Morphology and chemical composition of airborne Saharan dust during the AEROsol and Ocean Science Expeditions (AEROSE)

The morphology and chemical composition of aerosols associated with Saharan dust outbreaks between July 2006 and 2009 off-shore of the African continent above the tropical North Atlantic Ocean is investigated. Conducted aboard the NOAA research ship Ronald H. Brown (KHB). The trans-Atlantic AEROsol and Ocean Science Expeditions (AEROSE) are a series of intensive atmospheric field campaigns designed to investigate the surface chemistry and provide a unique data set to characterize the impact and microphysical evolution of Saharan dust during mobilization as a signature to different source regions. Elemental composition results for the 2006 AEROSE samples based on energy dispersive X-ray microanalysis system indicate a well-mixed dust urban plume regime and reveal the presence of Al, C, Ca, Cd, CI, Fe, K, Mg, Na, O, Pb, S, and Si; while the 2009 samples being predominantly dust aerosols were dominated by crustal elements such as Al, Ca, CI, Cu, Fe, K, Mg, Na, O, P, S, Si, Sn, Ti, and Zn. The secondary electron images for both years reveal a variety of morphologies, but were dominated by chain-like association of spherules and non-spherical particles. Raman Microscopy affords an interpretation of the surface chemical processing and mixing state and revealed the presence of significant hydrocarbons in 2006, and sulfate for both years. Back trajectories show an outflow of air masses from Mauritania, Senegal, and a weak outflow from Algeria-Mali border for 2006 and Libya for 2009.