Long-term characterisation of African dust advection in south-eastern Italy: Influence on fine and coarse particle concentrations, size distributions, and carbon content

Saharan dust (SD) is a relevant source of mineral particles (PM) for the Mediterranean region with potential impacts on air quality and climate. In this work, a long-term analysis of 56 SD events recorded between 2013 and 2018 at the Environmental-Climate Observatory of Lecce (SE Italy) was performed to investigate the effects and the seasonality of dust advection on PM2.5 and PM10, on carbon content, and on number and mass size distributions. The average duration of events was 2.6 days (10% of days) with a pronounced seasonality, 12.5% during warm seasons and 7.5% during cold seasons. The average contribution to PM10 was 1.5 μg/m3, between 1.4 μg/m3 (cold seasons) and 1.8 μg/m3 (warm seasons). Contribution to PM2.5 was significantly lower and not negligible during warm seasons (0.5 μg/m3). The impact of SD in south-eastern Italy is comparable with that in central Italy rather than to that observed in south-western Italy. Looking at PM10, 70 days exceeding legislation threshold were observed (4.8% of days), 22.9% of these exceedances were during SD. Extreme SD events (contributions > 100 μg/m3) cover 2% of the cases. Comparison of carbon content between SD and non-SD days shows that SD does not influence EC and eBC concentrations; however, SD contributes to secondary organic aerosol in the coarse fraction (PM10-2.5). Size distributions (in number and mass) measured during SD and non-SD days show that SD increases the particle number concentrations for diameters (Dp) larger than about 0.9–1 μm. Maximum increase was for Dp 2.5–3 μm.