Doctor of Philosophy (PhD)
Polycyclic aromatic hydrocarbons (PAH) are ubiquitous pollutants resulting from incomplete combustion and hence normally unavoidable. The kinetic aspects of the environmental degradation process have received considerable attention; however, not much is known about the degradation products themselves. Aqueous solutions of naphthalene, acenaphthene, 9H-fluorene, phenanthrene and pyrene were subjected to UVB light in a bulk-phase and a thin-film reactor to assess the identity of the formed photodegradation products. To aide in the challenging analysis of these mixtures, a novel analytical technique based on high performance liquid chromatography (HPLC) coupled to UV diode-array detection and dopant-assisted atmospheric pressure photoionization mass spectrometry (APPI-MS) was developed, including the optimization of the chromatography, the introduction of an online-concentration system for increasing sensitivity and the deployment of a novel gas-phase dopant delivery system for APPI-MS. The dopant-assisted APPI-MS (DAPPI-MS) was further optimized, to allow for qualitative analysis of oxygenated polycyclic aromatic compounds (OPAC). The application of the developed analytical technique allowed for the identification of 2-hdyroxy-9,10-phenanthrenequinone and 6H-dibenzo[b,d]pyran-6-ol as degradation products of phenanthrene and 9H-fluorene for the first time. Most studies address PAH degradation in the bulk-water phase, neglecting the fact that the most significant contribution to their environmental degradation takes place in aerosols, especially for volatile PAH (2-4 aromatic rings). PAH can accumulate on the air-water interface, which provides a unique venue for their photochemical degradation. The interfacial photodegradation of 9H-fluorene was evaluated by measuring the formation rate of its photooxidation products in films of different thickness in the thin-film reactor. By increasing the surface-to-volume ratio of a thin film by a factor of five, the formation rate of 9H-fluorene-9-ol, 9H-fluorene-9-one and 6H-dibenzo[b,d]pyran-6-ol was significantly enhanced, highlighting the importance of interfacial degradation of organic pollutants on hydrometeors with large surface-to-volume ratio, such as fog.
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Ehrenhauser, Franz Stefan, "Photochemical Reaction Products of Polycyclic Aromatic Hydrocarbons Adsorbed at an Air-Water Interface" (2011). LSU Doctoral Dissertations. 530.
Wornat, Mary Julia