Delhi Air Pollution Hit 4-Year High On Diwali; PM2.5 Peaked At 675

Delhi recorded its worst air quality on Diwali in four years, with pollution levels spiking sharply at night as PM2.5 concentrations peaked at 675 - a peak not seen since 2021.

Delhi's 24-hour average AQI at 4 pm on Monday was in the 'very poor' category at 345. In comparison, it was 330 in 2024, 218 in 2023, 312 in 2022, and 382 in 2021, according to data from the Central Pollution Control Board. Many climate experts on Tuesday claimed that data from peak hours went missing.

Environment Minister Manjinder Singh Sirsa, however, claimed that all data was intact and the department's website and apps were fully operational. According to the hourly bulletin, the city's AQI throughout the night remained high, with readings of 344 at 10 pm, 347 at 11 pm, 349 at midnight, and 348 at 1 am. Early Tuesday morning, the index continued to stay elevated: 346 at 5 am, 347 at 6 am, 351 at 7 am, 352 at 8 am, 356 at 9 am, 359 at 10 am, and remained at 359 through 11 am and noon, according to the bulletin.

Meanwhile, PM2.5 levels also recorded the worst figures in the last four years, peaking at 675 micrograms per cubic metre late at night on Diwali. The concentration of PM2.5 -- fine particles which easily penetrate the respiratory system and pose serious health risks, especially for children, the elderly and those with pre-existing respiratory conditions -- also exceeded the safe limit.

For comparison, PM2.5 levels were 609 micrograms per cubic metre in 2024, 570 micrograms per cubic metre in 2023, 534 micrograms per cubic metre in 2022, and 728 micrograms per cubic metre in 2021. Between 4 pm and 5 pm on Diwali, PM2.5 was 91 micrograms per cubic metre, rising steadily each hour - 106 at 6 pm, 146 at 7 pm, 223 at 8 pm, 371 at 9 pm, 537 at 10 pm, and peaking at 675 micrograms per cubic metre by midnight.

Its level began to drop, returning to 91 micrograms per cubic metre later on Tuesday. The Supreme Court had allowed the bursting of green firecrackers between 8 pm and 10 pm on the festival day, but celebrations reportedly continued well past the allotted time. Delhi's 24-hour average AQI on Tuesday, reported at 4 pm, remained in the 'very poor' category at 351. According to the CPCB, AQI between 0 and 50 is considered 'good', 51-100 'satisfactory', 101-200 'moderate', 201-300 'poor', 301-400 'very poor', and 401-500 'severe.'

Transport emissions contributed 14.6 per cent to the city's air pollution on Tuesday, while neighbouring states' contribution was as follows: Ghaziabad 6 per cent, Noida 8.3 per cent, Gurugram 3.6 per cent, and stubble burning 1 per cent, according to data from the Decision Support System (DSS).

The DSS - the city's only operational pollution-tracking model that estimates source-wise contributions to Delhi's PM2.5 levels - was reactivated earlier this month after being suspended last year over inaccuracies. On Diwali, satellite data detected 45 stubble-burning incidents in Punjab, 13 in Haryana, and 77 in Uttar Pradesh. Dipankar Saha, former additional director and the head of Air Laboratories at CPCB, Delhi, said that improving wind speeds will likely improve air quality.

He said the sudden rise in AQI was caused by a depression in the Bay of Bengal, which created low or calm wind speeds, preventing the dispersion of pollutants and leading to their accumulation. Earlier, on Sunday, the Commission for Air Quality Management (CAQM) invoked Stage II of the Graded Response Action Plan (GRAP) across Delhi-NCR.

The move followed a review by the GRAP sub-committee on Saturday and forecasts from the India Meteorological Department (IMD) and the Indian Institute of Tropical Meteorology (IITM). On October 15, the Supreme Court allowed the sale and bursting of green firecrackers in Delhi-NCR between 6 am and 7 pm and again from 8 pm to 10 pm on Diwali eve and Diwali.