Physicochemical characterization and size-resolved source apportionment of airborne particles in Himeji City, Japan

As a part of epidemiological study on the effects of the chemical composition of airborne particulate matter (PM) and ozone on asthma attacks, we carried out size-resolved sampling of PM in Himeji City, Japan and elemental and ionic composition analyses of the PM samples. Size-resolved PM was collected using a 3-stage NLAS impactor (Tokyo Dylec Co., Ltd.; particle cut size at sampling stages was 10, 2.5 and 1.0 μm for a flow rate of 3 L/min) with a 1-week sampling interval from November 2009 to May 2012. Concentrations of several elemental and ionic species in the PM samples were determined by PIXE and ion chromatography analysis, respectively. In addition, source apportionment analysis of the PM was performed by positive matrix factorization (PMF) model using the analytical data of size-resolved particles. The research results are important for the physicochemical characterization of PM in the atmosphere, enabling evaluation of various PM emission sources and atmospheric processes. Of particular note is that the PM10 consisted mainly of NO3- and SO42-, and PM2.5 consisted only of SO42-. This is believed to suggest the different formation processes of NO3- and SO42-. Based on the results from the PMF model analysis, the particles larger then PM2.5 were estimated to have been from soil and sea salt particles. On the other hand, the particles smaller than PM2.5 were estimated to have been from soot, smoke and secondary particles. In particular, the majority of particle smaller than PM1.0 were estimated to be secondary sulfate particles.