Bronte Wells
Air pollution is a critical threat to human health and the environment, causing over 4.5 million premature deaths in 2019. It is a significant concern in emerging and developing countries, where global environmental standards are often not met. The top 5 most polluted countries are Bangladesh, Pakistan, India, Bahrain, and Nepal. In 2025, the top 10 most polluted cities included Byrnihat, Delhi, and Karaganda, with 13 of the top 20 most polluted cities in India. The only city outside of Asia in the top 20 was N'Djamena, the capital of Chad in central Africa.
| Characteristics | Values |
|---|---|
| Location | The majority of the world's most polluted cities are in Asia, with 13 in India, 4 in Pakistan, and 1 in China and Kazakhstan respectively. The only city outside of Asia in the top 20 is N'Djamena, the capital of Chad in central Africa. |
| Health Impact | Air pollution can trigger asthma attacks, harm lung development in children, and even be deadly. It can also cause respiratory conditions, cardiovascular diseases, lung cancer, and increase the risk of early death, heart attacks, strokes, and emergency room visits. |
| Environmental Impact | Air pollution can lead to acid rain, eutrophication, and climate change. |
| Economic Impact | Air pollution results in increased medical costs and reduced productivity. |
| Causes | Major causes of pollution include fossil fuel use, vehicular emissions, industrial activities, agriculture, and poor waste management. |
| Solutions | Efforts to combat air pollution include the Paris Agreement, sustainable practices, cleaner technologies, and stronger industrial regulation. |
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What You'll Learn
Most polluted cities in the world
According to the World Health Organization (WHO), air pollution from burning coal, oil, and gas kills around 9 million people annually. Furthermore, 99% of the global population currently resides in areas where the air quality surpasses the WHO guideline limits. The biggest sources of air pollution are the burning of fossil fuels in power plants and for transportation.
In 2024-25, 126 out of 138 countries and regions assessed exceeded the WHO's annual guidelines for PM2.5 concentrations. Central and South Asia host the world's top seven most polluted cities, with India being home to 13 of the 20 cities identified as the most polluted globally. Byrnihat, on the border of Assam and Meghalaya, has been identified as the most polluted city in the world, with an annual average PM2.5 concentration of 128.2 μg/m³. Delhi, India's capital, remains the most polluted capital city globally for the sixth year in a row, with an average PM2.5 concentration of 13.2 times higher than the WHO's new limit. Other Indian cities like Ghaziabad have also been ranked among the most polluted in previous years.
Outside of India, Hotan in China is the second most polluted city, with an average Air Quality Index (AQI) of 110.1 in 2019. Hotan's pollution is attributed to rapid industrialization and frequent sandstorms.
It is worth noting that access to real-time pollution data is limited in many countries, especially within Africa and the Middle East, which may impact the accuracy of pollution rankings.
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Most polluted cities in the US
According to the American Lung Association's (ALA) 2024 and 2025 State of the Air reports, several cities in California are among the most polluted places in the United States when it comes to air quality. The reports rank cities based on their weighted average number of unhealthy air days, with the city with the highest number receiving a rank of #1.
In 2024, six of the top seven most polluted cities were in California, with Bakersfield, Visalia, and Fresno taking the top three spots. These cities are located in the Central Valley, a 450-mile flat valley bordered by the Coast and Sierra Nevada mountain ranges. The valley tends to trap pollution from the large population centres on the coast, and the southern end of the valley, where Bakersfield, Visalia, and Fresno are located, experiences drier and hotter conditions that further worsen air quality.
In 2025, the ALA's report again highlighted Bakersfield, Visalia, and Fresno-Madera-Hanford as the top three metropolitan areas with the worst year-round particle pollution. Other highly polluted cities outside of California included Eugene-Springfield in Oregon and Detroit-Warren-Ann Arbor in Michigan.
The high levels of air pollution in these cities are primarily driven by a combination of vehicle emissions, industrial facilities, wildfires, and geographical factors. Particulate matter in air pollution can be extremely small, allowing it to bypass the body's natural defences when inhaled. This can lead to serious health risks, including an increased risk of premature birth, lower birth weight in newborns, asthma attacks, and harm to lung development in children.
It is important to note that air pollution is not limited to specific cities but can vary within different areas of a city. Individuals can protect themselves by checking air quality forecasts and avoiding outdoor activities when unhealthy air quality is expected. Additionally, addressing air pollution requires collective efforts and policy interventions at all levels of government to implement and enforce effective pollution reduction measures.
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Causes of air pollution
Air pollution is a serious environmental threat to public health globally, impacting our health, development, and environment. It is caused by solid and liquid particles and certain gases that are suspended in the air. These particles and gases can come from car and truck exhaust, factories, dust, pollen, mould spores, volcanoes, and wildfires.
One of the major causes of air pollution is vehicle emissions. Cars, trucks, and other vehicles emit pollutants such as nitrogen oxides, carbon monoxide, and particulate matter. These emissions can lead to the formation of ground-level ozone, which is a major cause of smog in cities. Additionally, the combustion of fossil fuels, such as coal and petroleum, releases harmful particles and gases into the atmosphere.
