Air Pollution's Worst Offenders: Us Cities Exposed

Air pollution is a serious health issue in the United States, with over 40% of the population living in areas with unhealthy air quality. It can cause asthma attacks, harm lung development in children, and even lead to premature death. While California is known for having the worst air pollution in the US, with Los Angeles taking the top spot for ozone pollution, other states such as Oregon, Alaska, Arizona, and Washington also have cities with poor air quality. Race is a significant factor, with Black and Hispanic populations disproportionately affected by air pollution.

Los Angeles, California has the worst ozone pollution

Los Angeles, California, has the worst ozone pollution in the United States. According to the 2019 State of the Air report, which compared data across 229 metropolitan areas, Los Angeles topped the list for the highest ozone pollution. The report also noted that Los Angeles's air pollution is among the worst in the country for both PM2.5 and ozone.

Ozone is a gas pollutant formed when sunlight reacts with nitrogen oxides and organic substances. Vehicle exhaust contains both nitrogen oxides and reactive organic substances, so traffic is frequently identified as a leading source of ozone. Warmer temperatures, dry conditions, and less rainfall also contribute to higher levels of ozone pollution. This combination of factors makes Southern California particularly susceptible to bad ozone levels.

The health implications of ozone pollution are significant. Both ozone and PM2.5 contribute to the smog that Los Angeles is known for and can cause respiratory infections and inflammation, as well as increase the risk of premature death. According to the County of Los Angeles Public Health Department, one in ten children in the county have been diagnosed with asthma. The overall risk of cancer is also increased due to air pollution.

While Los Angeles has made progress in improving its air quality over the last few decades, it still has a long way to go to meet the U.S. EPA's national air quality standards. The city's air quality is currently rated as "good," but it continues to experience short-term spikes in particle pollution due to wildfires and other factors.

California's Central Valley has the worst particle pollution

California's Central Valley, specifically the San Joaquin Valley, experiences some of the worst air quality in the United States. The region is known for its agricultural productivity, contributing about 25% of the nation's food while occupying just 1% of the country's farmland. The direct and indirect impacts of agricultural production on the air quality in the valley are well-documented, with the mixing of dust and vehicle emissions near communities. The topography of the valley, surrounded by mountain ranges, also plays a role in trapping air pollutants.

The Central Valley's poor air quality is a result of various factors, including heavy truck traffic, diesel-burning locomotives, tractors, irrigation pumps, and wood-burning stoves. The region's unique geography, with surrounding mountain ranges, also traps polluted air, further degrading the air quality. The problem is particularly pronounced in cities like Bakersfield, Fresno, and Visalia, which consistently rank among the worst for particulate and ozone pollution. Between 2018 and 2020, Fresno experienced an average of 51 high particle pollution days, up from 34 days between 2017 and 2019.

The high levels of air pollution in the Central Valley have significant health impacts on residents. The fine particulate matter, known as PM2.5, can pass into the bloodstream and has been linked to various health conditions, including asthma, cardiovascular disease, and even premature death. The effects are more pronounced in disadvantaged communities, which tend to be located closer to pollution sources and have fewer resources to adapt. The outdoor workers in the region, who make up nearly 22% of California's outdoor workforce, are at particular risk of respiratory issues.

To address the air quality issues in the Central Valley, state and local air quality districts have implemented policies and regulations. These include efforts to phase out burning as a waste disposal method, incentivizing transitions to gas-powered heat, and creating regulations to reduce emissions from vehicles and equipment. The Environmental Protection Agency (EPA) has also been actively involved in improving air quality in the region. They have provided funding for cleaner locomotives, supported medical research on the health effects of pollutants, and collaborated with local organizations to reduce pollution and enforce compliance with permit limits.

The combination of agricultural practices, geographical factors, and human activities has made California's Central Valley, particularly the San Joaquin Valley, a hotspot for air pollution in the United States. The health risks associated with poor air quality have led to increased attention and efforts to implement policies and technologies that can mitigate pollution and improve the respiratory health of residents in the region.

Race is a predictor of air pollution exposure

Air pollution is a serious health threat in the United States, with nearly half of the population living in areas with failing air quality grades. While air pollution affects people of all backgrounds, race is a significant predictor of air pollution exposure, with people of color being disproportionately impacted.

Research has consistently shown that race and ethnicity are key factors in determining exposure to air pollution in the United States. A 2021 study by Tessum et al. published in Science Advances found that PM2.5 polluters disproportionately affect people of color across the country. This is supported by a 2023 analysis by The Guardian, which revealed that the worst hotspots for fine particle air pollution in the US are predominantly areas where Black and Hispanic populations live.

