Bronte Wells
Delhi, India's capital, is one of the world's most polluted cities. Every year, the city's air pollution reaches hazardous levels, causing severe health issues for its over 33 million residents. The primary causes of Delhi's poor air quality are stubble burning in neighbouring states, vehicle emissions, industrial activities, and construction dust. The city's geography, bordered by the Himalayas, also traps pollutants, worsening the smog. Despite emergency measures and short-term solutions, Delhi's pollution crisis persists, with a lack of political will and systemic failures hindering long-term progress.
| Characteristics | Values |
|---|---|
| Delhi's rank among polluted cities | Delhi is the most polluted city in the world. It has held this title for at least 6 years. |
| Air Quality Index (AQI) | On 18 November 2024, Delhi recorded an AQI of 491, the worst of the season. On 15 June 2025, the AQI was 123, classified as "poor". |
| PM2.5 concentration | 44µg/m³, which is 10.2 times the World Health Organization's annual guideline value. |
| PM10 concentration | 128µg/m³ |
| Temperature | 35°C |
| Impact on health | Air pollution in India is estimated to kill about 2 million people every year. It is the fifth largest cause of death in the country. India has the highest death rate from chronic respiratory diseases and asthma, according to the World Health Organization. |
| Impact on children | In Delhi, poor air quality has irreversibly damaged the lungs of 2.2 million children. |
| Impact on sports | In December 2017, during a cricket test match between Sri Lanka and India, several Sri Lankan players experienced breathing problems and vomiting due to the air pollution. They had to use face masks, and the match was eventually stopped. |
| Impact on monuments | During the smog season, the visibility is often so bad that famous monuments are reduced to smoky blurs on the horizon. |
| Impact on life expectancy | Pollution in Delhi reduces the life expectancy in India by 5 years. |
| Impact on politics | On 27 November 2021, the Delhi Government banned the entry of commercial petrol and diesel vehicles into the city. On 1 March 2025, the government decided that fuel stations would stop providing fuel to vehicles older than 15 years starting on 1 April 2025. |
| Main sources of pollution | Vehicles, stubble burning, industrial emissions, and the Bhalswa landfill fire. |
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What You'll Learn
Stubble burning in neighbouring states
Delhi's air pollution has become a recurring concern, especially as the winter months set in, bringing with them an increasing sense of dread about the smog that blankets the capital. While stubble burning in neighbouring states has long been blamed for the seasonal spike in pollution, the reality is far more complex.
The contribution of stubble burning to Delhi's air pollution varies year to year and depends on various factors. In 2024, between September 15 and October 21, Delhi experienced six "very poor" air quality days, with the worsening air quality making headlines. Official data revealed that stubble burning contributed only a little over 1% to Delhi's air pollution on October 19, 2024, according to the Indian Institute of Tropical Meteorology (IITM). However, the burning of crop residue was projected to contribute up to 2.4% to Delhi's bad air quality on October 21, indicating a worrying upward trend.
The impact of stubble burning on Delhi's air quality is influenced by wind patterns and the distance between the fires and the city. The north-west wind, in particular, makes Delhi's air quality unlivable from October to December. The fractional contribution of stubble-burning fires to Delhi's PM2.5 mass concentration was analysed for the period from September 23 to December 15, 2021. The modelling framework suggested a maximum daily mean contribution of around 30-35% during the turbulent hours of late morning to afternoon. The contribution of stubble burning is also influenced by the synchronised burning of different crops, as a consequence of the Punjab Subsoil Preservation Act of 2009, which gave farmers a shorter time window to burn the stubble.
While stubble burning in neighbouring states is a significant contributor to Delhi's air pollution, it is essential to recognise that local sources within the city, such as vehicular emissions, construction dust, industrial emissions, and the open burning of waste, also play a crucial role. To effectively combat Delhi's air pollution crisis, solutions must address both regional and local contributors.
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Vehicle emissions
Delhi's air quality is often described as "very poor", and vehicular emissions are the largest contributor to this. The number of vehicles on Delhi's roads increased fourfold between 2010 and 2018, and the city's population is increasing rapidly, leading to a rise in the number of vehicles without a corresponding increase in road length. The result is slow-moving traffic, with an average speed of just 20-30 km/h, leading to poor vehicle mileage and increased emissions.
