资源环境科技发展态势分析平台

We investigate the influence of near‐surface wind conditions on sub‐surface gas transport and on soil‐atmosphere gas exchange for gases of different density. Results of a sand tank experiment are supported by a numerical investigation with a fully coupled porous medium‐free flow model, which accounts for wind turbulence. The experiment consists of a two‐dimensional bench‐scale soil tank containing homogeneous sand and an overlying wind tunnel. A point source was installed at the bottom of the tank. Gas concentrations were measured at multiple horizontal and vertical locations. Tested conditions include four wind velocities (0.2/1.0/2.0/2.7 m/s), three different gases (helium: light, nitrogen: neutral, carbon dioxide: heavy) and two transport cases (1: steady‐state gas supply from the point source, 2: subsequent to termination of gas supply, transport under decreasing concentration gradient). The model was used to assess flow patterns and gas fluxes across the soil surface. Results demonstrate that flow and transport in the vicinity of the surface are strongly coupled to the overlying wind field. An increase in wind velocity accelerates soil‐atmosphere gas exchange. This is due to the effect of the wind profile on soil surface concentrations and due to wind‐induced advection, which causes sub‐surface horizontal transport. The presence of gases with pronounced density difference to air adds additional complexity to the transport through the wind‐affected soil layers. Wind impact differ between tested gases. Observed transport is multi‐dimensional and shows that heavy as well as light gases cannot be treated as inert tracers, which applies to many gases in environmental studies.