A University of Maryland-led team of researchers developed a new way to identify sources of methane in the air in a paper published last month.
The paper, which was published in the scientific journal Proceedings of the National Academy of Sciences, revealed methane emissions from wetlands may be much higher than scientists previously expected. It also asserts that microbial emissions propelled recent rises in atmospheric methane.
Researchers from this university’s geology, environmental science and technology and oceanic and atmospheric departments worked on the paper with researchers from the Massachusetts Institute of Technology and California Institute of Technology.
The researchers analyzed the composition of rare isotopic variants — or “flavors” of methane, as geology professor and paper co-author Alan Jay Kaufman described them — to trace how different methane samples were produced.
Mojhgan Haghnegahdar, a postdoctoral fellow in this university’s geology department and the paper’s lead author, said methane in the atmosphere comes from either human activity or natural sources. Information describing the composition of methane variants can help distinguish between the gas’ sources, she added.
“Recently, the concentration of methane has been increased … but people don’t know the reason behind it,” Haghnegahdar said. “Based on our model and what we were able to measure, we were able to … say which scenario is likely the one that has increased methane.”
The researchers concluded that microbial sources are responsible for recent methane increases.
The rate at which atmospheric methane levels rise has accelerated rapidly since 2007, according to data from the National Oceanic and Atmospheric Administration. In April, NOAA reported that 2022 saw the fourth-largest annual methane increase since the agency began recording measurements in 1983.
Each methane source has a different “fingerprint,” geology department chair James Farquhar said. This allows researchers to determine where methane came from by tracing the processes that affected it, he said.
Even though methane’s concentration is lower than that of carbon dioxide, it is more than 28 times as potent and absorbs much more heat, according to the U.S. Environmental Protection Agency. That means a dramatic rise in methane will result in greater warming of the planet’s surface, Kaufman said.
“Methane is probably the poorest understood of the greenhouse gases in terms of what its sources are,” Kaufman said.
The researchers collected samples of air from wetland, agricultural and urban sites in Maryland before isolating and purifying methane from them.
Jiayang Sun, a doctoral student in this university’s geology department and co-author of the paper, said it takes about six hours to extract a methane-concentrated gas from a pre-concentrated sample and an additional two hours to purify the gas into pure methane.
The researchers then used a high-resolution mass spectrometer, called the Nu Instruments Panorama, to measure the purified methane and look at its chemical properties. It takes about three days to get the final data from the Panorama after collecting a sample, Sun said.
This university’s Panorama is one of only two in the United States — UCLA was the first to have one.
Haghnegahdar, who earned her doctorate at UCLA, said she is the only person in the country who has worked with both.
While at UCLA, Haghnegahdar studied the theoretical potential of using two rare isotopes — atoms with the same number of protons but different numbers of neutrons — to track methane sources. At this university, Haghnegahdar proved her modeled predictions were right, with slight variations.
“When we were able to measure air, that was kind of like a dream come true for me,” Haghnegahdar said. “I did the modeling thing when I was a PhD student and at that moment, no one believed me.”
The team started work on the research in 2019 when they first installed the Panorama. But when unpacking the different Panorama parts, they found part of the mass spectrometer didn’t work.
After the instrument was rebuilt and realigned, the COVID-19 pandemic further slowed the research process.
“The fact that we had COVID meant I just brought parts home and just sat at home cleaning them out and rebuilding them and then trying to bring them back in to make it so that we could do the analysis,” Farquhar said.
After nearly four years of work, the team submitted their paper for review earlier this year, Sun said.
Sun said analyzing key methane sources and their proportions can help people understand potential ways to reduce methane emissions. According to Haghnegahdar, knowing the causes behind the increases in methane can also help policymakers make decisions about climate change.
“What we are seeing here could affect our short term, also long term future,” she said. “If we know more, we can decide better.”