(Health Effects Institute) This study confirmed the findings of previous studies on indoor nitrogen dioxide levels, showing that household characteristics such as the presence of gas cooking appliances are associated with elevated levels of nitrogen dioxide in infants' bedrooms. The study also found significant year-to-year variability in average bedroom nitrogen dioxide concentrations, which could not be explained by changes in temperature, outdoor levels of nitrogen dioxide, or housing characteristics.
Spengler, J., Schwab, M., McDermott, A., Lambert, W., and Samet, J., (1996) Nitrogen Dioxide and Respiratory Illness in Children. Health Effects Institute, No. 58. https://www.healtheffects.org/system/files/Research-Report-58-Part-4.pdf