The corresponding specific index of sulfur dioxide is determined by fitting the concentration of the average hourly concentrations in one of the fields listed in the following table:
| Field of concentrations of sulfur dioxide (µg / m3) | specific index |
| 0-100 |
1
|
| 100-200 |
2
|
| 200-350 |
3
|
| 350-500 |
4
|
| 500-750 |
5
|
| 750-1250 |
6
|
