New monitoring system identifies carbon dioxide resulting from fossil fuel burning; carbon-14 is the key
20 April 2012
Researchers have developed a new monitoring technique to distinguish emissions from the combustion of fossil fuels in the atmosphere from other gases, a technique that likely could be used to monitor the effectiveness of measures regulating greenhouse gases.
|Model representations of (left) Δ14C and (right) the fossil fuel component of total CO2 (Cff) in the atmosphere near the surface over North America. Miller et al. Click to enlarge.|
The team examined six years-worth of atmospheric gas measurements of carbon dioxide (CO2) and other gases, taken by aircraft every two weeks. Their method allowed them to separate CO2 derived from fossil fuels from CO2 being emitted by biological sources, such as plant respiration, said Scott Lehman, a senior research associate at the University of Colorado, Boulder, who led the study with John Miller, a research associate at the university and who is also with the National Oceanic and Atmospheric Administration’s (NOAA) Earth System Research Laboratory in Boulder.
The separation was made possible because CO2 released from burning of fossil fuels like coal, oil, and gas has no 14CO2 (carbon-14), a radioactive form of carbon that is constantly forming in Earth’s atmosphere. Because 14CO2 is radioactive, it decays, or transforms, into another, nonradioactive element over time. Half of a given amount of the substance 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 14CO2. It’s a significant enough difference for atmospheric scientists to detect, Lehman said.
In the long run, measuring 14CO2 in the atmosphere offers the possibility to directly track 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.
While the accounting-based approach is probably accurate at global scales, the uncertainties rise for smaller-scale regions. And as CO2 emissions targets become more widespread, there may be a greater temptation to under-report. But we’ll be able to see through that.—John Miller
A paper on the subject was published 19 April in the Journal of Geophysical Research-Atmospheres, a publication of the American Geophysical Union.
The researchers also measured concentrations of 22 other atmospheric gases tied to human activities. One surprise in the study was that the researchers detected continued emissions from 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 Stephen Montzka, with NOAA’s Earth System Research Laboratory, who worked on the study.
Miller, J. B., et al. (2012), Linking emissions of fossil fuel CO2 and other anthropogenic trace gases using atmospheric 14CO2, J. Geophys. Res., 117, D08302, doi: 10.1029/2011JD017048
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