Optical properties of Sydney aerosols

Abstract

Aerosol chemistry for PM2.5 and PM10 (particulate matter less than 2.5- and 10-μm aerodynamic diameter) samples collected in the Sydney region between November 2002 and December 2003 had been used to estimate size-resolved refractive index for Sydney. Seasonal PM10–2.5 chemistry was obtained by subtracting seasonal PM2.5 from seasonal PM10 chemical composition. The chemical compounds present were determined from the elemental composition using two methods: the SCAPE 2 chemical thermodynamic model and aerosol types based on marker elements. Refractive index was then calculated using a mass fraction approach. Both methods agreed within the error bars indicating that useful optical properties can be derived from elemental chemistry. For the fine mode (PM2.5), the real component of the refractive index was 1.46 ± 0.07 with no seasonal variation, but there were sea-sonal variations in imaginary component, 0.05 ± 0.02 in summer and 0.23 ± 0.05 in spring. The coarse mode (PM10–2.5) real refractive index was constant throughout the year at 1.47 ± 0.09, whereas the im-aginary refractive index was 0.01 ± 0.04 in summer and 0.04 ± 0.06 in spring. Representative refractive indices were then used to calculate aerosol scattering properties for three different size distributions to illustrate how this information could be used.