Nitrogen dioxide (NO2)


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

What is nitrogen dioxide?

Nitrogen dioxide is a nasty-smelling gas. Some nitrogen dioxide is formed naturally in the atmosphere by lightning and some is produced by plants, soil and water. However, only about 1% of the total amount of nitrogen dioxide found in our cities' air is formed this way.

Nitrogen dioxide is an important air pollutant because it contributes to the formation of photochemical smog, which can have significant impacts on human health.

The major source of nitrogen dioxide in Australia is the burning of fossil fuels: coal, oil and gas. Most of the nitrogen dioxide in cities comes from motor vehicle exhaust (about 80%). Other sources of nitrogen dioxide are petrol and metal refining, electricity generation from coal-fired power stations, other manufacturing industries and food processing.

Unflued gas heaters and cookers are the major sources of nitrogen dioxide in Australian homes.

How does nitrogen dioxide affect human health?

The main effect of breathing in raised levels of nitrogen dioxide is the increased likelihood of respiratory problems. Nitrogen dioxide inflames the lining of the lungs, and it can reduce immunity to lung infections. This can cause problems such as wheezing, coughing, colds, flu and bronchitis.

Increased levels of nitrogen dioxide can have significant impacts on people with asthma because it can cause more frequent and more intense attacks. Children with asthma and older people with heart disease are most at risk.

How much of a problem is nitrogen dioxide in Australia?

Since the early 1990s, even the highest levels of nitrogen dioxide reached in most Australian towns and cities are thought to be acceptable for humans.

In some of Australia's larger cities, it is possible that the concentration of nitrogen dioxide sometimes increases for a short time to levels that have an adverse health effect on people who are most at risk. Air pollution authorities are monitoring the situation to see if this is the case.

What's being done to manage nitrogen dioxide?

Because high concentrations of nitrogen dioxide can have adverse effects on human health, the Australian Government has taken steps to manage and reduce the amount of nitrogen dioxide produced. These include:

  • implementing national fuel quality standards;
  • supporting the implementation of tighter vehicle emission standards;
  • developing a National Environment Protection Measure for diesel, to improve the in-service performance of diesel vehicles;
  • developing and 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 standards for six key air pollutants in Australia, including nitrogen dioxide. (See fact sheet on National Standards for Criteria Air Pollutants in Australia). One of the aims of the Measure is to keep nitrogen dioxide in outdoor air below the following levels by the year 2008:

  • 0.12 ppm (parts per million) over a one hour period
  • 0.03 ppm averaged over a one year period.

These levels, when averaged over one hour or one year, have not been exceeded in any Australian capital city since the early 1990s.

For more information

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, ozone, particles, sulfur dioxide, air toxics; woodheaters and woodsmoke; and smoke from biomass burning.

See also our Air quality website.


1 In this context, 'ambient' means 'outdoor'.