Size – resolved properties of atmospheric aerosols in Sydney and regional NSW

In recent years it has become evident that the size resolved chemistry of atmospheric aerosols is important in determining their optical properties which in turn determine the way radiation is transmitted through the atmosphere. In this study the seasonal and spatial variations of aerosol chemical and optical properties of Sydney and regional NSW aerosols are investigated. PM2.5 and PM10 samples were collected from four sites during each season of 2003 using Ecotech MicroVol samplers. These samples were analyzed at ANSTO using Ion Beam Analysis to determine their elemental composition. The elemental composition was used to identify seasonal sources at each site using two approaches: composite variables / pseudo elements and Principal Components Analysis. There were seasonal, spatial and size-related variations within sites and between sites and good agreement between the approaches.The elemental composition was then used as input to the thermodynamic equilibrium model, SCAPE2, to predict the inorganic chemical composition of each aerosol sample for the conditions at the time of sampling. Two methods were used to determine seasonal average chemistry: SCAPE2 output for individual days was averaged; and seasonally averaged elemental composition was used as input to the program. The two methods gave similar results. Some seasonal variations in composition were identified, with the largest differences occurring between the urban sites and the rural sites.The chemical composition determined using SCAPE2 plus the other chemical components was used to estimate the refractive index and density at the time of sampling for each site using both molar refraction and mass fraction approaches. The real part of the refractive index was 1.45 – 1.47 ± 0.06 for PM2.5 and 1.45±0.08 for PM10, but strong seasonal and site variations were found for the imaginary part with yearly average of 0.11 – 0.18 ± 0.15 for PM2.5 and 0.06 ± 0.07 – 0.13 ± 0.12 for PM10. The hygroscopic behaviour of refractive index and density was also investigated. Scanning Electron Microscopy was used to determine particle size information for selected samples. This, along with refractive index for those days was used in Mie calculation of the scattering coefficient. The calculated values agreed, within the uncertainties, with nephelometer readings made on those days