Methane Emissions from Oil and Natural Gas Production and Use – How Accurate are the Estimates?
During a recent Environmental Law Institute teleconference, the climate change director of the US EPA’s air office cautioned that a better understanding is needed before drawing any conclusions from the top down or atmospheric sampling that was done to determine the level of methane emissions from the oil and gas industries.
Previous estimates of methane emissions from the oil and gas industries were based on ground level estimates that used emission factors for each type of source. In contrast, the top down approach gathers atmospheric samples using aircraft and then tries to trace methane levels back to various sources using meteorological data. Industry, and now the EPA itself, are questioning the accuracy of this methodology based on the inability of this process identify the sources of methane contributions where multiple sources might exist in an area. Activities such as agriculture and coal mining can emit significant amounts of methane and these activities often co-exist in areas where oil or natural gas development is occurring. The problem then becomes one of determining the amount of emissions that can be attributed to each source.
Some environmental groups have been arguing that the EPA is underestimating the methane emissions from this industry sector. They contend that the carbon footprint for natural gas use is high enough to question its value as a replacement for coal relative to addressing climate change concerns.
Given these shortcomings, the EPA is nevertheless interested in relying on this top down process to eventually calculate the greenhouse gas estimates for this industry sector. EPA believes that research into the use of top down sampling will reach a point where the results can be reliably used.
Industry, on the other hand, believes that the continued use of Best Available Monitoring Methods (BAMM) – which allows for emission estimates to be based on data provided by the equipment supplier or engineering calculations – should continue to be allowed. EPA had proposed eliminating this option in its proposed Subpart W revisions whose comment period closed on April 24, 2014.