The chemical and physical mechanisms that control the isotopic compositions of atmospheric H2 and NO2 were investigated in the laboratory and with numerical models of the atmosphere. For H 2, motivated by the need for an accurate global H2 budget to predict the potential consequences of a hydrogen fuel cell economy, the isotopic composition of H2 produced from CH4 oxidation (deltaDhnu), a major H2 source, was examined using 2D model simulations. Using known and estimating unknown isotope effects, model results showed that large variations in oxidant concentrations, temperature-dependent reaction rate coefficients, and wavelengths of available light lead to large variations in deltaDhnu with latitude, altitude, and season. Thus, previous estimates, which assumed that deltaDhnu could be easily extrapolated from observations of stratospheric H2, are neither accurate nor as precise as believed. Furthermore, this analysis demonstrated that measurements of the CHDO photolysis quantum yields as a function of wavelength are needed to resolve the large uncertainties in the global H2 isotope budget.List of Figures 2.1 Simplified schematic diagram of the reaction pathway from methane to 14 molecular hydrogen, modified from Rahn et al. ... (b) Annually- averaged deuterium isotopic composition of H2 (%o relative to VSMOW) predicted by S10. ... observations by the Airborne Chromatograph for Atmospheric Trace Species (ACATS-IV) during the SOLVE campaign (December 1999 - March 2000).
|Title||:||Investigation of the Stable Isotopic Compositions of Atmospheric Trace Gases: From Crossed Molecular Beam Experiments to Global Scale Modeling|
|Author||:||Kathleen Anne Mar|
|Publisher||:||ProQuest - 2008|