Meghan Hodges
Air pollution is a pressing global issue, with millions of people vulnerable to its deadly effects. It is a significant health risk, causing asthma attacks, hindering lung development in children, and contributing to premature deaths. Climate change exacerbates the problem by increasing the frequency of wildfires, which release harmful particle pollution into the atmosphere. In 2024, only 17% of cities met the World Health Organization's PM2.5 guideline, indicating that the majority of urban populations breathe unhealthy air. This paragraph introduces the topic of air pollution and sets the context for exploring the cities with the highest levels of air pollution.
| Characteristics | Values |
|---|---|
| City with the highest air pollution | Byrnihat, India |
| PM2.5 concentration | 128.2 micrograms per cubic meter |
| World Health Organization's recommended limit | 5 µg/m3 |
| Number of Indian cities in the top 20 | 11 |
| India's second-most polluted city | Delhi |
| Delhi's population | Over 30 million |
| Delhi's winter air pollution causes | Crop burning in nearby states, stagnant cold air, weak wind patterns |
| California cities in the top seven | Six |
| California cities | Bakersfield, Visalia, Fresno |
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What You'll Learn
- Indian cities dominate the list of the world's most polluted cities
- Delhi is India's most polluted city
- Pollution is caused by industrial emissions, vehicle exhaust, and fossil fuels
- Climate change increases the risk of wildfires, which spread particle pollution
- Air pollution is linked to health issues, including asthma, lung cancer, and heart disease
Indian cities dominate the list of the world's most polluted cities
Air pollution is a critical global health crisis, with many cities worldwide recording dangerous levels of air pollution. According to the World Health Organization (WHO), several cities have recorded annual pollution levels exceeding the recommended limit of 5µg/m3 by over 15 times. The presence of particulate matter in the air, particularly PM2.5, poses significant health risks to humans. These fine particles, measuring less than 2.5 micrograms in width, can infiltrate the lungs and bloodstream, increasing the risk of diseases such as stroke, lung cancer, heart disease, and respiratory illnesses.
Indian cities have consistently featured prominently on the list of the world's most polluted cities. Despite substantial efforts and investments in air pollution control programs, sixteen Indian cities were listed among the top 50 most polluted cities globally. This issue persists even after receiving close to Rs 1,000 crore collectively over eight years to combat air pollution. The ineffectiveness of these measures is concerning, with some cities under the National Clean Air Programme (NCAP) still struggling to improve their air quality.
In 2024, India witnessed a 7% decline in PM2.5 concentrations compared to the previous year, yet it remains home to six of the world's ten most polluted cities. This is attributed to various factors, including the widespread existence of large air pollution monitoring networks. The high population density and industrialization in these cities contribute to the persistent air quality issues.
While Indian cities dominate the list of the most polluted cities, it is important to recognize that air pollution is a global issue. Cities in other countries, such as those in the United States, also face significant air quality challenges. The American Lung Association's "State of the Air" report for 2025 revealed that nearly half of Americans live in areas where air pollution levels received a failing grade. Therefore, addressing air pollution requires a collective effort from governments, organizations, and individuals worldwide to implement effective policies and take concrete actions to improve air quality and protect public health.
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Delhi is India's most polluted city
Delhi, India's capital, has consistently been ranked as the world's most polluted capital city. In 2023, the city's air quality index (AQI) was recorded at 640, placing it in the ""hazardous" category. The poor air quality in Delhi is attributed to various factors, including industrial and vehicular emissions, crop stubble burning in neighbouring states, low wind speeds, and firecrackers during festivals. The pollution levels have severe health impacts, with Delhi's residents experiencing eye irritation, itchy throats, and respiratory issues.
Delhi's air pollution is a persistent issue, and in 2024, it was again ranked as the most polluted capital city in the world. According to the World Air Quality Report, Delhi had an average PM 2.5 concentration of 91.8 μg/m3, which is significantly higher than the World Health Organization's (WHO) annual PM2.5 guideline of 5 μg/m3. The high levels of PM2.5, or fine particulate matter, pose a serious risk to the health of Delhi's residents, as these particles can lodge deep in the lungs and cause a range of diseases.
The pollution in Delhi has severe consequences for the well-being of its residents. Studies have shown that air pollution in the city reduces life expectancy in India by an estimated five years. The high levels of PM2.5 pollution are linked to an increased risk of stroke, lung cancer, heart disease, and respiratory diseases. The situation is exacerbated by the lack of effective pollution-control measures and weak enforcement of environmental laws in India.
While Delhi has seen a slight improvement in air quality in recent years, dropping to the fifth most polluted country in the world in 2024, the National Capital Region (NCR) remains heavily polluted. The Indian government has taken some steps to address the issue, such as temporarily shutting down schools and colleges during periods of toxic air quality. However, more stringent measures and improved industrial regulation are necessary to combat the air pollution crisis in Delhi and other Indian cities.
Delhi's struggle with air pollution is indicative of a broader problem in India, where rapid industrialisation and weak environmental enforcement have led to dangerous levels of pollution. It is crucial for policymakers and stakeholders to prioritise clean air initiatives and strict pollution control regulations to protect the health and well-being of India's citizens. The situation in Delhi highlights the urgent need for collective efforts to address air pollution and mitigate its harmful impacts on human health and the environment.
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Pollution is caused by industrial emissions, vehicle exhaust, and fossil fuels
Air pollution is a pressing issue that poses significant health risks to millions of people worldwide. It is primarily caused by industrial emissions, vehicle exhaust, and the burning of fossil fuels, which release a complex mixture of gases, particles, and liquid droplets into the atmosphere. These pollutants have severe consequences for human health and the environment.
