CLEVELAND, Ohio (NASA PR) — Why should you be concerned about nanoparticles, and what are they anyway? You are probably being exposed to these extremely small particles every day and are unaware of their consequences. But is something so small really that scary? Scientists say the answer may be yes.
Nanoparticles, also known as ultrafines, are fragments of matter that are less than 100 nanometers in diameter. A nanometer is one-billionth of a meter, compared to a sheet of paper that is 100,000 nanometers thick. Environmental studies on particles this small have been limited because the instruments used to measure these particles are large and cumbersome, and they use a lot of power. The Microscale Particulate Classifier, however, is a miniaturized version of this larger instrument and was developed by NASA for use on future missions aboard the International Space Station.
This tool, co-developed with Professor Da-Ren Chen formerly of Washington University in St. Louis, will help NASA determine if these particles are present on spacecraft. This is important because of the confined space and the possible contamination of equipment if dust particles of this size are introduced on future trips to an asteroid or Mars. Astronauts that visited the moon during the Apollo missions, for instance, found that lunar dust became a significant problem on extended missions.
These nanoparticles not only cause mechanical failures but also are so small that if inhaled and enter the lungs, they actually can slide between the cells of the organ. Because people are seldom exposed to them, the body responds to the particles as an invader. It is this response that makes this size particle a health hazard.
“It’s important to first detect the presence of the particles so that filtering devices can be installed or protection devices provided to make the air safe to breathe,” said Paul Greenberg, Ph.D., at NASA’s Glenn Research Center in Cleveland, who was involved in developing the Microscale Particulate Classifier.
Ultrafines are found on Earth in the dust from volcanic eruptions, in the smoke from forest fires, in air pollution as aerosols and around industrial activity. The particles are so small that gravity doesn’t affect them, so they continue to float in the atmosphere until eventually they are trapped by water vapor in clouds.
Scientists at Glenn developed this miniaturized instrument to determine the size distribution of these tiny particles using a tool that is small, easy to use and low on energy consumption. This makes the instrument particularly helpful for occupational health personnel to provide on-location studies to determine the long-range effects of exposure and health risks posed by nanoparticles in a given environment.
The technique for characterizing these ultrafines is called electrical mobility classification. The instrument provides information on the number, size and concentration of the particles. Electric mobility uses the concept that when particles are charged and pass through an electric field, the small particles will be deflected more easily than the large ones.
Electric mobility classifiers have an exit that allows only those particles that are deflected to pass. This means only one size of particle will pass through the hole, based on the given electrical field. A separate detector counts each particle that passes through the hole. By scanning specific electric fields, the instrument counts and records the corresponding range of particle sizes that pass through the hole.
|This video demonstrates a standard electrical mobility classifier and how only one size particle will pass out the hole to be counted for a given electrical field. (Credit: Prof. Dr.-Ing H. Fissan, W. Arendt and D. Semleit at University of Duisburg-Essen)|
“Smaller, energy-efficient devices are needed for space applications,” said Greenberg. “The microscale classifier measures all of the sizes within a range of 20 to 500 nanometers, and to miniaturize the device, there were three major issues to overcome: size, efficiency and data analysis.”
Miniaturizing the classifier meant fewer particles would be available to count. Therefore, engineers had to increase the efficiency for charging each particle with a known charge so that most of the particles passing though the device would be counted. The resulting charging unit is called a unipolar corona charger. This increased the particle charging efficiency from seven percent to more than 90 percent.
The second important development was the data inversion algorithm—instructions used for doing mathematical calculations. This was an efficient algorithm embedded in a microprocessor for converting the data collected into a distribution of the various particle sizes. That data then is displayed on an LED screen on the mini-classifier. Thanks to these two changes, developers were able to reduce the classifier to the size of a three-inch cube compared to a standard electrical mobility classifier that is approximately the size of a one-foot cube and weighs more than 25 pounds.
This technology development won an R&D 100 award from R&D magazine in 2009, and the classifier recently was licensed to TSI Inc.of Shoreview, Minn., a manufacturer of particulate measurement instruments. The goal is to make this technology available soon commercially for air quality control both here on Earth and in spacecraft. Now that we can detect, measure and provide protection from these minute particles, they are a lot less scary.
by Linda Nero
ISS and Human Research Office
NASA’s Glenn Research Center