DOI: 10.25675/10217/234550
title: Dataset associated with "A cautionary report of calculating methane emissions using low-cost fence-line sensors"

description: A simulated fence-line was constructed at the Colorado State University Methane Emissions Technology Evaluation Center (METEC) site in Fort Collins, CO, USA between the August 27th and September 4th 2020. Four Figaro TGS2611-E00 sensors (Figaro Engineering, Inc.) were deployed with control from a Raspberry Pi and power supplied by solar panels. The sensors were mounted in holes in the bottom of a weather-resistant box and exposed to sample air passing the bottom of the box. Each sensor box also contained a DHT22 temperature and relative humidity sensor (Adafruit Industries). Data presented here were collected by the “Node 1” sensor 30 m away at 45 °N to the emission point, “Node 2” sensor 30 m away at 215 °N to the emission point, “Node 3” sensor 30 m away at 225 °N to the emission point, and “Node 4” sensor 30 m away at 315 °N to the emission point. Methane concentration data were collected every 5 seconds during a natural gas emission of 84 g CH4 h-1 between 2020-08-27 1800 UTC and 2020-08-29 1559 UTC, 167 g CH4 h-1 between 2020-08-29 1600 UTC and 2020-08-31 1559 UTC, and 313 g CH4 h-1 between 2020-08-31 1600 UTC and 2020-09-02 1457 UTC.
description: Methane is emitted during extraction, processing, and transport processes in the natural gas industry. As a powerful greenhouse gas, methane releases are harmful to the environment. Operators aim to minimize methane loss, and continuous monitoring using low-cost fence-line sensors are now being developed to observe methane enhancements downwind of operations. However, it is not clear how useful these systems are and whether they can be used to quantify emissions or simply identify the presence of a leak. To investigate this, we deployed four calibrated low-cost sensors 30 m from emissions of known rates over a 48-hour period. The aims were to determine: 1) how much of the time a fence-line system would detect a leakage event from a single, point source of the size typically seen at oil and gas production well pads; and 2) how accurately a fence-line system can estimate emissions using a relatively simple downwind dispersion method. Our results show that during the 48-hour measurement period the sensors could detect mixing ratios greater than an enhancement threshold of 2 ppm for methane releases of 84 g h-1 40% of the time, 100% of the time for emissions of 167 g h-1 and 100% of the time downwind of the 313 g h-1. We show that emissions can be overestimated by as much as 4 x 10102 times using a simple Gaussian plume equation, which was attributed to the inability of the equation to parameterize lateral dispersion at distances less than 100 m. Using two other methods, near real-time average emissions can be calculated to be within 23% of a known emission rate of the source, however individual emissions can vary by -100% and +1,885%. This study provides evidence to support the use of low-cost sensors as autonomous fence-line monitoring systems to detect and potentially quantify emissions. If the sensors are properly calibrated and sensor deployment location is optimized for prevailing wind directions at each site, fence-line systems could be used routinely to quantify emissions from oil and gas infrastructure.