Letters to Nature

Nature 424, 918-921 (21 August 2003) | doi:10.1038/nature01917; Received 24 January 2003; Accepted 15 July 2003

Extreme deuterium enrichment in stratospheric hydrogen and the global atmospheric budget of H2

Thom Rahn1,7, John M. Eiler1, Kristie A. Boering3,4, Paul O. Wennberg1,2, Michael C. McCarthy3, Stanley Tyler5, Sue Schauffler6, Stephen Donnelly6 & Elliot Atlas6

  1. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA
  2. Division of Engineering and Applied Sciences, California Institute of Technology, Pasadena, California 91125, USA
  3. Department of Chemistry, University of California at Berkeley, Berkeley, California 94720, USA
  4. Department of Earth and Planetary Science, University of California at Berkeley, Berkeley, California 94720, USA
  5. Earth Systems Science Department, University of California, Irvine, Irvine, California 92697, USA
  6. National Center for Atmospheric Research, Boulder, Colorado 80307-3000, USA
  7. Present address: Los Alamos National Laboratory, EES-6, MS-D462, Los Alamos, New Mexico 87545, USA

Correspondence to: Thom Rahn1,7 Email: trahn@lanl.gov

Molecular hydrogen (H2) is the second most abundant trace gas in the atmosphere after methane1 (CH4). In the troposphere, the D/H ratio of H2 is enriched by 120permil relative to the world's oceans2, 3, 4. 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)5, 6. 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 440permil, 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.