Supplementary material to "Influence of Tropospheric Temperature on the Formation and Aging of Secondary Organic Aerosol from Biogenic Vapor Mixtures"

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Section S1.Instruments, particle collection approach, and discussion of potential sampling artifacts in this work S1.1 Instruments SOA concentration was online detected by a high-resolution time-of-flight Aerosol Mass Spectrometer (HR-AMS, Aerodyne Inc.).The HR-AMS employs electron impact (EI) ionization, a hard ionization method that induces extensive fragmentation of organic molecules, being able to provide quantitative information on the bulk mass of organic aerosol but lacks molecular-level information.In addition, the particle-phase chemical composition of SOA was detected by a chemical ionization mass spectrometer (CIMS) coupled with a filter inlet for gas and aerosols (FIGAERO) using iodide (I -) as reagent ions with 1 Hz time resolution (Lopez-Hilfiker et al., 2014;Lee et al., 2014).FIGAERO-iodide-CIMS uses a soft ionization technique that is highly sensitive to polar and oxygenated organic compounds.Consequently, the organic aerosol components detected by CIMS represent a subset of the total organic aerosol, specifically those that are oxygenated organic compounds (Lee et al., 2014).The chemical composition measured by the HR-AMS and FIGAERO-iodide-CIMS is expected to be consistent, as the nature of SOA is oxygenated.However, the sensitivity of FIGAERO-iodide-CIMS towards different organic compounds varies significantly, inhibiting a quantification of individual molecules or the sum of the compounds detected by FIGAERO-iodide-CIMS without extensive calibration.Data analysis was done using Tofware 3.2.2(Aerodyne).Note that the reagent ion I -(m/z = 126.904)was subtracted from the molecular mass weights presented in this work.The mass resolution of FIGAERO-CIMS was 4000.Formulas were assigned with a mass accuracy of better than 20 ppm based on the mass resolution.We also note that the sensitivity of FIGAEROiodide-CIMS is highly dependent on the functionalities of the organic compounds and can vary by orders of magnitudes (Lopez-Hilfiker et al., 2016a;Lee et al., 2014;Riva et al., 2019).Therefore, the results shown in this work are based on signal intensities but not mass concentrations. S1.2 Particle collection approachThe particle data presented in this work stems from offline analysis.Particles were collected on Polytetrafluorethylene (PTFE, 1 µm, SKC Inc.) filters with a sampling flow of 6.4 L/min for 5 minutes, when particle concentrations stabilized during the experiments.The number of samples obtained at each temperature was as follows: one at 213 K, three at 243 K, and two each at 273 K, 298 K, and 313 K.In addition, one filter was sampled after warming was completed.The filter samples were analyzed using a FIGAERO-iodide-CIMS. Thermal desorption was performed under a flow of ultra-high-purity nitrogen as the carrier gas.The temperature was first ramped from 296 K to 473 K over 15 min and then held at 473 K for an additional 20 min, resulting in a total desorption time of 35 min (Lopez-Hilfiker et al., 2016a;Lee et al., 2014;Riva et al., 2019). S1.3 Discussion of potential sampling artifacts in this workThe filter sampling setup and all instruments were installed in the laboratory outside the chamber at room temperature (295±2 K).To minimize the effect of temperature differences between the chamber temperatures (213 K, 243 K, 273 K, 298 K, 313 K) and room temperature on the gas-phase chemical composition, the sampling line to the CIMS was partially insulated and the residence time in the Teflon sampling line was only 2 s.The residence time in the stainless-steel line for filter sampling was about 1 s.The sampling time of Telflon filters at all experiments were typically 5 minutes plus a few minutes of handling time before the sample

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