![]() ![]() “Bottom-up” estimates, such as those used in the EPA Inventory of U.S. The two primary methods in current use – “bottom up” inventories and “top down” atmospheric studies used in regional campaigns – each have their strengths and weaknesses. top-downĪccurately calculating emissions of carbon dioxide from burning fossil fuels has challenged scientists for years. “We can then add these up and compare to other emissions estimates at various time and space scales” Bottom-up vs. “It provides us with a tracer we can track to sources on the ground. ![]() “Carbon-14 allows us to pull back the veil and isolate CO 2 emitted from fossil fuel combustion,” said Lehman, one of the paper’s authors. While the link between fossil CO 2 emissions and atmospheric 14C has been known for many decades, the construction of a national-scale emission estimate based on atmospheric 14Crequired the simultaneous development of precise measurement techniques and an emissions estimation framework, largely spearheaded over the past 15 years by NOAA scientist John Miller and University of Colorado scientist Scott Lehman. He is now a scientist at NASA’s Goddard Space Flight Center in Maryland. “This is a new, independent, and objective method for evaluating emission inventories that is based on what we actually observe in the atmosphere,” said lead author Sourish Basu, who was a CIRES scientist working at NOAA during the study. Knowing the location, date and time when the air samples were taken, the research team used a model of atmospheric transport to disentangle the CO 2variations 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. Careful laboratory analysis can identify the degree of 14C-depletion of the CO 2 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 CO 2” contribution. The carbon in fossil fuels has been buried for millions of years and therefore is completely devoid of 14C. 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 (CO 2) emissions obtained by observing CO 2 and its naturally occurring radioisotope, carbon-14, from air samples collected by NOAA’s Global Greenhouse Gas Reference Network.Ĭarbon-14, or 14C, a very rare isotope of carbon created largely by cosmic rays, has a half-life of 5,700 years. 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. ![]()
0 Comments
Leave a Reply. |