Přehled o publikaci

Black carbon (BC) is a dominant aerosol light absorber, and its brown carbon (BrC) coating can enhance absorption and lead to uncertainties concerning the radiative forcing estimation. This study investigates the mass absorption cross-section of equivalent BC (MAC(eBC)) during a long-term field measurement (2013-2017) at a rural Central European site. The MAC enhancement factor (E-abs) and the contribution of BrC coatings to the absorption coefficient (B-abs) were estimated by combining different approaches. The annual mean B-abs and MAC(eBC) values decreased slightly over the measurement period associated with change in the submicron aerosol size distribution. Regardless of the wavelength, B-abs exhibited clear seasonal and diurnal variations, with higher values in winter when a higher absorption Angstromexponent (1.4) was observed due to the local biomass burning (BB). In contrast, MACeBC did not have a distinct temporal trend at 600 nm (7.84 +/- 2.79 m(2) g(-1)), while it showed a seasonal trend at 370 nm with higher values in winter (15.64 +/- 4.77 m(2) g(-1)). During this season, E-abs_(660) was 1.18 +/- 0.27 and did not exhibit any clear wavelength dependence, despite the influence of BB. During the study period, BrC-attributed absorption was observed in 31% of the samples, with a contribution of up to 40% of total Babs. In summer, the E-abs_(660) increased to 1.59 +/- 0.60, when a larger BC coating could be formed by secondary aerosol fractions. During this season, MAC(eBC)_ (660) and E-abs_(660) showed comparable source profiles that were mainly associated with aged air masses over central Europe, thereby supporting the fact that characteristics of coating materials formed during atmospheric aging are a major factor driving the MAC(eBC)_(660) measured at the regional background site. Further field investigations of the composition of BC coatings would help to better understand and estimate uncertainties related to the radiative effect of aerosols.