Delhi experienced significant disruptions in air travel on Tuesday as dense fog enveloped the city, leading to the delay of over 150 flights at Indira Gandhi International Airport. The flight tracking website Flightradar24 reported that these delays occurred between midnight and 8 am, affecting both domestic and international operations.

The persistent fog also compounded existing air quality challenges in the national capital. While there was a slight improvement in air quality, the 24-hour rolling average Air Quality Index (AQI) recorded at 8 am stood at 388, which falls in the “very poor” category. This is an improvement from Monday afternoon, when the AQI had reached 401, classified as “severe.” December 2025 is on track to become Delhi’s most polluted month since 2018, with the average monthly AQI recorded at 349 until December 29 — the highest in seven years.

Visibility Levels and Fog Alerts

Visibility in the city dropped sharply late Monday night. At Palam, it fell to 100 metres around 10:30 pm on Monday and remained at 50 metres until 5:30 am Tuesday. Similarly, at Safdarjung, visibility decreased to 50 metres around midnight and stayed in that range until approximately 8 am, improving to 200 metres by 8:30 am.

Meteorologists classify fog according to visibility levels:

• Shallow fog: 500–1000 metres
• Moderate fog: 200–500 metres
• Dense fog: 50–200 metres
• Very dense fog: below 50 metres

Due to the low visibility, the India Meteorological Department (IMD) issued a red alert for Delhi around 10:30 pm on Monday. A yellow alert has also been issued for New Year’s Eve, warning of moderate to dense fog conditions.

Flight and Rail Disruptions

The dense fog led to widespread flight delays and cancellations. On Tuesday morning, more than 150 flights were reported delayed at Delhi airport. On Monday, the disruptions were even more severe, with over 550 flights delayed, 130 flights cancelled, and eight diverted to other airports.

Rail services were also affected by the poor visibility. Northern Railways reported that several trains experienced delays on Tuesday morning as operations were adjusted for safety. Commuters were advised to check schedules and plan for additional travel time.

Air Quality and Health Concerns

The prolonged pollution in Delhi has been exacerbated by the winter season, crop-burning in neighbouring states, and vehicular emissions. The AQI of 388 recorded on Tuesday morning is considered “very poor,” indicating that everyone may experience adverse health effects, and sensitive groups — including children, the elderly, and those with respiratory or heart conditions — are at higher risk.

December 2025 is on track to be the worst December for air quality since 2018, when the monthly average AQI was 360. Experts have noted that the combination of stagnant air, fog, and high pollutant concentration continues to trap particulate matter in the city, worsening the overall air quality.

Precautionary Measures for Residents

Authorities and health experts have advised residents to limit outdoor activity, especially for sensitive groups. Masks designed to filter particulate matter, indoor air purifiers, and avoiding strenuous physical activity outdoors are recommended. Schools and offices have been advised to stay alert to changing weather conditions, and commuters are urged to factor in extra travel time due to flight and rail delays.

With New Year’s Eve approaching, both residents and travelers have been cautioned about the combined challenges of dense fog and high pollution levels. Authorities continue to monitor air quality and visibility, issuing advisories and alerts as required to ensure safety across the city.