Submicron desert dusts: A sandblasting process

Mass size distributions of the major elements of the mineral aerosol of northern Sahara were obtained from measurements carried out with an inertial cascade impactor. A fitting procedure by data inversion was applied to these data. This technique considers the major mechanisms of nonideal behavior such as particle bounce-off, wall losses and cross sensitivity which affect the accuracy of impactor measurements of aerosol size distribution. Accurate size distributions of Saharan aerosol (range 0.1-20 {mu}m) were so obtained for different conditions of soil mobilization. These measurements, coupled with wind speed information, show the shape of the size distribution for desert aerosols in the considered range to be characterized by a similar pattern with a common mode of particles having diameter between 1 and 20 {mu}m whatever the weather conditions. A second mass peak of submicron particles appears when the wind speed increases above the threshold value for erosion. Scanning electron microscope photographs indicate that the whole granulometric spectrum of the sampled aerosol between 0.1 and 20 {mu}m mainly consists of clay easily disaggregated by sandblasting. The common origin of submicron particles with those between 1 and 20 {mu}m is established by showing the similar composition of dusts in the both modes.more » The results suggest that the presence of submicron mineral particles during dusty and sandstorm conditions is consistent with a sandblasting process.« less