Methane Sensor Characterization Using Colocated Ambient Comparisons and Simulated Emission Challenges

Methane sensing technologies have wide applications, including leak detection and repair in the energy sector and emissions monitoring from landfills and agriculture. Lower-cost units, as opposed to reference-grade instrumentation, may be deployed in many forms (e.g., sensor networks, unmanned aerial vehicles, and mobile monitoring) and allow vastly improved spatial and temporal data resolution owing to their scalability. Ultimately, early detection of unexpected emissions enabled by lower-cost sensing technologies provides industry with rapid operational feedback, allowing for emission reductions and improved process control. The expanded use of such technologies allows for consolidation and resolution of “bottom-up” emission inventories with results using emerging “top-down” techniques (e.g., satellite measurements), thereby improving emissions management on many scales. Here, we introduce a novel testing method to assess four leading commercial methane monitoring technologies that employ three distinct working principles: metal oxide (MOx) conductometry, tunable diode laser (TDL) spectrometry, and photoacoustic spectrometry (PAS). We assess both nominal baseline performance and sensor response using ambient measurements and controlled release experiments, respectively. We observe the PAS technology to provide the lowest baseline signal noise (and therefore the lowest detection limit), followed by TDL and MOx. We also observe PAS to have the highest agreement with reference instrumentation during simulated emission plume events (with TDL and MOx technologies generally trailing in accuracy). Outcomes of this work include guidance for researchers and practitioners seeking to better understand the best available commercial methane sensor technology. Analysis approaches employed here may also be applied to many other low-cost gas sensing technologies.