HR: 16:45h
AN: A42F-04 INVITED     [PDF]
TI: Deuterium Enrichment in Atmospheric Molecular Hydrogen and the Global Isotopic Budget
AU: * Rahn, T
EM: trahn@lanl.gov
AF: Los Alamos National Laboratory, Earth and Environmental Sciences EES-6 MS D-462, Los Alamos, NM 87545 United States
AB: Molecular hydrogen (H$_{2}$) is the second most abundant reduced gas in the atmosphere (after methane) with a globally averaged mixing ratio of $\sim$ 530 ppbv. Its largest sources are photochemical oxidation of methane (CH$_{4}$) and non-methane hydrocarbons (NMHCs) while other recognized sources include biomass burning, fossil fuel burning, nitrogen fixation, and ocean degassing. The potential for a future H$_{2}$ based fuel-cell economy has significant implications for the atmospheric H$_{2}$ budget. As with other volatile fuels, escape of H$_{2}$ during production, storage, and transfer processes is inevitable. Future increases in anthropogenic H$_{2}$ emissions may potentially lead to higher atmospheric concentration; this could have several as yet poorly understood consequences including moistening of the stratosphere, destruction of stratospheric ozone, and increased lifetimes of other reduced gases such as CH$_{4}$. As with other atmospheric trace gases, the stable isotopic content of H$_{2}$ has the potential to help quantify various aspects of its production and destruction. The average deuterium content of H$_{2}$ (expressed as $\delta$D$_{H2}$) is enriched by $\sim$130 $\permil$ relative to Vienna Standard Mean Ocean Water although those H$_{2}$ sources that have been measured are typically depleted in deuterium. We have recently shown that production of H$_{2}$ via the oxidation of methane results in $\delta$D$_{H2}$ that is enriched by ~210 $\permil$ (Rahn et al., 2003), shedding light on this puzzling enrichment. These results will be placed in the context of the overall H$_{2}$ isotopic budget and the potential effect of future anthropogenic perturbations on the isotopic budget will be discussed. Rahn et al., {\it Nature, 424}, 918-921, 2003.
DE: 0315 Biosphere/atmosphere interactions
DE: 0322 Constituent sources and sinks
DE: 0340 Middle atmosphere--composition and chemistry
DE: 1040 Isotopic composition/chemistry
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting