2002 Annual

Tuesday, 15 January 2002: 5:00 PM
Urban and Rural Ozone Pollution over Southern Africa from Satellite and SHADOZ Sondes during SAFARI-2000 (September 2000)
Anne M. Thompson, NASA/GSFC, Greenbelt, MD; and J. C. Witte, A. Phahlane, G. J. R. Coetzee, J. R. Herman, R. D. Hudson, and A. D. Frolov
In early September, throughout south central Africa, seasonal clearing of dry vegetation and the production of charcoal for cooking leads to intense smoke haze and ozone formation. These features are detected by the TOMS satellite through tropospheric ozone and smoke aerosol retrievals [Thompson and Hudson, 1999; Thompson et al., 2001a; Herman et al., 1997]. In addition, signatures of ozone pollution are detected in various layers in soundings made at SHADOZ stations [Thompson et al., 2001b; Southern Hemisphere ADditional OZonesondes, ] at Ascension Island, Reunion Island, Nairobi and Irene (South Africa). These observations have been augmented by ozone soundings made over Lusaka, Zambia (15.5S, 25E) during the SAFARI-2000 field campaign. During a six- day period in early September 2000 we recorded layers of high ozone (> 125 ppbv at 5 km) during two stagnant periods, interspersed by a frontal passage that reduced boundary layer ozone by 30%. Surface ozone concentrations ranged from 50-95 ppbv and integrated tropospheric ozone from the soundings was 39-54 Dobson Units (note 1.3 km elevation at the launch site). High ozone concentrations in the free troposphere were advected from rural regions in western Zambia where SAFARI aircraft observed intense biomass fires and elevated aerosol and trace gas amounts. Animations of satellite images and trajectories confirm pollutant recirculation over south central African fires, exit of ozone from Mozambique and Tanzania to the Indian Ocean and the characteristic buildup of tropospheric ozone over the Atlantic from western African outflow. SHADOZ station data (Irene, South Africa; Nairobi) in 2000 give further perspective to the Zambian observations.

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