EGU General Assembly 2020
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the Creative Commons Attribution 4.0 License.

Development of an in-situ CO­2 gradient sampler

Laurin Osterholt and Martin Maier
Laurin Osterholt and Martin Maier
  • Forest Research Institute Baden-Württemberg, Soil and Environment, Germany (

Gas fluxes between soil and atmosphere play an important role for the global greenhouse gas budgets. Several methods are available to determine soil gas fluxes. Besides the commonly used chamber methods the gradient method becomes more and more important. Chamber methods have the disadvantage that the microclimate can be influenced by the chamber which can affect gas fluxes. This problem does not occur with the gradient method. Furthermore the gradient method has the advantage that it can provide information about the depth profile of gas production and consumption in the soil.

The concept of the gradient method is to calculate gas fluxes by the vertical concentration gradient of a gas in the soil. For the calculation of the flux the effective diffusivity coefficient of the soil is needed. This can be approximated by models or by lab measurements. However, both of these approaches often fail in explaining site specific characteristics and spatial variability. Another way to determine soil gas diffusivity is to apply the gradient method using a tracer gas. By the injection of a tracer gas with known flux soil gas diffusivity can be measured in-situ.

We developed an innovative sampling set-up to apply an improved gradient method including the possibility to determine soil gas diffusivity in situ. We designed a sampler with build-in CO2 sensors in multiple depths that can easily be installed into the soil. With this sampler CO2 concentrations can be measured continuously in several depths. This enables the identification of short-time effects such as the influence of wind-induced pressure pumping on gas transport. The sampler allows tracer gas injection into the soil for in-situ diffusivity measurement. We decided for CO2 as a tracer gas because it can be measured with small sensors which keep the set-up simple. To account for the natural CO2 production in the soil we developed a differential gas profile approach. Using an additional reference sampler allows measuring the natural CO2 gradient without the tracer signal, and thus subtracting the tracer CO2 signal from the natural CO2 signal.

The sampler consists of one 3D print segment per depth each containing one CO2 sensor. These parts can be combined to a sampler with flexible amount of measurement depths. The construction with individual segments allows a better maintenance in case of sensor defects. For the installation of the sampler a hole has to be drilled, into which the sampler is inserted. To prevent gas bypassing along the wall of the drill hole we equipped each segment with an inflatable gasket between the measurement locations.

In a next step we will evaluate the sampler and test it in the lab and under different environmental conditions. We expect that with this sampler we will be able to run gas transport experiments in the field with a high temporal resolution and relatively low effort.


We thank Alfred Baer and Sven Kolbe for the technical support.

How to cite: Osterholt, L. and Maier, M.: Development of an in-situ CO­2 gradient sampler, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7272,, 2020.


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  • CC1: Comment on EGU2020-7272, Nicholas Nickerson, 08 May 2020

    Very cool idea. Are the inflatable gaskets available commercially or are you building them yourselves. Are the CO2 sensors from Dynament? Do you have multiple sensors on a single channel (adressable sensors?) , or are all of the sesnors on seperate wire pairs? Finally for the windows that are open to the soil air, are they protected by a membrane?

    Do you have any data on drift over time? Also how easy is it to extract the profiler if you want to take the sensors back for calibration?

    • AC1: Reply to CC1, Laurin Osterholt, 12 May 2020

      Hi Nicholas,

      Cool that you’re interested in our project.

      1. The inflatable gaskets are self-built. They are made out of pieces of bicycle tubes that are glued to the 3D-print parts. The pressurized air is distributed through holes in the 3D-print. At the connection between the separate segments we used O-rings for sealing.
      2. The CO2 Sensors are from Dynament, yes.
      3. Till now we use the analog output of the sensors. So analog out and power supply goes on separate wires for each sensor. We are also experimenting with the Rx Tx Digital Output which would make Data reading more flexible (e.g. also accessing temperature signal).
      4. We use a membrane covering the sensor. It is glued to the 3D-print part over the hole were the sensor is installed. The windows that are open to the soil air are only protected by fabric against animals.
      5. We don’t have any data on drift over time yet. But we’re just starting.
      6. The profiler can easily be extracted out of the soil. The sensors themselves are more difficult to extract. You would have to take apart the single 3D-print segments which are connected by a threaded bar, then remove the membrane that is covering the sensor and finally pull out the sensor with the wires that is soldered to the sensor. But it’s also possible to put the whole sampler (without extracting the sensors) into a closed chamber to determine correction factors for the individual sensors.



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