A mosaic of aerosol sources in the central Mediterranean: insights from dry deposition and single-particle analyses

Abstract. Flux-based dry deposition observations are scarce in the central Mediterranean, leaving unresolved how transport shapes deposited composition. Dry deposition was sampled concurrently at Lecce, southern Italy, and San Lawrenz, Malta, from spring 2017 to winter 2018 within the XMed-Dry network, using flat-plate collectors with 48–72 h exposures. Up to 5000 particles per sample were classified by scanning electron microscopy with X-ray fluorescence, and source regions were derived from FLEXPART backward simulations weighted first by hourly PM₁₀ and then by class-resolved deposition rates. Mineral dust dominated the deposited mass in 95 % of samples at inland Lecce but 69 % at coastal San Lawrenz, where the sea-salt flux was an order of magnitude higher. Dust sources peaked over northern Algeria and Tunisia at Lecce but over Libya at San Lawrenz, and sea salt at Lecce reached the northeastern Atlantic, increasingly with size, while at San Lawrenz it remained within the western Mediterranean. Intensity instead separates the classes. The five strongest events carried about 20 % of the dust mass at both sites but 40 % of the sulfate mass. Within several intrusions, silicate-sulfate and silicate-sea-salt mixtures peaked after the dust maximum, indicating progressive processing as the event decayed, and these episodes carried higher iron proportions across all size fractions. Such processing reportedly raises iron solubility, increasing bioavailable iron delivered to surface waters. Mineral classes intercorrelate strongly except Ca-rich particles, whose mass at San Lawrenz held through boreal winter, when Saharan input reached its seasonal minimum, indicating a local carbonate source.