Population intervention models to estimate ambient NO2 health effects in children with asthma

Health effects of ambient air pollution are most frequently expressed in individual studies as responses to a standardized unit of air pollution changes (e.g., an interquartile interval), which is thought to enable comparison of findings across studies. However, this approach does not necessarily convey health effects in terms of a real-world air pollution scenario. In the present study, we use population intervention modeling to estimate the effect of an air pollution intervention that makes explicit reference to the observed exposure data and is identifiable in those data. We calculate the association between ambient summertime nitrogen dioxide (NO2) and forced expiratory flow between 25% and 75% of forced vital capacity (FEF25-75) in a cohort of children with asthma in Fresno, California. We scale the effect size to reflect NO2 abatement on a majority of summer days. The effect estimates were small, imprecise, and consistently indicated improved pulmonary function with decreased NO2. The effects ranged from -0.8% of mean FEF25-75 (95% confidence interval (CI): -3.4, 1.7) to -3.3% (95% CI: -7.5, 0.9). We conclude by discussing the nature and feasibility of the exposure change analyzed here given the observed air pollution profile, and we propose additional applications of population intervention models in environmental epidemiology.