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| Titel |
The impact of soil uptake on the global distribution of molecular hydrogen: chemical transport model simulation |
| VerfasserIn |
H. Yashiro, K. Sudo, S. Yonemura, M. Takigawa |
| 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 ; 11, no. 13 ; Nr. 11, no. 13 (2011-07-13), S.6701-6719 |
| Datensatznummer |
250009911
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| Publikation (Nr.) |
 copernicus.org/acp-11-6701-2011.pdf |
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| Zusammenfassung |
| The global tropospheric distribution of molecular hydrogen (H2) and its
uptake by the soil are simulated using a model called CHemical AGCM
(atmospheric general circulation model) for the Study of the Environment and
Radiative forcing (CHASER), which incorporates a two-layered soil
diffusion/uptake process component. The simulated distribution of deposition
velocity over land is influenced by regional climate, and has a global
average of 3.3×10−2 cm s−1. In the region north of
30° N, the amount of soil uptake shows a large seasonal variation corresponding
to change in biological activity due to soil temperature and change in
diffusion suppression by snow cover. In the temperate and humid regions in
the mid- to low- latitudes, the uptake is mostly influenced by the soil air
ratio, which controls the gas diffusivity in the soil. In the semi-arid
regions, water stress and high temperatures contribute to the reduction of
biological activity, as well as to the seasonal variation in the deposition
velocity. A comparison with the observations shows that the model reproduces
both the distribution and seasonal variation of H2 relatively well. The
global burden and tropospheric lifetime of H2 are 150 Tg and 2.0 yr,
respectively. The seasonal variation in H2 mixing ratios at the
northern high latitudes is mainly controlled by a large seasonal change in
the soil uptake. In the Southern Hemisphere, seasonal change in net chemical
production and inter-hemispheric transport are the dominant causes of the
seasonal cycle, while large biomass burning contributes significantly to the
seasonal variation in the tropics and subtropics. Both observations and the
model show large inter-annual variations, especially for the period
1997–1998, associated with large biomass burning in the tropics and at
Northern Hemisphere high latitudes. The soil uptake shows relatively small
inter-annual variability compared with the biomass burning signal. Given
that the thickness of biologically inactive layer plays an important role in
the soil uptake of H2, its value in the model is chosen to achieve
agreement with the observed H2 trends. Uncertainty of the estimated
soil uptake flux in the semi-arid region is still large, reflecting the
discrepancy in the observed and modeled seasonal variations. |
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