Methane Emissions Research Summary No.1: Scientific Challenges of Monitoring, Measuring, Reporting, and Verifying Greenhouse Gas Emissions from Natural Gas Systems [By David Allen, Arvind Ravikumar, and Erin Tullos, PhD from UT Austin's EEMDL Center]
This short viewpoint article covers the scientific challenges of MMRV. This paper briefly covers the role of methane in global warming and the importance of methane emission measurements in developing accurate GHG emission inventories. Based on the paper, global emissions of methane in the oil and gas sector, from wellhead to burner tip, are ∼2% of production, amounting to approximately 100 Tg/yr. It reports that emission estimates based on generic emissions factors and engineering estimates underestimate emissions by 50% or more.
The development of systems for monitoring, measuring, reporting, and verifying emissions at a spatial and temporal resolution needed to differentiate among individual natural gas supply chains is one of the challenges mentioned in this article. The paper describes different types of emissions from the oil and gas sector, including large numbers of sources that emit at relatively low rates and small numbers of sources that emit at large rates. In addition, emissions may be continuous or episodic and may be intended or unintended, making their characterization challenging.
Converting measurement data collected using different atmospheric sensors into information on methane emissions is another challenge. Atmospheric measurement uncertainties (variation in detection limits and uncertainty levels of each sensing technology) and modeling uncertainties (to convert sensor data to emission rate estimates) add to this complexity.
Limitations in spatial and temporal coverage of emissions by measurement technologies (due to measuring at a subset of the oil and gas sites, and/or during a limited time period) require extrapolations in emission estimates to have the whole picture. This process is complex and adds to the uncertainties of emission estimates. The paper reports that depending on the characteristics of emissions, particularly large episodic emissions, these extrapolation uncertainties can be 50% or more.
Integrating and reconciling measurements and engineering calculations made at multiple spatial and temporal scales are presented as a remedy to reduce the above-mentioned uncertainties. For example, emission event durations established using continuously operating ground methane monitors, or other relevant parametric process data, could be integrated with engineering calculations or emission quantification measurements made using aircraft overflights. As another example, measurements of total production basin emissions that sum emissions over thousands of sites and measurements of multiple co-emitted species could also be used to place constraints on the extrapolation of individual site-level measurements.
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