The Most Polluted Cities in America [+Emission Sources]

While air pollution in the U.S. has improved remarkably since the passage of the Clean Air Act, the Environmental Protection Agency (EPA) estimates that 137 million people nationwide still live in counties where air pollution levels exceeded air quality standards.

This article dives deep into the most polluted cities in America. There are several different types of pollution in the cities with the most pollution. Ozone pollution, which appears in warmer temperatures (also known as smog), causes sunburn of the lung. Breathing ozone can lead to shortness of breath, coughing and asthma attacks and can shorten lifespan.

Particle pollution results from many sources that generate particulate matter in the air, such as wildfires, wood-burning devices, coal-fired power plants, and diesel engines. The concentration of particles can enter the bloodstream and the lungs and lead to various forms of cancer, heart diseases, strokes, and asthma.

In 2018, the U.S. emitted 76 million tons of pollution into the atmosphere, which according to the American Lung Association, contributes to increased rates of lung cancer and reduced lifespans among American families.

Air quality standards for common pollutants that pose a health threat to the public are managed by the EPA. These pollutants include ozone, fine and coarse particulate matter (PM2.5 and PM10), sulfur dioxide, lead, carbon monoxide, and nitrogen dioxide.

From 1980 to 2018, the greatest air quality improvements occurred in lead, sulfur dioxide, and carbon monoxide levels.

According to the EPA, efforts to remove lead from automobile gasoline alone helped reduce levels of lead in the air by 89 percent over three decades.

Similarly, a 1990 update to the Clean Air Act known as the Acid Rain Program set a permanent cap on emissions of sulfur dioxide and nitrogen oxides from power plants. The cap helped reduce sulfur dioxide to 9.0 percent of the 1980 value and the level of nitrogen dioxide to 39 percent over the same time period.

While levels of nitrogen dioxide, carbon monoxide, sulfur dioxide, and lead are all below 40 percent of their respective 1980 values, ozone and particle pollution continue to present a major public health risk. With these trends in mind, our researchers at BuyAutoInsurance.com analyzed data from the EPA to find the U.S. metropolitan areas with the highest levels of air pollution.

The EPA uses air pollution measures  known as the Air Quality Index (AQI) to report daily air quality, with higher values corresponding to greater levels of air pollution.

Values between 0-50 are considered good; values between 51-100 are moderate; values between 101-150 are unhealthy for sensitive groups; and values above 151 are unhealthy for the general public. Researchers used AQI data to determine air quality rankings for small, midsize, and large metropolitan areas.

The findings among the small and midsize metros are in line with the findings among the large metros. Specifically, locations in California make repeated appearances on these lists.

When comparing air pollution levels of large metropolitan areas, five of the top 15 metros were found to exist in the coastal state. The incidence is higher among the top 15 small and midsize metros.

Here are the small and midsize metropolitan areas with the worst air quality:

In this article, you’ll find information on the most polluted cities in the world, the most polluted cities in the US, the most polluted countries, and a special look at the most polluted cities in California.

Often, a car owner’s environment can affect their insurance rates. Find out more about different types of auto insurances and how they might apply to you on our auto insurance coverages page.

If you’re looking for auto insurance quotes right away, just enter your ZIP code into our online quote comparison tool. You’ll get the best rates in your area based on your information.

The 15 Large Metros with the Worst Air Quality

#15 – New York-Newark-Jersey City, NY-NJ-PA

• Median AQI: 53
• Max AQI: 210
• Good air quality: 156 days per year
• Moderate or unhealthy for sensitive groups: 206 days per year
• Unhealthy, very unhealthy, or hazardous: 3 days per year
• Most common pollutant: Fine particulate matter (PM2.5)

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#14 – San Francisco-Oakland-Hayward CA

• Median AQI: 53
• Max AQI: 245
• Good air quality: 147 days per year
• Moderate or unhealthy for sensitive groups: 206 days per year
• Unhealthy, very unhealthy, or hazardous: 12 days per year
• Most common pollutant: Fine particulate matter (PM2.5)

#13 – Detroit-Warren-Dearborn, MI

• Median AQI: 54
• Max AQI: 151
• Good air quality: 137 days per year
• Moderate or unhealthy for sensitive groups: 226 days per year
• Unhealthy, very unhealthy, or hazardous: 2 days per year
• Most common pollutant: Fine particulate matter (PM2.5)

