Free radicals amp up pine tree pollution

CARNEGIE MELLON (US) — Aerosols emitted by pine trees and free radicals are a volatile combination—and they’re making air pollution worse, say researchers.


New research from a team led by Carnegie Mellon University’s Neil Donahue provides the first experimental evidence that the biogenic particles formed from pine tree emissions are chemically transformed by free radicals—the same compounds that age our skin—after they are first formed in the atmosphere.


“We have been able to show conclusively that biogenics are chemically transformed in the atmosphere. They’re not just static. They keep going, they keep changing, and they keep growing,” says Donahue, professor of chemistry, chemical engineering, engineering, and public policy, and director of Carnegie Mellon’s Center for Atmospheric Particle Studies.

“Quite a few atmospheric models, which are commonly used to inform research and policy, have been assuming that that doesn’t happen. What we really need to have in the models is an accurate representation of what’s really going on in the atmosphere, and that’s what this lets us do.”

The air that we breathe is chock-full of particles called aerosols. These tiny liquid or solid particles come from hundreds of sources including trees, volcanoes, cars, trucks, and wood fires. The small particles influence cloud formation and rainfall, and affect climate and human health.




Smog chambers

Donahue and colleagues in the Center for Atmospheric Particle Studies were the first to describe the chemical processes involving free radicals that transform aerosols emitted by human-made sources like diesel exhaust. But this mechanism didn’t explain what happens to natural compounds when they enter the atmosphere.

“It was too aggressive and made too much stuff, so the modelers simply turned off biogenic aging entirely. This seemed a little extreme,” Donahue says. He suspected that the biogenic particles would age too, but in a different way.

Donahue, together with colleagues in Germany, Sweden, Denmark, and Switzerland, set out to test this hypothesis using fake atmospheres called smog chambers, which contain several cubic meters of air in an enclosed space in the laboratory.

They fed alpha-pinene, an aerosol released by pine trees, and ozone into the smog chambers and then added hydroxyl (OH) radicals, which are naturally-occurring, highly-reactive molecules that drive reactions with other chemicals present in the air.

The researchers gathered data from four different smog chambers and fed it into a computer model that they developed. They discovered that OH ages the particles, altering their properties and concentrations, and producing three times more particulate matter than what was originally released into the atmosphere.

“The most intriguing part is that humans may influence the way that chemistry plays out,” Donahue says. “The trees emit the stuff, but since human activity changes the chemistry taking place in the atmosphere, those changes can affect the amount and properties of the natural aerosols.



EUROCHAMP, the Swiss National Science Foundation, Swedish Research Council, and the US EPA funded the research.

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chat2 Comments



  1. Judith Barrington

    Next time you do an article on a specific tree species make sure it is accompanied by a picture of same… Those trees from “Shutterstock ” are fir or spruce trees not pine trees. Or do you mean all conifers produce these organic gases?

  2. Pavel Stopka Dr. PhD.

    Very interesting publication. We study free radicals and antioxidants using EPR spectroscopy. What can we do for you? P. Stopka, Prague, Czech rep.

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