The National Environment Protection Measure (NEPM) sets standards in Australia for ambient air quality to protect human health and the environment.
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. VOCs and sunlight influence the rate at which ozone is produced.
The major NOx contributors are fuel-burning processes, including:
- 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 NOx and VOCs that large vegetation fires produce.
Ozone is measured in Southeast Queensland (SEQ), South West Queensland (SWQ) and Gladstone. It was measured in Townsville until 2016.
Exceedances of the National Environment Protection (Ambient Air Quality) Measure 8-hour average ozone standard of 0.065ppm have only occurred in SEQ and SWQ.
- Before 2008, exceedances occurred on average at least once a year in SEQ.
- Since 2008, SEQ has experienced exceedances in four of the past 16 years — in September 2011, October 2012, February 2018 and November/December 2019.
- SWQ has experienced exceedances in two years of the past six — in December 2019 and October 2021.
- These exceedances were all associated with bushfires combined with favourable weather conditions for photochemical smog formation.
- Apart from short-term increases in years with enhanced bushfire activity, ozone levels have remained stable over the past 16 years in all regions 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.
