomass burning. During
the biomass burning season in each hemisphere, the lower troposphere exhibits layers
of enhanced ozone (i.e. 70 ppbv over the coast of
Gulf of Guinea in December-February and 85 ppbv over Congo in June-August). The characteristics
of the ozone monthly mean vertical profiles are clearly connected to the regional
flow regime determined by seasonal dynamic forcing. The mean ozone profile
over the coast of Gulf of Guinea in the burning season is characterized by
systematically high ozone below 650hPa ; these are due
to the transport by the Harmattan and the AEJ of the pollutants originating from upwind fires.
The confinement of high ozone to the lower troposphere is due to the high stability of the Harmattan and
the blocking Saharan anticyclone which prevents efficient vertical mixing. In contrast,
ozone enhancements observed over Central Africa during the local dry season (June-August) are not
only found in the lower troposphere but throughout the troposphere. Moreover, this study
highlights a connection between the regions of the coast of Gulf of Guinea
and regions of Congo to the south that appears on a semi annual basis. Vertical profiles in
wet-season regions exhibit ozone enhancements in the lower troposphere
due to biomass burning products transport from fires situated in the opposite dry-season hemisphere.
Citation: Sauvage, B., Thouret, V., Cammas, J.-P., Gheusi, F., Athier, G., and Nédélec, P.: Tropospheric ozone over Equatorial Africa: regional aspects from the MOZAIC data, Atmos. Chem. Phys., 5, 311-335, doi:10.5194/acp-5-311-2005, 2005.