Independent and interactive effects of traffic-related noise and air pollution on lung function: A randomized crossover study in healthy young adults.

Traffic noise and air pollution are major environmental stressors linked to adverse respiratory outcomes. We conducted a randomized crossover study in 51 healthy adults during evening rush hour beside a busy urban road to explore the independent and interactive effects of traffic noise and air pollution on lung function. Participants underwent four different interventions. For each intervention, noise levels and concentrations of ozone (O3), nitrogen dioxide (NO2), PM1, PM2.5, and PM10 were monitored, and lung function of participants were measured, including Forced Vital Capacity (FVC), Forced Expiratory Volume in one second (FEV1), FEV1/FVC, and forced expiratory flows (FEF25, FEF50, FEF75, FEF25-75). Linear mixed-effects models (adjusted for age, sex, and BMI) were used to evaluate associations of traffic noise and/or air pollution with lung function. We found that after adjustment, higher traffic noise exposure was associated with declines in indicators reflecting dynamic ventilatory function. Regarding air pollutants, O3 and PM10 exhibited independent adverse effects on distal airways. Specifically, a 10 μg/m3 increase of O3 was associated with a 0.224 L/s reduction in FEF75, and the value is 0.215 L/s for a 10 μg/m3 increase of PM10. More importantly, exploratory analyses identified potential synergistic interactions: noise co-exposure amplified declines in FEV1 and small-airway flow associated with PM1 and PM2.5, and enhanced the adverse effects of O3 on mid-to-small airway flow. Therefore, to better protect respiratory health, especially during peak traffic hours, interventions should simultaneously target reductions in both traffic noise and air pollution levels, for vulnerable populations and healthy young adults.