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What US States Have the Worst Air Quality?

You want the air that you breathe to be as clean as possible; after all, you need air in order to live and it stands to reason that the quality of the air that you breathe has a direct impact on your overall health and well-being. Unfortunately, however, air quality in the United States has increasingly declined over the past few years. The American Lung Association reports that an estimated 43 percent of the US population, or four in 10 Americans reside in counties where ozone levels in the air (high ozone levels is referred to as “smog”) and/or particulate matter in the air (commonly known as “soot”), and both forms of pollution can have serious negative effects on your health. Furthermore, when outdoor air quality is poor, indoor air quality worsens, too.

While the air in the vast majority of locations throughout the United States is actually cleaner than it was 10 years ago, due to worsening weather conditions in some cities, air pollution levels have been exacerbated. This is largely due to the fact that temperatures have been rising and rain patterns have been changing; these factors, combined with the fact that wildfires have been rampant in recent years, have led to increased ozone and particulate matter in the air in some locations.

What locations have the worst air quality in the United States? Below, we highlight the seven spots with the worst air pollution in the US, based on data that was compiled and ranked by the 2019 State of the Air report, which was published by the American Lung Association.


While California is arguably one of the most beautiful states in the country, but sadly, it consistently ranks as one of the most polluted states in the country overall. Of the top 10 most polluted cities in the country (as per year-round particulate matter), six of those cities are located in California, with the Fresno-Madera region receiving the most polluted city in America title. Other California cities also sit on the list for the worst pollution, with Bakersfield having the worst short-term particulate matter pollution in the air and Los Angeles with the worst ozone pollution in the country.

With the fifth largest economy in the world, the Golden State is the most populated state in the nation, and these two facts certainly contribute to the air pollution problem. The most significant sources of air pollution in the state are caused by vehicle traffic and industrial pollution. Additionally, the Golden State’s topography, particularly in farming regions, combined with the year-round warm weather in many locations, help to trap air pollution within the valley walls, which directly contributes to increased ozone levels. Smoke from wildfires – which have markedly increased in the past few years – also contribute to the decreasing air quality in California. According to the State of the Air report, California’s air quality was the worst in the nation in 2019, and it is projected that the air quality will only worsen in the future.


Pennsylvania has long been a large producer of the coal that has powered many US factories and warmed the homes of countless Americans; however, the state’s coal industry has largely contributed to the state’s high ozone and particle pollution levels. Five cities in the Keystone State sit on the list of the top 25 most polluted cities for year-round particulate matter pollution in the nation, with Pittsburgh sitting at the #7 position on this list. As a key metropolitan sub-region of New York City, Pennsylvania’s air quality is negatively impacted by regional ozone pollution. Furthermore, State Impact Pennsylvania, 16 of 36 counties that the ALA had compiled data about received a grade of D or F for ozone levels. 

While this information may sound depressing, it isn’t all doom-and-gloom; there is good news, as there has been a big shift to using natural gas over coal. As such, particulate matter air pollution has steadily decreased since 2003.


The Lone Star State may be famous for a great many things, but there is something that it’s infamous for, too; it’s home to two of the top 25 most polluted cities for year-round particle pollution. Texas is second most populated state in the country, which has helped to push the decreased air quality in some locations. Two major airports are located in the Houston area, and the city ranked 17th out of 203 metro areas for year-round particle pollution.

According to the Texas Commission on Environmental Quality, pollution in the state largely comes from “point” and “non-point” sources. Point sources of pollution have a tendency to be large and stationary; examples include power plants, smelters, industrial boiler, petroleum refineries, and manufacturing plants that are powered by fossil fuels. Non-point sources comprise all other sources of pollution; most notably on- and non-road mobile, as well as biogenic sources.


Four of the top 25 cities for short-term particle pollution are located in Washington State, and two locations are in the top 10. The 2019 State of the Air report found that wildfires, which have been increasing in recent years, have had a major impact on the air quality of the Seattle-Tacoma area. In fact, the impact has been so significant that the region was the most polluted in the nation in 2018, and it moved to the ninth most polluted in 2019 for short-term particle pollution. The Yakima region sat at the #6 position.

A lot of Washington State’s outdoor air pollution is directly related to vehicles, wood smoke, and outdoor burning, reports the Washington State Department of Health. Gas- and diesel-powered equipment, as well as some types of industries and wildfires largely contribute to the air pollution the state experiences.


Oregon is another Pacific Northwest state that sits on the list for the most polluted locations. It’s home to four of the top 25 most polluted cities for short-term particle pollution, which includes Medford and Grants Pass, as well as the Portland area. As per the Oregon Department of Environmental Quality, the amount of particle matter in Oregon is high as a result of so-called “air toxics”, which typically come from motor vehicles and industrial sources; diesel soot, benzene, and byproducts from vehicle exhaust and industrial sources; metals, such as manganese, lead, and nickle, too.


