According to the U.S. EPA, methane is the second most prevalent greenhouse gas and accounts for about 10% of all U.S. greenhouse gas emissions from human activities. However, methane is a much more powerful greenhouse gas than carbon dioxide though it survives in the atmosphere a shorter time. Methane is emitted by natural sources such as wetlands and the breakdown of organic material, as well as human activities such as, sewage treatment, landfills, leakage from natural gas systems and the raising of livestock.
In the past most of the effort in improving methane emission estimates has targeted oil- and natural gas-production, because the U.S. Environmental Protection Agency (EPA) had estimated that to be the source of most of the leakage from natural gas. Now, a new NOAA and University of Michigan study using an instrumented airplane has found unexpectedly large emissions over five major cities along the East Coast. These cities have natural gas distribution systems and deliver natural gas to households.
The NOAA & UM study directly measured emissions coming from these five cities. The amount of methane measured was much larger than had been estimated. The work was published in the journal Geophysical Research Letters. The methods used allowed scientists to quantify the total amount of methane coming from the city; and the ratio of ethane to methane to calculate how much methane was due to natural gas leakage, and found 10 times the amount of methane previously estimated by the EPA as coming from natural gas.
Ethane is a component of natural gas, but is not generated by landfill, and sewage. Gas utilities have precise measurements of how much ethane is in the gas they deliver. So it’s useful as a tracer for separating emissions coming from fossil fuel from those coming from landfills. Gas distribution companies are well aware of the leaks in the system. The companies calculate the difference between the gas pumped into the distribution system and what is metered at the end user. This is referred to as "lost and unaccounted-for" gas is often a surcharge on customer bills. These leaks are wasteful, dangerous and a significant source of greenhouse gas released into the environment. Distribution companies prioritize finding and fixing leaks likely to be explosion hazards, where gas is collecting and concentrating and ignore the small losses from deteriorating iron pipe, which turns out to be significant.
While there have been a handful of other studies of urban areas scattered around the country, there has been a real lack of data in this area. Previously, Robert B. Jackson, formerly of Duke University and now at Stanford, Nathan Phillips, of Boston University Department of Earth and Environment and Robert Ackley of Gas Safety Inc., and Eric Crosson of Picarro Inc., who performed a study of gas leaks in Boston and Washington DC in 2012 and 2013.
They mapped the gas leaks under the city using a new, high-precision methane analyzer provided by Picarro installed in a GPS-equipped car. In Boston they drove all 785 road miles within city limits, and discovered 3,356 leaks. The leaks were found to be associated with old cast-iron underground pipes, rather than neighborhood socioeconomic indicators. Levels of methane in the surface air on Boston’s streets exceeded 15 times the normal atmospheric background value. Similar results were found in Washington DC.
The current NOAA study sampled one of the largest metropolitan megaplexes, home to about 12% of the US population. According to lead author Genevieve Plant, of the University of Michigan. “The amount of natural gas that flows into these older cities is very large.... We found methane emissions in the five largest cities that we sampled are ... about double what the EPA estimates for the total emissions.”
Based on this research detecting and reducing gas leaks are critical for reducing greenhouse gas emissions, improving air quality and consumer safety, and saving consumers money. In addition to the explosion hazard, natural gas also poses a major environmental threat: Methane, the primary ingredient of natural gas, is a powerful greenhouse gas that degrades air quality. Leaks in the United States are reported to contribute to $3 billion of lost and unaccounted for natural gas each year. Repairing our infrastructure could significantly reduce these releases.
No comments:
Post a Comment