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UW Prof Confirms Pine Trees Make Particles From Thin Air, Counteract Greenhouse Effect

When you walk into an evergreen forest, you get a whiff of that unmistakable smell of pine.

It turns out some of those vapors come from newly-discovered particles that seem to come out of nowhere and cool the forest. 

Researchers at the University of Washington have confirmed the finding, which they say will help scientists more accurately forecast climate change.

'It's Hard To Convey How Crazy These Particles Are'

UW associate professor Joel Thornton says he first heard the theory about forest air at a 2011 conference. A Finnish researcher presented his hypothesis about particles forming, almost from thin air.

“And it’s hard to convey how crazy these particles are to an atmospheric chemist. And I would say that when it was first presented, there were quite a few, if not agnostic, just outright disbelievers that such molecules could form at the rate that he was arguing they were being formed at,” Thornton said.

So Thorton decided to devote his sabbatical the next year to trying to replicate Mikael Ehn’s theory. The UW atmospheric chemist packed up the mass spectrometer his team had built in Seattle, and joined Ehn, a Helsinki professor, in Germany. 

Together they unraveled how pine trees emit molecules that become particulate matter, and why that's impotrant.

Counteracting Human-Produced Carbon Pollution

Why is all this important? Thorton says the trees’ emissions counteract the greenhouse effect of human-produced carbon pollution with a cooling effect.

“And it doesn’t take many aerosol particles to have a significant impact. So understanding the sources of aerosol particles is important for understanding how climate will respond to increasing greenhouse gases,” he said.

The process has revealed some complexities. For example, planting forests near large urban areas that are highly polluted might actually increase smog problems. Thorton says that’s a topic for more research.

The findings were published in the journal Nature.

Bellamy Pailthorp covers the environment for KNKX with an emphasis on climate justice, human health and food sovereignty. She enjoys reporting about how we will power our future while maintaining healthy cultures and livable cities. Story tips can be sent to