Variability in the mass absorption cross-section of black carbon (BC) aerosols is driven by BC internal mixing state at a central European background site (Melpitz, Germany) in winter. - Jinfeng Yuan; Modini, Robin Lewis; Zanatta, Marco; Herber, Andreas B.; Müller, Thomas; Wehner, Birgit; Poulain, Laurent; Tuch, Thomas; Baltensperger, Urs; Gysel-Beer, Martin (Atmospheric Chemistry & Physics Discussions, 2020)