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 (NOx) from freeways and non-freeway roads; and predicted annual average nitrogen oxide, nitrogen dioxide, and NOx 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.