Effect of Product Cross-Reactions from Oxidation of Cyclic and Acyclic Monoterpene Mixtures on Secondary Organic Aerosol

SIJIA LIU, Sergey Nizkorodov, Celia Faiola, University of California, Irvine

     Abstract Number: 616
     Working Group: Aerosol Chemistry

Abstract
Plants produce up to 1 million secondary metabolites that function in growth, defense, and reproduction. Biogenic volatile organic compounds (BVOCs) are the metabolites emitted from plants to the atmosphere. The shifting of BVOC emission profiles in stressed environments (e.g., drought, herbivory and pollution stress) changes chemical composition, hygroscopicity, and optical properties of SOA formed fr, prompting the change in aerosol climate effects. Previous studies have investigated aerosol chemistry extensively using a single reference compound, such as α-pinene to represent a conifer system. In this study, photooxidation of mixtures of cyclic (limonene) and acyclic (b-myrcene) monoterpenesare used to probe the effect of RO2-RO2 cross-reactions on SOA composition and properties. SOA was prepared in a smog chamber from mixtures representing a range of reactivity ratios of myrcene/limonene while keeping the overall OH reactivity constant. The chemical composition of gas-phase SOA precursors was analyzed using proton-transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS) and thermal desorption–gas chromatography–mass spectrometry (TD-GC-MS). The physico-chemical properties of SOA were measured using a scanning mobility particle sizer (SMPS), and offline ultra-high performance liquid chromatography coupled to high-resolution mass spectrometry (UHPLC-HRMS). The preliminary data suggest that mixtures with higher myrcene/limonene reactivity ratios have higher dimer/monomer ratios in the SOA particles. The inferred volatility for the systems dominated by myrcene (>50%reactivity) is also lower compared to the mixtures dominated by limonene (>50% reactivity). The results are unexpected because acyclic terpenes should fragment more compared to cyclic terpenes during oxidation. Potential chemical mechanisms resulting from the interaction between acyclic/cyclic terpene oxidation products will be presented. This study will provide information to improve predictions of biogenic SOA formation from complex plant emission mixtures.