Why a HEPA air filter can catch particles smaller than 0.3 micron

So you have read about the various air filters on the market, not only the mechanical ones, but also air filters that are filter-less such as electrostatic precipitators, ozone generators and the like.

You’ve come to the conclusion that you would prefer a mechanical air filter such as a HEPA filter, but are a bit concerned that it can not remove particles smaller than 0.3 micron. That concern is justified, because many allergen are smaller than 0.3 micron.

However, here is surprising (and good!) news for you: HEPA air filters actually do filter out particles smaller than 0.3 micron. There is a catch though, and that is that they are not as efficient as with particles 0.3 micron and larger.

So how is this feat accomplished? A HEPA air filter is more than just a sieve that catches particles between it’s fibers, rather it relies on three other characteristics:

• Inertial impaction – instead of being able to follow the airstream and slipping in between the fibers of the air filter, their inertia causes these particles to collide head-on with the filter fibers.
• Direct interception – if the air stream comes within a half particle diameter of the fiber the particle gets stuck on the side of the fiber.
• Brownian diffusion – if a particle is smaller than 0.1 micron than it gets carried by the motion of the air molecules, causing it to “wobble”, and in effect covering an area larger than it’s own size. This in turn increases the chance of it hitting one of the fibers.

Source: The Airplane Cabin Environment
Issues Pertaining to Flight Attendant Comfort
By: Elwood H. Hunt and David R. Space

So how effective will a HEPA filter be with removing particles smaller than 0.3 micron?

This depends pretty much on the manufacturer. For example Amaircare HEPA air filters are 95% efficient at 0.1 microns, and IQ Air systems guarantee their products capture at least 99% of all particles below 0.3 microns.

For more information on related products, please choose from the following:

HEPA Air Cleaners |Electrical / Ionic Air Purifiers | Ozone Air Purifiers | Whole House Purifiers | Replacement Filters