Size distribution of polycyclic aromatic hydrocarbons in indoor airborne particulates.

A survey of the particle-size distribution of 17 polycyclic aromatic hydrocarbons (PAHs) in indoor and outdoor air was performed in 20 homes in several Japanese cities. Highest PAH concentrations were found in the fine-particle fraction (smaller than 2.5 μm in diameter). The pro· portion of indoor PAH concentrations in fine particles was found to be higher than that of outdoors. For 4-ring PAHs, indoor sources elevated the indoor PAH concentrations in the 2.5- to 10-μm and > 10-μm fractions, whereas the indoor PAH concentrations in particles smaller than 2.5 μm were comparable with or lower than the outdoor concentrations. In contrast, for PAHs with more than 5 rings, the indoor concentrations were determined essentially by outdoor concentrations. The indoor/ outdoor benzo[a]pyrene concentration ratio varied considerably in homes with smokers because the residents opened the windows of the room in which smoking took place.