Characterization of atmospheric pollen fragments during springtime thunderstorms

Thunderstorm asthma is a very interesting topic. What happens to pollen and pollen particles during such a storm? How do you measure this? Some questions about this research done by Betsy Stone and her team from Iowa University.

1.What’s your job at University of Iowa ?

I am an associate professor in the Departments of Chemistry and Chemical and Chemical Engineering at the University of Iowa.

Foto 1: From left to right is: Dagen Hughes, Vingie Ng, Elizabeth Stone, Chamari Mampage, and Lillian Jones.  These are members of the field team in May 2019. They are shown here at the field site, located on the University of Iowa Campus, where they conducted measurements of fluorescent particles, airborne particles, meteorology, and collected samples of particles from the atmosphere.


2. What was the goal of the research?

Our research objectives were to, 1) characterize the properties of pollen fragments in the atmosphere and 2) assess the environmental conditions associated with pollen fragments.

3. Can you explain what actually happens to pollen during a thunderstorm, what makes them burst?

The prevailing hypothesis was introduced by Taylor and Jonsson (DOI: 10.1007/s11882-004-0092-3), which states that pollens are lifted into the atmosphere where they encounter high humidity and rupture, releasing hundreds of pollen fragments per pollen grain.  Thunderstorm downdrafts and outflows then transport these pollen fragments to the Earth’s surface.

4. How relevant are the pollen fragments for hayfever patients? What’s the difference with being triggered by whole pollen?

Pollen fragments are much smaller (0.25 – 2.5 micrometers) than intact pollen grains (10-100 micrometers).  This means that compared to intact pollen grains, the pollen fragments have longer atmospheric lifetimes, can be transported longer distances, and can even penetrate deeper into the human respiratory tract.

5. You measured various meteorological parameters like temperature, precipitation and humidity. But also looked at some more “unusual suspects” like potential temperature, air pressure, saturated vapour pressure and absolute humidity. Are these interesting for these specific thunderstorm situations or also relevant under less extreme conditions?

We used equivalent potential temperature to track the downdraft, because it controls for differences in pressure even if water vapor condenses. We found this metric to be helpful in determining the strength of the downdraft, which is related to atmospheric instability in convective storms. Prior studies have shown that humidity, in the absence of rain, can cause pollen grains to rupture.

Foto 2: Chamari Mampage working on the pollen and spore sampler


6. How do you measure “lightning”?

We obtained these data from the National Lightning Detection Network.

7. There is a paper by a Dutch pollen researcher, mr. F.TH.M.Spieksma. The paper is called Evidence of Grass-Pollen Allergenic Activity in the Smaller Micronic Atmospheric Aerosol Fraction”. They collected pollen using a Burkard and looked at micronic pollenparticles using an electron microscope in 1988.  Which new technologies did you use?

In addition to pollen counting using a Burkhard, we used an online single-particle fluorescence spectrometer called a Wideband Integrated Bioaerosol Sensor. This sensor allowed us to measure fluorescent particles in the atmosphere with high time and size resolution. We also used chemical tracers, specifically fructose for pollen, to determine that these fluorescent particles were derived from pollen.

you can read more about different techniques to identify pollen in this post.

8. You quantified carbohydrates like fructose and mannitol, why?

These are chemical tracers of pollen and fungal spores, respectively. Our observation of fructose, a chemical tracer of pollen, enabled us to associate increases in fluorescent particles with diameters less than 1 micron with pollen, even though intact pollen grains are much bigger. In contrast, mannitol, a chemical tracer for fungal spores was primarily in particles with diameters greater than 1 micron.

9. How much longer can particles be airborn compared to intact pollen?

Hours to days

10. Figure S9-b shows particle concentration and rainfall, do all types of rain show an increase of particles or only severe storms?

Yes, we observed pollen fragments coincident with all 5 of the rain events on May 8. Pollen fragments during light rains, however, were much lower than during strong storms.

Foto 3: Chamari Mampage and Dagen Hughes are installing a pollen and spore sampler at the field site prior to the start of the campaign in April 2019. This sampler collects airborne particles like pollen grains and fungal spores onto microscope slides, so that concentrations and types can be determined.


11. Figure S9-d shows Pollen, pollen and background particles, what are those backgroundparticles?

These background levels refer to levels of pollen tracers on a preceding day with no rain. This helps us to distinguish what is associated with the rain.

12. Can you explain what is shown in figures S9e to S9i?

The observed size distributions of pollen fragments at each of the points marked with a star in panel b.

13. Does this phenomena occurs only during severe storms and lightning or also during more regular and mild rainshowers which are pretty common in the Netherlands?

We observe this phenomenon during light rain storms, too.  The highest concentrations, however, occurred during the strongest thunderstorms.

14. Most people, including hayfeverpatiënts, stay indoor during strong rainfall and storm by nature/common sense. Going outside when it stops raining, would it be better to wait a while?

If an individual is sensitive to pollen types in season, then I would recommend staying indoors for a couple of hours after a strong storm, and 1 hour or so after a light rain. Doing so would reduce their exposure to pollen fragments that could trigger an allergic response.

15. What was the main result/conclusion of this research?

Pollen fragments accompany may different types of rain events during pollen season, with the highest levels occurring during convective thunderstorms.

You can find the original paper here:


link to:

University of Iowa >>