#12 – St. Louis, MO-IL

• Median AQI: 54
• Max AQI: 182
• Good air quality: 157 days per year
• Moderate or unhealthy for sensitive groups: 206 days per year
• Unhealthy, very unhealthy, or hazardous: 2 days per year
• Most common pollutant: Fine particulate matter (PM2.5)

#11 – Pittsburgh, PA

• Median AQI: 55
• Max AQI: 154
• Good air quality: 136 days per year
• Moderate or unhealthy for sensitive groups: 228 days per year
• Unhealthy, very unhealthy, or hazardous: 1 day per year
• Most common pollutant: Fine particulate matter (PM2.5)

#10 – Philadelphia-Camden-Wilmington, PA-NJ-DE-MD

• Median AQI: 55
• Max AQI: 164
• Good air quality: 132 days per year
• Moderate or unhealthy for sensitive groups: 230 days per year
• Unhealthy, very unhealthy, or hazardous: 3 days per year
• Most common pollutant: Fine particulate matter (PM2.5)

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#9 – Chicago-Naperville-Elgin, IL-IN-WI

• Median AQI: 57
• Max AQI: 177
• Good air quality: 117 days per year
• Moderate or unhealthy for sensitive groups: 242 days per year
• Unhealthy, very unhealthy, or hazardous: 6 days per year
• Most common pollutant: Fine particulate matter (PM2.5)

#8 – Las Vegas-Henderson-Paradise, NV

• Median AQI: 61
• Max AQI: 154
• Good air quality: 122 days per year
• Moderate or unhealthy for sensitive groups: 242 days per year
• Unhealthy, very unhealthy, or hazardous: 1 day per year
• Most common pollutant: Ozone

#7 – Salt Lake City, UT

• Median AQI: 61
• Max AQI: 169
• Good air quality: 138 days per year
• Moderate or unhealthy for sensitive groups: 225 days per year
• Unhealthy, very unhealthy, or hazardous: 2 days per year
• Most common pollutant: Ozone

#6 – Sacramento-Roseville-Arden-Arcade, CA

• Median AQI: 61
• Max AQI: 314
• Good air quality: 124 days per year
• Moderate or unhealthy for sensitive groups: 217 days per year
• Unhealthy, very unhealthy, or hazardous: 24 days per year
• Most common pollutant: Ozone

#5 – San Diego-Carlsbad, CA

• Median AQI: 64
• Max AQI: 143
• Good air quality: 73 days per year
• Moderate or unhealthy for sensitive groups: 292 days per year
• Unhealthy, very unhealthy, or hazardous: 0 days per year
• Most common pollutant: Ozone

#4 – Denver-Aurora-Lakewood, CO

• Median AQI: 64
• Max AQI: 174
• Good air quality: 83 days per year
• Moderate or unhealthy for sensitive groups: 274 days per year
• Unhealthy, very unhealthy, or hazardous: 8 days per year
• Most common pollutant: Ozone

#3 – Los Angeles-Long Beach-Anaheim, CA

• Median AQI: 77
• Max AQI: 201
• Good air quality: 35 days per year
• Moderate or unhealthy for sensitive groups: 310 days per year
• Unhealthy, very unhealthy, or hazardous: 20 days per year
• Most common pollutant: Ozone

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#2 – Phoenix-Mesa-Scottsdale, AZ

• Median AQI: 77
• Max AQI: 996
• Good air quality: 42 days per year
• Moderate or unhealthy for sensitive groups: 304 days per year
• Unhealthy, very unhealthy, or hazardous: 19 days per year
• Most common pollutant: Coarse particulate matter (PM10)

#1 – Riverside-San Bernardino-Ontario, CA

• Median AQI: 97
• Max AQI: 296
• Good air quality: 25 days per year
• Moderate or unhealthy for sensitive groups: 275 days per year
• Unhealthy, very unhealthy, or hazardous: 65 days per year
• Most common pollutant: Ozone

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Air Quality Results for All US Metro Areas

Frequently Asked Questions: Cleanest Cities vs Most Polluted

Now that we’ve covered the most polluted cities in America, let’s get to your frequently asked questions. They include:

• What US city has the cleanest air?
• Which US state is the most polluted?
• What is the cleanest city in the world?

Scroll down for the answers to those questions and more.

#1 – Which US cities have the worst air quality?

