PTR-ToF-MS data
Volatiles were analyzed with a PTR-ToF-MS 8000 (IoniconAnalytik GmbH, Innsbruck, Austria) using H3O+ as reagent ion for the proton transfer reaction. The reaction takes place between H3O+ ions and all the biogenic or anthropogenic VOCs having a proton affinity higher than that of water (165.2 kcal mol−1). Separation of single ions happens accordingly to their mass to charge (m/z) ratio. Drift applied voltage was set at 600 V, temperature at 110 °C, and pressure at 2.25 mbar. For each sample, about 6 grams of material was transferred in a glass jar provided with a special lid that allowed Teflon connection to a zero-air generator (inlet) and the PTR-ToF system (outlet). The head space was then measured by direct injection into the PTR-ToF drift tube inlet for 150 seconds, after respectively 1 and 20 min of exposure.
Preliminary measurements on an empty jar were run before every experiment and used for background subtraction. All mass spectra up to m/z = 315 were simultaneously detected and recorded with 1 s as integration time. Internal calibration was based on m/z = 18.0338 (NH4+), m/z = 21.0202 (H318O+) and m/z = 29.9974 (NO+).