Air Pollution: Which City Has Improved The Most?

Air pollution is a pressing global issue, contributing to millions of premature deaths annually. While air pollution remains a significant concern in many densely populated regions, some cities have made notable improvements in air quality over the years. This positive change is often attributed to the implementation of stringent regulations and the efforts of environmental organizations working tirelessly to address this challenge. Despite the progress made, it is essential to recognize that nearly half of Americans and people worldwide still breathe unhealthy air, emphasizing the need for continued action and advocacy to ensure cleaner air for current and future generations.

The Clean Air Act: US air pollution dropped by 80% since the Clean Air Act was passed in 1963

Air pollution is one of the deadliest environmental threats globally, causing millions of premature deaths annually. In 2024, only 17% of cities met the World Health Organization's annual PM2.5 guideline, indicating that most urban populations breathe unhealthy air.

In the United States, air pollution has been a significant issue, with major cities like Los Angeles and Phoenix experiencing high levels of smog and ozone pollution. However, since the Clean Air Act was passed in 1970, with amendments made in 1990, air pollution has dropped by nearly 80% across the country. The Clean Air Act has successfully driven pollution reduction for over 50 years, improving air quality and protecting public health.

The Act has lowered levels of several pollutants, including particulate matter, ozone, lead, carbon monoxide, nitrogen dioxide, and sulfur dioxide. The Environmental Protection Agency (EPA) plays a critical role in enforcing the Act by monitoring air pollution, writing rules to address it, and ensuring enforcement. EPA partnership programs have also contributed to reducing conventional air pollution, improving energy efficiency, and reducing oil imports.

Despite the significant progress, air pollution remains a concern for nearly half of Americans, and recent data shows an increase in harmful pollutants. Climate change is exacerbating the problem, with wildfires impacting air quality in the West and reaching cities like New York. Additionally, the EPA faces staffing and funding cuts, threatening its ability to continue its vital work.

While the Clean Air Act has improved air quality, there are ongoing challenges in mitigating dangerous pollution levels and addressing the health risks associated with air pollution.

US cities with the worst air pollution: Los Angeles, Phoenix, Dallas, Fresno, and Bakersfield

Air pollution is a serious environmental threat, contributing to millions of premature deaths annually. It is linked to a range of health issues, from respiratory problems like asthma to heart disease, lung cancer, and chronic obstructive pulmonary disease. In the United States, nearly half of the population breathes unhealthy air, and certain cities are notorious for their poor air quality. Here's a look at five US cities with the worst air pollution: Los Angeles, Phoenix, Dallas, Fresno, and Bakersfield.

Los Angeles, California, is notorious for its smog problem, often attributed to heavy traffic, industry, and wildfires. The Los Angeles-Long Beach area ranks as the country's worst city for ozone pollution, with the American Lung Association's "State of the Air" report giving it an F grade in 2025. The report also highlights that the Bay Area, part of the Los Angeles metropolitan area, performs poorly in all three pollution categories: year-round particle pollution, high-pollution days, and ozone pollution.

Phoenix, Arizona, is another city that struggles with air pollution. It ranks among the top 10 most smog-heavy cities in the US. While specific data on Phoenix's pollution levels are scarce, it's clear that the city faces significant challenges in maintaining clean air for its residents.

Dallas, Texas, is also on the list of the most smog-heavy cities in the US. The Dallas metropolitan area experiences an average of 16 days of unhealthy ozone pollution each year. The city's pollution is likely influenced by a combination of industrial emissions, vehicle exhaust, and other factors.

Fresno, California, is known for its poor air quality, ranking as one of the worst cities for year-round particulate matter pollution. The city's air pollution is so severe that nearly three-fourths of its population of approximately 477,000 people are people of color, who are disproportionately affected by the health risks associated with air pollution.

Bakersfield, California, has the dubious distinction of being the most polluted city in the US by year-round air quality, according to the American Lung Association. Bakersfield's poor air quality is a result of emissions from the energy and agriculture industries, a dry and dusty climate, and its low-lying geography, which traps polluted air in the valley. The mountains surrounding Bakersfield on three sides further contribute to trapping pollution in the area.

While these five cities stand out for their poor air quality, it's important to recognize that air pollution is a widespread issue in the United States, affecting millions of people. Efforts like the Clean Air Act have led to significant improvements in air quality over the decades, but there is still much work to be done to ensure that all Americans can breathe clean air.

India's air pollution crisis: 11 of the top 20 most air-polluted cities in 2024 were in India

India is facing a severe air pollution crisis, with 11 of the top 20 most air-polluted cities in the world in 2024 located within the country. This crisis has profound implications for the health and well-being of its citizens, as air pollution is linked to millions of premature deaths annually and various health issues.

The city of Byrnihat in Assam, India, was identified as the most polluted city globally in 2024, with a PM2.5 concentration of 128.2 micrograms per cubic meter. This level is alarmingly over 25 to 30 times higher than the World Health Organization's (WHO) recommended annual limit of 5 µg/m³. Delhi, India's capital territory with a population of over 30 million, recorded the second-worst air pollution levels in 2024. The city experiences severe winter air pollution due to crop burning in nearby states, stagnant cold air, and weak wind patterns that trap smog.

