No abstract

Atmospheric H2S was measured by a fluorometric method (sensitivity 10 rig). In France, for aerated soils the emissions were between 0.8 and 27/•g m -2 h -t H2S (average 5/•g m -2 h-•). The soil temperature is an important factor governing this emission. The H2S concentrations in the air ranged from 0.017 to 0.17 gg m -3 (average 0.080/•g m-3). In the Ivory Coast the H•S emissions were estimated between 30 and 300 p.g m -• h -t. The measured concentrations of H2S in the air at ground level ranged from 0.10 to 8.7 t•g m -3. The relative importance of the measured emissions for anoxic soils of the humid equatorial forests in the global $ cycle is discussed.

Sources and sinks of atmospheric methane are studied in savanna regions of west and central Africa. Flux measured over dry savanna soils, using static chambers, is always negative the average uptake rate being 2×1010 molecules/cm2/s. In these regions, sources are linked to biomass burning. Methane and CO2 emission from combustion of savanna plants and wood is studied by both field experiments and laboratory experiments using a combustion chamber. For savanna plants most of the carbon (85%) contained in the biomaterial is volatilized as CO2 and 0.1 to 0.25% as methane. For graminaceous plants like loudetia simplex the ratio C‐CH4/C‐CO2 is 0.11%; it is 0.28% for hyparrhenia the other main type of savanna plants and it attains 1.4% for the combustion of wood. In natural fire plumes this ratio is around 0.26% for savanna fires and 0.56 to 2.22% for forest fires. These results show that methane release is highly dependent on the type of combustion. Methane to CO2 ratios are also studied in vertical profiles in the troposphere taken during the TROPOZ I campaign, an aerial research expedition carried out over west Africa during the bushfire period. Within polluted layers, the average ratio of CH4 to CO2 excess over ambient air concentration is 0.34%. These results show that biomass burning in tropical Africa constitutes an important source of atmospheric methane estimated to about 9.2×106 T(CH4)/yr.

No abstract

No abstract