Echelle en microgrammes/m3
 | < = 25 (excellent) |
| 26-45 (very good) |
 | 46-60 (good) |
 | 61-80 (quite good) |
 | 81-110 (average) |
 | 111-150 (poor) |
 | 151-200 (very poor) |
 | 201-270 (bad) |
 | 271-400 (very bad) |
 | > 400 (execrable) |
| < = 25 (excellent) |
| 26-45 (very good) |
| 46-60 (good) |
| 61-80 (quite good) |
| 81-110 (average) |
| 111-150 (poor) |
| 151-200 (very poor) |
| 201-270 (bad) |
| 271-400 (very bad) |
| > 400 (execrable) |