The assistant professor in Cornell's Sibley School of Mechanical and Aerospace Engineering is leading a project to study the air quality before, during and after the Olympic Games, which begin Aug. 8.

Zhang's general research interests lie in what happens to the particles emitted from cars, trucks and power plants.

"I am interested in how these particles are made and how they disperse -- how they transport and transform in the air," Zhang said.

Although scientists have been studying the adverse effects of breathing urban air pollutants for years, Zhang notes that as combustion engines have become increasingly efficient, their exhaust particles have gotten smaller and more easily absorbed by the body.

Modern engines, he also notes, emit many more particles smaller than 100 nanometers than do older engines (a nanometer is one-billionth of a meter). And nanoparticles are rapidly transformed in the atmosphere, Zhang points out. When particles are emitted from the tailpipe of a car, they can be 50 nanometers. But after traveling just 100 meters (11 yards), the particles can shrink to about 20 nanometers.

"In that short distance, the particles you are breathing are very different from what's being emitted," said Zhang, who is originally from Qufu, China.

In 2006 the Chinese government began massive efforts to clean up Beijing before the Olympics by implementing emission controls and traffic restrictions. Zhang realized he could use the city as a laboratory to see if the efforts would work and to what extent.

Zhang and graduate student Xing Wang traveled to Beijing in the summer of 2007 to take initial measurements of airborne particles in various spots around the city, from heavily trafficked highways to residential communities -- even inside restaurants. They used real-time analytical instruments to capture the changes in particle size and concentrations in a matter of seconds.

Zhang plans to repeat tests in Beijing during the Olympics, and then again a year later. The study is supported by Cornell's Jeffrey Sean Lehman Fund for Scholarly Exchange with China and the U.S. Environmental Protection Agency.

Zhang also is collaborating in an air quality project in Syracuse, N.Y., helping to design a controlled ventilation system for a building to be placed at the intersection of Interstates 81 and 690 -- a major hub in downtown Syracuse. The building will house the Syracuse Center of Excellence in Environmental and Energy Systems, which is funding the study.

The ventilation's control system would turn up or down, depending on the quality of air around the building at any given time. To design it, Zhang is using cameras to measure traffic levels. He is developing computer algorithms to simulate how the plume of pollution would disperse into the building.

"I think it's novel in terms of linking the building to the surrounding environment," he said. "When people think about a building, they only think about the building alone. They never think, 'The building has to be somewhere.'"

Zhang is excited at the opportunity to work on such a project, because he has long studied traffic dispersion and how it relates to the air people breathe.

"The cities are my laboratory," he said.

He also is working on air quality studies in Rochester and in South Bronx, N.Y., where high rates of asthma in schoolchildren are believed to be caused by heavy, prolonged traffic congestion.

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