Study shows air pollution in Delhi-NCR persists longer after Diwali than in Chennai and Hyderabad

Following the Diwali celebrations, there was a significant deterioration in air quality across major Indian metropolitan areas. According to data from the Central Pollution Control Board (CPCB), around November 8-9, 2026, the average Air Quality Index (AQI) in Delhi fluctuated between 376–400, which is classified as 'very poor'. At some monitoring stations, the level exceeded 400, reaching 'hazardous' levels, such as at Burari crossing (441), Vivek Vihar (437), and Delhi Technological University (434). In neighboring cities like Noida, Ghaziabad, Gurugram, and Faridabad, the AQI also exceeded 300.

While the overall AQI in Mumbai ranged from 132–171, corresponding to the 'moderate' category, smog formed in local areas, including Bandra, Ghatkopar, and Chembur, up to levels of 200–260. Other cities recorded the following figures: the AQI in Kolkata was around 162–164, in Chennai—138–211, and in Bangalore—around 129. Additionally, in cities such as Lucknow, Pune, Jaipur, and Ahmedabad, the air was classified as 'poor' or 'very poor'. Overall, North India was the most affected, while southern and coastal cities were in relatively better condition.

The primary scientific reason for smog formation—a mixture of smoke and fog—in Delhi-NCR is linked to weather conditions. In winter, a phenomenon known as 'temperature inversion' occurs: on normal days, warm air above the ground rises, dispersing pollutants. However, in winter, the ground cools down, and a layer of warm air forms above it, preventing the rise of pollutants. Furthermore, wind speed significantly decreases, causing dust, smoke, and fine particles (PM2.5 and PM10) to remain close to the ground.

The situation is exacerbated by smoke from straw burning in Punjab and Haryana, which reaches Delhi. Studies show that open burning (burning straw, garbage, and domestic fuel) accounts for over half of the particulate matter in Delhi. In addition to this, vehicle exhaust fumes, industrial emissions, construction dust, and chemical substances from Diwali fireworks contribute. These pollutants contain toxic chemicals, such as benzene, which poison the blood. At night, the drop in temperature leads to gas condensation, forming dense fog.

Mumbai, being a coastal city, receives some relief from sea breezes, preventing it from reaching the critical levels seen in Delhi. Nevertheless, local smog arises from Diwali fireworks, heavy traffic, construction activities, industrial emissions, and waste burning. With high humidity, particles absorb water, leading to visible fog formation.

In cities like Kolkata, Chennai, Bangalore, Hyderabad, and Pune, the main pollution sources are similar: increasing number of vehicles, industry, construction dust, waste burning, and seasonal factors. The geographical location of the Indo-Gangetic Plain in the northern regions contributes to pollutant retention, whereas in southern cities, wind speed and rain sometimes provide relief.

Besides PM2.5 and PM10, nitrogen oxides, sulfur dioxide, and volatile organic compounds (VOCs) are dangerous for health, as they form secondary, even more toxic particles.

Long-term inhalation of such air increases the risk of developing asthma, bronchitis, heart disease, and premature death. The government is taking measures, such as implementing GRAP plans, banning fireworks, and attempting to stop straw burning. However, achieving a sustainable solution requires modernizing transport to clean fuels, strengthening public transport, tightening control over industry, increasing green spaces, and improving waste management.

Citizens can also contribute by reducing personal car use, wearing masks, and raising awareness. Collective effort is the only way to preserve clean air in the country's megacities, otherwise, every winter will repeat this story.

The air in the capital city of Delhi has become extremely polluted this season. On Monday morning, a thick haze hung over the city, and pollution levels sharply increased. Although previous rains provided some relief, the air once again turned toxic.

According to data from the Central Pollution Control Board (CPCB), at 7:05 AM on Monday, the Air Quality Index (AQI) reached 349, which falls into the 'very poor' category. The average daily AQI on Sunday was 261 (poor), while the day before that it was 117 (moderate). On Friday after the rain, the AQI dropped to 60, marking the cleanest day in October in four years, but the situation worsened again.

Ninety-eight percent of the available data was collected from 58 out of 59 air quality monitoring stations in Delhi. At 36 of these stations, the air was in the 'very poor' category. The Jahangirpuri station was the only one where the AQI reached 417 and entered the 'hazardous' category. Five stations showed a 'moderate' level, and the rest were classified as 'poor.'

In the morning, PM2.5 was the main pollutant at most stations. PM2.5 was the primary source of pollution at 51 of the 58 stations, and PM10 at the remaining seven. CPCB defines air quality as follows: 0-50 — good, 51-100 — satisfactory, 101-200 — moderate, 201-300 — poor, 301-400 — very poor, and 401-500 — hazardous.

According to NASA satellite observations, 1394 instances of field burning were detected in Punjab and Haryana between November 1 and November 1: 1249 in Punjab and 145 in Haryana. Only 171 fires were registered on November 1. Last year, 1861 fires were detected during a similar period. However, this data does not reflect the full picture, as most straw is now burned in the evening. In 2025, about 98 percent of fires occurred after 3:00 PM, compared to 94 percent in 2024. Since the satellite passes around 1:30 PM, evening fires often go unnoticed. These burnings are one of the main external factors affecting the air in Delhi.

The rise in AQI is due to a combination of several scientific reasons. Firstly, there are local pollution sources: vehicle exhaust, factories, construction work, and road dust release pollutants daily. Rain washed away these substances, but as soon as the rain stopped, these sources became active again. Secondly, a significant factor is the smog from straw burning in Punjab and Haryana, which is carried by the wind into Delhi-NCR. Thirdly, and this is a very important factor, are adverse weather conditions. Meteorologist Navdeep Dahiya noted that the wind is blowing from the northwest and has a very low speed, meaning it is calm. With calm winds, pollutants do not disperse and remain in the air for a long time. During winter, temperature inversion is often observed, where the air near the ground remains cold, and a warm layer forms above it. This layer prevents pollutants from rising, causing them to accumulate near the ground surface. PM2.5 particles are very small and can penetrate the lungs, coming from transport, burning, and industry. When the wind is still, these particles easily accumulate, and the AQI rises quickly. With the approach of Diwali, the use of fireworks and burning may intensify pollution.

Meteorologist Navdeep Dahiya warned that the smog season has begun. Most sensors in Delhi-NCR show an AQI above 300, and at night in many places, it approaches 400-500. With calm winds from the northwest, all emissions will remain in the atmosphere for a long time. Favorable weather conditions are not expected for the next seven to ten days, which means a possible further intensification of smog. This year, Delhi last recorded 'very poor' air quality on February 11, when the average AQI was 305; before that, on February 4, it reached 339. The worsening situation in early November is causing concern.

The government is implementing measures to combat smog and is carrying out pollution control measures. Fines amounting to millions of rupees have been imposed in a single day, and many vehicles have been impounded. However, long-term relief is only possible with a reduction in field fires, decreased transport emissions, and favorable weather conditions. Citizens are advised to spend less time outdoors in the morning and evening, use masks, and pay special attention to children and the elderly. Home air purifiers can help. The air in Delhi reached the 'very poor' category for the first time this season. After the relief from the rains, pollution took over again. Straw burning, local emissions, and adverse weather jointly increase the AQI. From a scientific point of view, calm wind and temperature keep pollutants near the ground. The situation may worsen in the coming days. Only caution and collective efforts can bring relief.