New Delhi, Dec. 24 -- Delhi's air quality remained in the "severe" zone for the third straight day on Sunday as weak winds locked in local emissions and extended residents' exposure to a host of respiratory illnesses.

The Capital on Sunday clocked an average 24-hour air quality index (AQI) of 411 at 4pm, as against 450 on Saturday and 409 on Friday.

The city usually goes through three fortnights where the AQI is routinely in the severe zone: The first half of November, the second half of December, and then mid-January. During the first phase, the toxicity is fuelled largely by smoke from farm stubble fires in Punjab. The second and third phases are, however, down largely to local sources of pollution like vehicular and industrial emissi...