Descriptive data of the participants
| Variable | Non-oral cancer cases (n=481 042) | Oral cancer cases (n=1617) | P values |
| PM2.5 | |||
| PM2.5<26.74 | 110 752 (23.02) | 356 (22.02) | <0.0001* |
| 26.74≤PM2.5<32.37 | 152 790 (31.76) | 432 (26.72) | |
| 32.37≤PM2.5<40.37 | 109 291 (22.72) | 330 (20.41) | |
| PM2.5≥40.37 | 108 209 (22.49) | 499 (30.86) | |
| PM10−2.5† | |||
| PM10−2.5<18.88 | 115 603 (24.03) | 351 (21.71) | <0.0001* |
| 18.88≤PM10−2.5<23.66 | 141 381 (29.39) | 408 (25.23) | |
| 23.66≤PM10−2.5<32.42 | 141 433 (29.4) | 524 (32.41) | |
| PM10-25≥32.42 | 82 625 (17.18) | 334 (20.66) | |
| SO2 | |||
| SO2<2.96 | 74 999 (15.59) | 269 (16.64) | <0.0001* |
| 2.96≤SO2<3.61 | 138 189 (28.73) | 380 (23.5) | |
| 3.61≤SO2<4.43 | 134 173 (27.89) | 497 (30.74) | |
| SO2≥4.43 | 133 681 (27.79) | 471 (29.13) | |
| O3 | |||
| O3<28.69 | 198 106 (41.18) | 583 (36.05) | <0.0001* |
| 28.69≤O3<30.97 | 146 672 (30.49) | 567 (35.06) | |
| 30.97≤ O3<33.79 | 74 951 (15.58) | 235 (14.53) | |
| O3≥33.79 | 61 313 (12.75) | 232 (14.35) | |
| Age (mean±SD) | 61.2±12.77 | 60.69±10.89 | 0.0614 |
| Betel chewing (%) | |||
| Never | 444 633 (92.43) | 1456 (90.04) | <0.0001* |
| Occasional | 22 631 (4.70) | 79 (4.89) | |
| Frequent | 13 778 (2.86) | 82 (5.07) | |
| Smoking (%) | |||
| Never | 366 597 (76.21) | 1131 (69.94) | <0.0001* |
| Occasional | 84 315 (17.53) | 341 (21.09) | |
| Frequent | 30 130 (6.26) | 145 (8.97) | |
PM, particulate matter; SO2, sulfur dioxide.
*P<0.05.
†PM10minus PM2.5.