Vertical differences in the composition of PM10 and PM2.5 in the urban atmosphere of Osaka, Japan

Vertical differences in PM10 and PM2.5 suspended particles were investigated using a building in Osaka, Japan. Samples were collected on the roof of the building (200 m above ground level) and on the ground during 5–9 August and 2–6 December 2002. In addition to determination of sample mass, concentrations have been analyzed for major chemical components including elemental carbon (EC) and organic carbon (OC). Particle mass concentrations of the samples collected at 200 m were lower than those collected on the ground. “Others” species, defined as the difference between the total particle mass and the sum of the masses of the measured species, dominantly accounted for the vertical difference in mass concentrations in summer, whereas EC and OC were the major contributors in winter. Vertical profiles of relative humidity observed simultaneously indicated that relative humidity on the ground was higher than that at 200 m during the summer sampling period. Hence, it is likely that the higher concentrations of “others” species in the samples collected on the ground were probably caused by water having been absorbed by deliquescent components of the particles. Vertical temperature profiles during the winter sampling period suggested that stable meteorological conditions in winter resulted in the accumulation of primary particles, mainly emitted from vehicle exhaust, leading to the high concentrations of EC and OC on the ground.