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Analysis of harmattan dust over Accra, Ghana

Harmattan aeolian dust from the Sahara desert which occurs in West Africa was monitored at Accra (5°32'N, 0°12'W) during the 1993/94 harmattan season. Dust deposition for 1993/94 harmattan season at Accra amounted to 4.8287 x 10 -3 kg m -2 . Particle size analysis as well as X-ray fluorescence and neutron activation analyses were carried out on the harmattan dust. The particle size analysis indicated that the great majority of the particles deposited have a diameter above 1 μm with mean, mode and median diameters of 2.11, 2.00 and 1.73 μm, respectively. The deposition velocities, calculated by the Stokes formula, are 3.51 x 10 -4 , 3.15 x 10 -4 and 2.36 x 10 4 m s -1 , for these sizes respectively. X-ray fluorescence analysis of the dust showed the presence of the following elements, with the order of abundance as Fe > Ca > Cu > Ti > Zr > Pb > Sr > Rb > Y > Nb. In addition to these elements, neutron activation analysis also revealed the presence of elements: Na, K, Mn and Mg.