Images of BBOA retrieved using a confocal laser scanning fluorescence microscope also clearly show the presence of two phases (Fig. ). The image in the y-z plane shows a partial ellipsoid (contact angle 125 °) within a spherical calotte (contact angle 72 °). Due to the contact angles of the two phases with the glass slide, the outer phase is either very thin or not continuous at the top of the BBOA particle (less than the resolution of the microscope). Similar morphologies have been observed for phase-separated particles deposited on substrates . As the particles in this work are deposited on substrates, the resulting morphology is influenced by the glass slide. Atmospheric particles that contain two phases are expected to exhibit a core-shell or partially-engulfed morphology when suspended in the atmosphere . Previous work has shown that particles deposited on hydrophobic substrates with morphologies similar to those shown here have core-shell morphologies when levitated in the gas phase , however, experiments are needed to confirm this for BBOA.