Vehicles contribute about 64% of the pollution in Delhi. The main pollutants emitted by vehicles are carbon monoxide (CO), nitrogen oxide (NOx), and particulate matter (PM). In 2008-09, the estimated emissions of these pollutants were 509, 194, and 15 tons/day, respectively. The highest emissions are at ITO, one of the busiest traffic intersections in Delhi, where CO, NOx, and PM emissions are approximately 15, 6, and 0.5 tons/day, respectively. The share of vehicular emissions in Delhi increased from 25.4% in 2010 to 41% in 2018, according to the Indian Institute of Tropical Meteorology (IITM).
The transport impact is dominated by two and three-wheelers (50%) and heavy-duty vehicles (30%). The contribution from the local on-road transport sector to diurnal mean PM2.5 is largest (18%) during the evening traffic peak. The commercial four-wheeler segment, including app-based cab aggregators such as Ola and Uber, was one of the major polluting sources in Delhi in 2018. The emissions of CO and NOx due to personal cars are found to be about 34% and 50% respectively, while heavy commercial vehicles (HCVs) contribute about 92% of PM. The analysis of fuel-wise emissions reveals that CO is mainly contributed by petrol, and NOx and PM are contributed by diesel.
To combat this, the Delhi government has implemented several measures, including banning the entry of diesel-guzzling trucks into the city and encouraging carpooling and the use of public transport. By 2021, the entire Delhi Metro was expected to be 100% powered by solar energy. Smog towers will also be installed in the city to purify and clean the air.
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Construction industry fumes
Delhi's air pollution is a complex issue with multiple contributing factors, one of which is the construction industry. The construction sector plays a significant role in the city's poor air quality, and there are several ways in which it contributes to the problem.
Firstly, construction sites generate a significant amount of dust, which becomes airborne and contributes to the overall particulate matter in the air. This dust consists of tiny particles, including PM2.5, which are extremely harmful to human health. When inhaled, these particles can lodge deep in the lungs and cause a range of respiratory issues, particularly for vulnerable groups such as children, the elderly, and people with pre-existing health conditions. The constant construction of highways, flyovers, and other infrastructure projects, as mentioned by Avinash Chanchal, the deputy programme director at Greenpeace South Asia, exacerbates this issue.
Secondly, the construction industry often uses diesel generators, which produce exhaust emissions that further pollute the air. These generators are a significant source of pollution, particularly in areas with a high density of construction sites. In recognition of this problem, the Delhi government has implemented measures to ban diesel generators in the city, with some exceptions for hospitals and emergencies.
The construction industry in Delhi also contributes to the city's air pollution through the use of heavy machinery and vehicles that burn fossil fuels. The combustion of petrol, diesel, and other fuels by construction vehicles adds to the overall vehicle emissions in the city, which are a major contributor to Delhi's air pollution. The large number of vehicles used in construction, including trucks, excavators, and cranes, means that the industry has a significant impact in this regard.
Additionally, the construction sector's demand for materials and resources can indirectly contribute to air pollution. The production and transportation of construction materials, such as concrete and steel, often involve industrial processes that release pollutants into the atmosphere. The extraction and processing of raw materials, as well as the energy required for manufacturing, can result in emissions of harmful gases and particulate matter.
To mitigate the impact of the construction industry on air pollution in Delhi, several measures can be implemented. These include stricter regulation and enforcement of dust control measures on construction sites, such as water sprinkling and vacuum cleaning of roads. Additionally, encouraging the use of cleaner energy sources for machinery and vehicles, such as electric or renewable alternatives, can reduce emissions. Promoting sustainable practices within the industry, such as the use of recycled materials and the implementation of eco-friendly construction methods, can also help to reduce the industry's environmental footprint.
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Firecrackers during Diwali
Delhi's air pollution is a complex issue influenced by various factors, including firecrackers during the Hindu festival of Diwali. The use of firecrackers in Delhi during Diwali has been a longstanding tradition, with family-run businesses producing fireworks for generations. However, in recent years, there has been a growing concern about the impact of firecrackers on the city's air quality.
Diwali usually falls between October and November, a period when Delhi's air quality typically deteriorates due to crop stubble burning in neighbouring states. The festival's firecrackers add to this pollution, creating a dense layer of smoke that reduces visibility and severely affects respiratory health. Despite a ban on firecrackers, many people in Delhi continue to use them during Diwali, defying the restrictions. In 2024, the city's 24-hour average Air Quality Index (AQI) during Diwali reached 330, classified as "'very poor,'" with key areas plunging into the "severe" category.
The firecrackers contribute to the concentration of PM2.5 particles, which are extremely harmful to human health. A 2018 study found a "small but statistically significant" effect of Diwali fireworks on PM2.5 levels, with increases of almost 40% by the second day of the festival. The Indian government's Central Pollution Control Board has identified 15 substances in fireworks that are hazardous and toxic, posing risks to respiratory health, especially for children, the elderly, and those with pre-existing conditions.
