25 Places With the Most Hazardous Air in America

Air pollution in Bakersfield, California — Matt Gush / Shutterstock.com

There’s something in the air — and it’s not love.

The 2025 State of the Air report from the American Lung Association grades the levels of particle and ozone pollution that Americans were exposed to over a three-year period.

It also grades the worst short-term (24-hour) spikes in pollution, which can come from wildfires, for example.

Particle pollution consists of microscopic particles that come from sources such as wood-burning stoves, factories, power plants and diesel and gas engines. And while ozone is good up high in the atmosphere, at ground level, ozone pollution can be harmful.

These pollutants can trigger asthma attacks, respiratory infections and other serious health problems.

The 2025 report finds that “even after decades of successful efforts to reduce sources of air pollution, 46% of Americans — 156.1 million people — are living in places that get failing grades for unhealthy levels of ozone or particle pollution.”

According to the ALA, that adds up to nearly 25 million more people breathing unhealthy air compared with last year’s report and more than in any other report in the last 10 years.

Older folks are particularly vulnerable, the report says, and “faced a higher risk of premature death even when levels of short-term particle pollution remained well below the current national standard. This was consistent whether the older adults lived in cities, suburbs or rural areas.”

Following are the cities with the worst year-round particle pollution according to the ALA, along with their rankings for short-term particle and ozone pollution.

1. Bakersfield-Delano, CA

Pollution in Bakersfield, California — Matt Gush / Shutterstock.com

Population: 913,820

Rank for year-round particle pollution: 1

Rank for short-term particle pollution: 1

Rank for ozone pollution: 3

According to the nonprofit climate change research group First Street, Bakersfield’s high temperatures and low humidity contribute to increased ozone levels — which the ALA describes as one of “the most dangerous and pervasive air pollutants nationwide.”

Also contributing to low air quality in the area are industrial, power-generation and transportation emissions. While 15 years ago there were about 25 poor air quality days (when the air quality index, or AQI, is over 100) per year, First Street says there are about 36 days this year.

2. Visalia, CA

Visalia, California — Jacob Boomsma / Shutterstock.com

Population: 479,468

Rank for year-round particle pollution: 2

Rank for short-term particle pollution: 3

Rank for ozone pollution: 2

First Street predicts that the number of unhealthy air quality days in this area will continue to grow over the next 30 years. There were an average of 22 poor air quality days per year 15 years ago, compared with 41 now.