While hourly ozone levels in Townsville, Gladstone and South West Queensland have never exceeded the National Environment Protection (Ambient Air Quality) Measure 1-hour average standard of 0.100ppm, in the past 14 years South East Queensland experienced exceedances on 2 days in 2011, and 1 day in 2015, 2018 and 2019. All exceedances are linked to extra emissions of photochemical smog-forming pollutants from major bushfires.
Ozone is a major component of photochemical smog. It is not directly emitted to the atmosphere: it forms when oxides of nitrogen (NOx) and volatile organic compounds (VOCs) react in sunlight. The reaction also forms secondary particles (haze) which can reduce visibility.
The amount of NOx influences the total amount of ozone produced while VOCs and sunlight influence the rate at which it is produced.
The major NOx contributors are fuel-burning processes:
- motor vehicles
- power stations
- industrial combustion.
The most significant sources of VOCs are:
- motor vehicles
- 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 NOx and VOCs that large vegetation fires produce.
Ozone is measured in South East Queensland (SEQ), South West Queensland and Gladstone, and in Townsville until 2016.
Exceedances of the National Environment Protection (Ambient Air Quality) Measure 1-hour average ozone standard of 0.100ppm have only occurred in SEQ.
- Prior to 2006, exceedances occurred on average at least once per year.
- SEQ has experienced exceedances in 4 of the past 14 years — September 2011, March 2015, February 2018 and November 2019.
- These were all associated with bushfires coupled with favourable weather conditions for photochemical smog formation.
- Levels have remained fairly stable over this period with no definite trends.
Higher predicted temperatures due to climate change and an increased incidence of vegetation fires are likely to increase the potential for ozone formation.
Relevant Sustainable Development Goals’ targets
Trends in number of exceedances of National Environmental Protection Measures (NEPM) Air Quality Standards for ozone concentrations (smog) by airshed for the period 2000–2019.