Measurement of atmospheric gasesin the West and Central African ecosystems

Experimental data on gases concentrations in Great African ecosystems have been obtained under the INDAAF (International Network to study Deposition and Atmospheric chemistry in AFrica) program. In this paper, data covering a complete wet and dry seasons (1998 to 2013) at three remote sites in West and Central Africa are presented. Those sites are representative of Great African ecosystems and are located along the latitudinal transect: dry savanna (Banizoumbou in Niger)-wet savanna (Lamto in Ivory Coast)- equatorial forest (Zoetele in Cameroon). For each type of these ecosystems, the monthly, seasonal and annual concentration and dry deposition variability have been determined and analyzed. Results show that at the dry savanna site, seasonal concentrations of all the five gases are higher in the wet season. In opposite, concentrations are higher during the dry season in wet savanna and in forest. The annual average concentrations of these gases measured in dry savanna are higher than those measured in wet savanna and in forest. The obtained values of annual average concentrations for the three ecosystems show the influence of the density of animal population in dry savanna and the seasonal gradient of solar radiation intensity that controls the dynamic of atmospheric air masses and photochemical reactions along the transect. We also notify the most important role that play terrigenous dust suspension, vegetation density and moisture along this transect of ecosystems. The annual average dry deposition for the five polluting gases is measured in dry savanna, wet savanna and equatorial forest. Concentrations and dry depositions of these gases depend on human activities, meteorological parameters of each ecosystem and physicochemical processes in the atmosphere.