Saharan Dust Transport in the Mediterranean: Circulation Patterns, Air Quality Monitoring, and Chemical Composition Analysis

In the Mediterranean basin, long-range transport of desert dust, mostly of Saharan origin, can increase the concentration of PM10, leading to exceedances of the EU limit value. Episodes of high mineral dust concentrations can also have adverse effects on human health (Domínguez-Rodríguez, 2021). In recent years, the intensity and frequency of desert intrusions have been increasing, most likely related to meteorological anomalies due to climate change (Cuevas-Agulló, 2020). In this context, a meteorological analysis that identifies the most frequent circulation patterns associated with desert intrusions can be useful not only to better understand the phenomenon, but also to highlight its variations in frequency and intensity. In this study, a method implemented at the LaMMA Consortium for the classification of 'weather types' is presented. This method has already been used in other applications (Salinger, 2020). Furthermore, the present study utilises data measured by numerous low-cost stations of the AirQino network (https://www.airqino.it) to assess the temporal and spatial evolution of desert dust transport episodes, in particular the PM10 and PM2.5 concentration data recorded on hourly basis, which make it possible to estimate the spatio-temporal tracking of the desert dust plume. The low-cost Airqino stations, developed at the Institute for BioEconomy of the National Research Council, integrate sensors for detecting the main air pollutants (CO, O3, NO2, PM2.5, PM10), CO2 and meteorological parameters such as temperature, air humidity. The stations have been employed in large-scale monitoring networks currently ensuring a considerable coverage of the Italian territory. Several of such measurement points are present in European cities too, including Cannes and Marseille in France, Budapest and Debrecen in Hungary, Bucharest in Romania, and Barcelona in Spain. The data produced by the AirQino network stations is freely available in real time via a dedicated web platform (https://www.airqino.it/). Precedent analyses of desert intrusions affecting central Italy in the period 2018-2023 (Calastrini, 2024) allowed to identify some recurring configurations evidencing that Saharan dust intrusions in Italy are not only related to southerly and south-westerly flows (direct cases), but that can also be the result of more complex flow pattens, driving desert dust plumes along longer paths with markedly different terminal directions of provenience (indirect cases). These features are illustrated by analysing two episodes corresponding to each one of the two typologies, the direct and the indirect case intrusion. In order to provide detailed insights into the mineral dust chemical composition, samples of PM10 collected during such intrusions in Tuscany (Central Italy) have been analysed using a range of techniques, including ion chromatography, thermo-optical analysis, PIXE and ICP-AES, allowing to put in evidence the desert component, through the presence of marker elements specific to the areas of origin or of those covered by the plume's trajectory. Calastrini, F. et al. (2024) Long-Range Mineral Dust Transport Events in Mediterranean Countries. Air. 2, 444-467. Cuevas-Agulló, E. et al.(2024) Sharp increase in Saharan dust intrusions over the western Euro-Mediterranean in February–March 2020–2022 and associated atmospheric circulation. Atmos. Chem. Phys. 24, 4083–4104. Domínguez-Rodríguez, A. et al. (2021) Impact of Desert Dust Events on the Cardiovascular Disease: A Systematic Review and Meta-Analysis. J. Clin. Med. 10, 727. Salinger, M. J.et al. (2020). Linking crop yields in Tuscany, Italy, to large-scale atmospheric variability, circulation regimes and weather types. The Journal of Agricultural Science. 158(7), 606–623.