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AirHistory

Updated April 2026 · EPA Air Quality System

Worst Air Quality Cities in America

The 200 U.S. cities with the worst air over the past decade, ranked from EPA Air Quality System monitoring data. The top 10 here average roughly 77 unhealthy-air days per year — three-plus weeks annually when sensitive groups are advised to limit outdoor activity, and a real signal for anyone with asthma, COPD, heart disease, or pregnancy.

Health Implications, Not Just Numbers

Sustained exposure to fine particulate matter (PM2.5) and ground-level ozone is one of the better-documented environmental health risks in the United States. EPA AirNow publishes daily alerts on the same data that drives this ranking, and the EPA Air Quality System archives the long historical record. The World Health Organization's air-quality guidelines document the dose-response curve linking long-run PM2.5 exposure to cardiovascular disease and reduced life expectancy.

For people in the cities below, that evidence translates into a daily decision: when to exercise outside, when to keep windows closed, when to consider a HEPA air cleaner indoors, and — if the option exists — whether to relocate. People with severe asthma, COPD, recent cardiac events, or pregnancy face the steepest costs. Even healthy adults notice chest tightness and reduced exercise capacity when running or cycling on high-AQI days. The personal exposure estimator shows what cumulative exposure looks like in a specific city.

Top 10 Worst-Air Cities at a Glance

#City5-yr Median AQIUnhealthy Days (5yr)GradeDominant Pollutant
1Maricopa, Arizona90628FOzone
2BAJA CALIFORNIA NORTE, Country Of Mexico81175FPM2.5
3Inyo, California57163FOzone
4San Bernardino, California82690FOzone
5Los Angeles, California75501DPM2.5
6Riverside, California82643DOzone
7San Diego, California67160DPM2.5
8Plumas, California52179DPM2.5
9Tulare, California75546DOzone
10Harris, Texas59144DPM2.5

What Makes the Bottom Tier Different

The cities in this ranking are not simply "above-average AQI" places — they are statistical outliers on multiple dimensions. The top 50 worst-air cities average a 5-year median AQI of 55, roughly 40% above the national city-level average of 39, and they typically log far more "Unhealthy for Sensitive Groups" and worse days each year than the national norm.

Geography is the single biggest factor. Bowl-shaped valleys behind mountain ranges (California's Central Valley, Utah's Wasatch Front, parts of the Mountain West) experience temperature inversions that trap pollution close to the ground for days at a time. Heavy-freight corridors and port complexes (Los Angeles basin, Houston, parts of New Jersey) concentrate vehicle and industrial emissions. And in the West, wildfire smoke can swing a city's grade by a full letter in a bad fire year.

Personal Mitigation

Three high-leverage steps reduce personal exposure even in a worst-tier city. First, sign up for AirNow.gov alerts at your specific zip code — within-metro AQI varies, and the city-level number is an aggregate. Second, run a HEPA air cleaner sized to a bedroom or family room; well-sized indoor HEPA cuts PM2.5 by 80%+ during smoke or high-particulate days. Third, treat N95 or KN95 masks as a meaningful tool for outdoor activity on flagged days; surgical masks do not provide useful protection against fine particulate.

For a longer-term decision, the cleanest-air cities ranking shows where U.S. air quality runs reliably below the national average — useful context for relocation decisions for asthma, COPD, or heart-disease patients.

