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10 Most Polluted Cities in the U.S. (2024 Update)

San Diego City California

Around 90% of the world’s population currently lives where air quality levels exceed the World Health Organization’s limits of air pollution. Air pollution poses a considerable health risk and can lead to coronary and respiratory diseases, higher cancer chances, and premature death.

It is caused by vehicle emissions, power plants, chemical fumes, and even natural substances like smoke from wildfires. But which cities leave the residents more at risk? We’ve taken the time to dive deep into the world of air pollution and have ranked cities in the United States based on their overall levels of air pollution.

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The 10 Most Polluted Cities in the United States

Our list of U.S. cities with the most air pollution took overall pollution levels into consideration; we did not distinguish between natural causes and human-caused air pollution. Our list is based on current air pollution data from official sites that are maintained by federal, state, and local governments.

1. Fresno Madera, CA

It should come as no surprise that a California city comes first on our list. California is well known for its air quality issues, and with Fresno coming first on our list, it’s not difficult to see why. The Fresno area experiences persistent air pollution due to its geographic location.

This deadly combination of warm, stable weather fronts and valley walls keeps the pollution in place. Out of 220 metropolitan areas, Fresno ranked fourth for its high ozone days. Due to the city being a major hub of the agricultural industry and being the intersection of several major highways like Route 99 and the I-5, Fresno consistently ranks as one of the most polluted cities in the U.S.

2. Bakersfield, CA

Another California City, Bakersfield, is another farming community with a high pollution level. Bakersfield sits in a giant bowl, allowing it to collect soot, ozone, and chemicals from the agricultural practices themselves. This potent combination turns into smog in warm weather.

If that weren’t enough, Bakersfield is California’s oil capital, which causes an even higher rate of emissions in the city. Bakersfield and the surrounding valley remain among the most polluted regions in the United States. According to multiple reports, the area’s overall levels of smog and soot are the leading causes of respiratory problems, lung cancer, and heart attacks.

3. Visalia, CA

Located in California’s central valley, Visalia’s high levels of air pollution are a combined effort of the local’s wood fires and the significant car and diesel truck traffic. Visalia holds onto pollution due to it being at a lower altitude in the valley, and the intense sun and heat can also increase and contribute to the overall smog levels in the city.

According to the American Lung Association, the Visalia region consistently rates among the top five most polluted areas. According to the same studies, Visalia was the second smoggiest city in 2019 and had the fourth worst levels of total particle pollution 3 years in a row.

4. Los Angeles, CA

It may be a surprise that Los Angeles is not number one on our list since it has previously ranked as the most polluted city in the United States. On average, the Los Angeles region scores high for high ozone days but ranks 7th for overall particle pollution. The Los Angeles metro area is considered to have some of the worst overall air pollution, and pollution is only increased by wildfires and heavy smoke during the wildfire season. Out of more than 200 metropolitan areas nationwide, Los Angeles’ pollution problem is practically doubled thanks to the smoke and high temperatures worsening climate change and air quality.

5. San Jose, CA

California’s Bay Area also experiences high levels of pollution. According to the American Lung Association, San Jose was fourth for the worst yearly particle pollution. The city’s primary cause of ozone pollution is vehicle exhaust mixed with warmer weather.

In addition, wildfires during the summer and wood fires during the winter significantly impact the overall air quality in the area. Because San Jose is part of the Bay Area, transportation emissions, such as emissions from ships, planes, and general car travel, are another one of the leading causes of high pollution in the area. Poor air quality is a common occurrence practically all summer and fall.

6. Medford Grants Pass, OR

Our first non-California city, the Medford and Grants Pass area in Oregon, is a more recent addition to the most polluted cities list. This is likely due to the increase of wildfires up and down the west coast. Wildfires happened more frequently and lasted twice as long as they had during previous years, and because of this, particle pollution levels in Oregon and other surrounding areas skyrocketed.

According to American Lung Association’s annual report, Grants Pass has some of the worst air quality in Oregon and the United States.

7. Fairbanks, AK

Ranked third for both year-round and short-term pollution, it is impossible for us not to include Fairbanks, Alaska, on our list. Not only does the Fairbanks community face challenges that come with cold inversions during winter, but Fairbanks residents often use woodstoves and wood fire heaters during the winter, leading to one of the area’s biggest particle pollution causes.

Fairbanks is the second largest city in Alaska, so it should come as no surprise that it is one of the most polluted cities in the state. The smoke from wood fires and other emissions during winter causes Fairbanks to have one of the highest winter pollution levels across the U.S.

8. Phoenix – Mesa, AZ

Phoenix, Arizona, holds the record for high pollution levels and air quality warnings for over 149 days in a row. Car emissions and travel are the leading cause of high pollution levels in Phoenix, and the summer months bring higher ozone pollution while the winter months trap the cooler yet still filthy air down in the valley.

The city is currently undergoing efforts to reduce the overall pollution levels and is implementing an advanced dust control program attempting to repave roads and road shoulders to reduce emissions and particle pollution. If the emission level were not enough of an issue, the year-round high heat advisories increase the ozone level consistently.

9. Chico, CA

As a fairly large city in the Sacramento Valley, Chico finds its way onto our list. With smoke generated from the chimneys of homes during winter and overall car emissions, Chico holds its place among the most polluted cities in the United States. Chico authorities have advised residents to avoid using wood-burning stoves and use less polluting heat options.

10. El Centro, CA

With a 50-day in-a-row streak of unsafe air quality and pollution warnings, El Centro brings us to the end of our list. Most heavily polluted cities are found in the West, particularly California. California continues to be the state with the most cities on the high pollution list, and El Centro is no different. The primary cause of pollution in El Centro is a large amount of vehicle emissions. The proximity to Mexico also plays a role in the overall impact of pollution in the Imperial County area. Pollution from the heavily populated Mexicali city, nestled right across the border, carries over into El Centro. Mexicali’s metro area has almost five times the population of Imperial County, and the smog from cars and trucks in this area floats across the border.

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Final Thoughts

Air pollution is inescapable, with various factors causing pollution and leading to unhealthy air days and air advisories across the United States. However, some cities are more prone to air advisories than others. Weather and climate can add to the pollution levels by trapping the pollutants in one area, worsening the existing problem.

Around 90% of people consistently inhale air that contains dangerous levels of pollution. Whether the pollution comes from the ozone, car emissions, or wildfires, the detrimental impacts on health remain the same. Short-term impacts of air pollution include asthma, and in the long term, it can lead to heart disease and lung cancer from exposure. The cities on this list are the most polluted cities in the United States, but they are not the only regions affected.

Featured Image Credit: Jesse MacDonough, Pixabay


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