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| Titel |
The stable isotopic composition of molecular hydrogen in the tropopause region probed by the CARIBIC aircraft |
| VerfasserIn |
A. M. Batenburg, T. J. Schuck, A. K. Baker, A. Zahn, C. A. M. Brenninkmeijer, T. Röckmann |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250059926
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| Zusammenfassung |
| Atmospheric molecular hydrogen (H2) has been little studied for some time, but has recently
drawn more attention due to its expected future use as an energy carrier. Concerns have been
raised that this use may lead to large-scale leakage of H2 into the atmosphere, with
implications for the atmosphere’s oxidative capacity and stratospheric ozone chemistry. A
thorough understanding of the global H2 cycle is therefore needed, but at present, the
uncertainties are still large.
Studying the stable isotopic composition of H2 (δD(H2)) is a promising way to gain more
information about the H2 cycle. Over the last decade, studies of the isotope effects in
H2 source and sink processes have appeared, δD(H2) has been incorporated into
global chemical transport models and many more environmental observations of
δD(H2) have been published. However, some knowledge gaps can be easily identified.
Stratosphere-Troposphere Exchange (STE) has a strong influence on tropospheric δD(H2),
but very few δD(H2) data are available from samples taken around the tropopause, where this
exchange takes place. For large regions of the globe, no δD(H2) data have been
published.
In the CARIBIC project, air samples are collected in the Upper Troposphere-Lower
Stratosphere (UTLS) region with a commercial passenger aircraft and routinely analysed for
various gases. This sampling platform can potentially provide global coverage. More
than 450 CARIBIC samples have been analysed for H2 mixing ratios (m(H2)) and
δD(H2).
More than 120 of these samples consisted of lowermost stratosphere (LMS) air. They
show the lack of variation in m(H2) and the δD(H2) increase that is typical for
the stratosphere, caused by the competing and deuterium-enriching source and
sink processes of H2 in the stratosphere. The deuterium-enrichment signal grows
stronger with distance above the tropopause. As a result of the relatively long lifetimes
of H2, CH4 and N2O, strong negative correlations appear between δD(H2) and
m(CH4) and between δD(H2) and m(N2O). These are similar to previously published
results obtained from stratospheric balloon campaigns. The similarity between
different campaigns indicates that these correlations likely hold globally and can be
used for parameterizing the δD value of H2 that is imported to the troposphere by
STE.
This dataset also contains the first δD(H2) data collected in or over India. A marked decrease
in δD(H2) is observed in the summer monsoon season, which correlates with the monsoon
increase in m(CH4), but is not reflected in a change in m(H2). The correlation with m(CH4)
and the lack of change in m(H2) lead to the hypothesis that the δD(H2)-lowering is at least
partly caused by the microbial production of H2, which has a very deuterium-depleted source
signature. |
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