Greater nitrogen dioxide concentrations at child versus adult breathing heights close to urban main road kerbside

Nitrogen dioxide (NO2) is a ubiquitous air pollutant with high concentrations particularly close to main roads. The focus of this study was on possible differences in NO2 concentrations between adult and child heights as a function of different distances from heavily trafficked roads in urban areas. Passive diffusion tubes were used to measure NO2 concentrations at heights of 0.8 m (approximate inhalation height of children and closer to vehicle exhaust height) and 2.0 m (approximate inhalation height of adults) above the ground at a number of locations and over several weeks in the city of Edinburgh, UK. Evidence for significant differences in NO2 between heights was observed up to at least 1.2 m from kerbside of busy roads, with tubes at 0.8 m measuring concentrations 5-15 % (a few mu g m(-3)) greater than at 2.0 m. The vertical NO2 concentration difference was not observable at distances 2.5 m or greater from the kerbside. Fitting of horizontal transects of NO2 concentrations away from main roads demonstrated the strong influence of wind speed in yielding faster fall-off in NO2 concentration from the roadside, and in near-ground vertical gradient in NO2, and lower background NO2 concentrations. These observations have potential public health implications for differential NO2 exposures between children walking, or in buggies, close to heavily trafficked urban roads compared with adults.