Open or Closed? Measurement Performance of Open- and Closed-Path Methane Sensors for Mobile Emissions Screening
Date
2024-01-11
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Abstract
Ground-based vehicle systems are being increasingly used by industry, regulators, and service providers in the upstream oil and gas sector to measure methane emissions. However, the suite of methane sensors affixed to these systems is non-standardized and existing literature displays a scarcity of direct comparisons regarding their measurement performance. Gaussian dispersion models are often used to supplement measured data and derive estimates of emission intensity in screening applications based on data measured by these sensors. Existing literature indicates these models perform with considerable uncertainty. As such, equivalence of performance between existing vehicle-based emission screening systems is difficult to assess. To address this issue, field-based controlled release experiments were conducted to compare concentration data from an open- and closed-path sensor deployed in tandem onboard a vehicle. Performance of a forward Gaussian dispersion model was assessed relative to measured data from both sensors. 801 transects were driven through methane plumes dispersed downwind of a controlled emission source at various measurement distances and driving speeds, as well as a range of atmospheric conditions. Measurement performance was predicated on three primary descriptors of concentration data: the maximum concentration within each plume (maximum enhancement), plume width, and plume area (total methane sampled within the plume). Results showed that the measurement performances of both sensors were not equivalent. Relative to the open-path sensor, the closed-path sensor reported maximum enhancements that were ~40% smaller on average and plume widths that were ~42% larger on average, while measures of plume area displayed near 1:1 parity. Measurement discrepancies are largely explained by differences in sensor measurement frequency and intrinsic sampling mechanisms. Forward Gaussian dispersion model performance displayed uncertainties ranging from 12.3% to 1207.0%. The origin of this uncertainty is largely determined by generalizations of atmospheric stability and simplistic representations of downwind plume migration within the model.
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Keywords
Methane, Emissions, Oil and gas, Emissions measurement, PoMELO, Methane sensing, Gaussian dispersion model, Closed-path methane sensor, Open-path methane sensor
Citation
Billinghurst, C. D. (2024). Open or closed? Measurement performance of open- and closed-path methane sensors for mobile emissions screening (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.