Identification of Sources of PM2.5 and PM10 Aerosols in Brisbane

Urban health problems and visibility degradation problems are associated with particulate matter in the air, especially PM10 and PM25 (particles with aerodynamic diameter less than 10 j.tm and 2.5 jsm, respectively). The aim of this study was to investigate the characteristics and sources of PM25 and PM20 aerosols in Brisbane. This study collected aerosol samples over a period of two and a half years at five sites around Brisbane. Source samples of soil dusts, road-side dusts and sea salt were also collected and analysed to provide information on source emission composition. The aerosol samples were analysed by a wide range of techniques, including Ion Beam Analysis and Scanning Electron Microscopy, for their chemical composition and particle size distribution. Some methodologies have been specifically developed in this study. The results presented here show that the chemical composition of PM20 aerosols in Brisbane varies largely with particle size and locations. The chemical composition of the samples are generally related to the land use near the monitoring sites. On average, the major components in the PM10 aerosol samples at five sites in Brisbane were identified as: crustal matter (27% by mass), organic matter (16%), sea salt (12%), soot (11%), and ammonium sulphate (7%). Among the Australian studies, in general, the results show that the composition of the PM25 aerosol samples collected at the Griffith University site (Brisbane) is closest to those of the New South Wales samples. The samples from Melbourne and Perth are generally richer in industry-and vehicle-related species. The major components of the PM25 aerosols at the GU site were identified as: organic matter (27% by mass), elemental carbon (23%), ammonium sulphate (14%), sea salt (9%) and crustal matter (6%). The results show that contribution of emission sources also has large particle size, temporal and spatial variations. Based on the results of source apportionment from the chemical mass balance method, the major contributors of PM20 aerosol mass in samples collected at five sites in Brisbane were found to include: soiL/road-side dusts (25% by mass, results of analysis also indicate a higher contribution from road-side dusts than from soil dusts), motor vehicle exhausts (13%, more than 80% of which are from diesel trucks/buses), elemental carbon and secondary products (around 15%), sea salt (12%), Ca/Ti-rich compounds from cement plant and mineral processing industries (11%), and biomass burning and bioaerosols (7%). On average, the PM25 aerosol mass at the Griffith University (GU) site was found to have contributions mainly from sources related to combustion. These sources include elemental carbon (24% by mass), secondary organics (21%), biomass burning (15%) and secondary sulphate (14%). Although motor vehicle exhausts contribute directly to only 6% of the PM25 aerosol mass at the GU site, their actual contribution could be substantial because most of the elemental carbon and secondary products are related to motor vehcile exhausts. On average, the results show that the visibility degradation problems in Brisbane are worse in winter/autumn than in summer. Soot and sulphate particles are the main visibility degrading species. In terms of visibility degrading sources, the main contributors are (excluding the contribution of NO2 gas): motor vehicles (up to 50%, including the secondary products), secondary sulphates (17%) and biomass burning (10%). In general, emission sources which contribute more to the fine particle fraction, and to gaseous pollutants, are most responsible for the aerosol associated health problems and visibility degradation problems. In Brisbane, these sources include motor vehicle exhausts, soil dusts, biomass burning and industrial dust.