Specific index corresponding to nitrogen dioxide is determined by fitting the concentration of the average hourly concentrations in one of the fields listed in the following table:
| Range for nitrogen dioxide (g / m3) | specific index |
| 0-40 |
1
|
| 40-90 |
2
|
| 90-120 |
3
|
| 120-230 |
4
|
| 230-340 |
5
|
| 340-1000 |
6
|