Development of a low-cost gas sensor network for atmospheric methane concentration monitoring

The production of shale gas in the US increased from less than 1 trillion cubic feet (TCF) in 2006 to more than 8 TCF in 2011. This growth in production was made possible by recent advances in horizontal drilling combined with hydraulic fracturing (‘hydrofracking' or just ‘fracking'). The impact of fracking operations on the greenhouse effect is the subject of much debate; burning natural gas rather than coal to produce electricity significantly reduces the amount of CO2 emitted, but fugitive methane from gas well completions and gas transmission could offset the savings gained from CO2 reductions. While researchers are divided on whether shale gas is an appropriate fuel to reduce CO2 equivalent emissions most studies agree that there is a need for more data on the emissions and atmospheric concentrations of methane.

Typically, the concentration of methane is measured by gas chromatography or by laser-based spectrometry. Both methods are expensive, and cover only a small portion of the spatiotemporal domain of interest: an instrument either measures one, and only one, location continuously, or it is used on infrequent transects, covering a lot of terrain but without recording a continuous evolution of the methane concentration in time.

To fill this gap, we are developing a low-cost methane sensor assembly based on metal oxide sensor technology, which is capable of measuring methane concentrations in the ppm range. This assembly would allow scientists and local communities to continuously collect data on atmospheric methane concentrations at various locations. A network of these sensors could be setup near fracking sites to monitor methane emissions. The main component of the sensor assembly is a Figaro TGS26xx-series gas sensor. As this type of sensor is also sensitive to temperature and relative humidity (rH), we lab-calibrated the gas sensor for its response to these properties, and we continuously monitor ambient temperature and rH during methane measurements. The data are stored locally and are also sent to an online application, myObservatory, where the data are collected, post-processed and published online in real-time.

Here we describe the different assembly components and how they are connected, as well as the procedures and equipment that were used to calibrate the gas sensors with respect to rH, temperature and methane concentration. Finally, we present results from field tests and from sensors deployed near fracking sites in West Virginia.