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Laser Induced Breakdown Spectroscopy

 

Los Alamos laser measures carbon in soils

David Cremers, left, and Monty Ferris of Advanced Chemical Diagnostics (C-ADI) use Laser-Induced Breakdown Spectroscopy to determine the amount of carbon in a sample of soil contained in the tube at right. The bright flash on the soil sample is where a pulse of laser light vaporizes a bit of the soil. By analyzing the spectral characteristics in the flash of light, the researchers are able to determine the amount of carbon contained in the soil. Carbon-LIBS is being developed to allow scientists to determine the carbon budget of terrestrial areas -- knowledge that can help scientists gain a better understanding of forces that influence global warming. Photo by James E. Rickman, Public Affairs

 

Laboratory scientists have developed a small, portable instrument that uses a laser to analyze the amount of carbon in soils, which can give scientists a better understanding of terrestrial processes that could accelerate or retard global warming.

With increasing international concern about greenhouse gases and global warming, scientists have sought better and more cost-effective approaches for measuring significant changes in the amount of land-based carbon, much of which is located in soils. But because the amount of carbon varies considerably from one spot to the next, measuring changes in land-based carbon in fields, ranch lands and forests is difficult. The newly developed Los Alamos technology will aid scientists as they try to determine how soil-based carbon is released into the air through natural or manmade causes, or whether atmospheric carbon is being absorbed into soils. The new technology was highlighted recently in a paper appearing in the Journal of Environmental Quality.

"Carbon truly is the currency of life," said Los Alamos ecologist David Breshears of Environmental Dynamics and Spatial Analysis (EES-10) and a co-author of the paper. "For years, scientists have sought to improve accounting of Earth's carbon budget. This instrument will help us improve that accounting and our understanding of how soil carbon responds to different types of land management."

Using a technology called Laser-Induced Breakdown Spectroscopy - known simply as LIBS - scientists can now point a flashlight-sized laser device at a soil sample in the field or taken from the ground and determine how much carbon the sample contains. LIBS works by firing a brief, very intense pulse of laser light at a surface. The laser beam vaporizes a spot on the target sample that's roughly the size of a pencil point. A small spotting scope mounted near the laser source captures light emitted from the vaporized area and directs it to a spectral analyzer. This analyzer, part of the LIBS device, looks at the signature of the light to determine what elements are present. Each element creates its own spectral fingerprint.

In field trials conducted on agricultural soil, the research team, led by Los Alamos physicist David Cremers of Advanced Chemical Diagnostics (C-ADI) and soil scientist Michael Ebinger of EES-10, configured the spectral analyzer to measure the carbon signature coming from the soil. Subsequent field trials on woodland soils with Carbon-LIBS, or C-LIBS for short, have shown that the instrument can be used reliably to determine the carbon content of different soils.

The Los Alamos researchers plan to take the instrument to other areas to determine how C-LIBS can be used to quantify carbon in soils throughout the world.

"With C-LIBS, we now have a rapid way to collect many measurements of soil carbon and come up with better estimates of how much carbon is in a field plot or across a landscape, and how that amount of carbon is changing over time," Ebinger said.

Added Breshears, "Appropriate land management could increase soil carbon retention. Conversely, disturbances like fires could result in rapid losses of soil carbon. We plan to apply C-LIBS to help scientists get a better handle on these tradeoffs."

Laser-Induced Breakdown Spectroscopy technology itself is not new. Earth and space scientists have proposed using the technology to determine the composition of the surfaces of other planets, asteroids, moons and comets. The device is small, rugged and portable, and is easy to use and maintain. In other Earth-bound applications, LIBS can analyze samples from as far as 50 feet away, or can be used to analyze areas inside tight nooks and crannies that might not be convenient to sample by conventional methods.

The C-LIBS team includes Breshears, Cremers, Ebinger, Los Alamos biologist Pat Unkefer of Szilard Resource (B-3) and Joel Brown of the U.S. Department of Agriculture.

Funding for the project came from the Department of Energy's Office of Science and is part of a terrestrial carbon program at Los Alamos co-sponsored by DOE's National Energy Technology Laboratory and the USDA.

--James E. Rickman, LANL Public Affairs

posted 11/20/02


 
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