Table 3.

Spearman correlation coefficients among the exposure variables.

Variable	NO2	SO2	CO	Ozone	PM2.5	T	RH
NO2	1.00	0.58 *	0.61 *	−0.29 *	0.61 *	−0.24 *	0.13 *
SO2	-	1.00	0.68 *	−0.46 *	0.48 *	−0.60 *	−0.21 *
CO	-	-	1.00	−0.43 *	0.68 *	−0.42 *	0.18 *
Ozone	-	-	-	1.00	−0.09 *	0.79 *	0.15 *
PM2.5	-	-	-	-	1.00	−0.05 *	0.40 *
T	-	-	-	-	-	1.00	0.36 *
RH	-	-	-	-	-	-	1.00

NO₂, nitrogen dioxide; SO₂, sulfur dioxide; CO, carbon monoxide; PM_2.5, particulate matter that is 2.5 µm or less in diameter; T, temperature; RH, relative humidity. * p < 0.001.