The overwhelming role of soils in the global atmospheric hydrogen cycle

T. S. Rhee (1) , C. A. M. Brenninkmeijer (1) , T. Röckmann (2)

1 MPIC - Max Planck Institute for Chemistry
2 MPIK - Max Planck Institute for Nuclear Physics

The removal of molecular hydrogen (H₂) from the atmosphere is dominated by the uptake in soils. Notwithstanding, estimates of the magnitude of this important process on a global scale are highly uncertain. The CARIBIC aircraft observations of the seasonal variations of H₂ and its D/H isotopic ratio in the northern hemisphere allow an independent, better constrained estimate. We derive that 82% of the annual turnover of tropospheric H₂ is due to soil uptake, equaling 88 (±11) Tg a^?1, of which the northern hemisphere alone accounts for 62 (±10) Tg a^?1. Our calculations further show that tropospheric H₂ has a lifetime of only 1.4 (±0.2) years ? significantly shorter than the recent estimate of ~2 years ? which is expected to decrease in the future. In addition, our independent top-down approach, confined by the global and hemispheric sinks of H₂, indicates 64 (±12) Tg a^?1 emissions from various sources of volatile organic compounds by photochemical oxidation in the atmosphere. This estimate is as much as up to 60% larger than the previous estimates. This large airborne production of H₂ helps to explain the fairly homogeneous distribution of H₂ in the troposphere.

Domaines: Océan, Atmosphère

T. S. Rhee, C. A. M. Brenninkmeijer, T. Röckmann. The overwhelming role of soils in the global atmospheric hydrogen cycle. Atmospheric Chemistry and Physics Discussions, 2005, 5 (6), pp.11215-11248. ⟨hal-00301903⟩