Understanding Aerosols: UD Invention Measures Particles 10 Times Smaller Than Most Other Instruments
Contact: Ginger Pinholster, 302-831-6408, [email protected]
* Patent disclosure and photographs available
NEWARK, DE.--A new device may help researchers more effectively analyze environmental events such as global warming by measuring the composition of individual aerosol particles as small as 10 nanometers--roughly one order of magnitude smaller than existing transportable instruments, say University of Delaware researchers who recently filed a patent disclosure.
Dubbed RSMS-II (for Rapid Single-Particle Mass Spectrometer), the instrument analyzes particles "at the critical early stages of their growth," before they accumulate in clouds, says Anthony S. Wexler, associate professor of mechanical engineering. Whether particles are produced by human activities such as industrial combustion, or by natural events including volcanic eruptions, aerosols clearly play a key role in global climate changes, Murray V. Johnston III, UD professor of chemistry, notes.
Atmospheric aerosols may have "direct" or "indirect" effects on climate around the world, Wexler explains. Specifically, he says, aerosols may counter global warming directly, by scattering light. Or, they may indirectly cool various regions of the Earth by accumulating in clouds that act like a mirror, bouncing sunlight back into space. Despite these regional cooling effects, the United Nations' prestigious Intergovernmental Panel on Global Climate Change expects average global temperatures to rise by 2 degrees Celsius between 1990 and 2000.
But, researchers struggling to predict global climate change have had a tough time calculating aerosol impacts, in part because measuring the composition of particles smaller than 100 nanometers using traditional technologies is difficult. Wexler estimates that each cubic centimeter of air contains approximately 1,000 aerosol particles between 20 micrometers and 10 nanometers in size. (One nanometer equals one billionth of a meter.)
Understanding these tiny particles is a crucial step toward explaining aerosol impacts on climate. "We want to look at aerosol particles before they grow into clouds, and we need to measure the number of naturally occurring aerosol particles in the atmosphere," Wexler says. "If we don't know how many naturally occurring aerosol particles are in the atmosphere, we can't figure out what level of anthropogenic [human-generated] aerosols would perturb the global energy balance."
Aerosol particles smaller than two microns may have an impact on human health, as well as the global climate, he added. Very tiny aerosol particles can penetrate homes, office buildings and people's lungs, he says.
COUNTING TINY PARTICLES -- A CHORE NO MORE
To measure very small individual particles, Wexler and Johnston developed a technique for souping up a conventional mass spectrometer, which generates a `fingerprint' of different chemicals. Specifically, the instrument produces a graph showing the spectrum of ions, or charged atomic fragments, based on their relative masses and abundance within a sample.
Samples analyzed in the RSMS-II are sucked through a nozzle attached to a tube-like apparatus, Johnston says. As the sample squeezes through the nozzle at high speed, gas molecules are stripped away, while aerosol particles pass into the tube, where they enter the path of an excimer laser firing concentrated light pulses 100 times per second. The laser zaps and disintegrates roughly one of every 100 aerosol particles, forming ions. The ions are then captured for analysis in the mass spectrometer. "From the ions, we can infer the chemical composition of the particles," Johnston explains.
A key to the RSMS-II is a special ion focusing lens that increases its "hit rate," or the number of particles struck by the laser. The lens more effectively directs ions, making it possible to capture fragments over a 4-centimeter region, Wexler says. Other instruments capture ions only within a smaller region, he noted.
Equipped with wheels and small enough to be transported "in a van or small truck," the RSMS-II should prove useful for studying a variety of aerosols in the field, Johnston says. Natural forms of atmospheric aerosols include, for instance, soot from forest fires, sulfuric emissions from volcanoes and marine photochemistry--which generates sulfuric and methanesulfonic acids resulting from the oxidation of dimethylsulfide, a metabolic byproduct of phytoplankton. Sulfuric acid also forms from sulfur dioxide emitted by combustion processes. Johnston and Wexler's work, conducted in the new $20 million Lammot du Pont Laboratory, could ultimately support a wide variety of interdisciplinary research. In addition to aerosol analysis, Johnston and his colleagues within the Department of Chemistry and Biochemistry are investigating DNA, polymers, proteins and soils by mass spectrometry. Research described here was supported by the National Science Foundation, the U.S. Environmental Protection Agency, Electric Power Partners and the DuPont Co.
RSS