Study of the variability of the optical properties on the source emission area

The optical properties of desert aerosols are strongly dependent on their mineralogical composition, including the presence of iron oxide. The mineralogy of soils of the Sahara and the Sahel is spatially variable; therefore aerosols emitted from different source areas might have different optical properties. Our objective is therefore to assess the variability of the optical properties of aerosols according to their source regions.

The possibilities of access to these areas are very limited for geo-political reasons, aerosols are collected at the ground in short-transport regions, or during airborne campaigns. From this point of view, the western Africa Sahel is extremely well located, as aerosols that are collected may come, according to the seasons, from different Saharan and Sahel sources.

Several past and future measurement campaigns provide a set of data for a fine description of optical and physico-chemical properties of aerosols from different sources (Formenti et al., 2008; 2011; Klaver et al., 2011; Chou et al., 2008; McConnell et al., 2008; 2011). Regional signatures of the optical properties should be integrated in 3D models of the mineral dust atmospheric cycle to improve the estimate of their direct radiative effect.

Figure: Analyses on samples collected at the ground or onboard research aircraft show different levels of iron oxides depending on the source region of collected dust, presented here for cases where it has been identified without ambiguity (Formenti et al., 2008).