Nitrogen Emission and Deposition Budget in Africa

Galy-Lacaux1, C. Delon1, K. Pienaar2, M. Adon1,3, V. Yoboué3, B. Diop4, L. Sigha5, D. Laouali6, A. Akpo7

1 Laboratoire d’Aérologie, Université de Toulouse, CNRS, Toulouse, France, mailto:[email protected]

2 School of Physical and Chemical Sciences, North-West University, Potchefstroom, South Africa

3 Université de Cocody, Abidjan, Côte d’Ivoire

4 Université de Bamako, Mali

5 Université de Yaoundé CRH IRGM, Yaoundé, Cameroun

6 Université de Niamey, Niger

7 Université Abomey Calavi, Cotonou, Benin

Abstract

Atmospheric nitrogen concentrations depend on land surface exchanges of nitrogen compounds. In Africa, deposition and emission fluxes of nitrogen compounds are poorly quantified, and are likely to increase in the near future due to land use change and anthropogenic pressure. This work is part of the long term deposition monitoring project IDAF initiated in the 1990s. IDAF (IGAC/DEBITS/Africa) is the African contribution to study deposition in the IGAC/DEBITS programme and contributes to the WMO-GAW programme. This work proposes an estimate of an atmospheric N compounds budget in Africa, along an ecosystem transect, from dry savanna to wet savanna and forest, for the years 2000 to 2007. The budget takes into account: (1) gaseous dry deposition fluxes estimated by considering N compounds concentrations at the monthly scale and modeling of deposition velocities at the IDAF sites, (2) wet deposition fluxes calculated from measurements of ammonium and nitrate chemical content in precipitations and (3) N emission sources taking into account simulated NO biogenic emission from soils, NH3 emission by volatilization and NOx and NH3 emission from biomass burning and domestic fires. This regional N emission deposition budget should give the present status at the scale of the main African ecosystems and should help to quantify the processes that may contribute to the changing levels of N deposition.