Abstract View
First-Generation Alkyl and Alkoxy Radical Fates Foreshadow SOA Yields from Cyclic Monoterpenes
DANIELLE C. DRAPER, Thomas Almeida, Michelia Dam, Nanna Myllys, Theo Kurten, James Smith, University of California, Irvine
Abstract Number: 171
Working Group: Aerosol Chemistry
Abstract
It is widely accepted that oxidation of monoterpenes can be a significant source of secondary organic aerosol (SOA). However, numerous studies have shown that different combinations of monoterpenes and oxidants can lead to drastically different SOA yields, and this observation is still poorly understood from a mechanistic perspective. NO3 radical oxidation of cyclic monoterpenes (e.g. α-pinene , β-pinene, Δ-carene, sabinene, limonene) is one such example where reported experimental SOA yields range from 0% to >100% for different monoterpenes. Using quantum chemical calculations of unimolecular reaction kinetics, we have determined that the fate of the first-generation alkyl and/or alkoxy radical are quite different for each of these structurally similar molecules. Radical intermediates such as these can either continue propagating through additional oxidation steps or may terminate from uni- or bi-molecular chemistry. Our results show that the monoterpenes with higher observed SOA yields generate radical intermediates with readily available radical propagation pathways, whereas those with lower yields have dominant termination pathways early in the oxidation mechanism. These computational mechanisms are supported with chemical ionization mass spectrometry (CIMS) measurements during monoterpene+NO3 chamber experiments. While specifically applied to organonitrate radical intermediates in this study, this inter-monoterpene comparison provides valuable insight for mechanism development for other oxidant / monoterpene systems as well.