The overwhelming role of soils in the global atmospheric hydrogen cycle

International audience; 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.