A Robust OB-QEPAS Sensor for In-Situ Detection of Dissolved Methane in Natural Waters

= 0.9994) across the 10-1000 ppm range. Field measurements in Lake Chaohu successfully quantified dissolved methane concentrations ranging from 3.65 to 22.49 ppm across different aquatic habitats, showing excellent agreement (deviation <1%) with tunable diode laser absorption spectroscopy (TDLAS) data. The observed gradient empirically resolved two distinct methane dynamics endmembers: production driven by urban eutrophication and consumption mediated by wetland oxidation. This work delivers both a high-performance analytical tool and a generalizable framework for robust optical gas sensors, highlighting their potential to advance from environmental monitoring to biogeochemical process analysis.