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 μg 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.