New Delhi, Dec. 16 -- Even as residents across Delhi continued to gasp for breath, parts of north Delhi were exposed to what is arguably the worst possible air that can be recorded, with the air quality index (AQI) maxing out at 500 - the highest value on the official scale - at two monitoring stations, Rohini and Wazirpur, for the second consecutive day.

What has heightened concern among experts and residents alike is that both stations are located in areas surrounded by dense residential neighbourhoods, exposing large populations to extreme pollution levels.

At Rohini, one of Delhi's largest residential localities, the AQI touched 500 at around 6pm on Sunday and remained pegged at that level till 1pm on Monday. After 2pm, the station'...