Ozone Air Purifiers

Ozone, a triatomic molecule, consists of three oxygen atoms. Two of these form the basic oxygen molecule necessary for life, while the third acts like a free agent, combining with other substances that react with organic material to form substances that can endanger health. Ozone is a toxic gas.

Outdoor ground-level ozone, a component of smog, is the result of interaction between ultraviolet rays in sunlight and air containing hydrocarbons and nitrogen oxides. Motor vehicle exhaust, industrial emissions, power plants, diesel and gasoline vapors and chemical solvents emit nitric oxides. Volatile organic compounds (VOCs) also interact with sunlight to produce ground-level ozone. This makes it way into homes and contributes to indoor air pollution.

Ozone is harmful to humans and to the environment. Indoors, it has a damaging effect on plants, fabrics, rubber and electrical wire coatings. For humans, exposure can result in chest pain, coughing, throat and airway irritation, congestion and difficulty in breathing. Ozone is also a trigger for asthma and COPD, affecting lung function and causing scarring of lung tissue. It sensitizes the lung to other irritants and increases susceptibility to respiratory illness. Repeated exposure is known to result in irreversible lung damage.

With the explosion of media interest in allergies and respiratory diseases such as asthma, manufacturers have rushed to provide the public with air cleaners, making spurious claims that ozone generators are safe and effective. Ironically, most of the air purifiers tested, including personal wearable air purifiers, produced concentrations of ozone higher than the safety levels established by the Environmental Protection Agency (EPA).1 The EPA has not approved the use of any of these devices in occupied spaces, noting that “Recovery from the harmful effects can occur following short-term exposure to low levels of ozone, but health effects may become more damaging and recovery less certain at higher levels or from longer exposures”.2

Ozone generators do not:
•    improve air quality
•    remove carbon dioxide
•    remove dust and pollen from the air
•    remove formaldehyde from the air
•    remove bacteria, viruses, odour-causing chemicals, mold and tobacco smoke
•    decontaminate indoor air

Ozone generators do
•    react with other chemicals to produce a variety of aldehydes, including formaldehyde
•    increase the concentration of organic chemicals in the air
•    increase the indoor concentrations of formic acid that can irritate the lungs

In a field experiment, Wang and colleagues quantified ozone emission rates on indoor surfaces that involved four homes in summer. They found that a three-hour exposure to ozone resulted in high levels of formaldehyde and other aldehydes, particularly nonanal (an alkyl adhehyde that is a colourless, oily liquid) being emitted by carpets and especially counter tops that are frequently cleaned or which are covered in cooking oil.3 Ozone and the resulting compounds due to its interaction with particles and materials were stated to be “potentially damaging to both human health and materials”.4

Ozone can also be a by-product of ionization. In 2011, Waring and colleagues studied ion generators. They found that regardless of the presence of terpenes (to be found in air fresheners), ion generators also emit ozone resulting in increased levels of formaldehyde and nonanal. They suggest that the use of these devices be limited since the production of ozone would “degrade air quality”. They also noted an increased level of ultrafine respirable organic pollutants when ion generators functioned in the presence of a plug-in air freshener that releases terpenes.5 These respirable particles can be less than 0.7 microns in diameter.6

According to the EPA, ozone generators may produce concentrations that exceed health standards even when used as directed by the manufacturer. The EPA concluded that current scientific evidence shows that “at concentrations that do not exceed public health standards, ozone is generally ineffective in controlling indoor air pollution”. Avoiding the use of ozone generators will help reduce air pollution indoors.

[For the effects of outdoor ozone, a noted air pollutant, please see the article titled “A Breath of Fresh Air . . . and what else?” – with the subtitle ‘Air Pollution and Asthma’]


  1. Britigan N, Alshawa A, Nizkorodov SA. Quantification of ozone levels in indoor environments generated by ionization and ozonolysis air purifiers. J Air Waste Manag Assoc. 2006 May;56(5):601-10. Abstract.
  2. http://www.epa.gov/iaq/pubs/ozonegen.html Accessed August 2015
  3. Wang H, Morrison GC. Ozone-initiated secondary emission rates of aldehydes from indoor surfaces in four homes. Environ Sci Technol. 2006 Sep 1;40(17):5263-8.
  4. Weschler CJ. Ozone in indoor environments: concentration and chemistry. Indoor Air. 2000 Dec; 10(4):269-88.
  5. Waring MS, Siegel JA. The effect of an ion generator on indoor air quality in a residential room. Indoor Air. 2011 Aug;21(4):267-76. doi: 10.1111/j.1600-0668.2010.00696.x.
  6. 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