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Effects of policy-driven hypothetical air pollutant interventions on childhood asthma incidence in southern California

Significance Asthma is one of the leading chronic diseases among children, and there is increasing evidence that air pollution plays a role in the development of this disease. We found that had NO2 or PM2.5 concentration in 9 southern Californian communities been lower than observed in the 1990s and early 2000s, there would have been a corresponding reduction in childhood asthma incidence, with larger effect estimates for NO2. Our findings may have implications for air quality regulations, as all communities examined in this study had ambient concentrations well below the current US Environmental Protection Agency annual standard of 53 ppb for NO2. Childhood asthma is a major public health concern and has significant adverse impacts on the lives of the children and their families, and on society. There is an emerging link between air pollution, which is ubiquitous in our environment, particularly in urban centers, and incident childhood asthma. Here, using data from 3 successive cohorts recruited from the same 9 communities in southern California over a span of 20 y (1993 to 2014), we estimated asthma incidence using G-computation under hypothetical air pollution exposure scenarios targeting nitrogen dioxide (NO2) and particulate matter <2.5 μm (PM2.5) in separate interventions. We reported comparisons of asthma incidence under each hypothetical air pollution intervention with incidence under the observed natural course of exposure; results that may be more tangible for policymakers compared with risk ratios. Model results indicated that childhood asthma incidence rates would have been statistically significantly higher had the observed reduction in ambient NO2 in southern California not occurred in the 1990s and early 2000s, and asthma incidence rates would have been significantly lower had NO2 been lower than what it was observed to be. For example, compliance with a hypothetical standard of 20 ppb NO2 was estimated to result in 20% lower childhood asthma incidence (95% CI, −27% to −11%) compared with the exposure that actually occurred. The findings for hypothetical PM2.5 interventions, although statistically significant, were smaller in magnitude compared with results for the hypothetical NO2 interventions. Our results suggest a large potential public health benefit of air pollutant reduction in reduced incidence of childhood asthma.