Ozone State of Knowledge Study

Learn more about the findings from a scientific study into ozone pollution and events contributing to high ozone levels in the Sydney, Illawarra and the lower Hunter regions.

What is the Ozone State of Knowledge Study?

The Ozone State of Knowledge study, completed in 2010, consolidated and expanded knowledge on ground level ozone pollution in New South Wales.

The study included the analysis of ozone concentration measurements from the NSW Air Quality Monitoring Network for the period 1994–2004, with a detailed description provided of ozone events occurring in the Sydney, Illawarra, lower Hunter (Newcastle) and Bathurst regions during this period.

Ozone is formed in the air from the photochemical reaction of oxides of nitrogen (NOx) and volatile organic compounds (VOCs) in the presence of sunlight. The CIT airshed modelling system, able to account for ozone formation and transport, was used to better understand events contributing to high ozone levels. Modelling was undertaken for four ozone exceedance days occurring in December 2000 and January 2001; case study days being selected to account for most typical chemistry and meteorological conditions giving rise to ozone exceedances in the Sydney Basin.

Regional air quality modelling was also used to investigate how changes in the emissions to air of ozone precursor pollutants (NOx, VOCs) would affect ozone levels in future years to 2026.

More information is available in the study report (PDF 7.9MB).

What did the study find out about ozone?

The Sydney Basin experienced more frequent exceedances of the national air quality standard for ozone. Ozone exceedances were more infrequent in the Illawarra and lower Hunter regions, with no exceedances reported in Bathurst.

High ozone levels mainly occur in warm months, with ozone exceedance days in most cases occurring on days with maximum air temperatures of over 30°C. Other meteorological conditions, such as land and sea breeze circulations, contribute to the circulation of ozone precursor pollutants within the Sydney Basin and the formation of ozone over inland areas such as south west Sydney.

Ozone exceedances are usually localised and of short duration, with maximum ozone levels most likely to occur in western Sydney. Bushfires can significantly contribute to ozone concentrations, with more ozone exceedance days being measured during hot, bushfire affected periods.

Ozone chemistry was studied using the Integrated Empiric Rate (IER) model developed by CSIRO. Most ozone exceedance days were found to be NOx-limited, particularly in western Sydney. This means that reducing NOx emissions is expected to be effective in reducing ozone concentrations on such days. On thirty percent of ozone exceedance days in central and eastern Sydney it was concluded that ozone reductions would not benefit from NOx control alone.

CIT airshed modelling results showed that reducing emissions of both NOx and VOCs is important for reducing ozone pollution levels within the Sydney basin, with reductions in VOC emissions in the short-term and longer-term strategies to reduce NOx emissions beneficial.

Increases in population and associated growth were noted to be a potential challenge for achieving the emission reductions required, with motor vehicle emissions being the most significant source to control ozone levels into the future.

How are the results of this study used?

This study provided a better understanding of ozone levels and factors contributing to high ozone levels in the Sydney basin, Illawarra and lower Hunter regions. The results from this study have contributed to the evidence base that the NSW Government relies on to inform policies and programs to reduce ozone pollution.