Boulder scientists distinguish sources of CO2 in the air

Apr 23 - McClatchy-Tribune Regional News - Laura Snider Daily Camera, Boulder, Colo.

 

Boulder scientists have developed a method to determine whether carbon dioxide in the air came from the burning of fossil fuels, such as oil and coal, or from a natural process, such as plant or animal respiration.

The results may help scientists better measure the emission rates of carbon dioxide derived from fossil fuels and help policymakers understand how any future regulation of greenhouse gases is working.

The key to the new technique -- which was developed by researchers at the National Oceanic and Atmospheric Administration and the University of Colorado -- is the ability to distinguish among different types of carbon in the air. The scientists can now pick out different carbon isotopes -- versions of carbon that have different numbers of neutrons -- in the carbon dioxide.

Biological sources of carbon dioxide are rich in an isotope known as carbon-14. But because carbon-14 breaks down relatively quickly, lasting just thousands of years, it's not found in the carbon dioxide emitted from burning fossil fuels, which form over millions of years.

 

Scientists first measured carbon-14 in the air in the 1980s, but the Boulder scientists were able to reduce the amount of air that's needed to make the measurement, and therefore, make it easier to apply the technique to smaller-sized air samples.

"This permits us to work with much smaller samples that are routinely collected around the world," said Scott Lehman, a CU senior research associate who led the study with another CU researcher, John Miller. "We typically work with 2 liters of air in small glass flasks."

The old method required about 15 cubic meters of air to determine the presence of carbon-14.

Now, estimates of carbon dioxide emissions are typically made using an "accounting-based approach." For example, if scientists know how much gas has been sold in the United States over a certain time period, they can calculate how much carbon dioxide is released when that gas is burned.

The new carbon-14 approach allows scientists to measure what is actually in the atmosphere from all fossil fuel sources.

"While the accounting-based approach is probably accurate at global scales, the uncertainties rise for smaller-scale regions," said Miller, also a scientist at NOAA's Earth System Research Laboratory in Boulder. "And as CO2 emissions targets become more widespread, there may be a greater temptation to underreport. But we'll be able to see through that."

For the new study -- published in the Journal of Geophysical Research: Atmospheres -- the researchers used air samples that were collected every two weeks by aircraft over a six-year period in the northeastern United States.

Besides measuring the carbon-14 present, the researchers also measured other gases found in the sample. Because the emissions of some gases are regulated, scientists can find out how much is being released in any particular area. When they compare the total amount they know was released to the amount measured, they come up with a ratio that they can then use to figure out the total amount of carbon dioxide that was also released in the same area.

Knowing the total amount of carbon dioxide that's in the air from fossil fuels can, in turn, help scientists create a baseline record of carbon dioxide that can be used in the future to evaluate methods of reducing greenhouse gases.

"It's hard to regulate gases if emissions are imperfectly known," Lehman said. "We need this baseline."

Measuring other gases in the samples also led to another discovery: Some gases that were outlawed in the Montreal Protocol because of their negative impact on the ozone layer are still being emitted.

"That's not the kind of thing you see in bottom-up inventories," Lehman said.

Lehman said the researchers' next step is to expand the testing of carbon dioxide and other gases to locations around the country.

"The initial goal is to do this more thoroughly in the U.S.," he said.

Contact Camera Staff Writer Laura Snider at 303-473-1327 or sniderl@dailycamera.com.

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