India, July 13 -- After a spell of clean air, Delhi witnessed a steep deterioration in air quality on Sunday as the overall air quality index (AQI) slipped into the "poor" category with a reading of 261, the highest in over 85 days.

Within Delhi, Anand Vihar monitoring station recorded the worst air quality, falling in the "severe" category with an AQI of 449, followed by Jahangirpuri and Alipur, which recorded AQIs of 344 and 311 (very poor), respectively.

According to Central Pollution Control Board (CPCB) data, the overall AQI was the highest since April 17, with 263.

The city recorded AQI of 48 on Thursday, 65 on Friday, and 140 on Saturday, while air quality remained in the "moderate" and "satisfactory" categories for most of the ...