Ozone (O3) is a gas. High in the atmosphere, it protects us from UV radiation. But at ground level, ozone is a pollutant.

Ozone can occasionally cause poor air quality during summer. It’s the main pollutant in summer smog. We measure ozone at some of our air monitoring sites.

Sources of ozone

Ozone forms when volatile organic compounds (VOCs) and nitrous oxides react together in the atmosphere. This happens during warm, sunny weather. The main sources of VOCs and nitrous oxides include:

Read more about ozone depleting substances.

Read more about protecting the ozone layer.

Health effects of ozone

Breathing in high levels of ozone can irritate the lining of your throat and lungs. This can make it difficult to breathe. People most sensitive to ozone include:

  • those with lung conditions
  • children
  • people over 65.
Infographic showing: the sources of ozone. how we’re exposed to ozone and the health impacts of ozone.

Ozone on EPA AirWatch

We show ozone data on EPA AirWatch using air quality categories.

Air quality category Ozone averaged over 1 hour (parts per billion)
Good   Less than 50
Moderate   50–100
Poor   100–150
Very poor   150–300
Hazardous   More than 300

Current standards for ozone

We compare our ozone data to national air quality standards. Victoria has adopted a more stringent ozone standard in the Environment Reference Standard.
National standard, in parts per million (and parts per billion) Averaging time
0.065 ppm (65 ppb) 8 hours
Environment Reference Standard  
0.060 ppm (60 ppb) 8 hours

Read more about air quality

Air pollution

Carbon monoxide in the air

Nitrogen dioxide 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 30 March 2022