Understanding the Science of Pollen Counting

Spring—widely regarded as the most enchanting season of the year. Temperatures rise, and across the United States, festivals commemorate the season's arrival along with the vibrant blooms it brings. It’s a wonderful time to be alive, unless you’re one of the 50 million Americans battling allergies.

You likely associate pollen with your itchy eyes, stuffy nose, and scratchy throat, but these tiny grains have an important role to play in fertilizing plants that goes beyond causing your discomfort.

While most allergies are triggered by airborne pollen, not all types are allergenic. Certified pollen specialists across the globe monitor and identify pollen grains, often daily, so allergy sufferers can stay informed about what’s in the air and its concentration levels.

The Pollen and the Bees

Pollen appears as powder because it consists of numerous tiny grains, which are the male gametophytes of seed plants. These grains can range from 10 to 100 micrometers in size, still making them microscopic. Just a fingertip full of pollen collected from your car’s hood could contain thousands of grains. These grains, which produce sperm, are essential for fertilization.

"Without pollen, there would be no seeds or fruit," Dr. Estelle Levetin, professor and chair of Biological Science at The University of Tulsa, said in our conversation in 2019. She is also a member of the aerobiology committee that oversees the National Allergy Bureau (NAB), a division of the American Academy of Allergy, Asthma & Immunology (AAAAI).

Levetin explains that in flowering plants, pollen is transferred from the male reproductive parts, the anthers where pollen is produced, to the female reproductive part, the carpel, which creates the ovules. Pollen is carried by animals, like bees, or by the wind.

"Wind-pollinated plants are typically small and unobtrusive, producing vast quantities of lightweight pollen easily dispersed by the wind," Levetin explains. "On the other hand, insect-pollinated plants are generally large and vibrant, often with brightly colored petals, fragrances, and nectar. Typically, the airborne pollen that triggers allergies comes from wind-pollinated plants. "Occasionally, we might detect a few grains from insect-pollinated plants in our air samples."

Monitoring the Pollen Count

If you watch a weather forecast during pollen season, you’ll probably hear them discuss the daily pollen count. You might even wonder if this "count" is some kind of air quality estimate. While the idea of counting microscopic pollen grains daily might seem unbelievable, that is exactly what happens, and there’s much more to it.

"The pollen count refers to the number of pollen grains present in one cubic meter of air over a 24-hour period," explains Katie Walls, a meteorologist at Spectrum News 1 in Charlotte, North Carolina. (At the time we spoke with her in 2019, she was a meteorologist at WSB-TV, the ABC affiliate in Atlanta.) She further explained that certified counters from Atlanta Allergy & Asthma begin their work early in the morning, counting the number of pollen particles on a glass slide that has been outside for the past 24 hours. "The number you see on WSB-TV reflects the count from that morning and represents the pollen present in [metro Atlanta]."

More specifically, pollen is captured using a volumetric air sampling tool, which means, as Levetin notes, a set volume of air is sampled. There are two types of instruments: rotating arm impactors, such as the Rotorod Sampler, and Hirst-type spore traps, like the Burkard Sampler. Both are volumetric but operate on different principles, and both require microscopic analysis to interpret the samples.

The rotating arm version has a head that spins at 2,400 revolutions per minute. While spinning, two small, greased rods descend, capturing pollen and spores. These rods are then placed into a specialized microscope adapter for examination. The Hirst-type instrument, however, employs a suction trap to pull in air and particles that stick to a greased microscope slide inside. The slide moves toward the intake at a rate of 2 millimeters (0.07 inches) per hour, allowing for an hour-by-hour examination of the particles that have passed through the air.

Certification in Pollen Counting

Using a volumetric air sampling tool, some pollen stations collect and analyze pollen year-round, sampling the air every day. Other stations collect samples on weekdays or just three days a week. However, not every city or town has the capability to count pollen, and pollen stations operate in different ways depending on location.

Some pollen counting stations are managed by public health departments at the city or county level, while others are run by allergists like Atlanta Allergy & Asthma. "A few stations are operated by academics like me who study airborne pollen as part of their research," says Levetin. "It requires specialized training to understand the morphology of pollen, and analyzing air samples takes time," she adds.

Pollen counting certification is offered by the AAAAI and NAB. The certification process includes completing an accredited course on pollen and spore identification, passing a written exam, and succeeding in a pollen and fungal spore identification test. To be certified, counters must learn to identify the microscopic morphology of various pollen grains.

Pollen identification training is essential because merely counting the pollen isn't sufficient.

"People with allergies refer to the types of pollen listed in the morning count to determine how they might be affected throughout the day," explains Walls. "Technicians identify the different pollen types using a microscope. This allows them to figure out which trees, weeds, and grasses are pollinating and causing issues for people. Not everyone reacts to the same allergens in the same way."

Don't Count Pollen Out

Pollen may cause months of discomfort, but it's also essential for our survival. It plays a key role in producing the foods we rely on, such as fruits, grains, and seeds. Additionally, it has a wide range of fascinating uses. According to Levetin, pollen is utilized in forensic science to help trace the origin of objects (just ask Jack Hodgins from the TV show "Bones"). Archaeologists study fossilized pollen to uncover the plants used by ancient civilizations, while geologists analyze it to understand the composition of ancient plant life. Even exploration geologists use fossil pollen to identify potential oil deposits.

For more insights on pollen, check out "Pollen and Spores: Applications with Special Emphasis on Aerobiology and Allergy" by S N Agashe and Eric Caulton. Mytour recommends related books based on titles we believe you'll enjoy. If you decide to purchase one, we'll earn a small commission from the sale.