Open Access

Camille E. Yver, Isabelle C. Pison, Audrey Fortems-Cheiney, Martina Schmidt, Frédéric Chevallier, Michel Ramonet, Armin Jordan, Ole Amund Søvde, Andreas Engel, Rebecca E. Fisher, David Lowry, Euan G. Nisbet, Ingeborg Levin, Samuel Hammer, Jaroslaw Necki, Jakub Bartyzel, Stefan Reimann, Martin Vollmer, Martin Steinbacher, Tuula Aalto, Michela Maione, Jgor Arduini, Simon O'Doherty, Aoife Grant, William T. Sturges, Grant L. Forster, Chris Rene Lunder, Viacheslav I. Privalov, Nina N. Paramonova

• This paper presents an analysis of the recent tropospheric molecular hydrogen (H2) budget with a particular focus on soil uptake and surface emissions. A variational inversion scheme is combined with observations from the RAMCES and EUROHYDROS atmospheric networks, which include continuous measurements performed between mid-2006 and mid-2009. Net H2 surface flux, soil uptake distinct from surface emissions and finally, soil uptake, biomass burning, anthropogenic emissions and N2 fixation-related emissions separately were inverted in several scenarios. The various inversions generate an estimate for each term of the H2 budget. The net H2 flux per region (High Northern Hemisphere, Tropics and High Southern Hemisphere) varies between −8 and 8 Tg yr−1. The best inversion in terms of fit to the observations combines updated prior surface emissions and a soil deposition velocity map that is based on soil uptake measurements. Our estimate of global H2 soil uptake is −59 ± 4.0 Tg yr−1. Forty per cent of this uptake is located in the High Northern Hemisphere and 55% is located in the Tropics. In terms of surface emissions, seasonality is mainly driven by biomass burning emissions. The inferred European anthropogenic emissions are consistent with independent H2 emissions estimated using a H2/CO mass ratio of 0.034 and CO emissions considering their respective uncertainties. To constrain a more robust partition of H2 sources and sinks would need additional constraints, such as isotopic measurements.