Industrial activities are another significant contributor to air pollution. Factories, power plants, and other industrial facilities release pollutants through manufacturing processes, fuel combustion, and chemical production. These emissions include particulate matter, carbon monoxide, nitrogen oxides, and volatile organic compounds. Poor waste management practices in industries can also lead to air pollution.
Agricultural practices can also contribute to air pollution. The use of fossil fuels and fuel oils in agriculture, as well as the burning of crop residues, release harmful pollutants into the air. Additionally, open fires and simple stoves used for cooking and heating, especially in low- and middle-income countries, expose billions of people to dangerous levels of household air pollution.
Natural sources, such as wildfires and volcanic eruptions, also play a role in air pollution. Wildfires release smoke and particulate matter into the atmosphere, while volcanic eruptions emit ash, gases, and hazardous substances. Climate change further exacerbates air pollution by enhancing conditions for ozone pollution and increasing the risk of wildfires.
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Health impacts of air pollution
Air pollution is a major threat to global health and prosperity. It is caused by a mix of hazardous substances from both human-made and natural sources. Vehicle emissions, fuel oils, natural gas used to heat homes, by-products of manufacturing and power generation, and fumes from chemical processes are some of the major sources of air pollution. Air pollution is the presence of contaminants such as dust, fumes, gases, mist, odour, smoke, or vapour in the atmosphere in quantities that can be harmful to human health.
The main pathway of exposure to air pollution is through the respiratory tract. Pollutants like fine particulate matter (PM) can penetrate deep into the lungs, enter the bloodstream, and travel to organs, causing systemic damage to tissues and cells. Ozone (O3), a powerful lung irritant, is another common pollutant that causes inflammation and damage to the lining of the small airways, impacting multiple body systems. Other major pollutants include carbon monoxide (CO), nitrogen dioxide (NO2), and sulphur dioxide (SO2).
Health problems in children and adults can occur due to both short-term and long-term exposure to air pollution. Short-term exposure to higher levels of air pollution is associated with reduced lung function, triggering asthma attacks, and causing respiratory problems such as coughing, chest tightness, and shortness of breath. It can also lead to cardiac issues, including heart attacks. Long-term exposure to air pollution increases the risk of various diseases, including stroke, heart disease, chronic obstructive pulmonary disease, lung cancer, and other types of cancer.
Certain populations are more vulnerable to the health impacts of air pollution. Children, the elderly, pregnant women, and people with pre-existing health conditions, especially heart and lung disease, are more susceptible to adverse effects. Additionally, psychosocial stress factors such as poverty, racial discrimination, and residency status can amplify the harmful effects of air pollution. Maternal exposure to air pollution has been linked to adverse birth outcomes, such as low birth weight, pre-term birth, and an increased risk of hypertensive disorders during pregnancy.
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Efforts to combat air pollution
Air pollution is a critical environmental threat to public health globally, impacting our health, development, and environment. The top 10 most polluted cities in 2025 include Byrnihat, India; New Delhi, India; and Karaganda, Kazakhstan. The top 5 most polluted countries are Bangladesh, Pakistan, India, Bahrain, and Nepal. Major causes of pollution include fossil fuel use, vehicular emissions, industrial activities, agriculture, and poor waste management.
Sustainable practices and cleaner technologies
The Paris Agreement and companies like Oizom aim to combat air pollution through sustainable practices and cleaner technologies. Oizom offers advanced air quality monitoring devices that provide accurate, real-time data on pollutants and environmental conditions.
Education, guidance, and incentives
Organizations like the Minnesota Pollution Control Agency (MPCA) provide education, guidance, and incentives to reduce air pollution. They offer programs for businesses, cities, nonprofits, and communities to address a range of environmental problems, including air quality.
Reducing vehicle emissions
Vehicle exhaust is a major source of air pollution. Individuals can contribute by driving less, carpooling, biking, using public transportation, or opting for electric vehicles. Keeping vehicles well-maintained and fixing exhaust and oxygen sensor problems can also help reduce emissions.
Limiting backyard fires
Smoke from backyard fires can cause unhealthy conditions, especially during stagnant weather. In some cities, it is illegal to burn waste in fires. It is recommended to keep fires small and brief, burn only dry firewood, and avoid campfires during air quality alerts.
Energy conservation and efficient appliances
Using less energy and choosing efficient appliances and heating systems can help reduce air pollution. Getting an energy audit and following the recommendations is a good step towards energy conservation.
Tree planting and greening initiatives
Trees filter pollutants, absorb carbon dioxide, release oxygen, and help cool the atmosphere. Initiatives like GreenStep Cities aim to promote local ordinances, create incentives for beneficial behaviors, and educate residents on best practices for improving air quality.
These collective efforts are crucial in combating air pollution and mitigating its harmful impacts on human health and the environment.
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Frequently asked questions
The countries with the highest air pollution are Bangladesh, Pakistan, India, Bahrain, and Nepal.
The cities with the highest air pollution include Byrnihat, Delhi, Karaganda, and N'Djamena.
Air pollution can cause respiratory conditions, cardiovascular disease, lung cancer, and premature death. It can also trigger asthma attacks and harm lung development in children.
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