Cities like Houston are dotted with air-sniffing monitors that measure levels of benzene and other potentially unhealthy air pollutants. But those monitors can't answer the question we care about most: Is the air safe?

That's because there's no simple relationship between toxic air pollutants and health risks. Researchers at the University of North Carolina in Chapel Hill are trying to get a leg up on that problem. They are building an instrument that uses human lung cells to measure health hazards in the air more directly.

To work on the instrument, researchers here cook up their own dirty air in a greenhouse on top of a campus building. Professor Harvey Jeffries leads us up a steep ladder and into the greenhouse, which is made of clear Teflon film.

"So it's filled with clean air to begin with, but we can create any kind of atmosphere in here that simulates any place on the earth — or any place in Los Angeles," Jeffries says. "We can try diesel cars, or we can try diesel trucks."

Pipes draw exhaust from tailpipes right up to this chamber. You wouldn't want to inhale the gases right out of a tailpipe, of course. But breathing exhaust from the air turns out to be even worse.

"If you put the same material in here and cook it in the sun for a day, it becomes anything from five to 12 times more toxic," Jeffries says.

He suspects that sunlight triggers these particles to soak up nasty chemicals in the air. The particles, which might start out as a puff of carbon in diesel exhaust, get transformed into little packages that deliver chemicals deep into lung tissue when you inhale.

Unfortunately, health officials don't take that sort of synergy into account. Jeffries says they assume a particle is a particle is a particle.

"If you don't do this kind of chemistry, you miss what's really going on in the atmosphere," he says.

The air from here gets piped into a laboratory directly below. Jeffries' collaborator, Will Vizuete, says this research is challenging the conventional wisdom about particles and health. It's not simply how much of the stuff you breathe in that counts.

"Not all particles are created equal. Some particles happen to be more toxic than other particles," Vizuete says.

And Jeffries concurs: "The health effects for particle exposure in New York are different from health effects for particle exposures in South Carolina and in the desert or in California."

The effects depend on what happened to that particle while it was circulating in the sunny air. And that's where the new instrument comes in.

In a lab directly underneath the rooftop greenhouse, Vizuete and Jeffries show off a machine that sucks in air from the chamber above. The air blows across samples of human lung cells, which grow in small indentations in the instrument. If the air is toxic, the cells send out hormone-like distress signals that scientists can measure. The worse the air, the more "Help! Help!" signals the cells send out.

"The advantage of using a biological sensor is it says 'I'm being harmed. I don't care if you don't know what's causing me harm, I'm being harmed,' " Jeffries says. "That means it draws attention, it makes you do the work and do a better job of figuring out what's going on."

And it tells you, whatever's going on — watch out for that air.

Jeffries and Vizuete see this approach as an important departure from the way air is tested today. Current tests measure chemicals in the air and then infer health risks based on some simple assumptions. Vizuete says the goal here is to build devices like this and sell them to scientists who can put them up all around cities to monitor the air for actual biological hazards.

Hardware is actually being built in the building's basement. This school of public health has an unusual facility: a fully equipped machine shop, full of lathes and other digitally driven shop tools.

On the day of our visit, the first prototype was still under construction. Eventually researchers hope to put the parts together into a plastic frame about the size of a paperback book.

Of course this being a university, not a factory, the instrument is only being developed here.

"So right now, the hope is to maybe get two — or hopefully five — of these out of this shop, and then immediately find another kind of tech shop to produce these at a large scale," Vizuete says. Chapel Hill has small tech companies that could easily do this work. The human lung cells are already commercially available.

The instrument isn't as simple to operate as the current chemical "sniffers," though — technicians must collect samples from the devices by hand. Those samples then get analyzed in a lab.

Vizuete has started a company, called Biodeptronics, to mass-produce these instruments. And he's hoping that they'll be for sale later this year. The first customers would be academics who are interested in learning more about air pollution. But Vizuete's vision is that someday these biological sensors will get scattered around cities. Instead of simply telling us what chemicals are in the air, they might tell us something about the actual health risks.



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MELISSA BLOCK, HOST:

This is ALL THINGS CONSIDERED from NPR News. I'm Melissa Block.

ROBERT SIEGEL, HOST:

And I'm Robert Siegel. Scientists want to better understand how chemicals in the air interact with each other to make people sick, so they're building an instrument that should help them find out. Yesterday, in our series Poisoned Places, we heard from a community in Baton Rouge, Louisiana that could benefit from information like that. People there live next to the second largest gasoline refinery in the country and they wonder how their health may be affected by their exposure to air pollution from the plant.

It's a difficult question to answer, not just a matter of measuring chemicals in the air. Today, NPR's Richard Harris tells us how this new device uses lung cells to measure health hazards in the air more directly.

