Laboratory Studies of Planetary Atmospheres and Organic Hazes

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.</p

Exploring the Atmosphere of Neoproterozoic Earth: The Effect of O2_{2} on Haze Formation and Composition

Previous studies of haze formation in the atmosphere of the Early Earth have focused on N$_{2}$/CO$_{2}$/CH$_{4}$ atmospheres. Here, we experimentally investigate the effect of O$_{2}$ on the formation and composition of aerosols to improve our understanding of haze formation on the Neoproterozoic Earth. We obtained in situ size, particle density, and composition measurements of aerosol particles produced from N$_{2}$/CO$_{2}$/CH$_{4}$/O$_{2}$ gas mixtures subjected to FUV radiation (115-400 nm) for a range of initial CO$_{2}$/CH$_{4}$/O$_{2}$ mixing ratios (O$_{2}$ ranging from 2 ppm to 0.2\%). At the lowest O$_{2}$ concentration (2 ppm), the addition increased particle production for all but one gas mixture. At higher oxygen concentrations (20 ppm and greater) particles are still produced, but the addition of O$_{2}$ decreases the production rate. Both the particle size and number density decrease with increasing O$_{2}$, indicating that O$_{2}$ affects particle nucleation and growth. The particle density increases with increasing O$_{2}$. The addition of CO$_{2}$ and O$_{2}$ not only increases the amount of oxygen in the aerosol, but it also increases the degree of nitrogen incorporation. In particular, the addition of O$_{2}$ results in the formation of nitrate bearing molecules. The fact that the presence of oxygen bearing molecules increases the efficiency of nitrogen fixation has implications for the role of haze as a source of molecules required for the origin and evolution of life. The composition changes also likely affect the absorption and scattering behavior of these particles but optical properties measurements are required to fully understand the implications for the effect on the planetary radiative energy balance and climate.Comment: 15 pages, 3 tables, 8 figures, accepted in Astrophysical Journa

Visualizing Nanoparticle Dissolution by Imaging Mass Spectrometry

We demonstrate the ability to visualize nanoparticle dissolution while simultaneously providing chemical signatures that differentiate between citrate-capped silver nanoparticles (AgNPs), AgNPs forced into dissolution via exposure to UV radiation, silver nitrate (AgNO₃), and AgNO₃/citrate deposited from aqueous solutions and suspensions. We utilize recently developed inkjet printing (IJP) protocols to deposit the different solutions/suspensions as NP aggregates and soluble species, which separate onto surfaces <i>in situ</i>, and collect mass spectral imaging data <i>via</i> time-of-flight secondary ion mass spectrometry (TOF-SIMS). Resulting 2D Ag⁺ chemical images provide the ability to distinguish between the different Ag-containing starting materials and, when coupled with mass spectral peak ratios, provide information-rich data sets for quick and reproducible visualization of NP-based aqueous constituents. When compared to other measurements aimed at studying NP dissolution, the IJP-TOF-SIMS approach offers valuable information that can potentially help in understanding the complex equilibria in NP-containing solutions and suspensions, including NP dissolution kinetics and extent of overall dissolution