Unveiling Light-Absorbing Carbonaceous Aerosols at a Regional Background Site in Southern Balkans

This study examines the seasonality of Black Carbon (BC) and Brown Carbon (BrC) spectral absorption characteristics at a continental background site (Kozani) in southern Balkans (NW Greece). It aims to assess the seasonality and impact of different sources on light absorption properties, BC concentrations, and the fraction of BrC absorption. Moderate-to-low BC concentrations were observed, ranging from 0.05 µg m−3 to 2.44 µg m−3 on an hourly basis (annual mean: 0.44 ± 0.27 µg m−3; median: 0.39 µg m−3) with higher levels during winter (0.53 ± 0.33), reflecting enhanced emissions from residential wood burning (RWB) for heating purposes. Atmospheric conditions are mostly clean during spring (MAM) (BC: 0.34 µg m−3), associated with increased rainfall. BC components associated with fossil fuel combustion (BCff) and biomass burning (BCbb), maximize in summer (0.36 µg m−3) and winter (0.28 µg m−3), respectively, while the absorption Ångstrôm exponent (AAE370–880) values ranged from 1.09 to 1.93 on daily basis. The annual mean total absorption coefficient (babs,520) inferred by aethalometer (AE33) was 4.09 ± 2.65 Mm−1 (median: 3.51 Mm−1), peaking in winter (5.30 ± 3.35 Mm−1). Furthermore, the contribution of BrC absorption at 370 nm, was also high in winter (36.7%), and lower during the rest of the year (17.3–29.8%). The measuring station is located at a rural background site 4 km outside Kozani City and is not directly affected by traffic and urban heating emissions. Therefore, the regional background atmosphere is composed of a significant fraction of carbonaceous aerosols from RWB in nearby villages, a characteristic feature of the Balkan’s rural environment. Emissions from the lignin-fired power plants, still operating in the region, have decreased during the last years and moderately affect the atmospheric conditions.