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