Fifteen years ago, while driving west through southern California, I watched the brilliant blue sky turn ominous, an orangey-brown hue foreign to my eastern eyes. Was that a storm approaching? Then it hit me; it was just Los Angeles.
Why did the sky look so gruesome? Car exhaust, I thought, and the fact that L.A. sits in a sun-drenched valley. But I was ignorant of the reason why smog is visible: particles. Smog is full of tiny toxic blobs that turn the horizon ugly as they bake in the sunlight. They can cause severe health problems from asthma attacks to lung cancer. That’s why the EPA regulates those kinds of particles. But the methods scientists use to pinpoint the nastiest particles are far from perfect, according to chemical engineer William Vizuete. “We’re not even sure what happens in our bodies when we breathe in the particles that wind up killing us,” he says. To find out, scientists need better ways to study how particles interact with living cells. Vizuete thinks his team has built a better way—a device they can take on the road, to test the air anywhere.
Burning wood, coal, gasoline, or just about anything else creates particles as byproducts. The particles combine with each other; gases get attached to them. The two main sizes of particles, by the EPA’sreckoning, are pm 2.5 and pm 10. The pm stands for particulate matter and the 2.5 means 2.5 micrometers in diameter. (A strand of human hair has a diameter of about 480 micrometers.) Researchers have found that particles smaller than 2.5 micrometers are the ones that can get lodged deep in our lungs and trigger disease. The larger particles can get lodged in our upper airways and cause problems there.
Epidemiologists have found that hospital visits for respiratory ailments increase as air quality worsens. But in lab experiments, toxicologists haven’t been to show why. They’ve tested the effects of automobile exhaust on live human lung cells, on mice, and directly on humans, but they haven’t witnessed the same sort of adverse effects that epidemiologists find in hospital patients. “Toxicologists have to increase the particulate matter one hundredfold to get the same effect,” Vizuete says.
There are probably a few reasons for this. People rarely inhale fresh car exhaust, he says. We breathe pollution that’s been in the air a while, and that makes it different from pure car exhaust. Also, toxicology tests don’t mirror reality. “When toxicologists run their experiments, they pump exhaust through a filter to capture particles,” Vizuete says. “Then they scrape off the particles into a liquid solution and drip it onto lung cells or feed it to mice.” Then they measure how the cells or mice respond. “The test is simple, cheap, and convenient,” he says. “But we don’t like it. The liquid causes the particles to cluster, losing their original size and shape. People don’t breathe liquid, and that solution strips off a lot of stuff that had been attached to particles.” Stuff such as gases, which can change how particles interact with live cells.
So UNC scientists created an alternative. They can pump exhaust into a Teflon film chamber atop the Gillings School of Global Public Health and let the exhaust age in sunlight. Then, instead of using the standard liquid toxicology test, Vizuete and his colleagues use a more accurate system of their own devising.
In 2002, atmospheric chemist Harvey Jeffries wanted to build a better air quality testing system. He looked at a contraption in his house that uses an electrostatic field to filter out particulate matter. Jeffries wondered if he could mount a special plate on his device, put cells on that plate, and use the electrostatic field to force the particles onto the cells to see what happened. His colleague David Leith reminded him that there was a similar machine—an electrostatic precipitator—in a lab in Rosenau Hall. They dusted it off, replaced the electronics, and created a special receptacle to house the cells. “We still have this prototype,” Jeffries says. “And it still works.”
Jeffries, Leith, Vizuete, atmospheric chemist Ken Sexton, and others at UNC have used that piece of equipment to test the effects of bad air quality on lung cells. In one test, Jeffries and toxicologist Ilona Jaspers exposed lung cells to fresh diesel exhaust and found that the exhaust causes lung cells to secrete a signaling protein called interleukin-8 that’s usually associated with inflammation. Then Jaspers decided to see what would happen to lung cells exposed to diesel exhaust that had been aged in sunlight over the course of a day. Turned out, aged exhaust caused an inflammatory response about five times greater than fresh exhaust did.
UNC researchers are now using this technique to run experiments to find out how different cell lines, various species of mice, and different human genes respond to toxic air. But all their tests have to be run at UNC using piped-in air from the rooftop chambers because the repurposed electrostatic precipitator is connected to equipment the size of a large refrigerator. It can’t be hauled out to Los Angeles, for instance, to test the air there.
Vizuete had the idea to make a smaller, portable version. Something that could maintain a stable temperature and humidity level, like an incubator or a human body.
It took a few years, but Vizuete’s team designed and built a working prototype. The size of a briefcase, it’s a white plastic box with tubes and wires connected to disembodied electronics. The device sucks in air that flows through an ionic-charge field to charge the particles. Then the air flows beneath a plate of the same charge so that the particles are repelled downward onto a waiting tray of cells. Early tests have shown the patented device to be sixteen times more sensitive than the traditional liquid solution method. And Jaspers has used it to accurately replicate her experiment with aged exhaust and interleukin-8.
The prototype has gotten the attention of the EPA, which is letting Vizuete’s team conduct field-site tests in Raleigh and is thinking about buying several prototypes for its researchers to experiment with. “The goal is to get feedback from them,” Vizuete says, and then make any necessary modifications. If all goes well, Vizuete and colleagues will make the device commercially available through their startup company, BioDeptronix.
“The idea is to put the device in schools or sell it to anyone interested in testing the toxicity of air,” Vizuete says. Communities close to refineries, he says, might like to know if the air there is less than optimal. But Vizuete and other researchers need such a system so they can figure out how certain particles become toxic, and then study what that toxicity does to different kinds of cells and genes.
Vizuete’s team has already used the device to see what nontoxic particles do to lung cells: very little. Then Vizuete put the particles with gases found in a typical urban atmosphere and ran it through the new exposure system. “We proved that the inert nontoxic particle was made toxic by these other gases,” he says. The mass of the particle had nothing to do with the toxicity; it was all about the gases the particle was in.
“And that’s kind of scary,” he says, “because all of our regulations are based on mass. That’s the easiest and simplest to get at.” But mass and size are only part of the story.