Table 4.

The association between NO₂, PM_2.5 and mortality in subgroups

Subgroups	N (%)	Single pollutant model				Two-pollutant model
		NO2 (per 10 μg/m3)		PM2.5 (per 10 μg/m3)		NO2 (per 10 μg/m3)		PM2.5 (per 10 μg/m3)
		HR (95% CI)	p value	HR (95% CI)	p value	HR (95% CI)	p value	HR (95% CI)	p value
Age < 75	2077 (19.3%)	1.301 (1.179, 1.434)	< 0.001	1.824 (1.697, 1.96)	< 0.001	0.845 (0.75, 0.953)	0.006	1.93 (1.777, 2.096)	< 0.001
Age: [75, 85)	2282 (21.2%)	1.298 (1.215, 1.387)	< 0.001	1.538 (1.471, 1.609)	< 0.001	0.967 (0.894, 1.046)	0.402	1.554 (1.477, 1.635)	< 0.001
Age: [85, 95)	3410 (31.7%)	1.105 (1.057, 1.155)	< 0.001	1.231 (1.193, 1.27)	< 0.001	0.969 (0.921, 1.019)	0.218	1.243 (1.2, 1.287)	< 0.001
Age ≥ 95	2990 (27.8%)	1.02 (0.978, 1.065)	0.357	1.059 (1.026, 1.093)	< 0.001	0.99 (0.945, 1.037)	0.674	1.062 (1.026, 1.099)	0.001
Female	6127 (56.9%)	1.119 (1.081, 1.158)	< 0.001	1.225 (1.195, 1.256)	< 0.001	1.001 (0.963, 1.041)	0.954	1.225 (1.191, 1.259)	< 0.001
Male	4632 (43.1%)	1.113 (1.068, 1.16)	< 0.001	1.276 (1.24, 1.314)	< 0.001	0.947 (0.903, 0.992)	0.022	1.298 (1.257, 1.34)	< 0.001
Urban	3746 (34.8%)	1.057 (1.018, 1.096)	0.004	1.18 (1.142, 1.219)	< 0.001	0.962 (0.922, 1.003)	0.071	1.199 (1.155, 1.244)	< 0.001
Rural	7013 (65.2%)	1.219 (1.172, 1.268)	< 0.001	1.295 (1.264, 1.326)	< 0.001	1.04 (0.996, 1.086)	0.079	1.284 (1.251, 1.317)	< 0.001
Education:0 year	6868 (63.8%)	1.102 (1.067, 1.138)	< 0.001	1.214 (1.187, 1.243)	< 0.001	0.986 (0.952, 1.022)	0.455	1.219 (1.189, 1.25)	< 0.001
Education:1–6 year	2928 (27.2%)	1.147 (1.088, 1.21)	< 0.001	1.34 (1.289, 1.392)	< 0.001	0.946 (0.89, 1.006)	0.077	1.363 (1.305, 1.423)	< 0.001
Education: > 6 year	963 (9.0%)	1.15 (1.039, 1.273)	0.007	1.241 (1.152, 1.337)	< 0.001	1.026 (0.916, 1.148)	0.661	1.231 (1.135, 1.337)	< 0.001
Smoking: Heavy smoker	413 (3.8%)	1.372 (1.124, 1.675)	0.002	1.571 (1.367, 1.804)	< 0.001	0.898 (0.699, 1.153)	0.398	1.636 (1.384, 1.934)	< 0.001
Smoking: Light smoker	1485 (13.8%)	1.16 (1.076, 1.25)	< 0.001	1.439 (1.356, 1.526)	< 0.001	0.956 (0.88, 1.038)	0.282	1.459 (1.368, 1.556)	< 0.001
Smoking: Former	1731 (16.1%)	1.092 (1.027, 1.161)	0.005	1.191 (1.141, 1.244)	< 0.001	0.981 (0.916, 1.051)	0.594	1.198 (1.142, 1.257)	< 0.001
Smoking: Never	7130 (66.3%)	1.111 (1.075, 1.148)	< 0.001	1.227 (1.198, 1.256)	< 0.001	0.985 (0.949, 1.022)	0.415	1.232 (1.201, 1.264)	< 0.001
Alcohol: Heavy drinker	1127 (10.5%)	1.172 (1.068, 1.287)	0.001	1.397 (1.309, 1.492)	< 0.001	0.966 (0.872, 1.07)	0.504	1.411 (1.314, 1.515)	< 0.001
Alcohol: Moderate drinker	661 (6.1%)	1.115 (0.992, 1.253)	0.068	1.248 (1.141, 1.365)	< 0.001	0.992 (0.87, 1.13)	0.9	1.251 (1.134, 1.381)	< 0.001
