© Author(s) 2010. This work is distributed under the Creative Commons Attribution 3.0 License. Atmospheric Chemistry and Physics

Abstract. In order to gain insights into the characteristics of the mineral dust particles incorporated in the actual cloud droplets and the related cloud processing, the French ATR-42 research aircraft equipped both with a counterflow virtual impactor (CVI) and community aerosol inlet was deployed in Niamey, Niger (13◦30 ′ N, 02◦05 ′ E) in August 2006 within the framework of the African Monsoon Multidisciplinary Analysis (AMMA) project. Cloud residual and clear-sky particles were collected sep-arately and analyzed individually using a transmission elec-tron microscope (TEM) and a scanning electron micro-scope coupled with an energy dispersive X-ray spectroscopy (SEM-EDX). The analysis revealed interesting characteris-tics on the coarse dust particles (Dp>1µm), particularly those which likely had acted as CCN. Traces of heterogeneously formed secondary sulfate, chlo-ride and nitrate were found on many dust particles (though fraction of sulfate may be present in the form of gyp-sum as primary dust component). These secondary species were particularly enhanced in clouds (i.e. cloud processing). The study illustrates that calcium-rich particles assumed to be carbonates (Calcite, Dolomite) contained the secondary species in significantly larger frequency and amount than the silicates (Quartz, Feldspar, Mica, Clay), suggesting that they represent the most reactive fraction of the mineral dust. A surprisingly large fraction of the Ca-rich particles were al-ready found in deliquesced form even in clear-sky condi-Correspondence to: A. Matsuk