To detect the gas phase molecules emitted by the SOA material while heating, we connected a Vocus PTR-ToF-MS (Tofwerk/Aerodyne) to the temperature-controlled cell discussed above using a 1/4" OD fluorinated ethylene-propylene (FEP) sample line. A stream of nitrogen air (1000 sccm) continuously flowed through the temperature-controlled cell and into the Vocus to detect gas-phase molecules. Prior to each experiment, the temperature-controlled cell was thoroughly cleaned with isopropyl alcohol and dried with clean air.