The National Mall gives an unobstructed view of a growing thunderstorm. (Phil Yabut via Flickr)

Those pollen grains in the air that make you miserable may have a surprising side effect: heavier rain. A new study says bits of pollen lofted into the atmosphere by springtime winds make their way into clouds, seed them and may even intensify downpours.

The study, “Pollen as atmospheric cloud condensation nuclei”, is the among the first to propose the idea that pollen helps enhance clouds.

“The [pollen] 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, a professor atmospheric science at the University of Michigan and study lead author, in a press release.

But Steiner and her colleagues, from Texas A & M University, knew from the medical literature that, when it triggers allergies, pollen breaks up into little pieces in the air . In the laboratory, they verified that pollen – when it gets wet – does indeed fragment into small-enough particles for clouds to form.

Close-up of tree pollen under microscope (U.S. Army Allergen Extract Lab) Close-up of tree pollen under microscope (U.S. Army Allergen Extract Lab)

The team soaked pollen samples from oak, pecan, birch, cedar and pine trees, as well as ragweed in water and reduced them into sprays. They then ejected the different pollen sprays into a cloud-making chamber to simulate the atmosphere.

They found the pollen fragments (or sub-pollen particles) “activate” into the building blocks for water droplets in clouds.  Known as cloud condensation nuclei, these tiny particles are the collectors for water vapor when it converts to a liquid in the condensation process.

“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,” Steiner said.

Because the experiments were conducted in a laboratory-setting rather than the actual atmosphere, it’s not clear how big the cloud-building effect of pollen is, but the authors seem convinced it’s real.

“Our estimates suggest that SPP [sub-pollen particles] can account for a fraction of the known organic CNN [cloud condensation nuclei] in pollen-influenced mid-latitude regions,” the study said.

In an email, Steiner said she think it’s “plausible” elevated pollen levels could enhance rain downwind of the pollen’s release but cautioned confirmation requires field evidence.

It’s also possible, she said, that any rain generated by pollen could have the beneficial impact of removing some of the existing pollen in the air – relieving allergies. But she also explained any pollen-enhanced rain could trigger more plant growth, releasing additional pollen. “We are really not sure yet which way the feedback cycle could go,” she said.

Steiner and her colleagues hope to next conduct field and modeling experiments to better understand the role of pollen on weather and climate.