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Journal article

The impact of soil uptake on the global distribution of molecular hydrogen: Chemical transport model simulation

Yashiro H, Sudo K, Yonemura S, Takigawa M ...see all

Atmospheric Chemistry and Physics, vol. 11, issue 13 (2011) pp. 6701-6719

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Abstract

The global tropospheric distribution of molecular hydrogen (H-2) 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 3.3x10(-2) cm s(-1). In the region north of 30
degrees 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 H-2 relatively well. The global burden and
tropospheric lifetime of H-2 are 150 Tg and 2.0 yr, respectively. The
seasonal variation in H-2 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 H-2, its value in the model is
chosen to achieve agreement with the observed H-2 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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Authors

  • H. Yashiro

  • K. Sudo

  • S. Yonemura

  • M. Takigawa

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