Air quality is an important issue for many people right now. To help determine the pollution level of key cities in the United States, the American Lung Association released its 2019 “State of the Air” report. They found that more than four in 10 Americans live in a city with unhealthy air quality. Climate-related weather changes, like wildfires, are making it worse.

There are several different types of pollution. Ozone pollution, which forms more frequently in warmer temperatures and is also known as smog, causes “sunburn of the lung,” the American Lung Association said. Inhaling ozone can lead to shortness of breath, coughing and asthma attacks and can shorten lifespan.

Particle pollution results from any number of sources that produce particulate matter in the air, including wildfires, wood-burning devices, coal-fired power plants and diesel engines. These particles can enter the bloodstream as well as the lungs and are tied to several forms of cancer, heart attacks, strokes and asthma.

Read on to see the top 25 most polluted city areas based on ozone pollution, from No. 25 to the most polluted at No. 1.

25. Atlanta-Athens-Clarke County-Sandy Springs, Georgia-Alabama

These regions of Georgia and Alabama, with a population of over 6.7 million people, have high instances of asthma, with nearly 150,000 cases of pediatric asthma and over 428,000 cases of adult asthma.

It ranked 25th out of 228 metropolitan areas for high ozone days. It also came in 64th for 24-hour particle pollution out of 217 metropolitan areas and 19th for annual particle pollution out of 203 metropolitan areas.

24. Fort Collins, Colorado

Despite its abundance of nature, Fort Collins, Colorado, ranked 24th for high ozone days out of 228 metropolitan areas. It also made the list at 52nd for 24-hour particle pollution out of 217 metropolitan areas.

It was 156th for annual particle pollution out of 203 metropolitan areas. With these stats, it’s probably no surprise that it has high occurrences of adult asthma — 25,586 cases — and 11,943 cases of chronic obstructive pulmonary disease (COPD).

23. Hartford-East Hartford, Connecticut

Hartford, the capital of Connecticut, with a population of almost 1.5 million people, ranked 23rd for high ozone days out of 228 metropolitan areas. Though it ranked 104th for annual particle pollution out of 203 metropolitan areas, it tied for first for the cleanest metropolitan area in the country for 24-hour particle pollution. The area has high occurrences of adult asthma, COPD, cardiovascular disease and diabetes.

22. El Paso-Las Cruces, Texas-New Mexico

This region of New Mexico ranked 22nd for high ozone days out of 228 metropolitan areas and 42nd for 24-hour particle pollution out of 217 metropolitan areas. It also came in at 56th for annual particle pollution out of 203 metropolitan areas. There were 23,352 cases of pediatric asthma, as well as adult asthma, COPD and 87,607 cases of adult diabetes.

21. Philadelphia-Reading-Camden, Pennsylvania-New Jersey-Delaware-Maryland

This east coast region of more than 7.2 million people ranked 21st for high ozone days out of 228 metropolitan areas and 43rd for 24-hour particle pollution out of 217 metropolitan areas. It ranked 18th for annual particle pollution out of 203 metropolitan areas.

Lung-related diseases are especially high here, with 556,550 cases of adult asthma, 136,257 cases of pediatric asthma and 367,118 cases of COPD. Additionally, there were 4,538 cases of lung cancer.

20. Sheboygan, Wisconsin

This Midwestern town ranked 20th for high ozone days out of 228 metropolitan areas. Adult asthma, cardiovascular disease and COPD are common health conditions here for a relatively small population of 115,344.

19. Chico, California

The college town of Chico, California, ranked 19th for high ozone days out of 228 metropolitan areas and 43rd for 24-hour particle pollution out of 217 metropolitan areas. For annual particle pollution, it came in 83rd out of 203 metropolitan areas. Disease runs high here as well for related conditions including asthma, COPD, cardiovascular disease and diabetes.

18. Chicago-Naperville, Illinois-Indiana-Wisconsin

The Chicago area ranked 18th for high ozone days out of 228 metropolitan areas, 35th for 24-hour particle pollution out of 217 metropolitan areas and 19th for annual particle pollution out of 203 metropolitan areas.

