17 Most Polluted Cities in the US That May Surprise You

When you think of the United States, perhaps things like baseball, McDonald’s, the New York Times Square, or the Grand Canyon are the first things to pop into your mind. But what about pollution? Probably not. 

According to the “State of the Air” 2023 report, about 36% of Americans live in the most polluted cities in the US. The country has made strides to reduce unhealthy levels of ozone or particle pollution by cleaning up sources of air pollution, but there’s still much to be done.

So before you relocate or visit a city in the US, make sure you check the air quality. The same goes for global travel. Have a look at the most polluted cities in the world so you won’t have to deal with thick clouds of smog, trash-filled streets, or overflowed sewages on vacation.

How Are These Polluted Cities Ranked?

Before I dive into this list of the most polluted cities in the United States, let’s unpack how the pollution levels of these cities are decided. The Air Quality Index (AQI) is an indicator used to determine how clean or polluted the air is in places around the world.

There are several aspects to consider when figuring out AQI. Factors such as particle pollution, ground-level ozone, carbon dioxide, nitrogen dioxide, and sulphur dioxide levels all affect the AQI of a city. This is measured from 0 to 400+, with 0 being good and 400+ being hazardous. 

This guide unpacks cities with the highest amount of ozone, or “smog”, as per the American Lung Association’s recent State of the Air report. Ozone aggressively attacks lung tissue and causes many health issues. 

If you don’t live in any of the cities mentioned, you can check the air quality of where you are on the AQI website.

17 Most Polluted Cities in the US

Now that you are aware of how air quality is determined and how it affects you let’s dive into the most polluted cities in the United States. The cities are ranked on the annual average number of high ozone days.

1. Los Angeles-Long Beach, CA

Image by Lisa Larsen from Pixabay

Average number of high ozone days: 177.3

Topping the list is the metropolitan area of Los Angeles and Long Beach. The region has again ranked number one for the most ozone-polluted area in the United States for 23 out of 24 years of the annual “State of the Air” report.

The Los Angeles-Long Beach area has a high population density, which causes a lot of competition for basic resources like food, water, and shelter. This population density translates to high vehicle emissions and an increased level of smog.

High levels of ground-level ozone pose significant health risks to the people living in this area. The chemical has been known to cause shortness of breath and asthma, ultimately reducing people’s lifespans.

2. Visalia, CA

Photo by Jacob Padilla on Unsplash

Average number of high ozone days: 92.2

Known as the gateway to the lush Sequoia National Forest, Visalia is famous for its agricultural sector and plenty of outdoor activity opportunities. Ironically, the city is also known for having a high level of ozone pollution.

Carbon dioxide emissions and intensive farming practices mainly cause Visalia’s pollution. The city’s surrounding mountain ranges are also to blame, as their bowl-shaped landscape traps the smog within the valley.

The city has a low population density, with about 500,000 residents. However, heavy traffic in and out of the San Joaquin Valley to places like Los Angeles or San Francisco is a major factor in air pollution.

Affordable housing is in short supply in Visalia, which can lead to higher rates of homelessness. This could negatively impact the pollution levels in the city as well.

3. Bakersfield, CA

Photo by Jabez Impano on Unsplash

Average number of high ozone days: 86.7

Nicknamed the “breadbasket of California”, Bakersfield is famous for its fertile soil and ideal climate for growing agricultural produce. The city’s crop cultivation is expansive, ranging from fruits and nuts to cotton. However, farming chemicals are a major contributor to high levels of ozone.

Other pollutants in Bakersfield include fumes from trucks and trains and residue from the city’s oil and gas industry. Although it ranks third for ozone pollution, Bakersfield actually tops the list for the worst annual particle pollution in the United States. 

Similar to Visalia, the city also has mountains around it that trap toxic chemicals from leaving the valley.
Bakersfield’s population density is relatively high with a nearly a million residents. The competition for resources is also high, so an increased crime rate and cost of living could worsen pollution in Bakersfield.

4. Fresno-Madera-Hanford, CA

Photo by Grant Porter on Unsplash

Average number of high ozone days: 54

The Fresno metropolitan area lies at the heart of California’s agricultural region, but the city is more than just dust and farms. Fresno offers “big city” amenities like gorgeous recreational parks, shopping opportunities, and an amazing restaurant scene.

