Closing in on a fugitive
DRI scientists developing ‘Swirler’ technology to fight dust, improve air quality

Field testing a dust detector. Dr. Vic Etyemezian, pointing, discusses the settings for the prototype Swirler with Anthony DeLeon, right, a civil engineering sophomore at UNLV, during a field test. On the left, UNLV electrical engineering senior Djordje Nikolic controls the Swirler from a laptop while Sean Ahonen, another UNLV electrical engineering senior, center, prepares for the test. The metal part in front of the prototype is an example of the device’s annular ring that spins up to 4,000 rpm to create wind shear to simulate wind blowing across the surface.(Photo by John Doherty)

A team of DRI scientists is building a new device that will potentially enable local air quality regulators to pinpoint quickly and inexpensively likely sources of windblown dust emissions in their communities, allowing them to work with landowners, developers and others to prevent and reduce health-threatening violations of federal airborne particulate level standards.

The device, for which DRI has obtained a provisional patent, is known as a “Swirler,” though in some circles it is also referred to as the PI-SWIRL, short for “Portable In-Situ WInd eRosion Laboratory.” It works by simulating wind blowing across the ground that lofts dust and soil particles into the air. Swirler electronically measures the size and number of the particles being “entrained” or taken up into the air over a span of several minutes.

Swirler works by spinning a circular metal ring parallel to the ground about two-and-a-half inches off the surface to create a shear force that lofts dust particles and passes them through a particulate counter. By controlling the ring’s spin speed, the dust emission potential of a variety of surface soils at different wind speeds can be determined.

Dr. Vic Etyemezian, an air quality scientist in DRI’s Division of Atmospheric Sciences, who leads the DRI team on the project, says local officials are currently limited to using visual observations of dust sources backed up by ambient air quality monitoring over a broad, general area to locate sources of “fugitive dust”–dust emissions created as a result of human activities.

“The only other way to get this kind of site specific data on dust potential is by setting up a portable wind tunnel,” Etyemezian points out. “The larger wind tunnels that have been used require several people working for several hours to set up and conduct tests, plus time to dismantle the tunnel and conduct the follow-up analysis. The larger portable wind tunnels will provide more accurate data than the present Swirler design, but we can match the accuracy of smaller wind tunnels and do it more quickly and much cheaper.”

Your own personal whirlwind. Using a small video camera inside Swirler, DRI researchers can evaluate the device’s effectiveness in generating wind shear to simulate natural wind’s erosive force on the Earth’s surface. In this frame captured at 3,450 rpm, an array of pins and flags describes the pattern of wind generated over a non-erosive surface during a lab test. DRI is designing instrumentation upgrades for Swirler. With no moving parts, the upgrades will allow real-time measurements of dust and soil particles blowing through the Swirler and will be more resistant to damage.

Etyemezian envisages an air quality officer pulling up by a vacant lot, fallow farm field or along a dirt road, and lifting a Swirler out of the trunk and quickly analyzing conditions for dust emission potential. “If necessary, a number of data points can be taken in around a piece of land to really get a representative picture of how much dust this site will contribute to local airborne particulate levels. From that information, a decision can be made on the level of dust suppression measures that needs to be taken.”

This kind of advantage was immediately clear to San Joaquin Valley Air Pollution Control District Meteorologist Evan Shipp, whose duties involve grappling daily with multiple sources of air pollutants, including dust, in all or part of eight central California counties. “If this technology is proven and becomes portable enough to use easily, we could quickly identify where effective mitigation measures will give us some relief from noncompliance conditions. Anything that can reduce or remove the uncertainty about the sources of pollutants is a major advantage for improving air quality.”

The new technology has also attracted research funding from the U.S. Navy Facility Engineering Service Center, through a national dust-suppression technology company, ENCAPCO. The study is part of an evaluation of the effectiveness of using commercial dust suppression treatments to bind soil particles to the ground’s surface at the U.S. Department of Energy’s Nevada Test Site. The success of such a binding agent would have important implications for potentially stabilizing soils that are contaminated with toxic or radioactive materials. Using a new improved version of DRI’s original prototype Swirler, Etyemezian and his colleagues will compare the dust lofting potential of land surfaces before and after treatment. Bechtel Nevada is also involved in the project to analyze the effectiveness of the treatments in reducing the transport of soils by surface water runoff following the region’s infrequent precipitation events.

This is one example, Etyemezian says, of how there will be commercial applications for land developers to proactively determine the best strategy for suppressing dust by tailoring their mitigation methods to the specific dust potential of a site.

Etyemezian says the Swirler concept was born three years ago during discussions with DRI air quality scientist Dr. Hampden Kuhns and Dr. Marc Pitchford, a U.S. National Oceanic and Atmospheric Administration scientist who works out of DRI’s Las Vegas office. Two University of Nevada, Las Vegas electrical engineering seniors, Sean Ahonen and Djordje Nikolic, and UNLV civil engineering sophomore, Anthony DeLeon, have been designing and building custom electronic controls and processors to improve performance and dramatically reduce the size and cost of the instrument.

Dr. Hans Moosmüller, an optical physicist at DRI specializing in air pollution measuring technology, is working to replace the Swirler’s off-the-shelf particulate measuring unit with an optical device with no moving parts and greater durability. DRI’s resident wind erosion expert, Dr. Jack Gillies, is also helping to calibrate the measurements with known dust suspension characteristics.

Etyemezian anticipates that up to three more years will be required to complete the miniaturization and other engineering improvements. This time will also allow him and his colleagues to finish calibrating the Swirler measurements with wind tunnel data so that users will be confident of the validity of the dust potential data they obtain.

The alternative to Swirler. This 10-meter long wind tunnel is the conventional method of directly assessing the dust loading potential of land surfaces. Wind tunnels require considerable time and resources to obtain information on a single spot. Swirler will allow one person to sample quickly a number of spots in a selected area. The tunnel below is being operated by Dr. Bill Nickling’s group at the University of Guelph in Canada and is shown in use on a DRI project at Ft. Bliss, Texas. (Photo by Dr. Jack Gillies)

With Swirler in the future, fugitive dust can blow, but it can’t hide, and we’ll all breathe a bit easier for it.

—John Doherty