Pollen is known to cause severe allergies in people, especially during summer, but according to a new study, these tiny particles can also form clouds and cause heavy rainfall.

Researchers from the University of Michigan (UM) and the Texas A&M University (TAMU) studied a possible connection between pollen and rain.

UM associate professor Allison Steiner and her colleagues collected two grams of pollen from well-known allergic plants such as ragweed, pecan, birch, cedar, oak and pine trees. They exposed the pollen samples to water for an hour then made the fragments into spray using an atomizer.

The researchers sent the pollen spray to a cloud-making chamber where it was tested under the supervision of Sarah Brooks, professor of atmospheric science at Texas A&M.

They discovered that while normal grains of pollen are too large to affect the climate, these particles are broken down after they are exposed to raindrops. The resulting subpollen can then collect water in the atmosphere and form rain-carrying clouds.

"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 said.

According to UM researchers, experts studying airborne particles or aerosols know little about pollen despite being one of the leading causes of seasonal allergies in the United States.

The authors of the study hope that their findings will help provide better understanding on the link between the release of pollen and the formation of rain clouds. They, however, explained that further research is needed to get the bigger picture regarding the phenomenon.

"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."

The Asthma and Allergy Foundation of America (AAFA) states that allergies affect an estimated 20 percent of people in the country. Spending for allergy medications and visits to doctors is at $14.4 billion annually.

The study is profiled in the journal Geophysical Research Letters.

Photo: Lennart Tange | Flickr