LEAKS IN WASHINGTON: Although the results for the District of Columbia are not final, preliminary numbers indicate that the nation's capital has thousands of leaks from its natural gas distribution system. Image: Flickr/Eric Magnuson
Bob Ackley may be the only person who has driven up and down every single street -- 1,500 miles total -- in Washington, D.C.
While Ackley, a plain-speaking New Englander, enjoyed exploring the nation's capital, which he described as "beautiful," this was serious business. He was measuring leaks of methane, a potent greenhouse gas that is also the main component of natural gas. Measured in terms of warming the atmosphere, methane is 25 times more potent than carbon dioxide.
In January, the former gas inspector drove around with researchers Robert Jackson, a scientist at Duke University's Nicholas School of the Environment, and Boston University's Nathan Phillips. They were trying to create a map of all the gas leaks in the district, some of which can pose a safety hazard as well as causing climate change.
"It took me 21 days, working about 14 hours a day," said Ackley.
The team was replicating an experiment they did last year in Boston. There, as in D.C., they drove a car equipped with special sensors, made by the Santa Clara, Calif., company Picarro Inc., that detected and mapped leaks from the aging pipeline systems underlying the city.
Although the results for the District of Columbia are not final, preliminary numbers indicate that the nation's capital has thousands of leaks from its natural gas distribution system. It has a number of leaks per road mile similar to that of Boston, but has about twice as many miles of road, said Jackson.
The district also appears to have bigger leaks than Boston's, he said. In Boston, the researchers counted 3,356 leaks. They also determined whether leaks were from natural gas pipes or more natural sources, such as landfills, where it is created by decaying garbage.
Since methane has different ratios of carbon isotopes in it, instruments can determine whether methane is coming from a fossil fuel source or from a landfill or a wetland.
A problem in older cities
Most of the leaks the researchers found came from the pipeline system, said Phillips. This is not surprising, given the age of many of the pipeline systems in older cities.
"The problem that we've seen in Boston is not unique to Boston. It's something that characterizes the Eastern Seaboard," said Phillips.
The technology the team used was pioneered by Picarro. It allowed the researchers to measure leaks and the concentrations of methane in those leaks and map them. That's the first phase of the work.
Next, they try to learn more about the rate at which gas from various leaks is being released to the atmosphere. To do that, the researchers have to make a second trip, returning to the source of a representative set of leaks.
They're currently doing this in Boston. Many of the leaks, said Phillips, are at manholes, or on curbs where the sidewalk meets the asphalt.
To measure the leak rate, the researchers cover the leaking area with an empty container of a known volume and measure the rate at which the container fills up with gas.
Once they have measured leak rates from various locations, they plan to use create a statistical distribution to represent an overall estimate of just how much methane is leaking, said Phillips. The researchers plan to compare this to the results of another experiment in which sensors are monitoring the city's air from the tops of buildings, seeing how much methane can be measured rising out of the city into the atmosphere.
Seeping from long-buried pipes
Just how big the volumes of methane leaking from the aging pipes of Boston or the District of Columbia are is a measurement that might change whether natural gas can be regarded as a more climate-friendly source of energy.
The effort to figure out where those leaks occur, and how big they are, is in its infancy.