Methane emissions from local natural gas distribution systems in cities and towns throughout the United States have decreased as much as 70% over the past 20 years, according to a team led by researchers from Washington State University (WSU).
Upgrades in metering and regulating stations, changes in pipeline materials, better instruments for detecting pipeline leaks and regulatory changes all contributed to a 36-70% decrease in methane emissions compared with Environmental Protection Agency (EPA) estimates released two years ago and based on 1990s emission data, according to the WSU study, which was published this week in the journal Environmental Science & Technology. It was the most comprehensive direct measurement yet of emissions from the distribution system, the researchers said.
"Emission factors were derived from direct measurements at 230 underground pipeline leaks and 229 metering and regulating facilities using stratified random sampling," according to the report. The researchers estimated that methane emissions from the distribution system are about 393-854 gigagrams (gg) per year, which is 0.1-0.2% of the methane delivered nationwide. EPA previously estimated 1,329 gg/year, based largely on measurements from a national study in the early 1990s in which the WSU researchers also participated.
The analysis found significant variation by region, with some areas showing higher than average emissions because of large differences in the age and type of pipes, the researchers said.
"The eastern region of the United States accounted for more than a third of the total U.S. emissions from pipeline leaks. The western region, where systems tend to be newer, contributed 17% of total emissions," they said.
The study was done in coordination with major natural gas utilities and the Environmental Defense Fund (EDF), and was sponsored by the American Gas Association, Con Edison, EDF, National Grid, Pacific Gas & Electric and Southern California Gas.
The study "shows once again that the natural gas industry has been reducing emissions substantially and that innovation and cooperative efforts have led to much greater reductions at a faster pace than any regulation would," said America's Natural Gas Alliance CEO Marty Durbin. "Just as the production sector has cut methane emissions since the shale revolution began in 2005, the distribution sector also has taken steps to upgrade systems and reduce emissions.
"We hope that the administration will take note of the broad industry reductions as shown in this and previous EDF studies and in the Environmental Protection Agency's own data and will continue with cooperative steps that can lead to further substantial emissions reductions."
AGA CEO Dave McCurdy credited "a concerted effort by natural gas utilities to upgrade our nation's pipeline network" with contributing significantly to the declining emissions trend.
A study conducted by the University of Texas at Austin and sponsored by EDF found that methane emissions from the development and production sectors of the natural gas industry have declined from previous studies (see Daily GPI, Dec. 9, 2014).
An industry-backed study of methane emissions from natural gas pipeline and storage infrastructure released earlier this year found that the majority of measured emissions came from only a handful of the sites studied, suggesting that such emissions generally result from faulty equipment and are not endemic to natural gas infrastructure (see Daily GPI, Feb. 10).