mmation could be identified between healthy students and students with asthma.
The importance of accurate assessment of pollution exposure in health effects studies has been recognised since at least the early 1980's. The most accurate measurement tool, personal exposure monitoring, is expensive and logistically difficult, and does not easily lend itself to panel studies involving large numbers of subjects, particularly children. Differing exposures at home compared to work/school also decreases the accuracy of exposure assessment. The effect of cigarette exposure, both personal and via passive smoking, acts as a confounder for the assessment of health effects of air pollution. This study attempted to circumvent these issues by studying schoolchildren living and studying in the same, smoke-free environment. Other potential confounders such as dietary variation might also be expected to be reduced by central institutional catering. The close relationship between indoor and outdoor air pollution levels compares favourably with similar studies which have used personal exposure monitoring . The difference in pollution levels measured at the school, compared with the central monitoring station argues strongly against relying solely on central monitoring for exposure assessment.
A limitation of the approach of studying students in boarding houses of private schools is the potential for decreased generalisability of these results to the rest of the population. Students in this study were all male, predominantly identified themselves as European, and were from wealthier backgrounds than the population of Christchurch generally. It was felt, however, that the advantages of comprehensive pollution and respiratory health monitoring in this panel of non-smoking students out-weighed any potential limitations due to generalisability.
Urinary 1-hydroxypyrene has previously been proposed as a biomarker of exposure to polycyclic aromatic hydrocarbons (PAHs) . Early studies primarily focussed on occupational exposure to PAHs, while recent studies have investigated environmental exposure to PAHs, including via vehicle emissions or indoor sources such as coal burning stoves and tobacco smoke [21, 22]. The current study is the first to investigate the utility of 1-OHP for assessing environmental exposure to PAHs suggested to be primarily derived from wood-burning for home-heating. PAH concentrations are highly correlated with particulate air pollution in Christchurch . The potential use of 1-OHP as a biomarker of pollution exposure in this population is explored in more detail elsewhere .
Small effects of peak air pollution levels on some lung function measurements were detected in the asthmatic subjects. The effects on afternoon peak flow and decreased variability between morning and evening FEV1 might represent a 1/2–1 day lag effect of pollution on lung function in this group. Generally, the effect sizes were small. No significant independent effect of air pollution on lung function was detected in the population as a whole. It is unlikely that reliever use in the asthmatic children significantly reduced any effect size seen, since reliever use was generally very low, and the variable used for any reliever use was only retained in one model in the multivariate analysis. Even attempting to force the variable into the multivariate models did not alter the analyses. The effects in asthmatic students were only seen associated with peak pollution levels, as averaged over a 10 minute period. No association was seen between lung function and 24 hour average pollution levels in the multivariate analyses. This contrasts with the study of Trenga and co-workers who identified a relationship between 24 hour mean pollution levels and lung function in children with asthma .
This study also demonstrated small but statistically significant effects of pollution on ear, nose and throat symptoms in this population. This is consistent with previous studies of wood-smoke air pollution .
The power of the study may have been reduced by relatively low pollution 