Aeolian dust falls in northern Italy in autumn 1996: chemical and mineralogical comparison

This paper describes two dust fall events in Genoa and Turin (northern Italy) on 12 November 1996 and 7 December 1996 respectively. Meteorological data suggest that the dust-bearing rain that fell on Genoa originated in north-eastern Morocco, where dust mobilisation was reported two days earlier, and had been carried straight to the north-western Italian coast by very strong winds. But the dust fall observed in Turin was not characterised by any specific synoptic situation inducing dust transport from the southern Mediterranean. The analyses include a quantitative and a qualitative study of two dust samples collected in downtown Genoa and Turin. The total amounts of dust that fell give two very high values of 4.05 g m-2 for Genoa and 0.54 g m-2 for Turin. The median sizes of the dust particles were 14.6 µm and 25.8 µm respectively. Most of the dust material collected in Genoa showed a yellowish-brown to red colour due to surface weathering by ferric hydroxides, and was sometimes coated with clayey particles. This attests to the Saharan origin of the particles. On the contrary, only 15% of the material sampled in Turin was coated with red-like clayey material from the desert. A large part of the sample was covered with a carbon-like substance. In addition, the proportion of organic matter (pollen grains and seeds) and anthropogenic fibrous material was much higher. This suggests that the dust fall observed in Turin very likely originated from local pollution mixed with a low proportion of long-distance Saharan dust.