To measure concentrations that low, you need an extremely sensitive measurement technique, and such a technique already exists.Archaeologists have been relying on it for decades.
Among other things, it will allow scientists to measure how much of the carbon dioxide (CO2) in the atmosphere came from burning fossil fuels, and to estimate fossil fuel emissions in an area as small as a city or as large as a continent.
This is possible because carbon atoms occur in heavy and light forms, or isotopes, and measuring the relative amounts of each can reveal the source of the carbon.
Using carbon isotopes in this way is not a new idea, but it requires extremely precise--and expensive--measurements.
The new instrument, developed by NIST chemists Adam Fleisher and David Long and based on a technology called cavity ringdown spectroscopy (CRDS), promises to dramatically reduce the cost of those measurements. "Measuring carbon isotopes is an extremely useful technique, but until now, it has found limited use because of the cost," said Long.
Areas with high fossil fuel emissions, such as cities and industrial zones, will have below-normal concentrations of heavy CO2.