Many towns and cities use passive samplers (diffusion tubes) to monitor nitrogen dioxide (NO 2) concentration. However, literature studies have shown large horizontal and vertical concentration gradients for diffusion tubes placed over short distances, raising concerns over the representativeness of monitoring locations. This study examines variations in NO 2 concentrations with height at two roadside locations along a busy urban road in Newcastle upon Tyne (UK) over an 8-month period. NO 2 concentrations were passively monitored at building facades (approximately 7.0 m from the roadside) at heights of 0.7 m, 1.7 m and 2.7 m to replicate child breathing height in prams and buggies, adult breathing height and the Newcastle City Council sampling height (for 2017), respectively. Paired t tests indicated that NO 2 concentrations were significantly lower at 2.7 m (4.7% lower, n = 16, p = 0.001) and 1.7 m (7.1% lower, n = 14, p = 0.007) compared with those at 0.7 m. There was no statistically significant difference between NO 2 concentrations measured at 2.7 m and 1.7 m, indicating that UK local authority practice of placing diffusion tubes at higher than adult breathing height does not result in underreporting of NO 2 concentrations for regulatory purposes. The results have clear public health implications as they provide evidence that young children, in an urban setting and close to busy roadways, may be exposed to higher NO 2 concentrations compared with adults in the same location. We have shown that such differences might not be adequately reflected in the monitoring data from municipal authorities.