Estimates of emissions from natural gas-fueled plants much too low, study finds

March 14, 2017 by Steve Tally, Purdue University
Purdue researchers flew an airborne chemistry laboratory over natural gas-fueled power plants and refineries to measure greenhouse gases. They found that although these facilities are much better for the environment than coal or oil-fueled plants, the actual amount of pollutants produced is as much as 42 times higher than estimates by the Environmental Protection Agency. Credit: Purdue University photo

Power plants that burn natural gas produce significantly less pollutants and greenhouse gases than coal-burning plants, according to current estimates of how much methane escapes from such power plants, as well as from oil refineries, and estimates could be off by a wide margin, a new Purdue University study finds.

For the past decade, has been replacing coal as a fuel for electric . It's become relatively inexpensive, and it's much less damaging to the environment if – and it's an important "if" – it doesn't leak out of the system before it is burned to make power.

That's because although burning natural gas is much cleaner than coal or oil, (which is mostly what natural gas consists of) has the potential to be even more damaging over the short term than coal or oil if it isn't handled properly, says Paul Shepson, Purdue's Jonathan Amy Distinguished Professor of Analytical and Atmospheric Chemistry.

"Methane is a 34 times more than is carbon dioxide," he says. "It's a better fuel all around as long as you don't spill it. But it doesn't take much to ruin your whole day if you care about climate change."

The breaking point for natural gas leakage is about 3 percent. If more than that leaks, the fuel has a bigger climate effect than burning coal.

"The good news from our study is that while emissions are greater than anticipated, natural gas-burning power plants are still cleaner, relative to burning coal" Shepson says. Shepson said this pilot study found that the amount of methane escaping from the plants was only 0.3 percent on average.

Even taking into account previous estimates of methane leakage in the supply chain of 1.7 percent, the total methane emissions are still below the 3 percent threshold, the study found.

The study also found that methane emission rates were significantly higher than two sets of estimates reported by the Environmental Protection Agency; the EPA's Greenhouse Gas Inventory of Emissions and Sinks estimated that total methane emissions from all U.S. refineries and natural was negligible in 2014.

However, this study estimated that annual methane emissions may actually be 11-90 times higher for refineries and 2 -120 times higher for natural gas power plants than those calculated from data provided by facility operators and reported to the EPA's Greenhouse Gas Reporting Program, and used in the Greenhouse Gas Inventory of Emissions and Sinks.

"There is much more methane being released into the atmosphere by leaky compressors, valves, and industrial hardware," Shepson says. "But the good news here is that you can take a specialized infrared camera around the plant to find the leaks and then patch the them with a wad of bubblegum. I'm joking about that, of course, but the point is that it's a relatively easy thing to fix."

The study's paper was released today by the journal Environmental Science & Technology, which is produced by the American Chemical Society.

The study conducted in collaboration with the New York-based Environmental Defense Fund, with funding provided by the Alfred P. Sloan Foundation.

Joseph Rudek, a lead senior scientist at the Environmental Defense Fund and a co-author on the paper, says that natural gas power plants and refineries could be a significantly unaccounted-for source of methane emissions. "More measurements are needed to better understand the methane emissions from these sectors."

Steve Hamburg, chief scientist at the Environmental Defense Fund, says that the leaking methane will especially diminish the environmental effects of using natural gas over the first few critical decades.

"There is the capacity to cost-effectively reduce associated with use and production of natural gas, so there's no excuse for the waste and serious long-term impacts" he says.

The study was conducted using Purdue's flying atmospheric chemistry laboratory, the Airborne Laboratory for Atmospheric Research, or ALAR. The ALAR is a modified Beechcraft 76 Duchess that flies at a height of 6,000 to 12,000 feet (2 to 4 kilometers) collecting air samples and conducting sophisticated measurements.

"ALAR is a unique machine, and it was created by combining three of Purdue's major strengths: atmospheric sciences, analytical chemistry, and aviation technology," Shepson says.

Shepson says the benefit of this research is that everyone involved will be able to improve the emission factor formulas used in calculating the amount of methane entering the atmosphere based on the total emissions of the plants, not just the amount going up the smokestacks.

"But the important overall message of the study is to say while natural gas power plants appear to provide a climate benefit, it can still be easily improved'" he says.

Explore further: Is replacing coal with natural gas actually good for the climate?

More information: Tegan N. Lavoie et al. Assessing the Methane Emissions from Natural Gas-Fired Power Plants and Oil Refineries, Environmental Science & Technology (2017). DOI: 10.1021/acs.est.6b05531

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3.7 / 5 (3) Mar 14, 2017
Yes. Seems to be deliberately overlooked when calculating the damage done by natural gas plants. It is only a blink in time from when we saw gas stacks flaring, the open air burning of excess gas. Of course the leaks are totally omitted but not when the public breaths.
1.9 / 5 (9) Mar 14, 2017
One more reason to replace all of our generation with less-polluting renewables. Natural gas was supposed to only be a bridge to the new technologies.

Maybe the bridge needs to be shortened.
1.5 / 5 (8) Mar 14, 2017
Here is a little problem:

"Study: Bakken oil field leaks 275,000 tons of methane yearly"
3.7 / 5 (3) Mar 15, 2017
One more reason to replace all of our generation with less-polluting renewables. Natural gas was supposed to only be a bridge to the new technologies.

Maybe the bridge needs to be shortened.
"Gas not a bridge. It's a plank."
If renewables were really reliable, Greenpeace would already be using windmill generators and solar panels instead of diesel to propel their ship and motorboats across the oceans.
5 / 5 (1) Mar 15, 2017
Thorium fueled nuclear power plants are the real solution for global warming--and long term energy generation. But trying to hype methane releases as a global warming threat is not just wrong, it is silly.

There are lots of huge methane sources, like methane clathrates in coastal waters, some types of vegetation, and permafrost. But the level of methane in the atmosphere is 0.00017% more than two hundred times lower than CO2. Why? Because methane in the air gets rapidly turned into CO2. So yes, methane is 34 times as much of a greenhouse gas than CO2--for a month or three. (Water is the most potent, and the most prevalent, and the most variable greenhouse gas in the atmosphere, but let's not go there.)
Captain Stumpy
3 / 5 (2) Mar 15, 2017
(Water is the most potent, and the most prevalent, and the most variable greenhouse gas in the atmosphere, but let's not go there.)
why not go there?
it's not like it's not studied nor talked about at all... hell, i've personally attempted to share this with people

in fact, Lacis et al 2010 and Lacis et al 2013 both discuss the link between CO2 and water vapor and it's cycle & feedback, which is very, very relevant

and it's not a matter of speculation because Lacis has studied and measured this in multiple publications and you can drag those up anytime you want (even through NASA pubs)

more to the point, it's also been validated and it's something that has been repeatedly discussed here on PO by myself, Thermodynamics, Runrig and quite a few others

it's not like this is speculation, conspiracy or anything else - it's just a matter of some people ignoring the data for whatever reasons

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