NOX EMISSIONS FROM AFRICAN SAVANNA FIRES

Fire of Savanna/Dynamique et Chimie Atmospherique en Foret Equatoriale (FOS/DECAFE-91) and Southern African Fire-Atmosphere Research Initiat ive (SAFARI-92) were two multidisciplinary experiments organized in Af rica to determine the gas and aerosol emissions due to prescribed sava nna fires. These two experiments took place in two types of savannas w hich have very different ecological properties: Lamto, Ivory Coast (FO S/DECAFE-41), in the Guinean area, is wet (80% moisture content) and d ense (9 to 10 t ha(-1)) and has little litter (2 to 5% of total biomas s); Kruger Park, in South Africa (SAFARI-92), on the contrary, is dry (10 to 20% moisture) and has a low biomass (3 to 6 t ha(-1)) and 40% o f its total biomass in the form of litter. The experimental strategy u sed to determine the emission ratios Delta CO/Delta CO2 and Delta NOx/ Delta CO2 was to measure at ground level, in the same volume of the pl ume above the fire, the CO, CO2 and NOx concentrations. The mean carbo n content of the two savannas was similar (about 43%), and the Delta C O/Delta CO2 ratio, the indicator of the burning process, was comparabl e in back and head fires with mean ratios between 4.5 and 6.1%. These Delta CO/Delta CO2 ratios were characteristic of intense flaming combu stion with the formation of mainly fully oxidized compounds for both s avannas. The Delta CO/Delta CO2 ratio for the head fires can be divide d into two distinct phases: a flaming period and a smoke period which immediately follows. Nitrogen concentration of the two savannas varied from as low as 0.3% in Lamto to 0.80% of dry mass in the Kruger Park in the Faai plot. In this study we could clearly identify a linear dep endency between the nitrogen concentration of the dry and wet savannas of Africa and the NOx/CO2 emission ratio, Delta NOx/Delta CO2 = 0.66 N% - 0.01, with a correlation coefficient of 0.93, statistically signi ficant at a confidence level better than 99%. This result enables the quantification of the emissions of NOx from African savanna burning by measuring the nitrogen concentration of the vegetation and monitoring the type of burn.