Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 8 3 2008 10.5194/acpd-8-10057-2008 http://www.atmos-chem-phys-discuss.net/8/10057/2008/ http://www.atmos-chem-phys-discuss.net/8/10057/2008/acpd-8-10057-2008.html http://www.atmos-chem-phys-discuss.net/8/10057/2008/acpd-8-10057-2008.pdf 10057 10103 2008-05-29 Increase of the aerosol hygroscopicity by aqueous mixing in a mesoscale convective system: a case study from the AMMA campaign S. Crumeyrolle suzanne.crumeyrolle@cnrm.meteo.fr L. Gomes P. Tulet A. Matsuki A. Schwarzenboeck K. Crahan GAME/CNRM,METEO-FRANCE – CNRS, Toulouse, France Laboratoire de Meteorologie Physique, Clermont-Ferrand, France Aerosol properties were measured during an airborne campaign experiment that took place in July 2006 in West Africa within the framework of the African Monsoon Multidisciplinary Analyses (AMMA). The goal of the present study was to determine the main microphysical processes that affect the aerosols during the passage of a mesoscale convective system (MCS) over the region of Niamey in Niger. A main difference in the aerosol profiles measured before and after the passage of the MCS was found for a layer located between 1300 and 3000 m where the aerosol concentration has drastically decreased after the passage of the MCS. Concurrently, a significant increase of the cloud condensation nuclei fraction was also observed during the post-MCS period in the same layer. Moreover, the results of the elemental composition analyses of individual particles collected in this layer after the MCS passage have shown higher contributions of sulfate, nitrate and chloride to the total aerosol. A mesoscale atmospheric model with on-line dust parameterization and Lagrangian backtrajectories was used to interpret the impact of the MCS on the aerosol properties. 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