University of Iowa researchers report that tree pollen fragments remain in the air for as many as 11 hours after heavy rains, and those granules can make their way deep into the lungs, potentially exacerbating allergies. The researchers base their findings on first-time direct measurements of pollen fragment concentrations during and after spring rains of varying severity in spring, 2019.
“Our results show that while pollen grains decrease substantially during rain, peak concentrations of submicron pollen fragments occur during rain events and then persist for several hours,” says Elizabeth Stone, associate professor in the Department of Chemistry and corresponding author on the paper, published online in the journal Environmental Science & Technology Letters. “People who are sensitive to pollen in season should avoid going outdoors during rain events, especially thunderstorms, and for several hours afterward.”
Pollen grains are pretty hardy, but they can rupture when subject to high humidity. This can happen during rains when a storm’s updraft carries the grains to the cloud base, where humidity is quite high. The fragments then are shot back toward the surface by falling rain and the storm’s downdraft.
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