Saharan dust impact on the chemical composition of PM10 and PM1 samples over south-eastern Italy

Abstract

Angstrom exponents (A) and dust concentrations from the Barcelona Supercomputing Center-Dust REgional Atmospheric Model (BSC-DREAM) were used to infer the impact of long-range transported desert dust particles at the ground level and evaluate their role on the chemical composition of PM1 and PM10 samples. A values were calculated from the scattering coefficients at 450 and 635 nm, retrieved from integrating nephelometer measurements. Nephelometer measurements were performed at a coastal site (Lecce, 40.33° N, 18.11° E) of south-eastern Italy from December 2011 till November 2012. Days characterized by A daily mean values smaller than 0.95 and modelled daily dust concentrations larger than 0.1 μg m−3 at 86 m above the ground level were considered representative of days affected by African dust particles up to the ground level (dusty days). Both criteria have allowed identifying 86 dusty days during the investigated period. The analysis of 24-h simultaneously collected PM10 and PM1 samples revealed that the PM1 mass concentrations increased linearly with PM10 both in dusty and dust-free days, which were identified as the ones characterized by A daily mean values larger than 1.3 and PM1/PM10 ratios larger than 0.35. These results suggested that the PM1 samples were also affected by desert particles on dusty days. In fact, chemical analyses revealed that the Al and Fe mean mass concentrations were larger in dusty day PM1 and PM10 samples. Then, we found that the crustal matter contribution was nearly twice and more than twice larger in dusty PM1 and PM10 samples, respectively, than in corresponding dust-free samples. Mass contributions of organic and elemental carbon, sulfates, and ammonium even if smaller in dusty samples than in dust-free PM1 and PM10 samples revealed the significant role of the anthropogenic pollution also on dusty days.