Ozone, O3, is composed of three oxygen atoms joined together. Two oxygen atoms joined together form the basic oxygen molecule O2. The additional third atom makes ozone an unstable, highly reactive gas. Ozone is found in two areas of the Earth’s atmosphere: in the upper atmosphere and at ground level. Ozone in the upper atmosphere protects us by filtering out damaging ultraviolet radiation from the sun.

On the other hand, ozone at ground level is damaging to our health. Ground level ozone is the main component of smog and is the product of the interaction between sunlight and emissions from sources such as motor vehicles and industry. Ground level ozone is more readily formed during the summer months and reaches its highest concentrations in the afternoon or early evening.

Ozone can travel long distances and accumulate to high concentrations far away from the sources of the original pollutants. Ground level ozone can be harmful to our health even at low levels. This includes ozone generated by ozone generators.

Potential health effects from exposure to ozone:

  • Irritation and inflammation of eyes, nose, throat and lower airways: coughing, sore and scratchy throat or uncomfortable feeling in chest
  • Reduced lung function: not able to breathe as deeply or vigorously as you normally would
  • Exacerbation of asthma and chronic respiratory diseases such as chronic bronchitis (also called chronic obstructive pulmonary disease or COPD)
  • Increased susceptibility to respiratory infections
  • Can continue to damage lungs when symptoms have disappeared


To learn more, visit our section ‘Who is affected by air pollution’ and ‘Simple steps to protect your health’.For further information on ozone generators, please see our section on air quality factsheets. To learn more about the air quality index, please see our section on air quality index.

Current as at: Monday 29 April 2013
Contact page owner: Environmental Health