Full Ranking — Bottom 200 Worst-Air Cities

#1Maricopa, Arizona

Median AQI: 725yr Avg: 90↑ Worsening

Primary pollutant: Ozone

F

#2BAJA CALIFORNIA NORTE, Country Of Mexico

Median AQI: 665yr Avg: 81↑ Worsening

Primary pollutant: PM2.5

F

#3Inyo, California

Median AQI: 615yr Avg: 57↑ Worsening

Primary pollutant: Ozone

F

#4San Bernardino, California

Median AQI: 715yr Avg: 82↓ Improving

Primary pollutant: Ozone

F

#5Los Angeles, California

Median AQI: 675yr Avg: 75↓ Improving

Primary pollutant: PM2.5

D

#6Riverside, California

Median AQI: 795yr Avg: 82↓ Improving

Primary pollutant: Ozone

D

#7San Diego, California

Median AQI: 675yr Avg: 67→ Stable

Primary pollutant: PM2.5

D

#8Plumas, California

Median AQI: 505yr Avg: 52↑ Worsening

Primary pollutant: PM2.5

D

#9Tulare, California

Median AQI: 695yr Avg: 75↓ Improving

Primary pollutant: Ozone

D

#10Harris, Texas

Median AQI: 645yr Avg: 59↑ Worsening

Primary pollutant: PM2.5

D

#11Pinal, Arizona

Median AQI: 645yr Avg: 66↓ Improving

Primary pollutant: PM10

D

#12Mono, California

Median AQI: 245yr Avg: 33↑ Worsening

Primary pollutant: PM2.5

D

#13Bernalillo, New Mexico

Median AQI: 595yr Avg: 59↑ Worsening

Primary pollutant: Ozone

D

#14El Paso, Texas

Median AQI: 645yr Avg: 60↑ Worsening

Primary pollutant: PM2.5

D

#15Salt Lake, Utah

Median AQI: 545yr Avg: 57↑ Worsening

Primary pollutant: Ozone

D

#16Kern, California

Median AQI: 695yr Avg: 77↓ Improving

Primary pollutant: Ozone

D

#17Clark, Nevada

Median AQI: 615yr Avg: 62→ Stable

Primary pollutant: Ozone

D

#18Catano, Puerto Rico

Median AQI: 525yr Avg: 42↑ Worsening

Primary pollutant: PM2.5

D

#19Imperial, California

Median AQI: 615yr Avg: 61↓ Improving

Primary pollutant: PM2.5

D

#20Kings, California

Median AQI: 585yr Avg: 64↓ Improving

Primary pollutant: Ozone

D

#21Placer, California

Median AQI: 525yr Avg: 54↑ Worsening

Primary pollutant: Ozone

D

#22Tarrant, Texas

Median AQI: 575yr Avg: 53↑ Worsening

Primary pollutant: PM2.5

D

#23Fresno, California

Median AQI: 645yr Avg: 68↓ Improving

Primary pollutant: Ozone

D

#24Stanislaus, California

Median AQI: 545yr Avg: 57↓ Improving

Primary pollutant: PM2.5

D

#25Jefferson, Colorado

Median AQI: 495yr Avg: 47→ Stable

Primary pollutant: Ozone

D

#26Rock Island, Illinois

Median AQI: 515yr Avg: 47↑ Worsening

Primary pollutant: PM2.5

D

#27Winnebago, Illinois

Median AQI: 525yr Avg: 48↑ Worsening

Primary pollutant: Ozone

D

#28Weld, Colorado

Median AQI: 555yr Avg: 53↑ Worsening

Primary pollutant: Ozone

D

#29Eddy, New Mexico

Median AQI: 495yr Avg: 47↑ Worsening

Primary pollutant: Ozone

D

#30Asotin, Washington

Median AQI: 495yr Avg: 43↑ Worsening

Primary pollutant: PM2.5

D

#31SONORA, Country Of Mexico

Median AQI: 535yr Avg: 44↑ Worsening

Primary pollutant: Ozone

D

#32Boulder, Colorado

Median AQI: 505yr Avg: 50↑ Worsening

Primary pollutant: Ozone

D

#33Sangamon, Illinois