The city boasts an affordable cost of living, but you’ll have to deal with ozone pollution if you relocate to Fresno. The main pollutants in the city include emissions from vehicles, factories, and pesticides from farming. Smoke from wildfires in the nearby mountains is also a big contributor. 

Other factors like low education levels and poverty add to the competition for resources, which leads to more combustible fuels being burned for cooking and heating. Fresno also has issues with high rates of crime, homelessness, and gun violence.

5. Phoenix-Mesa, AZ

Photo by Taylor Finklea on Unsplash

Average number of high ozone days: 41.2

Located in the East Valley of the Phoenix metropolitan area, Mesa is a city of giant flat-topped hills, desert shrubs, and remnants of the native Hohokam people. 

Arizona’s third-largest city offers plenty of outdoor excursions, as well as museums and spacious parks to explore. And let me not forget its inaugural Arizonan pumpkin patch picking opportunities throughout October.

However, Mesa ranks highly in ozone pollution. This can be attributed to common causes like vehicle and factory emissions and road repairs, which release toxic metals such as lead and mercury into the atmosphere. The intense heat in Mesa worsens the pollution, as it creates an environment for hydrocarbons to react. 

The Phoenix-Mesa area has a population of almost five million residents. High population density, cost of living, and water shortages caused by the ongoing drought also affect the pollution levels. 

6. Denver-Aurora, CO

Photo by Bill Griepenstroh on Unsplash

Average number of high ozone days: 35.2

Considered one of the best places to raise a family, Aurora acts as a gateway to the Rocky Mountains. The city is a great place for outdoor activities like camping, hiking, and skiing, so it’s not a surprise that you may want to visit or relocate there.

Aurora has a high ozone pollution due to commuting residents’ large-scale use of vehicles. The city’s proximity to Denver makes it a hotspot for those escaping high rental prices in the state’s capital. Other pollutants, like emissions from power plants, factories, and construction sites, also affect these levels.

The Denver-Aurora metropolitan area has a population of about 3.6 million people, with a fairly moderate population density. But this city has an affordable housing crisis, which increases homelessness, negatively affecting pollution levels. A growing population has also been noted as a possible contributor, as more people means more burning of fuels.

Tip: If you do visit Denver, don’t forget to soak in the balmy waters at Radium Hot Springs in your spare time.

7. Sacramento-Roseville, CA

Photo by Jorge Maya on Unsplash

Average number of high ozone days: 27

Roseville ranks as one of the best places to live in California. The city offers residents a little bit of everything, with great public schools, recreational hubs, and an abundance of shopping opportunities. But there’s more to Roseville than what meets the eye, especially in the air.

Heavy traffic sees tons of toxic fumes being released into the air, while raging wildfires, factory farms, and extreme heat further contribute to pollution. Roseville experiences high temperatures throughout the year, so the heat can react with pollutants from vehicle emissions on a daily basis. The city’s location in the Sacramento Valley also makes it prone to trapped air pollutants.

With a population of over 2.6 million residents, the Sacramento-Roseville metropolitan area has a relatively low population density. That may soon change as the city is undergoing a building boom. These construction sites and the increased number of vehicles will add to the pollution.

You might want to read my articles on the most polluted countries in the world and the most polluted cities in Europe.

8. San Diego-Chula Vista-Carlsbad, CA

Photo by Samantha Fortney on Unsplash

Average number of high ozone days: 24.7

Famously known as the “Lemon Capital” for its abundance of citrus trees, Chula Vista-Carlsbad offers exciting outdoor activities along its shores, five-star resorts, and golf courses. The city’s small-town charm attracts most of its visitors, but it’s mostly the residents who have to deal with Chula Vista-Carlsbad’s air pollution.

Carbon dioxide emissions from cars and locomotives are the main driver of pollution in the city. The area’s coastal location also contributes to pollution levels through a process called “marine inversion”. This is when cooler air near the surface gets trapped by warmer air from above and ultimately traps pollutants from leaving the atmosphere.