The primary causes of air pollution in India include burning biomass, industrial activity, and automobile emissions, as well as agricultural practices, vehicle emissions, and rapid urbanization. These factors contribute to high levels of PM2.5 pollution, which are tiny particles smaller than 2.5 microns that can enter the bloodstream and lungs. Long-term exposure to PM2.5 pollution is associated with respiratory problems, cardiovascular issues, and increased mortality rates.

Despite a 7% decrease in PM2.5 concentrations in 2024, India's air pollution crisis persists. Experts emphasize the need for stronger enforcement of air quality laws, the adoption of cleaner energy sources, and improvements in public transportation to address the growing pollution levels. Former WHO top scientist and health ministry advisor Soumya Swaminathan highlighted the importance of increasing access to LPG for cooking to replace biomass, which could help lower both indoor and outdoor pollution levels.

While India grapples with its air pollution crisis, it's important to recognize that air pollution is a global issue affecting many countries. For example, the United States has made long-term progress in improving air quality, with the Clean Air Act driving pollution reduction for over 50 years. However, nearly half of Americans still live with unhealthy air pollution, and efforts to roll back key air quality regulations could exacerbate the problem.

Air pollution and health: Air pollution is linked to asthma, lung cancer, and heart disease

Air pollution is a serious environmental threat, contributing to millions of premature deaths each year. In 2024, only 17% of cities worldwide met the World Health Organization's annual PM2.5 guideline of less than 5 µg/m3, indicating that the vast majority of urban populations are exposed to unhealthy air.

Air pollution is a complex issue influenced by various factors, including industrial emissions, vehicle exhaust, and the burning of fossil fuels. It is comprised of harmful pollutants such as particulate matter, ozone, nitrogen dioxide, sulfur dioxide, carbon monoxide, and methane. These pollutants have detrimental effects on human health, with prolonged exposure leading to severe health issues and even premature death.

One of the most prevalent health concerns associated with air pollution is asthma. Ground-level ozone, a common air pollutant, is highly irritating to the lungs and airways, triggering asthma attacks and exacerbating symptoms in asthmatics. Nitrogen dioxide (NO2) and other pollutants can also induce the development of asthma in previously healthy individuals. People with asthma are more susceptible to the harmful effects of air pollution, experiencing worsened symptoms and an increased risk of hospitalisation.

In addition to asthma, air pollution has been linked to an elevated risk of lung cancer. Ultrafine particles in polluted air can penetrate the body's natural defences, causing cellular injury and systemic inflammation. This inflammation increases the likelihood of lung cancer, particularly in individuals who have never smoked. Exposure to fine particle pollution has been associated with a higher risk of mortality from lung cancer.

Furthermore, air pollution contributes to cardiovascular diseases, including heart disease, stroke, and congestive heart failure. Studies have found a direct correlation between increased levels of particulate matter, specifically PM2.5 and PM10, and the incidence of cardiovascular health issues. The presence of larger particles and black smoke in the air has also been implicated in the exacerbation of asthma and other respiratory conditions.

While air pollution affects people from all walks of life, certain groups are more vulnerable to its health impacts. Children, older adults, and individuals with pre-existing lung diseases are at a heightened risk of adverse health effects. Additionally, people of colour and those with lower incomes are disproportionately affected by air pollution, facing higher exposure and subsequent health risks.

Air quality index: The Environmental Protection Agency (EPA) uses the AQI to grade air quality

Air pollution is a serious environmental threat, causing millions of premature deaths annually. It is linked to an increased risk of premature birth, lower birth weight, asthma, lung development issues in children, and other serious health issues. According to the 2025 State of the Air report, nearly half of Americans are exposed to unhealthy air pollution. However, the Clean Air Act, implemented in 1963 and significantly updated in 1970, has played a crucial role in improving air quality in the United States over the past five decades.

To effectively communicate about outdoor air quality and its health implications, the Environmental Protection Agency (EPA) employs the Air Quality Index (AQI). The AQI is a tool that provides an easy-to-understand daily report on air quality, using six color-coded categories. Each category is associated with a range of index values that indicate the level of air pollution and the potential health risks. For instance, an AQI value of 50 or below signifies good air quality, while a value over 300 represents hazardous air quality. AQI values at or below 100 are generally considered satisfactory, while values above 100 indicate unhealthy air quality, initially for sensitive groups and then for everyone as values increase.

The AQI covers five major pollutants regulated by the Clean Air Act: ozone, particle pollution (or particulate matter), carbon monoxide, nitrogen dioxide, and sulfur dioxide. These pollutants are known to have detrimental effects on human health. By utilizing the AQI, individuals can access information about the health impacts of these pollutants and take appropriate steps to reduce their exposure to air pollution.

The NowCast AQI, provided by the EPA, offers real-time information on air quality. As air quality can fluctuate throughout the day, the NowCast AQI also changes, helping individuals make informed decisions about their outdoor activities. Additionally, AQI forecasts are available for several days in advance, aiding in planning outdoor activities during periods of better air quality.

The EPA's AQI is a valuable resource for individuals to stay informed about their local air quality and take necessary precautions to minimize the health impacts of air pollution. It is essential to recognize that air quality is a dynamic issue that can vary daily and even within a day, underscoring the importance of staying updated through tools like the AQI.

Frequently asked questions