Research suggests widely used models may under predict pollution

provided by University of Florida

ew research by a University of Florida professor suggests the complex computer models underlying regulations on pollution from cars and other sources in many of the nation's largest cities may significantly underestimate pollution levels.

Jean Andino, a University of Florida assistant professor of environmental engineering, said the models are based in part on studies of how gases combine to form smog in clean laboratory environments. Her research, set to appear in a leading international atmospheric environmental science journal this spring, indicates some of these gases may react far more quickly when mixed with tiny particles often found in urban and natural atmospheres.

"Traditionally, researchers have done studies in laboratories in what I call pristine atmospheres,'" Andino said. "The problem is that the real atmosphere is not pristine -- it not only has gaseous compounds, it also has particles -- and we've found these particles can act as catalysts for the reactions and actually increase reaction rates of some gases."

Andino said her results, which will appear in the British-based journal Atmospheric Environment, indicate the particles may speed up the reactions of a selection of smog-forming gases as much as 26 percent. Tests of simple models based on the sped-up reactions have resulted in increases as high as 30 percent in the models' predicted levels of ozone, a crucial ingredients of smog, she said.

"We just looked at the chemistry, so our models were very simple compared with the real models, which consider meteorology and many other factors," she said. "Still, we think that 30 percent is a fairly significant increase, and further study is warranted."

Many of the nation's large cities and urban regions use air quality models to predict the outcome of pollution control efforts such as requiring vehicle inspections or providing special lanes for carpooling, said Roger Atkinson, a professor in the departments of environmental sciences and chemistry and director of the Air Pollution Research Center at the University of California at Riverside. The models also are used to forecast future pollution levels and help policy-makers decide whether regulations may be required in advance to keep a city or region within federal pollution standards.

The models take into account the reactions of smog-forming chemicals such as a myriad array of volatile organic compounds emitted by cars, Andino said. But they ignore another pollutant especially common in urban environments: tiny particles emitted in diesel engine exhaust, aerosol sprays or from a range of other sources.

"Particles can come directly from sources such as diesel trucks or they can be formed in the atmosphere," Andino said. "Gases can react to form compounds that essentially condense and form very small, liquid particles."

Her experiments show the introduction of different types of small particles sped up the reaction rates of several types of alcohol that are ingredients of gasoline. Other gasoline ingredients, including an aromatic compound and an alkane, did not react more quickly, but only a few varieties were tested, Andino said. The particles in the tests included ammonium nitrate and ammonium sulfate aerosols, both common particles in urban areas, she said.

Atkinson said Andino's results would have little impact on the computer models in use by cities currently, but they are intriguing. "If it's true for more alcohols, then it could be beginning to be important," he said. "I think the other line is that it probably needs to be confirmed by other labs."

Future research will examine a much broader array of smog constituents with the hope of improving the accuracy of the air quality models, Andino said. "The next step is really to look at a whole series of compounds to see if we can generate some kind of nice correction factor for the data used for these models," she said.

Andino's research, part of a five-year project funded with more than $280,000 from the National Science Foundation, is in its third year. She received the grant as part of an NSF Faculty Early Career Award, designed to help promising scientists and engineers develop simultaneously their contributions to research and education early in their careers.

Jean Andino, (352) 846-1744,