Sep. 25, 2000 GAINESVILLE, Fla. --- A University of Florida professor has found a way to detect and identify extremely low levels of air pollution, a step that comes as concerns mount over the health impacts of breathing in small particles.
David Hahn, a UF professor of mechanical engineering, developed the technique -- a unique application of a well-known technique called Laser Induced Breakdown Spectroscopy -- with the assistance of Sandia National Laboratories in Livermore, Calif.
The process begins with an air sampler, located on a rooftop at UF's nuclear sciences building, that filters out relatively large particles and pumps the air into a nearby lab. Next, the air passes through the pulsing beam of a powerful infrared laser, and a small part of it heats up to over 35,000 degrees.
The heat vaporizes airborne molecules and particles, resulting in a flash of light and a loud crack. Although the eye can't see it, each atomic element in the vaporized sample produces a different wavelength of light. A spectrometer records these "fingerprints" and determines which elements are present, providing a real-time picture of the airborne particles.
Hahn tested his technique over the Fourth of July holiday, measuring increased airborne concentrations of magnesium, a metal used in fireworks, for as long as a week after fireworks displays ended. The increases were so small they posed no threat to human health, but the test demonstrated the technique could also detect similarly low levels of more harmful particles, such as arsenic, chromium or lead.
"The test really demonstrated the ability of this technique to measure particulate concentration levels several orders of magnitude below regulatory standards," Hahn said. "That's steadily becoming more important as people involved in pollution control seek to more accurately monitor pollution and better determine its sources."
The diameter of a human hair ranges from 50 to 100 microns, with 1 micron measuring a millionth of a meter. Hahn says his technique can measure particles as small as one-tenth of a micron, determining both mass and composition. The technique also detects particles in extremely low concentrations. With the fireworks, the technique measured week long post-fireworks magnesium concentrations at an average of 44.4 parts per trillion, compared with 2.8 parts per trillion before the fireworks.
Hahn said recent research indicates that very small particles are more dangerous than larger ones because the body's natural defenses capture and expel the larger particles, while small ones lodge in the lung cavities and cause damage over time. A major component of smog, airborne particles have been tied to asthma and other diseases. One recent study attributed 3 percent of deaths annually in Austria, France and Switzerland to particluates.
In response to such research, federal regulators increasingly have sought to study and regulate small particles. Two years ago, for example, the Environmental Protection Agency dropped its standard to regulate particulate matter down to particles as small as 2.5 microns.
Environmental officials would like to know more about what small particles the air contains -- at different times of the day and in different weather conditions -- and where the particles are coming from. The LIBS technique can help answer both questions because it picks up the presence of low levels of small particles in real time, Hahn said. That creates the potential for regulators to create much more effective, more targeted regulations, he said. "Right now, there's not a very good feel for what sources are producing what particles,"Hahn said. "If we can determine with a lot more specificity that these particles are coming from cars or plants or agriculture, then we can go after these sources and fix them."
Ben Smith, a scientist in UF's chemistry department, said Hahn's technique is one of two current techniques that can detect and measure extremely small, sparsely distributed particles. The equipment for the other technique, however, is both more complex and more expensive, costing at least $150,000 compared with about $80,000 for Hahn's technique.
"Scientists are becoming more and more interested in really small particles and how they impact human health," Smith said. "David's technique has real potential for both industrial and environmental monitoring."
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