AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
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Experimental Investigation of the Gas- and Particle-Phase Products and Mechanism of Reaction of Δ-3-Carene with NO3 Radicals
MARLA DEVAULT, Paul Ziemann, University of Colorado
Abstract Number: 665 Working Group: Aerosol Chemistry
Abstract Oxidation products of monoterpenes have been shown to contribute to SOA formation in the atmosphere. However, the nighttime oxidative processes, which are dominated by nitrate (NO3) radical addition to alkenes, are not well understood. In order to fill this gap, we have quantified the yields of gas- and particle-phase products of the nitrate radical-initiated oxidation of Δ-3-carene, a monoterpene that is primarily released by coniferous plants. Based on these yields, we have developed a reaction mechanism and calculated branching ratios for key reaction pathways. Experiments were conducted at ambient temperature and pressure at 55% RH in a dark 8 m3 Teflon chamber using N2O5 to generate NO3 radicals via thermal decomposition. The initial monoterpene:N2O5 ratio was 3:1, deliquesced ammonium sulfate seed particles were used, and the aerosol was monitored online using an Electron Ionization Thermal Desorption Mass Spectrometer and a Scanning Mobility Particle Sizer. After reaction completion, SOA was collected onto a Teflon filter and extracted for analysis. The bulk functional group composition was determined using a set of derivatization-spectrophotometric analysis techniques and Fourier-Transform Infrared Spectroscopy. Products containing nitrate groups (comprising most of the SOA) were separated and quantified using HPLC-UV-Vis and identified using an Electrospray Ionization Mass Spectrometer, Chemical Ionization Ion-Trap Mass Spectrometer, and Electron Ionization Mass Spectrometer. Gas-phase products were collected onto an annular denuder coated with a derivatizing agent for carbonyl groups, extracted, and analyzed by the same methods. Altogether, the mechanism derived from the measured gas- and particle-phase product yields will inform regional and global models on the contribution of nighttime oxidation of monoterpenes to SOA.