Key finding

Ozone is a major component of photochemical smog. It is not directly emitted to the atmosphere: it forms when oxides of nitrogen (NO_x) and volatile organic compounds (VOCs) react in sunlight. The reaction also forms secondary particles (haze) which can reduce visibility.

The amount of NO_x influences the total amount of ozone produced while VOCs and sunlight influence the rate at which it is produced.

Fuel-burning processes are the major NO_x contributors:

• motor vehicles
• power stations
• industrial combustion.

The most significant sources of VOCs are:

• motor vehicles
• industry
• biogenic emissions from vegetation.

While the potential for significant amounts of ozone to be produced only occurs on warm sunny days under light wind conditions, elevated levels of ozone have been observed when bushfires are prevalent due to the combined NO_x and VOCs that large vegetation fires produce.

Ozone is measured in South East Queensland (SEQ) and Gladstone, and in Townsville until 2016.

Exceedances of the National Environmental Protection Measures (NEPM) air quality standards have only occurred in SEQ, and only during two of the past 12 years (September 2011 and March 2015). The exceedances in 2011 and 2015 were both associated with added emissions of precursor pollutants from bushfires coupled with favourable weather conditions for photochemical smog formation. Levels have remained fairly stable over this period with no definite trends. Prior to 2006, exceedances occurred on average at least once per year.

Higher temperatures predicted in the future due to climate change are likely to increase the potential for ozone formation.

More information:

• Air quality

• Next Visibility-reducing particles