Buying an Air Purifier for Pollen
Pollen is a trigger for seasonal allergies. Let’s take a closer look at exactly what pollen is.
This will help us determine how to remove it from the air.
How it starts
Flowering plants reproduce. Part of that reproductive process involves pollen grains.
A part of the plant’s flower - the anther - releases the pollen grains. Wind or animals pick up the pollen grains and spread them to the
- same plant (self-pollination) or
- other plants (cross-pollination)
Pollen grains are small and light - perfect for being picked up by the wind. Pollen grains are also shaped in a way to help them get picked up by the wind.
Pollen grain structure
Most pollen grains are spherical in shape. The pollen grain has both an external and an internal wall. The external wall is strong and rigid to provide structural support, protect the grain’s contents and allow for proper transport. The internal wall is not as rigid as it only has to keep things together inside the pollen grain. It does not provide structural support.
What are the “things” the inner wall is keeping together inside the pollen grain?
The “things” – the contents - relevant to this discussion are allergenic particles.
A tale of multiple irritants
In the world of air quality pollen grains are very large particles. Take a look at the table below in which we list some of the worst offenders (plants) when it comes to allergy inducing pollen and the size - in microns - of the pollen grains they produce.
|maple/ box elder||20-51|
Note how the grains don’t really get much smaller than 16 microns. This is very large. Mold spores are about the same size but many other particles you may want to remove from the air in your home are much smaller. Most fine particle pollution in the US consists of particles 2.5 microns or smaller. Tobacco and wildfire smoke particles are between 0.1 and 0.7 microns. Dust particles can easily be smaller than 1 micron, and so on and so forth.
The good thing here is that particles the size of pollen grains don’t stay airborne for long. We know that 10 μm particles do not stay airborne for longer than a few minutes (8.2 minutes to be exact). 100 μm particles fall to the ground in mere seconds.
Here’s the problem though:
Pollen grains are shaped in a way to allow them to travel on air – thus
they stay in the air much longer than the average particle their size
it doesn’t take much to disturb them (e.g. simply walking through a room can do it)
Pollen grains are not the only concern
The real bad guys
Pollen grains are too large to enter your lower airways. It takes a particle smaller than 10 μm to do that. Particles larger than 10 μm get stuck in the upper airway passages – nose, nasal cavity, and throat. This is where pollen grains land.
For years, researchers were puzzled why so many pollen allergy sufferers experienced symptoms related to their lower airways (e.g. asthma). Pollen grains are simply too large to get that far.
Now we know that
are only part of the problem when it comes to pollen allergies. These allergies can also be caused by
fragments of pollen grains
– the scientific name for these is sub-pollen particles (SPPs)
These particles are exactly what their name describes – fragments of pollen grains. SPPs were studied to fall in the 0.5 to 4.5 μm range.
Researchers have found pollen allergen activity in different parts of the plant outside of the pollen grain itself. The study cited here found pollen allergen in plant debris particles ranging from greater than 6 μm all the way down to 0.3 μm.
More on that next.
Allergenic particles are allergenic particles
When we discussed pet allergies we narrowed down the focus of our research to the allergens themselves. After all, it’s the allergen – not the vessel that holds the allergen – that triggers an allergic reaction.
We found that pet allergens are glycoproteins. They’re very small (0.0025 microns was one estimate) and because of their small size and jagged shape have a habit of clinging to other particles on surfaces or in the air. Thus, any study of pet allergens can’t be limited to the allergen itself but also needs to consider what those allergens (proteins) land on.
The same logic applies here. Pollen allergens are also glycoproteins. The most common pet allergen is fel d 1 (cats). The most common pollen allergen is lol p 1 (the “lol” stems from the genus from the genus Lolium - Rye Grass).
Lol p 1 and other pollen allergens are similar in size to fel d 1 and allergens like it – in the 0.0025 micron range. Again, our research found that because of their small size, pet allergens have a tendency to “associate” with (land on and stick to) other particles. These particles range in size from <4.7 μm to >9 μm. Essentially any particle that is a household dust particle is a particle that a pet allergen can associate with.
We did not find comparable research – particle size association in the home - for pollen allergens. Still, we think it’s safe to assume that the same thing can happen with pollen allergens – because of their small size they can easily associate with other small particles in the home. How can we make such an assumption? See the following:
Recall the rigid outer wall of a pollen grain. How do the pollen allergens get outside this wall?
- The pollen grain lands on a mucous membrane on your body (upper airway mucosa - eg. nasal cavity) and the allergenic proteins diffuse into the mucosa. This triggers an immediate allergic symptom.
- The pollen grain comes into contact with a hypotonic (a lower osmotic pressure) medium (eg. rain water). The pollen grain is rapidly hydrated which causes the expulsion of allergenic proteins.
