Ambient exposure to nitrogen dioxide and lung function: a multi-metric approach

Most studies evaluating chronic ambient exposure to nitrogen dioxide (NO₂) have used averages as the exclusive exposure metric. However, this approach may lead to an underestimation of potential health effects. The objective of this study is to evaluate the association between ambient exposure to NO₂ assessed by various metrics, and lung function in a cohort of healthy male youth. A cross-sectional analysis of 5,462 subjects was conducted using multivariate linear regression. Exposure to NO₂ was assessed by spatial interpolation using Empirical Bayesian Kriging (EBK). Five different exposure metrics were evaluated over two years, including average concentration, the number and intensity of exceedances of the 24-h NO₂ World Health Organization air quality guideline (AQG), and the number and intensity of 1-h NO₂ peaks. Lung function indices, including percent predicted forced expiratory volume in one second (FEV₁), forced vital capacity (FVC), forced expiratory flow between 25% and 75% of vital capacity (FEF_25-75), and FEV₁/FVC ratio, were assessed. The intensity of the 24-h AQG exceedances was associated with the largest reductions in FEV₁ (-0.82%, 95% CI: -1.61%, -0.03%) and FVC (-1.03%, 95% CI: -1.86%, -0.20%), while FEF_25-75 showed a significant decline only with the 1-h peak intensity metric (-2.78%, 95% CI: -5.02%, -0.54%). The study results support integrating diverse exposure metrics as part of NO₂ chronic exposure assessment, as these metrics may capture a wider range of potential health effects that could be underestimated or overlooked when relying only on average concentrations.