Air Pollution's Worst Offenders: Cities And Regions Exposed

Air pollution is a serious health threat that triggers asthma attacks, harms lung development in children, and can even be deadly. It is among the biggest health problems of modern industrial society and is responsible for more than 10% of all deaths worldwide. Particle pollution, which can be smaller than 1/30th of a human hair in diameter, can cause early death, heart attacks, strokes, and other serious health issues. The World Health Organization's recommended limit for particulate matter pollution is 10 micrograms per cubic meter, but national guidelines often vary. Climate change enhances conditions for ozone pollution and makes it harder to clean up communities with high ozone levels. In the United States, cities in California make up a significant proportion of the country's most polluted metropolitan areas, with Bakersfield, Visalia, and Fresno-Madera-Hanford ranking as the top three areas with the worst year-round particle pollution.

California cities top the list

Particle pollution, or soot, can have severe health consequences. It has been linked to an increased risk of premature birth, lower birth weight in newborns, and can trigger asthma attacks. The tiny particles in air pollution can be inhaled, bypassing the body's natural defenses, and leading to serious health issues such as lung cancer, heart attacks, strokes, and even early death. Children, older adults, and people with lung diseases are especially vulnerable to the harmful effects of air pollution.

California's air quality is significantly impacted by various factors. The state's large population contributes to higher emissions and, consequently, higher levels of air pollution. Additionally, California's geography, including mountainous and valley regions, can trap pollution, allowing it to build up to higher concentrations. Wildfires, such as the Eaton Fire in Altadena, also play a role in California's poor air quality, as the smoke releases dangerous particle pollution into the air.

While California cities face significant air pollution challenges, it is important to recognize that air pollution is a widespread issue across the United States. According to the "State of the Air" report, nearly half of the US population lives in areas with failing air quality, and more than 42 million people reside in counties that received failing grades for all three measures of pollution: ozone and short-term and year-round particle pollution. The report highlights the urgent need for policymakers and organizations like the US Environmental Protection Agency (EPA) to address air quality issues and protect the health of their citizens.

Population and geography matter

Geography and land type also play a significant role in air pollution. Mountainous or valley regions can trap pollution, causing it to build up to higher concentrations. In contrast, flatter areas allow pollution to dissipate more easily as it is carried away by the wind. The topography of an area can either contain or disperse pollutants, significantly impacting the air quality experienced by residents.

Additionally, certain geographic locations are more susceptible to the effects of climate change, which exacerbates air pollution. For example, areas prone to wildfires or extreme heat waves can experience episodic spikes in particle pollution as smoke and soot linger in the air. Climate change intensifies the challenges of maintaining clean air in these regions.

The interaction between population and geography further complicates the issue. Highly populated areas with specific geographic features can experience exacerbated pollution levels. For instance, a densely populated city situated in a valley may struggle with concentrated air pollution due to both the number of emissions sources and the geographic constraints hindering dispersal.

Moreover, the social dynamics within a population can also influence the impact of air pollution. People of color and individuals with lower incomes are disproportionately affected by air pollution, facing higher health risks. This disparity underscores the importance of addressing air pollution as a public health issue, especially in vulnerable communities.

Climate change makes it worse

According to the American Lung Association's (ALA) 2025 "State of the Air" report, cities in California make up a significant proportion of the country's most polluted places in terms of air quality. Bakersfield, Visalia, and Fresno-Madera-Hanford ranked as the top three metropolitan areas with the worst year-round particle pollution. The findings were based on air quality data collected between 2021 and 2023, examining ground-level ozone air pollution (smog) and spikes in particle pollution (soot). Other cities with poor air quality include Bakersfield-Delano, Fairbanks-College, and Eugene-Springfield, which had the worst short-term particle pollution.

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. Over 156 million people reside in counties that received a failing grade for either ozone or particle pollution, and more than 42 million people live in counties that failed in all three air pollution measures. Particle pollution can have severe health consequences, including early death, heart attacks, strokes, and respiratory issues. It can also trigger asthma attacks, harm lung development in children, and increase the risk of lung cancer. Those who live or work near busy highways and those who work or exercise outside are at higher risk of adverse health effects from air pollution.

Climate change exacerbates the issues associated with air pollution. It creates conditions that promote ozone pollution and makes it more challenging to mitigate high ozone levels. The interaction between climate change and air pollution forms a negative feedback loop, with climate change intensifying air pollution and air pollution contributing to climate change. Warmer temperatures caused by climate change increase the frequency and intensity of wildfires, which produce smoke that spreads dangerous particle pollution. The impact of wildfires on air quality can be seen in the ALA's report, where cities with high particle pollution are often influenced by wildfires.

