Using near-surface atmospheric measurements as a proxy for quantifying field-scale soil gas flux

Abstract

We present a new method for deriving surface soil gas flux at the field scale, which is less fieldwork intensive than traditional chamber techniques and less expensive than those derived from airborne or space surveys. The “open-field” technique uses aspects of chamber and micrometeorological methods combined with a mobile platform and GPS to rapidly derive soil gas fluxes at the field scale. There are several assumptions in using this method, which will be most accurate under stable atmospheric conditions with little horizontal wind flow. Results show that soil gas fluxes, when averaged across a field site, are highly comparable between the open-field method and traditional chamber acquisition techniques. Atmospheric dilution is found to reduce the range of flux values under the open-field method, when compared to chamber-derived results at the field scale. Under ideal atmospheric conditions it may be possible to use the open-field method to derive soil gas flux at an individual point; however this requires further investigation. The open-field method for deriving soil–atmosphere gas exchange at the field scale could be useful for a number of applications including quantification of leakage from CO2 geological storage sites, diffuse degassing in volcanic and geothermal areas, and greenhouse gas emissions, particularly when combined with traditional techniques.