Ozone air purifiers and generators: what you need to know

In recent years, ozone air purifiers have decreased in popularity amongst consumers in the home and the workplace. Understandably so: these devices may be doing more harm than good. What are ozone generators? What does Eoleaf recommend? Read on to learn more.

What is ozone?

Ozone is a highly-reactive, colourless gas that is both natural and man-made. Its chemical structure consists of three oxygen atoms: O3. Ozone can either be beneficial or harmful to human health depending upon where it is found in the atmosphere: the stratosphere or the troposphere. As coined by the Environmental Protection Agency (EPA), ozone is ‘good up high, and bad nearby’1.

A diagram of atmospheric layers

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Good ozone

Stratospheric ozone, also known as ‘good ozone’, is an essential part of the Earth’s atmosphere. It is found 25 to 30 kilometres (10 to 20 miles) from the Earth’s surface. Its purpose is to protect all life on our planet from the dangers of the sun’s ultraviolet rays.

Having initially been discovered in 1973, the famous ‘hole in the ozone layer’ prompted worldwide concern. What had caused the hole? Humans’ use of ozone-depleting substances (ODS) was causing our stratospheric ozone layer to degrade. ODS include CFCs and HCFCs, halons, methyl bromide, carbon tetrachloride, and methyl chloroform, substances commonly found in home and professional appliances like refrigerators, foam, fire extinguishers, air conditioners, and soil fumigants4. When released into the atmosphere, ODS remain intact whilst passing through the troposphere, but they significantly degrade when exposed to ultraviolet light in the stratosphere. Their degradation releases ozone-depleting chlorine or bromine atoms3.

The discovery of the hole in the ozone layer in 1973 led to the signing of an international treaty called the Montreal Protocol in 1987. This treaty required all United Nations member states to reduce CFC use by 20% by 1994 and 50% by 1998. In September of 2000, the hole reached its maximum size, the largest ever recorded since 1979, measuring 28.4 million km2. This is equivalent to about seven times the size of the European Union5

Annual progression of the ozone hole from 1979 to 2022

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Thankfully, as a result of swift action and control taken by UN member states to phase out ODS, the ozone layer is expected to make a full recovery by the mid-21st century, 30 years earlier than predicted5. Kofi Annan, former UN Secretary-General, has been declared the Montreal Protocol ‘perhaps the single most successful international agreement to date’6. A healthy ozone layer means that life on Earth will continue to be protected from the sun’s rays for many years to come.

Bad ozone

Ozone found in the troposphere is also referred to as ‘ground-level ozone’ or ‘bad ozone’. Ground-level ozone is a secondary pollutant. It is not directly emitted into the atmosphere but is formed when chemical reactions take place between other airborne pollutants, specifically nitrogen oxides (NOx) and volatile organic compounds (VOCs), in the presence of sunlight. NOx and VOCs can also have natural sources, but they are typically emitted into the air when fossil fuels and coal are burned. Vehicles, industry, and domestic use are some of the most common anthropogenic sources of these pollutants7.

How ozone forms in the atmosphere

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This is the type of ozone that is harmful to human health.

The impact of ozone on health

Ozone can cause a host of negative health effects to both humans and animals.

Who is most at risk?

The most vulnerable groups of individuals experiencing adverse effects due to ozone are the same groups that are most at risk of experiencing air pollution-related disease. They include:

People who perform vigorous exercise outdoors are also at high risk as they have a higher level of exposure to ozone.

What are the effects on health due to ozone exposure?

Exposure to ozone has a variety of effects on health. Some of the most common effects are:

  • Respiratory system and eye irritation
  • Headaches
  • Coughing
  • Reduced lung function and capacity
  • Difficulty breathing and shortness of breath
  • Chest pain
  • Aggravation of respiratory diseases like asthma (triggering of asthma attacks)
  • Increased risk of premature death from heart or lung disease9

Additionally, a 2007 study found that ozone exposure has an impact on the early immune response. This makes it more difficult for the human body to fight off infections from bacteria and viruses. Ultimately, a compromised immune system leads to higher risk of falling ill from bacteria and viruses like COVID-19, school absences, work absences, doctors’ visits, and emergency room visits10.

The dangers of ozone air purifiers and generators

How do they work?

Ozone generators work by taking oxygen, O2, from the air and giving it a strong electrical charge. This forces the oxygen molecules to rearrange, forming ozone, O3, as a result. Some commercial ozone generators emit 5,000 mg of ozone or more per hour into the room.

An ozone-emitting device

Why are they unsafe?

Manufacturers of ozone-generating devices claim that when ozone reacts with airborne pollutants in a room, it renders those air pollutants completely harmless, producing only carbon dioxide, oxygen, and water as byproducts. The EPA has conducted a review of scientific studies on the efficacy of ozone generators and has found these claims to be not only baseless, but potentially harmful.

The following provides a summary of the EPA’s findings:

  • Ozone does not react with common indoor air pollutants , and even if it did, it may take months or years for the reaction to take place
  • Ozone generators cannot remove carbon monoxide, also known as the ‘silent killer’, or formaldehyde, a known carcinogen and VOC
  • The chemical reaction that occurs between ozone and the chemicals with which ozone does react creates harmful byproducts and more toxic airborne pollutants, endangering respiratory and overall health
    • This includes aldehydes, formic acid, and a general increase in concentration of airborne organic chemicals
    • These substances may cause lung and respiratory irritation and can be reactive themselves, leading to potentially more harmful byproducts
  • The removal of airborne allergenic particles, like pollen and dust, does not occur when exposed to ozone
  • Ozone generators do not combat unpleasant odours and smells: one study found that ozone may mask body odour smells but does not remove it
  • Ozone would need to be diffused into rooms in concentrations that are 5 to 10 times higher than public health standards allow (levels that would cause health concerns) for the removal of bacteria and viruses enough to prevent their proliferation

The EPA went as far as to state that ozone air sterilisers introduce ozone at such high concentrations that it may directly lead to adverse health effects. These ozone air cleaners often diffuse 0.5 to 0.8 ppm of ozone which is 5 to 10 times the limits of public health standards12.

