Field measurements of size-resolved particle number concentrations of PM2.5 and ultrafine particles (UFPs) (<0.3μm) were performed using an ultrafine particle counter (UFPC) at a roadside and indoor / outdoor of a building located about 50m away from the roadside. Similar behavior of both UFP and PM2.5 were found for number concentrations at all measuring sites, and it was made clear that the wind speed influences UFP concentration more significantly than rainfall. In addition, high correlations between UFP concentration and nitrogen monoxide (NO) and elemental carbon (EC) concentrations indicated that the particles emitted from motor vehicles, particularly diesel emission particles, are transported near the building and penetrated into the indoor space of the building. Furthermore, since the indoor / outdoor ratios (I / O ratios) of UFP and PM2.5 increased when a fan ventilator was used, it was thought that UFP and PM2.5 come into the building through the gaps between windows and doors with the walls.
