Hantschke, Luisa Lamberta ORCID: 0000-0002-8417-5531 (2022). Oxidation of monoterpenes studied in atmospheric simulation chambers. PhD thesis, Universität zu Köln.
PDF
Dissertation_Energie und Umwelt 589 Hantsche, Luisa Lamberta.pdf Bereitstellung unter der CC-Lizenz: Creative Commons Attribution. Download (23MB) |
Abstract
Monoterpenes are volatile organic compounds (VOC) that are emitted into the atmosphere from biogenic sources, such as trees and vegetation, or from anthropogenic sources, such as consumer care products. The mean global emission of monoterpenes is estimated to be 160 Tg a year. In the atmosphere, the monoterpenes react with the main oxidants, the OH radical, ozone (O3), or nitrate radicals (NO3). Products of these oxidation reactions influence the atmospheric composition. Especially formation and growth of organic aerosols and the formation of ozone can have effects on air quality, human health and climate warming. The oxidation of atmospheric organic compounds by the OH radical initiates a radical chain reaction that involves hydroperoxy radicals (HO2) and organic peroxy radicals (RO2, R=organic group). Depending on the environment, the RO2 radicals can either undergo bimolecular reactions with NO, HO2 or other RO2, or unimolecular reactions. Unimolecular reactions of RO2 include H-shift reactions and endocyclizations. From these autoxidation reactions, higher oxidized species can be formed rapidly. Whether unimolecular reactions of RO2 are competitive with bimolecular reactions is also highly dependent on the molecules structure. Detailed knowledge about the oxidation mechanism of atmospherically relevant species is crucial for understanding the atmospheres’ oxidation capability. This thesis aims to elucidate some key aspects of the oxidation mechanism of three monoterpenes, β-pinene, myrcene and Δ3-carene. The oxidation mechanisms of myrcene, Δ3-carene and caronaldehyde, a main daytime product of the oxidation of Δ3-carene, were investigated in a total of 10 experiments conducted in the atmospheric simulation chamber SAPHIR (Simulation of Atmospheric PHotochemistry In a large Reaction chamber). A large set of analytical instruments was used in every experiment, allowing the measurement of the concentrations of OH, HO2 and RO2 radicals as well as OH reactivity, VOC mixing ratios and mixing ratios of NO, NO2, HONO and oxidation products. Physical parameters such as the temperature, relative humidity and radiation parameters were also measured. The analysis of the experimental results included the determination of reaction rate constants, product yields and radical budgets. The reaction rate constants determined for the reactions of myrcene and Δ3-carene with OH and for the ozonolysis of Δ3-carene were in good agreement with previously reported values. A new method for the determination of organic nitrate yields in experiments in the SAPHIR chamber was developed. Organic nitrates are formed from the reaction of RO2 with NO. Due to their usually low vapour pressure, they are prone to condense on atmospheric particles, thereby contributing to the growth and formation of secondary organic aerosols. The nitrate yield of organic nitrates formed in the oxidation of Δ3-carene was reported in the gas phase for the first time. The measured yields were compared to values obtained from structure-activity relationship (SAR) considerations. The results of these comparisons showed discrepancies between the SAR estimates and the results obtained in the experiments, underlining the importance of the investigations of oxidation mechanisms of individual monoterpenes. The analysis of the radical budgets revealed that there are no unknown but relevant radical reformation reactions in the oxidation of Δ3-carene for the experimental conditions in the SAPHIR chamber (298 K, low NO mixing ratios). Contrary, the analysis of the experiments investigating the oxidation of myrcene indicates that there are unknown radical formation reactions for the conditions in the chamber experiments (298 K, low NO mixing ratios). It can be assumed that unimolecular reactions of the RO2 formed in the oxidation of myrcene may be the source of the missing radical formation processes due to structural similarities of myrcene to isoprene. Unimolecular reactions have been shown to be of high importance in the oxidation of isoprene. The oxidation of β-pinene was studied in the SAPHIR-STAR chamber at Forschungszentrum J¨ulich and at the free-jet flow system at the TROPOS institute in Leipzig. The initially formed RO2 radical and the RO2 radicals formed in two subsequent unimolecular reactions as well as the bimolecular reaction products of all three RO2 families were measured by a CIMS (chemical ionization mass spectrometry) instrument applying a recently developed detection scheme using protonated primary amines. The development of the CIMS based detection scheme for the use at the SAPHIR-STAR chamber was realized in this thesis. The RO2 radical ratios obtained in the experiments in the free-jet flow system were compared to ratios of the RO2 radicals obtained from a model run using a published β-pinene oxidation mechanism including reaction rate constants of unimolecular reactions. The reaction rate constants of the unimolecular reactions leading to the formation of highly oxidized RO2 radicals were experimentally determined for the first time. The results obtained in this thesis contribute to further understand the importance of unimolecular reactions in the oxidation mechanisms of the investigated monoterpenes. Furthermore, the use of newly developed techniques for the measurement of RO2 radicals, key species in the oxidation of monoterpenes, is shown to be a powerful tool for the further improvement of our understanding of the atmospherically relevant oxidation processes.
Item Type: | Thesis (PhD thesis) | ||||||||
Translated abstract: |
|
||||||||
Creators: |
|
||||||||
URN: | urn:nbn:de:hbz:38-640667 | ||||||||
Series Name: | Schriften des Forschungszentrums Jülich, Reihe Energie & Umwelt | ||||||||
Volume: | 589 | ||||||||
Date: | November 2022 | ||||||||
Publisher: | Forschungszentrum Jülich GmbH, Zentralbibliothek, Verlag | ||||||||
Place of Publication: | Jülich | ||||||||
ISSN: | 1866-1793 | ||||||||
ISBN: | 978-3-95806-653-3 | ||||||||
Language: | English | ||||||||
Faculty: | Faculty of Mathematics and Natural Sciences | ||||||||
Divisions: | Außeruniversitäre Forschungseinrichtungen > Forschungszentrum Jülich | ||||||||
Subjects: | Chemistry and allied sciences | ||||||||
Uncontrolled Keywords: |
|
||||||||
Date of oral exam: | 26 August 2022 | ||||||||
Referee: |
|
||||||||
Refereed: | Yes | ||||||||
URI: | http://kups.ub.uni-koeln.de/id/eprint/64066 |
Downloads
Downloads per month over past year
Export
Actions (login required)
View Item |