The Forest for the Trees

May 20, 2020
green and teal forest with complimentary lake.

Harvard scientists investigate how trees, from pre-industrial to modern forests, impact pollution and climate change

Department of Chemistry & Chemical Biology

By Caitlin McDermott-Murphy

Everyone knows that telltale pine forest smell. Candles and deodorants try to duplicate the scent. The most iconic air fresheners are even shaped like little pine trees. But that perfume may not be so innocent.

"The plants don't do this because we find it pleasurable to walk around in a pine forest," said Frank Keutsch, Professor of Chemistry and Chemical Biology at Harvard. Although scientists have demystified much of plant chemistry, some questions—like why pine forests smell so darn good—still don't have a clear answer.

For Keutsch, an atmospheric chemist, this question is intriguing for reasons far more important than fragrance. Pine scent comes from a collection of molecules known as volatile organic compounds (VOCs). When trees emit these chemicals, they can react with oxidants to form other pollutants like particulate matter and ozone, both of which can impact climate change and also respiratory diseases, potentially even COVID-19.

To figure out exactly how forests impact air quality and human health, experts like Keutsch first need to understand the complex oxidation chemistry behind that pine forest smell. To do that, he and two chemistry PhD candidates in the Graduate School of Arts and Sciences—Joshua Shutter and Joshua Cox, or "Team Plant"—are studying what happens when specific VOCs interact with plant leaves and how these interactions are different now, in modern air, compared to pre-industrial.

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