2 The Sahelian dust transect 3 stations on

2. The Sahelian dust transect = 3 stations on the main pathway of Saharan and Sahelian dust toward the Atlantic Ocean Latitude (°) mm. yr-1 Longitude (°) M'Bour, Senegal Cinzana, Mali Banizoumbou, Niger (Marticorena et al. , 2010) _ The stations are operational since 2006

2. The Sahelian dust transect DEPOSITION FLUX MEASUREMENTS Total deposition collector (Inverted freesbee + aerodynamic disc + marbles) Wet deposition automatic collector (MTX) Decantation Weighting Drying Total and wet deposition mass flux (insoluble) Collection with water

4. Results : average annual fluxes Spain 5. 3 g. m-2. yr-1 _ Our measurements (average 2006 -2012) are consistent with data from the litterature _ Deposition fluxes decrease from the sources to the transport regions in all directions Corsica 11. 2 g. m-2. yr-1 Turkey 13 g. m-2. yr-1 Kriti 11 -23 g. m-2. yr-1 M’Bour 92 g. m-2. yr-1 Cinzana 119 g. m-2. yr-1 Ghana (dry season) 42 g. m-2. yr-1 Banizoumbou 133 g. m-2. yr-1 Lybia 129 g. m-2. yr-1

3. Monthly PM 10 concentrations - The concentrations are extremely high (>100 µg. m-3 in monthly means) - They exhibit a typical seasonal cycle (max in June-July min in Sep-Oct) - An east-to west gradient (Niger > Mali > Senegal)

4. Results : Seasonal cycle Cinzana 2006 -2012 50 400 350 40 300 35 250 30 25 200 20 15 100 10 PM 10 concentration (µg, m-3) Précipitation (mm) Total deposition (g. m-2) Wet deposition (g. m-2) 45 50 5 0 0 J F M A M J J A S O N D Ø PM 10 concentrations are maximum in spring (March) Ø Précipitation are maximum in summer (August) ↔ minimum concentration Ø High concentrations + précipitation ↔ wet deposition maximum in June

4. Results : Seasonal cycle East Higher [PM 10] Lower precipitation : 505 mm -> wet deposition = 52% of total deposition Precipitation 735 mm -> wet deposition = 62% of total deposition West Lower [PM 10] Lower precipitation : 594 mm -> wet deposition = 8 % of total deposition

4. Results : Multiannual pattern Banizoumbou (Niger) M’Bour (Senegal) Cinzana (Mali) - The year to year variability is maily due to wet deposition; it results from the phasing between precipitation and concentrations associated with convective activity in Niger and Mali - In Senegal, there is not such convective systems producing high dust concentrations and wet deposition fluxes, the variability of deposition is driven by the concentrations

A contribution to the WP 1 (Dust observations for model evaluation) of the Dust-Clim Project funded by the European ERA 4 CS Joint Call for Transnational Collaborative Research Projects 2016 Dust. Clim • Dust Storms Assessment for the development of user-oriented Climate Services in Northern Africa, Middle East and Europe PI : S. Basart, Barcelona Supercomputing Center, Spain Partners : BSC, Spain; AEMET , Spain; LISA, France; CNR-DTA, Italy, FMI, Finland September 2017 – August 2020