India, Oct. 18 -- Delhi's air quality deteriorated on Sunday, with the Air Quality Index (AQI) reaching 187 at 4pm, up from 90 on Friday and 159 on Saturday.

The city had recorded the same AQI (187) on October 4. During the current season, Delhi saw an AQI higher than 187 earlier on July 13, when the AQI reached 246,according to the Central Pollution Control Board data.

Of the 58 active air quality monitoring stations in Delhi, 21 recorded air quality in the poor category. Officials attributed the rise in pollution levels to a lack of rain, slow wind speeds and localised emissions.

According to the CPCB standards, an AQI of 0-50 is considered 'good', 51 to 100 'satisfactory', 101 to 200 'moderate', 201 to 300 'poor', 301 to 400 'very p...