Table 3 Relative risk (with 95% CI) for the pollutants per 10 μg/m³ increase in the concentration of air pollutants for hospitalisations due to an acute exacerbation of COPD (single pollutant model).

Lag days	NO2	PM10	O3 (8 h)	SO2	PM2.5
Lag 0	1.009 (1.005 to 1.013)**	1.003 (1.000 to 1.005)*	1.002 (0.998 to 1.005)	1.007 (1.001 to 1.014)*†	1.002 (0.998 to 1.001)
Lag 1	1.001 (0.997 to 1.005)	1.005 (1.002 to 1.007)**	1.011 (1.008 to 1.015)**	0.991 (0.981 to 1.001)	1.003 (0.999 to 1.007)**
Lag 2	1.003 (0.999 to 1.007)	1.010 (1.007 to 1.012)**	1.011 (1.008 to 1.020)**	0.992 (0.985 to 1.000)	1.011 (1.007 to 1.014)**
Lag 3	1.010 (1.007 to 1.014)**	1.011 (1.008 to 1.013)**	1.011 (1.012 to 1.019)**	1.006 (0.999 to 1.013)	1.013 (1.010 to 1.017)**
Lag 4	1.010 (1.007 to 1.014)**	1.008 (1.006 to 1.011)**	1.011 (1.008 to 1.015)**	1.004 (0.998 to 1.011)	1.011 (1.008 to 1.015)**
Lag 5	1.008 (1.004 to 1.012)**	1.007 (1.004 to 1.009)**	1.006 (1.003 to 1.010)**	1.004 (0.997 to 1.010)	1.009 (1.006 to 1.013)**
Lag 0–1	1.007 (1.003 to 1.011)**	1.005 (1.002 to 1008)**	1.011 (1.006 to 1.014)**	0.998 (0.991 to 1.006)	1.004 (0.999 to 1.008)
Lag 0–2	1.009 (1.004 to 1.013)**	1.011 (1.008 to 1.014)**	1.019 (1.015 to 1.023)**	0.993 (0.985 to 1.001)	1.010 (1.006 to 1.015)**
Lag 0–3	1.026 (1.022 to 1.031)**†	1.016 (1.013 to 1.019)**	1.027 (1.02 to 1.031)**	0.998 (0.989 to 1.007)	1.018 (1.013 to 1.022)**
Lag 0–4	1.021 (1.017 to 1.026)**	1.020 (1.017 to 1.024)	1.031 (1.027 to 1.036)**	1.001 (0.991 to 1.010)	1.024 (1.019 to 1.029)**
Lag 0–5	1.026 (1.022 to 1.031)**	1.024 (1.021 to 1.028)**†	1.034 (1.030 to 1.040)**†	1.004 (0.994 to 1.014)	1.031 (1.026 to 1.036)**†

SO₂, sulphur dioxide; NO₂, nitrogen dioxide; O₃, ozone; PM₁₀, PM_2.5, particulates with an aerodynamic diameter <10 μm or <2.5 μm.

*p<0.05, **p<0.001.

†Highest χ² score (best lag).