Spatial distributions of ultrafine particles and their behavior and chemical composition in relation to roadside sources

Vertical and horizontal distributions of the chemical components of ultrafine particles (UFP; <0.1 μm) in relation to roadside sources were investigated by using a newly developed PM0.1 collection system with a UFP impactor filter (50% cut-off, 0.1 μm; air flow rate, 40.0 L min−1). UFP were measured at a suburban roadside, at two background sites in Saitama (summer 2007 and winter 2008), and at two levels on a high-rise building in Tokyo (summer and winter 2005). The results from the high-rise building showed that ultrafine elemental carbon from vehicle exhaust can reach the upper atmosphere regardless of season because of the high diffusivity of UFP. The total concentrations of the carbonaceous and ionic components at all sites except the roadside site in summer were mostly within the same range. Therefore, UFP diffuse both vertically and horizontally, and its chemical components are distributed uniformly. The UFP composition in summer reflected not only the vehicle exhaust contribution but also photochemical formation, especially at the low-elevation sites, where the samplers were installed several meters above ground level. The results also showed that ionic components contributed to increases in the UFP levels.