Tropospheric H2 budget and the response of its soil uptake under the changing environment

Molecular hydrogen (H2) 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 alter its atmospheric burden. The magnitude of the emissions associated with a future H2-based economy is difficult to predict and remains a matter of debate. Previous attempts to predict the impact that a future H2-based economy would exert on tropospheric chemistry were realized by considering a steady rate of microbial-mediated soil uptake, which is currently responsible of ~ 80% of the tropospheric H2 losses. Although soil uptake, also known as dry deposition is the most important sink for tropospheric H2, microorganisms involved in the activity remain elusive. Given that microbial-mediated H2 soil uptake is influenced by several environmental factors, global change should exert a significant effect on the activity and then, assuming a steady H2 soil uptake rate for the future may be mistaken. Here, we present an overview of tropospheric H2 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 H2 dry deposition and to identify microorganisms involved H2 soil uptake activity.