(Journal of Exposure Science & Environmental Epidemiology) A study of 2891 children in six US cities found that indoor nitrogen dioxide exposure was significantly associated with a 50% increased annual risk of lower respiratory symptoms after adjusting for age, gender, city, parental history of respiratory diseases, and smoking inside the children's home.
Li, R., Weller, E., Dockery, D. et al. (2006) Association of indoor nitrogen dioxide with respiratory symptoms in children: Application of measurement error correction techniques to utilize data from multiple surrogates. J Expo Sci Environ Epidemiol 16, 342–350. https://doi.org/10.1038/sj.jes.7500468