Median AQI: 515yr Avg: 46↑ Worsening

Primary pollutant: PM2.5

D

#34Neosho, Kansas

Median AQI: 545yr Avg: 48↑ Worsening

Primary pollutant: Ozone

D

#35Henderson, Kentucky

Median AQI: 535yr Avg: 53↑ Worsening

Primary pollutant: PM2.5

D

#36Sanders, Montana

Median AQI: 375yr Avg: 36↑ Worsening

Primary pollutant: PM2.5

D

#37Siskiyou, California

Median AQI: 435yr Avg: 41↑ Worsening

Primary pollutant: Ozone

D

#38Douglas, Colorado

Median AQI: 495yr Avg: 47↑ Worsening

Primary pollutant: Ozone

D

#39Cook, Illinois

Median AQI: 575yr Avg: 57→ Stable

Primary pollutant: PM2.5

D

#40DuPage, Illinois

Median AQI: 535yr Avg: 49↑ Worsening

Primary pollutant: PM2.5

D

#41McLean, Illinois

Median AQI: 505yr Avg: 48↑ Worsening

Primary pollutant: PM2.5

D

#42Jackson, Mississippi

Median AQI: 515yr Avg: 46↑ Worsening

Primary pollutant: PM2.5

D

#43Dona Ana, New Mexico

Median AQI: 525yr Avg: 54→ Stable

Primary pollutant: Ozone

D

#44Butler, Ohio

Median AQI: 565yr Avg: 50↑ Worsening

Primary pollutant: Ozone

D

#45Codington, South Dakota

Median AQI: 455yr Avg: 40↑ Worsening

Primary pollutant: PM2.5

D

#46Uintah, Utah

Median AQI: 545yr Avg: 51↑ Worsening

Primary pollutant: Ozone

D

#47Valley, Idaho

Median AQI: 365yr Avg: 37↑ Worsening

Primary pollutant: PM2.5

D

#48Pima, Arizona

Median AQI: 545yr Avg: 53↑ Worsening

Primary pollutant: Ozone

C

#49Chaffee, Colorado

Median AQI: 585yr Avg: 53↑ Worsening

Primary pollutant: Ozone

C

#50Delta, Colorado

Median AQI: 445yr Avg: 42↑ Worsening

Primary pollutant: Ozone

C

#51Canyon, Idaho

Median AQI: 345yr Avg: 41↑ Worsening

Primary pollutant: PM2.5

C

#52Madison, Illinois

Median AQI: 555yr Avg: 55↑ Worsening

Primary pollutant: PM2.5

C

#53Sumner, Kansas

Median AQI: 515yr Avg: 47↑ Worsening

Primary pollutant: Ozone

C

#54Wayne, Michigan

Median AQI: 615yr Avg: 58→ Stable

Primary pollutant: PM2.5

C

#55Lincoln, Montana

Median AQI: 535yr Avg: 52↑ Worsening

Primary pollutant: PM2.5

C

#56Douglas, Oregon

Median AQI: 535yr Avg: 36↑ Worsening

Primary pollutant: PM2.5

C

#57Klamath, Oregon

Median AQI: 395yr Avg: 44→ Stable

Primary pollutant: PM2.5

C

#58Yakima, Washington

Median AQI: 465yr Avg: 49↑ Worsening

Primary pollutant: PM2.5

C

#59Johnson, Wyoming

Median AQI: 405yr Avg: 40↑ Worsening

Primary pollutant: Ozone

C

#60Mariposa, California

Median AQI: 475yr Avg: 49↓ Improving

Primary pollutant: Ozone

C

#61Trinity, California

Median AQI: 315yr Avg: 32↑ Worsening

Primary pollutant: PM2.5

C

#62Archuleta, Colorado

Median AQI: 355yr Avg: 39↑ Worsening

Primary pollutant: Ozone

C

#63Larimer, Colorado

Median AQI: 515yr Avg: 51→ Stable

Primary pollutant: Ozone

C

#64Marion, Indiana

Median AQI: 605yr Avg: 57→ Stable

Primary pollutant: PM2.5

C

#65Lafourche, Louisiana

Median AQI: 535yr Avg: 48↑ Worsening

Primary pollutant: PM2.5

C

#66Bolivar, Mississippi

Median AQI: 525yr Avg: 47↑ Worsening

Primary pollutant: PM2.5

