We generated BBOA particles by heating pine wood to 400 °C in a quartz furnace tube leading to smoldering combustion only (no flaming). The resulting BBOA was sampled onto glass slides coated with a hydrophobic and oleophobic coating for a high contact angle between particles and substrate. The RH-dependent phase behavior was then observed by placing the slide into a flow cell with temperature and RH control coupled to a widefield fluorescence microscope.