Abstract View
Experimental Investigation of the Gas- and Particle-Phase Products and Mechanism of NO3 Radical Oxidation of Δ-3-Carene, α-Pinene, and Limonene
MARLA DEVAULT, Paul Ziemann, University of Colorado
Abstract Number: 125
Working Group: Aerosol Chemistry
Abstract
Oxidation products of monoterpenes have been shown to contribute to secondary organic aerosol (SOA) formation in the atmosphere. However, the nighttime oxidative processes, which are dominated by nitrate radical (NO3) addition to alkenes, are not well understood. In order to address this gap, we have measured the SOA yields and identified gas- and particle-phase products of the nitrate radical-initiated oxidation of Δ-3-carene, α-pinene, and limonene. Based on these analyses, we have developed a chemical mechanism for each monoterpene that includes both gas- and particle-phase reactions, and quantified major SOA products. Experiments were conducted at ambient temperature and pressure, at 55% RH in a dark 8 m3 Teflon chamber, and 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 particle beam mass spectrometer (EI-TDPBMS) and scanning mobility particle sizer. In addition, an iodide chemical ionization mass spectrometer measured gas-phase products. After reaction completion, SOA was collected onto Teflon filters and extracted for analysis. The bulk functional group composition was determined using a set of derivatization-spectrophotometric analysis techniques and attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy. Products containing nitrate groups, which includes most of the SOA, were separated and often quantified using high performance liquid chromatography with UV-Vis detection at 210 nm. Fractions collected based on this chromatogram were then analyzed using an electrospray ionization mass spectrometer, the EI-TDPBMS, ATR-FTIR, and derivatization-spectrophotometric techniques, leading to the identification of several acetal and hemiacetal dimer products. The mechanisms derived from the measured gas- and particle-phase products will inform regional and global models on the contribution of nighttime oxidation of monoterpenes to SOA.