Tracking Atmospheric Pollen During Extreme Weather Events

Exposure to atmospheric pollen causes seasonal health disorders in more than 24 million Americans. While whole pollen grains between 15 and 100 microns affect the upper respiratory system causing mild rhinitis, sub-micrometer pollen fragments that form by osmotic rupturing of pollens during thunderstorms can penetrate deeper into the lung and cause more serious health impacts. Although pollen counting has been used to model the seasonal and diurnal patterns of intact pollen concentrations, these methods have not yet been used to infer the presence of atmospheric pollen fragments. A field campaign was conducted during the springtime tree pollen season in 2019 in Iowa City, Iowa to study the abundance and type of pollens and pollen fragments and their response to local meteorology. Our specific objectives were to determine the meteorological conditions that correlate with tree pollen concentrations in ambient aerosols, infer which conditions cause pollen bursting events, and identify pollen species present during pollen rupturing events. Ambient levels of intact pollen declined sharply with any amount of precipitation, with the decrease proportional to the amount of precipitation. These observations suggest that pollen bursting events follow the onset of rain and that the reduction in intact pollen concentration is correlated with an increase in pollen fragments. These data will be compared with fluorescence and chemical measurements to gain a thorough understanding of the seasonal and meteorological conditions that release sub-micrometer-sized pollen fragments to the atmosphere. Future work will focus on ragweed pollens and their fragments in late summer. With a better understanding of the conditions that cause high levels of pollen fragments in the atmosphere, the negative health impacts associated with pollen fragments can be reduced.