New Delhi: Flight operations were affected at the capital’s Indira Gandhi International (IGI) Airport on Monday as Delhi and its adjoining areas woke up to a thick blanket of fog that affected rail, road and air traffic. 530 flights were delayed and 40 were cancelled; additionally, 21 Delhi-bound flights, too, had to be diverted.

“The general visibility is slightly improving at Delhi Airport. Passengers are requested to contact the airline concerned for updated flight information. Any inconvenience caused is regretted,” the last update on Delhi Airport’s official Twitter handle said.

Due to poor visibility, only CAT-IIIB compliant aircraft could land at the airport, using an instrument landing system (ILS). A CAT-IIIB system helps with a precision approach and landing when the runway visibility is at no less than 15 metres and at a visual range less than 200 metres, but not less than 50 metres.

The IGI Airport is the country’s busiest, as well as sixth busiest in Asia. It is also the twelfth busiest airport in the world.

Due to severe cold, the temperature in the city fell to 2.6 from 2.8 degree Celsius recorded on Sunday, less than even Shimla’s three degree Celsius. The air quality in the national capital, too, worsened, sliding into the ‘severe’ category, with Air Quality Index (AQI) of 462 and 494 being reported by Anand Vihar observatory and Okhla Phase-2 centre respectively.