Acute effects of outdoor air pollution on forced expiratory volume in 1 s: a panel study of schoolchildren with asthma.

Urban air pollution has been associated with morbidity but little information exists on how it affects diurnal variation of lung function in children with asthma. The purpose of this study was to investigate the acute effects of traffic-related pollution on lung function among children with asthma. We recorded morning and evening forced expiratory volume in 1 s (FEV(1)) for 28 consecutive days in 182 elementary schoolchildren with physician-diagnosed asthma, and monitored ambient hourly air pollution concentrations. An interquartile range (IQR) increase (6.0 microg m(-3)) in the previous 24-h (20:00 h to 20:00 h) mean concentration of fine particulate matter 2.5 microm in diameter (PM(2.5)) was associated with a 0.54% (95% confidence interval (CI) 0.06-1.02) decrease in bedtime FEV(1) (p = 0.027). This association persisted in two-pollutant models with ozone, nitrogen dioxide and sulphur dioxide. An IQR increase in mean daytime (08:00 h to 20:00 h) PM(2.5) of 6.5 microg m(-3) was associated with a 0.73% (95% CI 0.10-1.37) decrease in FEV(1) over the course of the day expressed as 100 x (FEV(1) bedtime - FEV(1) morning)/FEV(1) morning (p = 0.024). This study suggests that, in children with asthma, relatively low concentrations of urban air pollution worsen lung function over a short period of time, even within a day. Of the pollutants measured, PM(2.5 )appears to be the most important.