Preprints
https://doi.org/10.5194/acp-2021-964
https://doi.org/10.5194/acp-2021-964

  02 Dec 2021

02 Dec 2021

Review status: this preprint is currently under review for the journal ACP.

Autoxidation of terpenes, a common pathway in tropospheric and low temperature combustion conditions: the case of limonene and α-pinene

Roland Benoit1, Nesrine Belhadj1,2, Maxence Lailliau1,2, and Philippe Dagaut1 Roland Benoit et al.
  • 1CNRS-INSIS, ICARE, Orléans, France
  • 2Université d’Orléans, Orléans, France

Abstract. The oxidation of monoterpenes under atmospheric conditions has been the subject of numerous studies. They were motivated by the formation of oxidized organic molecules (OOM) which, due to their low vapor pressure, contribute to the formation of secondary organic aerosols (SOA). Among the different reaction mechanisms proposed for the formation of these oxidized chemical compounds, it appears that the autoxidation mechanism, involving successive events of H-migration and O2 addition, common to both low-temperature combustion and atmospheric conditions, is leading to the formation of highly oxidized molecules (HOM). In atmospheric chemistry, the importance of autoxidation compared to other oxidation pathways has been the topic of numerous studies. Conversely, in combustion, autoxidation under cool flame conditions is the main oxidation process commonly taken into account. An analysis of oxidation products detected in both conditions was performed, using the present combustion data and literature data from tropospheric oxidation studies, to investigate possible similarities in terms of observed chemical formulae of products. To carry out this study, we chose two terpenes, α-pinene and limonene (C10H16), among the most abundant biogenic components in the atmosphere, and considered in many previous studies. Also, these two isomers were selected for the diversity of their reaction sites (exo- and endo- carbon-carbon double bonds). We built an experimental database consisting of literature atmospheric oxidation data and presently obtained combustion data for the oxidation of the two selected terpenes. In order to probe the effects of the type of ionization used in mass spectrometry analyses on the detection of oxidation products, we used heated electrospray ionization (HESI) and atmospheric pressure chemical ionization (APCI), in positive and negative modes. The oxidation of limonene-oxygen-nitrogen and α-pinene-oxygen-nitrogen mixtures was performed using a jet-stirred reactor at elevated temperature (590 K), a residence time of 2 s, and atmospheric pressure. Samples of the reacting mixtures were collected in acetonitrile and analyzed by high-resolution mass spectrometry (Orbitrap Q-Exactive) after direct injection and soft ionization, i.e. (+/−) HESI and (+/−) APCI. This work shows a surprisingly similar set of chemical formulae of products, including oligomers, formed in cool flames and under simulated atmospheric conditions. Data analysis showed that a non-negligible subset of chemical formulae is common to all experiments independently of experimental parameters. Finally, this study indicates that more than 40 % of the detected chemical formulae in this full dataset can be ascribed to an autoxidation mechanism.

Roland Benoit et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-964', Anonymous Referee #1, 23 Dec 2021
    • CC1: 'Reply on RC1', Roland Benoit, 13 Jan 2022
    • CC3: 'Reply on RC1', Roland Benoit, 13 Jan 2022
  • RC2: 'Comment on acp-2021-964', Anonymous Referee #2, 04 Jan 2022
    • CC2: 'Reply on RC2', Roland Benoit, 13 Jan 2022
    • CC4: 'Reply on RC2', Roland Benoit, 13 Jan 2022

Roland Benoit et al.

Roland Benoit et al.

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Short summary
While the oxidation kinetics of alpha-pinene and limonene have been extensively studied and mechanisms of OH and/or ozone oxidation have been proposed, further studies are needed to better understand their oxidation pathways. This work provides further insight into the oxidation mechanisms of alpha-pinene and limonene, particularly autoxidation, and presents graphical tools that are increasingly used for the processing of high resolution mass spectrometry data.
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