(Image source from: PTI)
At 373, Delhi marked its highest Air Quality Index (AQI) for October in three years on Thursday. The last time the AQI was higher for October was in 2022 when it hit 392 on the month's final day. Thursday brought a heavy layer of fog in the capital. The city's air quality dropped nearly 100 points from the previous day, falling deep into the "very poor" category, according to the Central Pollution Control Board (CPCB). On Wednesday, the average AQI was 279, classified as ‘poor’.
This drop was caused by slow surface winds, high humidity, and lower night temperatures, which caused a temperature inversion—where warm air traps cooler air below, stopping pollutants from spreading out.
On Thursday, the highest temperature reached 27 degrees Celsius, which is four degrees lower than usual and the lowest for October in the past two years. The only time a lower temperature was noted during this month was on October 17, 2023, when it measured 26.2 degrees Celsius. The lowest temperature recorded was 20.1 degrees Celsius, which is four degrees higher than normal. The IMD reported that south-easterly winds were active over Delhi in the last 24 hours, reaching speeds of up to 10 kmph. The combination of weak winds and low temperatures limited the mixing of the air, leading to pollutants gathering near the ground. Visibility dropped significantly in many areas of the city. Around 7:30 am, Palam recorded visibility of 1,000 m and Safdarjung 800 m. Locations like Kartavya Path, Burari, Akshardham, and Anand Vihar were covered in haze.
The Air Quality Early Warning System indicated that Delhi’s ventilation index, which shows how well the atmosphere can disperse pollutants, stayed below the ideal level of 6,000 sq m per second. Both a low mixing height and high humidity near 90% further restricted how pollutants spread upward. Information from the Decision Support System showed that while stubble burning contributed modestly to Delhi’s PM2.5 levels at 2.57%, vehicle emissions were responsible for almost 16.7% as of Wednesday. Anand Vihar and Vivek Vihar showed “severe” air quality with AQI readings of 408 and 415, respectively. As reported by CPCB data, 33 monitoring stations in the city noted “very poor” air quality with values above 300.
The unusually low maximum temperature and weak wind conditions hindered the dispersion of pollutants, according to IITM. The IITM predicted that the air quality would likely stay in the “very poor” category in the coming days, with calm winds and stable atmospheric conditions expected to persist. The minimum temperature is expected to drop to around 15 to 17 degrees Celsius by November 5, while the maximum is projected to stay between 29 and 31 degrees Celsius.
