Optical Properties and Radiative Forcing Estimations of High-Altitude Aerosol Transport During Saharan Dust Events Based on Laser Remote Sensing Techniques (CLIMPACT Campaign 2021, Greece)

We present three case studies of tropospheric aerosol transport observed over the high-altitude Helmos observatory (1800–2300 m a.s.l.) in Greece during September 2021. Two cases were linked to Saharan dust intrusions, and one to a mixture of biomass burning and continental aerosols. Aerosol vertical profiles from the AIAS mobile backscatter/depolarization lidar (532 nm, NTUA) revealed distinct aerosol layers between 2–6 km a.s.l., with particle linear depolarization ratio values up to 0.30–0.40, indicative of mineral dust. The elevated location of Helmos enabled measurements of free-tropospheric layers, minimizing boundary-layer influence, and providing clearer attribution of long-range transport. Radiative impacts were quantified using the LibRadtran model. For the 27 September dust outbreak, simulations showed strong shortwave absorption within 3–7 km, peaking at 5–6 km, with surface forcing reaching −25 W/m2 and TOA forcing around −12 W/m2, implying a net cooling of the Earth–atmosphere system. In contrast, the 30 September biomass burning case produced substantial solar attenuation, a surface heating rate of 2.57 K/day, and a small positive forcing aloft (~0.05 K/day). These results emphasize the contrasting radiative roles of dust and smoke over the Mediterranean and the importance of high-altitude observatories for constraining aerosol–radiation interactions.