Introduction The oxidative potential (OP) of particulate matter (PM) has been proposed as a health-relevant metric, but currently few epidemiological studies investigated associations of OP with health. Our main aim was to assess associations of long-term exposure to OP with respiratory health in children. Our second aim was to evaluate whether OP is more consistently associated with respiratory health than PM mass, PM composition or nitrogen dioxide (NO₂).

Methods For 3701 participants of a prospective birth cohort, annual average concentrations of OP (assessed by spin resonance (OP^ESR) and dithiothreitol assay (OP^DTT)), PM with an aerodynamic diameter of less than 2.5 µm (PM_2.5) mass, NO₂, and PM_2.5 constituents at the home addresses at birth and at all follow-up addresses were estimated by land-use regression. Repeated questionnaire reports of asthma and hay fever until age 14 years, and measurements of allergic sensitisation, lung function and fractional exhaled nitric oxide at age 12 years were linked with air pollution concentrations.

Results Asthma incidence, prevalence of asthma symptoms and rhinitis were positively associated with OP^DTT (adjusted OR (95% CI) per IQR increase in exposure 1.10 (1.01 to 1.20), 1.08 (1.02 to 1.16), 1.15 (1.05 to 1.26), respectively). These associations persisted after adjustment for most co-pollutants. Forced expiratory volume in 1s and forced vital capacity were negatively associated with OP^DTT. These associations were sensitive to adjustment for NO₂. Respiratory health was not significantly associated with PM_2.5 mass and OP^ESR.

Conclusions Respiratory health was more strongly associated with OP^DTT than with PM_2.5 mass; OP^DTT associations with lung function, but not symptoms, were sensitive to adjustment for NO₂.