Effects of Wind Speed and Wind Gustiness on Subsurface Gas Transport

Abstract

Core Ideas Subsurface gas transport as related to near‐surface wind speed and gustiness was measured. Increased wind gustiness tended to decrease subsurface gas movement at greater depth. Horizontal gas concentration gradients and gas movement in the subsurface are important. Wind action appears to induce an advective gas flow pattern in the subsurface. The impact of near‐surface wind speed and wind speed fluctuations (gustiness) on subsurface gas transport and exchange with the atmosphere was investigated with a focus on assessing the extent of vertical and horizontal gas transport in the subsurface. Investigations involved the use of a 40‐ by 40‐cm, 35‐cm‐deep stainless steel container filled with a dry granular porous medium (2–4‐mm grain size), applying CO2 and O2 as tracer gases. Experiments were performed under controlled (laboratory) conditions for different wind speeds (0–5.6 m s−1) under both gusty and non‐gusty wind conditions. Horizontal gas movement in the porous medium both parallel and perpendicular to the wind direction was controlled via a set of separation walls that could be installed inside the porous medium to assess the importance of horizontal gas velocities in the porous medium. Results indicate that average wind speed was the most important parameter controlling porous medium gas transport, especially near the surface. However, at greater depths, wind gustiness and horizontal gas movement also had significant impacts on the overall gas transport.