A gas-flow funnel system to quantify advective gas emission rates from the subsurface

Abstract

The estimation of greenhouse gas emission rates from the subsurface into the atmosphere is an important part of climate-related research activities and associated efforts concerning the global carbon cycle. For the direct quantification of gas emission rates from the subsurface to the atmosphere a large variety of gas detection and flux quantification techniques exists. With the goal of measuring advective CO2 gas exhalations circumventing limitations of available systems such as e.g. accumulation-chamber systems or eddy-flux covariance methods, we developed a simple, robust, and low-cost gas-flow funnel system. The device allows for the continuous measurement of mass flow rates with a free, unrestricted gas flow from advectively dominated gas exhalation spots. For the design of the gas-flow funnel we used custom-made, though easy-to-produce components, and sensors that are typically already available when working at such sites. Our general design can easily be applied at sites with focused, advectively driven gas exhalation like volcanic areas, shale-gas seeps, landfills, and open boreholes. For the proof-of-concept we tested the system during three field campaigns at a site with natural CO2-bound emissions associated with a geologic fault in southwestern Germany. The measurements showed to be comparable and repeatable throughout the three campaigns, and are consistent with findings from other field sites with comparable CO2 exhalations.