Numerous researchers have proposed that surface area is a more appropriate indicator than mass for evaluating pulmonary inflammatory responses caused by exposure to fine and ultrafine particles. In this study, measurements of surface area concentrations of aerosols were conducted in Yokohama, Japan, using the diffusion charging method. PM2.5 mass concentration and black carbon concentration in PM2.5 were also measured. The 24-hour continuous measurement campaigns were conducted 39 times from March to November, 2014. The surface area concentration was more closely correlated with the black carbon concentration than with the PM2.5 mass concentration. It is considered that the abundance of black carbon particles significantly affects the surface area concentration of PM2.5. The strength of the correlation between the surface area and black carbon concentrations varied considerably among the measurement campaigns. A relatively weaker afternoon correlation was observed compared with the other time zones (morning, evening, and night). We consider that these phenomena are due to the transportation/formation of the particles other than black carbon that affects surface area concentration and/or the variation of the surface condition of the black carbon particles.
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