The high population of almost 10 million people may account for its high disease statistics. There were 640,266 instances of adult asthma and 514,130 cases of COPD. Pediatric asthma cases were 132,522.

17. Dallas-Fort Worth, Texas-Oklahoma

This part of the Lone Star State ranked 17th for high ozone days out of 228 metropolitan areas and 64th for annual particle pollution out of 203 metropolitan areas. But it tied for first with Hartford, Connecticut, for the cleanest metropolitan area in the country for 24-hour particle pollution.

There are numerous cases of adult asthma, COPD and cardiovascular disease. Diabetes instances were especially high at 685,209 among the population of over 7.8 million people.

16. Washington-Baltimore-Arlington, District of Columbia-Maryland-Virginia-West Virginia-Pennsylvania

This populous region near the nation’s capital ranked 16th for high ozone days out of 228 metropolitan areas, 69th for 24-hour particle pollution out of 217 metropolitan areas and 43rd for annual particle pollution out of 203 metropolitan areas.

Lung diseases are prevalent. There are 202,582 cases of pediatric asthma and 709,893 cases of adult asthma. Additionally, there were 765,846 cases of diabetes.

15. El Centro, California

This Southern California town near the Arizona border ranked 15th for high ozone days out of 228 metropolitan areas, 14th for 24-hour particle pollution out of 217 metropolitan areas and eighth for annual particle pollution out of 203 metropolitan areas. There are 10,265 cases of adult asthma and 3,245 cases of pediatric asthma for a population of just 182,830.

14. Salt Lake City-Provo-Orem, Utah

This high desert area of Utah ranked 14th for high ozone days out of 228 metropolitan areas, eighth for 24-hour particle pollution out of 217 metropolitan areas and 72nd for annual particle pollution out of 203 metropolitan areas. Related diseases are prevalent in this population of just over 2.5 million people, with 102,957 cases of cardiovascular disease and 121,102 cases of diabetes.

13. Las Vegas-Henderson, Nevada

Las Vegas is not only known for its famous strip but also its poor air quality. The area ranked 13th for high ozone days out of 228 metropolitan areas, 27th for 24-hour particle pollution out of 217 metropolitan areas and 26th for annual particle pollution out of 203 metropolitan areas.

Lung conditions abound in this population of just over 2.2 million people. There are 180,575 cases of adult asthma, 118,876 cases of COPD, 40,464 cases of pediatric asthma and 1,046 cases of lung cancer.

12. Denver-Aurora, Colorado

The skies may look clear in this region of Colorado, but the same can’t always be said for its air quality. The region ranked 12th for high ozone days out of 228 metropolitan areas, 32nd for 24-hour particle pollution out of 217 metropolitan areas and 86th for annual particle pollution out of 203 metropolitan areas. Adult asthma cases are especially high: 253,102, for a population of 3.5 million people. Diabetes cases are also high at 193,027.

11. Redding-Red Bluff, California

This Northern California region ranked 11th for high ozone days out of 228 metropolitan areas, 58th for 24-hour particle pollution out of 217 metropolitan areas and 172nd for annual particle pollution out of 203 metropolitan areas.

With a relatively small population of only 243,847 people, lung conditions are quite prevalent. Adult asthma cases are at 15,276 and COPD cases are at 9,848.

10. New York-Newark, New York-New Jersey-Connecticut-Pennsylvania

The Big Apple and surrounding areas ranked 10th for high ozone days out of 228 metropolitan areas, 89th for 24-hour particle pollution out of 217 metropolitan areas and 30th for annual particle pollution out of 203 metropolitan areas.

The collective population of these regions is over 23 million people. Such density can manifest in high numbers of disease. There are 1,651,293 cases of adult asthma here, 448,996 cases of pediatric asthma, 996,592 of COPD and 13,532 cases of lung cancer.

9. Houston-The Woodlands, Texas

This Texas region ranked ninth for high ozone days out of 228 metropolitan areas and 58th for 24-hour particle pollution out of 217 metropolitan areas. It ranked 17th for annual particle pollution out of 203 metropolitan areas.

