published_or_final_version / abstract / Chemistry / Master / Master of Philosophy

Thesis (M. Phil.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

Thesis (Ph.D.)--York University, 2008. Graduate Programme in Chemistry. / Typescript. Includes bibliographical references (leaves 143-152). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:NR38991

Thesis (M.S.)--University of Nevada, Reno, 2007. / "December, 2007." Includes bibliographical references (leaves 117-121). Online version available on the World Wide Web.

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published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

Trace gases can have a significant impact on the Earth's climate, and the analysis of changes in these gases and an understanding of how much of these changes are a result of human activity is important for understanding global climate change. Methane (CH4) is the second only to CO2 in radiative forcing over the last 200 years, and its concentration in the atmosphere has more than doubled since 1750. Sources and sinks of CH4 have characteristic isotopic effects, which shift the relative concentration of the methane isotopologues. Spectroscopic techniques for of analysis the isotopic composition of methane have been evolving since the early 1990's, and promise real-time, in-situ measurements that would provide unprecedented information on the methane atmospheric cycle. Here we present our development and results of a new optical spectroscopic isotope ratio instrument using cavity ringdown spectroscopy in the near IR region using the ν2+2ν3 overtone band. This region has limited interference from other molecules, and an advantageous juxtaposition of a 13CH4 triplet, and a single 12CH4 peak, allowing near-simultaneous measurement of both isotopologues. We present the results of two datasets showing high linearity over a wide range of isotope ratios, which achieved a precision of ±4 /. We present analysis of the data and consider the effects of temperature and molecular interference.

Thesis (Ph. D.)--University of Hong Kong, 2008. / Also available in print.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 141-146).

Environmental contamination has become a significant threat to the health and well-being of mankind as well as to the environment, prompting the establishment and implementation of stringent environmental regulations. The ability to accurately detect and quantify contaminants, such as mercury (Hg), uranium (U), and volatile organic compounds (VOCs), in real-time, in situ is of significant importance to monitoring and remediation efforts. In an effort to develop a real-time, fast-response detector that is portable, highly sensitive, and cost efficient, this research explored the feasibility of utilizing cavity ringdown spectroscopy (CRDS) in conjunction with various plasma sources and vacuum cavities to accurately detect trace quantities of contaminants. The feasibility of detecting Hg with a low power, low temperature candle-shaped microwave-induced plasma (MIP) and a copper surfatron microwave cavity with various plasma discharge tube configurations in conjunction with cavity ringdown spectroscopy (MIP-CRDS) is discussed. Detection limits were on the order of 221 ppt Hg in the vapor phase for the candle-shaped MIP and improved by a factor of 10 with the tube-shaped plasma. The ability to detect elemental Hg naturally-evaporating from contaminated soils and solutions was evaluated, and 10’s of ppt were consistently obtained. Additionally, the fine structure of the Hg 253.65 nm transition was observed with each iteration of this approach. The potential of effectively generating uranium atoms and ions with a low-power, lowlow rate microwave-induced plasma was evaluated. Uranium emission spectra covering 320 – 430 nm were obtained, labeled, and compared to the available literature values. Calibration curves were generated, and the detection limits were determined to be ~0.4 ppm. The feasibility of measuring U incorporating diode laser-plasma-CRDS was explored. The preliminary studies clearly show the ability to detect U vapor with this technique and sub-ppm detection limits were obtained. A continuous wave cavity ringdown spectroscopy system (CW-CRDS) incorporating commercially available telecommunications diode lasers was constructed, and the overall sensitivity of this system was evaluated by utilizing the absorption of the asymmetric C-H stretch overtones of several VOCs, including benzene, chlorobenzene, 1,2-dichlorobenzene, toluene, and acetone. Detection limits are determined to be in the ppb’s for each of the organics examined.