Questions on Ozone

1. What is Ozone (O₃)?
2. How does Ozone affect human health?
3. How are we exposed to Ozone ?
4. Should current Ozone guidelines be reconsidered?
5. Conclusions on Ozone

See also:
General issues & Recommendations

1. What is Ozone (O₃)?

Ozone (O₃) is a gas that can form and react under the action of light and that is present in two layers of the atmosphere. High up in the atmosphere, ozone forms a layer that shields the Earth from ultraviolet rays. However, at ground level, ozone is considered a major air pollutant.

Ground-level ozone– the focus of this study – is formed from other pollutants and can react with other substances, in both cases under the action of light. Concentrations are often low in busy urban centres and higher in suburban and adjacent rural areas, particularly on sunny days in summer. However, ozone can be transported through air over long distances and across borders. Ozone is known to cause adverse health effects, but more research is needed. More...

Source:Queensland Government EPA,www.epa.qld.gov.au

2. How does Ozone (O₃) affect human health?

Short-term exposure to ozone peaks can temporarily affect the lungs, the respiratory tract, and the eyes. It can also increase the susceptibility to inhaled allergens. Long-term exposure to relatively low concentrations of ozone can reduce lung function. More...

2.1 Human population studies at ozone levels currently observed in Europe have reached inconsistent conclusions regarding effects of ozone on the frequency of asthma. They have provided little evidence of long-term effects on lung cancer or mortality. However, results suggest that long-term ozone exposure may affect lung function growth in children. More...

2.2 Ozone appears to have effects on health independently of other pollutants, particularly in the case of short-term exposure to concentration peaks which occur especially in the summer. More...

2.3 The presence of other air pollutants, especially particulate matter, can enhance or otherwise influence the effects of ozone, and vice versa. More...

2.4 Individuals in a population respond differently to ozone exposure, depending on how old they are, if they are asthmatic, how much air they breathe in, and for how long they have been exposed to ozone. The reasons for this difference in responsiveness remain largely unexplained but appear to be partly linked to genetic differences. More...

2.5 No exposure threshold has been identified below which nobody’s health is affected by ozone exposure. This is because different individuals respond very differently to ozone exposure. A threshold has been determined for lung damage and inflammation, but studies on this topic have generally not tested especially sensitive subjects. More...

3. How are we exposed to Ozone (O₃)?

3.1 Ozone (O₃) is formed when other pollutants react under the action of light. It is mainly formed outdoors. More...

3.2 Outdoor ozone levels vary across city areas and times of the day, with peaks in the afternoon. Ozone concentrations indoors are generally 50% lower than those outdoors. Indoor sources of ozone include photocopiers and electrostatic air cleaners. More...

3.3 Unlike levels of other air pollutants, ozone levels tend to be lower in urban polluted areas. This is because ozone disappears when it reacts with other pollutants, such as nitric oxide (NO). At places and times when peak levels occur, short-term exposure can temporarily affect the lungs, the respiratory tract and the eyes, and increase susceptibility to inhaled allergens. Since days with mildly elevated ozone levels are much more frequent than days with high peaks, their overall impact on public health may be expected to be greater. More...

4. Should current O₃ guidelines be reconsidered?

4.1 Though the effects of ozone (O₃) reductions on public health have seldom been evaluated independently from other air pollutants, it was noted that O₃ reductions may have some beneficial effects on lung function and asthma. More...

4.2 It is recommended that a guideline for short-term exposure to ozone be set based on an 8-hour averaging time. Because of insufficient information, no long-term guideline has been recommended yet. More...

4.3 Current WHO Air quality guidelines describe the relationships between exposure to ozone (O₃) and various health effects, and they propose a guideline value for short-term (8-hour) exposure only. New scientific evidence justifies reconsidering these guidelines. More...