C

#67Cuyahoga, Ohio

Median AQI: 575yr Avg: 56↑ Worsening

Primary pollutant: PM2.5

C

#68Oklahoma, Oklahoma

Median AQI: 535yr Avg: 53↑ Worsening

Primary pollutant: PM2.5

C

#69Harney, Oregon

Median AQI: 435yr Avg: 44↑ Worsening

Primary pollutant: PM2.5

C

#70Bexar, Texas

Median AQI: 525yr Avg: 54→ Stable

Primary pollutant: PM2.5

C

#71Columbia, Washington

Median AQI: 395yr Avg: 32↑ Worsening

Primary pollutant: PM2.5

C

#72Okanogan, Washington

Median AQI: 495yr Avg: 49↑ Worsening

Primary pollutant: PM2.5

C

#73Madison, Alabama

Median AQI: 495yr Avg: 48↑ Worsening

Primary pollutant: PM2.5

C

#74Mendocino, California

Median AQI: 535yr Avg: 46↑ Worsening

Primary pollutant: PM2.5

C

#75Denver, Colorado

Median AQI: 545yr Avg: 54→ Stable

Primary pollutant: PM2.5

C

#76Bonner, Idaho

Median AQI: 345yr Avg: 33↑ Worsening

Primary pollutant: PM2.5

C

#77Kane, Illinois

Median AQI: 465yr Avg: 43↑ Worsening

Primary pollutant: Ozone

C

#78Shawnee, Kansas

Median AQI: 485yr Avg: 46↑ Worsening

Primary pollutant: PM2.5

C

#79Ottawa, Oklahoma

Median AQI: 545yr Avg: 51↑ Worsening

Primary pollutant: PM2.5

C

#80Lane, Oregon

Median AQI: 495yr Avg: 45→ Stable

Primary pollutant: PM2.5

C

#81York, South Carolina

Median AQI: 475yr Avg: 44↑ Worsening

Primary pollutant: Ozone

C

#82Culberson, Texas

Median AQI: 205yr Avg: 37↑ Worsening

Primary pollutant: PM2.5

C

#83Duchesne, Utah

Median AQI: 515yr Avg: 48↑ Worsening

Primary pollutant: Ozone

C

#84Idaho, Idaho

Median AQI: 445yr Avg: 42↑ Worsening

Primary pollutant: PM2.5

C

#85Cass, Minnesota

Median AQI: 325yr Avg: 32↑ Worsening

Primary pollutant: PM2.5

C

#86Jefferson, Alabama

Median AQI: 615yr Avg: 57→ Stable

Primary pollutant: PM2.5

C

#87Nevada, California

Median AQI: 425yr Avg: 47→ Stable

Primary pollutant: Ozone

C

#88Sacramento, California

Median AQI: 515yr Avg: 53↓ Improving

Primary pollutant: Ozone

C

#89Adams, Colorado

Median AQI: 515yr Avg: 50↑ Worsening

Primary pollutant: Ozone

C

#90Johnson, Kansas

Median AQI: 495yr Avg: 44↑ Worsening

Primary pollutant: Ozone

C

#91Scott, Minnesota

Median AQI: 515yr Avg: 41↑ Worsening

Primary pollutant: Ozone

C

#92St. Louis City, Missouri

Median AQI: 585yr Avg: 55→ Stable

Primary pollutant: PM2.5

C

#93Josephine, Oregon

Median AQI: 445yr Avg: 38↑ Worsening

Primary pollutant: PM2.5

C

#94Arapahoe, Colorado

Median AQI: 475yr Avg: 46→ Stable

Primary pollutant: Ozone

C

#95Garfield, Colorado

Median AQI: 545yr Avg: 50↑ Worsening

Primary pollutant: Ozone

C

#96Broward, Florida

Median AQI: 525yr Avg: 49↑ Worsening

Primary pollutant: PM2.5

C

#97Duval, Florida

Median AQI: 525yr Avg: 52↑ Worsening

Primary pollutant: PM2.5

C

#98Bannock, Idaho

Median AQI: 415yr Avg: 37↑ Worsening

Primary pollutant: PM2.5

C

#99McHenry, Illinois

Median AQI: 495yr Avg: 49↑ Worsening

Primary pollutant: PM2.5

C

#100Saint Clair, Illinois

Median AQI: 545yr Avg: 50↑ Worsening

