When elevated concentrations of particulate matter of less than 2.5 microns (PM_2.5) are measured, it is important to understand the source of the particles to be able to control them. The Upper Hunter Air Quality Monitoring Network (UHAQMN) regularly measures elevated PM_2.5 concentrations in Muswellbrook and Singleton during winter. Because there are multiple sources of PM_2.5, including mining, coal-fired power generation, diesel vehicles, road and rail transport, solid fuel heaters and prescribed burning, the New South Wales Office of Environment and Heritage (OEH) and the New South Wales Ministry of Health commissioned a research study to better understand the composition and likely sources of fine particles that the populations in Muswellbrook and Singleton are exposed to.

The Upper Hunter Valley Fine Particle Characterisation Study (Hibberd et al. 2013) was undertaken at the UHAQMN sites in Singleton and Muswellbrook for the whole of 2012, with samples collected across 24 hours every third day. The samples were analysed using a range of techniques to determine concentrations of organic carbon, elemental carbon, soluble ions (including chloride, nitrate, sulfate, ammonium and sodium), levoglucosan and mannosan (markers for wood smoke); elemental composition; black carbon; and gravimetric mass.

The chemical composition of all the samples from each site was analysed using a mathematical technique called positive matrix factorisation (PMF), which is widely applied internationally for identifying sources contributing to ambient pollution. In the first step, the PMF statistical technique is applied to identify correlations between the concentrations of individual chemical species, grouping correlated species into ‘factors’. Factors have distinct chemical patterns or fingerprints. In this study, 8 factors were identified, with this number of factors found to provide the best explanation of the measured data. Further analysis then identified the most likely source of emissions identified in each factor and the contribution that each source makes to the total PM_2.5 concentrations.

Table ATM6 lists the PMF factors identified based on the dominant sources identified in their fingerprints. The contribution of each factor to total annual PM_2.5 concentrations measured at Singleton and Muswellbrook is also provided.

The annual variation in the contribution of the various factors is shown in Figure ATM35 for Muswellbrook. PM_2.5 levels are higher in the cooler months of the year, from May to October, with wood smoke the dominant contributor: an average of 62 per cent in winter compared with 0 per cent in summer. This is because of emissions from local domestic wood heaters, and the light winds and shallow inversions that are common on cold winter nights, leading to the build-up of pollution levels. In Singleton, wood smoke contributed an average of 38 per cent to the observed winter PM_2.5 concentrations.

In summer, secondary sulfate and pollutant-aged sea salt are the dominant factors. This is because of the higher contribution of fossil fuel combustion–related particles and sea salt during these months, both of which represent large-scale regional sources.

Results from this type of study provide communities with scientific information about what the fine particles are in their local environment. They also add to the evidence base that governments rely on to inform policies and better target programs aimed at reducing fine particle pollution.

Table ATM6 Factors identified in PM_2.5, and their relative contributions and potential sources

NO_x = nitric oxide and/or nitrogen dioxide; NO₂ = nitrogen dioxide; PM_2.5 = particular matter less than 2.5 microns; SO₂ = sulfur dioxide

Source: Hibberd et al. (2013)