A low-cost IoT-based accumulation chamber for measuring diffuse CO2 fluxes: Design, user-friendly software, calibration, and field validation at Nea Kameni volcano (Santorini)

This work introduces a low-cost, custom-built, portable Internet of Things (IoT)-based Accumulation Chamber (IoT-AC), which integrates an ESP32 microcontroller, a Sensirion SCD30 CO2 sensor, and a servomotor for air homogenization, all controlled by a user-friendly, cross-platform application. Laboratory calibration confirmed the system's exceptional linearity (R2 0.9997) from CO2 rates of ~1 to ~1400 ppm·s-1, corresponding to CO2 diffuse fluxes ranging from ~30 (i.e., organic background fluxes) to ~38,900 g·m-2·d-1 (i.e., high fluxes in volcanic areas). During a rigorous field campaign at the Nea Kameni volcano in Santorini, Greece, the IoT-AC demonstrated a striking similarity to an industry-standard. Geostatistical analysis of the parallel datasets yielded comparable estimates of total diffuse flux (~9 tons·day-1 of CO2). This study validates the IoT-AC as a viable and scalable open-source alternative for diffuse soil volcanic CO2 monitoring, successfully lowering the financial barrier to high-quality data collection, making it accessible within practically any scientific budget, and hence enabling quantitative improvements in volcanic hazard assessment and the resolution of critical uncertainties in global volcanic carbon budgets.