Delhi smog explained: Why air turned hazardous and early respite looks bleak

It’s not just Delhi that is under a blanket of the annual early-winter smog, making the city’s air hazardous for its 20 million residents. The entire National Capital Region (NCR), which includes Noida, Gurugram, Faridabad and Ghaziabad, is reeling from the onslaught of very high concentration of particulate matter (PM) in the air.
On November 13, Delhi woke up to a layer of thick smog that severely impaired visibility on the roads in the early hours. According to the Central Pollution Control Board (CPCB), the AQI (air quality index)—a standard benchmark to gauge the severity of pollution—reading hovered at an average 418 (“severe”) over the past 24 hours. CPCB data showed that around 18 per cent of the air pollutants were from stubble-burning by farmers in Punjab and Haryana.
Predictably, Gurugram had “very poor” air (an average AQI of 321). Ghaziabad, Greater Noida and Noida too were in the “very poor” range, with average AQI values of 350.
AQI readings show the concentration of PM2.5 (very fine particulate matter that poses grave health risks) and the larger PM10 suspended in the air.
Haryana’s industrial areas, such as Bahadurgarh and Ballabgarh, too are battling “very poor” air. In Uttar Pradesh, Bulandshahr and Baghpat have reported AQI numbers between 300 and 350. Clearly, the problem extends beyond Delhi, affecting millions across Haryana, Uttar Pradesh and even parts of Rajasthan.
Despite many dissuasive efforts, including the threat of financial penalties, many farmers in Delhi’s neighbouring states continue to burn crop stubble, worsening air pollution. Data monitored by the CPCB shows 7,029 stubble-burning instances in Punjab and over 1,000 in Haryana since September 15 this year.
As on November 11, stubble-burning contributed about 18 per cent to Delhi’s PM2.5 levels. Though lower than past years, it remains significant and shows the problem’s scale. Punjab’s 7,029 fires since September 15 were 70 per cent fewer than the 23,730 fires reported in the corresponding period in 2023 and 82 per cent fewer than the 40,677 fires in 2022.
Haryana reported 1,008 fires since September 15. Last year, the figure was 1,703 fires and 2,880 in 2022. These numbers show some progress in how crop stubble is being managed. Nevertheless, many farmers continue with this way of clearing their fields for sowing the next crop, releasing pollutants into the NCR’s stagnant winter air.
The NCR’s main problem is high levels of PM2.5, a pollutant under 2.5 microns in size. For perspective, a single PM2.5 particle is about 1/30th the width of human hair and roughly 40 times smaller than a fine grain of sand.
PM2.5 particles can go deep into the lungs, potentially triggering breathing problems, heart trouble, worsening asthma and even causing cancer in the long term. They even reach the bloodstream. The World Health Organization (WHO) recommends no more than average 25 µg/m3 (micrograms) of PM2.5 exposure over 24 hours. In Delhi, the exposure is multiple times higher.
As winter sets in, the AQI trends in NCR show air quality is rapidly worsening. Delhi invariably has “very poor” to “severe” AQI levels at this time of the year. CPCB records don’t show many “good” air days. In 2023, AQI was already in “very poor” range in November. That remains unchanged this year. What’s worse, weather forecasts in the near future suggest winds not strong enough to dispel the pollutants, which means air quality will stay “very poor”.
The not-for-profit Centre for Science and Environment (CSE), in its latest analysis of government data, has found that vehicles continue to be the highest contributor to Delhi’s bad air. “The average PM2.5 concentration has almost stagnated and is the highest in the past five years. Peaks can be highly variable due to the atmospheric conditions. But the increase in average level is a matter of worry,” says Anumita Roychowdhury, executive director (research and advocacy), CSE.
There was a 9 per cent increase in average concentration in air pollution in 2023-24 as against 2019-20, the CSE’s analysis found. “This upward trend reflects elevated levels of pollution and the high impact of atmospheric conditions. It needs immediate action,” says Roychowdhury.
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