Researchers from NOAA and the University of Colorado Boulder have devised a breakthrough method for estimating national emissions of carbon dioxide from fossil fuels using ambient air samples and a well-known isotope of carbon that scientists have relied on for decades to date archaeological sites.
In a paper published in the journal the Proceedings of the National Academy of Sciences, they report the first-ever national scale estimate of fossil-fuel derived carbon dioxide (CO2) emissions obtained by observing CO2 and its naturally occurring radioisotope, carbon-14, from air samples collected by NOAA’s Global Greenhouse Gas Reference Network.
Carbon-14, or 14C, a very rare isotope of carbon created largely by cosmic rays, has a half-life of 5,700 years. The carbon in fossil fuels has been buried for millions of years and therefore is completely devoid of 14C. Careful laboratory analysis can identify the degree of 14C-depletion of the CO2 in discrete air samples, which reflects the contribution from fossil fuel combustion and cement manufacturing (which also has no 14C), otherwise known as the “fossil CO2” contribution. Knowing the location, date and time when the air samples were taken, the research team used a model of atmospheric transport to disentangle the CO2variations due to fossil fuel combustion from other natural sources and sinks, and traced the man-made variations to the fossil CO2 sources at the surface.
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Image: CIRES scientist Duane Kitzis approaches the air sampling station on Niwot Ridge, Colorado, part of NOAA's Global Greenhouse Gas Reference Network, in this 2017 photo. The first air sample analyzed for carbon-14 as part of research into a new method of estimating fossil fuel emissions from ambient air was collected here in 2003. (Credit: James Murnan, NOAA)