Chemical characterization of particles in winter-night smog in Tokyo

Continuous measurement of PM10, PM2.5 and carbon (organic, elemental composition) concentrations, and samples of PM10 and PM2.5 collected on a polycarbonate membrane filter (Nuclepore®, pore size: 0.8 μm), were carried out during a period from December 1998 to January 1999 at Shinjuku in Tokyo in order to investigate the chemical characterization of particles in winter-night smog within a large area of the Japan Kanto Plain including the Tokyo Metropolitan area. These were measured using an ambient particulate monitor (tapered element oscillating microbalance—TEOM) and a carbon particulate monitor. Elemental compositions in the filter samples of PM10 and PM2.5 were determined by means of particle-induced X-ray emission (PIXE) analysis. Ionic species (anion: F−, Cl−, NO3−, SO42− and C2O42−; cation: Na+, NH4+, K+, Ca2+ and Mg2+) in the filter samples were analyzed by ion chromatography. The temporal variation patterns of PM2.5 were similar to those of PM10 and carbon. PM2.5 made up 90% of the PM10 at a high concentration, and 70% at a low concentration. Concentrations of 22 elements in both the PM10 and PM2.5 samples were consistently determined by PIXE, and Na, Mg, Al, Si, S, Cl, K, Ca, Fe, Zn and Pb were found to be the major components. Among these S and Cl were the most dominant elements of the PM2.5 and PM10 at high concentrations. Ionic species were mainly composed of Cl−, NO3−, SO42− and NH4+. The component proportion of carbon, the other elements (total amount of measured elements other than S and Cl) and secondary-formed particles of PM2.5 was similar to that of PM10. The major component was carbon particles at a low concentration and secondary-formed particles at a high concentration. The proportion of NH4NO3 and NH4Cl plus HCl in secondary-formed particles at a high concentration, in particular, was as high as 90%.