Source apportionment of fine and coarse atmospheric particles in Auckland, New Zealand

Atmospheric fine particles (with a diameter less than 2.5 μm) and coarse particles (with a diameter between 2.5 and 10 μm) were collected simultaneously at an urban background site in Auckland, New Zealand, in the summer and winter of 2003. Major water-soluble ions, black carbon (BC), and some elements in the samples were analysed, and the data compiled into two sets. Selected trace gases (NH3, HONO, HNO3, and SO2) were also collected at the same time. Application of positive matrix factorisation to the particle data resolved five sources for the fine particles and five for the coarse particles. Weighted multiple linear regression was used to investigate the mass contributions of the sources. It was found that although natural sources had significant contributions to the coarse particles, anthropogenic sources dominated the contributions to the fine particles, particularly in winter. Significant seasonal changes of the sources were observed. Overall, sea salt and wind-blown soil had significantly stronger contributions in the summer; in contrast, the winter contribution of vehicle emissions, road dust, and industry and incineration sources was significantly higher. These seasonal changes may be explained by variations in meteorological conditions and atmospheric chemistry. The nonparametric correlations between the atmospheric concentrations of the trace gases and the mass contributions of the resolved sources demonstrate that these sources are realistic, providing a useful supplementary approach for the assessment of receptor modelling.