Background Short-term changes in air pollution exposure in children may be associated with transient increases in exhaled nitric oxide (NO), a marker of airway inflammation. Also, children living in areas with high air pollution levels and/or high traffic densities appear to have chronically increased levels of exhaled NO. No studies have simultaneously addressed the long-term and short-term associations between traffic-related air pollution and exhaled NO.

Objectives To investigate associations between exhaled NO in school children and both short-term changes in outdoor PM₁₀ and long-term traffic exposures.

Methods Offline exhaled NO measurements were conducted in 812 children from nine Dutch schools within 400 m of motorways. Daily levels of particulate matter with a 50% cut-off aerodynamic diameter of 10 μm (PM₁₀) were obtained from background monitoring stations. Long-term exposure to traffic-related air pollution was assessed using specific traffic-related characteristics such as total, car and truck motorway traffic and the distances of the children's homes and schools from the motorway.

Results A positive association was found between ambient PM₁₀ concentrations on the day of exhaled NO measurement and exhaled NO (adjusted geometric means ratio (95% CI) 2.24 (1.37 to 3.65)) over the range of daily PM₁₀ concentrations of 44 μg/m³), which was largely attributable to a pollution peak associated with high particulate matter emissions from traditional Easter fires. There were suggestive associations between exhaled NO and traffic counts only in children with asthma, which were not statistically significance.

Conclusions Short-term changes in ambient PM₁₀ largely attributable to biomass burning are associated with increased levels of exhaled NO.