AGING OF SAVANNA BIOMASS BURNING AEROSOLS - CONSEQUENCES ON THEIR OPTICAL-PROPERTIES

During the FOS-DECAFE experiment at Lamto, Ivory Coast, in January 199 1, various ground studies were undertaken simultaneously in order to i nvestigate the physical and chemical characteristics of smoke emitted by savanna biomass burning. Here we present sunphotometer ground-based results which allow the measurements of the spectral optical depth be tween 450 and 850 nm, the atmospheric water vapour content and the par ticle size distribution spectrum. The carbonaceous content of the sava nna biomass burning aerosols is also investigated. This is the first t ime that the physical characteristics of particles emitted by savanna plumes are obtained from ground-field studies. All the results suggest that a rapid aging of the smoke occurs first hundred metres from the savanna fire emission source. They show a relationship between the opt ical properties of smoke and the chemical aging of the aerosols primar ily due to particle growth and a loss of organic material relative to the black carbon content.