Physico-chemical composition of freshly emitted dust aerosol collected during field observations in Morocco

Abstract:

The FRontiers in dust minerAloGical coMposition and its Effects upoN climate (FRAGMENT) project is dedicated to understand, constrain and calculate the global mineralogical composition of dust along with its effects upon climate. In September 2019 an intensive dust field campaign was conducted as a part of FRAGMENT near M’hamid El Ghizlane in Morocco, at the edge of the Sahara Desert. Airborne dust samples were collected on sticky carbon substrates with cascade impactors, flat-plate samplers, and free-wing impactors. The size-resolved particle composition, morphology, and mixing-state were determined by single particle analysis with electron microscopy coupled with energy dispersive X-ray detection. Based on their chemical composition, particles are classified into different mineralogical groups. Preliminary analyses of the collected samples show the presence of silicates (illite-like, kaolinite-like, Ca-Si mixture, and quartz-like) in greater abundance. Other particle groups present are feldspar-like, calcite-like and gypsum-like, and hematite-like. The composition with respect to clay minerals shows high illite-like/kaolinite-like ratio as observed in previous measurements close to the arid source region. The aspect ratio distribution of the particles shows that they are typically nonspherical and have considerable shape heterogeneity. The present study will provide detailed information on the dust emitted during different event types as well as on the physicochemical properties of soil dust aerosol from a major source region.