All about ionisation

What is ionisation?

What does an air ioniser do?

Eoleaf’s air purification devices serve as both air purifiers and air ionisers. But you may be asking yourself: what, exactly, is an air ioniser? Simply put, an air ioniser is a device capable of generating and diffusing negatively-charged ions (negative ions) with the goal of improving indoor air quality. It is the only method used to ‘actively’ filter your air in our devices. Rather than purifying the air by passing it through the purifier, ionisation diffuses negatively-charged ions directly into the ambient air. This allows real-time protection of the targeted space undergoing air purification.

By generating a localised electric arc in the electric field, it removes positive charges (a positive ion or cation) from a neutral molecule. This creates a negative ion (or anion). These negative ions (which are negatively-charged) are then diffused into the air via eight conductive filaments, as you will read below. An air ioniser applies a strong electric charge to fight against airborne pollutant molecules, making your air feel cleaner due to the lack of air pollutants clouding your indoor space1.

A woman doing yoga


Ozone-generating products have been marketed as an efficient way to clean indoor air and potentially remove other air pollutants. Products using ozone to clean the air were used in places like public transport during the COVID-19 pandemic. However, ground-level ozone is a harmful, irritating indoor pollutant that has negative effects on human health and the environment.

As a secondary pollutant, ozone is not emitted directly through domestic or industrial practices. Instead, ground-level ozone is created when other air pollutants form chemical reactions when exposed to sunlight. Read more about ozone in our article here.

Eoleaf has been able to develop powerful ionisation technology all without emitting harmful ozone. Thanks to an innovative design that uses eight separate conductive filaments, our devices generate more than 20 million ions per cm3. At a distance of one metre, they generate more than 6.3 million ions; and at a distance of 3 metres, 0.5 million ions. All with a total radius of 5 metres.

Our air purifiers use air ionisers that only start to emit ozone when two conditions are met: 1) when it reaches a certain value in the electric field, and 2) when the electronic density is high enough in the air. We designed our air purifiers to avoid these ozone-generating events from occurring by dividing our discharge outlet in eight different filaments. We use ‘needlepoint bipolar ionisation’ with a voltage charge of 5.0 kV. This technology has been utilised for twenty years and sends electrical charges from the point of a small metal needle.

‘Corona discharge ionisation’, another ionisation technology, leads to emission of harmful levels of ozone. It uses the corona effect to ionise the air which concentrates a high-voltage electric field. It is worth noting that any form of ionisation leads to some generation of ozone, but it is negligible (less than 0.05 PPM). That is why many air ionisers have now switched to this ‘ozone-free’ technology.

We also tested our units (using Octopus Labs) and were able to confirm that, if they emit any ozone at all, it would be less than 0.01 PPM. This test was simply for the sake of transparency since, even if our units did emit ozone, it would be filtered/reabsorbed by the activated carbon filter and photocatalysis, two other technologies we use in our systems.

You can also turn the ioniser function off if you so wish.

A dandelion blowing in the wind

Ionisation targets which types of pollution?

Particulate pollution: fine particles and nanoparticles

Ionisation is a technique that is particularly recognized for its high efficacy against particulate pollution (fine particles and nanoparticles found in smoke and dust, for example). Negative ions are highly reactive (due to their polarity). They attach themselves to pollution particles and molecules of positive polarity and will either disintegrate these positively-polar particles or will weigh them down and drop them to the ground, far away from your lungs.

A 2023 study tested five different types of air ionisers over a period of seven days. A source of fine particulate pollution was emitted into the air (in this study, smoke formed by burning incense was used). The devices that use bipolar ionisation were by far the most efficient at fighting fine particle pollution. As seen below, BAI Model 4, a device that uses bipolar ionisation technologies, decreased particulate matter concentration by 79.7% for PM2.5 and 80.4% for PM102

A bar graph showing how ionisation technologies reduce particulate matter concentrations

Source 2

Moreover, according to the above study, air ionisers using bipolar ionisation technologies were not observed to release abnormal amounts of ozone. This is why Eoleaf’s devices all use bipolar needle ionisation.

Bacteria and viruses: germs and the flu virus

Studies are still being undergone on this particular subject, but ionisation has also shown promising in its ability to remove airborne germs. Targeting their membranes and changing their functions, negative ions were shown to attack bacteria and viruses.

Three studies in particular have shown the benefits of negative ions in fighting against viruses and bacteria:

  • Evidence of negative ions’ efficiency on viruses dates back to studies in 1954: one study found that though the presence of water protects some viruses from inactivation, ionisation radiation on water leads to the formation of hydrogen and hydroxyl radicals, having a deactivation effect on viruses3
  • A 2015 study on laboratory guinea pigs showed that the effect of an air ioniser protected 100% of the animals from infection of the influenza A virus, calicivirus, and rotavirus4
  • A 2018 study has found negative ions to have ‘multiple health benefits and positive effects on humans/animals, that negative ions inhibit growth and/or kill certain microorganisms, and even promote plant development’5
A zoomed up view of a virus

Ionisation’s benefits

Improve indoor air quality and inhibit mould proliferation

Throughout the past century, negative ions have been established as having a significant effect on indoor air quality. Negative ions are attracted to common indoor air pollutants like dust, mould spores, pollen, and other allergens5. (Remember: fungal allergens like mould and mildew proliferate by releasing spores into the air to allow them to spread to other locations of your space! Removing airborne spores stops the spread).

