Unimolecular Reaction Kinetics of Dimethyl-Substituted Stabilized Criegee Intermediate Acetone Oxide

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http://urn.fi/URN:NBN:fi:hulib-202104282078
Julkaisun nimi: Unimolecular Reaction Kinetics of Dimethyl-Substituted Stabilized Criegee Intermediate Acetone Oxide
Tekijä: Vuorio, Niko
Muu tekijä: Helsingin yliopisto, Matemaattis-luonnontieteellinen tiedekunta
University of Helsinki, Faculty of Science
Helsingfors universitet, Matematisk-naturvetenskapliga fakulteten
Julkaisija: Helsingin yliopisto
Päiväys: 2021
Kieli: eng
URI: http://urn.fi/URN:NBN:fi:hulib-202104282078
http://hdl.handle.net/10138/329498
Opinnäytteen taso: pro gradu -tutkielmat
Koulutusohjelma: Kemian ja molekyylitieteiden maisteriohjelma
Master's Programme in Chemistry and Molecular Sciences
Magisterprogrammet i kemi och molekylära vetenskaper
Opintosuunta: Ilmakehän kemia ja analyysi
Atmospheric Chemistry and Analysis
Atmosfärens kemi och analys
Tiivistelmä: The Criegee intermediates (CIs) have been the topic for several studies and their role in global atmospheric chemistry is becoming better understood. Isoprene and monoterpenes form a large portion of the total biogenic volatile organic compound emissions in the forested regions of the world, isoprene being the most abundant non-methane hydrocarbon in the Earth's atmosphere. The carbon-carbon double bonds in these compounds are efficiently ozonized (the reaction where an unsaturated compound reacts with ozone) in the atmosphere leading to primary ozonides that subsequently decompose into Criegee intermediates and carbonyl compound molecules. Approximately 50 % of the CIs derived from acyclic alkenes immediately decompose in unimolecular reactions forming, e.g., hydroxyl radicals, the most important oxidizing species in the Earth’s atmosphere. The remainder is stabilized in atmospheric conditions in collisions with other molecules and are subsequently called stabilized Criegee intermediates (sCI). The sCI yields are often smaller, around 20 %, for Criegee intermediates formed in ozonolysis of cyclic alkenes, such as α-pinene. These sCIs can further react with atmospheric constituents (H2O, (H2O)2, SO2, NO2, organic acids etc.) in bimolecular reactions or decompose/isomerize in unimolecular reactions. The bimolecular reactions of sCIs with SO2 contribute significantly to the formation of atmospheric gas phase sulphuric acid and as such are an important factor in nucleation and formation of clouds. In the lower atmosphere, H2SO4 also has adverse health effects on humans and animals and causes corrosion of building materials. Additionally, unimolecular decay and bimolecular reactions of sCIs produce OH radicals. The experimental studies done so far have largely focused on the few simplest sCIs, i.e., formaldehyde oxide (H2COO), acetaldehyde oxide (CH3COO), and acetone oxide ((CH3)2COO). The studies on more complex sCIs, such as methyl vinyl ketone oxide and sCIs formed via ozonolysis of terpenes, are mostly done computationally. The literature review part of this work presents the basic mechanisms of formation and natural removal of sCIs as well as results of recent direct kinetic studies of sCIs with focus on the simplest ones (CH2OO, CH3CHOO, and (CH3)2COO). The methods of detection used in experimental studies are also considered. The experimental section concentrates on measurements of unimolecular decay kinetics of acetone oxide (CH3)2COO above and below room temperature using a new photolytic precursor (CH3)2CIBr. In the experimental section also the apparatus utilized in the research is presented along with the modifications and improvements made on the setup in this work. The calibrations done to ensure accurate measurements are also presented.
Avainsanat: Criegee intermediates
acetone oxide
unimolecular reaction kinetics
atmospheric chemistry
absorption spectroscopy


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