# Application of a High-Performance, Low-Cost Portable NDIR Sensor Monitoring System for Continuous Measurements of In Situ Soil CO2 Fluxes

## TL;DR

A new low-cost, portable CO2 sensor system was developed and tested for reliable and accurate soil CO2 flux measurements.

## Contribution

A portable, low-cost soil respiration system using NDIR and LoRa technology was developed and validated against a commercial system.

## Key findings

- The SRS showed high agreement with the LI-8100A with R² values of 0.996 and 0.997 in simulated and field experiments.
- Bland–Altman analysis confirmed consistency between the SRS and LI-8100A measurements.
- The system enables multi-point measurements and wireless data transmission for monitoring soil CO2 fluxes.

## Abstract

Monitoring soil CO2 is essential for accurately quantifying the sources and sinks of atmospheric greenhouse gases and for providing carbon emission reduction strategies. However, the limited portability and high cost of conventional soil CO2 monitoring equipment have severely restricted large-scale and long-term field observations. To address these constraints, this study has successfully designed and fabricated a portable and low-cost soil respiration system (SRS) based on non-dispersive infrared (NDIR) sensor technology and Long-range radio (LoRa) wireless communication. The SRS enables multi-point synchronous measurements and remote data transmission. Its reliability was rigorously evaluated through both simulated and field comparative experiments against the LI-8100A. The results demonstrated a high level of agreement between the measurements of the SRS and the LI-8100A, with the coefficients of determination (R2) of 0.996 and 0.997, respectively, for the simulation and field experiments, with the corresponding root mean square error (RMSE) of 0.090 and 0.089 μmol·m−2·s−1. The Bland–Altman analysis further confirmed the consistency between the two systems, with over 95% of the data points falling within the acceptable limits of agreement. These findings indicate that the self-developed SRS substantially reduces costs while maintaining reliable measurement accuracy. With its wireless transmission and multi-point deployment capabilities, the SRS offered an efficient and practical solution for addressing the challenges of monitoring spatial heterogeneity of soil respiration, demonstrating considerable potential for broader application in CO2 flux monitoring research.