The world now is facing the problem of air pollution leading to the most severe environmental health problems globally. This air pollution contributes to millions of premature deaths each year.
One of the measurements used to determine pollutants in certain areas is using fine particulate matter concentration, namely particles with a diameter of 2.5 micrometers or less. These are especially dangerous since they can penetrate deep into the lungs and bloodstream.
Referring to the contamination of these pollutants in the world, out of many cities, there are four of the most polluted cities: Delhi in India, Lahore in Pakistan, Hotan in China, and Dhaka in Bangladesh. According to the IQAir World Air Quality Report, all four cities record PM2.5 levels that are many times above the WHO annual guideline of 5 µg/m³.
| City | Country | Annual PM2.5 (2024) | Times Above WHO Guideline | Primary Pollution Source |
|---|---|---|---|---|
| Delhi | India | 108.3 µg/m³ | More than 20x | Vehicle emissions, crop burning |
| Lahore | Pakistan | 102.1 µg/m³ | More than 20x | Vehicle exhaust, brick kilns |
| Hotan (Hetian) | China | ~100+ µg/m³ | ~20x | Desert dust, coal burning |
| Dhaka | Bangladesh | 78 µg/m³ | 15.6x | Brick kilns, traffic, industrial emissions |
Contents
Causes, Impacts, and Solutions That Make These Cities Polluted
Delhi, India
Delhi is India’s capital and one of the biggest world megacities with a population over 32 million people. It has one of the highest average PM2.5 concentrations among large cities. In 2024, Delhi’s annual average PM2.5 was 108.3 µg/m³. This level is more than 20 times the WHO guideline and higher than many previous years on record.
Here are some causes of this pollution. The major causes are vehicle emissions and industrial and power plant emissions. Since this city has millions of vehicles like cars, trucks, and two-wheelers on the road, transport is a dominant cause of nitrogen oxides and particulate emissions leading to pollution.
Industrial and power plant emissions in Delhi also contribute to the level of airborne pollution in this city. The pollutants penetrate densely populated neighborhoods.
Other causes are crop burning and construction and road dust. Delhi sees seasonal agricultural burning in surrounding areas like Punjab and Haryana. This adds large amounts of smoke and PM2.5 into the air. While construction and road dust come from the city’s rapid development that worsens smog during dry winter months.
The pollution creates health and social impacts. Studies correlate Delhi’s air pollution to a range of health problems, such as respiratory and cardiovascular diseases. These are due to long-term PM2.5 exposure. There are also premature deaths, namely over 17,000 pollution-related deaths annually.
Experts estimate reduced life expectancy caused by chronic exposure up to eight years in some worst-affected districts. The pollution also leads to an increased economic burden. Families and public services face high healthcare costs and lost productivity.
To solve pollution in Delhi, the Indian government and local authorities have applied some policies. To reduce road congestion, there are odd-even vehicle restrictions and expansion of electric vehicle incentives. The policy is also concerning stricter emissions standards and enforcement of industrial pollution limits. Both efforts will be necessary for lasting improvement.
Lahore, Pakistan
Lahore as Pakistan’s cultural capital with over 14 million population also faces high levels of pollution with an annual average PM2.5 concentration of 102.1 µg/m³ in 2024. It ranks among the most polluted cities on Earth.
The main cause is almost similar to Delhi, namely vehicular emissions. With a large population, Lahore has an estimate that around 83% of poor air quality stems from vehicle exhaust and traffic congestion.
Other causes are from seasonal crop burning, brick kilns using outdated brick manufacturing technologies, and also uncontrolled waste burning from solid waste. All of which add to toxic air loads.
Lahore’s air pollution results in some health problems such as increased respiratory illnesses such as bronchitis and asthma, cardiovascular risks, and increasingly higher hospitalization rates during smog episodes. The pollution also leads to poor visibility and transportation delays which then affects daily life and commerce.
The government has taken some approaches to solve the pollution. They are modernizing brick kilns by using cleaner technologies, implementation of stricter vehicle emission standards to decrease the level of emission, and also creating better urban planning and waste management systems.
Hotan, China
Hotan, also known as Hetian, is a city in China’s Xinjiang region located at the edge of the Taklamakan Desert. It is also one of the most polluted cities in the world with a PM2.5 level that regularly exceeds 100 µg/m³ annually, roughly 20 times the WHO guideline.
Here are some causes of this pollution. One of the unique major causes is natural desert dust. The Taklamakan Desert produces massive dust storms that push huge amounts of fine particles into the city. This is different from most other polluted cities where human activity is the dominant source.
Other causes are from coal burning for residential heating during the cold winter season, light industrial activities, and vehicle emissions. All of which add to the already high dust load in the air.
The pollution creates health and social impacts. Residents face high rates of respiratory illness, especially during dust storm episodes when PM2.5 spikes suddenly. Long-term exposure to combined mineral dust and combustion particles creates serious risk of lung disease.
