Air nicotine concentrations* (μg/m3) by vehicle and travelling characteristics
| No | Median (IQR) smokers | No | Median (IQR) non-smokers† | Crude ratio (95% CI) | Adjusted‡ ratio (95% CI) | |
| Overall | 17 | 9.6 (5.3–25.5) | 5 | ⩽0.1 | – | – |
| No of cigarettes smoked | ||||||
| 0 | 0 | – | 5 | ⩽0.1 | 1.00 (reference) | 1.00 (reference) |
| 1–3 | 4 | 8.3 (3.7–10.2) | 0 | – | 35.75 (7.83 to 163) | 72.40 (15.8 to 332) |
| ⩾4 | 13 | 12.5 (5.3–31.7) | 0 | – | 122.28 (37.2 to 403) | 293.56 (87.2 to 981) |
| Per cigarette smoked | – | – | 1.79 (1.41 to 2.27) | 1.96 (1.43 to 2.67) | ||
| Size of car¶ | ||||||
| Midsize/large | 11 | 7.5 (5.3–12.5) | 2 | ⩽0.1 | 1.00 (reference) | 1.00 (reference) |
| Compact/small | 6 | 32.3 (7.0–43.9) | 3 | ⩽0.1 | 0.76 (0.11 to 5.51) | 4.34 (1.44 to 13.0) |
| Windows opened§ | ||||||
| Less than halfway | 7 | 9.6 (5.3–12.5) | 4 | ⩽0.1 | 1.00 (reference) | 1.0 (reference) |
| More than halfway | 10 | 13.0 (5.3–31.7) | 1 | ⩽0.1 | 2.94 (0.44 to 19.5) | 0.40 (0.13 to 1.21) |
| Air conditioning | ||||||
| Off | 8 | 7.4 (6.1–14.0) | 1 | ⩽0.1 | 1.00 (reference) | 1.0 (reference) |
| On | 9 | 12.5 (5.3–39.1) | 4 | ⩽0.1 | 0.81 (0.11 to 5.84) | 0.44 (0.13 to 1.50) |
| Total sampling time (minutes) | ||||||
| ⩽60 | 3 | 7.0 (0.3–7.3) | 0 | – | 1.00 (reference) | 1.0 (reference) |
| >60 | 14 | 11.7 (5.3–31.7) | 5 | ⩽0.1 | 1.48 (0.09 to 25.3) | 6.88 (1.32 to 35.9) |
*Average of front and rear air nicotine concentrations.
†Air nicotine concentrations of all five vehicles of non-smokers were below the limit of detection.
‡Ratios adjusted for all other variables with adjustment for cigarette smoked conducted using the categorical variable, except for the model per cigarette smoked.
¶Vehicle types included compact and midsize cars, minivans and SUVs.
§For most of the trip.