Airway Inflammation Responses to Walking Roadside and Park Routes After School: A Real-World Crossover Study

Active travel to and from school is encouraged as a form of daily exercise. However, a significant proportion of children's pollution exposure has been attributed to this time due to road traffic volume. We investigated fractional exhaled nitric oxide (FeNO) responses in children walking roadside and park routes after school. 18 children (9.6 ± 1.0 years) completed six 30 min walks immediately after a school day (three in each environment). FeNO was measured before and after, with pollution concentrations measured during each walk. FeNO was reduced following roadside (20.87 ± 17.14 vs. 18.96 ± 15.63 ppb and p = 0.006) and park walks (19.13 ± 2.22 vs. 16.60 ± 2.74 ppb and p < 0.001). The reductions were not different between the two environments. The ICC for all pre-walk FeNO was good (0.882 95% CI: 0.792, 0.947). Measured PM_2.5 (5.9 ± 2.2 vs. 6.5 ± 2.6 μg/m³), PM₁₀ (14.9 ± 11.9 vs. 14.8 ± 8.1 μg/m³) and VOCs (132 ± 91 vs. 80 ± 50 ppb) were not different between roadside and park conditions, respectively. Modest reductions in FeNO after walking suggest a normal response to light to moderate intensity exercise. The similar responses for roadside and park environments suggest that the benefits of active travel outweigh potential risk of pollution exposure where pollution concentrations are below current World Health Organisation thresholds. FeNO can also be reliably measured at the end of a school day with little direct control of behaviour in the hours before measurement.