Monitoring natural CO2 emissions using a low cost sensor network

The natural carbon dioxide (CO2) emission of the Eyach valley (between Horb and Rottenburg, Northern Black Forest, Germany) is observed and analysed in the proposed project. CO2 can accumulate near the surface and become hazardous for animals and humans. Also, CO2 is a climate-active greenhouse gas and contributes to the climate change.

The CO2 concentrations in the Eyach valley have never been quantified with scientific methods. Similar and much larger areas with CO2 mofetta exist in various regions of the world and are not quantified. Thus the contribution of natural CO2 emission from geological sources to the atmospheric gas budget is entirely unknown.

Goal of the project is the monitoring of the geological CO2 emission into the lower atmosphere in the Eyach valley and its surrounding. The experimentally gathered data will be used to quantify the amount of emitted CO2 and to specify the horizontal and the vertical gas fluxes, including temporal (diurnal and seasonal) variations.

In order to reach this goal, a network of low-cost sensors will be installed, supported by a single eddy-covariance (EC) station. The low costs of a single sensor allow for the deployment of a larger number of sensors. The network gives both data with horizontal resolution and (after integration) area-representative numbers, including high temporal resolution.

During the last years, the environmental-physics group at the University of Tübingen developed the suited type of low-cost sensors for this project. The usual disadvantage of low-cost equipment compared to high-grade sensors is a reduced absolute accuracy. Therefore, the sensor network will be complemented by an EC station that does not only deliver higher accuracy for the calibration of the network, but also the directly measured turbulent gas and heat fluxes, at least at one single location. The EC station is thus the reference for the calibration, for the determination of the turbulent exchange coefficients and for the long-term stability of the network.

In addition to the CO2 measurement, the low-cost sensors will also be equipped with air temperature and air humidity sensors. Within the project, all sensors have to be obtained, but not financed: the entire equipment for the proposed project is already funded by the Alfred-Teufel foundation. Finally, the measured data will be added to a data base and offered to the science community via an internet interface.

The project is structured in two phases of three years duration each. Here only the first phase is applied for. During the second phase, the measured data are used for the initialisation and verification of a numerical dispersion model. Furthermore, the developed methods will be exported to other regions with geological CO2 emission.