RICHARD HARRIS, BYLINE: Before we talk about the instrument itself, let's take a minute to lay out the problem that it is trying to solve. This story begins with a greenhouse that sits on the top of the building in Chapel Hill, North Carolina. Scientists at the UNC School of Public Health use it to cook up a toxic soup.

WILL VIZUETE: I'll show you real quick, you can see it from here.

HARRIS: Will Vizuete is a rising star in the world of air pollution. He's trying to build a new air pollution instrument. And to do that he makes his own dirty air. He's teamed up with a recently retired professor at the school, Harvey Jeffries.

HARVEY JEFFRIES: Now watch your head. You'll find it amazingly bright because there's a lot of reflective light.

HARRIS: Jeffries leads us up a steep ladder from the roof of the building into the greenhouse, which is made of clear Teflon film. This is where they cook up their air pollution.

JEFFRIES: So it's still clean air to begin with, but then we can create any kind of atmosphere in here that simulates anyplace on the Earth or anyplace in Los Angeles or we can try diesel cars, we can try diesel trucks.

HARRIS: So would you want to be up here during an experiment?

JEFFRIES: Oh, no. No, no, no, no. No, no, no.

HARRIS: Is it because it's that toxic?

JEFFRIES: It can be, yeah.

HARRIS: Pipes draw exhaust from tailpipes right up to this chamber. You wouldn't want to inhale the gases right out of the tailpipe, of course, but breathing exhaust from the air turns out to be even worse.

JEFFRIES: If you put the same material in here and let it cook in the sun for a day, it becomes anywhere from five to twelve times more toxic.

HARRIS: Jeffries suspects that sunlight triggers these particles to soak up nasty chemicals in the air. These particles, which might start off as a puff of carbon in diesel exhaust, get transformed into little packages that deliver chemicals deep into lung tissue when you inhale. Unfortunately, health officials don't take that transformation into account. Jeffries says they assume a particle is a particle is a particle.

JEFFRIES: If you don't do this kind of chemistry, you miss what's really going on in the atmosphere.

HARRIS: The air from here gets piped into a laboratory directly below. Vizuete says, this research is challenging the conventional wisdom about particles and health. It's not simply how much of the stuff you breath in that counts.

VIZUETE: Not all particles are created equal. Some particles happen to be more toxic than other particles.

JEFFRIES: The health effects for particle exposure in New York are different than the health effects for particle exposures in South Carolina and in the desert or in California.

HARRIS: It all depends on what happened to that particle while it was circulating in the sunny air. And that's where the new instrument comes in. Vizuete and Jeffries show off a machine that sucks in air from the chamber on the roof. The air blows across samples of human lung cells, which grow in small indentations in the instrument. If the air is toxic, the cells send out hormone-like distress signals that scientists can measure. And the worse the air, the more help help signals they send out.

JEFFRIES: The advantage of using a biological sensor, it says I'm being harmed. I don't care if you don't know what's causing me harm, I'm being harmed. That means it draws attention. It makes you do the work and do a better job of figuring out what's going on.

HARRIS: And it tells you whatever's going on, watch out for that air. Jeffries and Vizuete see this approach as an important departure from the way air is tested today. That involves measuring chemicals in the air and inferring health risks based on some simple assumptions. Vizuete says the goal here is to build compact devices like this and sell them to scientists who can put them up all around cities to study the air.

VIZUETE: So do you want to go down and see the commercial device?

HARRIS: Sure, yeah, yeah, yeah.

VIZUETE: Okay.

HARRIS: Vizuete leads us down to the basement of the building to see something you don't ordinarily find at a school of public health, a fully equipped machine shop.

JEFFRIES: Isn't this shop amazing? They do wood, metal, everything.

HARRIS: So where's the gizmo?

JEFFRIES: Yeah, so we're going to show...

GLENN WALTERS: It's all over the place.

HARRIS: Glenn Walters is director of this design center. Over one shoulder he points to a clump of electronics, which will one day supply the power to the air sensor. And he picks up a white piece of plastic about the size of a paperback book. Eventually, all the parts will fit into this frame.

WALTERS: Assuming that it all works that we expect it to, and there's been plenty of work done to assure us that it will, this will be very similar to a final production module.

HARRIS: Of course, this being a university not a factory, the instrument is only being developed here.

VIZUETE: So right now we're - the hope is maybe get two, hopefully five of these out of this shop and immediately find another kind of tech shop to kind of produce these on a large scale.

HARRIS: Vizuete has started a company called Biodeptronics to mass-produce these instruments. And he's hoping that they'll be for sale later this year. The first customers would be academics who are interested in learning more about air pollution. But Vizuete's vision is that someday these biological sensors will get scattered around cities. Instead of simply telling us what chemicals are in the air, they might say more directly just how much our health is at risk. Richard Harris, NPR News.

SIEGEL: Poisoned Places is a collaboration with the Center for Public Integrity. You can hear all of the stories in this series at NPR.org. Transcript provided by NPR, Copyright NPR.