Pollen may play role in formation of clouds, new NSF-funded study says

illustration that shows how pollen can seed clouds

Illustration: Division of Research

Pollen may seed clouds as well as flowers and trees, according to a new study from the University of Michigan and Texas A&M University.

Researchers found that pollen may affect Earth’s climate. Their research could provide a newly discovered link between plants and the atmosphere. The team published its work in the current issue of Geophysical Research Letters. The National Science Foundation funded the project.

Atmospheric scientists who study aerosols – the airborne particles that scatter heat and light, and thus play a role in forming clouds – have generally ignored pollen.

In the lab-based experiment at Texas A&M, researchers tested pollen from oak, pecan, birch, cedar and pine trees, as well as ragweed. These are the most common sources of wind-driven pollen in the United States.

Researchers soaked two grams from each source in pure water for an hour. They used an atomizer to produce a spray of the moist pollen fragments. The pollen fragments then entered a cloud chamber in the laboratory of Sarah Brooks, an associate professor of atmospheric sciences at Texas A&M.

Of the six types, the team found that three sizes – 50, 100 and 200 nanometers – began to pull in moisture and form clouds. For confirmation, researchers examined the samples under a scanning electron microscope, and saw that grains that had begun as 10-20 micrometer diameter had ruptured, releasing many fragments of 100 nanometer or greater diameter in size, well within the size that can lead to cloud formation.

Brooks said, “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.”

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