Table 3.

HR (95% CI) for all-cause mortality considering both NO₂ and PM_2.5

Model	NO2 or PM2.5 (μg/m3)	n	Two pollutants model—NO2 + PM2.5
			HR (95% CI)	p value
Model a	Per 10 μg/m3 increment
	NO2	10,759	0.978 (0.950, 1.008)	0.148
	PM2.5	10,759	1.252 (1.227, 1.279)	< 0.001
Model b	NO2 (μg/m3)
	[ 1.22, 10.00)	2704	1.111 (0.965, 1.278)	0.143
	[ 10.00, 20.00)	4564	0.980 (0.861, 1.114)	0.753
	[ 20.00, 30.00)	2216	1.101 (0.970, 1.250)	0.136
	[ 30.00, 40.00)	786	1.019 (0.884, 1.174)	0.795
	[ 40.00,109.04]	489	Reference	/
	PM2.5 (μg/m3)
	[ 14.8, 25.0)	218	0.171 (0.134, 0.218)	< 0.001
	[ 25.0, 35.0)	1149	0.209 (0.183, 0.237)	< 0.001
	[ 35.0, 50.0)	3834	0.516 (0.473, 0.563)	< 0.001
	[ 50.0, 70.0)	4226	0.728 (0.677, 0.783)	< 0.001
	[ 70.0,133.1]	1332	Reference	/
Model c	Combination of NO2 and PM2.5 (median cut-off)
	NO2 < 16 & PM2.5 < 51	3701	Reference	/
	NO2 ≥ 16 & PM2.5 < 51	1765	1.295 (1.197, 1.401)	< 0.001
	NO2 < 16 & PM2.5 ≥ 51	1889	1.641 (1.521, 1.770)	< 0.001
	NO2 ≥ 16 & PM2.5 ≥ 51	3404	1.843 (1.715, 1.981)	< 0.001
Model d	Combination of NO2 and PM2.5 (guideline cut-off)
	NO2 < 20 & PM2.5 < 35	1221	Reference	/
	NO2 ≥ 20 & PM2.5 < 35	146	1.797 (1.380, 2.338)	< 0.001
	NO2 < 20 & PM2.5 ≥ 35	6047	2.756 (2.501, 3.038)	< 0.001
	NO2 ≥ 20 & PM2.5 ≥ 35	3345	3.241 (2.909, 3.610)	< 0.001

Model a, b, c, and d all adjusted for age, gender, education, household income, marital status, smoking status, drinking status, physical activity, residence, geographical region of residence, BMI, annual temperature mean, and annual temperature standard deviation