Table 1.

Baseline characteristics of study participants stratified by ${\mathrm{PM}}_{2.5}$ quintiles between 2001 and 2011.

Characteristics	All ($\mathrm{N}=100629$)	1st quintile ($\mathrm{N}=20119$)	2nd quintile ($\mathrm{N}=20130$)	3rd quintile ($\mathrm{N}=20122$)	4th quintile ($\mathrm{N}=20136$)	5th quintile ($\mathrm{N}=20122$)
Mean 2-year ${\mathrm{PM}}_{2.5}$${\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$ (range)	$27.1\pm 8.0$ (5.8–49.6)	$19.1\pm 1.8$ (5.8–21.1)	$22.2\pm 0.6$ ($>21.1–23.3$)	$24.2\pm 0.6$ ($>23.3–25.5$)	$29.0\pm 3.4$ ($>25.5–36.1$)	$41.1\pm 2.9$ ($>36.1–49.6$)
Age mean ± SD, (years)	$38.9\pm 11.3$	$39.9\pm 11.6$	$38.8\pm 11.2$	$38.1\pm 11.0$	$38.6\pm 11.3$	$39.0\pm 11.3$
Male	52,837 (52.5)	10,280 (51.1)	10,694 (53.1)	10,669 (53.0)	10,774 (53.5)	10,420 (51.8)
Education
Lower than high school	13,354 (13.3)	3,074 (15.3)	2,472 (12.3)	2,271 (11.3)	2,722 (13.5)	2,815 (14.0)
High school	20,351 (20.2)	4,320 (21.5)	3,901 (19.4)	3,631 (18.0)	4,081 (20.3)	4,418 (22.0)
College	25,534 (25.4)	5,289 (26.3)	5,003 (24.9)	5,074 (25.2)	4,856 (24.1)	5,312 (26.4)
University	29,777 (29.6)	5,389 (26.8)	6,046 (30.0)	6,470 (32.2)	6,029 (29.9)	5,843 (29.0)
Postgraduate	11,613 (11.5)	2,047 (10.2)	2,708 (13.5)	2,676 (13.3)	2,448 (12.2)	1,734 (8.6)
Cigarette smoking
Never	74,172 (74.2)	14,855 (73.8)	14,791 (73.5)	14,923 (74.2)	14,903 (74.0)	15,240 (75.7)
Former	5,441 (5.4)	1,136 (5.6)	1,098 (5.5)	1,049 (5.2)	1,123 (5.6)	1,035 (5.1)
Current	20,476 (20.3)	4,128 (20.5)	4,241 (21.1)	4,150 (20.6)	4,110 (20.4)	3,847 (19.1)
Alcohol drinking
Never	84,024 (83.5)	16,758 (83.3)	16,904 (84.0)	16,849 (83.7)	16,787 (83.4)	16,726 (83.1)
Former	2,292 (2.3)	470 (2.3)	430 (2.1)	459 (2.3)	433 (2.2)	500 (2.5)
Current ($\ge 1\text{time}/\text{week}$)	14,313 (14.2)	2,796 (14.4)	2,796 (13.9)	2,814 (14.0)	2,916 (14.5)	2,896 (14.4)
Body mass index mean ± SD, (${\mathrm{kg}/\mathrm{m}}^2$)	$22.9\pm 3.5$	$22.9\pm 3.4$	$22.9\pm 3.4$	$22.8\pm 3.5$	$23.0\pm 3.5$	$22.9\pm 3.5$
Systolic blood pressure mean ± SD, (mmHg)	$117.0\pm 16.4$	$116.9\pm 16.4$	$117.0\pm 16.3$	$116.9\pm 16.1$	$116.8\pm 16.6$	$117.2\pm 16.7$
Fasting glucose mean ± SD, (mg/dL)	$98.1\pm 17.7$	$98.2\pm 18.4$	$98.1\pm 17.3$	$98.2\pm 17.1$	$98.1\pm 18.0$	$97.8\pm 17.7$
Total cholesterol mean ± SD, (mg/dL)	$190.1\pm 34.6$	$189.9\pm 34.1$	$190.4\pm 34.7$	$190.5\pm 35.0$	$191.1\pm 34.9$	$188.7\pm 34.4$
eGFR mean ± SD, ($\mathrm{mL}/\text{min}/1.73{\mathrm{m}}^2$)	$87.0\pm 14.9$	$86.5\pm 14.5$	$87.5\pm 15.0$	$87.9\pm 15.1$	$86.5\pm 14.9$	$86.7\pm 14.8$
Self-reported heart disease or stroke	2,122 (2.1)	481 (2.4)	390 (1.9)	440 (2.2)	406 (2.0)	405 (2.0)
Hypertension	12,603 (12.5)	2,684 (13.3)	2,534 (12.6)	2,393 (11.9)	2,432 (11.1)	2,560 (12.7)
Diabetes	3,242 (3.2)	682 (3.4)	626 (3.1)	584 (2.9)	670 (3.3)	680 (3.4)
Address
Residential address	84,055 (83.5)	18,839 (93.6)	16,755 (83.2)	15,560 (77.3)	15,515 (77.1)	17,386 (86.4)
Company address	16,574 (16.5)	1,280 (6.4)	3,375 (15.8)	4,562 (22.7)	4,621 (22.9)	2,736 (13.6)

Note: Data are presented as $\text{mean}\pm \text{SD}$ for continuous variables and number (percentage) for categorical variables. Data are complete for all variables.