Characterization of atmospheric pollen fragments during springtime thunderstorms

While falling rain washes pollen grains from the atmosphere, rain can also induce pollen rupturing into submicrometer pollen fragments. Compared to intact pollen, such fragments can penetrate deeper into the human respiratory system and persist longer in the atmosphere. Herein, we provide the first online characterization of pollen fragments during thunderstorms and rain events. For the first time, we combine single-partide fluorescence spectroscopy with offline measurements of chemical tracers to provide direct evidence of atmospheric pollen fragments. We show a significant increase in pollen fragments with diameters of 0.25-1.0 mu m coincident with precipitation. Pollen fragment concentrations peak during convective thunderstorms with strong downdrafts, high rates of rainfall, and numerous lightning strikes, although lightning is not required for the fragments' release. After storms, pollen fragments persist in the atmosphere for several hours. Our results show that while pollen grains decrease substantially during rain, peak concentrations of submicrometer pollen fragments occur during rain events and then persist for several hours. This study provides new information on the abundance, size distribution, and meteorological drivers of pollen fragments in the atmosphere. Because pollen fragments potentially carry allergens and thunderstorms are predicted to increase in frequency and strength, understanding human exposures to pollen fragments is increasingly important.