Air Purifiers - A Guide to the Technology

There are quite a variety of air purifiers on the market. Their objective is to improve the quality of the air we breathe and eliminate airborne pollutants, be they odours, particles or bacteria and viruses.

Here is a brief guide to the technology used inside the main air purifiers currently available for home use:

HEPA Filter
HEPA stand for “High Efficiency Particulate Air”. This technology was developed during the 1940’s as part of the Manhattan Project (the development of the first nuclear bomb) with the objective of capturing airborne radioactive particles. The filter system comprises of a mat of randomly arranged fibres that can remove airborne particles that are 3 micrometers or larger in size. To put that in perspective, a human hair is 70-100 micrometers.

Air purifiers that incorporate HEPA filters use a fan to draw the air through the filter. They are very effective at removing airborne pollutants but will need replacement filters from time to time and due to the fan, will make some noise. Often these types of air purifiers have different power settings for maximum or quiet operation.

Active carbon
This type of filtration is used to remove odours and chemicals from the air. Active carbon, or activated carbon as is it often called, is micro-porous and has a very large surface area that absorbs chemicals on a molecular basis. It is often used in conjunction with other filters, typically HEPA, as by itself it is not capable of removing larger particles from an atmosphere.

Ioniser / Plasma ioniser
An ioniser produces electrically charged molecules called negative ions. These adhere to particles in the air and encourage them to fall out of the atmosphere, as they are attracted to positively charged surfaces.

Some ionisers, such as plasma ionisers, will contain an internal electrostatic plate. As the air enters the air purifier the pollutants are bombarded with charged ions that adhere to the pollutants. These ion-charged pollutants are attracted to the electrostatic plate as they travel through the air purifier, thus removing them from the air.

Germicidal UV / TiO2 technology / Photocatalytic Oxidation
Exposure to ultraviolet (UV) light will oxidize airborne organic pollutants breaking down their DNA and destroying them. This technology is effective at removing 99.9% of germs and bacteria. This is not a filtration process so is often used in addition to other physical barrier methods to catch particles, such as a HEPA filter. This prevents particles from “shadowing” bacteria stopping them from being degraded.

In addition to UV light, TiO2 technology can be employed to amplify the effectiveness of the UV oxidisation.

UV bulbs will dull with age and need to be replaced about once a year.

Incinerators
An incinerator type air purifier, such as the AirFree, works by drawing air through the core of a ceramic cylinder with high internal temperatures (around 250 degress C). The heat incinerates any airborne particles, viruses and bacteria. A major advantage with this system is that it is totally silent and does not require replacement filters.

Ozone generators
Ozone generators are used to remove residual smells from a room. Although it is important to remove the source of the odour otherwise it will return. Ozone is a power oxidising agent that attacks organic compounds like mould, bacteria and spores. These are often used in nursing homes, hotel rooms, by second hand car dealers and in waste storage areas to remove odour.

The more ozone that is produced by a unit, the larger an area it can treat. However, ozone is harmful to humans in high concentrations so should be used in unoccupied areas. Once a room is ventilated the ozone rapidly degrades to oxygen and is harmless. Some units are designed to provide small amounts of ozone for use in occupied areas such as public toilets.

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