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April 19th, 2012

New monitoring system clears up murky questions about greenhouse gases

Chad Wolak in the Laboratory for AMS Radiocarbon Preparation and Research (NSRL). Photo by Ethan Welty,

A team of researchers has developed a new monitoring system to differentiate natural and man-made emissions of carbon dioxide (CO2) and trace gases in the atmosphere, a technique that likely could be used to monitor the effectiveness of measures regulating greenhouse gases.

The research team, led by INSTAAR Fellow Scott Lehman and CIRES Research Associate and NOAA scientist John Miller, looked at atmospheric gas measurements taken every two weeks from aircraft over a six-year period over the northeast United States to collect atmospheric samples. Their method allowed them to separate CO2 derived from fossil fuels from CO2 being emitted by biological sources like plant respiration, said Lehman.

The separation was made possible by the fact that CO2 released from burning fossil fuels like coal, oil, and gas has no carbon-14 (14C), a radioactive form of carbon that is constantly forming in Earth’s atmosphere. Half of a given amount of 14C decays every 5,700 years so fossil fuels, which are derived from remains of plants and other organic matter that accumulated millions of years ago, no longer contain the radioactive carbon.  In contrast, CO2 emitted from current biological sources is relatively rich in 14C. It’s a significant enough difference for atmospheric scientists to detect, Lehman said.

The team also measured concentrations of 22 other atmospheric gases tied to human activities, said Miller.  The gases impact climate change, air quality and the recovery of the ozone layer, but their emissions are poorly understood.  The authors used the ratio between the concentration level of each gas in the atmosphere and that of fossil fuel-derived CO2 to estimate the emission rates of the individual gases.

“Even if we lack the will to regulate emissions, the public has a right to know what is happening to our atmosphere. Sticking our heads in the sand is not a sound strategy.” - Scott Lehman

In the long run, measuring 14C in the atmosphere offers the possibility to directly measure country and state emissions of fossil fuel CO2, said Miller.  The technique would be an improvement over traditional, “accounting-based” methods of estimating emission rates of CO2 and other gases, which generally rely on reports from particular countries or regions regarding the use of coal, oil and natural gas, he said. 

One surprise in the study was that the researchers detected continued emissions of methyl chloroform and several other gases banned from production in the United States. Such observations emphasize the importance of independent monitoring, since the detection of such emissions could be overlooked by the widely used accounting-based estimation techniques, said NOAA scientist Stephen A. Montzka.
Said Miller, “As CO2 emissions targets become more widespread, there may be a greater temptation to underreport. But we’ll be able to see through that.”

“We think the approach offered by this study can increase the accuracy of emissions detection and verification for fossil fuel combustion and a host of other man-made gases,” said Lehman.

Unfortunately, NOAA’s greenhouse gas monitoring program has been cut back by Congress in recent years, said Lehman. “Even if we lack the will to regulate emissions, the public has a right to know what is happening to our atmosphere. Sticking our heads in the sand is not a sound strategy,” he said.

A paper on the project was published in the April 19 issue of the Journal of Geophysical ResearchAtmospheres. Co-authors include INSTAAR Chad Wolak and former INSTAAR Jocelyn Turnbull.

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