You’ve seen the images: floating islands of plastic in the ocean, marine life entangled in nets and lines. Whether in the ocean or on land, plastic pollutants—and their effects—are often visible.
But not all pollutants are.
“What most people don’t realize is that there has been pollution for a long time,” says Desiree Plata, an environmental engineer and chemist at the Massachusetts Institute of Technology (MIT). “Most of it we just can’t see.”
Enter methane, a colorless, odorless chemical that, like carbon dioxide and other greenhouse gases, contributes to climate change by collecting in our atmosphere and trapping radiation from the sun. Methane is emitted into the air by many sources, including melting permafrost, gassy cows, and oil and gas drilling sites. And it’s about 86 times more potent than carbon dioxide, according to the Intergovernmental Panel on Climate Change.
Methane is the main ingredient in natural gas, which powers 48% of homes in the United States. Commercial natural gas is scented with odorants to make a potential gas leak detectable, alerting a resident to shut off their stove or track down the leak.
“I like to call methane ‘the elephant in the atmosphere,’” Plata says. “It’s the gas everyone should be talking about, but few people know about.”
But now, a team at MIT is producing sensors to allow people to “see” methane, and ultimately track down its sources and mitigate its harmful effects.
Sensor technology: by chemicals, for chemicals
These methane sensors, developed by chemist Tim Swager and his team at MIT, vary in size depending on how large of an area a user would like to monitor. The sensors could be big, shaped like a laptop briefcase for easy carrying. Or they could be small, about the size of a sticker, and shaped like the flat chip in your credit card.
The sensors are inexpensive, low-power devices that can detect methane emissions in nature and at industrial sites, Swager said in an email. The company C2Sense is working with his team’s technology, which could be on the market within a few years.
Though they’re not yet licensed for commercial use, Swager’s methane sensors have the potential to be as widely used as the carbon monoxide detectors we have in our homes. Methane is present in natural, industrial, and agricultural environments, and sometimes leaches into drinking water through the ground in the form of tiny gas bubbles, meaning that anyone—from a farmer to an engineer to a homeowner—could use a sensor to get a better idea of the chemical’s presence in their air or water.
All of Swager’s team’s sensors are powered by the same thing: chemical elements. Platinum and oxygen naturally react with methane, so they can be used in the sensors to detect methane in an environment, Swager explains.
Here’s how: The platinum in the sensor reacts with oxygen in the atmosphere, bonding to create a chemical compound. This compound then reacts with any methane present in the surrounding environment. “Basically, you’re oxidizing the methane,” Swager says. This reaction between the platinum-oxygen compound and methane sets off the sensor, which sends a notification to a specialized device (for an industrial-use sensor) or a cell phone (for a personal-use sensor).
The sensor’s platinum and electrode sensing component “is very tiny—and that means that you could put it into lots of different structures,” says Plata, who’s not involved in Swager’s work. Unlike some other machinery that’s weighed down by the bulky essential technology within it, C2Sense’s sensors rely on very little to work, so they can be easily integrated into homes, barns, drilling sites, and other environments where methane is present.
Gas sensors that can detect volatile organic compounds, including methane, already exist. But they’re not tailored to detect methane alone, Swager said in an email, and require temperatures higher than 570 F to operate. This makes them both costly and potentially dangerous around high concentrations of methane, a flammable gas.
Conversely, Swager's sensors can operate in ambient conditions and have low power requirements—they can run at submicrowatts—making them inexpensive to operate. And unlike existing sensors on the market, which generally need a battery pack or wiring to work, Swager's sensors can be powered wirelessly and read by a smartphone.
Some of the smaller prototype methane sensors are 0.08 inch (2mm) cubes, approximately as thick as a nickel. They can potentially help pinpoint leaks in homes or wells, attaching physically to an area where methane may spew from. The sensors can also attach to a cell phone for on-the-go sensing, reporting the changes in air or water quality right to a “mobile-friendly sensor platform” on the phone, Swager explains.
That said, personal-use sensors may be a ways off, Swager cautions. Currently, odorants added to methane-containing gas serve as the main indicator for gas leaks in homes. Unfortunately, scent is only useful if you’re present and able to smell it. “Houses can blow up if there’s too much natural gas,” Swager says. When someone is away from their home or is unable to smell a leak, it’s harder to protect against a possible gas fire—or worse, explosion.
Another possible application for the sensors, Swager says, is to test well water, which millions of people in the U.S. rely on. When methane is drilled underground, the gas sometimes escapes from the pipe it’s being pumped into, travels through the porous earth, and rises from the ground. “In the process of drilling down, you've created another pathway for the methane to reach the surface. It could come up 100 yards from the well pad depending on the location, even get into the groundwater,” Swager says. Because the gas is considered nontoxic by several state departments of public health, methane doesn’t have a Safe Drinking Water Act maximum contaminant level. (Although the U.S. Department of the Interior suggests a specific methane level at which homeowners should vent their wells.)
Larger sensors can sense transient leaks (leaks that start and stop) over large swaths of land. Intended for use by engineers, park rangers, and other professionals, industrial-use sensors could identify methane leaks at natural gas drilling sites, where methane comes up from the earth; forests, where raging fires can emit the chemical; or large farms, where methane-emitting livestock live.
Cattle farming is the leading cause of methane emissions in the U.S., with nearly 2% of total greenhouse gas emissions annually coming from the methane cows burp and fart (and the U.S. is the world’s largest producer of beef). Scientists have looked for ways to lower methane emissions from cattle farming, going so far as to put masks on cows to catch their burps.
Addressing the elephant in the room
As methane and other greenhouse gases collect in the atmosphere, they “work as a blanket,” says Andra Garner, a climate scientist at Rowan University in New Jersey. “Methane is a much thicker and heavier blanket than carbon dioxide and if you add too many blankets, we start to get way too warm,” she explains.
Beyond climate change and immediate safety risks of methane, the health effects of being exposed to high levels of methane over a prolonged period of time are also a concern, but haven’t been thoroughly investigated. Communities that have dealt with large amounts of methane leaking into their air—like the residents of Belmont County, Ohio, where one of the biggest methane leaks ever recorded in the U.S. happened in 2018—have reported respiratory problems and dizziness after being exposed to methane gas. In-home methane sensors could notify residents of leaks when their noses can’t, just like carbon monoxide and smoke detectors do.
“You probably hear headlines all the time, ‘Everywhere we look for plastics in the environment, we find them,’” Plata says. “The same is true of most industrial chemicals, but the problem is I can’t pull out my cell phone and take a picture of [them]. Tim’s sensors are helping to close that gap.”
Being able to see where methane comes from is the first step to controlling its effects on our planet. “Any time we have more data, that’s better; we get a better handle on where these emissions are coming from,” Garner says. After all, Plata says, “Getting chemicals out of the environmental system is a bigger challenge than trying to keep them from getting there in the first place.”