Aerial methane survey finds a fraction of point sources responsible for more than a third of California’s methane emissions
An aerial methane survey conducted by the California Air Resources Board (CARB), California Energy Commission (CEC) and NASA has found that just 10% of the point sources were responsible for 60% of the total methane emissions detected. Researchers believe that statewide, these relatively few super emitters are responsible for about a third of California’s total methane emissions.
The study is published in 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.
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 from 2013 levels by 2030.
Building on previous efforts to measure and detect methane sources and levels, CARB and the CEC partnered with NASA’s Jet Propulsion Laboratory (JPL) to conduct the state’s first systemic mapping of highly localized methane point sources.
Methane is invisible to the human eye, but can be detected by NASA’s Airborne Visible InfraRed Imaging Spectrometer - Next Generation (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% of point source emissions, manure management accounted for 26% and oil and gas accounted for 26%.
The most startling finding, however, was that less than 0.2% of infrastructure in the state (based on a survey of 272,000 facilities and components) is responsible for 34-46% 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% 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.
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 methane 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.
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 other methane projects can be viewed at an experimental NASA data portal.
Duren, R.M., Thorpe, A.K., Foster, K.T. et al. (2019) “California’s methane super-emitters.” Nature 575, 180–184 doi: 10.1038/s41586-019-1720-3