A Self-Developed Low-Cost Automated Soil Gas Flux System for Real-Time Monitoring: Design and Field Validation

High-frequency and long-term measurements of soil gas fluxes are essential for quantifying terrestrial carbon cycling and for monitoring fluid migration processes associated with hydrological, tectonic, and volcanic activity. However, the widespread application of automated soil gas flux observations remains limited by the high cost, power consumption, and operational complexity of commercial systems.

We present a self-developed, low-cost automated soil gas flux (ASF) system designed for real-time, long-term field monitoring. The system is based on a closed-chamber circulation concept integrating a low-cost NDIR CO₂ sensor, controlled gas mixing and flushing, humidity regulation using a drying module, and environmental correction for soil temperature and atmospheric pressure. A modular hardware architecture, combined with a microcomputer-based controller, enables flexible configuration, autonomous operation, and wireless data transmission. The system is powered by a solar-assisted lithium battery unit, allowing continuous deployment in remote environments.

Laboratory validation shows that CO₂ concentrations measured by the ASF system exhibit excellent linearity when compared with a high-precision cavity-enhanced gas analyzer (LGR M-GGA-918), with deviations generally within ±5% across a wide concentration range. Field deployments lasting more than three months demonstrate stable system performance, energy autonomy, and the ability to resolve high-temporal-resolution variability in soil CO₂ fluxes. A dedicated data-processing workflow is implemented to identify stable accumulation intervals and convert high-frequency concentration time series into instantaneous and diel-scale fluxes.

The ASF system provides a cost-efficient, scalable, and reproducible solution for continuous soil gas flux monitoring. Its open and modular design makes it suitable for applications ranging from ecosystem carbon exchange and ecohydrological studies to fault-zone degassing and volcano-related gas monitoring, and facilitates integration into multi-parameter geophysical and geochemical observation networks.