A European aerosol phenomenology - 9: Light absorption properties of carbonaceous aerosol particles across surface Europe

Abstract

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.

Keywords: Air quality; European overview; Light absorption; Long-term datasets; Organic aerosols.