Effect of near-surface wind speed and gustiness on horizontal and vertical porous medium gas transport and gas exchange with the atmosphere

Effects of wind speed and wind gustiness on horizontal and vertical subsurface gas transport and subsurface-atmosphere gas exchange were investigated experimentally using a 40cmx40cm, 35-cm-deep stainless steel container, filled with a dry granular porous medium (crushed basalt) of 2-4-mm grain size. Experiments used CO2 and O-2 as tracer gases and were conducted under both steady and gusty wind at speeds ranging from 0 to 5.6ms(-1). Tracer gas breakthrough curves were measured at 20 locations within the porous medium to assess both horizontal and vertical gas movement. Results indicated that horizontal gas movement in wind-exposed porous materials is important, especially near the wind-exposed surface, and suggested considerable effects of both wind speed and wind gustiness on both horizontal and vertical gas transport inside the porous medium as well as subsurface-atmospheric gas exchange. Although wind-induced subsurface gas transport is likely to be multidimensional, one-dimensional model simulations indicated that vertical transport is an adequate approximation of the resulting average gas transport and exchange with the atmosphere over a larger area.