Abstract We demonstrate a novel experimental arrangement for measuring wind turbulence-induced gas transport in dry porous media under controlled conditions. This equipment was applied to assess the effect of wind turbulence on gas transport (quantified as a dispersion coefficient) as a function of distance to the surface of the porous medium exposed to wind. Two different strategies for the measurement of wind-induced gas transport were compared. Experiments were carried out with O 2 and CO 2 as tracer gases with average vertical wind speeds of 0.02–1.06 m s −1.

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Oxygen breakthrough curves as a function of distance to the wind-exposed surface of the porous medium were analysed numerically with a finite-difference-based model to assess gas transport. We showed that wind turbulence-induced gas transport is an important transport mechanism that can be 20–70 times larger than molecular diffusion-induced transport.

Pediatrics In Review Rapidshare. Wind conditions and properties of the porous medium had strong controlling effects on this relationship. Importantly, we show that even though wind-induced gas transport is greatest near to the wind-exposed surface, it can have marked effects on the variation in gas concentration at much greater depths.

Highlights • We explored the effect of atmospheric wind turbulence on gas transport in porous media. • We measured the depth relation of wind-induced dispersion in porous media for real wind conditions.

• Wind-induced gas dispersion coefficients were 20–70 times larger than molecular diffusion. • Wind turbulence can potentially have a considerable effect on gas transport in porous media. • • Introduction Greenhouse gases play an important role in global warming.

Soil is a source of some greenhouse gases, such as methane (CH 4), carbon dioxide (CO 2) and nitrous oxide (N 2O). Various soil properties affect soil gas emissions, such as humidity, temperature, air pressure and vegetation (Oertel et al., ). Furthermore, the emission of methane, which is an important greenhouse gas, can result from land management practices; for example, from rice paddy soil and landfill sites that receive organic matter (Topp & Pattey, ). Radon (Rn) is a radioactive gas that can move from soil to the atmosphere with the potential to affect human health.

Advective flow controlled by wind and the difference between indoor and outdoor temperatures are the main factors in the transport of radon from soil to air and buildings (Nazaroff, ). Oliver & Khayrat () found that in addition to lithology, factors such as elevation, soil depth and particle size can affect the spatial variation in radon in the soil atmosphere.

Wind action (high-frequency velocity or pressure fluctuations caused by wind turbulence) has been shown in several cases to play an important role in the transport of gaseous compounds in soil and other porous media, and the exchange of these compounds with the atmosphere. Examples include: radon (Rn) transport into buildings (Riley et al.,; Wang & Ward, ), landfill gas emissions (Poulsen et al.,; Poulsen & Moldrup, ), water evaporation from soil (Hanks & Woodruff,; Acharya & Prihar,; Ishihara et al.,; Novak et al.,,b) and exchange of natural soil gases with the atmosphere (Takle et al.,; Massman & Frank,; Maier et al., ). In particular, Poulsen & Moldrup () identified that wind-induced turbulence was responsible for 40% of total landfill gas emissions at a Danish landfill site during a 7-day period. Hanks & Woodruff () found that the rate of water evaporation increased two to six times for soil mulches and 10–15 times for gravel and straw when wind speed increased from 0 to 40 km h −1. Wind turbulence (gustiness) affects gas transport in porous media by inducing high-frequency, multi-directional fluctuations in gas velocity with durations of up to 1 minute within the pore system of the porous medium (Takle et al.,; Poulsen & Moldrup,; Maier et al., ). These fluctuations, in turn, result in gas transport by advection and dispersion in addition to the molecular diffusion that is always present (Maier et al., ). Several studies have modelled the effect of the gustiness of wind on gas transport in porous media in one, two and three dimensions (Farrell et al.,; Scotter & Raats,; Kimball & Lemon,; Colbeck, ).