EC-06. Particle-Phase Products of Δ-3-Carene Oxidation by NO3 Radicals in the Atmosphere

Abstract
Oxidation products of monoterpenes have been shown to contribute to SOA formation in the atmosphere. However, the nighttime oxidative processes, often dominated by nitrate radical addition to alkenes, are not well understood. In order to fill this gap, we have identified and quantified the major particle-phase products of the nitrate radical oxidation of Δ-3-carene, a monoterpene that is primarily released by coniferous plants. Reactions for this study took place in an 8 m3 Teflon chamber at a monoterpene:nitrate radical ratio of 3:1, with 55% RH, and deliquesced ammonium sulfate seed. Online particle-phase measurements were taken using an electron ionization thermal desorption mass spectrometer and scanning mobility particle sizer. After reaction completion, SOA was collected onto Teflon filters. Bulk measurements of functional group contributions were taken using attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy and a set of derivatization-spectrophotometric analysis techniques. After separation on an HPLC, individual particle-phase products were identified using an electrospray ionization mass spectrometer, ATR-FTIR and derivatization-spectrophotometric analyses. When possible based on HPLC separation, products were quantified. The mechanism that results from these measurements and expected reactivity is supported by online gas-phase measurements from an iodide chemical ionization mass spectrometer. Notably, we have measured an ROOR dimer in both the gas- and particle-phases. Overall, the vast majority of particle-phase products of this Δ-3-carene oxidation are acetal dimers, which aligns with measurements of an analogous study of β-pinene.