Lack of PM2.5 data could have increased air pollution levels in Delhi by 49% during Diwali

Delhi recorded the most polluted day in the last five years during the Diwali festival, when the Air Quality Index (AQI) reached 376 by 4:00 PM on November 8th, marking the worst reading since 2021. However, the city managed to avoid the worst post-Diwali day in five years: on Monday, the AQI rose to 370 by 11:00 AM, then improved to 344 by 4:00 PM, which is better than the post-Diwali readings in 2025.

Historical data shows that the AQI during Diwali in 2025 was 345, and in 2024 it was 328; in 2023 it was 218, in 2022 it was 312, and in 2021 it was 382. Regarding post-Diwali readings, they were 351 in 2025, 339 in 2024, 358 in 2023, 303 in 2022, and 462 in 2021. The day before Diwali this year, November 7th, the AQI was the highest since 2016, reaching 369.

Meanwhile, some monitoring stations failed to provide crucial AQI data. Initially, hourly data from 35 air quality monitoring stations was missing. Although DPCC later updated data at some of its stations, several stations remained blank during peak pollution hours, and only 47 stations contributed to the average AQI on Diwali day. Delhi has 60 monitoring stations operated by DPCC, CPCB, IITM, and IMD, with one of them being non-operational for several months.

According to IITM data as of 9:00 AM on November 8th, fireworks were the largest source of pollution leading up to Diwali (Choti Diwali), accounting for 41.1% of the total load. Traces of lead, potassium, and sulfur were confirmed in the air, but officials stated that the presence of mercury could only be confirmed through long-term study.

At midnight on November 8th, IITM registered the highest average PM2.5 concentration, which was 671.1 micrograms per cubic meter (µg/m³). Among individual stations, in Jahangirpuri, located in northwest Delhi, a peak of 4985 µg/m³ was recorded on Sunday evening and Monday morning. Nevertheless, DPCC later adjusted the PM2.5 level in the park to 776 µg/m³ by 11:00 AM on Sunday. In Mundka, west of Delhi, the PM2.5 level reached 3744 µg/m³ at 2 AM, remaining unchanged, and then stood at 3023.2 µg/m³ in the JNU area. The established national 24-hour average limit for PM2.5 is 60 µg/m³.

The average PM2.5 concentration during Diwali 2026 was 257 µg/m³, compared to 228 µg/m³ last year, 201 µg/m³ in 2024, 134 µg/m³ in 2023, 176 µg/m³ in 2022, and 318 µg/m³ in 2021.

On Monday, Delhi experienced the first dense fog of the season, causing visibility in Safdarjung to drop to 50 meters at 6:30 AM, keeping the AQI in the upper range of very poor quality. However, a sudden and unusual wind shift from northwest to strong east, which facilitated faster dispersion, helped prevent smoke from stubble burning in Punjab and Haryana from penetrating, avoiding a sharp spike, especially considering that November 8th saw the highest number of forest fires of the season in Punjab—1152.

Experts believe that the relief after Diwali was due more to meteorological factors than to the results of pollution control measures. They added that with the onset of winter conditions, a return to the usual 'cocktail' of pollutants is quite likely.

Ghufran Baig, founder of the System of Air Quality and Weather Forecasting and Research (SAFAR) and Professor at the National Institute of Advanced Studies (NIAS), noted that Delhi was 'very lucky' this year, but this does not mean the air became cleaner. He explained that 'an unusual weather phenomenon related to an approaching cyclone and western disturbance caused the winds to turn eastward instead of their usual northwest direction. These winds, moving at a speed of about 6.7 meters per second from the surface to almost 400 meters, unlike the usual 3–4 m/s, contributed to the rapid dispersion of pollutants and prevented stubble burning smoke from reaching Delhi.' Eastern winds were expected to persist until Tuesday morning, after which they might revert to a northwest direction.

Anumita Roychowdhury from the Centre for Science and Environment (CSE) described this situation as a reflection of the region's worsening fight against emission control, stating: 'This post-Diwali pollution crisis is a direct result of a toxic combination of adverse winter meteorology, increased traffic congestion before Diwali, and the growing contribution of agricultural fires. Fireworks became an uncontrolled tipping point.' She added that Delhi and the wider region are losing the battle to limit emissions from both constant local sources and episodic surges, leading to very high health costs.

The scale of the fireworks' contribution was even clearer in the analysis by Sunil Dahia, founder and lead analyst at Envirocatalysts. He calculated that fireworks added approximately 450 µg/m³ to the PM2.5 concentration during peak hours and contributed about 270–400 µg/m³, meaning over half of the PM2.5 breathed by Delhi residents between 9:00 PM and 2:00 AM. Dahia reported that pollution began to accumulate around 8:00 PM, peaked between 1:00 AM and 3:00 AM, and remained above 500 µg/m³ for four hours.

A thick layer of pollution enveloped the Indian capital after fireworks illuminated the sky of New Delhi during the Diwali festivities, known as the Festival of Lights.

The use of rockets further raised pollution levels, which were already dangerously high, intensifying the annual seasonal air quality crisis affecting the city. Despite restrictions imposed on fireworks, New Delhi residents celebrated the Hindu festival of lights using rockets on Sunday night, releasing smoke and fine particulate matter into the atmosphere.

The following morning, the Air Quality Index exceeded 350 in various parts of the capital, classifying it in the 'severe' category and presenting considerable health risks. Monitoring stations spread across the city recorded equally worrying levels, while visibility decreased under a grayish haze covering both streets and tall buildings.

In October, the Supreme Court of India sought to mitigate the pollution generated by Diwali by limiting traditional fireworks and authorizing only so-called 'eco-friendly fireworks,' provided they were approved under specific conditions and within three-hour windows on Saturday and Sunday. However, even these alternative rockets, although emitting fewer gases, are not free from pollution, as they also release particulate matter and other contaminants, worsening the already dangerous air quality in the region.

New Delhi and its metropolitan area, home to over 30 million inhabitants, consistently rank among the most polluted regions on the planet during the winter period. The situation worsens when Diwali fireworks coincide with colder weather and smoke resulting from agricultural waste burning in the neighboring states of Punjab and Haryana.

After the rice harvest, farmers often burn crop residues to prepare the soil for the next planting. This smoke is carried by the wind towards New Delhi, adding to the pollution originating from vehicles, industries, construction dust, and other local sources. The problem reaches a special level of severity between late October and November, a period when lower temperatures, low wind speed, and atmospheric stagnation prevent adequate pollutant dispersion, resulting in a dense haze that can persist over the capital and its surroundings for several days.

New Delhi authorities have implemented various measures to control pollution, including restrictions on construction activities and the use of diesel-powered generators, as well as judicial interventions to limit the use of pyrotechnics. However, these measures have proven insufficient to prevent the annual return to severe contamination levels. Environmentalists argue that long-term solutions, such as adopting cleaner energy sources and imposing stricter controls on vehicle emissions, are essential to prevent the recurring crisis.