Level | Comprehensive pollution index | Pollution levels |
1 | P ≤ 0.7 | Cleanliness (Safety) |
2 | 0.7 < P ≤ 1.0 | Clean (warning line) |
3 | 1.0 < P ≤ 2.0 | Light pollution |
4 | 2.0 < P ≤ 3.0 | Moderate pollution |
5 | P > 3.0 | Heavy pollution |