India, Dec. 15 -- Visibility plummeted to zero in parts of the national Capital as a thick layer of 'dense' to 'very dense' fog engulfed the region -- the first for this winter season -- combining with already high pollution levels in the region to create a toxic layer of thick smog which impacted flights and rail traffic in the early hours.

Delhi's air quality continued to remain at alarmingly high levels on Monday morning, with it firmly in the 'severe plus' category.

The 24-hour rolling average AQI stood at 452 at 9am -- marginally lower than a reading of 461 at 4pm on Sunday, which was December's second worst air day ever. It was 431 on Saturday, making this the third straight severe day.

The India Meteorological Department (IMD) s...