A portable low-cost device to quantify advective gas fluxes from mofettes into the lower atmosphere: First application to Starzach mofettes (Germany)

Abstract

In this study, we introduce a portable low-cost device for in situ gas emission measurement from focused point sources of CO2, such as mofettes. We assess the individual sensors’ precision with calibration experiments and perform an independent verification of the system’s ability to measure gas flow rates in the range of liters per second. The results from one week of continuous CO2 flow observation from a wet mofette at the Starzach site is presented and correlated with the ambient meteorological dynamics. In the observed period, the gas flow rate of the examined mofette exhibits a dominant cycle of around four seconds that is linked to the gas rising upwards through a water column. We find the examined mofette to have a daily emission of 465 kg ±16 %. Furthermore, two events were observed that increased the flow rate abruptly by around 25 % within only a few minutes and a decaying period of 24 hours. These types of events were previously observed by others at the same site but dismissed as measurement errors. We discuss these events as a hydrogeological phenomenon similar to cold-water geyser eruptions. For meteorological events like the passages of high pressure fronts with steep changes in atmospheric pressure, we do not see a significant correlation between atmospheric parameters and the rate of gas exhalation in our one-week time frame, suggesting that on short timescales the atmospheric pumping effect plays a minor role for wet mofettes at the Starzach site.

CO2 Dynamics in a Mofette: Measurement and Modeling

“…Based on these criteria, we chose the STC31 sensor 18 for the 𝐶𝑂 2 concentration measurement, which had previously been successfully used by another research group for measuring carbon dioxide concentration in a wet mofette under similarly challenging measurement conditions 8 . We used 20 STC31 sensors mounted on an extruded aluminum rod at intervals of 5 cm using 3D-printed holders.…”

“…However, focused emissions like those from mofettes present an opportunity to study 𝐶𝑂 2 release mechanisms under a different lens. These emissions are intense and localized, providing a contrast to the broad-scale diffuse emissions 8 . Despite their potential for offering insights into underground gas dynamics and their inŕuence on local environments, focused emissions from natural sources like mofettes have received less attention in scientiőc literature compared to their diffuse counterparts.…”