SOA was generated from the dark ozonolysis of catechol in a continuous-flow environmental chamber, described in detail elsewhere. In addition, α-pinene + O3 SOA was generated by the dark ozonolysis of α-pinene in the same environmental chamber and used as a reference system for some of the experiments. For the remainder of the document, we refer to catechol + O3 SOA and α-pinene + O3 SOA as just catechol SOA and α-pinene SOA, respectively.