Source-Dependent Optical and Mineral Signatures of Dust Outbreaks over the Mediterranean

Abstract. Dust events frequently affect the Mediterranean Basin, however, the evolution of their optical and microphysical properties during transport remains poorly characterized. This study examines four major dust outbreaks in 2021–2022 affecting the Mediterranean, originating from the Eastern, Western, and Central Sahara and the Middle East. Combining ground-based AERONET sun photometers (24 stations), satellite (IASI, MODIS MIDAS) dust optical depth (DOD) data, and HYSPLIT back-trajectories, we track these events across multiple Mediterranean sites. Results reveal clear regional differences in dust optical properties, such as aerosol optical depth, single scattering albedo, and asymmetry factor, arising from source regions and transport processes. Saharan events are dominated by coarse, scattering mineral dust, while the Middle East event featured finer, more absorbing particles, likely influenced by anthropogenic sources. MIDAS DOD-to-AOD ratios indicate that only one East-Central Saharan event maintained high dust fractions (DOD-to-AOD > 0.8), suggesting relatively pure dust, while other events exhibited stronger spatial variability, with the Middle East event showing the lowest ratios, reflecting enhanced mixing with anthropogenic or marine aerosols. A regional case study in Cyprus using in situ elemental and absorption
measurements shows that Middle East dust, despite lower mass concentrations, exhibits stronger absorption than Saharan dust.
METAL-WRF mineralogical simulations indicate broadly similar dominant mineral fractions (silicates and calcium-rich minerals) across events, suggesting that optical variability was mainly driven by dust-to-total aerosol ratio and mixing state rather than mineralogy. UAV-based composition data further validate modeled variability, although discrepancies in aluminum and magnesium highlight limitations in current dust representations.