How Does the Pollen Count Work?

Your local weather report may include a pollen count, but what does that mean, and how do they calculate it? Learn the science behind this sneeze factor in today's episode of BrainStuff.

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Episode Transcript

Speaker 1 (00:02):
Welcome to brain Stuff from How Stuff Works. Hey, brain Stuff,
I'm Lauren Vogelbaum, and as I record this episode, it
is spring. It's arguably the most beautiful time of the year.
Weather turns warmer. Festivals around the world celebrate the season
and the blooming of the trees and flowers it brings.
It's just a great time to be alive unless you

(00:23):
are one of the fifty million Americans who has allergies.
While you probably know that pollen is to blame for
your congestion, burning eyes, and scratchy throat, there's a lot
more to these little grains, which are actually hard at
work at fertilizing plants. Although most allergies are caused by
airborne pollen, not all of that is allergenic. Certified pollen

(00:43):
experts around the world count and identify pollen grains, often
on a daily basis, so that those with allergies can
know what's floating around outside and how much of it
there is. Pollen looks like powder because it consists of
lots of tiny grains. These grains are the male gametophytes
of ants that produce seeds. These grains can be as
small as ten micrometers or as large as a hundred micrometers,

(01:06):
which still means they're all microscopic. Just a fingertipful collected
from the hood of your car could contain thousands of
pollen grains. These tiny grains, which produce sperm, are needed
for fertilization. We spoke with Dr Estelle Leviton, professor and
chair of Biological Science at the University of Tulsa. She's
also a member of the Aerobiology Committee that oversees the

(01:27):
National Allergy Bureau, which is part of the American Academy
of Allergy, Asthma, and Immunology. Leviton explains that without pollen,
we wouldn't have seeds or fruit or grains. In flowering plants,
pollen must be transported from the male parts of the plant,
the anthers where the pollen is produced, to the carpal,
the female part of the plant that produces the ovules.

(01:48):
Pollen can be transported by animals like bees and butterflies,
or by the wind. Leviton said. Wind pollinated plants are
small and inconspicuous and produce large amounts of lightweight pollen
that's easily carried by wind. Insect pollinated plants tend to
be large and showy. They often have brightly colored petals,
are fragrant and produce nectar. Generally, airborne pollen is from

(02:11):
those wind pollinated plants and is the kind that attacks
those of us with allergies. If you tune into a
television weather forecast during pollen season, you'll likely hear people
talk about the day's pollen count. You may be even
wondered whether the count was some sort of estimate of
air quality. Literally counting microscopic grains of pollen every day
might sound a little bit ridiculous, but that's actually just

(02:33):
the beginning of what's happening. The pollen count is the
number of pollen grains in a cubic meter of air
over a twenty four hour period. To measure it, pollen
is captured by a volumetric air sampling instrument. There are
two types of these instruments, rotating arm impactors like the
rotorode sampler, and hearst type spore traps like the buck
Art sampler. They are both volumetric, but they operate on

(02:56):
different principles, and microscopic analysis is needed to analyze both
type of samples. The rotating arm version has a head
that spins at two thousand, four hundred revolutions per minute
while it spins two small greased rods dropped down, capturing
pollen and fungal spores. These rods are placed into a
special microscope adapter and examined. The hearst type instrument, on

(03:18):
the other hand, has a section trap that sucks in
air and particles that adhere to a greased microscope slide inside.
In this case, the slide moves toward the intake orifice
at two millimeters per hour, so it's possible to see
what was swirling through the air hour by hour during
examination using one of the volumetric air sampling instruments. Some
pollen stations sample air and collect pollen three hundred and

(03:41):
sixty five days a year. Other stations run samples on
week days or only collect three days a week, but
not every city or town has the ability to count pollen,
and pollen stations are operated in a variety of ways.
Some are run by the city or county public health departments,
others by allergists. For example, in Metroid, Alanta, a city
with a lot of green space and a notoriously high

(04:02):
pollen count, certified counters from Atlanta Allergy and asthma, get
up early and physically count the number of pollen particles
on the glass slide from a hearst type instrument that's
been outside for the prior twenty four hours. That number
is what Atlanta residents may here reported by various news outlets.
Leviton explained a few stations are run by academics like
me who study airborne pollen as a research topic. It

(04:24):
takes training to learn the morphology of pollen, and it
takes time to analyze air samples. Certification in pollen counting
is available through a few organizations. The process requires pollen
counters to take an approved pollen and spore identification course,
pass a written exam, and pass a pollen grain and
fungal spore identification test, which means that the counters have

(04:45):
to learn the microscopic morphology of individual pollen grains. The
training and pollen identification is critical because just counting pollen
isn't enough. After all, not everyone is allergic to the
same things. Pollen counts also include data on what types
of pollen are heaviest in the air. That is, what
types of trees, weeds, and grasses are pollinating that day.

(05:06):
People can undergo allergy testing to determine which plants pollen
irritates them and use the specific information from morning counts
to learn how they might be impacted during the day.
Pollen may be to blame for months of discomfort, but
remember it also has an important job. It gives us
our daily bread by way of fruits, grains, and seeds,
and it has a lot of other neat applications too.

(05:28):
Levidon says that pollen is used in forensic science because
it can help determine where an object originated. Archaeologists also
examine fossil pollen to study which plants early human society
is used, and geologists use it to determine the composition
of ancient plant communities. Exploration geologists even use fossil pollen
to help locate oil deposits. Today's episode was written by

(05:54):
Carrie Whitney, PhD and produced by Tyler Clang. Brain Stuff
is a production of iHeartMedia's how Stuff Where. For more
on this and lots of other blooming topics, visit our
home planet, how stuff works dot com, and for more
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