Abstract
A super-sonic impactor using a Laval nozzle, which was developed for size control of ultra-fine aerosol particles down to nano-size range, was applied to the sampling of ultra-fine ambient aerosol. Ambient aerosol was classified into two size fractions by the super-sonic impactor and PAHs in each fraction were analyzed as a typical index of anthropogenic air pollutants. The concentrations of individual PAH compounds in the particles collected by the supersonic impactor were compared with those collected on the backup filter and those of total suspended particulates in order to evaluate the wall loss as well as the influence of super-saturation of vapor components in the supersonic flow. As a result, ambient particles were successfully classified into two size fractions at 200-300 nm using the supersonic impactor. When the air was humid, the concentration of PAHs with benzene rings more than four in the smaller size fraction collected on the backup filter was decreased because the condensation of water vapor onto particles led to an increase in particle size. It was also suggested that there is a possibility of increased collection of semi-volatile compounds on the backup filter due to the super-saturation.
