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Identifier 000449134
Title Ατμοσφαιρική αποικοδόμηση και επίδραση στην ποιότητα της ατμόσφαιρας και την κλιματική αλλαγή προϊόντων καύσης βιομάζας με βάση το Φουράνιο : κινητική και μηχανιστική διερεύνηση
Alternative Title Atmospheric degradation and air-quality and climate change impact of Furan-based biomass burning emission products: a kinetic and mechanistic study
Author Αγγελάκη, Μαρία Ε.
Thesis advisor Κανακίδου, Μαρία
Reviewer Άγγλος, Δημήτριος
Μήλιος, Κωνσταντίνος
Μιχαλόπουλος, Νικόλαος
Πανδής, Σπυρίδων
Σπύρος, Απόστολος
Παπαδημητρίου, Βασίλειος
Abstract In the present PhD thesis, the kinetic parameters and the mechanism for the reactions of OH radicals and Cl atoms with a series of furans, in the gas phase, were determined and further their tropospheric degradation was investigated. Furans are cyclic oxygenated semi or low volatile organic compounds that are emitted in the atmosphere through biomass burning (BB) processes. As far as their atmospheric degradation is concerned, there is little knowledge in literature. Regarding their low volatility and the double bonds they contain, once they are emitted in the atmosphere, furans are expected to be photochemically converted into secondary pollutants that will eventually lead to increased tropospheric ozone (O3) levels and secondary organic aerosols (SOA) formation. These secondary pollutants are expected to have an adverse effect in Air-Quality, Climate and Health. In this study, rate coefficients kX(T, P) for the gas phase reactions of OH radicals and Cl atoms with furan (C4H4O k1), 2-(k2) and 3-methyl-furan (2 and 3-C5H6O k3), 2-furaldehyde (2-C5H4O2) and furan-2,5-dione (maleic anhydride, C4H2O3) were determined over the range of temperature and pressure, Τ = 263 – 363 K and P = 0.002 – 760 Torr, respectively. Kinetic parameters were determined by the combined use of three independent experimental setups and three different detection techniques (FTIR, SIFT-MS, QMS) which aimed both to thoroughly investigate reactions’ mechanisms and also to cross validate the kinetic results. In particular rate coefficients kX( (T, P), were measured by systematic variation in temperature and pressure – first kinetic and mechanistic study in low pressure regime –that allowed to map out the several mechanistic pathways that coexist in the total reaction mechanistic scheme. The majority of the experiments were performed by using the static technique of the Thermostated Photochemical Reactor, coupled with Fourier Transformed Infrared Spectroscopy (TPCR/FTIR, UoC), that enables to variate both temperature and pressure, in a range that is relevant to the atmosphere. The experiments were also performed in a thermostated atmospheric simulation chamber, that is coupled with a series of detection techniques i.e. FTIR and SIFT-MS, (THALAMOS, Douai), but lucks in the variation of the experimental conditions i.e pressure control. Furthermore, well-designed experiments were conducted at the low pressure regime (~2 mTorr) with the continuous flow technique of the Very Low Pressure Reactor, in which an effusive molecular beam is analyzed with Quadrupole Mass Spectrometry (VLPR/QMS). Using the obtained kinetic results, atmospheric lifetime of furans was determined. The determination, firstly was performed, by taking into account exclusively OH chemistry and subsequently, by introducing Cl chemistry in the total lifetime. In this way, it was possible to assess the contribution of each oxidant to both lifetime and atmospheric distribution of the end oxidation products. Measured lifetimes for all furanic compounds were relatively small in the range of 0.13 – 28 d, based solely in OH chemistry ([OH] ]avg = 1 ×106 molecule cm-3). By combining Cl chemistry, the lifetimes were decreased from 4 up to 88 %, regarding with the local characteristics the emission regions. Both atmospheric lifetime and IR spectra that were also measured in the present thesis, were used to estimate atmospheric metrics i.e. radiative efficiency (RE) and global warming potential (GWP). Finally, end oxidation products for each furanic compound (OH and Cl) were characterized and quantified. Results deriving from kinetic and mechanistic study, pinpoint that reactions of the two atmospheric oxidants with furans are conducted through a complex reaction mechanism that includes the production of a relatively unstable intermediate (adduct), that under certain conditions can be stabilized and subsequently be oxidized. Low pressure experiments indicate the contribution of parallel reaction channels to the total mechanistic scheme, in which reaction intermediate can be transformed leading to the formation of different products. Furthermore, the direct Hydrogen atom abstraction pathway, may also occur. Although this pathway seems to have minor contribution to the total mechanism of the reaction, it cannot be ignored. Finally, total results indicate a structure-reactivity relationship and thus the substitution of furanic ring is expected to play a key role in the distribution of the primary and secondary oxidation products. Although furans are expected to sink rapidly from the atmosphere, due to their physical properties (unsaturated compounds of low volatility), it is expected that their atmospheric oxidation products will impact on gas phase chemistry – secondary production of tropospheric ozone, chlorinated products –. Furthermore, their tropospheric degradation may also affect heterogeneous chemistry via their condensation in particles. Thus furans is expected to have, in total, an adverse effect in Air-Quality, Climate and Human Health.
Language Greek
Subject Atmospheric impact
Ατμοσφαιρική επίδραση
Issue date 2022-07-25
Collection   School/Department--School of Sciences and Engineering--Department of Chemistry--Doctoral theses
  Type of Work--Doctoral theses
Permanent Link https://elocus.lib.uoc.gr//dlib/a/1/6/metadata-dlib-1655909544-957877-31640.tkl Bookmark and Share
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