Rosanka, Simon 
ORCID: 0000-0001-5929-163X
(2021).
A comprehensive assessment of the influence of oxygenated volatile organic compounds on the atmospheric composition.
PhD thesis, Universität zu Köln.
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Abstract
Global atmospheric chemical models are an important tool to improve our understanding of the Earth’s atmospheric processes and to address the influence of anthropogenic activities on the Earth’s climate. In this context, one of the most important greenhouse gases is ozone (O3), whose photochemical production in the troposphere is fueled by volatile organic compounds (VOCs). An important sub-group of VOCs are oxygenated VOCs (OVOCs), which are photolabile and water soluble. Thus, a realistic simulation of tropospheric O3 in global atmospheric models also relies on the realistic representation of OVOCs. The overall objective of this thesis is to provide a comprehensive assessment of the influences of OVOCs on the atmospheric composition, by addressing three important aspects and their model representation. These aspects are: OVOCs’ photochemistry in the gas-phase, their uptake and transformations in the aqueous phase, and their emissions. With this aim, five studies are performed. Gas- and aqueous-phase mechanisms are built from chemical kinetic data, which are obtained from experiments, quantum chemical and theoretical kinetic calculations, or the literature. In order to investigate the importance of each mechanism on the atmospheric composition, they are implemented into the global ECHAM/MESSy Atmospheric Chemistry (EMAC) model. For analysing the impact of VOC emissions from biomass burning, a combination of the developed mechanisms is applied. The first study shows that EMAC underestimates gas-phase OVOC and hydroxyl radical (OH) concentrations, when ignoring isomerization reactions of isoprene peroxy radicals under low-NOx (NOx=NO+NO2) conditions. The second study demonstrates that in case of isocyanic acid (HNCO), its heterogeneous loss is far more important than its gas-phase chemical loss. In the third and fourth study, the development of the Jülich Aqueous-phase Mechanism of Organic Chemistry (JAMOC) allows to address the importance of in-cloud OVOC oxidation on tropospheric oxidants. This process leads to a significant reduction in gas-phase concentrations of OVOCs and HOx (HOx=OH+HO2). Elevated in-cloud HO2(aq) concentrations introduce an enhanced destruction in O3(aq) resulting in reduced gas-phase O3 concentrations. Thus, EMAC’s bias towards too high tropospheric O3 concentrations is diminished. Finally in the fifth study, the investigation of the 2015 Indonesian peatland fires reveals the significant impact of biomass burning VOC emissions on the regional tropospheric oxidation capacity. At the same time, enhanced phenol concentrations are predicted in the lower stratosphere leading to an enhanced destruction of O3 by phenoxy radicals, potentially contributing to the variability of O3 observed in satellite retrievals. The complete assessment demonstrates that a comprehensive and explicit representation of all OVOC fluxes and transformations in global models is one key to guide the activities solving humanity’s current and upcoming challenges related to climate change and air pollution. Especially, the development of JAMOC shows great potential to investigate the influence of aqueous-phase OVOC oxidation on acids and secondary organic aerosols (SOA) in future studies.
| Item Type: | Thesis (PhD thesis) | ||||||||
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| URN: | urn:nbn:de:hbz:38-538285 | ||||||||
| Date: | 2021 | ||||||||
| Language: | English | ||||||||
| Faculty: | Faculty of Mathematics and Natural Sciences | ||||||||
| Divisions: | Faculty of Mathematics and Natural Sciences > Department of Geosciences > Institute for Geophysics and Meteorology | ||||||||
| Subjects: | Natural sciences and mathematics Chemistry and allied sciences Earth sciences |
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| Date of oral exam: | 26 January 2021 | ||||||||
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| Refereed: | Yes | ||||||||
| URI: | http://kups.ub.uni-koeln.de/id/eprint/53828 |
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