Hydrogen’s potential as a clean fuel could be capped by a chemical reaction in the lower atmosphere, according to research from Princeton University and the National Oceanic and Atmospheric Association.
This is because hydrogen gas readily reacts in the atmosphere with the same molecule primarily responsible for breaking down methane, a potent greenhouse gas. If hydrogen emissions exceed a certain threshold, this combined reaction is likely to lead to a buildup of methane in the atmosphere — with climate consequences over decades.
“Hydrogen is theoretically the fuel of the future,” said Matteo Bertani, a postdoctoral researcher at Hay Meadows Environmental Institute who works on the carbon mitigation initiative. “In practice, though, it raises many environmental and technological concerns that still need to be addressed.”
Bertani is the first author of a research article published in Nature Communications, where the researchers modeled the effect of hydrogen emissions on atmospheric methane. They found that above a certain threshold, even when replacing fossil fuel use, a leaking hydrogen economy can cause environmental damage in the near term by increasing the amount of methane in the atmosphere. The harm risks are compounded for hydrogen production methods using methane as an input, highlighting the critical need to manage and reduce emissions from hydrogen production.
said Amilcare Porporato, Thomas J. Professor of Civil and Environmental Engineering and High Meadows Institute of the Environment. Purpuratto is a principal investigator and a member of the Leadership Team for the Carbon Abatement Initiative and a faculty member at the Endlinger Center for Energy and the Environment.
The problem boils down to a small, hard-to-measure molecule known as a hydroxyl radical (OH). Often dubbed the “tropospheric cleaner,” OH plays a critical role in eliminating greenhouse gases such as methane and ozone from the atmosphere.
The hydroxyl radical also interacts with hydrogen gas in the atmosphere. And since only a limited amount of OH is produced each day, any rise in hydrogen emissions means that more OH will be used to break down hydrogen, leaving less hydroxide to break down methane. As a result, methane will stay longer in the atmosphere, adding to the warming effects.
According to Bertani, the effects of rising hydrogen that would occur as government incentives for hydrogen production expand could have climate consequences for the planet for decades to come.
“If you release some hydrogen into the atmosphere now, it will lead to a gradual build-up of methane in the following years,” Bertani said. “Even though hydrogen only has a lifespan of about two years in the atmosphere, you can still get a methane reaction out of that hydrogen in 30 years from now.”
In the study, the researchers pinpoint the tipping point at which hydrogen emissions may lead to an increase in atmospheric methane, thus undermining some of the near-term benefits of hydrogen as a clean fuel. By setting this threshold, the researchers set goals to manage hydrogen emissions.
“It is essential that we be proactive in establishing thresholds for hydrogen emissions, so that they can be used to inform the design and implementation of hydrogen infrastructure in the future,” Purpurato said.
For hydrogen referred to as green hydrogen, which is produced by splitting water into hydrogen and oxygen using electricity from renewable sources, Bertani said the critical threshold for hydrogen emissions is about 9%. This means that if more than 9% of the green hydrogen produced escapes into the atmosphere — whether that be at the point of production, sometime during transportation, or elsewhere along the value chain — atmospheric methane will increase over the next few decades. , and cancel out some of the climate benefits of moving away from fossil fuels.
And for blue hydrogen, which refers to hydrogen produced by methane reformation with carbon capture and storage, the emission threshold is lower. Since methane itself is the primary input to the methane reforming process, blue hydrogen producers have to consider direct methane leaks in addition to hydrogen leaks. For example, the researchers found that even with the methane leakage rate reduced to 0.5%, hydrogen leakage would have to remain below 4.5% to avoid increasing methane concentrations in the atmosphere.
“Managing hydrogen and methane leakage rates will be critical,” Bertani said. “If you have a small amount of methane leakage and a little bit of hydrogen leakage, the blue hydrogen you’re really producing might not be much better than using fossil fuels, at least for the next 20 to 30 years.”
The researchers emphasized the importance of the time scale on which the effect of hydrogen on atmospheric methane is considered. In the long term (over a century, say), Bertani said, shifting to a hydrogen economy is likely to yield net climate benefits, even if levels of methane and hydrogen leakage are high enough to cause nearly-term warming. Eventually, he said, concentrations of the gas in the atmosphere will reach a new equilibrium, and the shift to a hydrogen economy will prove its climate benefits. But before that happens, the potential near-term consequences of hydrogen emissions could lead to irreversible environmental, social, and economic damage.
Thus, if the institutions are to hope to meet mid-century climate goals, Bertani warned that leakage of hydrogen and methane into the atmosphere must be curbed as hydrogen infrastructure begins to unfold. Because hydrogen is such a small molecule that is notoriously difficult to control and measure, he explained that managing emissions will likely require researchers to develop better ways to track hydrogen losses across the value chain.
“If companies and governments are serious about investing money to develop hydrogen as a resource, they need to make sure they do it right and efficiently,” Bertani said. “Ultimately, the hydrogen economy must be built in a way that does not conflict with efforts in other sectors to mitigate carbon emissions.”