Development of a method for analyzing the composition of ambient PM_2.5 floating dust particles by micro-PIXE

In this paper, we developed a technique for analyzing individual PM_2.5 particles using micro-PIXE. PM_2.5, a designation for extremely small particulate matter (PM) in the air, has recently become the center of attention because high levels of PM_2.5 were recorded in parts of western Japan, especially Fukuoka Prefecture, in January 2013. For a better understanding of their formation mechanism, analysis of individual particles is indispensable. We collected PM_2.5 on a $4\mu \text{m}$ thick Prolene foil using a multi-nozzle cascade impactor at Fukuoka Women’s University, Fukuoka, Japan. Its elemental analysis was carried out using a micro-PIXE system at Tohoku University. Although elemental concentration ratios of scanned areas were similar, those of individual particles were quite different from each other. Elemental concentration ratios for individual particles were categorized into five groups, indicating that the PM_2.5 particles came from at least five different sources. Although elemental concentrations obtained by averaging over single particles formed in different processes will lose detailed information, we were able to derive comprehensive elemental compositions of individual PM_2.5 particles using our novel technique. The individual particle analysis technique for PM_2.5 will provide important information to identify pollution sources and particle formation mechanisms.