BIOMASS BURNING IN THE TROPICAL SAVANNAS OF IVORY-COAST - AN OVERVIEWOF THE FIELD EXPERIMENT FIRE OF SAVANNAS (FOS DECAFE-91)/

FOS/DECAFE 91 (Fire of Savannas/Dynamique et Chimie Atmospherique en F oret Equatoriale) was the first multidisciplinary experiment organized in Africa to determine gas and aerosol emissions by prescribed savann a fires. The humid savanna of Lamto in Ivory Coast was chosen for its ecological characteristics representative of savannas with a high biom ass density (approximate to 900 g m(-2) dry matter). Moreover the vege tation and the climate of Lamto have been studied for more than twenty years. The emission ratios (Delta X/Delta CO2) of the carbon compound s (CO2, CO, NMHC, CH4, PAH, organic acids and aerosols), nitrogen comp ounds (NOx, N2O, NH3 and soluble aerosols) and sulfur compounds (SO2, COS and aerosols) were experimentally determined by ground and aircraf t measurements. To perform this experiment, 4 small plots (100 x 100 m ) and 2 large areas (10 x 10 km) were prepared and burnt in January 19 91 during the period of maximum occurrence of fires in this type of sa vanna. The detailed ecological study shows that the carbon content of the vegetation is constant within 1% (42 g C for 100 g of vegetal dry matter), the nitrogen content (0.29 g N for 100 g of dry matter) may v ary by 10% and the sulfur content (0.05 g S/100 d.m.) by 20%. These va riations of the biomass chemical content do not constitute an importan t factor in the variation of the gas and particle emission levels. Wit h the emission ratios characteristic of humid savanna and flaming cond itions (Delta CO/Delta CO2 of 6.1% at the ground and 8% for airborne m easurements), we propose a set of new emission factors, taking into ac count the burning efficiency which is about 80%: 74.4% of the carbon c ontent of the savanna biomass is released to the atmosphere in the for m of CO2, 4.6% as CO, 0.2% as CH4, 0.5% as NMHC and 0.7% as aerosols. 17.2% of the nitrogen content of the biomass is released as NOx, 3.5% as N2O, 0.6% as NH3 and 0.5% as soluble aerosols.