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This page provides information on what ozone gas is and its effects on health.  It includes usual levels in New Zealand, and standards and guidelines values to protect human health.

This page has not yet been updated to reflect changes as a result of Our air 2018 report.

Chemical formula and description

Ozone diagram

The chemical formula for ozone is O3.

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


Ozone is present in two different areas of the atmosphere and plays two different roles. It 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 which 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 which can damage our health and the environment.

At the Earth’s surface, ozone is not directly emitted but is formed by reactions of other pollutants such as nitrogen oxides and volatile organic compounds (VOCs), and sunlight. This is known as a photochemical reaction and often produces photochemical smog.

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

Effects on health

Effects on health caused through exposure to ozone can include increased mortality, respiratory and cardiovascular disease.

Short-term health effects include irritation to eyes, nose and throat, coughing and headaches. It contributes to asthma as it 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
older people, particularly those with heart disease

Standards and guideline values to protect health

The national environmental standard for ozone is 150 µg/m3 as a 1-hour average.

The national ambient air quality guideline for ozone is 100 µg/m3 as an 8-hour average.

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

Auckland, Hamilton and Christchurch have the highest potential for ozone pollution.  Monitoring around these centres has indicated no exceedances of the ambient standard.  However, the Musick Point monitoring site in Auckland did exceed the ambient guideline twice in 2002. These exceedances were attributed to pollution from bush fires near Sydney.  

For more information see Environment Aotearoa 2015.

Areas where ozone may affect health and the environment

Given the time required for chemical reactions that form ozone to take place, highest concentrations of ozone occur well away and downwind from cities where the pollutants are usually emitted.