Greta Jimenez
Air pollution is a serious health threat, affecting millions of people worldwide. In 2024, many of the world's most polluted cities were located in India, Pakistan, and other parts of Asia. Indian cities, in particular, struggled with severe air pollution due to industrial emissions, vehicle exhaust, and the reliance on fossil fuels, all exacerbated by weak regulations and seasonal weather patterns. Lahore, Pakistan, topped the list for PM2.5 pollution, while Byrnihat in India recorded the worst air pollution globally in 2024, with PM2.5 concentrations over 25 times higher than the World Health Organization's recommended limit. Aside from Asia, N'Djamena in Chad was the only non-Asian city to rank among the top 20 most polluted cities.
| Characteristics | Values |
|---|---|
| Cities with the worst air pollution in the world | Byrnihat, India; Lahore, Pakistan; Delhi, India; N’Djamena, Chad |
| Number of Indian cities in the top 20 | 11 |
| Number of Chinese cities in the top 20 | 3 |
| US cities with the worst air pollution | Bakersfield, California; Los Angeles-Long Beach, California; Sacramento and Roseville, California; Grants Pass, Oregon; Medford, Oregon |
| US states with the worst air pollution | Western states, especially California |
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What You'll Learn
Indian cities dominate the list
Several factors contribute to the severe air pollution in Indian cities. These include industrial emissions, vehicle exhaust, and a reliance on fossil fuels. In addition, weak regulations and seasonal weather patterns can worsen the situation. However, it is important to note that the presence of many Indian cities on the list may also be due to the extensive air pollution monitoring networks in place, which detect pollution levels accurately.
Other cities with notable air pollution levels include those in the western United States, particularly California. Cities in California made up six of the top ten cities with the worst air quality in the US, including Bakersfield, Fresno, Visalia, and Los Angeles-Long Beach. The poor air quality in these areas is influenced by factors such as emissions from energy and agriculture industries, dry and dusty climates, and low-lying geography that traps polluted air.
Additionally, people of color are disproportionately affected by air pollution in the United States. In California, 63% of the nearly 44 million residents living in counties with the worst air quality were people of color. This disparity has significant health implications, as air pollution has been linked to various issues such as stroke, heart disease, asthma, lung cancer, and chronic obstructive pulmonary disease.
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Lahore, Pakistan leads the 2024 rankings
Lahore, the second-most populous city in Pakistan, has consistently ranked among the top cities with the worst air quality in the world. In 2024, Lahore's air quality index (AQI) was significantly high, securing its position as the city with the worst air pollution globally.
The city's air pollution is caused by a combination of factors, including vehicle and industrial emissions, smoke from brick kilns, agricultural burning and the burning of crop residue, general waste, and construction site dust. The problem is exacerbated during the winter season, from October to February, when farmers in the wider Punjab province burn crop remnants, generating smoke that contributes to the smog. Temperature inversion during this period traps warm air, preventing the dispersal of air pollutants.
Lahore's high air pollution levels have shocked the public and gained media attention. In 2017, the publication of actionable air quality data for the first time in Pakistan spurred citizens to take action. A network of citizen-operated sensors began monitoring and reporting fine particulate matter (PM2.5) data in real time, revealing Lahore's severe air pollution. This led to a public interest petition, resulting in the Lahore High Court ordering authorities to develop an updated smog response action plan and publish daily pollution updates.
Despite these efforts, Lahore's air quality remains a pressing issue. In November 2024, certain high-smog devices and activities, such as unfiltered barbeques and auto rickshaws, were temporarily banned to mitigate the smog crisis. However, the city's AQI readings have been criticized as too lenient, potentially underreporting the severity of the pollution. As of November 2019, Pakistani authorities did not publish real-time PM2.5 data, relying instead on non-government sensors and U.S. State Department data.
Lahore's air pollution has had tangible impacts on its residents, with smog outbreaks causing respiratory issues and making it difficult to breathe. The city's air quality crisis underscores the urgent need for effective measures to reduce industrial and vehicular emissions, address agricultural burning, and improve overall air quality, ensuring the health and well-being of Lahore's citizens.
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California cities make up six of the top 10 US cities
California is known for its strict environmental regulations, so it may come as a surprise that, according to a 2018 report by the American Lung Association, the state is home to eight of the top 10 most polluted cities in the US. The report, which looked at pollution levels from 2014 to 2016, ranked cities based on their weighted average number of unhealthy air days.
The Los Angeles/Long Beach area was the nation's most ozone-polluted city, a position it has held for nearly the entire 19-year history of the report. Other California cities on the list include Bakersfield, Fresno, Sacramento, and San Diego. The only non-California metro areas in the top 10 were Phoenix and New York City.
The report also noted that overall, about 133 million Americans live with unhealthful levels of air pollution, placing them at risk for premature death and other serious health effects such as lung cancer, asthma attacks, cardiovascular damage, and developmental and reproductive harm.
While California has taken significant steps to counteract air pollution, the state continues to face challenges due to its large population, busy highways, and other factors that contribute to ozone and particle pollution. These efforts have had some success, as a subsequent report by the Lung Association in 2022 showed that California cities made up six of the top 10 US cities with the worst air pollution. The report also listed the nation's cleanest cities, which included Bellingham, Washington; Burlington, Vermont; Casper, Wyoming; Honolulu, Hawaii; Melbourne, Florida; and Wilmington, North Carolina.
