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Title: Tropospheric photochemistry of organic nitrates
Author: Higgins, Christina Mary
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2013
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The research presented in this thesis explores the tropospheric photochemistry of various organic nitrates (RON02). Interest in the atmospheric community has flourished regarding these species due to their potential role in tropospheric oxidation processes. Initially, a brief introduction to the atmosphere is given and followed by a more detailed description of the tropospheric chemistry surrounding the formation and destruction of RON02. Cavity ring-down spectroscopy was employed to determine the N02 quantum yields from the photoexcitation of organonitrates at tropospherically relevant wavelengths between 290 and 315 nm. Alkyl nitrate (methyl, ethyl, n-propyl and isopropyl nitrate) photolysis was found to have pressure-independent N02 quantum yield of unity. The photolysis of an unsaturated dinitrate species at 290 nm was estimated to have a quantum yield of ~ 0.25. Gas and liquid phase RON02 absorption cross-sections were shown to decrease steeply with increasing wavelength (320 - 240 nm). These absorption cross-sections were combined with quantum yields to estimate atmospheric lifetimes. Theoretical calculations were performed to explore the electronic ground and excited state structures of alkyl nitrates and multifunctional nitrates. DFTIB3L YP calculations struggled to reproduce the energies of charge transfer transitions in multi functional nitrates and the CAM-B3L YP level of theory was shown to be more suitable. Global abundance and distribution of organonitrates was analysed using the global chemistry transport model, STOCHEM, with comparison made between model and field measured data. In general, the model reproduced field measured RON02 mixing ratios, highlighting the soundness of the peroxy radical and NOx budgets used in the model. Finally, the atmospheric fate of the organonitrates studied is discussed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available