Table 2.
Baseline urbanization level among quartiles of daily average concentration of air pollutants in Taiwan.
| Air Pollutant Concentration | Quartile 1 (Q1) (lowest) | Quartile 2 (Q2) | Quartile 3 (Q3) | Quartile 4 (Q4) (highest) | * p-Value | ||||
|---|---|---|---|---|---|---|---|---|---|
| N = 161,970 | n | (%) | n | (%) | n | (%) | n | (%) | |
| Sulfur dioxide (SO2) | <0.001 | ||||||||
| Urbanization level | |||||||||
| 1 (highest) | 12,662 | (29.9) | 13,928 | (36.4) | 19,315 | (41.6) | 9993 | (28.6) | |
| 2 | 13,428 | (31.7) | 11,114 | (29.1) | 13,820 | (29.8) | 14,282 | (40.8) | |
| 3 | 4829 | (11.4) | 5479 | (14.3) | 8887 | (19.2) | 8212 | (23.5) | |
| 4 (lowest) | 11,411 | (27.0) | 7721 | (20.2) | 4389 | (9.46) | 2499 | (7.14) | |
| Nitrogen oxides (NOx) | <0.001 | ||||||||
| Urbanization level | |||||||||
| 1 (highest) | 8667 | (22.4) | 10,836 | (25.2) | 10,950 | (32.5) | 25,445 | (54.6) | |
| 2 | 13,095 | (33.9) | 15,717 | (36.5) | 12,480 | (37.0) | 11,352 | (24.4) | |
| 3 | 4777 | (12.4) | 8540 | (19.9) | 7358 | (21.8) | 6732 | (14.5) | |
| 4 (lowest) | 12,101 | (31.3) | 7932 | (18.4) | 2934 | (8.70) | 3053 | (6.55) | |
| Nitrogen monoxide (NO) | <0.001 | ||||||||
| Urbanization level | |||||||||
| 1 (highest) | 8329 | (21.0) | 9967 | (24.3) | 16,250 | (45.0) | 21,352 | (47.4) | |
| 2 | 13,887 | (35.0) | 13,634 | (33.2) | 11,368 | (31.5) | 13,755 | (30.5) | |
| 3 | 4255 | (10.7) | 10,186 | (24.8) | 5471 | (15.2) | 7495 | (16.6) | |
| 4 (lowest) | 13,244 | (33.4) | 7261 | (17.7) | 3035 | (8.40) | 2480 | (5.50) | |
| Nitrogen dioxide (NO2) | <0.001 | ||||||||
| Urbanization level | |||||||||
| 1 (highest) | 8313 | (23.1) | 11,056 | (23.4) | 21,609 | (45.0) | 14,920 | (48.7) | |
| 2 | 10,953 | (30.4) | 18,620 | (39.4) | 14,202 | (29.6) | 8869 | (29.0) | |
| 3 | 5454 | (15.1) | 7740 | (16.4) | 9075 | (18.9) | 5138 | (16.8) | |
| 4 (lowest) | 11,308 | (31.4) | 9850 | (20.8) | 3152 | (6.56) | 1710 | (5.58) | |
| Particulate matter (PM2.5) | <0.001 | ||||||||
| Urbanization level | |||||||||
| 1 (highest) | 22,062 | (47.4) | 14,301 | (40.2) | 10,754 | (27.5) | 8781 | (21.6) | |
| 2 | 13,032 | (28.0) | 10,350 | (29.1) | 13,593 | (34.7) | 15,669 | (38.5) | |
| 3 | 5443 | (11.7) | 6153 | (17.3) | 5749 | (14.7) | 10,062 | (24.7) | |
| 4 (lowest) | 6054 | (13.0) | 4733 | (13.3) | 9063 | (23.1) | 6170 | (15.2) | |
* Chi-square test. The urbanization level was categorized by the population density of the residential area into 4 levels, with level 1 as the most urbanized and level 4 as the least urbanized. The daily average air pollutant concentrations were categorized into 4 groups based on quartiles for each air pollutant.