DIURNAL CHARACTERISTICS OF SUSPENDED PARTICULATE MATTER AND PM_(2.5) IN THE URBAN AND SUBURBAN ATMOSPHERE OF THE KANTO PLAIN, JAPAN

摘要

Suspended paniculate matter (SPM) and PM_(2.5) in the urban and suburban atmosphere of the Kanto Plain of Japan, which includes the Tokyo metropolitan area, during the period 22-26 July 2002 were characterized. Samples of SPM and PM_(2.5) were collected by low-volume samplers at 6-h intervals at Suginami, Saitama, and Kisai. At all the sites, the major components of SPM and PM_(2.5) were organic carbon (OC), elemental carbon (EC), and sulfate. The ion balance, the size distributions of the ionic species, and the high correlation between SO_4~(2-) and NH_4~+ indicated that the main chemical form of sulfate was (NH_4)_2SO_4. The OC/EC ratios were larger in the daytime than in the nighttime. The correlation coefficients of OC, OC/EC, and SO_4~(2-) with ozone concentrations at inland sites (Saitama, Kisai) were higher than those at the coastal site (Suginami). Bound water and hydrogen and oxygen atoms associated with OC, the amounts of which were estimated with a mass closure model, contributed substantially to the total particle mass. The chemical characteristics of the particles indicated that two mechanisms led to high concentrations of SPM and PM_(2.5): (ⅰ) an active photochemical process produced high concentrations of OC and sulfate, leading to a high concentration of (NH_4)_2SO_4 in the particles and to production of secondary organic aerosols; (ⅱ) stable meteorological conditions resulted in accumulation of primary particles, mainly emitted from vehicle exhaust, resulting in high concentrations of OC and EC.