Other factors like the burning of fossil fuels and cooking with wood, charcoal, or dung are major contributors to both indoor and outdoor air pollution. The metropolitan area has a relatively high cost of living, with residents spending more than 40% of their income on rent and utilities. This could lead to a higher level of homelessness in the city and impact the air quality.

All-in-all, this is still a lovely place to visit, for a time at least. And if the San Diego sunset spots are anything to go by, you’ll have a mesmerising time nonetheless.

9. Houston-The Woodlands, TX

Photo by Alisa Matthews on Unsplash

Average number of high ozone days: 23.2

Located about 30 minutes from Houston, The Woodlands is one of Texas’s best places to live. This district boasts tons of sophisticated public parks, hiking trails, and shopping opportunities. It’s also home to some of the most famous landmarks in Texas. 

But “Houston, we have a problem”, and that’s pollution. With two of the biggest refineries in the United States located in this area, toxic pollutants are released into the air daily. The 400 chemical manufacturing plants in the city also add to the emissions.

The Woodlands is rapidly growing and fast on its way to becoming a city. This has caused an influx of people, but it’s not only people who are relocating. Several companies are also moving their headquarters there, which will negatively affect the air quality of the district. 

10. Salt Lake City-Provo-Orem, UT

Photo by Samuel Sweet on Pexels

Average number of high ozone days: 23

Known for its deep-rooted Mormon heritage, powdery ski slopes, and thriving arts and film scene, the Salt Lake City-Provo-Orem metropolitan area is one of the safest cities in the US. The city boasts one of the lowest property and violent crime rates in the state and the country.

But the safety of this metropolitan area doesn’t necessarily translate into breathable air. Vehicle emissions are responsible for about 50% of the air pollution in Salt Lake County, followed by winter inversions and fumes from wood burning in homes.

The Salt Lake City-Provo-Orem metropolitan area is among the top-performing cities in the US and has experienced an urban growth boom in the last decade. This has largely impacted the city’s housing market and cost of living, which worsens air pollution. 

11. San Jose-San Francisco-Oakland, CA

Photo by Dennis Yu on Unsplash

Average number of high ozone days: 20.2

Visiting the Bay Area is a delight, with some of the world’s finest vineyards in Napa Valley. Then there’s the dramatic beaches along its shores and tech-savvy communities like Silicon Valley. So, it’s not a surprise that this part of California is popular among those looking to relocate. 

That being said, ozone pollution is a big problem in the San Jose-San Francisco-Oakland metropolitan area. While the usual suspects, like extreme heat, wildfires, and droughts, are to blame for the pollution, stormwater drainage is the biggest culprit.

In a surprising twist, unlike many other cities on this list, the Bay Area is experiencing an exodus of residents instead of an influx. This is largely attributed to the high cost of living, increasing crime, and California’s lack of business-friendly policies. So perhaps air pollution could decline in the area over time.

12. New York-Newark, NY-NJ-CT-PA

Photo by John Cameron on Unsplash

Average number of high ozone days: 17.2

Although it needs no introduction, beautiful New York is a global financial, entertainment, and media hub that draws in millions of tourists each year. The New York-Newark metropolitan area is among the richest places to live, offering top-notch institutions like schools and healthcare centers.

But not all that glitters is gold. The metropolitan area has low-quality breathable air due to the city’s commercial and industrial activities. Both ozone and particle pollution are high in this area, leading to premature death and serious health issues like asthma. Vehicle emissions are also one of the main contributors to pollution levels.

The New York-Newark metropolitan area is an attractive place to relocate when looking for financial greener pastures. But the city also has some serious drawbacks like a high cost of living, overcrowdedness, and limited opportunities for job growth. 

You may want to read my article on the most polluted rivers in the world.

13. El Centro, CA

Photo by Kelley Ashbrook on Unsplash

Average number of high ozone days: 17

Boasting stunning canyons, mud volcanoes, and desert lands dotted with colorful wildflowers, El Centro is a hub of natural attractions. Unlike bigger cities nearby like San Diego and Los Angeles, El Centro offers quieter, less crowded, and more stable areas for raising children.

Carbon dioxide emissions from cars are largely to blame for air pollution, but factors like pesticides and solid waste also contribute a fair share. Emissions from neighboring Mexico have also been cited as a possible contributor as they blow into the valley.

