The World's Most Polluted Places

Air pollution is a global crisis that has severe implications for the environment and human health. According to the World Health Organization (WHO), around 9 million people die prematurely each year due to air pollution, with many more suffering from sickness, hospitalisation, reduced life expectancy, and the social and economic impacts of lost productivity and healthcare costs. While the problem is most prevalent in middle- to low-income countries, air pollution is a problem everywhere, and only 1% of the global population lives in places where WHO air quality guidelines are met. This article will explore the most polluted places in the world, the sources of their pollution, and the consequences for human health and the environment.

Air pollution kills millions annually

Air pollution is a pressing global issue that poses a significant threat to human health and the environment. According to the World Health Organization (WHO), air pollution is the "single biggest environmental threat to human health." It is linked to an estimated seven million premature deaths annually, surpassing the death toll of COVID-19 over the last two years.

The primary sources of outdoor air pollution include residential energy use for cooking and heating, vehicles, power generation, agriculture and waste incineration, and industrial activities. The burning of fossil fuels, responsible for approximately 80% of greenhouse gas emissions, is a major contributor to outdoor air pollution. This includes the combustion of coal, wood, and other biomass. In addition to its environmental impacts, air pollution has severe health consequences, particularly for vulnerable populations such as children, the elderly, pregnant women, and individuals with respiratory conditions.

The effects of air pollution are evident in cities with high pollution levels, such as Byrnihat and Delhi in India, and Dera Ismail Khan in Pakistan. These cities have recorded dangerously high levels of PM2.5, a type of fine particulate matter. In 2024, Byrnihat had a PM2.5 concentration of 128.2 µg/m³, over 25 times higher than the WHO's recommended limit. Delhi, with a population of over 30 million people, recorded an annual PM2.5 level of 108.3 µg/m³ in 2025. Breathing the air in these cities is equivalent to smoking nearly two to three cigarettes a day, posing significant health risks to residents.

The impacts of air pollution are devastating and far-reaching. In Bosnia and Herzegovina, for example, people living near outdated coal-fired power plants have shared stories of loved ones dying from cancer, cardiovascular ailments, and respiratory diseases, which they attribute to air pollution. The elderly in particular suffer from the debilitating effects of toxic air, often experiencing isolation, limited access to necessities, and a decline in their quality of life.

Addressing air pollution is crucial to protecting public health and the environment. Implementing policies and initiatives that promote sustainable land use, cleaner energy sources, improved waste management, and energy-efficient housing can effectively reduce air pollution levels. Transitioning from fossil fuels to clean energy, such as wind and solar power, is essential to mitigating both air pollution and climate change. By taking concerted action, we can save millions of lives and create a healthier, more sustainable future for all.

India: home to the world's most polluted cities

India is home to some of the world's most polluted cities, with 11-14 of the top 20 polluted cities worldwide in 2024. This number rose to 63 when considering the list of 100 most polluted places. Byrnihat, a city in northeastern India located on the Assam-Meghalaya border, has been named the most polluted city in the world, with a PM2.5 concentration of 128.2 µg/m³—over 25 times higher than the World Health Organization's recommended limit. Delhi, a metropolis of over 30 million people and the capital territory of India, recorded the second-worst air pollution levels in 2024 and has been ranked as the world's most polluted capital for six consecutive years. Other Indian cities that feature among the world's most polluted include Mullanpur, a town in Punjab, and West Bengal.

The air pollution in India is caused by various factors, including vehicular traffic fumes, diesel generators, the burning of fossil fuels for cooking, industrial activities, waste burning, and farmers setting fields alight after harvesting crops. These pollutants, particularly nitrogen oxides, react with ultraviolet radiation from the sun to form smog, which poses higher risks of respiratory illnesses. The consequences of air pollution are dire, with The Lancet estimating that air pollution kills more than 1 million people in India every year. According to the World Health Organization, air pollution from coal, oil, and gas-burning sources kills nearly 9 million people worldwide annually, with 91-99% of the global population living in areas where air quality exceeds WHO guidelines.

The Air Quality Index (AQI) categorizes air quality as 'satisfactory' when values are between 0 and 100. Values from 101 to 200 are considered unhealthy for at-risk groups, while 201 to 300 are deemed unhealthy for everyone, and levels above 300 are hazardous for all. As of March 17, 2025, Delhi's AQI had dropped to 85 ('Satisfactory' level), although the PM2.5 level of 41 µg/m³ was still 2.67 times higher than the WHO's safe limit. Similarly, Mullanpur's AQI was 124, falling under the 'Unhealthy' category.

