Limit values for fine dust emissions are based on total particle weight. It
is the ultra-fine particles, however, that are particularly harmful to health.
A new technique separates them by size and identifies their composition - directly
where they arise.
 | | Tracing ultra-fine dust
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Fine particle emissions have been the subject of heated debate for years. People
who live near industrial plants see the smoke being discharged into the atmosphere
and wonder how harmful it is. But visible emissions are not always the most
harmful. The highest risk is posed by fine dust particles which can easily penetrate
the human organism. These ultra-fine particles are difficult to measure, however,
because they are less than 100 nanometers in diameter.
Research scientists at the Fraunhofer
Institute for Laser Technology ILT in Aachen have developed a technique
by which the composition of such particles can be precisely analyzed. “The
statutory limit values for fine particle emissions are based on the total particle
weight,” explains Dr. Cord Fricke-Begemann, project manager at the ILT.
“Large particles are, however, much heavier than small ones. Weight measurements
do not provide any information on the quantity of ultra-fine particles in the
fine dust, but they are often more harmful than the larger particles.”
The measurement technique developed by the research scientists consists of
two steps. A gas stream separates the particles into size classes before they
are collected on filters. Their composition is then examined by means of laser
emission spectroscopy. “We are therefore able to identify harmful heavy
and transition metals, such as zinc, in the fine dust, and also to ascertain
the particle size at which they become particularly enriched,” explains
Fricke-Begemann. A key aspect of the method is that it delivers the results
in less than 20 minutes. What’s more, it can work at a high throughput
rate and enables measurements to be taken directly on site – e.g. in steel
plants. Emission values can be measured and monitored in real time during production
thanks to a further development of the technique in which the particles are
continuously drawn off via an air tube and analyzed.
All industrial plants produce fine dust emissions, and every process leaves
behind a characteristic “fingerprint” of the particle composition
and size distribution. With their measurement method the scientists can test
the air in nearby residential areas and identify where the particles are from.
They can also help to develop strategies for reducing emissions from the plants
concerned.
Posted October 5th, 2009
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