The Airborne Aerosol Measurements During SAMUM-1 and SAMUM-2: What Have we Learned About Dust?

Abstract

dust properties is poorly understood over many regions of the world. Major unknowns are the dust size distribution that spans a range from 0.01 μm to about 100 μm, and the vertical distribution of dust properties. The Saharan Mineral Dust Experiment (SAMUM) aimed to characterise the optical, physical, chemical, and radiative properties of Saharan dust. In a first field experiment (SAMUM-1), conducted in May/June 2006 in Morocco, the properties of pure dust close to the source were investigated. The second field experiment (SAMUM-2) took place in the Cape Verde area in January/February 2008 and focussed on the transformation of the dust properties during transport and mixing with biomass burning aerosol. For the field experiments, the DLR Falcon research aircraft was equipped with an extensive set of aerosol instruments for size, volatility, and absorption measurements, impactor sampling for chemical analyses and with a nadir- looking high spectral resolution lidar (HSRL). During SAMUM-1, three large-scale dust events were probed which extended from Morocco to Portugal. The upper boundary of the dust layers was found at altitudes between 4 and 6 km above sea level (a.s.l.). In all dust layers, particles with diameters larger than 10 μm were present, and in 80% of the layers no particles larger than 40 μm were present. During SAMUM-2, ten mission flights were conducted from Cape Verde providing data of dust and biomass burning plumes. On average, the dust plumes were situated below 2 km a.s.l., while the central African biomass burning layers covered the altitude range between 2 and 4-5 km. Presented results will cover profiles of dust size distributions and dust optical properties. The microphysical properties of dust measured during SAMUM-2 will be compared with those measured during SAMUM-1. Similarities and differences in the size distribution observed over Cape Verde compared