In 2024, Byrnihat, a city in northeastern India, recorded the worst air pollution globally, with a PM2.5 concentration of 128.2 micrograms per cubic meter. This level is alarmingly over 25 times higher than the World Health Organization's recommended limit of 5 µg/m3. Delhi, India's capital territory, recorded the second-worst air pollution levels in the same year, experiencing severe winter air pollution driven by crop burning, stagnant cold air, and weak wind patterns that trap smog.
The problem of air pollution is not limited to a single city or country. In 2024, 11 of the top 20 most polluted cities were in India, with other highly polluted cities located in Pakistan and other parts of Asia. N’Djamena, Chad, was the only non-Asian city to rank among the top 20. Additionally, nearly half of the people in the United States live in areas where the air quality received a failing grade in the "State of the Air" report for 2025.
The sources of air pollution vary depending on the location. For example, in rural areas, wildfires and cookstoves contribute significantly to air pollution, while in cities, road dust and diesel exhaust are major culprits. In the United States, farms, forest management and agricultural waste burning, and road dust were the top three local sources of PM2.5 emissions in 2023. Furthermore, air pollution has both health and economic impacts. It increases the risk of various diseases, including lung cancer, cardiovascular disease, and respiratory illnesses, and it also negatively affects worker productivity, increases absenteeism, and drives up healthcare costs.
To address the issue of air pollution, it is crucial to reduce industrial emissions, transition to cleaner energy sources, and implement measures to mitigate vehicle exhaust. Additionally, strengthening regulations and enforcing air quality standards are essential steps in combating this global health crisis. By raising awareness, advocating for policy changes, and adopting cleaner technologies, we can strive for cleaner and healthier environments for current and future generations.
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Climate change increases the risk of wildfires, which spread particle pollution
Climate change has been a key factor in increasing the risk and extent of wildfires. Warmer, drier conditions, caused by climate change, contribute to the spread of insects that weaken or kill trees, building up the fuel in forests. Research shows that changes in climate create warmer and drier conditions, with increased drought, and a longer fire season, all of which increase the risk of wildfires. For instance, Alaska's record-breaking heat and dry conditions in the summer of 2020 set the conditions for the state's historic wildfire season.
Wildfires themselves are a source of air pollution, releasing a range of pollutants into the atmosphere, including black carbon, carbon monoxide, nitrogen oxides, and particulate matter. These pollutants can combine with existing air pollution, further increasing the harmful effects of smoke on human health and the environment. The smoke from wildfires spreads dangerous particle pollution, which can cause severe health issues, especially for vulnerable groups such as children, older adults, and people with lung diseases.
The impact of wildfires on air quality can be significant and far-reaching. For example, the 2020 wildfires in California and Oregon caused historic levels of wildfire spread and damage, leading to weeks of unhealthy air quality for millions of people. Similarly, the 2023 wildfires in Chile resulted in increased levels of all air pollutants, with drastic increases in short-term exposure to ozone. The authors of the WMO bulletin noted the "extreme detriment to air quality caused by intense and persistent wildfire events made more common in a warming climate."
The relationship between climate change, wildfires, and air pollution is a vicious cycle. Wildfires release greenhouse gases and black carbon, a super pollutant that contributes to global warming and further increases the frequency and intensity of wildfires. This cycle threatens people, animals, and the planet, underscoring the urgent need for policymakers to address these interconnected issues.
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Air pollution is linked to health issues, including asthma, lung cancer, and heart disease
Air pollution is a pressing issue that poses significant risks to human health. It encompasses a range of pollutants, including particulate matter (PM), carbon monoxide (CO), ozone (O3), nitrogen dioxide (NO2), and sulphur dioxide (SO2). These pollutants have been linked to a higher risk of various diseases and adverse health outcomes.
One of the most concerning aspects of air pollution is its association with respiratory conditions such as asthma. Exposure to air pollution can trigger asthma attacks and exacerbate symptoms in people with existing asthma. Children are particularly vulnerable, as their lungs are still developing, and they breathe faster, inhaling more polluted air. Research indicates that children exposed to air pollution are at an increased risk of developing asthma and experiencing more severe asthma attacks, leading to higher hospitalization rates.
Air pollution has also been implicated in the development and progression of lung cancer. Particulate matter, especially the smaller PM2.5 particles, can reach the breathing sacs in the lungs and even cross into the bloodstream. These particles can carry toxic chemicals linked to cancer. Long-term exposure to fine particulate matter increases the risk of lung cancer, as evidenced by studies showing a correlation between air pollution and higher lung cancer incidence and mortality.
In addition to respiratory issues, air pollution contributes to cardiovascular problems. The inhalation of particulate matter can lead to heart attacks and influence the development of heart disease. This is supported by research indicating that long-term exposure to PM2.5 particles is associated with an elevated risk of early death, particularly from cardiovascular causes. The presence of particle pollution in the body can result in cellular injury and systemic inflammation, placing additional stress on the heart and other organs, thereby worsening existing heart conditions.
Lastly, air pollution has been linked to a range of other health issues. For example, ozone and particle pollution are associated with an increased risk of premature birth and lower birth weight in newborns. Exposure to air pollution can also worsen existing conditions such as diabetes, cognitive impairment, neurological diseases, and mental health issues such as clinical depression and anxiety. Overall, air pollution is a pervasive health concern that extends beyond asthma, lung cancer, and heart disease, underscoring the importance of addressing it to safeguard public health.
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Frequently asked questions
Bakersfield, California, is the most polluted city in the United States, according to the American Lung Association's 2024 State of the Air Report.
Visalia and Fresno, which are also in California, are ranked second and third, respectively.
Many Indian cities feature on the list of the world's most polluted cities, thanks to large and wide air pollution monitoring networks.