Alcohol: Former	1502 (14.0%)	1.011 (0.946, 1.081)	0.742	1.249 (1.187, 1.314)	< 0.001	0.872 (0.809, 0.94)	< 0.001	1.303 (1.233, 1.378)	< 0.001
Alcohol: Never	7469 (69.4%)	1.133 (1.098, 1.17)	< 0.001	1.23 (1.202, 1.258)	< 0.001	1.006 (0.97, 1.042)	0.761	1.228 (1.198, 1.259)	< 0.001
Ability to exercise regularily: current	2712 (25.2%)	1.141 (1.083, 1.202)	< 0.001	1.266 (1.216, 1.318)	< 0.001	1.009 (0.952, 1.07)	0.763	1.262 (1.208, 1.32)	< 0.001
Ability to exercise regularily: Former	1294 (12.0%)	1.003 (0.937, 1.074)	0.933	1.145 (1.09, 1.203)	< 0.001	0.905 (0.837, 0.979)	0.013	1.181 (1.118, 1.247)	< 0.001
Ability to exercise regularily: Never	6753 (62.8%)	1.143 (1.104, 1.184)	< 0.001	1.272 (1.241, 1.303)	< 0.001	0.993 (0.955, 1.033)	0.73	1.274 (1.241, 1.309)	< 0.001
Marriage_status: Married	3399 (31.6%)	1.227 (1.159, 1.3)	< 0.001	1.433 (1.377, 1.492)	< 0.001	0.969 (0.908, 1.035)	0.35	1.447 (1.383, 1.513)	< 0.001
Marriage_status:Not married	7360 (68.4%)	1.083 (1.051, 1.116)	< 0.001	1.194 (1.168, 1.22)	< 0.001	0.978 (0.946, 1.011)	0.189	1.202 (1.173, 1.23)	< 0.001
Household income: < 4000	2634 (24.5%)	1.221 (1.141, 1.308)	< 0.001	1.361 (1.304, 1.421)	< 0.001	1.02 (0.945, 1.1)	0.617	1.355 (1.294, 1.42)	< 0.001
Household income: < 10,000	2472 (23.0%)	1.122 (1.056, 1.194)	< 0.001	1.279 (1.227, 1.333)	< 0.001	0.964 (0.899, 1.033)	0.297	1.291 (1.235, 1.35)	< 0.001
Household income: < 20,000	2393 (22.2%)	1.149 (1.089, 1.212)	< 0.001	1.264 (1.214, 1.315)	< 0.001	1.026 (0.968, 1.088)	0.387	1.255 (1.202, 1.31)	< 0.001
Household income: ≥ 20,000	3260 (30.3%)	1.089 (1.043, 1.138)	< 0.001	1.181 (1.142, 1.221)	< 0.001	0.988 (0.94, 1.037)	0.618	1.186 (1.143, 1.231)	< 0.001
BMI: < 18.5	3628 (33.7%)	1.073 (1.027, 1.121)	0.002	1.23 (1.189, 1.271)	< 0.001	0.964 (0.919, 1.012)	0.137	1.242 (1.198, 1.288)	< 0.001
BMI: < 25	6232 (57.9%)	1.121 (1.081, 1.161)	< 0.001	1.262 (1.231, 1.293)	< 0.001	0.966 (0.928, 1.006)	0.096	1.274 (1.24, 1.31)	< 0.001
BMI: < 30	770 (7.2%)	1.251 (1.129, 1.386)	< 0.001	1.228 (1.14, 1.322)	< 0.001	1.12 (0.994, 1.262)	0.063	1.181 (1.085, 1.285)	< 0.001
BMI: ≥ 30	129 (1.2%)	1.473 (1.042, 2.082)	0.028	1.548 (1.173, 2.044)	0.002	1.195 (0.812, 1.76)	0.367	1.457 (1.071, 1.981)	0.017
Region: central	2974 (27.6%)	1.174 (1.102, 1.251)	< 0.001	1.246 (1.198, 1.296)	< 0.001	0.981 (0.91, 1.056)	0.607	1.253 (1.198, 1.31)	< 0.001
Region: eastern	3147 (29.2%)	1.269 (1.207, 1.335)	< 0.001	1.263 (1.217, 1.311)	< 0.001	1.151 (1.088, 1.217)	< 0.001	1.217 (1.169, 1.267)	< 0.001
Region: northeastern	904 (8.4%)	1.107 (1.022, 1.2)	0.013	0.98 (0.897, 1.071)	0.66	1.125 (1.035, 1.224)	0.006	0.943 (0.858, 1.035)	0.217
Region: northern	354 (3.3%)	1.227 (1.08, 1.394)	0.002	1.114 (1.038, 1.195)	0.003	1.15 (0.986, 1.341)	0.074	1.068 (0.981, 1.162)	0.128
