Which air purifier for your seasonal allergies?

Sept. 23, 2021

Spring is in the air! But how safe are you indoors and can you make it any safer for you and your family? The Cleaner Air research team at the University of Melbourne, led by A/Prof Robyn Schofield, provide some helpful tips on how to choose the right device.

Spring is in the air! A statement that usually bring up images of tiptoeing through the tulips; but for allergy and asthma sufferers it’s time to take cover.

For nearly 4.6 million people in Australia spring means a runny nose, sneezing, watery or itchy eyes.

Services such as the Melbourne Pollen Count and Forecast can help many sufferers plan their day and week ahead by providing users with sophisticated pollen forecasts for a range of aeroallergens.

But how safe are you indoors? Many of us spend 90% of our day inside. These indoor spaces can also be full of air pollutants such as pollen, dust and animal hair, that aggravate conditions like hayfever and asthma.

Air cleaners (sometimes also called air purifiers or scrubbers) have been used for decades to filter out particles in the air from our homes, offices, and classrooms.

Air cleaners are portable devices that you can use in an indoor space to reduce unwanted air particles.

How do air cleaners work?

Air cleaners usually consist of a filter, or multiple filters, and work by pulling in air from within a room and filtering out the pollutants such as smoke, pollen and respiratory aerosols and returning clean air to the room. Typically, filters are made of paper, fibre (often fibreglass), or mesh, and require regular replacement to maintain efficiency.

Most don’t remove gases, although the activated carbon filter does remove odours (known as volatile organic compounds or VOCs) from the air.

Types of filters

There are many different types of air cleaners and multiple filter types, though not all filters are the same.

  • HEPA filters: High-Efficiency Particulate Arresting (HEPA) filters are considered to be the most effective filters at targeting common allergens. Theoretically, HEPA filters remove at least 99.97% of dust, pollen, mould, bacteria, and any airborne particles with a size of 0.3 microns (µm).
  • Activated carbon filters: The carbon filtration system work through a method called adsorption, wherein pollutants such as smoke, chemicals and odours, in the air are treated and trapped inside the pore structure of a carbon media. However, they don’t filter allergens and bacteria and need to be replaced frequently.
  • Ozone generators: Ozone is a molecule composed of three atoms of oxygen. It is an unstable molecule that reacts with anything it bumps into. The chemical effectively removes odours and kills mould and mildew, but this type of device does not remove allergens or pollutants such as fine air particles. In fact, inhaling ozone, even in small amounts, can irritate the lungs and be very harmful. Specific effects may include throat irritation, coughing, chest pain and shortness of breath, as well as an increased risk of respiratory infections.
  • Ionization: Ionization of the air is performed using an electrical field to charge pollutants, making them stick to either a charged plate inside, or surfaces outside the devices. While this is somewhat effective in removing small particles, many of these devices don't have inbuilt fans and can therefore be ineffective for whole-of-room particle removal. Ionization also produces ozone and nitrogen oxides which can irritate the lungs and trigger asthma. While these devices essentially create lightning inside, and charge the air and deliver fast results, they can also be dangerous to our health.
  • Ultraviolet (UV) irradiation: air cleaners that employ UV are designed to use short-wave ultraviolet light (UV-C light) to inactivate airborne pathogens and microorganisms like mould, bacteria and viruses. UV filters can kill bacteria. However, in order to work, most bacteria need to be exposed for an extended period of time – much longer than most cleaners allow. UV-C is dangerous to skin and eyes and has the potential to produce ozone – so safety is also a concern with this technology in portable devices.

Which air purifier works best?

For allergy or asthma sufferers, an air purifier with a HEPA + activated carbon filter is likely to be most helpful as it is the most efficient in removing fine airborne particles and dust, pollen, mould and bacteria.

HEPA filters also remove 99.97 per cent of aerosolised virus particles in the air, which is of great interest in the current COVID-19 pandemic.

Associate Professor Robyn Schofield and her team from the University of Melbourne conducted a comparison of air cleaners based on clean air delivery and value for money.

The team collated devices available on the Australian consumer market. They provided purchasing guidance for products that are safe – that is they only use HEPA and activated carbon filtration and don’t operate as directional fans without filtration

Comparison of air cleaners based on clean air delivery and value for money. Graphic: University of Melbourne

Comparison of air cleaners based on clean air delivery and value for money. Graphic: University of Melbourne

Many popular brands didn’t meet these criteria, however many did, including the locally manufactured InovaAir device.

Things to avoid

  • Ioniser/plasma/ozone/photocatalytic oxidation/precipitators and UV purification or disinfecting add-ons. These are unproven/untested technologies, and in some cases actually dangerous technologies, significantly degrade the air quality by producing ions, ozone and oxidation products. Ozone and ions can also trigger asthma, so these technologies should be avoided
  • Directional fans without filtration blow air from person to person and could lead to unintended transmission for viruses

Things to consider when purchasing

  • When choosing an air purifier, the most important factor to consider is the type of filter (or filters). Look for an air purifier that has a HEPA filter.
  • The Clean Air Delivery Rate (CADR) needs to be sufficient for the room volume
  • Maximum tolerable noise. Fans can be noisy, and it can sometimes make sense to have two air quiet (40dB) cleaners rather than one large cleaner (50dB)
  • Cost. Prices can vary and you will also factor in the cost of replacement filters as you will need to replace them regularly to keep your air purifier working effectively.
  • Ideally Australian made

If you do decide to purchase an air purifier to reduce allergy symptoms, keep in mind that the effectiveness and noise of the devices can vary greatly. It is important to consider what air pollutants you would like to filter, and the size of the room you will be using it on.

Declaration: No funding from air cleaner manufacturers has been received to prepare this information piece. Indoor air does not have regulatory standards in Australia, and independent testing of air cleaning devices is not performed. If you found this information useful and would like more information you can contact A/Prof Robyn Schofield and the Cleaner Air research team at the University of Melbourne.

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