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| Titel |
Temporal and spatial variability in the isotopic composition of atmospheric molecular hydrogen: measurement time series from six EUROHYDROS stations |
| VerfasserIn |
Anneke Batenburg, Gerben Pieterse, Maarten Krol, Sylvia Walter, Ingeborg Levin, Martina Schmidt, Armin Jordan, Samuel Hammer, Camille Yver, 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 |
250047696
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| Zusammenfassung |
| Molecular hydrogen (H2) is present in the atmosphere at levels of ~0.5 ppm. Its sources are
the oxidation of methane and other hydrocarbons, combustion processes, and production by
nitrogen-fixing bacteria. About three quarters of the H2 thus produced is taken up by soils;
the other quarter is oxidized by the hydroxyl radical (OH). But while the contributions
to the global H2 budget are qualitatively known, large quantitative uncertainties
remain.
This is now a pressing matter, since the anticipated use of H2 as an energy carrier –with
potential benefits for air quality and climate-, will likely result in increased emissions of H2
to the atmosphere due to the inevitable leakage during production, storage and distribution.
The associated rise of atmospheric H2 levels may affect the lifetime of greenhouse gases such
as methane, and might also affect stratospheric ozone levels. The EUROHYDROS project
aims to improve our understanding of the H2 cycle with the establishment of a global network
for atmospheric H2 observations.
Isotope measurements can be a useful addition to hydrogen mixing ratio observations for
constraining the terms in the global budget. In the research presented here, weekly to monthly
air samples from six globally distributed locations in the EUROHYDROS network have been
analysed for the stable isotopic composition (, i.e. the deuterium content,) of the H2 (δD-H2),
in addition to the hydrogen mixing ratio (mH2). This has resulted in time series of between
one and five years long, which constitute the largest dataset of ground-based δD-H2
observations so far.
On average, the mH2 and δD-H2 values are higher at the Southern Hemisphere (SH) than
at the Northern Hemisphere (NH) stations. A δD-H2 minimum is observed at the NH
mid-latitudes, which is likely an effect of anthropogenic emissions of deuterium-depleted
hydrogen. The SH stations show small seasonal cycles in mH2, but no discernible seasonal
cycles in δD-H2. The three coastal/marine NH stations show larger cycles in mH2, and δD-H2
cycles that are five to six months out-of-phase with respect to the mH2 cycles. These large
relative seasonal variations have been used to make a rough estimate of the relative sink
strength of the two sinks, and the results are in agreement with the expectation that on the NH
the relative contribution of soil uptake to the total sink processes increases with
latitude.
This dataset has now been used to validate the TM5 global chemistry transport model,
in which the sources and sinks of deuterated and non-deuterated H2 have been
implemented. The TM5 results agree well with mH2 observations, but have a negative bias
with respect to the δD-H2 observations that can be resolved by adjusting the values
of a limited number of parameters within the range of uncertainty. However, to
uniquely constrain the global H2 isotope budget, more data are needed than are
available to date. The Gas Chromatography – Isotope Ratio Mass Spectrometry system
used for the isotope measurements is currently being automated to facilitate the
continuation of these observations, so that long-term δD-H2 time series can be obtained. |
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