Ground-level ozone (O3)
Air quality fact sheet
Department of the Environment and Heritage, 2005
In the context of air quality, the concern with ozone is the high levels that can occur at ground level.
This issue is different from depletion of the ozone layer in the stratosphere. Information about the ozone layer can be found at: http://www.environment.gov.au/atmosphere/ozone/index.html
'Photochemical oxidants' is the technical term for the type of smog found in Australian cities during the warmer months of the year. This type of smog can be invisible or it can appear as a whitish haze.
Photochemical oxidants are formed when sunlight falls on a mixture of chemicals in the air. Ozone is one of the main photochemical oxidants. Other chemicals such as formaldehyde are also found and, like ozone, have adverse health effects. Environment agencies measure the level of ozone because it indicates the total amount of photochemical oxidants in the air. Cities that have abundant sunshine over periods of time, together with moderate winds and high temperatures, are most likely to experience high levels of photochemical oxidants.
Ozone is a gas that is formed when nitrogen oxides react with a group of air pollutants known as 'reactive organic substances' in the presence of sunlight. (See fact sheet on air toxics.) The chemicals that react to form ozone come from sources such as: motor vehicle exhaust, oil refining, printing, petrochemicals, lawn mowing, aviation, bushfires and burning off. Motor vehicle exhaust fumes produce as much as 70% of the nitrogen oxides and 50% of the organic chemicals that form ozone.
The natural amount of ozone in the lower atmosphere is generally around 0.04 parts per million (ppm), and that amount is not harmful to human health. Vegetation can also emit organic chemicals that help form ozone. In Melbourne, up to 20% of these organic chemicals can come from vegetation and up to 64% in Brisbane.
Ozone can irritate the lining of the nose, airways and lungs. People who are exposed to enough ozone might feel some pain in their ears, eyes, nose and throat, and they might start to cough. Chest pains can also occur in some people. People with asthma might have more attacks and athletes might find it harder to perform as well as usual.
In most Australian towns and cities, the amount of ozone in the air does not exceed the national standards (see below). Only larger cities, like Australia's capital cities, have occasions when there is enough ozone in the air for it to be a risk to human health. In larger cities, the level of ozone exceeds the national standard several times a year. The highest levels are found most often in Sydney and Melbourne, but Brisbane and Perth can also experience high levels.
Because high levels of photochemical oxidants, particularly ozone, can have adverse health effects, the Australian Government has taken steps to reduce the production of chemicals that lead to their formation. These steps include:
- implementing national fuel quality standards and vehicle emission standards;
- promoting alternative fuels;
- developing pollution forecasting systems for Australia's major cities;
- promoting bicycle use for short journeys through CycleConnect; and
- working with the States and Territories through programs such as TravelSmart to influence passengers' transport choices.
Through the National Environment Protection Council, the Australian, State and Territory Governments have also agreed on a National Environment Protection Measure for Ambient1 Air Quality. The Measure contains national air quality standards for six key air pollutants, including ozone. (See fact sheet on National Standards for Criteria Air Pollutants in Australia) One of the aims of the Measure is to keep ozone in outdoor air below the following levels by 2008:
- 0.10 ppm (parts per million) of ozone measured over a one hour period, with an exceedence2 on only one day a year;
- 0.08 ppm of ozone measured over a four hour period, with an exceedence on only one day a year.
Related publications are available from the Community Information Unit of the Department of the Environment and Heritage, phone 1800 803 772. These include the State of the Air Report: Community Summary 1991–2001 and Air Quality fact sheets on:
- National Standards for Criteria Air Pollutants in Australia;
- carbon monoxide, lead, nitrogen dioxide, particles, sulfur dioxide and air toxics;
- woodheaters and woodsmoke; and
- smoke from biomass burning
See also our Air quality website.