New Delhi, Dec. 16 -- A dense sheet of toxic fog held the Capital in a chokehold on Monday, sending visibility plummeting to zero in swathes of the city, disrupting road and rail traffic, and causing over 800 flights to be delayed and another 228 cancelled as of 10pm, despite recent airport upgrades. The first 'dense to very dense' fog of the season blanketed a city already gasping for breath in air that remained in the severe category for a third consecutive day. The 24-hour average air quality index (AQI) stood at 427 at 4pm - marginally lower than Sunday's reading of 461, which was December's second worst air day ever. The noxious cocktail forced the Delhi government to shift schools from hybrid to online mode for students up to Class 5 ...