Tropospheric H-2 budget and the response of its soil uptake under the changing environment

Molecular hydrogen (H-2) is an indirect greenhouse gas present at the trace level in the atmosphere. So far, the sum of its sources and sinks is close to equilibrium, but its large-scale utilization as an alternative energy carrier would alterits atmospheric burden. The magnitude of the emissions associated with a future H-2-based economy is difficult to predict and remains a matter of debate. Previous attempts to predict the impact that a future H-2-based economy would exert on tropospheric chemistry were realized by considering a steady rate of microbial-mediated soil uptake, which is currently responsible of similar to 80% of the tropospheric H-2 losses. Although soil uptake, also known as dry deposition is the most important sink for tropospheric H-2, microorganisms involved in the activity remain elusive. Given that microbial-mediated H-2 Soil uptake is influenced by several environmental factors, global change should exert a significant effect on the activity and then, assuming a steady H-2 Soil uptake rate for the future may be mistaken. Here, we present an overview of tropospheric H-2 sources and sinks with an emphasis on microbial-mediated soil uptake process. Future researches are proposed to investigate the influence that global change would exert on H-2 dry deposition and to identify microorganisms involved H-2 soil uptake activity. (C) 2008 Elsevier B.V. All rights reserved.