MIT NEWS OFFICE Climate science takes to the streets Alison F. Takemura | Office of the Vice President for Research Tuesday, February 28, 2017

A dozen MIT students and community members clamber into a van on a bright morning in late January. There’s palpable excitement as the van drives down Main Street in Cambridge, Massachusetts, and crosses onto Portland Street. The chilly weather and light snow does nothing to dampen the group’s spirits. They’re on a hunt — for gas leaks, quiet but potent accelerators of climate change.

A passerby can easily smell a major gas leak; gas producers add a chemical called mercaptan, which smells like rotting eggs, as a safety measure. But our noses are crude instruments, says Audrey Schulman, the president of the Massachusetts nonprofit Home Energy Efficiency Team (HEET). That’s why the day’s activity — dubbed a gas leak safari — which trains citizens to be scientists who can wield data collection tools, is so valuable.

Outfitted with a $60,000 GPS-linked spectrometer, the van can “sniff out” tiny amounts of airborne natural gas close to the ground. As the van winds through the streets of Cambridge, it registers specifically the values of methane, which constitutes 95 percent of natural gas. When the number climbs past the background of 0.002 percent, they stop for a closer look. “Uh-oh,” someone in the van says as the methane level reaches 0.003 percent, indicating a small leak.

The measurements near MIT are mere mole hills, says Schulman. Out toward Somerville’s Pearl and Franklin streets, she says, “you get Swiss Alps.”

The excursion was part of a hands-on citizen science climate workshop co-organized by MIT’s ClimateX, MIT Alumni for Climate Action Leadership (MITACAL), Fossil Free MIT, and HEET. It was one of a number of climate change-related activities offered during MIT’s Independent Activities Period, which ran from Jan. 3 to Feb. 9.

Gas problem

When people hear “gas leaks,” they often think “potential explosions.” Leaks confined in small spaces or near a building foundation can build up enough to become life-threatening, so utility companies fix them immediately. But leaks that gush from the center of a street into the open, which are what this group is looking for, can go undealt with indefinitely.

These persistent leaks present a different kind of threat to the public. First, they have nontrivial economic consequences (as much as $90 million of gas is simply wasted through them every year). And their long-term consequences for climate stability are even more dire. Methane is a greenhouse gas that is 84 times more potent than carbon dioxide over a 20-year period; a little methane goes a long way toward warming the atmosphere.

As the van nears the intersection of Pearl and Cross streets in Somerville, the methane readings leap to new heights. Before long, the concentration has reached 0.0065 percent. “Oh, boy,” says Nathan Phillips, a professor at Boston University who’s coauthored numerous studies on urban gas leaks and is the day’s driver.

He parks and the occupants tumble out, eager to find the leak’s source.

Beep! A leak

Phillips takes out a handheld methane monitoring device: a “sniffer.” It looks like a large calculator, but acts like a small, noisy vacuum, sucking in air through a plastic nozzle. He pokes it between slabs of the sidewalk to see if he can find the leak’s source. Meanwhile, the rest of the group tries to uses their own, biological sniffers.

The device suddenly beeps. “That’s 0.85 percent methane,” Phillip says — more than a thousand times what the car detected wafting in the air. “But this is right at the surface,” he says. “If I went down further [just a few inches], this could be 90 percent gas.”

It was a leak, alright, potentially coming from a main line or even a service line branching to someone’s home. But the leak’s not an incendiary one. “If it were 4 percent [at the surface], then that would be a grade one explosive hazard,” Phillips says. “We would call it in, and [the utility] would come out immediately.” More than 15 percent, though, and there’s not enough oxygen for the gas to combust, he explains.

When the bough breaks

Another indicator of gas leaks, Phillips tells the group, is sick or dead trees. Walking along boulevards, “it's not what you see, but often what you don't see that matters,” he says. Near the gas leak he’s just found, he points out a square patch that looks like it once held a tree, but has been filled in with concrete. Because gas lacks oxygen, a leak could have suffocated a tree, he explains.

Another ominous sign right next to the leak is a young cherry tree that looks to be only a few years old; the rest of the street’s towering red maples are closer to 20 years and older. One of the participants asks whether another tree might have died here.

Phillips doesn’t know, but next to the sapling is an alarming clue to the gas leak’s past: a small mound of misshapen concrete, like a scab on the sidewalk’s skin. “That’s a sign the gas company came out here at some point to monitor [this leak],” Phillips says. It’s unclear why, if that’s the case, the street is still leaking methane.

Phillips puts the sniffer on top of the concrete blemish and the device blares its highest numbers yet: 1.2 percent methane. “This leak is too close to be good for this tree,” Phillips says. A tree physiologist, he gives a twig a test snap. “Look how it's breaking off. This tree's not in good health,” he says. “These tips are dead.”

People power

HEET is working with The Sierra Club, for which Phillips is an executive board member, to develop a program to train more citizen scientists. It’s still early days, but one vision of the program is to show people how to spot the signs of a leak — such as sick trees — and provide methane sniffers to the public via a lending library.

“HEET hopes to make these available … to do what we're doing. To use your nose, to use your eyes,” Phillips says. “For example, people might walk by, and say, ‘Ooh, I smell a leak.’” Then you could go and check out this instrument to investigate, he says, find where the leak is, and report it. This ability “empowers people to find out more.” 

Citizen science can also help keep utilities accountable. In 2014, Massachusetts passed a law requiring companies to map their leaks. “But the utilities get it wrong sometimes,” Phillips says. Leaks can also appear to go missing. According to work that was done by HEET and reported in the Boston Globe, about 30 percent of leaks came off the books on Dec. 31 in 2014, he says; “It doesn't make sense.” By working independently, citizen scientists could essentially audit gas companies.

That ability appeals to Laurel Regibeau-Rockett, a junior in physics, who reveled in the day’s experience. “This was awesome,” she says. “I didn't expect it to be as exciting as it was to find leaks – and they’re much bigger than I expected.”

Teaching people how to become citizen scientists is an exciting part of a shifting policy landscape, says Amanda Giang, a PhD candidate in the Institute for Data, Systems, and Society and one of the day’s leak hunters. “Many of the environmental challenges we're facing have a lot of uncertainty associated with them,” she says. “I think citizen science is this fantastic way of, one, bringing in this huge new data set, and, two, providing an avenue for democratic participation in environmental decision making.”

Both Regibeau-Rockett and Giang intend to use their new methane-sleuthing skills in the future.


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