都市域におけるエアロゾル中炭素成分の実態

抄録

Elemental and organic carbons (EC and OC) in PM_2.5 at roadside, urban, and rural sites were measured from 2002 to 2006 by thermal optical reflectance (TOR) method. Total carbon (TC) were 10 ∼ 40 μg/m³ at roadside sites, whereas 5 ∼ 15 μg/m³ at urban and rural sites. The fractions of TC in PM_2.5 (TC/PM_2.5) at roadside sites were larger than those at urban and rural sites. EC were 5 ∼ 32 μg/m³ at roadside sites, whereas less than 5 μg/m³ at urban and rural sites. The fractions of EC in TC (EC/TC) at roadside sites were more than 0.5, whereas 0.3 ∼ 0.5 at urban and rural sites, which indicated the influence of vehicle exhaust, especially EC-rich diesel exhaust at roadside sites. OC were about 5 μg/m³, however, those were higher at heavily polluted roadside sites and at a rural site in early winter probably owing to open biomass burning. Part of OC was pyrolized when OC and EC were thermally separated, and the fraction of pyrolized carbon in OC at urban and rural sites was higher than that at roadside sites. The concentration level of EC and OC, TC/PM_2.5, and EC/TC showed seasonal changes probably affected by meteorological conditions and seasonal differences in emission/formation. The size distributions of EC and OC were also measured by thermal method. The size distributions of EC had modal diameters at around 0.2 ∼ 0.3 μm at a roadside site, whereas at around 0.5 μm at an urban and a rural site, which reflected the differences in residence time and growth process such as coagulation and condensation.