The widespread use of firecrackers during Diwali has also led to safety concerns, with reports of explosions at fireworks shops and events almost every year. While the ban on firecrackers aims to address pollution and safety issues, it has disrupted the livelihoods of traditional firecracker-making communities, who now struggle to find alternative sources of income.
Overall, the use of firecrackers during Diwali significantly contributes to Delhi's air pollution, impacting the health and well-being of its residents. While efforts to enforce the ban on firecrackers have been made, the festival continues to be a challenging period for the city's air quality and the enforcement of the ban.
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Lack of strong winds
Delhi's air pollution is a complex issue influenced by various factors, including vehicular emissions, industrial activities, construction dust, and agricultural practices. One significant factor that often exacerbates the problem is the lack of strong winds, particularly during the winter months.
During winter, Delhi experiences a phenomenon known as "temperature inversion" or "winter inversion." This occurs when cooler earth surfaces reduce temperatures near the ground, preventing warm air from rising and dispersing pollutants. The stillness of the air, or lack of strong winds, allows pollutants to accumulate and linger close to the ground, forming a thick blanket of smog. This stagnant air traps a mix of emissions from vehicles, industries, and agricultural burning, creating a severe health hazard for Delhi's residents.
The absence of strong winds during winter is further compounded by other meteorological factors. For example, the Himalayas, located north of Delhi, can trap cold air within the city, hindering the vertical dispersion of pollutants. Additionally, Delhi's landlocked ecosystem and unique meteorology, coupled with high pollution levels and a dense population, contribute to the concentration of pollutants. The interplay of these factors results in a toxic cocktail of emissions that affect the air quality in Delhi and the surrounding Indo-Gangetic Plain (IGP).
The impact of weak winds on air quality is evident from wind pattern studies. In November 2023, Delhi experienced its slowest average surface wind speed in comparison to the previous six years, with a 21% decrease in wind speed. This reduction in wind speed restricted the horizontal movement of pollutants, leading to a rise in the annual average level of PM2.5, a harmful particulate matter. As a result, Delhi's air quality suffered, and the city consistently ranked among the most polluted areas globally.
The lack of strong winds during winter has severe consequences for public health and the environment. The trapped pollutants, including harmful particulate matter and toxic gases, contribute to respiratory issues, cardiovascular diseases, and other health problems for Delhi's residents. The situation is further exacerbated by the influx of pollution from neighbouring states, as Delhi receives nearly 60% of its pollution from outside the city. This complex interplay of weak winds, temperature inversion, and external pollution sources creates a challenging environment for effective air quality management in Delhi.
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Frequently asked questions
There are several factors contributing to Delhi's poor air quality. Firstly, the city is bordered by the Himalayas, which form a barrier and prevent air from dissipating. The geographical location also results in a lack of strong winds, making it difficult for air to circulate and disperse pollutants effectively. Secondly, during the winter months, a phenomenon called "temperature inversion" occurs, where cool air forms a layer near the ground, trapping pollutants and preventing their dispersion. This results in harmful chemicals concentrating in smaller areas. Additionally, Delhi's high population density and traffic contribute to vehicle emissions, with millions of cars, scooters, and auto-rickshaws on the roads, exacerbating the issue. The city's heavy construction activities and waste management issues, including landfill fires, further add to the pollution levels.
Delhi's air pollution has severe health consequences for its population. A recent study estimated that the approximately 30 million people living in and around the city could lose almost 12 years from their lives due to the detrimental effects of air pollution. The high levels of PM2.5, tiny particles that pose significant health risks, are particularly concerning. The pollution has led to hazardous conditions, especially for vulnerable populations, with an impact equivalent to smoking a large number of cigarettes daily. As a result, Delhi's air pollution contributes to a substantial number of deaths in the city annually, with more than one in ten deaths attributed to air pollution-related causes.
To tackle Delhi's air pollution, various measures have been implemented, although many of them have had limited success. These include emergency methods such as closing schools, stopping construction, and banning highly polluting vehicles during periods of severe pollution. The city has also deployed anti-smog guns and drones that spray water into the air to reduce pollution levels. Additionally, there have been attempts to restrict traffic through license plate number restrictions and the construction of smog towers. However, experts emphasize the need for a more comprehensive approach, including a radical change in energy policy, to effectively address Delhi's persistent air pollution issues.
