Measurements and modeling of the stable isotopic compositions of trace stratospheric gases

Measurements and modeling of the stable isotopic compositions of trace gas species are used to address fundamental questions regarding the sources, sinks, transport, and chemical history of atmospheric constituents. In this dissertation, new measurements of the isotopic compositions of CH4 and H2 collected from the NASA ER-2 aircraft and simulations using the Lawrence Livermore National Laboratory 2D model are used to investigate the isotopic compositions of methane (CH4), molecular hydrogen, (H2), water vapor (H2O), and carbon monoxide (CO) in the stratosphere. Since most sources and some sinks of these gases are located at the Earth's surface, the stratosphere provides a unique natural laboratory for investigating the photochemical evolution of the isotopic compositions of these chemically and radiatively important trace species isolated from surface influences.; Measurements of the carbon and hydrogen isotopic composition of CH 4 (i.e., delta13C-CH4, deltaD-CH 4), and H2 (i.e., deltaD-H2) in the stratosphere showed large enrichments relative to surface values. Combining these CH4 measurements with simulations of delta13C- CH4 and deltaD-CH 4 constrained the value of the kinetic isotope effect (KIE) for the CH4 + O(1D) reaction, which is important for understanding the stratospheric carbon enrichment in methane. Combining the ER-2 deltaD-H 2 measurements with simulations showed that heavy H2 is produced from CH4 oxidation, which helps to resolve a longstanding discrepancy in the global H2 isotope and concentration budgets. ER-2 observations of deltaD-H2 and deltaD-CH4 are also combined with remote observations of deltaD-H2O to empirically constrain the total deuterium budget in the stratosphere and to infer deltaD-H2O in air entering the stratosphere, which yields information on the mechanism(s) of stratosphere-troposphere exchange and may also be a sensitive indicator of climate change. Finally, model simulations of delta13C-CO indicate that the large KIE in the Cl + CH4 reaction can cause significant variability in monthly and interannual delta13C-CO values, which may be useful as a proxy for integrated Cl mixing ratios when more stratospheric measurements become available.