Effect of varying atmospheric conditions on methane boundary†layer development in a free flow domain interfaced with a porous media domain

Mitigation of atmospheric emission of methane from leaky underground infrastructure is important for controlling the global anthropogenic greenhouse gas burden. Overexposure to methane may also cause occupational health problems in indoor/outdoor environments at the local scale. Subsurface soil conditions (e.g. soil heterogeneity) affect methane migration in soils while near†surface atmospheric boundary conditions (e.g. wind and temperature) affect off†site emissions across the soil†atmosphere interface. This study investigated the above†surface methane concentration boundary†layer development under different soil conditions (homogenous and layered) and atmospheric boundary controls (wind and temperature). A series of controlled bench†scale experiments was conducted using an open†loop boundary†layer wind tunnel interfaced with a porous media tank inside which a simulated methane point source was embedded to mimic a buried leaky pipeline. Results revealed pronounced effects of wind and, to a lesser extent, temperature on above†surface methane boundary†layer development. High atmospheric temperature contributed to the concentration boundary†layer build†up whereas high wind velocity caused erosion of the boundary layer. The boundary†layer methane concentration profiles were adequately simulated within an advection†diffusion modeling framework combined with a Navier†Stokes free flow domain by coupling free air flow, heat flow and flow of a multicomponent gas mixture. Simulations further implied that the Fickian diffusion approach may have limited applications when pronounced non†isothermal conditions prevail within the system. © 2017 Society of Chemical Industry and John Wiley & Sons, Ltd.