Major study findings
- Fine particles (PM2.5) in the atmosphere contain a significant amount of organic matter in both autumn and summer, and high levels of sea salt in summer.
- Major sources of secondary organic particles in the air include volatile organic compounds (VOCs) from vegetation in summer and wood heaters in autumn.
What is the Sydney Particle Study?
Commissioned by the former Office of Environment and Heritage, the Sydney Particle Study (2010–13) aimed to provide:
- an improved understanding of the particle sources the population in the Sydney region is exposed to
- a qualitative model of such sources.
One of the most comprehensive observation and modelling studies of fine particles undertaken in Australia to date, this study involved:
- CSIRO
- the former Office of Environment and Heritage within the former Department of Planning and Environment
- NSW Environment Protection Authority (EPA)
- Australian Nuclear Science and Technology Organisation (ANSTO)
- Queensland University of Technology (QUT)
- Bureau of Meteorology (BOM)
- Shanghai Institute of Applied Physics
- Chinese Academy of Sciences (SINAP).
Air quality in Sydney is comparable with other cities in Australia and good by world standards. However, particle pollution and ozone concentrations occasionally exceed national air quality standards.
Particles in the air vary in size, with particles less than 10 microns in diameter (PM10) and fine particles less than 2.5 microns in diameter (PM2.5) being routinely monitored. These small particles can pass into the lungs and even the bloodstream. Inhalation of particles is associated with an increased risk of respiratory and cardiovascular disease. Fine particles are also moved by wind and other weather conditions, and can produce effects many kilometres from their source.
Particle pollution comes from:
- natural sources such as bushfires and dust storms
- human activities such as wood burning, mining, industrial processes and motor vehicle use
- chemical reactions between gases or between gases and other particles in the air.
The study comprised observation (measurement) programs and the development and implementation of a modelling framework.
Two observation programs were undertaken at Westmead located 26 kilometres west of the Sydney CBD to characterise particles under summer conditions (February to March 2011) and autumn conditions (April to May 2012).
Particle measurements accounted for:
- particle number and size
- particle mass
- light scattering by particles
- particle composition.
The chemical composition of gaseous pollutants which form particles through chemical reactions in the air was also measured.
The modelling framework included meteorological modelling and chemical transport modelling of pollutants released from natural and human activities.
Summer observations
The summer observations identified the major components of fine particles (PM2.5) as:
- Sea salt emissions from waves breaking in the open ocean and coastal surf breaks (34% of measured average PM2.5)
- Organic matter, including primary particles released from sources such as car exhaust, and secondary organic particles formed in the atmosphere (34% of measured average PM2.5). Up to 70% of organic matter assessed through the study could be secondary organic particles formed from gases released by biogenic sources.
- Secondary inorganic particles (15%), soil (11%) and elemental carbon (6%) were also present in significant amounts.
Secondary inorganic particles are fine particles of sulfate, nitrate and ammonium produced by chemical reactions in the atmosphere from sulfur dioxide, oxides of nitrogen and ammonia emissions. Elemental carbon is emitted directly to the air from sources such as vehicles, wood heaters and bushfires.
Autumn observations
During the autumn observation program:
- Organic matter was identified as the major component of fine particles (PM2.5), including primary particles released from sources such as car exhaust, and secondary organic particles formed in the atmosphere (57% of measured average PM2.5).
- Elemental carbon (16%), secondary inorganic particles (15%), soil (7%) and sea salt (5%) were also observed to be present in autumn PM2.5 particles.
Compared with summer readings, levels of sea salt in fine particles (PM2.5) were lower during the autumn study. Organic matter comprised a larger portion of the PM2.5 particles measured. The contribution from elemental carbon was also larger compared with summer, while the secondary inorganic contribution was about the same.
Chemical transport modelling
Chemical transport modelling indicated that the release of volatile organic compounds (VOCs) from vegetation was a major source of secondary organic particles during summer, whereas wood heaters were a dominant source of such particles in autumn.
In summary, this combined monitoring-modelling study showed seasonally varying composition of fine particles, with natural emissions such as sea salt and biogenic emissions (VOCs from vegetation and bushfires) contributing significantly to background PM2.5 concentrations. Secondary particles formed in the air were modelled to account for over 40% of the PM2.5 concentrations measured during the autumn and summer observational periods.
The department is using data and modelling tools from the study to develop its particle models to account for chemical transformation and secondary particle formation. Advanced particle modelling will provide more evidence to guide NSW air policy in future years.