Health effects of photochemical smog: seasonal and acute lung function change in outdoor workers

We investigated effects of summer air pollution exposure on outdoor workers in the Fraser Valley, Canada. Fifty farm workers performed spirometry daily before and after each 12–16 h workday from 1 July to 18 August 1994. The mean daily maximum (1 h) ambient ozone concentration was 39 ppb (range 10–89 ppb) and the mean daily maximum 8 h average ozone concentration was 31 ppb (range 5–66 ppb). PM₁₀ concentrations were low (mean 24 h average 16 μg m⁻³, range 6–30 μg m⁻³) and highly correlated with ozone. Due to the high level of correlation between ozone, temperature and PM₁₀ it was not possible to separately analyse the effect of each of these variables on lung function. In regression models including daily maximum ozone (an indicator of photochemical smog), an individual's mean lung function level and the Julian date, decreased afternoon FEV₁ and FVC, and the daily change (afternoon–morning) corrected for the morning measurement, were associated with ozone. These associations were still apparent the following morning, suggesting a persistent air pollution effect. These results reproduce our earlier finding of persistent lung function decrements in farm workers in the Fraser Valley associated with relatively low concentrations of ambient air pollution. In the subset of 12 individuals who participated in both studies, there was no correlation in individual responses to ozone between the two study periods. During both summer studies we observed a marked seasonal decline in lung function, although lung function levels improved to initial values between the two studies, suggesting a reversible seasonal effect of ozone on lung function. Copyright © 1999 John Wiley & Sons, Ltd.