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| Titel |
Carbon and hydrogen isotopic ratios of atmospheric methane in the upper troposphere over the Western Pacific |
| VerfasserIn |
T. Umezawa, T. Machida, K. Ishijima, H. Matsueda, Y. Sawa, P. K. Patra, S. Aoki, T. Nakazawa |
| 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. 17 ; Nr. 12, no. 17 (2012-09-10), S.8095-8113 |
| Datensatznummer |
250011436
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| Publikation (Nr.) |
 copernicus.org/acp-12-8095-2012.pdf |
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| Zusammenfassung |
| We present the mixing ratio, δ13C and δD of atmospheric CH4 using commercial aircraft in the upper
troposphere (UT) over the Western Pacific for the period December
2005–September 2010. The observed results were compared with those obtained
using commercial container ships in the lower troposphere (LT) over the same
region. In the Northern Hemisphere (NH), the UT CH4 mixing ratio shows
high values in the boreal summer–autumn, when the LT CH4 mixing ratio
reaches a seasonal minimum. From tagged tracer experiments made using an
atmospheric chemistry transport model, we found that such high CH4
values are due to rapid transport of air masses influenced by CH4
sources in South Asia and East Asia. The observed isotopic ratio data imply
that these areas have CH4 sources with relatively low δ13C and δD signatures such as biogenic sources.
Latitudinal distributions of the annual average UT and LT CH4 mixing
ratio intersect each other in the tropics; the mixing ratio value is lower in
the UT than in the LT in the NH and the situation is reversed in the Southern
Hemisphere (SH), due mainly to the NH air intrusion into the SH through the
UT. Such intersection of the latitudinal distributions is observable in
δD but not in δ13C, implying an
additional contribution from reaction of CH4 with active chlorine in the
marine boundary layer. δ13C and δD
show low values in the NH and high values in the SH both in the UT and in the
LT. We also observed an increase in the CH4 mixing ratio and decreases
in δ13C and δ
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