Known as “The Last Frontier”, Alaska is famous for wide, undisturbed expanses of nature. As such, it might come as a surprise to learn that two of the top 25 most polluted cities for short-term particle pollution are situated in Alaska. Furthermore, Fairbanks is the third most polluted city out of the top 10 most polluted cities in the nation for year-round particle pollution, and Anchorage is the 21 of the 25 most polluted cities in the country. Short-term particle pollution in cities like Fairbanks is exceptionally poor during the winter. This is largely due to the fact that those who reside in the city rely on wood-burning stoves and fireplace to stay warm.

As per the State of Alaska’s Division of Air Quality, the particle pollutant’s in the city are largely caused by dust, open burning for land clearing purposes, wood stoves, volcanic ash, and wood stoves. Vehicles, including cars and trucks, largely contribute to emissions, too.


Utah’s Salt Lake City and Logan are on the list of the top 25 most polluted cities for short-term pollution in the United States. Ozone is another type of pollution that is of concern; particularly in the winter, as temperature inversions, which happen when cold air on the surface becomes trapped underneath warm air. In Utah, the valley floors become covered with snow, and the snow cover reflects rather than absorbs heat. This effect stops “normal vertical mixing of warm and cold air that keeps pollutants from building up to unhealthy levels at the surface”.

The most significant sources of fine particles in the air in the state of Utah are derived from pollution that come for vehicle, as well as homes – especially those that use wood-burning stoves, small businesses, and commercial buildings, cites the Utah Department of Health. Gas stations, dry cleaners, home heating, and manufacturing plants also contribute to air pollution.

Other Locations Where Air Quality is a Concern

In addition to the states mentioned above, the following states are areas of concern for air pollution.


Three counties in the state of Montana are on the Top 10 counties for short-term particle pollution. Wild fires and changing temperatures have contributed to the increased levels of air pollution.

New York

New York City sits at the #10 position on the top 25 most ozone polluted cities in the United States. A lot of the pollution is directly linked to vehicle emissions, the combustion of fossil fuels (particularly for electrical power generation), and for heating and cooling residential buildings, reports the New York Department of Health.


Ozone pollution is a cause for concern in the state of Connecticut, as well as its neighbor, New Jersey. The ALA gave the state a grade of “F” for all counties, directly due to high ozone level days.

What factors lead to high air quality in these states?

In order to determine which states had the “worst” air quality, the findings that were published in the ALA’s State of the Air report were assessed. We looked to see the amount of times that a particular city (and where applicable, its counties) in a state were listed on the lists of the top 25 rankings for year-round particle pollution, short-term particle pollution (over a 24 hour period), as well as ozone days. We also considered the city’s proximity to major metropolitan regions. Furthermore, we looked at other key geographical factors that would lead to higher levels of ozone and particle pollution as per region (West and Southwest, where ozone levels are extremely high) and for areas where warmer temperatures lead to air pollution.

When discussing air pollution, the main sources are ozone and particle pollution. As per AirNow, particle pollution is made up of solid and liquid particles that are derived from several sources, including civilian and industrial emissions, fires, and chemical reactions that occur in the atmosphere. Ozone, which actually occurs naturally in the higher reaches of the atmosphere and protects us from the sun’s dangerous UV radiation, becomes a serious problem when it exists at ground levels, where it is generated by pollutants that react chemically with sunlight and that can have a negative impact on health.

To derive the data on its 2019 report, the ALA assessed the most recent data regarding pollution that was collected by federal, state, and local governments and tribes in 2015, 2016, and 2017. The report utilizes data that was collected by the US Environmental Protection Agency’s (EPA) Air Quality System.

Summing It Up

Since the air you breathe has a major impact on your overall health and well-being, it’s important to be aware of air pollution. Vulnerable individuals, such as children, the elderly, and those who suffer from chronic illnesses, are the most prone to experiencing adverse health effects as a result of air pollution; however, even individuals who are otherwise healthy can also be at-risk of developing serious health issues, such as heart disease, lung cancer, and asthma. Moreover, air pollution can interfere with normal lung function. Ozone can increase the risk of breathing issues, cardiovascular problems, and can even reduce lifespan.

The more you’re aware of the air quality in your area, the more you can do to protect yourself. In addition to increasing ventilation levels and remaining inside when air quality is poor, another way that you can protect yourself from being exposed to air pollution is by having your home tested for mold growth by a professional on a regular basis. Exposure to mold can have a big impact on your overall health and well-being, and since it can grow in inconspicuous locations, regular testing is important so that you can eliminate mold growth if it is present in your home.

For the most reliable mold testing in the US, contact MI&T. As one of the largest and most trusted mold testing companies in the nation, you count on us to determine if mold is, in fact, growing in your home.