Table 4.

Percent change (95% CI) in hospital admissions for stroke associated with a 10.0 μg/m³ increase in NO₂, SO₂, and ozone, and 1.0 mg/m³ increase in CO stratified by season.

Variables	All Days	Season		Test for Difference between Seasons
		Warm Season	Cold Season	Z Value	p Value
NO2
Lag0	0.82 (0.52 to 1.13) #	2.35 (1.76 to 2.94) #	0.40 (0.02 to 0.78) *	5.426	<0.001
Lag1	0.39 (0.11 to 0.67) *	1.80 (1.22 to 2.37) #	−0.13 (−0.46 to 0.20)	5.735	<0.001
Lag2	−0.14 (−0.40 to 0.12)	0.34 (−0.22 to 0.90)	−0.08 (−0.38 to 0.23)	1.281	0.200
3 days average	0.22 (−0.18 to 0.61)	2.24 (1.44 to 3.05) #	−0.37 (−0.84 to 0.10)	5.516	<0.001
SO2
Lag0	0.73 (0.44 to 1.03) #	2.38 (1.45 to 3.32) #	0.67 (0.35 to 1.00) #	3.406	0.001
Lag1	0.40 (0.11 to 0.68) *	1.20 (0.28 to 2.12) *	0.34 (0.04 to 0.64) *	1.741	0.082
Lag2	0.16 (−0.10 to 0.42)	0.43 (−0.45 to 1.33)	0.22 (−0.05 to 0.49)	0.451	0.652
3 days average	0.39 (−0.03 to 0.81)	0.32 (−0.91 to 1.56)	0.36 (−0.10 to 0.82)	−0.065	0.948
CO
Lag0	1.35 (0.60 to 2.11) #	−1.86 (−3.70 to 0.01)	2.07 (1.20 to 2.95) #	−3.714	<0.001
Lag1	0.34 (−0.33 to 1.01)	−4.26 (−5.98 to −2.51) #	0.78 (0.04 to 1.52) *	−5.143	<0.001
Lag2	−0.40 (−1.03 to 0.23)	−5.87 (−7.51 to −4.20) #	−0.25 (−0.94 to 0.45)	−6.016	<0.001
3 days average	−0.01 (−0.95 to 0.95)	−7.95 (−10.34 to −5.49) #	0.56 (−0.50 to 1.64)	−6.103	<0.001
Ozone
Lag0	0.23 (0.08 to 0.37) *	0.78 (0.62 to 0.95) #	−2.06 (−2.39 to −1.73) #	14.946	<0.001
Lag1	0.22 (0.09 to 0.36) *	0.60 (0.44 to 0.76) #	−1.48 (−1.78 to −1.18) #	11.862	<0.001
Lag2	0.03 (−0.11 to 0.16)	0.36 (0.20 to 0.51) #	−1.44 (−1.73 to −1.15) #	10.556	<0.001
3 days average	0.20 (0.00 to 0.40)	0.67 (0.44 to 0.91) #	−1.90 (−2.35 to −1.45) #	9.833	<0.001

CI, confidence interval; NO₂, nitrogen dioxide; SO₂, sulfur dioxide; CO, carbon monoxide. * p < 0.05; ^# p < 0.001.