Abstract

Objectives: NO₂ is a major urban air pollutant. Previously reported associations between ambient NO₂ and children’s respiratory health have been inconsistent, and independent effects of correlated pollutants hard to assess. The authors examined effects of NO₂ on a spectrum of 11 respiratory symptoms, controlling for PM₁₀ and SO₂, using a large pooled dataset.

Methods: Cross sectional studies were conducted in Russia, Austria, Italy, Switzerland, and the Netherlands, during 1993–99, contributing in total 23 955 children. Study-specific odds ratios for associations with ambient NO₂ are estimated using logistic regressions with area-level random effects. Heterogeneity between study-specific results, and mean estimates (allowing for heterogeneity) are calculated.

Results: Long term average NO₂ concentrations were unrelated to prevalences of bronchitis or asthma. Associations were found for sensitivity to inhaled allergens and allergy to pets, with mean odds ratios around 1.14 per 10 μg/m³ NO₂. SO₂ had little confounding effect, but an initial association between NO₂ and morning cough was reduced after controlling for PM_10. Associations with reported allergy were not reduced by adjustment for the other pollutants. Odds ratios for allergic symptoms tended to be higher for the 9–12 year old children compared with the 6–8 year old children.

Conclusions: Evidence for associations between NO₂ and respiratory symptoms was robust only for inhalation allergies. NO₂ most likely is acting as an indicator of traffic related air pollutants, though its direct effect cannot be ruled out. This remains important, as policies to reduce traffic related air pollution will not result in rapid reductions.