This populous region of over 7 million people has high incidences of lung conditions. There are also 604,114 cases of diabetes and 393,149 cases of cardiovascular disease.

8. San Jose-San Francisco-Oakland, California

These San Francisco Bay Area communities ranked eighth for high ozone days out of 228 metropolitan areas and fourth for 24-hour particle pollution out of 217 metropolitan areas. The area came in sixth for annual particle pollution out of 203 metropolitan areas.

Two related diseases are prevalent in this population of over 9.6 million people: asthma and diabetes. There were 598,338 cases of adult asthma and 793,587 cases of diabetes.

7. Phoenix-Mesa, Arizona

With the high temperatures in Arizona, which increase ozone, it’s unsurprising that this part of the state ranked seventh for high ozone days out of 228 metropolitan areas. It also ranked 13th for 24-hour particle pollution out of 217 metropolitan areas and 32nd for annual particle pollution out of 203 metropolitan areas. A significant number of people live in poverty here, 635,629, out of a population of 4.7 million.

6. San Diego-Chula Vista-Carlsbad, California

This Southern California region known for desert-like conditions and warm temperatures ranked sixth for high ozone days out of 228 metropolitan areas. It also ranked 69th for 24-hour particle pollution out of 217 metropolitan areas and 64th for annual particle pollution out of 203 metropolitan areas.

Of the more than 3.3 million people that live here, 728,528 are children under the age of 18. Of those, cases of pediatric asthma came in at 45,216.

5. Sacramento-Roseville, California

This area near California’s capital ranked fifth for high ozone days out of 228 metropolitan areas and 15th for 24-hour particle pollution out of 217 metropolitan areas. It ranked 32nd for annual particle pollution out of 203 metropolitan areas.

With a population of more than 2.5 million, the area also has large numbers of people who are at greater risk from the negative health effects of pollution, including 399,007 adults ages 65 and older and 598,140 youth ages 18 and under.

4. Fresno-Madera-Hanford, California

This central California region isn’t winning any awards for air quality. It ranked fourth for high ozone days out of 228 metropolitan areas and seconnd for 24-hour particle pollution out of 217 metropolitan areas. It was first for annual particle pollution out of 203 metropolitan areas.

Children and adults both are dealing with health conditions that may be caused or exacerbated by pollution, including 73,023 cases of adult asthma, 39,469 cases of COPD and 22,695 cases of pediatric asthma in a total population of around 1.3 million people.

3. Bakersfield, California

The further south one goes in California, the worse the air quality seems to get. Bakersfield ranked third for high ozone days out of 228 metropolitan areas and first for 24-hour particle pollution out of 217 metropolitan areas. It also came in second for annual particle pollution out of 203 metropolitan areas. Pollution is especially concerning for the 259,120 children ages 18 and under, 95,307 adults ages 65 and older and the estimated 182,948 people living in poverty, who are all at greater risk of health problems.

2. Visalia, California

This Southern California city ranked second for high ozone days out of 228 metropolitan areas and 12th for 24-hour particle pollution out of 217 metropolitan areas. It ranked fourth for annual particle pollution out of 203 metropolitan areas.

Adults, particularly older adults, are grappling with more health issues here. Out of a total population of 464,493, there are 51,669 adults ages 65 and older who are at greater risk of health conditions. There were 25,148 adult asthma cases and 13,466 cases of COPD, as well as 30,984 cases of diabetes.

1. Los Angeles-Long Beach, California

The populous area of Los Angeles and Long Beach, California, pays a price for having so many residents. The area ranked first for high ozone days out of 228 metropolitan areas. It also hit seventh for 24-hour particle pollution out of 217 metropolitan areas and fifth for annual particle pollution out of 203 metropolitan areas.

Though Southern California’s beaches may be good for one’s health in some ways, health conditions abound. There are 1,142,240 cases of adult asthma, 636,209 cases of COPD and 267,953 cases of pediatric asthma.

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This article originally appeared on GOBankingRates.com: 25 Most Polluted Cities in the US