The overwhelming role of soils in the global atmospheric hydrogen cycle

[摘要] The removal of molecular hydrogen (H₂) from the atmosphere is dominatedby the uptake in soils. Notwithstanding, estimates of the magnitude of thisimportant process on a global scale are highly uncertain. The CARIBICaircraft observations of the seasonal variations of H₂ and its D/Hisotopic ratio in the Northern Hemisphere allow an independent, betterconstrained estimate. We derive that 82% of the annual turnover oftropospheric 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 H₂has a lifetime of only 1.4 (±0.2) years – significantly shorter thanthe recent estimate of ~2 years – which is expected to decrease in thefuture. In addition, our independent top-down approach, confined by theglobal and hemispheric sinks of H₂, indicates 64 (±12)Tg a^-1emissions from various sources of volatile organic compounds byphotochemical oxidation in the atmosphere. This estimate is as much as up to60% larger than the previous estimates. This large airborne productionof H₂ helps to explain the fairly homogeneous distribution of H₂in the troposphere.

[学科分类] 大气科学