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Spectroscopy Technique Detects Carbon

Photonics Spectra
May 2002
Brent D. Johnson

Concern about climatic changes has researchers from Los Alamos National Laboratory examining ways to sequester carbon in the ecosystem.

There are basically two ways of dealing with the problem: direct reduction of emissions through regulation, or storage of carbon somewhere besides the atmosphere, such as terrestrial ecosystems. In the latter, scientists aim to return carbon to the soil by growing crops on land that is underutilized. Geological sequestration involves pumping carbon from the atmosphere into geological formations. Carbon also could be traded as a commodity, since soil with the highest carbon content makes the richest farmland.

Several independent analyses based on geochemical data and a series of carbon budgets based on data from forest inventories have shown that carbon is accumulating in terrestrial ecosystems. Courtesy of Woods Hole Research Center.

To make this process manageable, however, the carbon pool must be quantified to provide a better understanding of the carbon cycle. Los Alamos researcher David Cremers has developed a handheld device that can analyze carbon content in very small soil samples in the field. The US Department of Agriculture funded the research along with the National Energy Technology Laboratory; however, the program has its roots in the Kyoto Protocol.

Cremers has been working on the technology for more than 20 years and has employed grating spectrophotometers, array detectors and dry oxidation methods. However, each was primarily a lab-based experiment that required large samples.

Using laser-induced breakdown spectroscopy on very small samples, he can identify the spectral signature of each atom on the periodic table. If the method is properly calibrated, quantitative analysis of the key wavelengths for carbon at 247.8 and 391.0 nm is achievable.

The researchers focus a Continuum Q-switched pulsed Nd:YAG Minilite laser with a simple lens onto a soil sample, generating a spark (plasma). The sample is vaporized at temperatures of 8000 °C, releasing atoms that emit light. In a larger version of the device, they use an echelle spectrum analyzer from Catalina Scientific Corp. in Tucson, Ariz., that can detect light from 190 to 650 nm. In the smaller version, they use an intensified CCD array as the detector.

Testing in the field

The main benefit of this technology is that the scientists can collect relatively fine particles of soil and conduct real-time testing in the field. This allows them to rapidly measure carbon and to assess whether it is increasing (through respiration) or decreasing (through photosynthesis). They also can extract cores and raster-scan them to measure the carbon as a function of depth and time. In future trials, the device will be used to quantify carbon in soils throughout the world.


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