America is facing an air pollution crisis, or what many might call an “Airpocalypse.” Nearly half of the country’s population—some 156 million residents—are breathing dangerously filthy air, according to the American Lung Association’s 2025 State of the Air report. That’s nearly 25 million more people than last year’s assessment and the highest number in the previous decade, which is quite concerning given the possible health harms of air pollution.
Here, we list the 10 most polluted cities in the U.S. regarding unhealthy ozone days, annual particle pollution, and short-term particle pollution. We also explore what’s driving their air quality challenges, what it means for the people who call them home, and how to ensure the cleanest, healthiest air in your living or working spaces.
Bakersfield air quality is among America’s worst, topping the rankings for daily and annual particle pollution (also known as soot) and earning the third spot for ozone pollution (also known as smog). Home to roughly 914,000 residents, this low-slung farm city is in the San Joaquin Valley, nestled between mountains that create a dome that traps polluted air over the landscape. The air in Bakersfield hangs thick with dust from agriculture, exhaust from rail freight and road traffic, and fumes from wildfires, oil wells, and refineries—so much so that it obscures distant views. The sharp tang of petroleum and manure stench from dairy cows is often hard to miss while navigating the city.
When air pollution spikes, levels of soot or fine particulate matter (PM2.5) can reach 16 micrograms per cubic meter, well above the EPA’s recommended limit of 12. Residents describe the air as gritty, while some say you can taste the exhaust effluents, especially in the summer when the air becomes drier, hotter and more stagnant, and captures air pollutants like ozone close to the ground.
A little under 100 miles north of Bakersfield lies the city of Visalia, another Central Valley hotspot for shockingly high levels of air pollution. Visalia, which has a population of 480,000, ranks second for the most ozone-polluted U.S. cities in 2025, second for year-round particle pollution, and third for 24-hour particle pollution. Besides having a similar geography to the rest of Central California, Visalia’s heavy reliance on agriculture, including large-scale cattle operations, means the air is often filled with pesticides, dust, and smoke from crop burning. The smell of cow dung sometimes permeates the middle of the town, while truck traffic on major highways adds a steady stream of diesel exhaust to the air. Residents say that the resulting haze is dense with so much smog and fine particles that you can feel it in your throat, or your eyes may sting within minutes of being outside.
Despite some air quality improvements in the Fresno region over the past two decades, clean air is still more of a luxury for many of its over 1.3 million residents. That’s thanks to the seemingly never-ending toxic emissions from agriculture processing facilities, idling diesel trucks, nearby freeway traffic, and multiple industrial plants around the city. In 2025, the Fresno metropolitan area ranked third for yearly particle pollution and fifth for high ozone days. According to a report, more frequent, intense, and catastrophic wildfires in California contribute immensely to the city’s air quality woes, filling the area with billows of thick smoke and high amounts of PM2.5. Spending a certain amount of time outdoors in Fresno may expose you to dust, diesel fumes, and wildfire smoke.
An area known for its arts and music scene, incredible dining and microbreweries, and almost endless outdoor recreation, the Eugene-Springfield metro is one of the worst U.S. cities for air pollution in 2025. A recent nationwide air quality report places Eugene-Springfield at fourth for annual particle pollution and third for daily PM2.5 pollution, though it’s one of the cleanest metros for ozone pollution. A surge in wildfire smoke and industrial emissions drives the city’s particulate pollution problem. Its once-pristine air now carries a haze of fine particles, which some say is worsened by the city’s timber industry and ballooning manufacturing sector. Air quality monitors routinely show elevated levels of PM2.5, which has gotten so bad that local schools have had to cancel or relocate football games on certain days.
Once again, Los Angeles is America’s smoggiest city—and it’s not hard to see (or smell) why. With a population of over 18.3 million, the metro ranks worst in the nation for ozone pollution in 25 of the last 26 years and sixth for annual particle pollution in 2025. Various factors contribute to LA air pollution, including its massive car culture, local industries, and the Ports of Los Angeles and Long Beach that produce a combined 100 tons of smog every day. That’s more than the daily emissions of the six million cars in the Southern California region, the Environmental and Energy Study Institute (EESI) notes.
