CHARACTERIZATION OF TOTAL SUSPENDED PARTICULATE (TSP) ALONG HIGHWAY IN MIDSIZE CITY IN NORTHERN JAPAN

Abstract

Total suspended particulate (TSP) samples were collected along a highway (Barajima air pollution monitoring station) in the center of Akita City in northern Japan, from 9 – 11 May, 1996 (non-snow-clad period) and 7 – 9 February, 1997 (snow-clad period), with a one-hour sampling interval, The elemental composition and particle shape of TSP samples were determined and / or observed by Particle Induced X-ray Emission (PIXE) and a Scanning Electron Microscope (SEM) combined with Energy Dispersive X-ray (EDX) analysis. In the hourly TSP samples collected during the non-snow-clad period, 26 elements were determined. Na, Mg, Al, Si, S, Cl, K, Ca and Fe are the major components. On the other hand, 24 elements, excluding As, Rb and Nb, are found in the snow-clad period samples, and Gallium is only found in the snow-clad period samples. Dominant elements, i.e., major components, of the snow-clad period were the same as the non-snow-clad period. Comparing the arithmetic means of major elemental concentrations in TSP for the non-snow-clad and snow-clad periods, Na, Mg, Al, Si and Fe are similar. However, S and Ca levels in the non-snow-clad period samples were 4 and 6 times higher than those in the snow-clad period samples, respectively, while Cl and K levels in the snow-clad period samples were 1.5 and 2 times higher than those in the non-snow-clad period, respectively. In the non-snow-clad period, the temporal variation pattern of total elemental amount was consistent with the variation pattern of NO and CO, which are pollutants used to observe the effects of automobile exhaust gas, and it was comparatively consistent with the variation pattern of SPM. On the other hand, in the snow-clad period, the temporal variation pattern of total elemental amount was not consistent with the variation pattern of NO and CO when the wind was blowing from the southeast, so the TSP may be strongly influenced by wind direction and wind velocity in addition to automobile traffic. Factor analysis allowed us to identify four major sources, with automobile emission, industry and soil being the major contributors. With the aid of SEM and EDX analysis, aggregates of diesel exhaust particles (DEP), soil particles and small silicon-rich spherical particles were observed in the non-snow-clad and snow-clad period samples.