Relating wind-induced gas exchange to near-surface wind speed characteristics in porous media

The impact of near-surface wind speed characteristics on dry porous media gas transport and gas exchange across the medium surface were investigated experimentally using four different porous media subjected to 11 wind conditions with different wind speed characteristics. The tracer gases were O₂ and CO₂, applied with constant concentrations at the medium surface. Tracer gas breakthrough curves (gas concentrations as a function of time) were measured at multiple depths inside the porous media. Tracer gas breakthrough time (the time required for the gas concentration at a given depth to reach 50% of the surface concentration) was used as a measure of the gas exchange rate. Potential relationships between breakthrough time and wind speed characteristics in terms of average wind speed, wind speed standard deviation, and wind speed power spectrum properties in three dimensions were investigated. Statistical analyses indicated that wind speed had a very significant impact on breakthrough time and that the characteristics for the wind speed component perpendicular to the porous medium surface were especially important.