Widefield fluorescence microscopy images of pine BBOA particles showed two non-crystalline phases at all values of RH studied, as the humidity was ramped from low to high RH at 293 K (Fig. ). A shell represents one organic phase and the central core is a second organic phase. Hereon we refer to the inner as the hydrophilic phase since it swelled with increasing RH. We refer to the outer phase as the hydrophobic phase since both its volume and viscosity (see below) were insensitive to the RH. The existence of multiple phases in BBOA particles is consistent with previous reports that show BBOA comprise chemical compounds with a broad range of polarities . Both phases are visible under the fluorescence microscope indicating that BrC is present in both phases. The chemical identity of the BrC in each phase is not known, although it is expected to comprise molecules formed in the breakdown of lignin and cellulose such as phenolic compounds and polycyclic aromatic hydrocarbons .