US power plant emissions down, study finds

January 9, 2014
In 2013, Xcel Energy decommissioned this coal-fired power unit in Denver's Arapahoe Station. Shifts in the US energy industry, including less electricity from coal, have meant fewer emissions of greenhouse gases and other pollutants from power plant, according to a new CIRES-led analysis. Credit: Photo by Will von Dauster of National Oceanic and Atmospheric Administration

Power plants that use natural gas and a new technology to squeeze more energy from the fuel release far less of the greenhouse gas carbon dioxide than coal-fired power plants do, according to a new analysis accepted for publication Jan. 8 in Earth's Future, a journal of the American Geophysical Union. The so-called "combined cycle" natural gas power plants also release significantly less nitrogen oxides and sulfur dioxide, which can worsen air quality.

"Since more and more of our electricity is coming from these cleaner , emissions from the power sector are lower by 20, 30 even 40 percent for some gases since 1997," said lead author Joost de Gouw, an atmospheric scientist with NOAA's Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado Boulder. NOAA is the National Oceanic and Atmospheric Administration.

De Gouw, who works at NOAA's Earth System Research Laboratory (ESRL), and his NOAA and CIRES colleagues analyzed data from systems that continuously monitor emissions at power plant stacks around the country. Previous aircraft-based studies have shown these stack measurements are accurate for (CO2) and for nitrogen oxides and sulfur dioxide. Nitrogen oxides and sulfur dioxide can react in the atmosphere to form tiny particles and ozone, which can cause respiratory disease.

To compare pollutant emissions from different types of power plants, the scientists calculated emissions per unit of energy produced, for all data available between 1997 and 2012. During that period of time, on average:

  • Coal-based power plants emitted 915 grams (32 ounces) of CO2 per kilowatt hour of energy produced;
  • Natural emitted 549 grams (19 ounces) CO2 per kilowatt hour; and
  • Combined cycle plants emitted 436 grams (15 ounces) CO2 per kilowatt hour.

In combined cycle , operators use two heat engines in tandem to convert a higher fraction of heat into electrical energy. For context, U.S. households consumed 11,280 kilowatt hours of energy, on average, in 2011, according to the U.S. Energy Information Agency. This amounts to 11.4 metric tons per year of CO2 per household, if all of that electricity were generated by a coal power plant, or 5.4 metric tons if it all came from a natural gas power plant with combined cycle technology.

The researchers reported that between 1997 and 2012, the fraction of electric energy in the United States produced from coal gradually decreased from 83 percent to 59, and the fraction of energy from combined cycle natural gas plants rose from none to 34 percent.

That shift in the energy industry meant that power plants, overall, sent 23 percent less CO2 into the atmosphere last year than they would have, had coal been providing about the same fraction of electric power as in 1997, de Gouw said. The switch led to even greater reductions in the power sector's emissions of and , which dropped by 40 percent and 44 percent, respectively.

The new findings are consistent with recent reports from the Energy Information Agency that substituting natural gas for coal in power generation helped lower power-related in 2012.

The authors noted that the new analysis is limited to pollutants emitted during energy production and measured at stacks. The paper did not address levels of greenhouse gases and other pollutants that leak into the atmosphere during fuel extraction, for example. To investigate the total atmospheric consequences of shifting energy use, scientists need to continue collecting data from all aspects of exploration, production and use, the authors concluded.

Explore further: New emissions standards would fuel shift from coal to natural gas

More information: "Reduced Emissions of CO2, NOx and SO2 from U.S. Power Plants Due to the Switch from Coal to Natural Gas with Combined Cycle Technology," Earth's Future, 2014.

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5 / 5 (3) Jan 09, 2014
This is good news. It may not be everything we need, but it's good. And was anyone's quality of life diminished by this reduction in emissions? Is it still so scary to be more conscious of our emissions?

(edit, well I guess, if anything, the people who've had damage to water tables from hydraulic fracturing to gather the natural gas for this reduction of emissions maybe have seen a decrease in quality of life)
4 / 5 (4) Jan 09, 2014
Well shavera,given that my home is heated by natural gas, as are many thousands of others, and given the price of natural gas has fallen dramatically as a result of hydraulic fracturing, I am thinking that more people have benefitted than suffered.

No science to back that observation up, and I agree, this is good!
5 / 5 (4) Jan 09, 2014
Yeah, I can see natural gas as a mixed blessing, of course. Lord knows not everything needs to be either Science's gift to mankind nor a scourge on the planet. Maybe some things are both... you know, useful but also a bit damaging. If we can optimize use v. damage going forward... that'd really be great.

Fracking, in and of itself, doesn't seem to be *too* bad, we just need better regulations on how the wells are sealed and that the capture process is done cleanly. And we'd all be better off getting off of fossil fuel burning altogether, but better LNG/CNG than coal. It's a reasonable intermediate step while research on biofuels and renewables remains ongoing. (or while nuclear plants were being built, if we could get them built in a safe manner and store their fuel/waste safely.)

It's almost like... there are calm, rational compromise ways of doing good. Rather than shout matches over climate change's existence or not or how bad it would be to try to mitigate its effect.
4.2 / 5 (5) Jan 09, 2014
It's almost like... there are calm, rational compromise ways of doing good. Rather than shout matches over climate change's existence or not or how bad it would be to try to mitigate its effect.

Well put. We're seeing a transition to better, or at least less harmful, sources of energy for everything from appliances to vehicles. The voices of denialism/contrarianism fail to see that the main benefactors of the status quo are those who benefit from it the most.
Rational compromise. I like that.
3 / 5 (1) Jan 09, 2014
"The researchers reported that between 1997 and 2012, the fraction of electric energy in the United States produced from coal gradually decreased from 83 percent to 59 percent."

No, coal peaked at 57% in 1987 and 1988 then fell to 38% in 2012. It bounced back up a bit in 2013 to about 40% due to higher NG prices.

Coal will now continue its downward slide as we close 150 coal plants in the next couple of years.
4.5 / 5 (2) Jan 10, 2014
No way! Less coal = less emissions? Really?
... US studies are sooo smart. Now hurry, someone deny it.
3 / 5 (2) Jan 10, 2014
No way! Less coal = less emissions? Really?
... US studies are sooo smart. Now hurry, someone deny it.

Well, if we only do a 1:1 exchange for coal to NG and continue to let NG leak then we probably are gaining nothing, even making things worse. Methane is a nasty greenhouse gas.

If we control the leaks and use NG only as a fill-in for wind and solar then we get net gains.

We've got a lot of NG capacity. Capacity factor for NG in 2011 was under 25%. We can use some of that spare capacity to allow us to get more wind/solar on line while we figure out out best storage options.
5 / 5 (3) Jan 13, 2014
People should not forget that natural gas is also a large CO2 emitter. It's only about 1/4 as bad as coal or oil. Using natural gas does have an impact on reducing global warming but it's not the panacea that the fossil fuel industry would like to make you believe. Reading this glowing article makes you thing all is good, however mankind has so dirtied ir's nest that only ZERO CO2 emissions will insure the survival of mankind.

It's funny to see this article juxtaposed to an earlier one with the title
US carbon pollution up two percent in 2013

Bottom line is we need alternative sources for grid scale energy, but coal, oil and natural gas should not be the primary source ever in man's future.
5 / 5 (2) Jan 14, 2014
"natural gas should not be the primary source ever in man's future."

Absolutely. We need to get busy installing storage so we can cut back on NG.

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