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.

Distribution, the part of the gas supply chain that Jackson and Phillips focus on, involves a complicated patchwork of possibly leaky pipelines, particularly in older cities.

While gas utilities certainly prioritize plugging leaks that could cause explosions, they have fewer incentives to plug those that don't pose an explosion risk.

In a city like Washington, the pipeline distribution system consists of pipe materials that include cast iron, unprotected or protected steel, copper and plastic. Cast iron is often the oldest and leakiest, especially at the joints, although other pipeline materials can also develop leaks.

According to 2012 data reported to the Pipeline and Hazardous Materials Safety Administration by Washington Gas Light Co., the company has about 1,200 total miles of pipeline in the District of Columbia.

Of that length, 419 miles is cast iron. There is less than 100 miles of unprotected steel, and the majority of what's left is divided between coated steel and plastic.

Too small to explode
Gas companies prioritize finding and fixing any leaks known as "Grade 1" leaks. These are leaks likely to be explosion hazards, where gas is collecting and concentrating. If gas is leaking to the atmosphere and does not pose a safety hazard, it may not be made a priority for repair.

"Depending on the seriousness of the leak, the [Department of Transportation] guidelines state whether our crews repair the leak immediately or follow up with the repair at a later time," wrote Ruben Rodriguez, direct of corporate communications for the company, in an email.

While it might seem as if gas companies would prioritize fixing any large leaks, since they would result in lost profits, Jackson said those financial incentives are not always as strong as one might think.

Gas companies calculate the difference between the amount of gas they send out and the amount that is metered at customers' homes or businesses. The difference, which is primarily caused by leaks and pressure and temperature errors in gas measurement between where the gas is sent out and where it is metered, is referred to as "lost and unaccounted-for" gas.

Some public utility commissions allow the utilities to charge their customers for this difference. In the District of Columbia, the charge makes up 3 percent of a customer's monthly cost, The Washington Post reported in March.

"I think usually the gas companies know where the big leaks are," said Jackson. "It's very common for us to step out of a car and start sampling on the street and have people walk out of a house or restaurant and say, 'What are you doing?' When we tell them we are looking at natural gas leaks, you have someone say: 'I have called this leak in multiple times.'"

Jackson is quick to point out that the object of his work in D.C. and Boston is not simply to tell gas companies they have thousands of leaks. Rather, it's to understand which leaks are important to plug, and how they are distributed throughout the system.

If the researchers are able to determine that 10 percent of the leaks are leaking 90 percent of the gas, which is possible, then fixing just a few leaks will result in a big reduction in greenhouse gas emissions, said Jackson.

"It's not very useful for us to say 'There are 3,300 leaks in Boston; go fix them all.' It's much more useful to say, 'If we fix these 100 leaks, we'll keep 50 percent of the gas from leaking out of the system,'" he said.

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC., 202-628-6500