For the VOC line, the pure air flowed through a heated (T = ~373 K) round bottom flask and into the chamber. A solution of 2 wt% VOC (catechol, syringol, or guaiacol) was continuously injected from a glass syringe into the flask at a rate of 30-75 µL h -1 using a syringe pump. For experiments with OH oxidation, the solvent was Milli-Q water. For experiments with O3 oxidation, the solvent was 2-butanol, which acted as a scavenger for OH radicals, which can be formed during ozonolysis reactions. The oxidant supply line was set up differently depending on the oxidant being used. For OH oxidation, a 30 wt% solution of H2O2 in Milli-Q water was continuously injected (120 µL h -1 ) into a second heated (T = 303 K) round bottom flask, and the vapors were carried into the chamber with the pure air flow (2 L min -1 ). To induce H2O2 photolysis in the environmental chamber, 24 UV-lights (40W, λmax ~ 360 nm) surrounding the Teflon bag were turned on for the duration of the experiment to generate OH radicals. For O3 oxidation, the pure air instead flowed (1.25 L min -1 ) through an ozone generator which then entered the chamber. For all our ozonolysis experiments, excess O3 concentrations were measured at the chamber outlet to be 360-390 ppb using an O3 monitor (Thermo Scientific, 49i).