09 Dec 2022
09 Dec 2022
Status: this preprint is currently under review for the journal ACP.

Formation of highly oxygenated organic molecules from the oxidation of limonene by OH radical: significant contribution of H-abstraction pathway

Hao Luo1, Luc Vereecken2, Hongru Shen1, Sungah Kang2, Iida Pullinen2,a, Mattias Hallquist3, Hendrik Fuchs2, Andreas Wahner2, Astrid Kiendler-Scharr2, Thomas F. Mentel2, and Defeng Zhao1,4,5,6 Hao Luo et al.
  • 1Department of Atmospheric and Oceanic Sciences & Institute of Atmospheric Sciences, Fudan University, Shanghai, 200438, China
  • 2Institute of Energy and Climate Research, IEK-8: Troposphere, Forschungszentrum Jülich, Jülich, 52425, Germany
  • 3Department of Chemistry and Molecular biology, University of Gothenburg, Göteborg, 41258, Sweden
  • 4Shanghai Frontiers Science Center of Atmosphere-Ocean Interaction, Fudan University, Shanghai 200438, China
  • 5Institute of Eco-Chongming (IEC), 20 Cuiniao Rd., Chongming, Shanghai, 202162, China
  • 6CMA-FDU Joint Laboratory of Marine Meteorology, Fudan University, Shanghai 200438, China
  • anow at: Department of Applied Physics, University of Eastern Finland, Kuopio, 70210, Finland

Abstract. Highly oxygenated organic molecules (HOM) play a pivotal role in the formation of secondary organic aerosol (SOA). Therefore, the distribution and yields of HOM are fundamental to understand their fate and chemical evolution in the atmosphere, and it is conducive to ultimately assess the impact of SOA on air quality and climate change. In this study, gas-phase HOM formed from the reaction of limonene with OH radical in photooxidation were investigated in the SAPHIR chamber (Simulation of Atmospheric PHotochemistry In a large Reaction chamber) using a time-of-flight chemical ionization mass spectrometer with nitrate reagent ion (NO3-CIMS). A large number of HOM, including monomers (C9–10) and dimers (C17–20), were detected and classified into various families. Both closed-shell products and open-shell peroxy radicals (RO2), were identified under low NO (0.1 ppt–~0.2 ppb) and high NO conditions (17 ppb). C10 monomers are the most abundant HOM products and account for over 80 % total HOM. Closed-shell C10 monomers were formed from two peroxy radical familie, C10H15Ox•(x=7–12) and C10H17Ox•(x=8–13), and their respective termination reactions with NO, RO2, and HO2. While C10H17Ox• is likely formed by OH addition to C10H16, the dominant initial step of limonene+OH, C10H15Ox•, is likely formed via H-abstraction by OH. C10H15Ox• and related products contributed 43 % and 46 % of C10-HOM at low and high NO, demonstrating that H-abstraction pathways play a significant role in HOM formation in the reaction of limonene+OH. Combining theoretical kinetic calculations, structure activity relationships (SARs), literature data, and the observed RO2 intensities, we proposed tentative mechanisms of HOM formation from both pathways. We further estimated the molar yields of HOM to be 3.04−1.64+3.89 % and 0.82−0.44+1.05 % at low and high NO, respectively. Our study highlights the importance of H-abstraction by OH and provides yield and tentative pathways in the OH oxidation of limonene to simulate the HOM formation and assess their role in SOA formation.

Hao Luo et al.

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Hao Luo et al.


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Short summary
The oxidation of limonene, a common volatile emitted by trees and chemical products, by OH, a daytime oxidant, forms many highly oxygenated organic molecules (HOM), including C10–20 compounds. HOM play an important role in new particle formation and growth. HOM formation can be explained by chemistry of peroxy radicals and we found a minor branching ratio initial pathway play an unexpected and significant role. Considering this pathway enables accurate simulation of HOM and SOA concentrations.