The disparity in air pollution exposure is not simply a matter of income or class bias. Studies have found that racial disparities hold across all income levels. For example, in Birmingham, Alabama, a city known for its racial segregation, Black neighborhoods have significantly worse air quality than white areas just a few miles away. This pattern is not unique to Birmingham; it is a widespread issue across the United States.

The reasons for these disparities are complex and multifaceted. One factor is the historical and ongoing residential segregation that has led to people of color living in areas with greater exposure to pollution sources, such as industrial zones or areas with high traffic. Additionally, pollution sources tend to be located near disadvantaged communities, further increasing exposure to harmful pollutants for people of color.

The implications of these findings are significant. The higher exposure to air pollution among people of color contributes to health inequities and increases the risk of adverse health outcomes, including respiratory issues, lung development in children, and premature death. Addressing these disparities requires targeted air pollution reduction strategies and environmental justice considerations in policy-making to protect vulnerable communities.

Wildfire smoke causes accelerated skin ageing

Air pollution is a serious health threat in the United States, with around 156 million people living in counties with failing grades for ozone or particle pollution in 2025. California has consistently been ranked as the state with the worst air pollution in the country, with cities like Yosemite Lakes reporting the worst air quality nationwide in 2020. Race is also a significant factor, with predominantly Black and Hispanic neighbourhoods breathing worse air than nearby white areas.

In addition to the negative health effects of air pollution on the lungs, recent events have brought to light the impact of poor air quality on the skin. As wildfire smoke from Canada blanketed New York City in June 2023, doctors warned of the dangers it posed to the skin. Dr Doris Day emphasised that the skin is one of the first places to exhibit signs of damage from pollution, such as dry and dull skin, acne, light breakouts, and uneven skin tone. With prolonged exposure, more severe consequences can occur, including accelerated skin ageing and even skin cancer.

The skin, as the body's largest organ, acts as a barrier against harmful microbes and toxins and protects us from ultraviolet (UV) radiation. However, exposure to environmental pollutants, such as wildfire smoke, can lead to premature skin ageing. This is similar to the effects of tobacco smoke, where studies have shown that smoking increases the degradation of collagen, elastic fibres, and proteoglycans, resulting in accelerated skin ageing.

To protect the skin from the harmful effects of wildfire smoke, Dr Day recommends using a barrier cream designed to shield the skin from pollution. These creams are invisible and help protect the skin biome and the microbes that live on the skin. Additionally, applying antioxidants topically can help neutralise the free radicals formed by pollution.

While the recent focus on wildfire smoke has brought attention to the impact of air pollution on the skin, it is important to recognise that air pollution is a pervasive issue in the United States, affecting the health and well-being of millions of people.

Air pollution is linked to premature death

Air pollution is a serious health threat in the United States, and it is linked to premature death. Outdoor air pollution has been associated with asthma, heart attacks, strokes, and cancers. According to the National Institutes of Health (NIH), studies have shown a link between long-term exposure to air pollution and premature death. Additionally, NIH research found that short-term exposure to air pollution may also be dangerous. When air pollution from fine particles or ozone increases, even intermittently, there is a substantial increase in deaths within a 2-day period.

The United States Environmental Protection Agency (EPA) plays a crucial role in monitoring and regulating air pollution to protect public health. Despite their efforts, the EPA faces significant staffing and funding cuts that endanger their ability to continue this vital work. Race is a more significant predictor of air pollution exposure than income level, with Black and Hispanic populations experiencing higher levels of air pollution than white populations. California, specifically Yosemite Lakes, has been identified as the state and city with the worst air pollution in the US.

The sources of air pollution are diverse and context-specific. Outdoor pollution comes from residential energy use for cooking and heating, vehicles, power generation, agriculture and waste incineration, and industry. Fine particles (2.5 micrometres in diameter or less) from factories, power plants, and car exhaust contribute to air pollution, along with ozone, the main ingredient in urban smog. Black carbon, a major component of soot, is another pollutant with potent carcinogenic properties found in areas with high traffic.

The effects of air pollution are not limited to a single area but can spread across state lines. An analysis of air pollution exchange among the contiguous United States found that around half of the early deaths caused by a state's air pollution occur outside that state. This cross-state pollution poses additional regulatory challenges and underscores the need for coordinated efforts to address the issue.

To mitigate air pollution and reduce its impact on public health, various interventions and policies have been proposed. These include supporting sustainable land use, promoting cleaner household energy and transport, improving energy efficiency in housing and power generation, and enhancing municipal waste management. By implementing these measures, we can effectively reduce key sources of ambient air pollution and protect the health and well-being of millions of people in the United States.

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