Primary pollutant: PM2.5

C

#101Hancock, Mississippi

Median AQI: 505yr Avg: 45↑ Worsening

Primary pollutant: PM2.5

C

#102Missoula, Montana

Median AQI: 535yr Avg: 54↓ Improving

Primary pollutant: PM2.5

C

#103Cleveland, Oklahoma

Median AQI: 525yr Avg: 51↑ Worsening

Primary pollutant: PM2.5

C

#104McClain, Oklahoma

Median AQI: 485yr Avg: 44↑ Worsening

Primary pollutant: Ozone

C

#105Grant, Oregon

Median AQI: 445yr Avg: 45↑ Worsening

Primary pollutant: PM2.5

C

#106Allegheny, Pennsylvania

Median AQI: 565yr Avg: 56→ Stable

Primary pollutant: PM2.5

C

#107Cameron, Texas

Median AQI: 545yr Avg: 52↑ Worsening

Primary pollutant: PM2.5

C

#108Denton, Texas

Median AQI: 495yr Avg: 46→ Stable

Primary pollutant: Ozone

C

#109Davis, Utah

Median AQI: 475yr Avg: 46↑ Worsening

Primary pollutant: Ozone

C

#110Stevens, Washington

Median AQI: 465yr Avg: 42↑ Worsening

Primary pollutant: PM2.5

C

#111Horry, South Carolina

Median AQI: 435yr Avg: 37↑ Worsening

Primary pollutant: Ozone

C

#112Gila, Arizona

Median AQI: 465yr Avg: 46→ Stable

Primary pollutant: Ozone

C

#113Del Norte, California

Median AQI: 325yr Avg: 32↑ Worsening

Primary pollutant: PM2.5

C

#114Baker, Florida

Median AQI: 435yr Avg: 40↑ Worsening

Primary pollutant: Ozone

C

#115Washington, Georgia

Median AQI: 525yr Avg: 47↑ Worsening

Primary pollutant: PM2.5

C

#116Ada, Idaho

Median AQI: 445yr Avg: 45↑ Worsening

Primary pollutant: Ozone

C

#117Lake, Illinois

Median AQI: 425yr Avg: 40↑ Worsening

Primary pollutant: Ozone

C

#118Becker, Minnesota

Median AQI: 445yr Avg: 39↑ Worsening

Primary pollutant: PM2.5

C

#119Wright, Minnesota

Median AQI: 495yr Avg: 41↑ Worsening

Primary pollutant: PM2.5

C

#120Jackson, Missouri

Median AQI: 525yr Avg: 51↑ Worsening

Primary pollutant: PM2.5

C

#121Stark, Ohio

Median AQI: 525yr Avg: 51↑ Worsening

Primary pollutant: PM2.5

C

#122Lancaster, Pennsylvania

Median AQI: 585yr Avg: 55→ Stable

Primary pollutant: PM2.5

C

#123Hamilton, Tennessee

Median AQI: 515yr Avg: 49↑ Worsening

Primary pollutant: PM2.5

C

#124Bell, Texas

Median AQI: 445yr Avg: 45↑ Worsening

Primary pollutant: Ozone

C

#125Dallas, Texas

Median AQI: 555yr Avg: 50→ Stable

Primary pollutant: PM2.5

C

#126Galveston, Texas

Median AQI: 515yr Avg: 45↑ Worsening

Primary pollutant: Ozone

C

#127Travis, Texas

Median AQI: 545yr Avg: 52↑ Worsening

Primary pollutant: PM2.5

C

#128Milwaukee, Wisconsin

Median AQI: 525yr Avg: 49↑ Worsening

Primary pollutant: PM2.5

C

#129Waukesha, Wisconsin

Median AQI: 525yr Avg: 48↑ Worsening

Primary pollutant: PM2.5

C

#130Ward, North Dakota

Median AQI: 425yr Avg: 36↑ Worsening

Primary pollutant: Ozone

C

#131Washington, Arkansas

Median AQI: 445yr Avg: 46↑ Worsening

Primary pollutant: PM2.5

C

#132Park, Colorado

Median AQI: 505yr Avg: 49↑ Worsening

Primary pollutant: Ozone

C

#133Citrus, Florida

Median AQI: 455yr Avg: 43↑ Worsening

