Near-surface vertical profiles of urban roadside NOx and fine particles

Abstract

This paper presents daytime vertical profiles of the NOx concentration, and the number concentration and size distribution of fine particles near a major road in urban Tokyo during spring 2011. No significant height dependence was observed in the NOx concentration, presumably due to rapid diffusion. In contrast, the number concentration of particles under 0.5 μm diameter demonstrated an exponential decrease with increasing height above ground level. Vertical profiles derived from this study differ from those presented in previous studies, however, these differences may potentially be explained by the different tailpipe positions of Japanese and US heavy vehicles, as well as the meteorological conditions. This study demonstrates that in Tokyo, the fine particle concentration at 0.5 m above ground level was about 2.9 times higher than that at 2.0 m. The higher fine particle concentration immediately above ground level implies that children may be at greater risk of experiencing pollutant-related respiratory symptoms than adults.