Delhi pollution likely to enter emergency zone on Wednesday. According to the Central Pollution Control Bureau (CPCB), the overall air quality index (AQI) of Delhi read 425 at 4 pm on Tuesday. It was 360 at 4 pm on Monday. The noxious haze returned to Delhi and its suburbs on Tuesday with raging stubble fires in neighbouring states, fall in the temperature and wind speed pushing the air quality in the severe zone.