Primary pollutant: PM2.5

C

#134Columbia, Florida

Median AQI: 475yr Avg: 45↑ Worsening

Primary pollutant: PM2.5

C

#135Escambia, Florida

Median AQI: 515yr Avg: 49↑ Worsening

Primary pollutant: PM2.5

C

#136Hamilton, Illinois

Median AQI: 465yr Avg: 46↑ Worsening

Primary pollutant: PM2.5

C

#137Jersey, Illinois

Median AQI: 485yr Avg: 46↑ Worsening

Primary pollutant: PM2.5

C

#138Macon, Illinois

Median AQI: 515yr Avg: 49↑ Worsening

Primary pollutant: PM2.5

C

#139Will, Illinois

Median AQI: 535yr Avg: 51→ Stable

Primary pollutant: PM2.5

C

#140Linn, Iowa

Median AQI: 545yr Avg: 49↑ Worsening

Primary pollutant: PM2.5

C

#141Bell, Kentucky

Median AQI: 495yr Avg: 45↑ Worsening

Primary pollutant: Ozone

C

#142Pittsburg, Oklahoma

Median AQI: 495yr Avg: 47↑ Worsening

Primary pollutant: PM2.5

C

#143Tulsa, Oklahoma

Median AQI: 535yr Avg: 51→ Stable

Primary pollutant: PM2.5

C

#144Jackson, Oregon

Median AQI: 455yr Avg: 44→ Stable

Primary pollutant: PM2.5

C

#145Cache, Utah

Median AQI: 485yr Avg: 47→ Stable

Primary pollutant: Ozone

C

#146Eau Claire, Wisconsin

Median AQI: 465yr Avg: 42↑ Worsening

Primary pollutant: PM2.5

C

#147Grant, Oklahoma

Median AQI: 325yr Avg: 28↑ Worsening

Primary pollutant: PM2.5

C

#148Crittenden, Arkansas

Median AQI: 415yr Avg: 45↑ Worsening

Primary pollutant: PM2.5

C

#149Colusa, California

Median AQI: 555yr Avg: 47→ Stable

Primary pollutant: PM2.5

C

#150Madera, California

Median AQI: 525yr Avg: 56↓ Improving

Primary pollutant: Ozone

C

#151Merced, California

Median AQI: 515yr Avg: 54↓ Improving

Primary pollutant: Ozone

C

#152Shasta, California

Median AQI: 455yr Avg: 44→ Stable

Primary pollutant: Ozone

C

#153Sutter, California

Median AQI: 495yr Avg: 52↓ Improving

Primary pollutant: PM2.5

C

#154Tehama, California

Median AQI: 445yr Avg: 45→ Stable

Primary pollutant: Ozone

C

#155Clear Creek, Colorado

Median AQI: 495yr Avg: 48→ Stable

Primary pollutant: Ozone

C

#156Richmond, Georgia

Median AQI: 515yr Avg: 51↑ Worsening

Primary pollutant: PM2.5

C

#157Johnson, Iowa

Median AQI: 535yr Avg: 48↑ Worsening

Primary pollutant: PM2.5

C

#158Sedgwick, Kansas

Median AQI: 485yr Avg: 45↑ Worsening

Primary pollutant: Ozone

C

#159Wyandotte, Kansas

Median AQI: 515yr Avg: 50→ Stable

Primary pollutant: PM2.5

C

#160Jefferson, Kentucky

Median AQI: 555yr Avg: 54→ Stable

Primary pollutant: PM2.5

C

#161Kalamazoo, Michigan

Median AQI: 535yr Avg: 47↑ Worsening

Primary pollutant: PM2.5

C

#162Macomb, Michigan

Median AQI: 515yr Avg: 44↑ Worsening

Primary pollutant: Ozone

C

#163Missaukee, Michigan

Median AQI: 485yr Avg: 43↑ Worsening

Primary pollutant: Ozone

C

#164Ottawa, Michigan

Median AQI: 515yr Avg: 44↑ Worsening

Primary pollutant: Ozone

C

#165Dakota, Minnesota

Median AQI: 495yr Avg: 40↑ Worsening

Primary pollutant: PM2.5

C

#166Lyon, Minnesota

Median AQI: 465yr Avg: 38↑ Worsening

Primary pollutant: PM2.5

C

#167Stearns, