Explained: Why Delhi-NCR struggles with severe air pollution every winter

A study by the Centre for Science and Environment reveals that vehicular emissions are the largest contributor to Delhi's air pollution, accounting for 51.5 per cent of the city's pollution

The air quality in India’s capital has worsened, with the Air Quality Index (AQI) rising above 400, a level the World Health Organization calls ‘hazardous’. For the millions who live in Delhi and the National Capital Region, this is not merely an environmental crisis but a public health emergency. According to a recent study, India loses more than a million lives annually due to air pollution alone.

 

In response to this emergency situation, the Supreme Court has scheduled an urgent hearing on November 18 to review efforts made by the authorities to curb the pollution.

 

Why is winter air more polluted?

 

 

Although emissions remain similar throughout the year, pollution and hazardous air quality worsen in Delhi-NCR during winter months. This can be attributed to multiple factors including temperature inversion in which a layer of cool air forms near the ground, trapping pollutants and preventing them from dispersing. Also, low wind speeds during the winters reduce the dispersion of pollutants.

 

Then there is the problem of burning of crop residue in neighbouring states like Punjab and Haryana that makes headlines every year as the winter approaches. The resulting smoke, combined with wind patterns, contributes significantly to Delhi’s air pollution. 

 

History of Delhi’s Air Quality Index 

  New Delhi faced hazardous air quality for the third consecutive day on Friday, with the Air Quality Index (AQI) soaring to 409, according to the Central Pollution Control Board (CPCB). Thick smog continued to blanket the city, severely limiting visibility and disrupting both traffic and flight operations.     

Top contributor to air pollution in Delhi

 

A study by the Centre for Science and Environment reveals that during the time period of October 12- November 3, 2024, vehicular emissions are the largest contributor to Delhi’s air pollution, accounting for 51.5 per cent of the city’s pollution. Neighbouring districts add 34.97 per cent, farm fires contribute 8.19 per cent, and dust particles make up 3.7 per cent of the total air pollution in the city. 

 

The analysis is derived from data provided by the Decision Support System for Air Quality Management in Delhi, developed by the Indian Institute of Tropical Meteorology in Pune.

Another study by air quality tech company IQAir suggests that Delhi’s air quality is declining due to a combination of natural and human-made pollutants. Construction activities, landfills, and agricultural practices contribute significantly by releasing dust particles, which increase particulate matter in the air. Bare, open lands and fields also generate dust, especially during windy conditions, further deteriorating air quality.

 

Additionally, wildfires and the burning of waste produce harmful smoke and soot, adding to the pollution with toxic particulates and gases. Industrial emissions, including sulfur dioxide, nitrogen oxides, and volatile organic compounds, lead to the formation of secondary pollutants like ozone. Vehicle emissions, particularly from heavy traffic, release carbon monoxide, nitrogen oxides, and hydrocarbons, intensifying pollution in congested areas.

 

Stubble burning conundrum in Punjab and Haryana

 

As the Kharif harvest season begins, farmers in Punjab and Haryana engage in stubble burning to ready the field for the next harvest. This contributes to rising air pollution in Delhi and surrounding areas. On October 16, the Supreme Court had criticised both the states for failing to implement effective measures, calling the increase in stubble-burning incidents an “absolute defiance” of the Commission for Air Quality Management’s guidelines. Haryana’s chief secretary had been summoned to appear on October 23.

 

Data from the Indian Council of Agricultural Research shows mixed results in the fight against stubble burning. Punjab has made progress, with incidents of stubble burning dropping from 1,946 in 2021 to 1,113 in 2024, a 42.8 per cent reduction. In contrast, Haryana saw a sharp rise in stubble burning after a brief decline – incidents dropped from 850 in 2021 to 168 in 2022, but surged by 222.6 per cent in 2023 to 542, and increased slightly to 559 in 2024.

 

This rise in stubble burning, especially in Haryana, is raising concerns about deteriorating air quality as winter approaches, a time when pollution levels are typically high.

 

What Supreme Court said on Delhi air pollution

 

As Delhi’s ‘severe’ air quality is concerned, especially post-Diwali it has reached to the hazardous level, the Supreme Court has intervened to address the crisis. A bench comprising Justices Abhay S Oka and Augustine George Masih said no religion supports practices that harm the environment or public health. The judges stressed that religious activities should not contribute to pollution or compromise people’s well-being.

 

The Court also criticised the timing of the Delhi government’s firecracker ban, questioning why it was imposed only on October 14, just before Diwali. The bench speculated that stockpiling of firecrackers might have already occurred by then, undermining the effectiveness of the ban.

 

The top court ordered the Delhi government and police to ensure effective enforcement of the ban. It also instructed the Delhi Police Commissioner to file a personal affidavit detailing the steps taken, and directed all NCR states to report on their efforts to minimise pollution. The government has been given a deadline of November 25 to make necessary decisions on improving air quality.

 

How does winter pollution impact public health?

 

Air pollution in Delhi poses serious health risks, impacting citizens’ well-being in both the short and long term. As per IQAir, in the short term, people experience irritation in their eyes, throat, and nose, along with irregular heartbeats, asthma attacks, coughing, chest tightness, and difficulty breathing.

 

Prolonged exposure intensifies these risks, leading to severe long-term effects such as chronic respiratory illnesses like bronchitis, asthma, and emphysema. Pollutants can also damage lung tissue, increasing the likelihood of lung cancer. Air pollution raises the risk of heart attacks and strokes and has been linked to premature death, making it a major public health crisis in the region.

 

Govt’s efforts to curb air pollution in Delhi-NCR

 

Stage-III of the Graded Response Action Plan (Grap) is imposed in Delhi-NCR from 8 am on November 15 due to the deteriorating air quality in the region. Grap Stage-III is triggered when air pollution reaches the ‘severe’ category. Under this stage, measures such as a ban on construction and demolition activities are enforced, in-person classes for students up to Class 5 may be suspended, and a greater emphasis is placed on public transportation.

 

Under Grap Stage-III, strict measures have been enforced to combat air pollution in Delhi. These include a ban on inter-state buses (except electric, CNG, and BS-VI diesel models), suspension of construction and demolition activities to reduce dust, and halting mining operations in the region. Schools will switch to online classes for students up to Class 5 to minimise exposure to hazardous air quality. Authorities will also increase water sprinkling on major roads to control dust, while Bharat Stage-III petrol and Bharat Stage-IV diesel vehicles will face restrictions in Delhi and neighbouring regions like Gurugram, Faridabad, Ghaziabad, and Gautam Budh Nagar to protect public health during the ‘severe’ air quality phase.