Two pollutant models were used to adjust for the potential confounding effects of copollutants (Online Supplement Table S1). For acute exposure to each air pollutant, the effect of lag-1-day PM2.5 and PM10 on FVC and FEV1 remained significant in the two pollutant models, as well as the effect of lag-1-day O3 on MMEF, FEV1/FVC percentage, and MMEF/FVC ratio. The effect of SO2 on lung function was non-significant after adjusting for copollutants. For sub-chronic exposure, PM2.5, PM10, and ozone remained negatively associated with FVC, FEV1,and MMEF.