Mapping the physico-chemical properties of mineral dust in western Africa: mineralogical composition

Paola Formenti (1) , Sandrine Caquineau (2) , Karine Desboeufs (1) , Anne Klaver (1) , Servanne Chevaillier (1) , Emilie Journet (1) , Jean-Louis Rajot (3, 1)

1 LISA (UMR_7583) - Laboratoire Interuniversitaire des Systèmes Atmosphériques
2 BTP - Biogéochimie-Traceurs-Paléoclimat
3 iEES - Institut d'écologie et des sciences de l'environnement de Paris

In the last few years, several ground-based and air-borne field campaigns have allowed the exploration of theproperties and impacts of mineral dust in western Africa,one of the major emission and transport areas worldwide.In this paper, we explore the synthesis of these observationsto provide a large-scale quantitative view of the mineralogi-cal composition and its variability according to source regionand time after transport.This work reveals that mineral dust in western Africa is amixture of clays, quartz, iron and titanium oxides, represent-ing at least 92 % of the dust mass. Calcite ranged between0.3 and 8.4 % of the dust mass, depending on the origin. Ourdata do not show a systematic dependence of the dust min-eralogical composition on origin; this is to be the case as, inmost of the instances, the data represent the composition ofthe atmospheric burden after 1–2 days after emission, whenair masses mix and give rise to a more uniform dust load.This has implications for the representation of the mineraldust composition in regional and global circulation modelsand in satellite retrievals.Iron oxides account for 58±7 % of the mass of elementalFe and for between 2 and 5 % of the dust mass. Most of themare composed of goethite, representing between 52 and 78 %of the iron oxide mass. We estimate that titanium oxides ac-count for 1–2 % of the dust mass, depending on whether thedust is of Saharan or Sahelian origin.The mineralogical composition is a critical parameter forestimating the radiative and biogeochemical impact of min-eral dust. The results regarding dust composition have been used to estimate the optical properties as well as the iron frac-tional solubility of Saharan and Sahelian dust.Data presented in this paper are provided in numeri-cal form upon email request while they are being turnedinto a public database, the Dust-Mapped Archived Proper-ties (DUST-MAP), which is an open repository for compo-sitional data from other source regions in Africa and world-wide.

Domaines: Géophysique [physics.geo-ph]

Paola Formenti, Sandrine Caquineau, Karine Desboeufs, Anne Klaver, Servanne Chevaillier, et al.. Mapping the physico-chemical properties of mineral dust in western Africa: mineralogical composition. Atmospheric Chemistry and Physics Discussions, 2014, 14 (19), pp.10663-10686. ⟨10.5194/acp-14-10663-2014⟩. ⟨hal-01139584⟩