The high levels of air pollution in India highlight the urgent need for air quality improvements to protect public health and ensure a cleaner, safer environment for residents.

The dangers of PM2.5 particles

As of 2025, Byrnihat, India, is the most polluted place in the world, with a PM2.5 concentration of 128.2 µg/m³—over 25 times higher than the World Health Organization’s recommended limit. Delhi, India, is the world's most polluted capital for the sixth year in a row, with a PM2.5 level of 108.3 µg/m³.

PM2.5 refers to fine particles or particulate matter that are 2.5 microns or less in width. They are a mixture of many chemical species, composed of solids and aerosols composed of small droplets of liquid, dry solid fragments, and solid cores with liquid coatings. They can be emitted directly from sources like vehicle exhaust, burning wood, gas, and other fuels, or formed in the atmosphere through chemical reactions of gases.

PM2.5 particles are dangerous because they are small enough to be inhaled and deposited on the surface of the deeper parts of the lung. Exposure to PM2.5 particles has been linked to a variety of health problems, including:

• Premature death in people with heart or lung disease
• Increased respiratory symptoms, such as irritation of the airways, coughing, sneezing, a runny nose, and difficulty breathing
• Worsening of medical conditions like heart disease and asthma
• Increased risk for heart attacks
• Restricted activity days

Air pollution in Pakistan

Pakistan is an Islamic republic located in South Asia, with a population of about 212.2 million people, making it the fifth most populous country in the world. Pakistan's cities are among the most polluted in the world, with Gujranwala and Faisalabad ranking third and fourth, respectively, in terms of PM2.5 readings. These cities have high levels of smoke, haze, and smog, which have detrimental effects on the health of their inhabitants.

The main sources of air pollution in Pakistan include vehicle emissions, factory pollution, and seasonal activities such as stubble burning in the winter. In addition, the burning of fossil fuels, crop residues, and brick kilns also contribute significantly to the country's air pollution levels. Pakistan's contribution to global warming is less than 1%, but the impact of air pollution on human health within the country is significant. According to a report by the Energy Policy Institute at the University of Chicago, air pollution reduces the average life expectancy in Pakistan by 3.8 years, with a more severe impact of 7 years in the most polluted areas. The report also highlights the association between high ambient temperatures and an increase in intimate partner violence against women in low and middle-income countries in South Asia, including Pakistan.

The World Bank estimates that there are approximately 22,000 premature adult deaths in Pakistan annually due to air pollution, with respiratory disorders and cardiovascular problems being the leading causes, especially among vulnerable populations such as children and the elderly. A study by Ghani et al. found that 18% of residents in Karachi suffered from chronic respiratory symptoms, and an estimated 5% of all new cancer cases in Pakistan are lung cancers, the second most common type among men.

While Pakistan faces significant challenges in addressing air pollution, it is not alone in its struggle. Many neighbouring countries, including India, China, Iran, and Afghanistan, also grapple with substantial pollution problems. However, Pakistan's ranking as the second most polluted country in the world in 2019 underscores the urgency of improving air quality to protect the health and well-being of its citizens.

The world's cleanest countries

According to a 2024 study by the Environmental Performance Index (EPI), Estonia is the cleanest country in the world, with an EPI score of 75.3. The EPI measures 58 performance indicators across 11 categories related to three overarching policy objectives: ecosystem vitality, climate change performance, and environmental health. These categories include air quality, water and sanitation, biodiversity and habitat, and sustainability.

New Zealand has the cleanest air in the world, according to a 2024 report by Swiss air quality organisation IQAir. New Zealand's excellent atmospheric purity is partly due to its low population density, island status, and significant use of renewable energy. Abundant forests also absorb pollutants, while strict environmental regulations help maintain clean air.

Other countries that feature in the EPI's top ten include Luxembourg, Germany, Finland, the United Kingdom, Sweden, Norway, Austria, Switzerland, and Denmark. Notably, eight out of the top ten "cleanest" countries, according to the EPI, are in Europe. These countries have invested significantly in renewable energy infrastructure, waste management, and environmental policy.

The cleanest city in the world is Vienna, Austria, according to global consulting firm Mercer's Quality of Living City Ranking 2023. The country with the cleanest water is Italy, tied with the US, according to the EPI's latest rankings for unsafe drinking water quality.

Frequently asked questions