Aerosol sampling was performed using the AVIRAD aerosol sampling system newly developed for AMMA (Formenti et al., 2011). It consists of an iso-axial and isokinetic inlet whose 50% passing efficiency has been estimated at 9 µm in diameter. At the cruise speed of the ATR-42 (100 m s–1) the delivered volumetric flow rate is 350 l min–1, which was distributed to various instruments, including two SFU for collecting bulk aerosol samples. Samples were obtained by parallel filtration onto 42-mm diameter polycarbonate membranes (nominal pore size 0.4 µm Nucleopore, Whatman) on polyethylene supports. Samples were collected only during horizontal flight legs lasting not less than 20 minutes. Immediately after each flight, the loaded filters were stored in Petri dishes.