Atmospheric Chemistry and Physics Discussions
www.atmos-chem-phys-discuss.net
1680-7367
1680-7375
3
4
2003
10.5194/acpd-3-3745-2003
http://www.atmos-chem-phys-discuss.net/3/3745/2003/
http://www.atmos-chem-phys-discuss.net/3/3745/2003/acpd-3-3745-2003.html
http://www.atmos-chem-phys-discuss.net/3/3745/2003/acpd-3-3745-2003.pdf
3745
3768
2003-07-25
Heavy hydrogen in the stratosphere
T. Röckmann
T. S. Rhee
A. Engel
Max-Planck-Institut für Kernphysik, Bereich Atmosphärenphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany
Max-Planck-Institut für Chemie, Chemie der Atmosphäre, Becherweg 27, 55122 Mainz, Germany
Institut für Meteorologie und Geophysik, Universität Frankfurt, Georg Voigt Str. 14, 60325 Frankfurt, Germany
We report measurements of the deuterium content of molecular hydrogen
(H<sub>2</sub>) obtained from a suite of air samples that were collected during a stratospheric balloon flight between 12 and
33 km at 40º N in October 2002. Strong deuterium enrichments of up to 400
permil versus Vienna Standard Mean Ocean Water (VSMOW) are observed, while the
H<sub>2</sub>
mixing ratio remains virtually constant. Thus, as hydrogen is processed through the
H<sub>2</sub>
reservoir, deuterium is accumulated in H<sub>2</sub>. Using box model calculations we investigated the effects of
H<sub>2</sub>
sources and sinks on the stratospheric enrichments. Results show that considerable isotope
enrichments in the production of H<sub>2</sub>
from CH<sub>4</sub>must take place, i.e., deuterium is transferred preferentially to
H<sub>2</sub>
during the CH<sub>4</sub> oxidation sequence. This supports recent conclusions from
tropospheric H<sub>2</sub>
isotope measurements which show that H<sub>2</sub>
produced photochemically from CH<sub>4</sub> and non-methane hydrocarbons must be enriched in deuterium to balance the
tropospheric hydrogen isotope budget. In the absence of further data on isotope fractionations in the individual
reaction steps of the CH<sub>4</sub> oxidation sequence, this effect cannot be investigated further at
present. Our measurements imply that molecular hydrogen has to be taken into account when
the hydrogen isotope budget in the stratosphere is investigated.