ASSESSING THE OH-INITIATED BREAKDOWN CHEMISTRY OF CAMPHENE AND 3-CARENE UNDER NOX-FREE SIMULATED ATMOSPHERIC CONDITIONS

Camphene and 3-carene are key atmospheric monoterpenes used in cosmetics, fragrances, and food flavouring. In order to assess their impacts on human health and the environment it is essential to have a thorough understanding of the degradation mechanisms involved in their reactivity. The present study aimed to investigate the OH radicals initiated atmospheric degradation of camphene and 3-carene under simulated NOx-free conditions. The experiments were conducted using facilities provided by the 760 L Environmental Simulation Chamber made of Quartz (ESC-Q-UAIC) together with state-of-the-art instruments, including a proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS, model 6000 X2, IONICON) coupled with an aerosol chemical composition analyzer (CHARON). In the present study, the rate constants of the reactions of camphene and 3-carene with OH radicals were determined to be (7.81 � 0.95) ? 10-11 cm3 molecule-1 s-1 and (5.37 � 0.60) ?10-11 cm3 molecule-1 s-1, respectively. The obtained kinetic results, based on the relative rate technique with propene and 1,3,5-trimethylbenzene as reference compounds, are in agreement with the values reported in the literature. The measurements performed with the PTR-ToF-MS with CHARON particle inlet demonstrated that the photooxidation processes of camphene and 3-carene result in the formation of low-volatile species which play a significant role in the formation of secondary organic aerosols. Among the identified photooxidation products, camphenilone (C9H14O) and caronaldehyde (C10H16O2) were assigned to the signals at the mass-to-charge ratio values of 139.112 Da and 169.122 Da, respectively, in both gas- and aerosol-phase measurements. The findings of this study will offer crucial insights to be incorporated into the Master Chemical Mechanism (MCM) for the detailed description of the gas-phase chemical processes involved in the tropospheric degradation of camphene and 3-carene, which are currently lacking.