Ratio of concentrations on the underground platform to the surface
| Station | Line | Ratio of the concentration underground to that on the surface | |
|---|---|---|---|
| PNC | PM2.5 | ||
| *Data not available. | |||
| Hampstead Station | Northern Line | 0.38 | 16.0 |
| Oxford Circus | Victoria Line | * | 9.2 |
| 0.60 | 8.0 | ||
| 0.68 | 7.1 | ||