Assistant Professor
Sibley School of Mechanical and Aerospace Engineering

When he applied to China’s Tianjin University, where he earned a B.S.E. in thermal engineering, Max Zhang was interested in designing engines. “I thought the car industry was the driving force of the economy,” he says, “but when I was in college I realized that more cars without emissions controls was a serious problem. So my thinking changed from a pure engineering point of view to an environmental one.”

Today, Zhang, who earned his Ph.D. from the University of California at Davis, studies the air pollution created by car and truck engines. He’s specifically interested in particulates. These tiny particles, about one hundredth of a human hair in diameter, are considered the most harmful component of air pollution, which kills an estimated 60,000 people each year in the U.S.

“About a quarter of school-age children in the South Bronx and Harlem have asthma, largely due to the air pollution generated by local traffic,” says Zhang.

Today’s more efficient engines emit fewer particulates from their tail pipes, in terms of total weight, but emit more nanoparticles, which are small enough to travel through the lungs and into the blood stream where they can cause systemic damage.

Nanoparticles don’t emerge fully formed from the tailpipe, but are created in a complex process as they cool and disperse. Understanding this process is critical for protecting public health since a growing number of apartments, office buildings, and schools, are built very close to freeways.

“My Ph.D. work looked at what happens in the first few minutes, a few hundred meters from the highway,” says Zhang. “It’s a very dynamic process that has been ignored until now.”

Zhang hopes his study of “near-road plume dynamics” will lead not only to more accurate vehicle emissions testing, but also to intelligent building design. “You could control ventilation of the building based on the amount of traffic, how much pollution it’s generating, and current weather conditions,” he says.

He’s also interested in where particulates end up and how they get there. He is designing computer models of how particulates travel in the atmosphere and eventually fall to Earth. “With mercury pollution in aquatic ecosystems, for instance, the dominant source is from the atmosphere,” he says.

Particulates also play a little understood role in climate that Zhang would like to explore. “While larger particles can directly reflect and absorb sunlight, nanoparticles interact with climate by acting as seeds for cloud formation—so they can affect cloud dynamics,” he says. “And clouds are the most uncertain factor in predicting climate change.”

The first course Zhang will teach at Cornell is “Future Energy Systems,” which critically examines the technology of energy systems that will be acceptable in a world faced with global climate change, local pollution, and declining supplies of oil. “I think air pollution is an essential topic linking energy and the environment,” he says. “Air is everywhere.”

Prof. Zhang's Web page