The researchers combined 2019 satellite observations with an atmospheric transport model to generate a high-resolution map of methane emissions, which was then compared to EPA estimates from the same year. The researchers found:

• Methane emissions from landfills are 51% higher compared to EPA estimates
• Methane emissions from 95 urban areas are 39% higher than EPA estimates
• Methane emissions from the 10 states with the highest methane emissions are 27% higher than EPA estimates

“Methane is the second largest contributor to climate change behind carbon dioxide so it’s really important that we quantify methane emissions at the highest possible resolution to pinpoint what sources it is coming from,” said Hannah Nesser, a former PhD student at SEAS and first author of the paper. Nesser is currently a NASA Postdoctoral Program (NPP) Fellow in the Carbon Cycle & Ecosystems Group at the Jet Propulsion Laboratory.

The research, published in Atmospheric Chemistry and Physics, was a collaboration between scientists at Harvard and an interdisciplinary team of researchers from across the U.S. and around the world, including universities in China and the Netherlands.

The EPA estimates that landfills are the third-largest source of human-caused methane emissions in the U.S., but the EPA uses a bottom-up accounting method that often doesn’t match observations of atmospheric methane.

The EPA methane estimate for landfills uses the Greenhouse Gas Reporting Program, which requires high-emitting facilities to self-report their emissions annually. For landfills without methane capture, the emissions are simply calculated by looking at the amount of trash that comes in and estimating how much methane trash produces over time. That figure is then scaled up to include landfill operations that don’t report to the Greenhouse Gas Reporting Program.

Nesser and her colleagues’ top-down approach uses observations of atmospheric methane from the Tropospheric Monitoring Instrument (TROPOMI) aboard the Sentinel-5 Precursor satellite together with an atmospheric transport model to trace the path of emissions from the atmosphere back to the ground.

Using this method, the team zoomed in on 70 individual landfills across the U.S. In these facilities, the researchers found emissions that were on median 77% higher than the estimates from the Greenhouse Gas Reporting Program.

The disparity is wider for landfills that collect methane as part of their operations.

Landfills don’t measure the exact amounts of methane they are losing but rather estimate how efficient their collection systems are. The EPA assumes the default efficacy rate for methane collection is 75%.

But Nesser and her colleagues found that, in fact, landfills are much less effective at collecting methane than previously thought.

Of the 70 landfills the team studied, 38 recover gas. Among those facilities, the researchers found that methane levels were on median more than 200% higher than the estimates from the Greenhouse Gas Reporting Program.

“Our research shows that these facilities are losing more methane than they think,” said Nesser. “The EPA uses 75% efficacy as the default for methane collection, but we find that it’s actually much closer to 50%.”

The EPA estimates also do not capture one-off events, such as construction projects or temporary leaks, which could lead to a massive increase in methane emissions and contribute to the discrepancy between EPA estimates and observed atmospheric methane.

The research team also compared their analysis to the EPA’s new state-level greenhouse gas inventories.

The researchers found 27% higher methane emissions from the 10 top methane-producing states, with the largest increases in Texas, Louisiana, Florida, and Oklahoma. The team found that those 10 states are responsible for 55% of U.S. human-caused methane emissions. Perhaps unsurprisingly, Texas is responsible for 21% of anthropogenic methane emissions in the U.S., 69% of which is from the oil and gas industry.

At the city level, the researchers found that, on average, the 10 cities with the highest urban methane emissions actually have 58% higher emissions than previously estimated. Those cities include New York, Detroit, Atlanta, Dallas, Houston, Chicago, Los Angeles, Cincinnati, Miami and Philadelphia.

“All of these places have a different profile of emission sources, so there’s no one thing driving the methane underestimate across the board,” said Nesser.

The researchers hope that future work will provide more clarity on exactly where these emissions are coming from and how they are changing.

