During Olympics, Cornell's Max Zhang studies air-quality ...( As the world watches China prepare f...)

As the world watches China prepare for the Olympic Games, Cornell researcher Max Zhang has his eye on less visible matters -- the particles in Beijing's air that millions breathe every day, and that many more will be breathing when they descend on the city this summer.

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.

Graduate student Xing Wang monitors computer equipment that measures air quality in Beijing in August 2007. Wang and Assistant Professor Max Zhang are studying air quality in the Olympic city before and after the Games.

In 2006 the Chinese government began massive efforts to clean up Beijing before the Olympics by implementing emission controls and traffic restrictions. Zhang reali
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