Carbon monoxide (CO) is a clear, odourless gas. Smoke and exhaust fumes often contain carbon monoxide.

Carbon monoxide is a common air pollutant. In Victoria, carbon monoxide levels are normally low in the outside air and not harmful to human health. We measure carbon monoxide at some of our air monitoring sites.

Health effects of carbon monoxide

Carbon monoxide can affect your health. However, you’re very unlikely to experience high carbon monoxide levels in the outside air. High levels can happen in enclosed spaces inside. For example, due to a faulty gas heater in your living room.

You can experience serious symptoms from breathing in high levels of carbon monoxide. Unborn babies and people with heart conditions are at greatest risk.

High levels of carbon monoxide can cause ‘flu-like’ symptoms, including:

  • headaches
  • tiredness
  • dizziness
  • nausea.

High carbon monoxide levels can sometimes cause unconsciousness or even death.

Sources of carbon monoxide

Carbon monoxide forms when materials don’t burn completely. Sources of carbon monoxide can include:

Carbon monoxide on EPA AirWatch

We show carbon monoxide data on EPA AirWatch using air quality categories.

Air quality category Carbon monoxide (parts per million) averaged over 1 hour
Good   Less than 30
Fair   Doesn't apply
Poor   30–70
Very poor   Doesn't apply
Extremely poor

  More than 70

Read more about air quality

Air pollution

Nitrogen dioxide in the air

Ozone in the air

PM10 particles in the air

PM2.5 particles in the air



Sulfur dioxide in the air

Air pollution and visibility

Vehicle emissions and air quality

Wood smoke and air quality

Clean air and future air quality

Your health and the environment: learn and take action

Reviewed 16 March 2021