Delhi air quality plunges to 'very poor' category; AQI crosses 300 for first time this season ahead of Diwali

Delhi's air quality slipped into the “very poor” category for the first time this season on Monday, as a dense haze covered the national capital and pollution levels surged following a brief improvement brought by last week's rainfall.

The Air Quality Index (AQI) stood at 307 at 7.05 am on Monday. According to the Central Pollution Control Board's (CPCB) 4 pm bulletin, Delhi's 24-hour average AQI was 261 (poor) on Sunday, a significant deterioration from 117 (moderate) recorded a day earlier.

On Friday, the city's AQI had dropped to 60 (satisfactory) after heavy rainfall washed away pollutants, giving Delhi its cleanest October air quality reading in four years.

36 monitoring stations report very poor air quality

Of Delhi's 59 air quality monitoring stations, data was available for 58. As many as 36 stations recorded “very poor” air quality, while Jahangirpuri was the only location to fall in the “severe” category, with an AQI of 417. Five stations reported “moderate” air quality, while the remaining stations recorded “poor” levels.

According to the Central Pollution Control Board (CPCB), an AQI reading of 0-50 falls under the “good” category, 51-100 is classified as “satisfactory”, 101-200 as “moderate”, 201-300 as “poor”, 301-400 as “very poor” and 401-500 as “severe”.

PM2.5 identified as primary pollutant

At 6 am on Monday, the CPCB identified PM2.5 as the dominant pollutant at 51 of the 58 monitoring stations reporting data, while PM10 was the primary pollutant at the remaining seven. At the same time on Sunday, PM2.5 was the main pollutant at 46 of the 57 stations, while PM10 dominated at 11 stations.

Delhi last experienced “very poor” air quality on February 11 this year, when the 24-hour average AQI reached 305. Earlier, on February 4, the index had climbed to 339.

The deterioration comes just a week before Diwali, when the use of firecrackers typically contributes to a further increase in air pollution across the national capital.

NASA satellite data recorded 1,394 farm fires across Punjab and Haryana between October 1 and November 1, including 1,249 in Punjab and 145 in Haryana. Of these, 171 incidents were detected on November 1 alone. During the corresponding period last year, satellites had recorded 1,861 farm fires.

However, the figures may not offer a direct comparison, as stubble burning has increasingly shifted to later hours of the day. Data from Meteosat showed that around 98 per cent of the fire heat detected in 2025 occurred after 3 pm, compared with 94 per cent in 2024. The actual number of incidents in both years is likely to be higher, as most fires are now reported after the satellite's approximately 1.30 pm observation window.

Air pollution to deteriorate in coming days

Meteorologist Navdeep Dahiya warned that the smog season had set in and said unfavourable weather conditions were likely to aggravate pollution levels across the region in the coming days.

“Most AQI sensors across Delhi NCR are now reporting AQI levels above 300 and many are climbing the 400-500 range tonight. The flow of winds are from the north west with calm conditions. All emissions will persist in the atmosphere for longer duration,” he said in a post on X.