On rooftops in cities like Los Angeles, Dallas, and New York, you’ll find places to relax: pools, bars and restaurants, patios. On the rooftop of UNC’s School of Public Health, you’ll find a smog chamber full of the air those city folks are breathing. Or something like it.

Click to read photo caption. Photo by Kenneth Sexton, ©2007 Endeavors magazine.

The smog chamber is a giant structure made of Teflon film that looks similar to a greenhouse. In a lab just underneath it, the One Atmosphere Research Team — Ilona Jaspers, Ken Sexton, and Harvey Jeffries, along with several graduate students — have been cooking up what they call a “synurban mix.” Usually scientists study one atmospheric substance at a time — ozone, for instance. But this is limited in scope. The mix, on the other hand, imitates the average composition of the smog in America’s forty largest cities. And that’s what we’re really inhaling.

“You study ozone by itself, and you get the effects of ozone,” Jeffries says. “But in the real world, ozone is a soup of all kinds of organic material — aldehydes, radicals.” That material makes a big difference to our lungs, especially after it’s been in the air for a few hours, reacting with other toxins, particles, gases, and sunlight. In a short time, the original toxins can change into different toxins and compounds. “People are regulating the parent compound, the precursor,” Sexton says. “But they’re not regulating the secondary compound.”

“Congress wants to simplify the problem,” Jeffries says. “They say, ‘We want to make a law on air toxins. What’s an air toxin?’ So they just add items to a list. But it turns out lots of stuff on the list turns into even more hazardous air toxins. One that wasn’t on the list can become one that is, through a transformation. Some air toxins on the list even transform into non-toxins.”

So how does the team figure out what’s toxic? While Sexton and Jeffries determine the composition of the air samples, Jaspers grows human lung cells in incubators. Then they expose the cells to the air, and see whether and how much they’re inflamed. This strategy helps the team determine which air components the government should regulate. And then they tell the Environmental Protection Agency.

These days the team has turned its attention to the effects of vehicle emissions on lung cells, comparing exhaust from diesel and gasoline engines. Diesel is toxic to the lungs — no surprise there. “But daily exposure to it in the urban air is more complex than what comes directly out of the tailpipe,” Jaspers says. So far, the preliminary data show that diesel responds to sunlight, making it more toxic after a few hours outside the car. The team is also aging the exhaust, simulating what happens to it when it mixes with urban smog. The results aren’t pretty: diesel aged in smog is about twice as inflammatory as fresh exhaust, Jaspers says.

Sending out papers and applying for grants has been an uphill battle because of the combination of chemistry (Jeffries and Sexton) and toxicology (Jaspers). “You have to have a reviewer who knows both,” Jaspers says. “And you don’t usually find that in one person.” But One Atmosphere’s graduate students start their research careers well-versed in both areas. “People ask, ‘Are you a chemist, or a toxicologist?’” says Melanie Doyle, who worked extensively with the project as a graduate student. “And I say ‘Neither. I’m both.’”

Harvey Jeffries is a professor of environmental sciences and engineering in the School of Public Health. Ilona Jaspers is an assistant professor of pediatrics in the School of Medicine. Jeffries and Jaspers are principal investigators for the One Atmosphere Research Program. Ken Sexton is a research associate in the School of Public Health’s Department of Environmental Sciences and Engineering. Melanie Doyle graduated in summer 2006 with a doctorate in environmental sciences and engineering. One Atmosphere receives funding from the Environmental Protection Agency.