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In this study we provide a first estimate of the aethalometer multiple scattering correction Cref for mineral dust aerosols. The Cref at 450 and 660?nm was obtained from the direct comparison of aethalometer data (Magee Sci. AE31) with the absorption coefficient calculated as the difference between the extinction and scattering coefficients measured by a CAPS PMex and a nephelometer at 450?nm and the absorption coefficient from a MAAP (Multi-Angle Absorption Photometer) at 660?nm. Measurements were performed on seven dust aerosol samples generated in the laboratory by the mechanical shaking of natural parent soils issued from different source regions worldwide. The single scattering albedo (SSA) at 450 and 660?nm and the size distribution of the aerosols were also measured. Cref for mineral dust varies between 1.81 and 2.56 for a SSA of 0.85-0.96 at 450?nm and between 1.75 and 2.28 for a SSA of 0.98-0.99 at 660?nm. The calculated mean Cref for dust is 2.09 (±?0.22) at 450?nm and 1.92 (±?0.17) at 660?nm. With this new Cref the dust absorption coefficient by aethalometer is about 2?% (450?nm) and 11?% (660?nm) higher than that obtained by using Cref?=?2.14, usually assumed in the literature. This difference induces up to 3?% change in the dust SSA. The Cref seems independent of the particle fine and coarse size fractions, and so the obtained Cref can be applied to dust both close to sources and following transport. Additional experiments performed with pure kaolinite mineral and polluted ambient aerosols indicate a Cref of 2.49 (±?0.02) and 2.32 (±?0.01) at 450 and 660?nm (SSA?=?0.96-0.97) for kaolinite, and a Cref of 2.32 (±?0.36) at 450?nm and 2.32 (±?0.35) at 660?nm for pollution aerosols (SSA?=?0.62-0.87 at 450?nm and 0.42-0.76 at 660?nm). [ABSTRACT FROM AUTHOR]

In the context of the ChArMEx campaign, we present here some results concerning the quantitative comparison between simulated and observed radiances during a dust event occurred between June and July 2013 in the southern Mediterranean basin, involving the airmass above Lampedusa island. In particular, comparisons have been performed between radiances as observed by the Infrared Atmospheric Sounder Interferometer (IASI) and those simulated using the σ-IASI-as radiative transfer model, which takes into account aerosol extinction effect through a set of fast parameterizations. Simulations have been carried on with different sets of input complex refractive indices, which take into account the parent soils of the aerosols, and using the high-quality characterization of desert dust aerosol microphysical properties, achieved through direct measurements in the ChArMEx experiment; on the one hand, this comparison has offered the possibility to test the feasibility of the radiative transfer model. On the other hand, this work goes through a direct validation of different refractive indices sets for desert dust in the thermal infrared. Results show a good consistency between calculations and observations, especially in the spectral interval 800-1000 cm-1; moreover, the comparison between calculations and observations suggests that further efforts are needed to better characterize desert dust optical properties in the short wave (above 2000 cm-1). In any case, we show that it is necessary to properly tune the refractive indices according to the geographical origin of the observed aerosol. [ABSTRACT FROM AUTHOR]