Pine Tree Particles: Scientists Explain Chemistry Behind Aerosols And Their Impact On Climate
A study published Nature explains the importance of the particles that are formed from pine-scented vapors emitted by coniferous trees. The research conducted by German, Finnish, and U.S. scientists, explains the chemistry behind these particles' formation, which appear rather suddenly. These particles can reflect sunlight or promote cloud formation, making them an important component of the atmosphere.
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"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 study co-author, according to a press release Wednesday.
The study estimates that these particles may be an important source of aerosols over boreal or pine forests, which have been named by The Intergovernmental Panel on Climate Change as one of the biggest contributors to air pollution. Scientists have known for many years now that gases emitted from pine trees grow in size from just 1 nanometer to 100 nanometers in a day. These solid or liquid aerosols can reflect sunlight and at 100 nanometers large enough to condense water vapor and prompt cloud formation.
The scientists studied these particles in Finnish pine forests and then created particles with the same chemical composition in a lab at Germany's Jülich Research Centre. A new type of chemical mass spectrometry let researchers pick out 1 in a trillion molecules and follow their evolution. The experiment showed that when a pine-scented molecule combines with the surrounding ozone, the resulting free radicals grab oxygen at very high speeds.
"The radical is so desperate to become a regular molecule again that it reacts with itself. The new oxygen breaks off a hydrogen from a neighboring carbon to keep for itself, and then more oxygen comes in to where the hydrogen was broken off," said Thornton.
molecules could be added per day during oxidation, Thornton said. But it was observed that the free radical added 10 to 12 oxygen molecules in a single step. This new, bigger molecule wants to be in a solid or liquid state rather than gas, and condenses onto small particles of just 3 nanometers. These dynamic molecules can clump together and grow to a size big enough to alter the climate.
"I think unravelling that chemistry is going to have some profound impacts on how we describe atmospheric chemistry generally," Thornton said
This study is especially relevant to places in North America, Russia, and Europe, which have vast areas of pine forests. Other types of forests also emit similar vapors and studies of the rapid oxidation around pine forests can be applied to other atmospheric compounds as well.
"I think a lot of missing puzzle pieces in atmospheric chemistry will start to fall into place once we incorporate this understanding," Thornton said.
Forests are thought to produce more of these aerosols as temperatures rise and understanding their reactions with their surroundings will help predict how forested regions will respond to global warming. In a parallel study, Thornton's group also researched the impact of aerosols formed by reforested areas or pollution, over the Southeastern United States.
"It's thought that as the Earth warms there will be more of these vapors emitted, and some fraction of them will be converted to particles which can potentially shade the Earth's surface," Thornton said. "How effective that is at temperature regulation is still very much an open question."
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