Heavy smog in and around Chennai airport severely affected visibility, causing three flights to be diverted and several flights delayed, on Sunday, January 14. Three international flights were scheduled to land in Chennai airport but were diverted to Hyderabad due to the dense smog. The Air Quality Index (AQI) of Chennai also dipped, to as low as 289 in Perungudi.

According to the real-time AQI data by Central Pollution COntrol Board (CPCB), Alandur - where the airport is located - recorded an AQI of 126. The highest AQI was in Perungudi - 289, followed by Manali (272), Ennore (232), Arumbakkam (216), Royapuram (207), Kodungaiyur (156) and Velachery (103). AQI between zero and 50 is considered 'good'; 51 and 100 'satisfactory'; 101 and 200 'moderate'; 201 and 300 'poor'; 301 and 400 'very poor'; and 401 and 500 'severe'.

AQI is calculated by taking into account eight major pollutants - particulate matter (PM 10 and PM 2.5), carbon monoxide (CO), ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), ammonia (NH3), and lead (Pb).

The high levels of AQI on Sunday is attributed to increased burning activity in the city and surrounding areas owing to Bhogi festival. The traditional bonfire festival is celebrated every year signifying fresh aspirations and a new beginning on the eve of Pongal and the start of Tamil month, 'Thai', on the day of the harvest festival.

The Chennai airport authorities had appealed to people to celebrate a smoke-free Bhogi this year as dense smog can cause visibility issues. “Celebrate smoke-free Bhogi! Because black smoke mixed with dense fog can severely reduce visibility in and around the airport and affect flight operations.”