Potential of a low-cost gas sensor for atmospheric methane monitoring

In order to expand current atmospheric methane monitoring capabilities, we investigated the performance of an off-the-shelf, low-cost, metal oxide based methane (CH4) gas sensor. A sensor assembly was designed that powered the gas sensor and its resistive heater, provided ancillary temperature (T) and relative humidity (rH) measurements, and controlled sensor read-out and data storage. After calibrating the gas sensor with respect to methane concentration ([CH4]), T, and rH, we were able to estimate the [CH4] of lab air over a period of 31 days for a large range of T and rH conditions with a systematic error of −1.0 ppm and a variable error within ±1.7 ppm. The sensor showed no significant drift in [CH4] estimate. We show that sensor accuracy can likely be improved by optimizing the voltage regulator that powers the gas sensor's heater, and by measuring and compensating for the difference in partial oxygen pressure of the air that was sampled during calibration and validation experiments. Such improvements are expected to allow the use of the sensor assembly for fence-line methane monitoring, for example near fossil fuel extraction sites. In its current form, the sensor assembly is suitable for detecting fugitive methane from leak-prone equipment.