Tropospheric ozone over Equatorial Africa: regional aspects from the MOZAIC data

[摘要] We analyze ozone observations recorded over Equatorial Africa betweenApril 1997 and March 2003 by the MOZAIC programme, providing the firstozone climatology deriving from continental in-situ data over this region.Three-dimensional streamlines strongly suggestsconnections 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 Tradesand the regions of ozone precursors emissions by biomass burning. Duringthe biomass burning season in each hemisphere, the lower troposphere exhibits layersof enhanced ozone(i.e. 70 ppbv over the coast ofGulf of Guinea in December-February and 85 ppbv over Congo in June-August). The characteristicsof the ozone monthly mean vertical profiles are clearly connected to the regionalflow regime determined by seasonal dynamic forcing. The mean ozone profileover the coast of Gulf of Guinea in the burning season is characterized bysystematically high ozone below 650hPa ; these are dueto 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 andthe blocking Saharan anticyclone which prevents efficient vertical mixing. In contrast,ozone enhancements observed over Central Africa during the local dry season (June-August) are notonly found in the lower troposphere but throughout the troposphere. Moreover, this studyhighlights a connection between the regions of the coast of Gulf of Guineaand regions of Congo to the south that appears on a semi annual basis. Vertical profiles inwet-season regions exhibit ozone enhancements in the lower tropospheredue to biomass burning products transport from fires situated in the opposite dry-season hemisphere.

[学科分类] 大气科学