Also within LA borders are oil refineries, oil fields, active drilling sites, and major highways heavily traveled by diesel trucks transporting goods to and from the ports to inland railways. When it’s hot and busy, traffic fumes mix with industrial emissions and wildfire smoke, blanketing the city in an eye-watering, lung-searing brownish haze. The smog gives off a pungent, irritating odor that can be described as a mix of gasoline, smoke, and sometimes even a bleach-like smell.
Metro Detroit boasts numerous factories, manufacturing and power plants, major highways, and a resurging automotive industry. But that is essentially why it’s the sixth-worst location in America for year-round particle pollution and 22nd for short-term spikes. The region also received failing grades for its number of unhealthy days per year of ground-level ozone due to high industrial emissions and vehicle exhaust from heavy traffic. Some of the metro’s 5.3 million inhabitants report a strong petroleum smell, while in some neighborhoods, many say you can catch the scent of burning rubber. Like many other cities on this list, there’s also a visible haze over the skyline in Detroit on hazier or smoggier days.
San Jose is a cultural and tech hub for Silicon Valley, with a history of air pollution dating back to the mid-1960s. San Jose typically experiences higher rates of air pollution (particularly ozone and PM2.5) than other California cities due to its traffic congestion, weather patterns, and topography. Throngs of passenger cars, SUVs, and trucks emit soot and nitrogen dioxide into the atmosphere, while the area’s warmth and sun turn traffic emissions, wildfire smoke, and industrial discharge into smoggy gas. The mountains bordering Santa Clara County also play a role by trapping dirty air over the city like a lid on a pot.
Health authorities and air quality experts have taken notice, placing San Jose sixth for year-round particle pollution. The city’s air is often hazy or smoggy, especially during fire season when smoke from wildfires in Northern California drifts into the Bay.
Ranking seventh for high ozone days and eighth for annual particle pollution, Houston is ranked eighth on the list of U.S. cities with not-so-great air quality in 2025. Due to its proximity to large oil resources, the Houston metro area has a dense concentration of oil refineries and petrochemical facilities. It’s also home to 618 chemical manufacturing plants and many smaller operations, such as dry cleaners and gas stations. The toxic pollutants from these plants and industries create unhealthy air conditions for the region’s 7.7 million residents. Plus, as the country’s fourth-largest city, there’s a huge transportation demand in Houston. Unfortunately, Houstonians rely heavily on private vehicles to get around, which creates a lot of vehicular greenhouse gas emissions that worsen air pollution.
Air quality had improved slightly in the Cleveland metro area. But thanks to recent air pollution events across the region, it ranks ninth worst for annual particle pollution—a dramatic drop from its previous 54th position. The raging wildfires in western Canada are primarily to blame for Cleveland’s air quality decline. Southwesterly winds blew smoke and soot over the Cleveland metro, releasing “very unhealthy” levels of fine particulate matter into the air and bringing hazy skies, Case Western Reserve University reports. Industrial plants and factories, including major emitters like the Cleveland-Cliffs’ Middletown Works plant, have exacerbated the problem, as their processes are known to discharge particulate matter, nitrogen oxides, and other harmful chemicals into the atmosphere.
Fairbanks isn’t a surprising entry on this list, earning the title of America’s most-polluted city in 2018. In 2025, it placed 10th for year-round particle pollution and second for daily particle pollution. Alaska’s second-largest city and home to around 95,000 people, Fairbank’s air quality challenge stems from a mix of factors: bitterly cold winters (with temps dipping below -40°F) drive residents to burn wood to heat their homes, and the bowl-shaped Tanana Valley traps smoke and particulates close to the ground, creating problems for the environment and locals’ lungs. According to the EPA, fine particulates within those inversion pockets are typically close to twice the regulatory limit of 35 micrograms per cubic meter.
When the temperatures plummet, and wood stoves fire up across town, the air fills with a thick, smoky aroma ranging from the earthy scent of burning wood to something acrid if coal or even less common fuels are used. The smell is most potent in neighborhoods where wood and coal burning are most common, and it can vary block by block, depending on wind, elevation, and how many stoves are running nearby.
Air pollution is one of the biggest threats to public health. According to the 2020 State of Global Air report, ambient (outdoor) air pollution was linked to 4.5 million deaths in 2019, while indoor air pollution resulted in another 2.2 million fatalities worldwide. Extended exposure to outdoor fine particulate and ozone air pollution, in particular, is reportedly responsible for an estimated 8.34 million deaths globally per year.
