Particle Number and Mass Distributions above 10−4 cm Radius in Sand and Aerosol of the Sahara Desert

Abstract

Measurements of the particle size distribution in surface air and bulk soil (soil surface and 10 cm depth) were performed in the Sahara desert. This desert is a very important source for mineral dust transported over the Atlantic Ocean. Measurement restrictions limited the size range under investigation to 10?4 to 10?1 cm radius. In that range the size distributions in aerosol (toluene-insoluble component) and soil material (water-insoluble component) are similar in shape, except for a secondary maximum in soil particle size distributions. The results indicate that the aerosol and the soil size distributions are influenced by the soil and wind conditions over large areas. Differences between the soil surface and at depths of 10 cm were not observed within the precision of the measurements. Changes in the shape of the size distribution in the soil or surface air during and after a heavy sandstorm were not observed either?an indication that the loss of sand during a sandstorm is small compared to the reservoir of sand. Comparisons with measurements in surface air over the Atlantic Ocean in the northeast trade-wind region allow the conclusion of a redeposition of giant particles within the source area Sahara, thus contributing to the characteristic shape of the size distribution of particles in the soil.