Pine forests are especially magical places for atmospheric chemists. Coniferous trees give off pine-scented vapors that form particles, very quickly and seemingly out of nowhere.
New research by German, Finnish and U.S. scientists elucidates the process by which gas wafting from coniferous trees creates particles that can reflect sunlight or promote cloud formation, both important climate feedbacks. The study is published Feb. 27 in Nature.
"In many forested regions, you can go and observe particles apparently form from thin air. They're not emitted from anything, they just appear," said Joel Thornton, a University of Washington associate professor of atmospheric sciences and second author on the paper.
The study shows the chemistry behind these particles' formation, and estimates they may be the dominant source of aerosols over boreal forests. The Intergovernmental Panel on Climate Change has named aerosols generally one of the biggest unknowns for climate change.
Scientists have known for decades that gases from pine trees can form particles that grow from just one nanometer in size to 100 nanometers in about a day. These airborne solid or liquid particles can reflect sunlight, and at 100 nanometers they are large enough to condense water vapor and prompt cloud formation.
In the new paper, researchers took measurements in Finnish pine forests and then simulated the same particle formation in an air chamber at Germany's Jülich Research Centre. A new type of chemical mass spectrometry let researchers pick out one in a trillion molecules and follow their evolution.
Results showed that when a pine-scented molecule combines with ozone in the surrounding air, some of the resulting free radicals grab oxygen with unprecedented speed.
Boreal or coniferous forests give off the largest amount of these compounds, so the finding is especially relevant for the northern parts of North America, Europe and Russia. Other types of forests emit similar vapors, Thornton said, and he believes the rapid oxidation may apply to a broad range of atmospheric compounds.
Forests are thought to emit exponentially more of these scented compounds as temperatures rise. Understanding how those vapors react could help to predict how forested regions will respond to global warming, and what role they will play in the planet’s response.