On a global scale, Indian cities dominated the list of the most air-polluted cities in 2024, with Byrnihat and Delhi taking the top spots. Indian cities struggle with severe air pollution due to a mix of industrial emissions, vehicle exhaust, and reliance on fossil fuels, all worsened by weak regulations and seasonal weather patterns.
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Bakersfield, California ranks first for high-pollution days
Bakersfield, California, has been described as America's most air-polluted city. This is due to a combination of factors, including its location in a valley surrounded by mountains, its agricultural and industrial activities, and its climate. The city's geographical location in a bowl-shaped valley contributes to high-pressure systems that trap polluted air and prevent it from dispersing, leading to a build-up of pollutants over time.
Bakersfield's high-emission industries, such as agriculture, fossil fuel-based energy production, and oil refineries, are major contributors to the city's poor air quality. The city is a hub for energy production and agriculture, with Kern County, of which Bakersfield is the county seat, being the most productive oil-producing county in California. The oil and gas industry is the most polluting sector in the city, with Kern Oil, the primary oil refinery in the area, facing numerous Clean Air Act violations due to excessive emissions.
In addition to industrial emissions, Bakersfield also experiences significant pollution from road traffic and rail freight. The city is situated along a major north-south route, bringing in diesel trucks and contributing to the high levels of vehicle exhaust pollution. Freight trains hauling oil also pass through the city, adding to the emissions from the oil and gas industry. The combination of these sources of pollution has led to Bakersfield's reputation as one of the most polluted cities in the United States.
The American Lung Association's "State of the Air" report has consistently ranked Bakersfield highly for air pollution. In 2016, the city was ranked as the worst in the United States for short-term and year-round particle pollution and the second worst for ozone pollution. Bakersfield's particle pollution levels have shown some improvement in recent years, meeting the federal standard of less than 12 μg/m3 in 2019. However, it still has a long way to go to meet the World Health Organization's more stringent guideline of no more than 10 μg/m3 per year.
While Bakersfield has made some progress in improving its air quality, there are concerns that without stronger environmental regulations, the city may continue to struggle with poor air quality for the foreseeable future. Environmentalists and activists worry that a lack of stringent measures will allow highly polluting industries to continue contributing to the city's air pollution. Bakersfield's unique geographical and climatic conditions, combined with its high-emission industries, present a challenging situation that requires effective policy interventions to bring about significant and lasting improvements in air quality.
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Wildfire smoke impacts air quality in the western US
While air quality in the US has improved over the past 50 years, smoke pollution from wildfires threatens these gains. In 2023, a study found that smoke from wildfires had eroded about a quarter of the air quality improvements made in the preceding decades. The impact of wildfire smoke is more pronounced in the Western US states, where smoke-laden days are becoming an annual occurrence.
In 2020-2022, wildfire smoke was the primary cause of poor air quality in four Western states and a major contributor in 17 others. The states most affected include California, Washington, and Oregon, where wildfire smoke has wiped out nearly half of the air quality improvements made since 2000. The Midwest, South, and Eastern states are also impacted, with smoke plumes travelling far from the actual wildfires and causing poor air quality thousands of miles away. For example, in 2021, smoke from wildfires in the West caused a thick haze over Manhattan and triggered air quality warnings in Eastern states such as Connecticut and Maryland.
The increase in wildfires and their impact on air quality are linked to climate change and fire suppression policies. Climate change creates conditions that enhance ozone pollution and make it harder to improve air quality in affected communities. Additionally, decades of fire suppression policies have resulted in forests packed with more trees, providing fuel for larger and more destructive wildfires.
The health effects of wildfire smoke are significant, with millions of people exposed to elevated levels of fine particulate matter (PM2.5) that can negatively affect respiratory and cardiovascular health. PM2.5 particles are small enough to enter human lungs and can worsen respiratory conditions such as asthma and chronic obstructive pulmonary disease. The costs of addressing these health outcomes can exceed the billions already spent on wildfire suppression.
To protect themselves from the harmful effects of wildfire smoke, individuals can check air quality forecasts and avoid outdoor activities when unhealthy air is expected. While the Clean Air Act has effectively regulated point-source pollution, it is less effective at addressing the risks from smoke, which can affect people far from the wildfires themselves.
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Frequently asked questions
In 2024, Lahore, Pakistan, topped the list of cities with the worst air pollution, with 150.4 µg/m³ of PM2.5.
Many Indian cities feature on the list of the world's most polluted cities, with 11 of the top 20 cities in 2024. Delhi, India, recorded the second-worst air pollution levels in 2024. Other cities with poor air quality include Bakersfield, California, and Los Angeles-Long Beach, which is the US's worst city for ozone pollution.
Poor air quality can be caused by a combination of factors, including industrial emissions, vehicle exhaust, reliance on fossil fuels, and weak regulation. Wildfire smoke, energy and agriculture emissions, dry and dusty climates, and low-lying geography that traps polluted air can also contribute to poor air quality.
Air pollution is linked to various health issues, including stroke, heart disease, asthma, lung cancer, and chronic obstructive pulmonary disease. It can also increase the risk of cataracts, glaucoma, and macular degeneration. Particle pollution, with particles smaller than 1/30th the diameter of a human hair, can enter the lungs and bloodstream, causing serious health issues.