“This research highlights the importance of understanding these emissions,” said Daniel Jacob, the Vasco McCoy Family Professor of Atmospheric Chemistry and Environmental Engineering at SEAS and senior author of the paper. “We plan to continue to monitor U.S. emissions of methane using new high-resolution satellite observations, and to work with the EPA to improve emission inventories.”

The research was co-authored by Joannes D. Maasakkers, Alba Lorente, Zichong Chen, Xiao Lu, Lu Shen, Zhen Qu, Melissa P. Sulprizio, Margaux Winter, Shuang Ma, A. Anthony Bloom, John R. Worden, Robert N. Stavins and Cynthia A. Randles.

It was supported by the NASA Carbon Monitoring System (CMS) and the Harvard Climate Change Solutions Fund.

“Our digital technology operates through a series of electronic on-off switches that control the flow of current and voltage,” said Rajiv Giridharagopal, a research scientist at the University of Washington. “But our bodies operate on chemistry. In our brains, neurons propagate signals electrochemically, by moving ions — charged atoms or molecules — not electrons.”

Implantable devices from pacemakers to glucose monitors rely on components that can speak both languages and bridge that gap. Among those components are OECTs — or organic electrochemical transistors — which allow current to flow in devices like implantable biosensors. But scientists long knew about a quirk of OECTs that no one could explain: When an OECT is switched on, there is a lag before current reaches the desired operational level. When switched off, there is no lag. Current drops almost immediately.

A UW-led study has solved this lagging mystery, and in the process paved the way to custom-tailored OECTs for a growing list of applications in biosensing, brain-inspired computation and beyond.

“How fast you can switch a transistor is important for almost any application,” said project leader David Ginger, a UW professor of chemistry, chief scientist at the UW Clean Energy Institute and faculty member in the UW Molecular Engineering and Sciences Institute. “Scientists have recognized the unusual switching behavior of OECTs, but we never knew its cause — until now.”

In a paper published April 17 in Nature Materials, Ginger’s team at the UW — along with Professor Christine Luscombe at the Okinawa Institute of Science and Technology in Japan and Professor Chang-Zhi Li at Zhejiang University in China — report that OECTs turn on via a two-step process, which causes the lag. But they appear to turn off through a simpler one-step process.

In principle, OECTs operate like transistors in electronics: When switched on, they allow the flow of electrical current. When switched off, they block it. But OECTs operate by coupling the flow of ions with the flow of electrons, which makes them interesting routes for interfacing with chemistry and biology.

The new study illuminates the two steps OECTs go through when switched on. First, a wavefront of ions races across the transistor. Then, more charge-bearing particles invade the transistor’s flexible structure, causing it to swell slightly and bringing current up to operational levels. In contrast, the team discovered that deactivation is a one-step process: Levels of charged chemicals simply drop uniformly across the transistor, quickly interrupting the flow of current.

Knowing the lag’s cause should help scientists design new generations of OECTs for a wider set of applications.

“There’s always been this drive in technology development to make components faster, more reliable and more efficient,” Ginger said. “Yet, the ‘rules’ for how OECTs behave haven’t been well understood. A driving force in this work is to learn them and apply them to future research and development efforts.”

Whether they reside within devices to measure blood glucose or brain activity, OECTs are largely made up of flexible, organic semiconducting polymers — repeating units of complex, carbon-rich compounds — and operate immersed in liquids containing salts and other chemicals. For this project, the team studied OECTs that change color in response to electrical charge. The polymer materials were synthesized by Luscombe’s team at the Okinawa Institute of Science and Technology and Li’s at Zhejiang University, and then fabricated into transistors by UW doctoral students Jiajie Guo and Shinya “Emerson” Chen, who are co-lead authors on the paper.

“A challenge in the materials design for OECTs lies in creating a substance that facilitates effective ion transport and retains electronic conductivity,” said Luscombe, who is also a UW affiliate professor of chemistry and of materials science and engineering. “The ion transport requires a flexible material, whereas ensuring high electronic conductivity typically necessitates a more rigid structure, posing a dilemma in the development of such materials.”

