Table 1.

AQI level situation.

Numerical value	Air quality index level
0 < AQI < 50	Level 1 (excellent)
51 < AQI < 100	Level 2 (good)
101 < AQI < 150	Level 3 (mild pollution)
151 < AQI < 200	Level 4 (moderate pollution)
201 < AQI < 300	Level 5 (heavy pollution)
AQI > 300	Level 6 (severe pollution)

Heavy pollution days refer to Grade 5 (severe pollution) and Grade 6 (severe pollution) weather.