Dyson’s Guide to Choosing an Air Purifier for these Hazy Times

Air purifiers come in various shapes and sizes, remove different kinds of air pollutants in your homes, come with an array of specifications, and offer different features. To help you decide on what purifier to purchase, here are three areas to consider.

1. Intelligent Sensing

Some purifiers offer sensing capabilities, and are smart enough to respond by purifying the air automatically when pollutants are detected. To be able to sense, a purifier needs on-board air quality sensors. It should also have software and electronics that will allow it to process that information, and react intelligently to purify the air.

Dyson Pure CoolIn real life, the only way to truly know how well an air purifier is working is to monitor the air quality. Some machines also come with digital displays that show the live indoor quality, and even the types and concentration levels of particles. This enables the user to understand air quality trends in their homes better.

The latest range of Dyson Pure Cool air purifiers have a unique algorithm that processes the input from three on-product sensors to the Dyson Link app and the new LCD in real time. A particulate sensor uses lasers to measure and detect ultrafine particles.  A separate sensor detects the amount of VOCs (Volatile Organic Compounds, such as benzene and formaldehyde, emitted from paint, burning candles and materials in furniture) and NO2 present. A third sensor measures relative humidity and temperature.

2. Capturing: Efficient Filtration 

There are multiple methods of filtration in purifiers to consider. Here are four examples.

Ultraviolet light uses electromagnetic radiation to destroy bacteria, viruses and mould. However, it does not remove dust, allergens or particles in the air.

Activated carbon filters react chemically with pollutants to clear smoke, odours and gases from the air, but alone do not filter out harmful fine particles.

Air ionisers work by sending out a stream of charged ions to attract dust and allergens. However, they can produce ozone as a by-product. Ozone is a respiratory irritant, and a component of smog.

HEPA purifiers work by trapping pollutants and fine particle across a range of different sizes. These include pollen, bacteria, mould, dust mite debris and pet dander. They do not however, remove volatile organic compounds such as formaldehyde, benzene or Nitrogen Dioxide. It is also worth noting that not all HEPA filters are created equal. Some are able to capture ultrafine particles, while others do not.

Some purifiers combine HEPA filters with activated carbon enabling them to remove both particulate matter and volatile organic compounds.

Particles come in a range of sizes. The most commonly measured size is 2.5 microns. Particles of this size are referred to as PM2.5. Comparatively, PM0.1 is much smaller. Known as ultrafine particles, PM0.1 can be inhaled deeply into the lungs, deposited into alveoli to produce a host of harmful effects. Some purifiers can capture particles down to PM2.5, while others go beyond, and can trap particles as small as PM0.1.

The 360 degree fully-sealed filter system inside the Dyson Pure Cool purifying fan combines an activated carbon filter to remove gases, and a Glass HEPA filter that captures 99.95% of microscopic allergens and pollutants as small as 0.1 microns, including allergens, bacteria, pollen and mould. The carbon filter has been coated with Tris (Trishydroxymethylaminomethane) to increase the absorption efficiency, and remove gases including NO2, formaldehyde and benzene.

3. Projection: Whole-room Mixing and Circulation

Finally, projection is an important consideration. Aside from sensing and capturing pollutants, some purifiers can help circulate purified air across the room. This can help in situations where purifiers are placed in the far corner, or the far end of a room. In order to support air circulation and to distribute purified air to people who are some distance away from the machine, some purifiers also double up as fans.

The Dyson Pure Cool features Air Multiplier technology and an expanded 350° oscillation, allowing it to project up to 360 litres of purified air per second to every corner of the room, which ensures proper and uniform purification. The unique and new diffused mode allows for purified air to be projected towards the rear of the machine as opposed to the front, which is a highly relevant feature for times when you don’t want the airflow to be directly blowing on you.

What test standards to consider

Clean Air Delivery Rate (CADR)

The CADR test method involves parking a purifier in the middle of a small chamber, measuring 3.5 x 3.4 x 2.5m. This translates to about 12sqm of floor space. Above the purifier is a ceiling fan, which serves to mix and distribute the purified air within the chamber, and a single air quality sensor sits on one side of the chamber to measure changes in particulate matter concentration levels. While the CADR test is one valid way to look at purification, it does come with limitations –

For one, the size of the CADR test chamber is not reflective of a living space in a real home. Secondly, the test does not test the machine’s ability to project and mix purified air evenly across the environment. Thirdly, purification technology has advanced beyond machine that we turn on and off manually, without an understanding of just how polluted our indoor air quality is. As such, this test does not address how accurate or responsive the machines’ air quality sensors are.


Unlike the CADR test chamber, the POLAR test lab is based on a larger, more realistic room size of 27sqm. It also does not include a mixing fan to help the purifier project purified air around the room. In place of a single sensor, the POLAR test chamber features nine air quality sensors around the room in order to measure the evenness of purification.

Machines are tested via their automatic pollution detection function. This is because most people are not able to detect invisible air pollution, and want their purifier to be able to sense and remove pollution automatically. The test measures the machines’ abilities to remove harmful particles and gases, the uniformity of the cleaning performance delivered across the entire room, and airflow projection. This ensures that purifiers are engineered for efficient filtration and air projection, and not simply for coverage time. The Dyson Pure Cool™ purifying fan is tested to POLAR test standards.