大気中の元素状炭素粒子の粒径分布

概要

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Elemental carbon (EC) is produced by incomplete combustion of fossil fuel and vegetation. In this study, we determined size distribution of EC in the atmosphere. Observation was conducted at Shizuoka Univ., Mizugatsuka Park (the Mt. Fuji), the Mt. Norikura and Shigaraki. Aerosol samples were collected with an Andersen-type high volume air sampler as for the size-range of <1.1 μm, 1.1-2.0 μm, 2.0-3.3 μm, 3.3 - 7.0 μm and >7.0 μm in diameter, respectively. Concentration of EC in <1.1 μm-fraction was the higher than the other fraction on sunny days, suggesting a significant effect of EC in <1.1 μm-fraction on the level of total EC. Concentration of total EC on foggy days was as same as that of total EC on sunny days at the Mt. Norikura, while concentration of EC in >3.3 μm-fraction on foggy days was higher than that on sunny days. This result implies that EC acts as nuclei of cloud condensation, and its size becomes larger in the clouds compared to the original size. Concentration of EC in <1.1 μm-fraction was remarkably lower on rainy days than those on sunny days, while the difference in the other fractions was relatively small between rainy and sunny days, suggesting EC in <1.1 μm-fraction is dominantly taken into rainwater. Variation of EC in the total and <1.1 μm-fraction was markedly small (10 - 13%) at Midzugatsuka compared to that in the other sites, suggesting that some process would work to keep the level of EC as constant.