Guo and Chen observed under a microscope — and recorded with a smartphone camera — precisely what happens when the custom-built OECTs are switched on and off. It showed clearly that a two-step chemical process lies at the heart of the OECT activation lag.

Past research, including by Ginger’s group at the UW, demonstrated that polymer structure, especially its flexibility, is important to how OECTs function. These devices operate in fluid-filled environments containing chemical salts and other biological compounds, which are more bulky compared to the electronic underpinnings of our digital devices.

The new study goes further by more directly linking OECT structure and performance. The team found that the degree of activation lag should vary based on what material the OECT is made of, such as whether its polymers are more ordered or more randomly arranged, according to Giridharagopal. Future research could explore how to reduce or lengthen the lag times, which for OECTs in the current study were fractions of a second.

“Depending on the type of device you’re trying to build, you could tailor composition, fluid, salts, charge carriers and other parameters to suit your needs,” said Giridharagopal.

OECTs aren’t just used in biosensing. They are also used to study nerve impulses in muscles, as well as forms of computing to create artificial neural networks and understand how our brains store and retrieve information. These widely divergent applications necessitate building new generations of OECTs with specialized features, including ramp-up and ramp-down times, according to Ginger.

“Now that we’re learning the steps needed to realize those applications, development can really accelerate,” said Ginger.

Guo is now a postdoctoral researcher at the Lawrence Berkeley National Laboratory and Chen is now a scientist at Analog Devices. Other co-authors on the paper are Connor Bischak, a former UW postdoctoral researcher in chemistry who is now an assistant professor at the University of Utah; Jonathan Onorato, a UW doctoral alum and scientist at Exponent; and Kangrong Yan and Ziqui Shen of Zhejiang University. The research was funded by the U.S. National Science Foundation, and polymers developed at Zhejiang University were funded by the National Science Foundation of China.

Land users rely on subsidies, but money is not everything

The researchers focused on the motivation and challenges driving decision-making among all land users engaged in low-intensity grazing practices. This was despite economic considerations becoming increasingly important as land users’ revenue-generating activities are no longer sufficient to cover the rising cost of equipment, rent, and taxes.

“Money is not everything. Many of the land users we interviewed practice this type of grazing management because they think it is good, not out of economic motivation,” says first author Dr Julia Rouet-Leduc. Rouet-Leduc led the project as a former doctoral researcher at iDiv and UL and is now a postdoctoral researcher at the Stockholm Resilience Centre. Caring for nature and, in some cases, also the desire to maintain traditional agricultural practices were important aspects of the land users’ motivation. For example, a land user working with wild ponies in Galicia (Spain) shared: “The main reason for the maintenance of this system is that people … love the ponies; they ‘have a fever’, and this tradition runs very deeply in their hearts.”

The researchers found that many land users struggle with rules and regulations that are incompatible with low-intensity grazing management. For example, rules to mark or tag livestock — an extremely challenging task when animals are allowed to graze freely in large areas — were perceived as limiting. Land users also felt that the policies in place, especially the Common Agricultural Policy of the European Commission (CAP), were holding back nature-friendly and sustainable practices. For example, a land user in Romania noted that farmers were required to remove scrubs from their pastures or they would otherwise not be eligible for subsidies or even have to pay penalties. However, scrubs have important ecosystem functions, such as providing shade in the summer and as an additional food resource in the winter. In general, the CAP was perceived as too restrictive, and many land users chose not to apply for subsidies at all. “By not applying for CAP support, we have the freedom to really see what suits the local ecosystem,” a Belgian land user stated.

Rural exodus is putting traditional labour at risk

The interviews also showed that many land users struggle with socio-economic changes in the countryside. The so-called ‘Rural Exodus’ is leading to a lack of workforce, while physical work is still very much needed, especially for work with cattle or horses. “The next generation does not want to farm because it is too hard, too much work,” a land user from Lithuania said. “They usually move abroad and choose easier career options’.’

