Grade

Single factor pollution index classification standard

Pollution index

Pollution level

1

Pi ≤ 0.7

Excellent

2

0.7 ≤ Pi ≤ 1

Safety

3

1 ≤ Pi ≤ 2

Light pollution

4

2 ≤ Pi ≤ 3

Medium pollution

5

Pi ≥ 3

Heavy pollution