Vertical profiles of ultrafine to supermicron particles measured by aircraft over Osaka metropolitan area in Japan

Intensive aircraft- and ground-based measurements of ultrafine to supermicron particles in the Osaka metropolitan area, Japan, were carried out on 17–19 March 2003, in order to investigate vertical profiles of size-resolved particles in the urban atmosphere. Differently sized particles were observed at different altitudes on 19 March. Relatively higher concentrations of ultrafine particles (31 nm) and submicron particles (0.3–0.5 μm) were measured (100–200 cm−3) at altitudes of 300 and 600 m, whereas supermicron particles (2–5 μm) were present (300–600 cm−3) at higher altitudes (1300 m in the morning and 2200 m in the afternoon). The chemical composition analysis showed that supermicron particles evidently comprised mainly soil particles mixed internally with anthropogenic species such as carbonaceous components and sulfate. Numerical simulation using the Chemical weather FORecasting System (CFORS) suggested the long-range transport of soil dust and black carbon from the Asian continent. Total number concentrations of particles sized 10–875 nm ranged from 4.8×103 to 3.0×104 cm−3 at an altitude of 300 m and from 7.3×102 to 4.8×103 cm−3 at an altitude of 1300 m. Total number concentrations of particles sized 10–875 nm correlated very well with NOX concentrations, and, therefore, ultrafine and submicron particles were likely emitted from urban activities such as car traffic and vertically transported. Number size distributions at lower altitudes obtained by aircraft measurements were similar to those obtained by ground measurements, with modal diameters of 20–30 nm on 18 March and about 50 nm on 19 March.