“The CAP could support farmers in High Nature Value farming regions and put incentives in place to preserve or restore extensive grazing systems,” senior author Dr Guy Pe’er, a senior researcher at UFZ and iDiv, suggests. “It’s not a lack of budgets but rather the lack of ambition to support sustainable farming.”

More flexibility and improved market access needed

The researchers used the interviews to derive and suggest interventions to encourage better grazing practices. “What is needed is more flexibility for land users,” Rouet-Leduc says. “Current policies are, for the most part, not encouraging such practices, and particularly not offering a level playing field for land users.” While the EU’s CAP offers important economic support, it also drives counter-productive management due to problematic requirements, she adds. Additional financial incentives could improve the support for more sustainable grazing management, according to the study’s authors. Especially in areas where land has been abandoned, there can be opportunities for rewilding large herbivores, which ultimately provide multiple ecosystem services. However, such systems require flexibility since they differ from management approaches with domestic animals.

The researchers also call for better labelling and certification for environmentally friendly grazing practices to increase public support and to help develop markets for such products. Some of the interviewed land users felt that market access could be improved by supporting direct marketing, for example, via farm shops.

“There are clearly real challenges for farmers, and they are not easy to overcome,” Pe’er explains in light of ongoing farmers’ demonstrations in countries like Germany, Poland, and Italy. “But removing environmental standards will not help land users. They need a package that includes an ambitious CAP reform, providing real support for farmers who need it to be more sustainable; the Nature Restoration Law to improve the standards of good management; and a framework for sustainable food systems to improve the market options for sustainable farming.”

Methane is a far more potent greenhouse gas than carbon dioxide (CO₂). According to the International Energy Agency, the concentration of methane in the atmosphere is currently around two-and-a-half times greater than pre-industrial levels and is increasing steadily, with waste emissions and the burning of fossil fuels accounting for a significant proportion.

The research was published in the Journal of the American Chemical Society.

Australia recently joined the international methane mitigation agreement with the United States, the European Union, Japan and the Republic of Korea.

Lead author, Professor PJ Cullen from the University of Sydney’s School of Chemical and Biomolecular Engineering and Net Zero Initiative said: “Globally, landfills are a major emitter of greenhouse gases, mainly a mixture of CO₂ and methane. We have developed a process that would take these gases and convert them into fuels, targeting sectors that are difficult to electrify, like aviation.”

“Modern landfill facilities already capture, upgrade and combust their gas emissions for electricity generation, however, our process creates a much more environmentally impactful and commercially valuable product,” he said.

Global landfill emissions are estimated at 10-20 million tonnes of greenhouse gases per year, a value comparable to the emissions of the global energy sector.

Aviation currently accounts for approximately three percent of the world’s emissions. Creating a “closed loop” fuel based on existing emissions would eliminate the need for traditional and sustainable jet fuels, which add further emissions into the atmosphere.

How plasma makes the process work

The process would work by extracting methane from a landfill site, known as a methane well, which uses a shaft-like mechanism to extract gases.

“The beauty of this is that this simple process captures almost the exact composition that we need for our process,” said Professor Cullen.

“Non-thermal plasma is an electricity-driven technology which can excite gas at both a low temperature and atmospheric pressure. Essentially, what this means is this approach facilitates the conversion of the gas into value-added products by inducing plasma discharge within forming gas bubbles. The process doesn’t require heat or pressure, meaning it requires less energy, making it highly compatible with renewable energy power sources.”

DISCLOSURE

Authors PJ Cullen, Emma Lovell and Tianqi Zhang are associated with PlasmaLeap Technologies, the supplier of the plasma technology employed to generate plasma bubbles in this study.

The authors acknowledge the MagRes node at Sydney Analytical Core Research Facility for access to the NMR infrastructure, Michelle Wood at Sydney Analytical for additional assistance in ATR-FTIR and Aditya Rawal at the University of New South Wales Mark Wainwright Analytical Centre for solid-state NMR measurements.