Carbon Monoxide (CO)


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

What is carbon monoxide?

Carbon monoxide is a gas and is found in air. High levels of carbon monoxide are poisonous to humans and, unfortunately, it cannot be detected by humans as it has no taste or smell and cannot be seen.

The natural concentration of carbon monoxide in air is around 0.2 parts per million (ppm), and that amount is not harmful to humans. Natural sources of carbon monoxide include volcanoes and bushfires.

The main sources of additional carbon monoxide are motor vehicle exhaust and some industrial activities, such as making steel.

Tobacco smoke is one of the main indoor sources of carbon monoxide.

How does carbon monoxide affect human health?

Carbon monoxide affects healthy and unhealthy people. Increased levels of carbon monoxide reduce the amount of oxygen carried by haemoglobin around the body in red blood cells. The result is that vital organs, such as the brain, nervous tissues and the heart, do not receive enough oxygen to work properly.

No more than 2.5% of haemoglobin can be bound to carbon monoxide before some health effects become noticeable. At very high concentrations of carbon monoxide, up to 40% of the haemoglobin can be bound to carbon monoxide in this way. This level will almost certainly kill humans.

For healthy people, the most likely impact of a small increase in the level of carbon monoxide is that they will have trouble concentrating. Some people might become a bit clumsy as their coordination is affected, and they could get tired more easily.

People with heart problems are likely to suffer from more frequent and longer angina attacks, and they would be at greater risk of heart attack. Children and unborn babies are particularly at risk because they are smaller and their bodies are still growing and developing.

How much of a problem is carbon monoxide in Australia?

In most Australian towns and cities, the levels of carbon monoxide in air are below levels that are hazardous for human health. Only larger cities, like some of our capital cities, have the potential to have harmful levels of carbon monoxide.

What's being done to manage carbon monoxide?

Because raised levels of carbon monoxide can have significant impacts on human health, the Australian Government has taken steps to manage and reduce the amount of carbon monoxide produced. These include:

  • implementing national fuel quality standards;
  • promoting alternative fuels; and
  • supporting the implementation of tighter vehicle emission standards.

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 includes national standards for six key pollutants, including carbon monoxide. (See fact sheet on National Standards for Criteria Air Pollutants in Australia.)

One of the aims of the Measure is to keep the concentration of carbon monoxide in the air to less than 9 ppm (measured over eight hours) by the year 2008. This aim was largely achieved ahead of the 2008 goal, demonstrating that the steps taken to limit sources of carbon monoxide have been successful.

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:

See also our Air quality website.


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