Methane (CH₄) is the primary component of natural gas and is also a greenhouse gas (GHG), with a 100-year global warming potential (GWP) roughly 21 - 23 times that of CO₂ (IPCC, 1996 and IPCC, 2001). As documented in the U.S. Environmental Protection Agency’s Inventory of Greenhouse Gas Emissions, released in 2006 (EPA, 2006), emissions from natural gas production, processing, and distribution are among the top ten source categories of greenhouse gas emissions in the United States, expressed on a CO₂ equivalent basis. These emissions arise from “hundreds of thousands of wells, hundreds of processing facilities, and over a million miles of transmission and distribution pipelines” (EPA, 2006). The number and diversity of sources lead to uncertainties in the emissions estimates that are approximately 30% (118.8 Tg CO₂ Eq. per year with a lower bound of 84.3 and an upper bound of 155.5 Tg CO₂ Eq.) (EPA, 2006).

Currently, the primary source of information on CH₄ emissions from the natural gas industry is a study conducted in 1996 for the Gas Research Institute (GRI) and the U.S. Environmental Protection Agency (EPA). While the GRI/EPA Study serves as the basis for most natural gas industry CH₄ emission estimates worldwide, there have been significant changes in the industry since the time the study was performed and opportunities exist for reducing the uncertainties associated with the emission estimates.

The overall goal of the project is to update default CH₄ emission factors for selected processes and equipment used in the natural gas industry that take account of new data collected since the GRI/EPA study and reflect any significant changes in practices or equipment since the GRI/EPA study. The processes and equipment for which GHG emission factors will be evaluated are listed in the table below. The default emission factors will be updated by compiling and synthesizing existing data and by acquiring new emission rate measurement data for selected sources where existing data have unacceptably large uncertainties or are insufficiently representative of current practices or equipment.

References

Environmental Protection Agency, (2006) Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 – 2004, Washington, DC 20460, U.S.A., April 15, 2006.

Intergovernmental Panel on Climate Change, Climate Change 2001: The Scientific Basis (Cambridge, UK: Cambridge University Press, 2001).

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