Source apportionment of visibility degradation problems in Brisbane (Australia) using the multiple linear regression techniques

Different aspects of visibility degradation problems in Brisbane were investigated through concurrent visibility monitoring and aerosol sampling programs carried out in 1995. The relationship between the light extinction coefficients and aerosol mass/composition was derived by using multiple linear regression techniques. The visibility properties at different sites in Brisbane were found to be correlated with each other on a daily basis, but not correlated with each other hour by hour. The cause of scattering of light by moisture (bsw) was due to sulphate particles which shift to a larger size under high-humidity conditions. The scattering of light by particulate matter (bsp) was found to be highly correlated with the mass of fine aerosols, in particular the mass of fine soot, sulphate and non-soil K. For the period studied, on average, the total light extinction coefficient (bext) at five sites in Brisbane was 0.65×10−4 m−1, considerably smaller than those values found in other Australian and overseas cities. On average, the major component of bext is bsp (49% of bext), followed by bap (the absorption of light, mainly by fine soot particles, 28%), bsg (Rayleigh scattering, 20%) and bsw (3%). The absorption of light by NO2 (bag) is expected to contribute less than 5% of bext. On average, the percentage contribution of the visibility degrading species to bext (excluding bag) were: soot (53%), sulphate (21%), Rayleigh scattering (20%), non-soil K (2%) and humidity (3%). In terms of visibility degrading sources, motor vehicles (including soot and the secondary products) are expected to contribute more than half of the bext (excluding bag) in Brisbane on average, followed by secondary sulphates (17%) and biomass burning (10%).