Nitrogen dioxide exposure in school classrooms of inner-city children with asthma

Ambient and home exposure to nitrogen dioxide (NO₂) causes asthma symptoms and decreased lung function in children with asthma. Little is known about the health effects of school classroom pollution exposure.

We aimed to determine the effect of indoor classroom NO₂ on lung function and symptoms in inner-city school children with asthma.

Children enrolled in the School Inner-City Asthma Study were followed for 1 academic year. Subjects performed spirometry and had fraction of exhaled nitric oxide values measured twice during the school year at school. Classroom NO₂ was collected by means of passive sampling for 1-week periods twice per year, coinciding with lung function testing. Generalized estimating equation models assessed lung function and symptom relationships with the temporally nearest classroom NO₂ level.

The mean NO₂ value was 11.1 ppb (range, 4.3-29.7 ppb). In total, exposure data were available for 296 subjects, 188 of whom had complete spirometric data. At greater than a threshold of 8 ppb of NO₂ and after adjusting for race and season (spirometry standardized by age, height, and sex), NO₂ levels were associated highly with airflow obstruction, such that each 10-ppb increase in NO₂ level was associated with a 5% decrease in FEV₁/forced vital capacity ratio (β = -0.05; 95% CI, -0.08 to -0.02; P = .01). Percent predicted forced expiratory flow between the 25th and 75th percentile of forced vital capacity was also inversely associated with higher NO₂ exposure (β = -22.8; 95% CI, -36.0 to -9.7; P = .01). There was no significant association of NO₂ levels with percent predicted FEV₁, fraction of exhaled nitric oxide, or asthma symptoms. Additionally, there was no effect modification of atopy on lung function or symptom outcomes.

In children with asthma, indoor classroom NO₂ levels can be associated with increased airflow obstruction.