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Ozone

An ozone molecule is made up of three oxygen atoms. Chemical formula and description

The chemical formula for ozone is O3.

Ozone is a very reactive gas that can absorb Ultra Violet (UV) radiation.

Sources

Ozone is present in two different areas of the atmosphere and plays two different roles. Ozone is produced naturally in the outer layers of the atmosphere (the stratosphere) very high above earth. This stratospheric ozone helps protect the planet from the Sun's ultraviolet rays that can damage our skin and health. This ozone is typically known as the ozone layer.

Although ozone is vital in the stratosphere, here at the Earth’s surface, it is a pollutant that can damage our health and the environment.

Rather than being discharged, ozone is formed by other compounds reacting together in the air rather than being discharged itself – it is called a secondary pollutant. Ozone is formed by reactions of primary pollutants in the sunlight such as nitrogen oxides and volatile organic compounds (VOCs) (known as a photochemical reaction) and often produces photochemical smog.

Primary pollutants are produced mainly from motor-vehicle emissions, other combustion sources, and industrial and domestic use of solvents and coatings.

Effects on health

Studies show a wide variety of effects caused from exposure to ozone. In the short term, these include irritation to your eyes, nose and throat, coughing and headaches. It also contributes to asthma. Ozone can affect how your lungs perform.

Groups most sensitive to ozone

People with asthma and lung disease, healthy adults exercising for long periods of time outdoors, and older people, particularly those with heart disease.

Guideline values to protect health

In any 1-hour period, the average concentration of ozone in air should not be more than 150 µg/m3.

In any 8-hour period, the average concentration of ozone in air should not be more than 100 µg/m3.

Effects on ecosystems

Ozone and other chemicals formed by photochemical reactions are toxic to plants in high concentrations. They can affect photosynthesis and plant respiration, reduce growth rates, and affect reproduction.

Effects on buildings

Ozone is corrosive to most materials at high concentrations, including plastics and metals.

Effects on visibility

Photochemical reactions in the atmosphere produce fine particles, such as sulphates, nitrates and organic aerosols in the air. These contaminants scatter light and can affect visibility.

Usual levels in New Zealand

There has been little monitoring of ozone in New Zealand. Recent studies found that atmospheric conditions suitable for photochemical reactions occur around 10 days per year in Auckland, 15 days in Hamilton and 4 days in Christchurch. In Auckland, breaches of the guideline values were found at sites 35-40 kilometres north and south of the city. More monitoring is underway.

Areas where ozone may affect health and the environment

Because ozone forms over time, the highest concentrations are usually found in rural areas away from areas such as major cities where most contaminants are released.