What does Eoleaf recommend?

Eoleaf’s recommendations are in perfect alignment with the recommendations made by the EPA. When dealing with indoor air pollution, the EPA recommends the following steps:

Combat the air pollution at its source

A common example is if you are experiencing allergies and poor indoor air quality due to mould growth in your home. Controlling and treating the mould itself is crucial. Unfortunately, not all airborne pollutants can be combatted at their source. If you live in an urban environment or near areas with high levels of outdoor pollution (like a motorway or an industrial or construction site), the likelihood is that you are breathing significant levels of fine particle air pollution in your indoor spaces that may have a severe impact on your health. Also, when mould is present in the home, the removal of airborne spores is necessary in order to disrupt mould’s spread.


It is important to air out your home or workplace by opening doors and windows regularly which helps to renew stale, polluted indoor air with clean outdoor air. Again, sufficient ventilation may not be possible in some situations. Some of the situations in which ventilation may prove difficult include safety concerns with opening doors and windows, inability to open windows (as seen in many schools, blocks of flats, and office buildings), extreme outdoor temperatures (hot or cold), or the presence of high levels of outdoor air pollution.

Install an air purifier

The last step recommended by the EPA is to install a high-quality air cleaning device or air purifier. This is where Eoleaf comes in. Our devices, equipped with HEPA-certified filters as part of our proprietary 8-step filtration technology (8 filters and depollution methods in one filter block), remove 99.97% of all indoor air pollutants down to a size of 0.01 microns. This includes:

Our devices also contain activated carbon filters which are very effective at removing bad odours and smells from your home or workplace!

Eoleaf's 8-step filtration method

Even if you are able to properly ventilate your home or office, keep in mind that opening windows and doors may encourage more outdoor air pollution to enter your indoor space. This is why it is recommended to invest in an air purifier like Eoleaf’s that comes equipped with Automatic mode and other smart features. Upon sensing new indoor air pollutants, your air purifier will jump into action and automatically increase its fan speed until pollutant levels return to those that are safe (as recommended by the World Health Organization).

The technologies used in Eoleaf’s devices are not only certified ozone-free (meaning that they do not emit any ozone), it also removes ozone from your breathing air. Protect your health from the dangers of ozone with Eoleaf.


1 Ozone and your patients’ health | US EPA. Environmental Protection Agency. (2023, August 23). https://www.epa.gov/ozone-pollution-and-your-patients-health

2 NC Climate Education. NC State University. (2023). https://climate.ncsu.edu/edu/OzoneLayer

3 Ozone-depleting substance. European Environment Agency. (2017, February 14). Retrieved April 27, 2023, from https://www.eea.europa.eu/help/glossary/eea-glossary/ozone-depleting-substance

4 Ozone depleting substances. Department of Climate Change, Energy, the Environment and Water. (2021, October 3). Retrieved April 27, 2023, from https://www.dcceew.gov.au/environment/protection/ozone/ozone-science/ozone-depleting-substances

5 Environmental Protection Agency. (2021, August 30). International Treaties and Cooperation about the Protection of the Stratospheric Ozone Layer. EPA. Retrieved April 27, 2023, from https://www.epa.gov/ozone-layer-protection/international-treaties-and-cooperation-about-protection-stratospheric-ozone

6 United Nations. (2023, September 16). Ozone Day. United Nations. https://www.un.org/en/observances/ozone-day

7 Government of Canada / Gouvernement du Canada. (2016, May 19). Common air pollutants: ground-level ozone. Canada.ca. Retrieved April 27, 2023, from https://www.canada.ca/en/environment-climate-change/services/air-pollution/pollutants/common-contaminants/ground-level-ozone.html

8 Environmental Protection Agency. (2022, June 14). Ground-level Ozone Basics. EPA. Retrieved April 27, 2023, from https://www.epa.gov/ground-level-ozone-pollution/ground-level-ozone-basics

9 Ozone harmful to humans, plants and vegetation. Ontario newsroom. (2008, July 29). Retrieved April 27, 2023, from https://news.ontario.ca/en/backgrounder/2056/ozone-harmful-to-humans-plants-and-vegetation

10 Duke University Medical Center. "Ozone Shuts Down Early Immune Response In Lungs And Body." ScienceDaily. ScienceDaily, 3 October 2007. Retrieved October 31, 2023, from www.sciencedaily.com/releases/2007/09/070930083243.htm.

11 Hubbard HF, Coleman BK, Sarwar G, Corsi RL. Effects of an ozone-generating air purifier on indoor secondary particles in three residential dwellings. Indoor Air. 2005 Dec;15(6):432-44. doi: 10.1111/j.1600-0668.2005.00388.x. PMID: 16268833.

12 Ozone generators that are sold as Air Cleaners | US EPA. Environmental Protection Agency. (2023, June 27). https://www.epa.gov/indoor-air-quality-iaq/ozone-generators-are-sold-air-cleaners

Eoleaf's range of air purifiers

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