In all porosity ﹩\phi ﹩ = 0.02 simulations, methane evaporation increases the near-surface methane vapor mass mixing ratio. The rate and magnitude of this increase are determined by the initial methane profile (shown as different lines). Dashed lines show the final simulated time step (Tsol 5); solid lines show the initial time step. Individual lines show outcomes from simulations with different initial methane profiles.