Effect of Barometric Pressure Fluctuations on Gas Transport over Soil Surfaces

Abstract

Molar diffusion mechanism is generally considered to be the main physical process of gas transport at the soil–atmosphere interface. However, the advection mechanism in porous medium can considerably affect soil gas transport. Barometric pressure fluctuations caused by pressure pumps is one of the main factors that affects the advection mechanism. Most of the existing studies are overly focused on the construction of complex mathematical models and cannot exclude other environmental factors from interfering. In the present study, a simple attenuation form of barometric fluctuations was explored as a “minimum unit” of pressure wave in laboratory. A pressure attenuation model (PAM) was developed to verify the relationship between pressure difference and gas emission from soil surface by measuring the change in pressure attenuation. The effect of pressure fluctuations on soil surface gas fluxes was then quantified based on the calculated fluxes. In addition, the relationship between the physical properties of the soil medium and the change in pressure was also analyzed. The results show that fluctuations in air pressure can cause a change in soil CO2 fluxes by an order of magnitude (change of 1 Pa can result in approximately 100% change in flux for sandy loam). The sensitivity of different soil medium to pressure differences was positively correlated with soil gas permeability, which is the main physical property of soil that influences the response of gas to pressure fluctuations. These results provide important prerequisites for quantifying more complex pressure fluctuations in a future study.