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| Titel |
Correlations between the deuterium content of molecular hydrogen and other trace gases in the UTLS region obtained from CARIBIC samples |
| VerfasserIn |
Anneke Batenburg, Tanja Schuck, Angela Baker, Carl Brenningmeijer, Thomas Röckmann |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250047704
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| Zusammenfassung |
| Hydrogen (H2) is present in the atmosphere at levels of ~0.5 ppm. These levels are expected
to rise due to use of H2 as an energy carrier, which may affect methane (CH4) lifetimes and
stratospheric ozone depletion. Unfortunately, large uncertainties still exist in the global
H2budget.
The different sources and sinks of H2 have very distinct isotopic signatures and
fractionation coefficients, respectively. For this reason, measurements of the isotopic
composition of H2 are a promising tool to gain insight into H2 source and sink processes and
to constrain the terms in the global budget.
The CARIBIC project uses an automated instrument container on board of
a commercial passenger aircraft to carry out in situ atmospheric measurements
and to collect air samples, mostly in the Upper Troposphere Lower Stratosphere
(UTLS) region. The CARIBIC samples are routinely analyzed for various gases.
At present, more than 480 air samples of 19 CARIBIC return flights have been
analysed for molecular hydrogen mixing ratio (mH2) and H2 deuterium content
(δD-H2).
More than 80 of the analysed samples contain air from the lower stratosphere. In the
few previous experiments in the stratosphere it was found that production (from
CH4 oxidation) and destruction of H2 (by hydroxyl radicals) balance out, but that
H2 gets progressively more enriched in deuterium. Indeed, for the stratospheric
CARIBIC samples, mH2 does not vary with height above the tropopause, but δD-H2
increases with height. A compact correlation is found between δD-H2 and CH4 mixing
ratios; as the air is photochemically processed, the H2 becomes more enriched
as the CH4 is destroyed. The found slope of this relation is very similar to those
found in previous experiments, but the number of measurements is now increased
threefold.
Samples from three flights to India during the summer monsoon season have also been
analyzed. Schuck et al. [2010] found increased levels of CH4 here, due to larger upward
convection of boundary layer air, and increased microbial activity. Remarkably, in the
samples with enhanced CH4 the H2 is depleted, and δD-H2 and CH4 are correlated. The
deuterium depletion of H2 in the ‘Monsoon plume’ is likely also caused by the increased
upward convection, which brings deuterium-depleted hydrogen from the boundary layer to
cruising altitude. The absence of a clear increase in H2 concentration indicates that the source
must be isotopically very depleted, maybe even more than what is expected from combustion
sources. A possible explanation is that we observe increased microbial production of H2
during the summer monsoon season, as biological production is the most depleted source of
H2.
References
T. J. Schuck, C. A. M. Brenninkmeijer, A. K. Baker, F. Slemr, P. F. J. v. Velthoven, and A.
Zahn, Greenhouse gas relationships in the Indian summer monsoon plume measured by
the CARIBIC passenger aircraft,Atmos. Chem. Phys Discussions 10, 2031-1087,
2010
http://www.caribic-atmospheric.com |
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