Echelle en microgrammes/m3
 | < = 5 (excellent) |
 | 6-10 (very good) |
 | 11-15 (good) |
 | 16-20 (quite good) |
 | 21-30 (average) |
 | 31-40 (poor) |
 | 41-50 (very poor) |
 | 51-60 (bad) |
 | 61-70 (very bad) |
 | > 70 (execrable) |
| < = 5 (excellent) |
| 6-10 (very good) |
| 11-15 (good) |
| 16-20 (quite good) |
| 21-30 (average) |
| 31-40 (poor) |
| 41-50 (very poor) |
| 51-60 (bad) |
| 61-70 (very bad) |
| > 70 (execrable) |