Region: southern	2390 (22.2%)	1.027 (0.959, 1.1)	0.448	2.057 (1.906, 2.219)	< 0.001	0.824 (0.766, 0.886)	< 0.001	2.218 (2.044, 2.407)	< 0.001
Region: southwestern	990 (9.2%)	0.941 (0.866, 1.024)	0.158	1.885 (1.755, 2.025)	< 0.001	0.728 (0.668, 0.794)	< 0.001	2.051 (1.904, 2.21)	< 0.001
Self-reported respiratory disease: No	9718 (90.3%)	1.124 (1.093, 1.156)	< 0.001	1.247 (1.223, 1.273)	< 0.001	0.989 (0.958, 1.02)	0.487	1.251 (1.224, 1.279)	< 0.001
Self-reported respiratory disease: Yes	884 (8.2%)	1.062 (0.971, 1.162)	0.188	1.219 (1.138, 1.305)	< 0.001	0.934 (0.843, 1.035)	0.192	1.247 (1.155, 1.346)	< 0.001
Self-reported cardiovascular disease: No	10,020 (93.1%)	1.118 (1.088, 1.15)	< 0.001	1.253 (1.229, 1.278)	< 0.001	0.98 (0.951, 1.011)	0.208	1.26 (1.233, 1.288)	< 0.001
Self reported cardiovascular disease: Yes	568 (5.3%)	1.033 (0.919, 1.16)	0.589	1.074 (0.988, 1.168)	0.093	0.987 (0.867, 1.123)	0.84	1.078 (0.983, 1.183)	0.108
NO2 < 16	5590 (52.0%)	1.036 (0.949, 1.131)	0.432	1.521 (1.47, 1.574)	< 0.001	0.749 (0.681, 0.823)	< 0.001	1.566 (1.512, 1.623)	< 0.001
NO2 ≥ 16	5169 (48.0%)	1.098 (1.054, 1.143)	< 0.001	1.11 (1.082, 1.14)	< 0.001	1.047 (1.003, 1.093)	0.037	1.1 (1.07, 1.131)	< 0.001
PM2.5 < 51	5466 (50.8%)	1.109 (1.061, 1.158)	< 0.001	2.006 (1.895, 2.124)	< 0.001	0.967 (0.923, 1.013)	0.156	2.026 (1.91, 2.149)	< 0.001
PM2.5 ≥ 51	5293 (49.2%)	1.054 (1.016, 1.094)	0.005	1.051 (1.018, 1.085)	0.002	1.038 (0.998, 1.08)	0.062	1.04 (1.005, 1.076)	0.025
Temperature mean: [ 0.132,15.1)	3587 (33.3%)	1.143 (1.095, 1.194)	< 0.001	1.109 (1.077, 1.141)	< 0.001	1.083 (1.031, 1.138)	0.001	1.082 (1.048, 1.118)	< 0.001
Temperature mean: [15.083,17.8)	3587 (33.3%)	1.071 (1.02, 1.124)	0.005	1.254 (1.209, 1.3)	< 0.001	0.96 (0.911, 1.011)	0.118	1.267 (1.219, 1.318)	< 0.001
Temperature mean: [17.822,25.3]	3585 (33.3%)	1.094 (1.034, 1.156)	0.002	2.025 (1.918, 2.137)	< 0.001	0.843 (0.793, 0.896)	< 0.001	2.132 (2.014, 2.257)	< 0.001
Temperature SD: [4.28, 8.17)	3588 (33.3%)	1.036 (0.987, 1.088)	0.151	1.708 (1.635, 1.785)	< 0.001	0.876 (0.833, 0.922)	< 0.001	1.762 (1.684, 1.844)	< 0.001
Temperature SD: [8.17, 9.81)	3585 (33.3%)	1.128 (1.069, 1.19)	< 0.001	1.288 (1.24, 1.338)	< 0.001	0.982 (0.925, 1.042)	0.547	1.294 (1.242, 1.349)	< 0.001
Temperature SD: [9.81,17.18]	3586 (33.3%)	1.227 (1.175, 1.282)	< 0.001	1.174 (1.139, 1.21)	< 0.001	1.134 (1.08, 1.191)	< 0.001	1.128 (1.091, 1.168)	< 0.001

All models adjusted for age, gender, education, household income, marital status, smoking status, drinking status, physical activity, residence, geographical region of residence, BMI, annual temperature mean, annual temperature standard deviation and excluded the adjustment of the subgroup variable