Comparison of diffusion tube–measured nitrogen dioxide concentrations at child and adult breathing heights: who are we monitoring for?

Abstract

AbstractMany towns and cities use passive samplers (diffusion tubes) to monitor nitrogen dioxide (NO2) 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 NO2 concentrations with height at two roadside locations along a busy urban road in Newcastle upon Tyne (UK) over an 8-month period. NO2 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 NO2 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 NO2 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 NO2 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 NO2 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.