(Epidemiology) This study found that exposure to indoor nitrogen dioxide (NO2) was associated with increased asthma severity in children with asthma. The study recruited 1,342 children aged 5-10 years with active asthma from urban and suburban areas in Connecticut and Massachusetts. The exposure to NO2 was measured for four months and the results showed that every 5 ppb increase in NO2 exposure above a threshold of 6 ppb was linked to an increase in risk of higher asthma severity score, wheeze, night symptoms, and rescue medication use.
Belanger, K., Holford, T. R., Gent, J. F., Hill, M. E., Kezik, J. M., & Leaderer, B. P. (2013). Household levels of nitrogen dioxide and pediatric asthma severity. Epidemiology (Cambridge, Mass.), 24(2), 320–330. https://doi.org/10.1097/EDE.0b013e318280e2ac