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Identifier

000383732

Title

Κινητική μελέτη αντιδράσεων ριζών ΟΗ και ατόμων CI με το (CF3)2C=CH2 στην αέρια φάση και διερεύνηση της επίδρασής του στην ατμόσφαιρα και το κλίμα

Alternative Title

Kinetic study for the gas phase reactions of OH radicals and CI atoms with (CF3)2C=CH2 and implications in the atmosphere and climate

Author

Σπιτιέρη, Χριστίνα

Thesis advisor

Βελώνια, Καλλιόπη
Μιχαλόπουλος, Νικόλαος

Reviewer

Παπαγιαννακόπουλος, Παναγιώτης
Παπαδημητρίου, Βασίλειος

Abstract

In the present work the kinetic parameters and the mechanism for the reactions of chlorine atoms, Cl, and hydroxyl radicals, OH, with hexafluoroisobutylene, ((CF3)2C=CH2, HFIB), were studied in the gas phase and the tropospheric degradation of HFIB was investigated. HFIB is a member of HydroFluoroOlefins (HFO) class of compounds, HFO, that have been proposed as potent CFC alternatives. The unsaturated double bond is expected to result in increased atmospheric reactivity, compared to previously suggested CFC alternatives and to lower Global Warming Potentials (GWP). The kinetics of the title reactions were determined using relative rate methods. The experiments carried out using the Photochemical Thermostated Reactor technique, TPCR, coupled with Fourier Transformed Infrared Spectroscopy, FT-IR. Rate coefficient, k, for the reaction of Cl atoms with HFIB was measured as a function of temperature, 248 - 363 K, and pressure 40 - 700 Torr using three different reference reactions. The rate coefficient for the reaction of OH radicals with HFIB was determined at 296 K and 700 Torr, to be k(296 K, 700 Torr) = (7.91 ±0.20) x10-13 3 -1-1 cm molecule- s- . The quoted uncertainties are the 2σ precision (95% level of confidence) of the least-squares fit and do not include estimated systematic errors. Temperature and pressure dependence for the Cl rate coefficients, found to be well represented by Troe expressions that have been proposed for termolecular reactions proceeding via adduct formation: Γ -1 k KQO jk0T [Μ ] 1+1 lo The determined fall-off parameters were k0(T) = 8.0 x10- (T/300)- . cm molecule-s-1 and kro(T) = 3.7 x10-11 (T/300)-09 cm3 molecule-1 s-1. Room temperature rate coefficient, close to the high pressure limit, was measured to be k(296 K, 700 Torr) =(3.44 ±0.02) x10-11 cm3 molecule-1 s-1. The quoted uncertainties are the 2σ precision of the measurements and do not include estimated systematic errors. IR cross-sections were also measured as part of the present work and the radiative efficiency was estimated using Pinnock et al. model ((S. Pinnock, M. D. Hurley, K. P. Shine, T. J. Wallington and T. J. Smyth, J. Geophys. Res., [Atmos.], 1995, 100, 23227-23238)). The Global Warming Potential (GWP) of HFIB was calculated for 20, 100 and 500 time horizons using the kinetic results and the IR cross-sections to determine the tropospheric lifetime and the radiative efficiency, respectively. Finally, the atmospheric oxidation end-products were experimentally identified and the life cycle atmospheric impact of HFIB was discussed.

Language

Greek

Subject

Global warming potential

IR cross -section absorbance

Relative rate coefficient

Tropospheric chemistry

Unsaturated hydroflorocarbons

Ακόρεστοι υδροφθοράνθρακες

Δυναμικό παγκόσμιας θέρμανσης

Συντελεστής σχετικής ταχύτητας

Τροποσφαιρική χημεία