The objective of this work was to assess the yearly contribution of fossil fuel combustion (BC_ff) and wood burning (BC_wb) to equivalent black carbon (eBC) concentrations, in Athens, Greece. Measurements were conducted at a suburban site from March 2013 to February 2014 and included absorption coefficients at seven wavelengths and PM_2.5 chemical composition data for key biomass burning markers, i.e., levoglucosan, potassium (K) and elemental and organic carbon (EC, OC). A well-documented methodology of corrections for aethalometer attenuation coefficients was applied with a resulting annual dataset of derived absorption coefficients for the suburban Athens’ atmospheric aerosol. The Aethalometer model was applied for the source apportionment of eBC. An optimum Ångström exponent for fossil fuel (α_ff) was found, based on the combined use of the model with levoglucosan data. The measured eBC concentrations were equal to 2.4 ± 1.0 μg m⁻³ and 1.6 ± 0.6 μg m⁻³, during the cold and the warm period respectively. The contribution from wood burning was significantly higher during the cold period (21 ± 11%, versus 6 ± 7% in the warm period). BC_ff displayed a clear diurnal pattern with a morning peak between 8 and 10 a.m. (during morning rush hour) and a second peak during the evening and night hours, due to the shallowing of the mixing layer. Regression analysis between BC_wb concentrations and biomass burning markers (levoglucosan, K and OC/EC ratio) supported the validity of the results.

Black Carbon (BC) aerosol is a major climate forcer in the Arctic. Here, we present 15 years (2001–2015) of surface observations of the aerosol absorption coefficient b_abs (corresponding to Equivalent BC), obtained at the Zeppelin Observatory, Ny Ålesund, Svalbard, coupled with backward transport modeling with Flexpart in order to calculate the Potential Source Contribution Function (PSCF) for BC. The observed long‐term variability superimposed on a strong annual cycle is studied as a function of large‐scale circulation patterns represented by monthly index values for the North Atlantic Oscillation (NAO) and the Scandinavian pattern (SCAN). We find a 35% increase of b_abs values at Zeppelin during the SCAN⁻ phase in the winter half‐year compared to the SCAN⁺ phase but no significant difference in b_abs values between the NAO index phases. Both NAO and SCAN induce significant regional variability on the areas of origin of b_abs, mainly Siberia, Europe, and North America.

Carbonaceous aerosols (CA), composed of black carbon (BC) and organic matter (OM), significantly impact the climate. Light absorption properties of CA, particularly of BC and brown carbon (BrC), are crucial due to their contribution to global and regional warming. We present the absorption properties of BC (b_Abs,BC) and BrC (b_Abs,BrC) inferred using Aethalometer data from 44 European sites covering different environments (traffic (TR), urban (UB), suburban (SUB), regional background (RB) and mountain (M)). Absorption coefficients showed a clear relationship with station setting decreasing as follows: TR > UB > SUB > RB > M, with exceptions. The contribution of b_Abs,BrC to total absorption (b_Abs), i.e. %Abs_BrC, was lower at traffic sites (11-20 %), exceeding 30 % at some SUB and RB sites. Low AAE values were observed at TR sites, due to the dominance of internal combustion emissions, and at some remote RB/M sites, likely due to the lack of proximity to BrC sources, insufficient secondary processes generating BrC or the effect of photobleaching during transport. Higher b_Abs and AAE were observed in Central/Eastern Europe compared to Western/Northern Europe, due to higher coal and biomass burning emissions in the east. Seasonal analysis showed increased b_Abs, b_Abs,BC, b_Abs,BrC in winter, with stronger %Abs_BrC, leading to higher AAE. Diel cycles of b_Abs,BC peaked during morning and evening rush hours, whereas b_Abs,BrC, %Abs_BrC, AAE, and AAE_BrC peaked at night when emissions from household activities accumulated. Decade-long trends analyses demonstrated a decrease in b_Abs, due to reduction of BC emissions, while b_Abs,BrC and AAE increased, suggesting a shift in CA composition, with a relative increase in BrC over BC. This study provides a unique dataset to assess the BrC effects on climate and confirms that BrC can contribute significantly to UV-VIS radiation presenting highly variable absorption properties in Europe.