Childhood Asthma and Household Exposures to Nitrogen Dioxide and Fine Particles: A Triple Crossover Randomized Intervention Trial

To examine whether a reduction in household nitrogen dioxide (No₂) or fine particles results in decreased asthma symptoms in pediatric patients with persistent asthma.

The study included 126 children between the ages of 5 to 11 years with persistent asthma living in homes with gas stoves and household levels of No₂ of 15 ppb or greater between September 2015 to April 2019.

This is a triple-crossover, double-blind intervention trial in which patients were randomized to treatment arms involving three different air cleaners designed for No₂ reduction, particle reduction, or control. Each child was randomized to a treatment sequence and was exposed to each air cleaner for a 5-week treatment period. No₂ levels and data on the child’s asthma symptoms were obtained at the end of each treatment period. The primary outcome was the number of asthma symptom days during the final 14 days of each treatment period.

This study found that household No₂ levels were significantly lower with No₂-reduction (17.1 ppb) compared with particle-reduction (20.9 ppb) and control treatment (21.0 ppb). However, there was no statistically significant reduction in the number of asthma symptom days with No₂-reduction compared with the control treatment (0.33 fewer days, 95% confidence interval = −1.7 to 2.5). There were fewer asthma symptom days with particle-reduction compared with the control treatment; however, the finding did not reach statistical significance (1.8 fewer days, 95% CI = −0.32 to 3.9).

No₂-reducing air cleaners decreased household No₂ levels in homes with gas stoves. However, No₂-reduction did not lead to a reduction in days with asthma symptoms. Particle-reducing air cleaners led to a modest, but not clinically meaningful, reduction in asthma morbidity.

Nitrogen dioxide (No₂) is a byproduct of gas appliances and exposure may worsen respiratory symptoms in children with asthma. Previous studies showed that significant reductions in indoor No₂ levels by removing the source could improve asthma morbidity. Although this study showed that No₂-reducing air cleaners could decrease household No₂ levels in homes with gas stoves, there was no meaningful reduction in symptoms among children with persistent asthma. Larger randomized controlled trials are needed to determine if larger reductions in household No₂ levels could affect asthma morbidity.