Season's worst Delhi air at AQI 366, to enter ‘severe’ category soon

The air quality is very likely to be in the ‘severe’ category on Tuesday, before once again returning to ‘very poor’ on Wednesday”.

Delhi’s air quality stayed in the ‘very poor’ category on Sunday, touching a season high of 388 at 10 am, and the city is expected to record the year’s first ‘severe’ air day this week.

A haze seen covering the sky in Delhi on Sunday. (Sanjeev Verma/HT Photo)

At 4 pm, the average air quality index (AQI) marginally improved as winds picked up speed during the day, registering at 366 at 4pm, when the Central Pollution Control Board (CPCB) released its daily national bulletin. However, at least five individual active ambient air quality stations recorded AQIs in the ‘severe’ category.

In its daily bulletin, Centre’s Air Quality Early Warning System (EWS) said, “Delhi’s air quality is very likely to be in the ‘very poor’ category from Sunday till Monday. The air quality is very likely to be in the ‘severe’ category on Tuesday, before once again returning to ‘very poor’ on Wednesday”.

The CPCB classifies an AQI between 0-50 as “good”, 51 and 100 as “satisfactory”, 101 and 200 as “moderate”, 201 and 300 as “poor”, 301 and 400 as “very poor”, and over 400 as “severe”.

The capital has not officially recorded a ‘severe’ air day so far this year. The last such reading was on December 23, 2024, when the AQI was recorded at 406.

The air quality is very likely to be in the ‘severe’ category on Tuesday. (HT)

Long-term AQI trends show the capital has now entered its most polluted time of the year. A Delhi Pollution Control Committee (DPCC) assessment of CPCB’s air quality index (AQI) for Delhi between 2018 and 2022 had shown the period November 1-15 has the highest AQI in the entire year. This is followed by the period December 16-31, which has the second highest average over a 15-day period. A 2019 IIT-Delhi study similarly noted that the first peak in pollution usually comes between October 29-November 4, followed by a second peak between December 30-January 5.

On Sunday, at 4 pm, of the 39 active ambient air quality stations, five were in ‘severe’, which included Burari (404), Chandni Chowk (404), RK Puram (401), Vivek Vihar (402) and Wazirpur (418), according to CPCB data. Another 30 were in ‘very poor’.

Mahesh Palawat, vice president at Skymet meteorology said atmospheric conditions were unfavourable for dispersion of pollutants, leading to gradual accumulation. “Winds picked up – touching around 10 km/hr during the day on Sunday, which led to an improvement in the AQI. Otherwise, we were mostly seeing calm winds.”

Palawat further said that the wind direction was variable through the day, barring the afternoon period, when it switches to westerly and northwesterly — favourable for transport of stubble smoke to Delhi.

However, despite the influence of the western disturbance on the region on November 4 and 5, the capital is not expected to see any rain, which usually helps improve air quality. “It will impact the hills. Over Delhi, we will only see some cloudiness.”

Delhi’s AQI has seen dramatic oscillation over the past few days, registering at 373 on October 30, 218 on October 31, 303 on November 1 and 366 on November 2. The Delhi government has defended itself against allegations of data manipulation levied by the Aam Aadmi Party, saying the AQI stations are “tamper-free”.

Meanwhile, data from the Decision Support System (DSS) showed the contribution of stubble burning was fairly low, standing at 3.5% on Sunday, dropping from 9%, a season-high, on Saturday. In previous years, stubble burning has had an outsized impact on Delhi’s air pollution in winter months, with peak contribution, typically in the first week of November, rising up to 35%. However, this year, a delayed harvesting season has kept farm fires relatively low.

In comparison, the source with the biggest contribution to Delhi’s PM2.5 was Delhi’s transport sector (18.13%), followed by 11.2% from Jhajjar and 4.5% from Delhi’s residential sector. DSS also said around 36.8% was coming from unaccounted sources from outside Delhi.

At 16.8° Celsius Delhi’s minimum stood two degrees above normal, and the maximum of 30.7°C was around normal. While the minimum is expected to touch and possibly dip below 15°C after November 7, the maximum is likely to oscillate between 29-31°C till Wednesday.