Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 6 6 2006 10.5194/acp-6-1611-2006 http://www.atmos-chem-phys.net/6/1611/2006/ http://www.atmos-chem-phys.net/6/1611/2006/acp-6-1611-2006.html http://www.atmos-chem-phys.net/6/1611/2006/acp-6-1611-2006.pdf 1611 1625 2006-05-19 The overwhelming role of soils in the global atmospheric hydrogen cycle T. S. Rhee C. A. M. Brenninkmeijer T. Röckmann Max Planck Institute for Chemistry, Atmospheric Chemistry Division, Mainz, Germany Korea Polar Research Institute, Ansan, Korea Max Planck Institute for Nuclear Physics, Atmospheric Physics Division, Heidelberg, Germany 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.