Smog happens when emissions build up under certain weather conditions. The emissions can come from many sources, including: 

• industry 
• motor vehicles 
• home wood heaters
• open burning. 

Different kinds of smog happen in different seasons. 

Smog is a potential risk to human health and the environment. 

Summer smog

Summer smog can happen in Melbourne, usually between October and March. It can also happen in other parts of Victoria during bushfires.

Sunlight interacts with certain gases to form 'gas ozone' and it causes summer smog. As well as gas ozone, summer smog can have other fine particle pollutants. These can be harmful to human health.

Summer smog presents in Melbourne as brown haze in the sky and can limit visibility. It can stay over Melbourne for days when weather is calm, or winds are light and air temperatures are high. When wind picks up, it clears the smog. 

Summer smog in Victoria (publication 1188) has more information on summer smog. 

Autumn and winter smog

Autumn and winter smog can happen anywhere in Victoria during calm weather conditions. It results from a build-up in the air of fine particles from: 

• wood heaters 
• motor vehicle emissions and burning 
• industry
• land burning
• other fire activity. 

Fine particles in the air scatters sunlight and reduces visibility. Autumn and winter smog is present when two or more EPA monitoring stations record any of the below:  

• Visibility in dry air between 7:00 am and 7:00 pm below 20 kms  
• 24-hour PM₁₀ level above 50 mg/m3  
• Level of any other main pollutant, for example carbon monoxide, is above standard.

Find out more about smog

Smog

Smog and your health