Project Overview

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.


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

Environmental Protection Agency (1996a), Methane Emissions from the Natural Gas Industry
Volume 2: Technical Report, Final Report, GRI-94/0257.1 and EPA 600/R-96-080b. Gas
Research Institute and U.S. Environmental Protection Agency, June 1996.

Intergovernmental Panel on Climate Change, Climate Change 1995: The Science of Climate Change (Cambridge, UK: Cambridge University Press, 1996).

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


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