Some suggested policies to address the pollution include expanding shelterbelts and vegetation at the desert margins to reduce dust intrusion, transitioning residential heating from coal to cleaner energy sources, and improving emissions standards for local industry and transport.
Dhaka, Bangladesh
Another city with a high average PM2.5 level of 78 µg/m³ in 2024, namely about 15.6 times the WHO guideline, is Dhaka. This city is one of the world’s most densely populated cities.
Dhaka has its primary pollution causes such as brick kiln emissions in the city, heavy traffic and poorly maintained vehicles, industrial emission and construction dust, as well as waste burning and open biomass fuels. All of which add to airborne contaminants and contribute toxic smoke.
The population in Dhaka certainly faces health and social impacts of this pollution. They endure cardiovascular and respiratory mortality. Studies have shown that every 10 µg/m³ increase in PM2.5 has a significant correlation with actual increases in cardiovascular deaths. The pollution also leads to other chronic diseases related to long-term exposure including lung cancer and stroke.
As mitigation strategies, the government of Bangladesh must implement some policies. They are stricter enforcement of emission standards for vehicles and industries, relocation and regulation of industries with intensive pollution production away from residential areas, promotion of vehicles using clean fuels or electric public transport, and also expansion of green belts and urban forestry in order to absorb pollutants.
The pollution case in Delhi, Lahore, Hotan, and Dhaka presents the complex interplay of decreasing air quality caused by industrialization, urban growth, regional practices, and energy use. This affects the largest population health and causes economic losses. The issue can only be handled by multi-sectoral actions.
How to Protect Yourself From Air Pollution
While governments work on long-term policies, individuals can take steps to reduce their exposure. Since most people spend the majority of their time indoors, improving indoor air quality is one of the most practical things a person can do. A good air purifier with HEPA filtration can significantly reduce indoor PM2.5 concentrations. In heavily polluted cities, this can make a real difference to daily exposure levels.
Air pollution can also affect water quality over time, as particulates carrying heavy metals settle into water sources. Having a reliable water purifier at home adds another layer of protection in areas where environmental contamination is severe.
“In cities where outdoor PM2.5 regularly exceeds 100 µg/m³, the indoor environment becomes the most important space to protect. When we designed Legom’s air purifiers, we focused specifically on high-pollution environments where the filter load is heavy and the fine particle concentration is extreme. HEPA filtration can remove the vast majority of PM2.5 particles from indoor air. It does not solve the outdoor problem, but it gives families a real reduction in the daily exposure that adds up over months and years.”
— Maggie Shen, Founder of Legom
Frequently Asked Questions
What does PM2.5 mean?
PM2.5 refers to fine particulate matter with a diameter of 2.5 micrometers or less. These particles are especially dangerous because they can penetrate deep into the lungs and enter the bloodstream. The WHO sets an annual average guideline of 5 µg/m³. Cities like Delhi and Lahore regularly record levels more than 20 times this guideline.
Why is Delhi considered one of the most polluted cities in the world?
Delhi’s pollution comes from multiple major sources at the same time, namely millions of vehicles on the road, industrial and power plant emissions, seasonal crop burning in surrounding states, and construction dust. These combine with winter weather patterns that trap pollutants close to ground level. In 2024, Delhi’s annual average PM2.5 was 108.3 µg/m³, more than 20 times the WHO guideline.
What makes Hotan different from other polluted cities?
Unlike Delhi or Lahore where human activity is the dominant source of pollution, Hotan faces a major natural pollution source: the Taklamakan Desert. Dust storms from this desert push massive quantities of fine particles into the city. This natural dust combines with coal burning for winter heating and other local emissions, creating extreme PM2.5 levels that make Hotan one of the most consistently polluted cities in the world.
Can air purifiers help in polluted cities?
Yes. While an air purifier cannot clean outdoor air, it can significantly reduce indoor PM2.5 concentrations. Since most people spend the majority of their time indoors, a good HEPA air purifier can meaningfully lower the daily exposure that accumulates over time. This is especially relevant in cities like Delhi, Lahore, Hotan, and Dhaka where outdoor air quality is far above safe levels for extended periods of the year.
What are the long-term health effects of living in heavily polluted cities?
Long-term exposure to high PM2.5 levels is linked to respiratory and cardiovascular diseases, lung cancer, stroke, and premature death. Studies in Delhi show that chronic exposure has reduced life expectancy by up to eight years in the worst-affected districts. Research in Dhaka shows that every 10 µg/m³ increase in PM2.5 correlates with a statistically significant increase in cardiovascular deaths. The health impacts are not limited to the lungs. The particles enter the bloodstream and affect multiple organ systems over time.
Reviewed and updated by the LEGOM Technical Team on May 26, 2026. This article covers PM2.5 air pollution data for the world’s most polluted cities in 2025–2026, including Delhi, Lahore, Hotan, and Dhaka. Data is referenced from the IQAir World Air Quality Report. This article is updated periodically as new annual air quality data becomes available.