Relationship between PM_2.5, water-soluble organic carbon and oxidants in Tokyo during the summer

Abstract

PM_2.5 continuous monitors equipped with beta radiation attenuation/light scattering photometry detectors have been operated at four sites in Tokyo. The hourly concentrations of SO₄^2- and water-soluble organic carbon (WSOC) were analyzed using the instruments tape filters. The Measurement of the PM_2.5 using low-volume samplers and the chemical analysis including the carbon fraction were also performed at two sites to ensure the values of the continuous monitors and to determine the ratio of the WSOC to organic carbon. The PM_2.5 concentrations in the summer tended to increase when the high concentrations of the oxidants in consecutive days were observed. The SO₄^2- and WSOC concentrations were the major components in the PM_2.5. The WSOC concentrations were higher at the sites in which the O_X concentrations were higher although the differences in the SO₄^2- concentrations between the sites were not very clear. This indicates that the secondary formation of organic particulates occurred in the Tokyo area. The amount of the secondary organic matter may be around ten percent of the PM_2.5 mass. The Correlation of K⁺, which is an indicator of biomass burning, and the WSOC in the summer was not clear, while that in the winter was very clear. This indicates that theWSOC generated in the summer is derived from volatile organic compounds.