Extreme deuterium enrichment in stratospheric hydrogen and the global atmospheric budget of H2 |
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Authors: | Rahn Thom Eiler John M Boering Kristie A Wennberg Paul O McCarthy Michael C Tyler Stanley Schauffler Sue Donnelly Stephen Atlas Elliot |
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Institution: | Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA. trahn@lanl.gov |
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Abstract: | Molecular hydrogen (H2) is the second most abundant trace gas in the atmosphere after methane (CH4). In the troposphere, the D/H ratio of H2 is enriched by 120 per thousand relative to the world's oceans. This cannot be explained by the sources of H2 for which the D/H ratio has been measured to date (for example, fossil fuels and biomass burning). But the isotopic composition of H2 from its single largest source--the photochemical oxidation of methane--has yet to be determined. Here we show that the D/H ratio of stratospheric H2 develops enrichments greater than 440 per thousand, the most extreme D/H enrichment observed in a terrestrial material. We estimate the D/H ratio of H2 produced from CH4 in the stratosphere, where production is isolated from the influences of non-photochemical sources and sinks, showing that the chain of reactions producing H2 from CH4 concentrates D in the product H2. This enrichment, which we estimate is similar on a global average in the troposphere, contributes substantially to the D/H ratio of tropospheric H2. |
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