Paired Indoor and Outdoor Nitrogen Dioxide Associated With Childhood Asthma Outcomes in a Mixed Rural-Urban Setting: A Feasibility Study

Introduction: Nitrogen dioxide (NO₂) is known to be a trigger for asthma exacerbation. However, little is known about the role of seasonal variation in indoor and outdoor NO₂ levels in childhood asthma in a mixed rural-urban setting of North America. Methods: This prospective cohort study, as a feasibility study, included 62 families with children (5-17 years) that had diagnosed persistent asthma residing in Olmsted County, Minnesota. Indoor and outdoor NO₂ concentrations were measured using passive air samples over 2 weeks in winter and 2 weeks in summer. We assessed seasonal variation in NO₂ levels in urban and rural residential areas and the association with asthma control status collected from participants’ asthma diaries during the study period. Results: Outdoor NO₂ levels were lower (median: 2.4 parts per billion (ppb) in summer, 3.9 ppb in winter) than the Environmental Protection Agency (EPA) annual standard (53 ppb). In winter, a higher level of outdoor NO₂ was significantly associated with urban residential living area (P =.014) and lower socioeconomic status (SES) (P =.027). For both seasons, indoor NO₂ was significantly higher (P <.05) in rural versus urban areas and in homes with gas versus electric stoves (P <.05). Asthma control status was not associated with level of indoor or outdoor NO₂ in this cohort. Conclusions: NO₂ levels were low in this mixed rural-urban community and not associated with asthma control status in this small feasibility study. Further research with a larger sample size is warranted for defining a lower threshold of NO₂ concentration with health effect on asthma in mixed rural-urban settings.