PM consists of microscopically small solid particles or liquid droplets suspended in the air. Exposure to PM has been correlated with serious public health effects, such as higher instances of asthma, decreased lung function in children, increased hospital admissions and elevated mortality rates (WHO 2013).
PM10 is both primary and secondary in origin, and has often exhibited a seasonal cycle dependent on bushfire smoke and episodic dust storms. Concentrations of the secondary pollutant, in PM10 are sensitive to temperature. In winter, wood heaters are a significant source of PM10 in smoke for both urban and rural areas. In the 2011 assessment (which included data up to and including 2008), AQIs were good to very good for all Australian cities for PM10 (Figure ATM33); they have improved to very good for all cities except Darwin in the current assessment. The 50 µg/m3 NEPM was exceeded in 2012 in Darwin, and is part of a worsening of the assessment between SoE 2011 and SoE 2016. All the 2012 exceedances in Darwin took place during the dry season and were caused by smoke drifting into the airshed from biomass burning activities nearby (NT EPA 2013).
The September 2009 dust storm affected New South Wales and Queensland, and produced extreme 24-hour PM10 concentrations of 1000–2000 µg/m3 across many regions, including Sydney and Brisbane. This dust contained a significant fraction of fine PM, with 24-hour average PM2.5 concentrations reaching 150–200 µg/m3.