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

Abstract

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.

Odors Attracting the Long-Legged Predator Medetera signaticornis Loew to Ips typographus L. Infested Norway Spruce Trees

“…According to the literature, cutting induces changes in the volatile composition, such as increased release of oxygenated monoterpenes (Strömvall and Petersson 1991;Pettersson and Boland 2003). Mechanical damage increases the release of volatile terpenes from host trees that can auto-oxidize when exposed to the air generating more oxygenated monoterpenes (Keeling and Bohlmann 2006;Benoid et al 2021). In addition, exposed wounds can be contaminated with various types of microorganisms that can contribute to the emission of compounds from cut trees.…”

Odours attracting Medetera (Diptera) predators to spruce bark beetles in a multitrophic system

“…According to the literature, cutting induces changes in the volatile composition, such as increased release of oxygenated monoterpenes (Strömvall and Petersson 1991;. Mechanical damage increases the release of volatile terpenes from host trees that can auto-oxidize when exposed to the air generating more oxygenated monoterpenes Benoid et al 2021). In addition, exposed wounds can be contaminated with various types of microorganisms that can contribute to the emission of compounds from cut trees.…”

Autoxidation of glycols used in inhalable daily products: implications for the use of artificial fogs and e-cigarettes

“…34 Soon, this process was identied as the critical process to produce highly oxygenated organic molecules, including the production of carbonyls and organic acids from biogenic gaseous monoterpenes. [35][36][37] While autoxidation was associated with numerous compounds, such chemical processes on glycols did not gather enough attention in the past. Additionally, the oxidation of TEG is one of the major concerns in the natural gas dehydration industry, 38 leading to signicantly reduced productivity.…”