Pollen's purpose is to spread plant life across our planet, but could it also help drive the rain that fertilizes it?
New research suggests the bundles of genetic material have more of an effect on the world's climate than we thought, Texas A&M University reported.
"The grains were thought to be too large to be important in the climate system, too large to form clouds or interact with radiation," said Allison Steiner, an associate professor of atmospheric, oceanic and space sciences at U-M. "And also the large particles don't last in the atmosphere. They tend to settle out relatively quickly."
Steiner was sweeping pollen off her porch one morning, which inspired her to think about how behaves in the sky. To start, she looked at how pollen causes allergies in between 10 and 20 percent of U.S. residents.
"When we were looking in the allergy literature we discovered that it's pretty well known by epidemiologists that pollen can break up into these tiny pieces and trigger an allergic response," Steiner said. "What we found is when pollen gets wet, it can rupture very easily in seconds or minutes and make lot of smaller particles that can act as cloud condensation nuclei, or collectors for water."
To make their findings, a research team tested pollen from oak, pecan, birch, cedar, pine trees, and allergy-antagonizing ragweed. They soaked grams of each type of pollen in pure water for an hour and used an atomizer to create a spray of the wet pollen fragments. These pollen fragments were sent into a cloud chamber, in which the researchers observed pollen of all three sizes (50, 100 and 200 nanometers) started pulling in moisture to form clouds.
"Scientists are just beginning to identify the types of biological aerosols which are important for cloud formation. Our results identify pollen as a major contributor to cloud formation," said researcher Sarah Brooks.
To confirm their findings, the researchers looked at the pollen samples under a scanning electron microscope, and discovered grains that started out between 10 and 20 micrometers in diameter had ruptured, releasing tiny fragments 100 nanometers or greater; pollen of this miniscule size can lead to cloud formation.
"What happens in clouds is one of the big uncertainties in climate models right now," Steiner said. "One of the things we're trying to understand is how do natural aerosols influence cloud cover and precipitation under present day and future climate."
"Specifically, our results suggest that increased pollen could lead to the formation of thicker clouds and longer cloud lifetimes," Brooks added.
In the future, the researchers plan to conduct further studies on the subject using computer simulations.
"It's possible that when trees emit pollen, that makes clouds, which in turn makes rain and that feeds back into the trees and can influence the whole growth cycle of the plant," Steiner concluded.
The findings were published in a recent edition of the journal Geophysical Research Letters.
