Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 5 6 2005 10.5194/acpd-5-11215-2005 http://www.atmos-chem-phys-discuss.net/5/11215/2005/ http://www.atmos-chem-phys-discuss.net/5/11215/2005/acpd-5-11215-2005.html http://www.atmos-chem-phys-discuss.net/5/11215/2005/acpd-5-11215-2005.pdf 11215 11248 2005-11-02 The overwhelming role of soils in the global atmospheric hydrogen cycle T. S. Rhee rhee@mpch-mainz.mpg.de C. A. M. Brenninkmeijer T. Röckmann Max Planck Institute for Chemistry, Atmospheric Chemistry Division, Mainz, Germany Max Planck Institute for Nuclear Physics, Atmospheric Physics Division, Heidelberg, Germany now at: Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Utrecht, The Netherlands 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.