Jim Urquhart/Reuters/Corbis

The US Environmental Protection Agency (EPA) on 18 August proposed the nation's first regulations to curb methane emissions from oil and gas development. The action came as scientists reported1 that the amount of methane released by the US natural-gas sector may be severely underestimated.

The regulations target methane and smog-forming volatile organic compounds (VOCs) produced by oil and gas drilling operations, as well as emissions from new and modified facilities that collect, transport and store oil and gas. The proposal follows 2012 rules that limit emissions of toxic pollutants and VOCs produced by extracting natural gas through hydraulic fracturing; in doing so, these older rules should also reduce methane emissions.

The EPA says that the latest proposal and the 2012 rules could together reduce the US oil and gas sector's methane output by up to 30% by 2025, compared to 2012 levels. But further action will be required to meet President Barack Obama's more ambitious goal of a 40–45% reduction by 2025.

Masses of methane

Janet McCabe, acting assistant administrator of EPA's Office of Air and Radiation, says that the Obama administration will continue to seek opportunities to cut methane emissions. Last week, for example, the EPA proposed rules that are intended to curb the release of methane from landfills.

The government proposal landed on the same day as a study that suggests that the US natural-gas sector emits substantially more methane than previously thought. Gathering, processing and distributing natural gas releases 2.4 million tonnes of methane each year, concludes the analysis, which was published in Environmental Science and Technology1. That figure is nearly 87% higher than the EPA's most recent estimate, and amounts to an 18% increase in the amount of methane thought to be emitted by the entire US gas sector.

Researchers monitored methane emissions at 114 natural-gas gathering facilities and 16 processing plants, which together collect and purify natural gas from numerous wells, and funnel the fuel into pipelines that transport it across the United States.

The team deployed tracer gases at these production facilities, then used those tracers to estimate the leakage rate of methane based on downwind measurements of the gas. Researchers also analysed industry and government data to estimate how many such facilities operate in the United States, then used that data to help model cumulative methane emissions from oil and gas development.

Plugging leaks

Most of the newly identified emissions come from about 4,500 gathering facilities, says Anthony Marchese, director of the Engines and Energy Conversion Laboratory at Colorado State University in Fort Collins and lead author of the paper. These facilities collect, compress and often perform an initial purification of natural gas, with each typically serving 10 to 100 wells.

Most gathering facilities use compressed natural gas to open and close certain types of valves. Simply switching to using compressed air would stop the methane emissions from these valves, Marchese says.

“The good news is, I guarantee you we can reduce those emissions by 50% now that we know what they are,” he adds. For example, Marchese's team used an infrared camera to identify some major leaks at facilities included in the study, and site operators were able to address these leaks by tweaking valves.

But the EPA proposal would apply only to gathering facilities that are new or modified, excluding many sites that are now operating, says Mark Brownstein, vice-president of climate and energy at the Environmental Defense Fund, an advocacy group in New York that funded the study along with industry partners.

“The issue really is existing sources,” Brownstein says. “It’s clear that there’s a need to do more.”