Characterization of African dust over southern Italy

[摘要] Dust samples from rainfall residues have been collected in southeast Italy(40º 20' N, 18º6' E) during dust outbreaks occurred from April to June 2002 to characterizemorphological and elemental particle composition by different techniques, andinvestigate the dependence of particle properties on source regions. Four-day analyticalback trajectories and satellite images have been used to infer source regions of theinvestigated dust samples.

It has been found that the TOMS absorbing aerosol index was in the range0.7-2.2 over Southern Italy when samples have been collected. The particle-size and -shape analysisby a scanning electron microscope (SEM) has revealed either that the particle-diameterdistribution was between 0.3 and 30 mm with median-diameter values between1.7-2.4 mm,and that the particles were characterized by a roundness factor varying from 0.8 to2.5. The infrared transmission spectra have allowed recognizing that all dust samplescontained a significant amount of illite. The X-ray energy dispersive (EDX)measurements have revealed that the Al/Si ratio of the transported dust varies from 0.41to 0.50, and that the Al/Si, Ca/Al, K/Ca, and Fe/Ca ratios differ according to sourceregions and therefore can be used as indicators of dust source regions. Indeed, it has beenfound that dust samples with larger Ca/Al and Si/Al ratios and lower Fe/Ca and K/Caratios, have been collected along dust events with a source region in northwesternSahara. On the contrary, the samples collected along dust events with the origin mainlyin Chad, Niger, Algeria and Lybia were characterized by larger Fe/Ca and K/Ca ratios.

[学科分类] 大气科学