| Gotcha! And other triumphs of the 'sootprint' Gunning down the highway, the untuned diesel engine on your semi is belching black soot. You pass a factory where the mechanics must be asleep at the switch, to judge by the filthy stream of pollution coming from the chimney. Then you spy five diesel locomotives spewing a black cloud the length of an 80-car freight train. Two days later, some soot comes to rest in the lungs of a three-year-old. She coughs. Her lungs suffer a tiny bit of insult that might, years later, develop into the kind of lung disease the EPA is trying to prevent with its new air-quality regulations. Who is to blame for that particle? Where did it come from? Where should pollution control efforts be directed? |
|
|
|
|
|
The signature of these soot particles is contained in its microscopic structure, and in the spectrum of x-rays it emits when bombarded with electrons. Note the difference at idle, medium load, and heavy load. Courtesy of John Vander Sande. |
| Today, there's no way to trace soot back to the combustion chamber in which it originated. But some day, a microscopic signature -- inevitably dubbed the "sootprint" after a resemblance to a human fingerprint -- could help scientists do just that. Massachusetts Institute of Technology professor of materials science and engineering John Vander Sande has been using electron micrographs to examine the microscopic structure of soot from diesel engines. In recent years, he's added two other "channels" of information to the picture: |
|
 |
the x-rays emitted when the sample is bombarded with high-energy electrons, and |
|
|
energy-loss spectroscopy, a technique that measures the energy an electron loses as it passes through a solid. |
|
Vander Sande and colleagues Adel Sarofim and Bill Peters have spent years developing a sootprint library for diesel engines, and to a lesser extent, gasoline and jet engines. Once they analyze soot from coal- and oil-fired boilers, Vander Sande says, "We'd probably have the five major culprits. In time, I hope to construct a two-part encyclopedia, with images, and spectral information" for various kinds of soot. And that would offer the theoretical capacity to take a cubic millimeter of soot and trace it back to its origin. That's a skill that would interest neighbors of airports and other pollution-heavy facilities. It might also help communities like Denver, where the frequent brown haze has been blamed on everything from coal-burning generators to wood-burning stoves. Although fixing the real problem is expensive enough, fixing spurious ones is a waste of money. But, Vander Sande admits, some hurdles must be overcome before the sootprint can leave a real imprint on pollution controls. "The strength of this technique is also its weakness -- it's a particle-by-particle study, and to say anything definitive, you have to analyze hundreds of particles in each sample." Ideally, he says, an analyzer could be set up to run the three tests automatically, simultaneously. For more information, see "Soot Morphology:" in the bibliography. Care to fingerprint the credits and sources for this Why File? |
 |
 |
 |
 |
There are 1 2 3 4 5 6 7 8 9 10 11 12 13 documents. (Glossary | Bibliography)