Objectives To examine the association between long-term exposure to air pollution and lung function among Chinese schoolchildren in Southern China (Hong Kong).

Methods We conducted a cross-sectional study among 3168 schoolchildren (aged 8–10 years) in 3 districts in Hong Kong. Annual means of ambient PM₁₀ (particulate matter <10 µm), SO₂, NO₂ and O₃ from 1996 to 2003 were used to estimate the individual exposure of the subjects. Children's lung function was measured for forced vital capacity (FVC), forced expiratory volume in 1 s (FEV₁), forced expiratory flow between 25% and 75% of FVC (FEF_25–75) and forced expiratory flow at 75% of FVC (FEF₇₅). Analysis of covariance was performed separately by gender to estimate the impact of air pollution on lung function, with adjustment for socioeconomic characteristics, respiratory morbidities, height and weight, physical activity level, indoor air contaminants and short-term exposure to the air pollutants.

Results After controlling for potential confounding factors, FEV₁, FEF_25–75 and FEF₇₅ for boys in a high-pollution district (HPD) were significantly lower than those in a low-pollution district (LPD) by 3.0%, 7.6% and 8.4%, respectively. No significant differences were found for girls. Results from the comparison between a moderate-pollution district (MPD) and the HPD were similar. There were no differences between children in the LPD and MPD, except that a higher FEF₇₅ was found in boys in the MPD. PM₁₀ is the primary pollutant responsible for the lung function deficit. Asthmatic children were more vulnerable to exposure to air pollution.

Conclusions Long-term exposure to higher ambient air pollution levels was associated with lower lung function in Chinese schoolchildren, especially among boys. Adverse effects were observed on large and small airways, with a stronger effect on the latter.