India, Dec. 23 -- Delhi's air quality turned 'severe' even as dense fog enveloped the national Capital leading to delays in flight and rail operations.

Winds became calm overnight, sending the air quality plummeting. Delhi's 24-hour average air quality Index (AQI) stood at 416 at 9am on Tuesday -- up from a reading of 373 at 4pm on Monday.

Visibility meanwhile dipped to 50 metres at both Palam and Safdarjung as over 200 flights were delayed at Delhi's Indira Gandhi International (IGI) airport. Several trains were also delayed.

On Monday, over 500 flights were delayed and 14 cancelled as visibility came down to 150 metres in Delhi. At least 30 trains in Delhi were also delayed by 30 minutes or more.

India Meteorological Department (IMD...