The High Efficiency Particulate Air Filter, is the most popular and cost-effective method of filtering air.
They are capable of trapping particles as small as 0.3 microns with an efficiency of 99.97%.
A HEPA filter consists of millions of tiny fibres that form a dense web which traps particles in different ways.
- Impact: When a particle directly collides with the fibres and gets trapped
- Interception: when a particle is trapped between two fibres
- Diffusion: when a particle hits a fibre, reducing its travelling speed, and then is caught by another fibre.
HEPA filters are not only used in air purifiers, but you can also find them in N95 and N99 masks and in vacuum cleaners.
It is important to know that HEPA filters can only trap solid particles. They cannot filter out gases or odours.
An Activated Carbon filter is the perfect companion for the HEPA filter. While the HEPA filter is great for capturing solid particles, the carbon filter is used to adsorb gases, in particular Volatile Organic Compounds such as formaldehyde and benzene and odours such as cigarette and fresh paint smell.
The activated carbon filter works under the principle of adsorption, where particles from VOCs and smells stick to the outside of the activated carbon molecule.
Even though it can filter out VOCs and many smells, an activated carbon filter cannot fully remove carbon monoxide. It is also hard to determine when the filter is saturated and needs replacement.
Ionizers have become quite popular and can be found in many air conditioners apart from air purifiers.
This technology uses electricity to emit a cloud of negative ions with the purpose of attracting positively charged pollutants in the air. These particles then get stick to surfaces such as furniture and walls instead of flying around.
Ionizer technology is a bit controversial as humans are not made to breath ionized air and it doesn’t really remove pollutants but makes them stick in surfaces which could end up being your lungs.
Also, they can produce tiny quantities of Ozone in small indoor areas which can be very toxic for human beings.