Climate change also affects air pollution through its impact on weather patterns. Changes in weather conditions can influence the dispersion or concentration of pollutants in the atmosphere. For example, stagnant air masses can trap pollutants in certain areas, leading to higher pollution levels. Additionally, climate change can alter wind patterns, affecting the transport and dispersion of pollutants over long distances. The complex interplay between climate change and weather patterns can result in the formation of air pollution hotspots or the persistence of poor air quality in specific regions.

Furthermore, climate change interacts with socioeconomic factors to worsen air pollution. In emerging and developing countries, the challenges of meeting global environmental standards are amplified by climate change. The lack of resources and infrastructure to adapt to changing environmental conditions can hinder their ability to effectively address air pollution issues. As a result, vulnerable communities may experience a disproportionate burden of air pollution's health and environmental impacts, contributing to increased health risks and social inequalities.

To break this cycle, policymakers must address both climate change and air pollution simultaneously. Reducing greenhouse gas emissions can help mitigate climate change, while implementing policies to minimize air pollution can improve air quality and protect public health. By tackling these interconnected issues, policymakers can work towards creating a healthier and more sustainable future for all.

Wildfires and industrial emissions

Wildfires

Wildfires are a major driver of air pollution, releasing vast amounts of carbon and particulate matter into the atmosphere. The smoke from these fires can drift for thousands of miles, spreading air pollution far beyond the immediate vicinity of the blaze. This smoke contains harmful pollutants, including PM2.5 particles, which are minuscule particles that can infiltrate the body and cause severe health issues. Wildfires have become increasingly frequent and intense due to climate change, with human activities such as burning fossil fuels, transportation, and industrial processes contributing to the rise in global temperatures. The release of greenhouse gases and black carbon emissions from these fires further exacerbates climate change, creating a vicious cycle.

The impact of wildfires on air quality was evident in the 2019-2020 Australian wildfires, which produced carbon emissions estimated to be 1.6 times greater than the country's total emissions for that year. Similarly, the Canadian wildfires in 2024 released more carbon in five months than Russia or Japan's annual fossil fuel emissions for 2022. These fires not only devastate the environment but also have severe economic repercussions, as research by Stanford University's Institute for Economic Policy Research (SIEPR) has shown. Their studies revealed that exposure to wildfire smoke reduces employment and labor force participation, with smoke-induced earnings declines affecting certain sectors and demographic groups disproportionately.

Industrial Emissions

Industrial facilities are another significant source of air pollution, particularly in densely populated areas. Vehicle emissions and industrial processes release microscopic pollutants that contribute to the degradation of air quality. This is especially prevalent in metropolitan areas, where population density and geographic features can trap emissions, leading to higher concentrations of pollutants. California, for example, is home to several of the United States' most polluted cities, including Bakersfield, Visalia, and Fresno-Madera-Hanford, which rank high in year-round particle pollution.

However, it is important to recognize that industrial emissions are not limited to a specific region or country. Industrialization and economic activities contribute to air pollution worldwide, often in conjunction with other factors such as geography and weather patterns. As a result, many places worldwide experience poor air quality due to a combination of industrial emissions and other factors, creating a complex challenge that requires global cooperation and comprehensive solutions.

Health risks: asthma, lung development, cancer

Air pollution is a major public health concern, affecting nine out of ten individuals living in urban areas worldwide. It is the ninth leading risk factor for cardiopulmonary mortality, causing 3.2 million deaths each year. Recent studies have shown that exposure to air pollution is associated with acute and chronic cardiopulmonary mortality and all-cause mortality.

Air pollution has been linked to the development and exacerbation of asthma. Ozone, in particular, is extremely irritating to the lungs and airways, triggering asthma attacks. People with asthma are at greater risk from breathing in small particles and irritating gases, which can irritate the airways and make asthma worse. When air pollution is high, asthmatics should limit their time outdoors, especially from 11 am to 8 pm, and avoid exercising or working hard outdoors when the Air Quality Index (AQI) is at unhealthy levels.

In addition to asthma, air pollution has been associated with an increased risk of several types of cancer, including lung cancer, as well as breast, liver, and pancreatic cancer. A 2015 study found somatic genomic mutations attributed to household air pollution in lung tissue and blood samples from patients with non-small cell lung cancer (NSCLC). The International Agency for Research on Cancer (IARC) has classified outdoor air pollution as a class I human carcinogen based on data from human, animal, and mechanistic studies.

Air pollution can also affect lung development, particularly in children. A 2015 systematic review suggested that exposure to traffic-related air pollution (TRAP) containing PM2.5 in early childhood is associated with an increased incidence of asthma up to the age of 12 years. However, conflicting findings have also been reported, with the European Study of Cohorts for Air Pollution Effects (ESCAPE) finding no association between PM2.5, PM10, or NO2 and the prevalence of childhood asthma. More research is needed to fully understand the impact of air pollution on lung development.

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