Can pollen make it rain?

Researchers have discovered that broken pollen particles can trigger cloud formation.

Scientists at the University of Michigan used a cloud condensation nuclei counter and found that when pollen gets wet, it can break down to smaller particles which seed clouds.

“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,” said associate Professor Allison Steiner at the University of Michigan.

In the study, published in Geophysical Research Letters, the team tested oak, pecan, birch, cedar and pine trees, as well as ragweed – the most common sources of wind-driven pollen in the USA. By breaking down each type of pollen in pure water for an hour, the researchers could then spray the moist particles into a cloud chamber. They found that three different sizes of all six types of pollen – 50, 100 and 200 nm – began to pull in moisture and form clouds.

“Samples entering the cloud chamber are exposed to moist conditions representative of the relative humidity found in the atmosphere. If a sample is an effective cloud activator, droplets will rapidly grow on the sample fragments, forming large cloud droplets,” said research partner, Professor Sarah Brooks at Texas A&M University.

By using a scanning electron microscope, the scientists confirmed pollen particles that had been reduced to a smaller size range can lead to cloud formation.

Professor Steiner said: “It’s possible that 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”.

The team is now planning to investigate the potential link between pollen and the atmosphere in the field by using computer simulations.

Paper: http://onlinelibrary.wiley.com/doi/10.1002/2015GL064060/abstract

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