Exceptional wildfire smoke over Greece in summer 2023: a synergistic study of aerosol optical-microphysical and UVB radiative impacts

Abstract. During summer 2023, Greece experienced one of its most severe wildfire seasons in recent decades, with widespread fires across Evros, Rodopi, Attica, the Peloponnese, and several islands. This study investigates the aerosol optical and microphysical properties, as well as the impact on ground-level ultraviolet-B (UVB) radiation over Athens, focusing on two major wildfire episodes (18–21 July and 22–25 August). A synergistic approach was deployed, combining satellite imagery (MODIS), FLEXPART simulations, ground-based remote sensing, and in situ aerosol and radiation measurements. Elevated aerosol optical depths (AOD) up to 1.2, high fine-mode fractions (> 0.85), and Ångström exponents above 1.5 indicated a strong dominance of fine biomass burning aerosols. The Single scattering albedo (SSA) ranged from 0.85 to 0.98, showing enhanced absorption during biomass burning periods and weaker absorption when smoke was mixed with dust. At 320 nm, dust presence resulted in stronger absorption, with SSA below 0.8 for pure dust cases compared to smoke mixtures. Particle linear depolarization ratios (PLDR), varied between 0.03 and 0.20, with higher values (~0.10–0.20) reflecting the presence of non-spherical dust particles, and lower values (~0.03–0.08) indicating spherical smoke particles. Ground-level UVB irradiance decreased by up to 50 % during peak smoke episodes, highlighting strong aerosol radiative impacts. Concurrently, PM₁₀ and PM_2.5 concentrations increased to 94 and 49 µg m^-3, respectively, while organic aerosols peaked at 22.77 µg m^-3, consistent with intense fire activity. FLEXPART simulations confirmed long-range transport of smoke from active fire regions, with additional contributions from regional pollution and Saharan dust.