Residential Traffic-Related Pollution Exposures and Exhaled Nitric Oxide in the Children’s Health Study

Background: The fractional concentration of nitric oxide in exhaled air (Fe(NO)) potentially detects airway inflammation related to air pollution exposure. Existing studies have not yet provided conclusive evidence on the association of Fe(NO) with traffic-related pollution (TRP). Objectives: We evaluated the association of Fe(NO) with residential TRP exposure in a large cohort of children. Methods: We related Fe(NO) measured on 2,143 children (ages 7–11 years) who participated in the Southern California Children’s Health Study (CHS) to five classes of metrics of residential TRP: distances to freeways and major roads; length of all and local roads within circular buffers around the home; traffic densities within buffers; annual average line source dispersion modeled nitrogen oxides (NO(x)) from freeways and nonfreeway roads; and predicted annual average nitrogen oxide, nitrogen dioxide, and NO(x) from a model based on intracommunity sampling in the CHS. Results: In children with asthma, length of roads was positively associated with Fe(NO), with stronger associations in smaller buffers [46.7%; 95% confidence interval (CI), 14.3–88.4], 12.4% (95% CI, –8.8 to 38.4), and 4.1% (95% CI, –14.6 to 26.8) higher Fe(NO) for 100-, 300-, and 1,000-m increases in the length of all roads in 50-, 100-, and 200-m buffers, respectively. Other TRP metrics were not significantly associated with Fe(NO), even though the study design was powered to detect exposures explaining as little as 0.4% of the variation in natural log-transformed Fe(NO) (R(2) = 0.004). Conclusion: Length of road was the only indicator of residential TRP exposure associated with airway inflammation in children with asthma, as measured by Fe(NO).