Once negative ions seek out and bind themselves to air pollutants, the collective weight forces the pollutants to fall to the ground and/or surfaces. This protects your lungs from inhaling those air pollutants. However, be sure to dust and hoover after your negative ion treatment to ensure removal of chemicals and contaminants from your room or space.

Does ionisation fight VOCs?

Ionisation has proven to be effective in removing multiple types of air pollution from your indoor air. Unfortunately, they do not have an effect against airborne chemicals or gaseous pollutants like volatile organic compounds (VOCs). This is why we always recommend purchasing an air purifier that comes equipped with multiple air purification technologies as opposed to ‘just’ an air ioniser. An air purifier containing an activated carbon filter is the best way to combat indoor VOCs.

Eoleaf’s devices contain our proprietary 8-step air purification technology. With 8 different filtration and depollution technologies, our devices combat the three main types of air pollution:

  1. Biological pollution (allergens, germs, mould and spores)
  2. Chemical pollution (airborne chemicals and VOCs like formaldehyde, benzene, and toluene, all known human carcinogens)
  3. Fine particle pollution (particulate matter including PM10, PM2.5, and PM0.1, like those found in fossil fuel burning, all types of smoke, and dust)

Thanks to our combination of technologies including HEPA-certified filters, activated carbon filtration, ionisation, and photocatalysis, our devices are guaranteed to eliminate 99.97% of pollutants down to a size of 0.01 microns, including airborne chemicals like VOCs.

  • Note: ‘HEPA-type’ filters do not undergo third-party testing and are, therefore, not guaranteed the same amount of filtration as HEPA-certified filters.
Eoleaf's 8-step purification technologies

Well-being and health benefits

The bipolar needle ionisation technology used in Eoleaf’s devices is recognised and particularly powerful for its anti-pollution effects. However, the line is not drawn there: there are other benefits that are associated with ionisation.

While studies are still in the preliminary stages, research has begun to show that negative ions are commonly associated with a feeling of well-being and improved mood5. This phenomenon is commonly experienced in natural environments such as mountains, forests, and waterfalls. A natural space contains an amazing amount of negative ions: 100 to 1000 times more than the air of a city or urban environment!

Certain studies have also reported numerous health benefits thanks to the presence of negative ions. Negative ions have been shown to boost your immune system, improve your blood circulation, decrease stress levels, and improve the quality of your sleep5.

In summary, while the word ‘negative’ in ‘negative ions’ may naturally give it an undesirable connotation, they are beneficial for health. Positive ions have the opposite effect. The presence of positive ions often points to poor air quality and high airborne chemical concentrations. Positive ions are said to have many harmful effects on health and are generally associated with a feeling of increased stress, tension, and fatigue. Urban and polluted environments often have high concentrations of positive ions.

Eoleaf's AEROPRO 100 air purifier releasing negative ions

Frequently asked questions

What are the dangers associated with ionisation?

The process of ionisation is safe. However, the danger is when an ioniser emits ozone. Ozone is an irritating air pollutant that may cause many unpleasant respiratory symptoms including coughing, throat irritation, chest pain, shortness of breath, and difficulties breathing. Ionisers that emit ozone may also produce fine particles that may cause aggravation of asthma and other respiratory conditions. Before making your purchase, ensure that your ioniser is certified ozone-free.

Is ionisation technology safe for indoor air quality?

Ionisation technologies are completely safe for air quality as long as the device does not emit ozone. In fact, negative ions are very effective at combatting fine particles released from pollen, smoke, road traffic, industrial processes, etc.

Are there any potential health risks associated with ionisation technology?

The only potential health risks with ionisation may be caused if the ioniser emits ozone. If the device is certified ozone-free, it is beneficial in fighting indoor air pollution, particularly in removing harmful fine particles.

Does ionisation technology produce any harmful byproducts during air purification?

If the device is certified ozone-free, it is completely safe and a great tool in fighting indoor air pollution. If this is not the case, ozone is a harmful air pollutant that irritates the upper airways. It may lead to respiratory symptoms and aggravation of respiratory conditions like asthma, allergies, and COPD.



Cheng Qian 2021 J. Phys.: Conf. Ser. 2029 012026. doi:10.1088/1742-6596/2029/1/012026

2 Gupta, N., Agarwal, A.K., Singhal, R. et al. A Comparative Assessment of the Some Commercially Available Portable Bipolar Air Ionizers Particulate Pollutants (PM2.5, PM10) Removal Efficacies and Potential Byproduct Ozone Emission. Aerosol Sci Eng 7, 315–324 (2023). doi:10.1007/s41810-023-00182-9

3 Pollard, E. (1954). The Act of Ionizing Radiation on Viruses. Advances in Virus Research 2, 109-151. Retrieved from

4 Hagbom M, Nordgren J, Nybom R, Hedlund KO, Wigzell H, Svensson L. (2015, June). Ionizing air affects influenza virus infectivity and prevents airborne-transmission. Retrieved from

5 Jiang SY, Ma A, Ramachandran S. Negative Air Ions and Their Effects on Human Health and Air Quality Improvement. Int J Mol Sci. 2018 Sep 28;19(10):2966. doi: 10.3390/ijms19102966. PMID: 30274196; PMCID: PMC6213340.

Eoleaf's range of air purifiers

1 of 4