The main job of pollen is to help seed the next generation of trees
and plants, but a new study from the University of Michigan and Texas
A&M shows that the grains might also seed clouds.
The
unexpected findings demonstrate that these wind-carried capsules of
genetic material might have an effect on the planet's climate. And they
highlight a new link between plants and the atmosphere.
Pollen has
been largely ignored by atmospheric scientists who study
aerosols—particles suspended in the air that scatter light and heat and
play a role in cloud formation.
"The grains were thought to be too
large to be important in the climate system, too large to form clouds
or interact with the sun's radiation," said Allison Steiner, U-M
associate professor of atmospheric, oceanic and space sciences. "And
also the large particles don't last in the atmosphere. They tend to
settle out relatively quickly."
But Steiner and her colleagues
weren't sure that was the whole story. Sweeping a dusting off her porch
one spring morning, she wondered what happens to the grains in the air.
Steiner turned to the medical community. Pollen causes seasonal
allergies, which affect 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 that pollen can break up into these tiny pieces and
trigger an allergic response," Steiner said.
Smaller grains could have big implications. The research team set out to see if moisture could cause the pieces to break down.
"What
we found is when pollen gets wet, it can rupture very easily in seconds
or minutes and make lots of smaller particles that can act as cloud
condensation nuclei, or collectors for water," Steiner said.
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