The type of air filters used in an air purifier is one of the key specifications in determining the suitability of an air purifier in fulfilling your air purification needs. Various air filters have been designed to tackle specific indoor air pollutants and allergens so that when they are lined up inside an air purifier, the air passing through the layers of filters can be efficiently purified before being released into indoor environments.
High-efficiency particulate air filters, more commonly known as HEPA filters, are disposable, dry-type air filters with the ability to filter out at least 99.97% of particles as small as 0.3μm in size, as defined in the Australian Standard AS4260:1997. While air purifiers without a HEPA filter exist and are efficient up to a certain degree, HEPA filters are still a standard feature in many air purifier models sold in the Australian market.
While HEPA filters are commonly known for their ability to trap microscopic particles, research done by the Centers for Disease Control and Prevention (CDC) of the United States in 2020 has shown that the use of HEPA air purifiers, coupled with good ventilation, lowers the incidence rate of COVID-19 by 48%. These filters not only trap dust particles, but also any particulates with the size of 0.3μm and above, including bacteria and viruses.
Pre-filters are often seen as the least important of all the air filters in an air purifier. However, being the “gate-keeper”, a pre-filter prevents large airborne debris such as pet fur, hair, and clumps of dust from entering the air purifier and potentially clogging up the delicate HEPA filter. This greatly extends the lifespan of the HEPA filter and ensures that the HEPA filter has more capacity in trapping microscopic particles that are otherwise difficult to remove from the air.
Many pre-filters in the market can be cleaned by gently vacuuming the surface once in a while. Some pre-filters are washable as well. It is recommended to read the user manual or check with the manufacturer before removing pre-filters for cleaning. Regular maintenance of the pre-filter helps to make sure that the air purifier can run optimally without hindered airflow.
Activated carbon filter
Even though HEPA filters are efficient in removing microscopic particles in solid forms, indoor air pollutants in gaseous forms, such as the volatile organic compounds (VOCs), have no issue passing through them. VOCs are the source of odours that come from cigarette smoke, new furniture, and newly painted walls.
To tackle odour issues indoors, activated carbon filters, sometimes known as adsorbent filters or deodorising filters, are required. They capture VOCs through the adsorption process where VOCs are attached to the surfaces of the activated carbon atoms within the filter. The activated carbon technology is commonly used in water filtration systems as well.
Electrostatic filters are made up of two sections—the ionising section consists of wires where airborne particles in the air are given a positive charge when they pass through, and the collection section, where these positively charged particles are attached to negatively charged collection plates, removing them from the air.
Even though electrostatic filters are washable and save you the cost of having to replace air filters every 6 months, air purifiers that use electrostatic filters will be out of service when the filters are left to dry after cleaning. Besides, they potentially emit ozone into the surrounding air when in operation.
Titanium Dioxide (TiO2) filters utilise the photocatalysis process to break down organic compounds such as VOCs through oxidation. The filters are coated with the photocatalyst known as TiO2 which reacts with light to form oxygen radicals. These oxygen radicals react with organic compounds to destroy them, removing odour from the air.
Even though bacteria and viruses are considered organic, a study has shown that TiO2 has a limited germicidal capability when it comes to eradicating airborne germs.
Here’s an example of how some of the air filters are arranged, featuring Ionmax ION430.
Understanding the properties of various air filters not only helps you make good decisions in choosing an air purifier for your home, but it also prolongs the lifespan of your air purifier as you’d be equipped with the knowledge of how to maintain its filters properly. Aside from air filters, you can also look into other air purification technologies designed to enhance air purifier performance, such as ionisers and UV lights, before deciding on the air purifier that suits your needs best.
Disclaimer: The information provided in this article is for general reference only. Please seek advice from professionals according to your needs.