The high-tech efforts and important findings of the California Air Resources Board, California Energy Commission and NASA to pinpoint emissions of the climate super pollutant methane are detailed in an article published in the November 2019 issue of the journal Nature.

The results will be used to help state and local agencies and businesses prioritize investments to reduce emissions.

From August 2016 to October 2018, NASA, through a contract with the two state agencies, flew remote sensing equipment over selected portions of the state. Hundreds of methane point sources were identified during the California Methane Survey, including “super-emitters,” sources responsible for an outsized proportion of the total methane released into the atmosphere.

According to the survey, just 10 percent of the point sources were responsible for 60 percent of the total emissions detected. Researchers believe that statewide, these relatively few super emitters are responsible for about a third of California’s total methane emissions.

Methane is a powerful greenhouse gas and is 25 times more effective than carbon dioxide at trapping heat over a 100-year period. While it does occur naturally, major human-generated sources include landfills, refineries, oil and gas fields, natural gas infrastructure, dairies and wastewater treatment plants.

To reduce methane’s impact on the climate, California has set a goal to cut overall emissions in the state by 40 percent from 2013 levels by 2030.

Building on previous efforts to measure and detect sources and levels, CARB and the CEC partnered with NASA’s Jet Propulsion Laboratory to conduct the state’s first systemic mapping of highly localized methane point sources.

“This survey builds on a decade of cooperation between NASA, CARB and the Energy Commission to support California’s ambitious climate change mitigation programs,” said CEC Chair David Hochschild, “specifically on the study of methane emissions from the oil and gas sector.”

Methane is invisible to the human eye, but can be detected by NASA’s Airborne Visible InfraRed Imaging Spectrometer – Next Generation, or AVIRIS-NG. The sophisticated imaging equipment, carried by a twin-engine aircraft, identifies gases by analyzing sunlight passing through molecules in the atmosphere.

That advanced detection technology was employed by JPL crews in 2016, 2017 and 2018 who conducted dozens of flights over 10,000 square miles, identifying more than 550 point sources emitting plumes of highly concentrated methane.

Landfills accounted for 41 percent of point source emissions, manure management accounted for 26 percent and oil and gas accounted for 26 percent.

The most startling finding, however, was that less than 0.2 percent of infrastructure in the state (based on a survey of 272,000 facilities and components) are responsible for 34-46 percent of total methane emissions in California.

Of the 270 landfills surveyed, only 30 were observed emitting large plumes of methane. Those 30, however, were responsible for 40 percent of the total point source emissions detected during the survey.

The oil and gas production sector also included large sources of methane. Most were concentrated in the southern San Joaquin Valley, the region that produces more oil than any other in the state.

Los Angeles and Ventura Counties were next on the list.

“These findings illustrate the importance of monitoring point sources across multiple sectors of the economy and broad regions, both for improved understanding of methane budgets and to support emission mitigation efforts,” said JPL scientist Riley Duren, who led the study.

Preliminary results have been shared with selected facility operators in California to make them aware of the need to improve their methane leak detection processes and to institute better controls on methane emissions. Results will also be used to help state and local agencies and businesses prioritize investments in methane emission mitigation.

Although the survey provides a detailed map of methane emissions in the state, researchers caution that this was the first attempt to estimate emissions for individual methane sources from a large population distributed across a large region over multiple years. Some emissions were highly intermittent, others were affected by wind, and some were too small for accurate emission rate estimation.

The survey, however, represents a major advance in the use of remote sensing to detect this methane emission activity, and additional insight could be gained by expanding the use of the technology nationally and internationally.

“This new remote sensing technology addresses the continuing need for detailed, high-quality data about methane,” said California Air Resources Board Chair Mary D. Nichols. “It will help us and the Energy Commission develop the best strategies for capturing this highly potent greenhouse gas.”

In response to methane’s significant contribution to the state’s emissions and the requirements of Senate Bill 1383, California is taking a number of other steps to reduce methane emissions from various sources as part of the Short-lived Climate Pollutant strategy.

CARB is working with other state agencies to reduce emissions from dairy cattle and other livestock. CARB has also approved the Oil and Gas Production, Processing and Storage Regulation to limit methane emissions from the state’s main fossil fuel industries.

The final report of the California Methane Survey will be available later in the fall, but a condensed version was submitted to Nature earlier this year for peer review.

The data from the survey and related projects can be viewed at an experimental NASA data portal.