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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 |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 12, no. 10 ; Nr. 12, no. 10 (2012-05-24), S.4633-4646 |
| Datensatznummer |
250011172
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| Publikation (Nr.) |
 copernicus.org/acp-12-4633-2012.pdf |
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| Zusammenfassung |
More than 450 air samples that were collected in the upper troposphere –
lower stratosphere (UTLS) region by the CARIBIC aircraft (Civil Aircraft for
the Regular Investigation of the atmosphere Based on an Instrument Container)
have been analyzed for molecular hydrogen (H2) mixing ratios
(χ(H2)) and H2 isotopic composition (deuterium content,
δD).
More than 120 of the analyzed samples contained air from the lowermost
stratosphere (LMS). These show that χ(H2) does not vary appreciably
with O3-derived height above the thermal tropopause (TP),
whereas δD does increase with height. The isotope enrichment
is caused by H2 production and destruction processes that enrich the
stratospheric H2 reservoir in deuterium (D); the exact shapes of the
profiles are mainly determined by mixing of stratospheric with tropospheric
air. Tight negative correlations are found between δD and the
mixing ratios of methane (χ(CH4)) and nitrous oxide (χ(N2O)), as a result of
the relatively long lifetimes of these three species. The correlations are
described by δD[‰]=−0.35 ·
χ(CH4)[ppb]+768 and δD[‰]=−1.90·
χ(N2O)[ppb]+745. These correlations are similar to
previously published results and likely hold globally for the LMS.
Samples that were collected from the Indian subcontinent up to 40° N
before, during and after the summer monsoon season show no significant
seasonal change in χ(H2), but δD is up to
12.3‰ lower in the July, August and September monsoon samples. This
δD decrease is correlated with the χ(CH4) increase in
these samples. The significant correlation with χ(CH4) and the
absence of a perceptible χ(H2) increase that accompanies the
δD decrease indicates that microbial production of very
D-depleted H2 in the wet season may contribute to this phenomenon.
Some of the samples have very high χ(H2) and very low
δD values, which indicates a pollution effect. Aircraft engine exhaust
plumes are a suspected cause, since the effect mostly occurs in samples
collected close to airports, but no similar signals are found in other
chemical tracers to support this. The isotopic source signature of the H2
pollution seems to be on the low end of the signature for fossil fuel
burning. |
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