Kaiguang Zhao

Natural gas has been hailed by some as a crucial bridge fuel to a cleaner energy future. But how much cleaner is burning natural gas than burning oil or coal?

Concern over water contamination from fracking for natural gas aside, some argue that the much-advertised climate advantage of natural gas may be all but offset by the steady release of methane during its long journey from the well to the 65 million American households that depend on natural gas. Molecule per molecule, methane has more than 20 times the global warming potential of carbon dioxide.

Now researchers in Boston have given skeptics of the at-least-natural-gas-is-better- than- coal argument some additional ammunition.

In Boston and many other aging cities in the Northeast, a maze of underground low-pressure natural gas pipelines are riddled with leaks. The research team, led by Nathan Phillips, an associate professor of earth and environment at Boston University, measured atmospheric methane concentrations along all 785 miles of road within Boston’s city limits with a highly sensitive device known as a cavity-ring-down mobile CH4 analyzer.

They discovered 3,356 leaks of methane whose isotopic characteristics indicated that they originated in fossil fuel rather than microbial sources. Some leaks clocked in at more than 15 times the global background methane level, the researchers write in the journal Environmental Pollution.

“There are two ways to get a sense of the leak rate of methane,” Dr. Phillips said. “You can go out to the leaks on the ground and put chambers over them and measure how much is coming out, but that is incredibly tedious with over three thousand leaks in the city. Or, you can use the integrating power of the atmosphere itself.”

With the data, the team has created the first comprehensive and publicly available map of leaks in any city.



“We know there’s a lot of leaks in Boston and outside of Boston, too, and we know that there is a good chunk of industry-reported lost and unaccounted-for gas,” Dr. Phillips said. “What we don’t know, and what we, and a bunch of other people are trying to get a handle on, is how much methane is coming out of all of these leaks. What is the rate of flow? Is some of it just metering problems, or accounting issues?” Here’s Andrew C. Revkin’s take on the subject at the Dot Earth blog; check out the video about the research, too.)

Many of the pipes in Boston are more than a century old and are made of cast iron or in some cases even wood. While they are slowly being replaced by modern plastic pipes, only time will tell if these are truly more durable: many are designed to last only 50 years.

Replacing just one mile of pipeline costs around $1 million. And in the event of a rupture, newly paved roads may have to be dug up to repair a pipeline.

In addition to being a potent greenhouse gas, methane leaks kill trees, causing $133 million in property damage nationally each year. Methane also contributes to ozone formation, and natural gas explosions cause an average of 17 deaths and 68 injuries from year to year in the United States.

According to the Energy Information Administration, an average of $3.1 billion worth of natural gas is lost or unaccounted for nationally each year. Generally it is the consumer ratepayers, not the producers, who pay the penalty for the lost gas. “The consumers are bearing the cost of the inefficiencies in the system, and that needs to be shifted to give the operators and owners of the pipelines real incentives to fix those leaks,” Dr. Phillips said.

As for resolving the question of whether natural gas or coal generates more greenhouse gas emissions, Robert Jackson, a professor of biology at Duke University who was part of the research team, said that scientists need to study emissions from the production stage “all the way through the compressor stations to the end use.”

“We will continue to do this sort of mapping in other cities, but it’s not just a question of more geography,” he said. “We also need to get a better picture of every stage of natural gas production and distribution.”