title: Extreme deuterium enrichment in stratospheric hydrogen and the global atmospheric budget of H2.
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.
authors.affiliation: Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA. trahn@lanl.gov
authors.forename: Thom
authors.initials: T
authors.lastname: Rahn
authors.forename: John M
authors.initials: JM
authors.lastname: Eiler
authors.forename: Kristie A
authors.initials: KA
authors.lastname: Boering
authors.forename: Paul O
authors.initials: PO
authors.lastname: Wennberg
authors.forename: Michael C
authors.initials: MC
authors.lastname: McCarthy
authors.forename: Stanley
authors.initials: S
authors.lastname: Tyler
authors.forename: Sue
authors.initials: S
authors.lastname: Schauffler
authors.forename: Stephen
authors.initials: S
authors.lastname: Donnelly
authors.forename: Elliot
authors.initials: E
authors.lastname: Atlas
mesh_terms: D001272:Atmosphere; D018533:Biomass; D003903:Deuterium / Q000032:analysis* / Q000737:chemistry; D005579:Fossil Fuels; D005740:Gases / Q000032:analysis / Q000737:chemistry; D006859:Hydrogen / Q000032:analysis* / Q000737:chemistry; D008697:Methane / Q000032:analysis / Q000737:chemistry; D009609:Nitrous Oxide / Q000032:analysis; D010777:Photochemistry
chemical_list: D005579:Fossil Fuels; D005740:Gases; D006859:Hydrogen; D003903:Deuterium; D009609:Nitrous Oxide; D008697:Methane