A Low-Cost NDIR-Based N₂O Gas Detection Device for Agricultural Soils: Assembly, Calibration Model Validation, and Laboratory Testing

This research presents a low-cost, easy-to-assemble nondispersive infrared (NDIR) device for monitoring N₂O gas concentration in agricultural soils during field and laboratory experiments. The study aimed to develop a cost-effective instrument with a simple optic structure suitable for detecting a wide range of soil N₂O gas concentrations with a submerged silicone diffusion cell. A commercially available, 59 cm path-length gas cell, microelectromechanical systems (MEMS)-based infrared emitter, pyroelectric detector, two anti-reflective (AR) coated optical windows, and one convex lens were assembled into a simple instrument with secure preciseness and responsivity. Control of the IR emitter and data recording processes was achieved through a microcontroller unit (MCU). Tests on humidity tolerance and the saturation rate of the diffusion cell were carried out to test the instrument function with the soil atmosphere. The developed calibration model was validated by repeatability tests and accuracy tests. The soil N₂O gas concentration was monitored at the laboratory level by a specific experimental setup. The coefficient of determination (R²) of the repeatability tests was more than 0.9995 with a 1-2000 ppm measurability range and no impact of air humidity on the device output. The new device achieved continuous measuring of soil N₂O gas through a submerged diffusion cell.