Delhi’s AQI ‘severe’ as visibility drops to 50m; over 200 flights delayed

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

Delhi’s air quality turned ‘severe’ even as dense fog enveloped the national Capital leading to delays in flight and rail operations.

Delhi is yet to record a single day this month where the AQI has been below 200 or lower. (HT photo)

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) officials said moderate fog prevailed in Delhi till around 4am, with visibility at 350 metres at Safdarjung and 450 metres at Palam. However, it dipped sharply in the next hour and had fallen to 100 metres by 5:30am.

“As winds remained calm, visibility fell further and was 50 metres at both Palam and Safdarjung between 7:30am and 8am, before improving marginally to 100 and 150 metres respectively at 8:30am,” said the official.

To be sure, the IMD had no colour coded alert for Delhi in place. It has forecast shallow to moderate fog for the capital.

Fog is classified as shallow when it is between 500-1000 metres, as ‘moderate’ when between 200-500 metres and below 200 is ‘dense’ fog. If it dips below 50 metres, then it is called ‘very dense’ fog.

IMD data also showed multiple airports in Northern India saw zero visibility too. This included Amritsar, Agra, Jaisalmer, Gwalior, Kanpur, Hindon and Bareilly among others.

The IMD has forecast dense fog to persist in isolated pockets across the northern plains for the next few days, but has said northwesterly winds will strengthen from Wednesday - which will reduce overall fog intensity and spread.

However, dense to very dense fog is again expected by the end the year, with a feeble western disturbance expected to influence North India between December 28-31.

“We should see some marginal relief as wind speeds pick up from Wednesday as fog formation is less when wind speeds are high. However, a mild western disturbance is again approaching around December 28. This will slow down wind speed and also add moisture, thus creating dense to very dense fog,” said Mahesh Palawat, vice President at Skymet.

Till December 22, Delhi’s monthly average AQI stood at 350, while it was 295 in the same period last year. Delhi is yet to record a single day this month where the AQI has been below 200 or lower. In comparison, last December saw eight such days in the same time last month.