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Ground-level ozone (O₃)

Air quality fact sheet
Department of the = Environment=20 and Heritage, 2005

In the context of air quality, the concern with ozone is the high = levels that=20 can occur at ground level.

This issue is different from depletion of the ozone layer in the=20 stratosphere. Information about the ozone layer can be found at:=20 http://www.environment.gov.au/atmosphere/ozone/index.html

What are photochemical oxidants and = ozone?

'Photochemical oxidants' is the technical term for the type of smog = found in=20 Australian cities during the warmer months of the year. This type of = smog can be=20 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=20 chemicals such as formaldehyde are also found and, like ozone, have = adverse=20 health effects. Environment agencies measure the level of ozone because = it=20 indicates the total amount of photochemical oxidants in the air. Cities = that=20 have abundant sunshine over periods of time, together with moderate = winds and=20 high temperatures, are most likely to experience high levels of = photochemical=20 oxidants.

Ozone is a gas that is formed when nitrogen oxides react with a group = of air=20 pollutants known as 'reactive organic substances' in the presence of = sunlight.=20 (See fact sheet on air=20 toxics.) The chemicals that react to form ozone come from sources = such as:=20 motor vehicle exhaust, oil refining, printing, petrochemicals, lawn = mowing,=20 aviation, bushfires and burning off. Motor vehicle exhaust fumes produce = as much=20 as 70% of the nitrogen oxides and 50% of the organic chemicals that form = ozone.=20

The natural amount of ozone in the lower atmosphere is generally = around 0.04=20 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,=20 up to 20% of these organic chemicals can come from vegetation and up to = 64% in=20 Brisbane.

How does ozone affect human health?

Ozone can irritate the lining of the nose, airways and lungs. People = who are=20 exposed to enough ozone might feel some pain in their ears, eyes, nose = and=20 throat, and they might start to cough. Chest pains can also occur in = some=20 people. People with asthma might have more attacks and athletes might = find it=20 harder to perform as well as usual.

How much of a problem is ozone in=20 Australia?

In most Australian towns and cities, the amount of ozone in the air = does not=20 exceed the national standards (see below). Only larger cities, like = Australia's=20 capital cities, have occasions when there is enough ozone in the air for = it to=20 be a risk to human health. In larger cities, the level of ozone exceeds = the=20 national standard several times a year. The highest levels are found = most often=20 in Sydney and Melbourne, but Brisbane and Perth can also experience high = levels.=20

What's being done to manage ozone and = other=20 photochemical oxidants?

Because high levels of photochemical oxidants, particularly ozone, = can have=20 adverse health effects, the Australian Government has taken steps to = reduce the=20 production of chemicals that lead to their formation. These steps = include:

implementing national fuel quality standards and vehicle emission=20 standards;=20
promoting alternative fuels;=20
developing pollution forecasting systems for Australia's major = cities;=20
promoting bicycle use for short journeys through = CycleConnect;=20 and=20
working with the States and Territories through programs such as=20 TravelSmart to influence passengers' transport choices.

Through the National Environment Protection Council, the Australian, = State=20 and Territory Governments have also agreed on a National Environment = Protection=20 Measure for Ambient¹=20 Air Quality. The Measure contains national air quality standards for six = key air=20 pollutants, including ozone. (See fact sheet on National=20 Standards for Criteria Air Pollutants in Australia) One of the aims = of the=20 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,=20 with an exceedence²=20 on only one day a year;=20
0.08 ppm of ozone measured over a four hour period, with an = exceedence on=20 only one day a year.

For more information

Related publications are available from the Community Information = Unit of the=20 Department of the Environment and Heritage, phone 1800 803 772. These = include=20 the State=20 of the Air Report: Community Summary 1991=962001 and Air Quality = fact sheets=20 on:

National=20 Standards for Criteria Air Pollutants in Australia;=20
carbon=20 monoxide, lead,=20 nitrogen=20 dioxide, particles,=20 sulfur=20 dioxide and air=20 toxics;=20
woodheaters=20 and woodsmoke; and=20
smoke=20 from biomass burning

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Last updated: Wednesday, 16-Sep-2009 11:53:02 = EST

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Ground-level ozone (O3)