Seasonality of aerosol light−scattering properties and dominant types at a continental background site in the Southern Balkans (Kozani, NW Greece)

This study presents the first comprehensive year-long analysis of aerosol light-scattering properties and type classification at a continental background site in northwestern Greece, addressing a critical observational gap in the southern Balkans, while identifies the dominant seasonal aerosol regimes and their controlling processes in this climatically transitional region. Continuous measurements of scattering and absorption coefficients were conducted in 2023 at the University of Western Macedonia. The annual mean scattering coefficient at 525 nm (b sca,525 ) was 32.9 Mm -1 , with a summer maximum (41.8 Mm -1 ) linked to secondary aerosol formation and dust resuspension, and a spring minimum (27.7 Mm -1 ) coinciding with wet removal. The scattering Ångström exponent (SAE 450-525 ) averaged 1.65, peaking in spring–summer and reaching a minimum in autumn, reflecting seasonal shifts in particle size. The mean single scattering albedo (SSA 525 ) was 0.88±0.06 with weak spectral dependence, consistent with moderately absorbing aerosols; the asymmetry factor peaked in summer (g 525 : 0.67; annual mean: 0.60). Diurnal cycles revealed midday scattering enhancements likely attributed to new particle formation in summer, and SSA reductions during morning (traffic effect) and evening in winter due to residential wood burning (RWB) emissions. Aerosol-type classification combined SAE, SSA, and the absorption Ångström exponent (AAE) to distinguish dominant regimes. BC-dominated aerosols prevailed annually (38%), with winter influenced by BC/BrC mixtures from RWB (68%), summer by BC-dominated types (79%), and autumn by coarse BC–dust mixtures (32%). Atmospheric conditions reflected mostly low-to-moderate aerosol burden, while episodic pollution events in winter indicate fresh RWB emissions. Compared with urban Mediterranean sites, aerosols in Kozani are generally more scattering and less absorbing, presenting similar characteristics with regional/background sites in Europe. These findings provide a reference dataset for southeastern Europe, reduce uncertainties in aerosol radiative forcing, and offer a benchmark for assessing the impacts of biomass burning in a recognized climate-change hotspot. • First year-long study of aerosol scattering in the Southern Balkans. • Winter is dominated by BC/BrC from wood burning; summer by BC. • Autumn aerosols are coarse BC–dust mixtures with low SAE. • Episodic pure BrC events in winter reflected fresh biomass burning. • Background aerosols in the region are more scattering and less absorbing.