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We present observations of tropospheric aerosol and water vapor transport over West Africa and the associated meteorological conditions during the AMMA SOP-0 dry season experiment, which was conducted in West Africa in January-February 2006. This study combines data from ultra-light aircraft (ULA)-based lidar, airborne in situ aerosol and gas measurements, standard meteorological measurements, satellite-based aerosol measurements, air-mass trajectories, and radiosonde measurements. At Niamey (13.5 degrees N, 2.2 degrees E) the prevailing surface wind (i.e. Harmattan) was from the northeast bringing dry dusty air from the Sahara desert. High concentrations of mineral dust aerosol were typically observed from the surface to 1.5 or 2 km associated with the Saharan airmasses. At higher altitudes the prevailing wind veered to the south or southeast bringing relatively warm and humid airmasses from the biomass burning regions to the Sahel (<10 degrees N). These elevated layers had high concentrations of biomass burning aerosol and were typically observed between altitudes of 2-5 km. Meteorological analyses show these airmasses were advected upwards over the biomass burning regions through ascent in Inter-Tropical Discontinuity (ITD) zone. Aerosol vertical profiles obtained from the space-based lidar CALIOP on-board CALIPSO during January 2007 also showed the presence of dust particles (particle depolarization (delta) similar to 30%, lidar Angstrom exponent (LAE) <0, aerosol backscatter to extinction ratio (BER): 0.026 similar to 0.028 sr(-1)) at low levels (<1.5 km) and biomass burning smoke aerosol (delta <10%, LAE: 0.6 similar to 1.1, BER: 0.015 similar to 0.018 sr(-1)) between 2 and 5 km. CALIOP data indicated that these distinct continental dust and biomass burning aerosol layers likely mixed as they advected further south over the tropical Atlantic Ocean, as indicated an intermediate values of delta (10 similar to 17%), LAE (0.16 similar to 0.18) and BER (0.0021 similar to 0.0022 sr(-1)).