Simulation of Global Hydrogen Levels Using a Lagrangian Three-Dimensional Model

Many previous assessments of the global hydrogen budget have used assumed global averages of temperatures and levels of key reactants to calculate the magnitudes of the various sinks. Dry deposition is by far the largest hydrogen sink but has not been considered in detail in previous estimates of the hydrogen budget. Simulations of hydrogen using a global three-dimensional Lagrangian chemistry-transport model and two different dry deposition schemes were compared with surface measurements. An improved dry deposition scheme which included the effects of soil moisture gave better agreement between the modelled hydrogen levels and surface measurements. The seasonal variation in the hydrogen levels was also simulated much more accurately with the new dry deposition scheme. The model results at high southern latitudes were insensitive to the relative partitioning of the sources between fossil fuel combustion and biomass burning. The results indicate a global mean hydrogen dry deposition velocity of 5.3×10^–4 m s^–1 which is lower than the previously used 7×10^–4 m s^–1.