Studies show that this expulsion causes a dramatic increase in the concentration of fine particles associated with certain allergens (bet v 1) in the atmosphere.
Other studies show diesel soot particles associated with certain other pollen allergens (lol p 1).
Thus, while there are no studies we could find that directly associate pollen allergens with household particles, it’s not unreasonable to assume that if they can associate with atmospheric and exhaust particles that they can associate with household particles as well.
Assume the worst. When it comes to fighting back against pollen, take into account all forms in which it might manifest. This means combating:
- pollen grains - 16 to 100+ μm
- fragments of pollen grains - 0.5 to 4.5 μm
- plant debris particles - >6 μm to 0.3 μm
- other particles – household dust particle sizes
That’s a whole lot of different particles and many different size ranges. The good news? One type of filter will be able to capture all four of these particle types – a HEPA filter.
Even more good news? Most air purifiers on the market are in fact equipped with a HEPA filter.
However, not all air purifiers are created equally. Not all units offer the same level of versatility, energy efficiency, low noise output, durability, and value.
Our research and testing has shown that units in the $150 to $200 range (approx.), with approximately 250 CFM (cubic feet per minute) of processing power offer the best combination of all of the factors we listed above.
Smaller units – that is to say units with less CFM that can be bought for lower prices – are generally less energy efficient but most importantly are much more noisy at the same output.
A 250 CFM unit can be set to a lower fan speed and still output at approx. 100+ CFM. A smaller unit has to be set to maximum fan speed to output at 100+ CFM. On its maximum fan speed it’s a lot more noisy than the 250 CFM unit at the same output.
Smaller units are also less versatile. A 250 CFM unit can be used in a small space on lower settings but can also be used in a larger space up to 300 sq. ft. on maximum settings. A lower CFM unit simply cannot be used in such a large space.
What about more expensive units with a CFM greater than 250 CFM? Most are exorbitantly priced. 250 CFM units are simply a much better value. In fact, you can usually purchase two 250 CFM units for same price or less than one 300+ CFM unit. That’s a total of 500 CFM compared to 300, 400 CFM at an equal or lesser price. This is one of many reasons we recommend multiple 250 CFM units over a single higher CFM unit for extra-large spaces (larger than 300 sq. ft.)
The best 250 CFM air purifier – that is to say the best air purifier for pollen - currently on the market is the Winix 5500-2. It offers a true HEPA filter and sufficient CFM to make quick work of any and all pollen allergen containing particles in rooms up to 300 sq. ft. If you need an air purifier for a larger space we would recommend two Winix units.
A Quick Note on Pollen Count
Pollen count describes the concentration of pollen grains in a particular sample of air. This concentration is usually given in terms of the number of grains per cubic meter of air. For example, a pollen count of 100 equates to a pollen grain concentration of 100 pollen grains per cubic meter of air.
Problems with pollen count
Different standards and scales for low, med, high pollen count
What is a low pollen count? What is a high pollen count? Depending on where you get your pollen count, the standard and scale can change.
For example, the NAB (National Allergy Bureau) uses the standard pollen count metric described above – number of grains per cubic meter of air. They then give a chart for low, moderate, high, and very high counts of pollen grains in a particular sample of air. For grass, a count of 1 to 4 is low, a count of 5 to 19 is moderate, a count of 20 to 199 is high, and a count higher than 200 is very high.
Other sources set their own standards and scale. For example, pollen.com uses a scale of 0 to 12. The number between 0 and 12 does not equal the number of pollen grains per cubic meter of air. Instead, it’s simply a number that describes pollen level according to pollen.com’s own in-house metrics - low (0 to 2.4), low-medium (2.5 to 4.8), medium (4.9 to 7.2), high-medium (7.3 to 9.6), and high (9.7 to 12.0).
Pollen count only takes into account pollen grains
To determine pollen count grains of pollen are collected. They’re then inspected under a microscope to determine their exact number. The pollen count thus represents the total number of pollen grains.
Here’s the thing.
Pollen grains are not the only particles that contain pollen allergens. As we showed earlier, the actual allergens that trigger allergic symptoms may be contained in a whole slew of different plant parts other than whole pollen grains.
All of this means that air with even an extremely low pollen count – even a pollen count of 0 – can still trigger allergic symptoms if that same air contains other particles that contain pollen allergens.
Don't underestimate the sheer quantity of pollen in the air
Studies have shown that 100 sq. meters of rye-grass can generate as much as 100 kg of pollen. One gram – 1/1000 of a kg – may contain as many as 100 million pollen grains.
Add a Comment
Have a question or comment? Let us know below.