Outside of pollution, El Centro is also experiencing challenges in managing city facilities effectively. The public healthcare system’s financial constraints and lack of affordable housing are prevalent in Imperial County, and unfortunately, poor people are the most affected.

14. El Paso-Las Cruces, TX-NM

Photo by Yifu Wu on Unsplash

Average number of high ozone days: 16.7

Sitting about 45 minutes apart, El Paso and Las Cruces are two of the best places to visit in the Southwest. These cities make up the El Paso-Las Cruces metropolitan area and are a crossroad where American, Hispanic, and Native cultures coincide.

Pollution has been a long-standing problem in the metropolitan area, with vehicle emissions and the increase in oil and gas production being the leading contributors. Desert conditions don’t help; the sunny skies, high temperatures, and wildfires also significantly contribute to ozone and particle pollution.

Other related problems in the metropolitan area include diminishing groundwater levels and an influx of migrants from Mexico. Las Cruces’ high crime rate may also affect pollution levels as it incorporates vandalism or destruction of property. 

15. Las Vegas-Henderson, NV

Photo by Michael M on Unsplash

Average number of high ozone days: 16.2

Claiming the number one and two spots of the largest cities in Nevada, Las Vegas and Henderson form a metropolitan area that offers a wide variety of entertainment. Whether you are looking for a bustling nightlife in the city that never sleeps or stunning recreational spaces, there’s an abundance of things to do in Las Vegas and Co.

One of the main things you’ll have to contend with in this metropolitan area is pollution. Climate conditions like droughts and raging wildfires are top contributors to air pollution, as well as emissions from vehicles.

You’ll find property prices and the cost of food and transportation are significantly higher in Nevada than in other states. Making both Las Vegas and Henderson some of the most expensive places to live. And while those who can move have decided to relocate, poor people are at risk of being homeless, which can negatively influence pollution levels.

16. Chicago-Naperville, IL-IN-WI

Photo by Pedro Lastra on Unsplash

Average number of high ozone days: 15.5

Affectionately called “Chicagoland”, the Chicago-Naperville metropolitan area is home to vibrant neighborhoods, jaw-dropping architecture, and an extensive network of public parks. You’ll also find some of the world’s most famous landmarks here, like the Millennium Carillon.

Vehicle emissions are the main pollutant in Chicago, followed by wildfire smoke that drifts down from Canada and the burning of dirty coal. In Naperville, construction activities and industrial producers such as factories are the main contributors to outdoor air pollution.

Chicagoland has a number of challenges, ranging from unemployment to poverty and low education levels. Although these factors do not directly influence air pollution, they are secondary contributors. More wood and other combustible fuels are likely to be burned for heating, especially in the colder seasons.

17. Dallas-Fort Worth, TX-OK

Photo by Ryan Duffy on Unsplash

Average number of high ozone days: 15

The Dallas-Fort Worth metropolitan area is on the verge of becoming the next semigration capital of the United States. Why? The city boasts a vibrant arts and culture scene and a booming economy. You’ll also enjoy spending time in the zoos, parks, museums, and gardens.

Industry and vehicle emissions are some of the leading causes of air pollution in Dallas, while Fort Worth residents mostly suffer from fumes released by oil refineries. The poor air quality in both cities is worsened by the hot weather, which causes a reaction with many of the pollutants.

There are plenty of reasons to relocate to Dallas-Fort Worth, like the diversity, the healthy job economy, and the absence of state taxes in Texas. But keep in mind that the influx of people into the area not only increases crowding but also influences property prices to skyrocket. 

Most Polluted Cities in the United States | Wrapped Up

These polluted cities in the US continue to face air quality challenges, but it’s worth noting that efforts are being made to address these issues. Solutions include implementing stricter emission standards, investing in public transportation to reduce traffic, and using renewable energy sources as an alternative to burning fossil fuels.

For the latest air quality rankings and pollution levels in these cities, visit the United States Environmental Protection Agency (EPA) official website.

Before you make the big move, make sure to check the air quality of where you would like to live. These cities are more often than not tied to the most dangerous cities in the US, so remember to do your research.

I covered all of the costs of writing this article. This link does contain affiliate links. That means if you click through on some of the links in the article and end up making a purchase I will receive a small commission.