Carbon monoxide as a tracer of gas transport in snow and other natural porous media

The movement of air in natural porous media is complex and challenging to measure. Yet gas transport has important implications, for instance, for the evolution of the seasonal snow cover and for water vapor transport in soil. A novel in situ multi-sensor measurement system providing high-resolution observation of gas transport in snow is demonstrated. Carbon monoxide was selected as the tracer gas for having essentially the same density as air, low background concentration, low water solubility, and for being detectable to ≤ 1 ppmv with small, low-cost, low-power sensors. The plume of 1% CO injections 30 cm below the snow surface was monitored using 28 sensors (4 locations, 7 depths). The CO breakthrough curves obtained at distances of 0.5–1 m were in good agreement with a simple analytical advection-diffusion model. The tracer system appears suitable for a wide range of applications in experimental soil science and hydrology addressing moisture transport and evapotranspiration processes.