Let’s explore the health effects of these two common types of air pollution.
Invisible to the naked human eye, fine particulate matter, also known as PM2.5, comprises microscopic specks 30 times smaller in diameter than human hair. When you inhale these tiny particles, they can cruise past your nose and throat and lodge in your lungs. Those smaller than that can get into your bloodstream and flow to your heart.
Short-term exposure to PM2.5 often causes less harmful health impairments, including shortness of breath, sneezing, coughing, and irritation and inflammation of the nose, throat, and eyes. However, long-term exposure, even for a few days, can trigger bronchitis, lung cancer, and lung infections like chronic obstructive pulmonary disease (COPD). It may also worsen asthma and raise your risk of cardiovascular diseases, including myocardial infarction (MI), stroke, heart failure, and arrhythmias.
Older adults, unborn babies, and people with pre-existing respiratory conditions are especially vulnerable to the adverse effects of PM2.5 pollution. Research shows that PM2.5 is a possible risk factor for neurological disorders like dementia, Alzheimer’s disease, and Parkinson’s disease. In pregnant moms, these particles can cross the placenta, harming an unborn infant’s lung function and causing premature birth, lower birth weight, and a higher risk of autism if exposure occurs in childhood.
Learn more: 8 Reasons Your House is So Dusty and How to Fix It
A major component of smog, ground-level ozone is said to be one of the most widespread and toxic airborne pollutants in the U.S., yet one of the least well-controlled. Ozone is a powerful lung irritant, causing what experts describe as a “sunburn of the lungs.” When ozone is inhaled into the lungs, it reacts with the delicate lining of the airways, leading to inflammation or worsening a cascade of symptoms, the American Lung Association notes.
Short-term ozone exposure (less than eight hours) can cause immediate breathing problems, including:
Scientific studies warn that breathing ozone over long periods can increase respiratory illnesses, metabolic disorders, nervous system issues, and reproductive issues (including reduced male and female fertility and poor birth outcomes). It may also increase respiratory- and cardiovascular-related mortality, which are the main drivers of total mortality (total deaths that occurred particularly on a large scale, such as in a population or geographical area).
Learn more: Do Air Purifiers Remove Carbon Monoxide (CO)?
Staying indoors might seem like the best way to escape outdoor pollution, as that’s what authorities typically urge residents to do in areas with elevated air pollution levels. However, it doesn’t eliminate exposure to outdoor air pollution. In fact, the air you breathe in your home can be up to 100 times more polluted than outdoor air, especially in wildfire-prone regions or areas near traffic, construction, or industries.
Outdoor pollutants can waft into homes and workplaces through open doors or windows, cracks or gaps in walls and foundations, or faulty ventilation systems that pull in the toxins from outside and circulate them throughout the building. Once indoors, these pollutants can mix with pollution from indoor sources like building materials, flooring, pets, cooking, and fragrances to create even more harmful compounds that could cause issues for occupants who spend most of their time inside.
The average American spends 90 percent of their time indoors, so improving indoor air quality should be a top priority. One way to clean your air this is to use an air purifier with a HEPA filter. TrustedAir HEPA air purifiers are designed to capture airborne particles as small as 0.3 microns to ensure you breathe the cleanest, healthiest air, regardless of outdoor air quality. These devices draw air through microscopic filters that trap unwanted pollutants so you don’t inhale them. An air purifier for your home or office can also help combat allergies, respiratory problems, and infectious diseases. It can also clear the air of health-harming and allergy-triggering toxins like smoke particles, fine particulate matter, dust mites, ozone, pet dander, and airborne bacteria.
Learn more: 7 Benefits of an Air Purifier for Your Health and Home | How Air Purifiers Help Reduce Allergies and Which One to Buy
America’s air quality has improved drastically over the past few decades, but the country is now backsliding on air quality measures. Close to half of the nation’s population lives in places with failing grades for air quality due to unhealthy ozone levels and particle pollution. If you live in one of the polluted U.S. cities listed in this article and are concerned about your indoor air quality, a TrustedAir air purifier can rid your indoor air of ozone, PM2.5, and other potentially dangerous pollutants. That way, you can enjoy every breath with confidence.
If you need help finding the best air purifier for your needs and budget or want to learn more about how these devices can improve indoor air quality, please call TrustedAir at (877) 869-1507 or email us at [email protected].
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