Fig. 1— Relations between pollutant levels measured on the same day (lag 0), the previous day (lag 1), mean of 0–1 days (lag 0–1), 2 days previously (lag 2), 3 days previously (lag 3) and mean of 0–3 days (lag 0–3) and: a) morning peak expiratory flow (PEF); b) morning forced expiratory volume in 1 s (FEV1); c) evening PEF; and d) evening FEV1. PM10: particles with a 50% cut-off aerodynamic diameter of 10 μm. β: regression coefficient from generalised estimating equation models for panel data, controlling for temperature, relative humidity, atmospheric pressure, corticosteroid use and smoking habit (changes for 10 μg·m−3 increase in pollutant concentration (except for CO, for which the unit increase was 1 mg·m−3)); CI: confidence interval.