Which city has the worst air quality? The five most polluted cities in our ranking are the Riverside-San Bernardino-Ontario metro, the Phoenix-Mesa-Scottsdale metro, the Los Angeles-Long Beach-Anaheim metro, the Denver-Aurora-Lakewood metro, and the San Diego-Carlsbad metro.

#2 – What US city has the cleanest air?

Wondering which city has the cleanest air? A 2019 American Lung Association report named Bangor, Maine as the US city with the cleanest air. It was one of just six cities that received that distinction.

#3 – Which US state is the most polluted?

California, which has five metros in our ranking of the most polluted cities in the United States, is considered the most polluted state throughout the country.

#4 – Which US state has the cleanest air?

According to the World Population Review, Hawaii is the state with the cleanest air with an air quality index of 21.2, well into the “good” air quality index range.

#5 – What is the cleanest city in the world?

The cleanest city in the world, according to the European organization Clearwater, is Calgary, which is a city that actually has over a million people. Other incredibly clean cities include Zurich (Switzerland) and Luxembourg (a country in Europe).

#6 – What country is the most polluted?

Wondering what is one of the most polluted places in the world? According to Statista, Bangladesh is considered the most polluted country in the world with an average PM2.5 concentration of 77.1 micrograms per cubic meter of air.

#7 – What country is the cleanest?

New Zealand is considered the country with the lowest amount of pollution, likely due to its coastal geography and the low-density towns that are located around that coast.

#8 – Is Los Angeles a dirty city?

While “dirty” is a term that resides in the eye of the beholder, Los Angeles and its metro certainly suffer from the major consequences of a highly populated and dense city.  While it’s not the dirtiest city in the world, it definitely isn’t the cleanest. Some of its issues include increased amounts of pollution along with less greenage, which can lead to more air quality issues.

Methodology: Determining the Most Polluted Cities in America

Statistics on annual levels of air pollutants by metropolitan area for 2018 were obtained from the U.S. Environmental Protection Agency. For each metro, the EPA calculates a daily index value for each pollutant.

The highest of those index values are reported as the daily Air Quality Index (AQI) value, and the pollutant responsible for the highest index value is considered the main pollutant for the day. For each metro, the median of the daily AQI values is reported as the overall measure of air quality for the year—the median AQI.

Additionally, for each metro, the pollutant listed as the main pollutant for the greatest number of days in the year is listed as the most common pollutant in that metro. PM10 and PM2.5 represent coarse and fine particulate matter, respectively.

To improve relevance, metropolitan areas were grouped into the following cohorts based on population size:

• Large: 1,000,000 or more
• Midsize: 350,000-999,999
• Small: 100,000-349,999

Metros were ordered by their median AQI. In the event of a tie, both the maximum annual AQI and the number of unhealthy, very unhealthy, or hazardous days were considered.

Many of America’s most polluted metros are in California.

The rankings can be attributed to a few factors. First, California is the most populous U.S. state, which means more people are commuting, consuming, and ultimately polluting. Second, California is generally warm and sunny.

Ground-level ozone pollution is more likely to form in this type of climate as the sun and heat act as accelerants. California’s hot weather has also been linked to severe wildfires, which push more dangerous particles into the air.

Finally, many California cities exist on plains or in valleys that are encased by mountains. This topography helps trap pollutants in, keeping ambient air concentrations high.

Across the U.S., major sources of pollution vary by pollutant. For example, vehicles produce the largest share of carbon monoxide gas, while industrial processes and stationary fuel consumption (like power plants) are responsible for the majority of particulate matter and sulfur dioxide in the air.

Commonly, ground-level ozone pollution is caused by automobiles, power plants, chemical plants, refineries, and industrial boilers.

However, it can also be created through natural sources including trees. Prolonged exposure to this type of pollution can lead to numerous health problems, particularly those related to the lungs and respiratory system.

Air pollution in the U.S. has greatly improved since the passage of the Clean Air Act. Yet, millions of Americans continue to live in polluted cities where air pollution remains a threat.

To tackle this ongoing problem, the EPA and other federal, state, and local environmental agencies are implementing new policies and programs aimed at individuals and companies.

For example, the EPA SmartWay program helps companies identify more fuel-efficient ways to move goods. Similarly, cities and states across the nation are heavily investing in and promoting public transportation systems as a way to reduce air pollution and protect the environment.

Pollution can cause damage to your car, including upkeep. One way to save is to find the best rates on auto insurance. Just plug your ZIP code into our online quote generator to find the best auto insurance rates in your area based on your information.