Heavy hydrogen in the stratosphere
[摘要] We report measurements of the deuterium content of molecular hydrogen(H2) obtained from a suite of air samples that were collected during a stratospheric balloon flight between 12 and33 km at 40º N in October 2002. Strong deuterium enrichments of up to 400permil versus Vienna Standard Mean Ocean Water (VSMOW) are observed, while theH2 mixing ratio remains virtually constant. Thus, as hydrogen is processed through theH2 reservoir in the stratosphere, deuterium is accumulated in H2. Using box model calculations we investigated the effects of H2 sources and sinks on the stratospheric enrichments. Results show that considerable isotopeenrichments in the production of H2from CH4 must take place, i.e., deuterium is transferredpreferentially to H2 during the CH4 oxidation sequence. This supports recent conclusions fromtropospheric H2 isotope measurements which show that H2 produced photochemically fromCH4 and non-methane hydrocarbons must be enriched in deuterium to balance thetropospheric hydrogen isotope budget. In the absence of further data on isotope fractionationsin the individual reaction steps of the CH4 oxidation sequence, this effect cannot beinvestigated further at present. Our measurements imply that molecular hydrogen has to betaken into account when the hydrogen isotope budget in the stratosphere is investigated.
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[效力级别] [学科分类] 大气科学
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