Clutching a large, perforated disc dubbed "the showerhead," chemist Veronique Perraud perches beside what appears to be a huge, hissing missile. So it goes at UC Irvine’s Atmospheric Integrated Research unit, one of the world’s leading air pollution laboratories.
Situated in a suburb of smoggy Los Angeles, AirUCI's innovative experts are providing a likely answer to a sticky scientific problem. A growing body of research has shown that computer models used by federal regulators for decades significantly underestimate the quantity of organic aerosols, a major component of dangerous smog and the largest unknown in climate-change calculations.
To help solve the mystery, the UCI team injected common ingredients of household cleansers and outdoor air into a long, metal "aerosol flow" tube and mixed them evenly through the showerhead to form smog compounds. It had been assumed that the aerosols dissolve quickly in liquid droplets. But the researchers found that the gases get sucked deep into stubborn particles from which they cannot escape.
"They check in, and they don't check out. The material does not readily evaporate and may live longer and grow faster in total mass than previously thought," says chemistry professor and AirUCI director Barbara Finlayson-Pitts. "This is consistent with related studies showing that smog particles may be an extremely viscous tar."
The UCI findings, published in the Proceedings of the National Academy of Sciences, could significantly affect air pollution control strategies. Models long employed by the U.S. Environmental Protection Agency and others include far lower amounts of organic aerosols than have been detected in field studies. Such pollution blocks views of mountains and has been linked to everything from asthma to heart attacks.
"You can't have a lot of confidence in the predicted levels right now," says Perraud, lead author on the new paper. "It's extremely important, because if the models do a bad job of predicting particles, we may be underestimating the effects on the public."
UCI engineer and co-author Donald Dabdub, who designs sophisticated atmospheric simulations, agrees, calling the research results "critical to the modeling community."
"Currently, atmospheric assumptions do not account for a tar-like behavior inside particles," he says. "This will help us close the well-known gap between predictions and field observations of organic aerosols."
The AirUCI group worked with collaborators at Pacific Northwest National Laboratory, Portland State University and elsewhere. Alla Zelenyuk of PNNL traveled to Irvine from Washington with the unique, 900-pound instrument she designed known as SPLAT (a single particle mass spectrometer). Zelenyuk, who has flown over Alaska capturing soot from Asia, says she was glad to share the equipment for a few weeks to help ensure that dangerous pollution is properly understood and predicted.
While AirUCI monitors can record large numbers of particles, SPLAT can measure in real time the evaporation rate and other characteristics of a single 50-nanometer particle.
Other co-authors are Emily Bruns, Wayne Chang, Michael Ezell and Stanley Johnson of UCI, Yong Yu of the California Air Resources Board; M. Lizabeth Alexander of PNNL; Dan Imre of Imre Consulting; and James Pankow of Portland State University. Support was provided by the U.S. Department of Energy and the National Science Foundation.
— Janet Wilson, University Communications