Coniferous trees emit pine-scented vapors that form particles, reflect sunlight and promote cloud formation, a new study has found.
Joel Thornton, a University of Washington associate professor of atmospheric sciences and second author on the paper, said that in many forested regions, particles apparently form from thin air.
The study shows the chemistry behind these particles' formation, and estimates they may be the dominant source of aerosols over boreal forests.
Scientists have known for decades that gases from pine trees can form particles that grow from just 1 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 Julich Research Centre.
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.
The radical is so desperate to become a regular molecule again that it reacts with itself and 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, Thornton said.
Boreal or pine 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.
The study is published in journal Nature.