Date of Award
Doctor of Philosophy (PhD)
Margaret A. Tolbert
Eleanor C. Browne
Melissa G. Trainer
Paul J. Ziemann
Atmospheric organic hazes are present in many planetary and satellite atmospheres, possibly including the ancient Earth. Haze composition and how a haze influences surface and atmospheric processes will greatly depend on the atmospheric composition of the planetary body. Therefore, laboratory studies are necessary to determine these atmosphere specific haze properties. This thesis focuses on the chemical, optical and physical properties of Titan and Archean Earth organic haze analogs, along with gas-phase neutral and ion measurements during haze analog formation.
Titan haze analogs were formed by ultraviolet (UV) and spark discharge excitation of various concentrations of methane in nitrogen in a flow-through reactor. The optical properties of these hazes were measured as a function of methane concentration and were found to have increasing light absorption with increasing aromatic and nitrogen content. To monitor the gas-phase during haze analog formation, a new recirculating reactor was used. The concentration of smaller chained hydrocarbons and nitriles, and the isotopic fractionation of carbon in the methane and evolved ethane, was measured as a function of reaction time. Both methane and ethane become enriched in 13C relative to the starting gas mixture.
Archean Earth haze analogs were formed by UV excitation of methane, carbon dioxide, nitrogen and increasing amounts of molecular oxygen in a flow through reactor. As precursor molecular oxygen increases, the particles become more oxidized and non-absorbing. Therefore, haze produced in an oxygen containing atmosphere could form a non-absorbing haze.
Moreover, since Titan's haze is influenced by ion-neutral chemistry, it is possible similar chemistry occurred in the Archean Earth's atmosphere. Archean Earth haze analog production and negative ion concentrations were found to be inversely related, with aerosol mass loading decreasing with increasing precursor molecular oxygen. Additionally, the nitrogen containing ions switch from mainly organic nitrogen to inorganic nitrogen with increasing precursor molecular oxygen, possibly indicative of the chemistry that occurred during the rise of oxygen in Earth's atmosphere. Due to the differences in haze formation and haze properties based on precursor gases, the results of this thesis demonstrate the importance of considering the atmospheric species present during haze formation.
Ugelow, Melissa S., "Laboratory Studies of Planetary Atmospheres and Organic Hazes" (2018). Chemistry & Biochemistry Graduate Theses & Dissertations. 254.