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Soil gas carbon dioxide probe: laboratory testing and field evaluation
B M Patterson1, A J Furness, T P Bastow
1CSIRO Land and Water, Private Bag 5, Wembley, WA 6913, Australia. bradley.patterson@csiro.au
Environmental Science. Processes & Impacts
|April 9, 2013
Summary
A new automated instrument accurately measures carbon dioxide (CO2) in the vadose zone using diffusion-based sampling. This reliable method simplifies monitoring and reduces soil disturbance compared to traditional techniques.
Area of Science:
- Environmental Science
- Geochemistry
- Analytical Chemistry
Background:
- Vadose zone monitoring is crucial for understanding subsurface processes.
- Traditional methods for measuring soil gas CO2 concentrations are often labor-intensive and can disturb the soil profile.
- There is a need for automated, reliable, and less invasive techniques for continuous CO2 monitoring.
Purpose of the Study:
- To develop and evaluate an automated, semi-continuous on-line instrument for measuring CO2 gas concentrations in the vadose zone.
- To assess the reliability and accuracy of the developed instrument under challenging field conditions.
- To compare the performance of the new instrument with conventional grab sampling techniques.
Main Methods:
- Development of an automated instrument utilizing semi-permeable polymer tubing (CO2 probe) for diffusion-based sampling.
- Coupling the CO2 probe with an infra-red sensor for gas concentration measurement.
- System operation involved intermittent purging of the CO2 probe with a non-CO2 gas and monitoring the exiting gas at the surface.
- In situ probes were installed in the vadose zone for long-term (18 months) monitoring.
Main Results:
- The instrument provided reliable, automated, semi-continuous on-line measurements of CO2 concentrations in the vadose zone.
- The diffusion-based sampling technique showed no interference from non-CO2 gases or volatile organic compounds.
- Data obtained were comparable to conventional grab sampling techniques.
- The method proved reliable under aggressive and dynamic field conditions over 18 months.
Conclusions:
- The developed automated instrument offers a reliable and efficient method for long-term vadose zone CO2 monitoring.
- This diffusion-based sampling technique reduces labor and minimizes disturbance to soil CO2 profiles compared to conventional methods.
- The instrument is suitable for aggressive and dynamic environmental conditions, providing valuable data for subsurface studies.
