BB-SOA was produced in a continuous-flow environmental chamber from the oxidation of catechol, syringol, or guaiacol with OH, and the oxidation of catechol with O3. SOA from O3 oxidation of guaiacol and syringol was not studied because these reactions are much less important than OH oxidation of guaiacol and syringol in the atmosphere (Table ). All of the SOA studied here was generated via OH or O3 oxidation under NOx-free conditions. While high-NOx conditions are relevant for high temperature wildfires, low NOx conditions are relevant for lower temperature wildfires. In addition, low temperature wildfires produce more phenolic VOCs than high temperature wildfires. The environmental chamber used to generate the SOA consisted of a 1.8 m 3 Teflon bag housed in an aluminum enclosure as described in detail elsewhere. The chamber was operated in continuous flow mode, where a pure air generator was used to supply air for the chamber at a flow rate of ~18 L min -1 , yielding a residence time of ~1.7 h. At the chamber inlet, the flow from the pure air generator was split between two lines; one line for the VOC and one line for the oxidant.