Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 7 6 2007 10.5194/acpd-7-16253-2007 http://www.atmos-chem-phys-discuss.net/7/16253/2007/ http://www.atmos-chem-phys-discuss.net/7/16253/2007/acpd-7-16253-2007.html http://www.atmos-chem-phys-discuss.net/7/16253/2007/acpd-7-16253-2007.pdf 16253 16282 2007-11-22 Biogenic emissions of NO_x from recently wetted soils over West Africa observed during the AMMA 2006 campaign D. J. Stewart d.stewart@uea.ac.uk C. M. Taylor C. E. Reeves J. B. McQuaid School of Environmental Sciences, UEA, Norwich, UK Centre for Ecology and Hydrology, Wallingford, UK School of the Environment, University of Leeds, UK Chemical and meteorological parameters measured on board the Facility for Airborne Atmospheric Measurements (FAAM) BAe 146 Atmospheric Research Aircraft during the African Monsoon Multidisciplinary Analysis (AMMA) campaign are presented to show the impact of NO_x emissions from recently wetted soils in West Africa. NO_x emissions from soils have been previously observed in many geographical areas with different types of soil/vegetation cover during small scale studies and have been inferred at large scales from satellite measurements of NO_x. This study is the first dedicated to showing the emissions of NO_x at an intermediate scale between local surface sites and continental satellite measurements. The measurements reveal pronounced mesoscale variations in NO_x concentrations closely linked to spatial patterns of antecedent rainfall. Fluxes required to maintain the NO_x concentrations observed by the BAe-146 in a number of cases studies and for a range of assumed OH concentrations (0 to 1×10⁷ molecules cm^–3) are calculated to be in the range 4.7 to 37.3 ng N m^−2 s^−1. These values are comparable to the range of fluxes from 2 to 83 ng N m^−2 s^−1 reported from small scale field studies in a variety of tropical and sub-tropical locations reported in the review of Davidson and Kingerlee (1997). The fluxes calculated in the present study have been scaled up to cover the area of the Sahel bounded by 10 to 20 N and 10 E to 20 W giving an estimated emission of up to 0.05 TgN from this area for July and August 2006. 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