The corresponding specific index of particulate matter < 10 µm is determined by fitting the arithmetic average of hourly values recorded in the last 24 hours, in one of the areas the concentrations listed in the following table:
| Range for particulate matter (g / m3) | specific index |
| 0-20 |
1
|
| 20-40 |
2
|
| 40-50 |
3
|
| 50-100 |
4
|
| 100-150 |
5
|
| 150-1200 |
6
|