[1] We use space-based observations of NO 2 columns from the Global Ozone Monitoring Experiment (GOME) to map the spatial and seasonal variations of NO x emissions over Africa during 2000. The GOME observations show not only enhanced tropospheric NO 2 columns from biomass burning during the dry season but also comparable enhancements from soil emissions during the rainy season over the Sahel. These soil emissions occur in strong pulses lasting 1-3 weeks following the onset of rain, and affect 3 million km 2 of semiarid sub-Saharan savanna. Surface observations of NO 2 from the International Global Atmospheric Chemistry (IGAC)/Deposition of Biochemically Important Trace Species (DEBITS)/Africa (IDAF) network over West Africa provide further evidence for a strong role for microbial soil sources. By combining inverse modeling of GOME NO 2 columns with space-based observations of fires, we estimate that soils contribute 3.3 ± 1.8 TgN/year, similar to the biomass burning source (3.8 ± 2.1 TgN/year), and thus account for 40% of surface NO x emissions over Africa. Extrapolating to all the tropics, we estimate a 7.3 TgN/year biogenic soil source, which is a factor of 2 larger compared to model-based inventories but agrees with observationbased inventories. These large soil NO x emissions are likely to significantly contribute to the ozone enhancement originating from tropical Africa.

Abstract. In this paper we present the long term monitoring of ambient gaseous concentrations within the framework of the IDAF (IGAC-DEBITS-AFRICA) program. This study proposes for the first time an analysis of long-term inorganic gas concentrations (1998 to 2007) of SO 2 , NO 2 , HNO 3 , NH 3 and O 3 , determined using passive samplers at seven remote sites in West and Central Africa. Sites are representative of several African ecosystems and are located along a transect from dry savannas-wet savannas-forests with sites at Banizoumbou (Niger), Katibougou and Agoufou (Mali), Djougou (Benin), Lamto (Cote d'Ivoire), Zoetele (Cameroon) and Bomassa (Congo). The strict control of measurement techniques as well as the validation and inter-comparison studies conducted with the IDAF passive samplers assure the quality and accuracy of the measurements. For each type of African ecosystem, the long term data series have been studied to document the levels of surface gaseous concentrations. The seasonal and interannual variability have also been analyzed as a function of emission source variations. We compared the measured West and Central African gas Correspondence to: M. Adon (adonatma@yahoo.fr) concentrations to results obtained in other parts of the world. Results show that the annual mean concentrations of NO 2 , NH 3 , HNO 3 measured in dry savannas are higher than those measured in wet savannas and forests that have quite similar concentrations. Annual mean NO 2 concentrations vary from 0.9±0.2 in forests to 2.4±0.4 ppb in the dry savannas, NH 3 from 3.9±1.4 to 7.4±0.8 ppb and HNO 3 from 0.2±0.1 to 0.5±0.2 ppb. Annual mean O 3 and SO 2 concentrations are lower for all ecosystems and range from 4.0±0.4 to 14.0±2.8 and from 0.3±0.1 to 1.0±0.2 ppb, respectively. A focus on the processes involved in gas emissions from dry savannas is presented in this work, providing explanations for the high concentrations of all gases measured at the three dry savannas sites. At these sites, seasonal concentrations of all gases are higher in the wet season. Conversely, concentrations are higher in the dry season in the wet savannas. In forested regions, we measure no significant difference between wet and dry seasons. This unique database of long term gases concentrations monitoring is available at:

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Abstract. In this paper, we present the long term monitoring of ambient gaseous concentrations within the framework of the IDAF (IGAC-DEBITS-AFRICA) program. This study proposes for the first time to study long term gases concentrations (1998–2007) by determining the ambient concentration of the inorganic gases, i.e., SO2, NO2, HNO3, NH3 and O3 using passive samplers at seven remote sites in West and Central Africa. Sites are representative of a great African ecosystem and are located according a transect: dry savannas-wet savannas-forests with Banizoumbou (Niger), Katibougou and Agoufou (Mali), Djougou (Benin), Lamto (Cote d'Ivoire), Zoetele (Cameroon) and Bomassa (Congo). The validation and inter-comparison studies conducted with the IDAF passive samplers assure the quality and the control of the measurement technique to show the accuracy of the measurements. For each type of African ecosystems, we have studied the long term data series to document the levels of gaseous surface concentrations and the seasonal and interannual variations analyzed as a function of emission sources variations. We have tried to compare West and Central African gases concentrations to the results obtained in other parts of the world. Results show that the annual mean concentrations of NO2, NH3, HNO3 measured in dry savannas are higher than those measured in wet savannas and forests that have quite similar concentrations. Annual mean NO2 concentrations vary from 0.9±0.2 in forests to 2.4±0.4 ppb in the dry savannas, NH3 from 3.9±1.4 to 7.4±0.8 ppb, HNO3 from 0.2±0.1 to 0.5±0.2 ppb. Annual mean O3 and SO2 concentrations are lower for all the ecosystems and range from 4.0±0.4 to 14.0±2.8 and from 0.3±0.1 to 1.0±0.2 ppb, respectively. A focus on dry savannas processes involved in gases emission is presented in this work, explaining the high concentrations of all gases measured on the three dry savannas sites. For all gases, seasonal concentrations are higher in the wet season of dry savannas. Conversely, concentrations are higher in the dry season of wet savannas. In forest, we measure no significant difference between wet and dry seasons. This unique database of long term gases concentrations monitoring is available at: http://www.obs-mip.fr/idaf/.

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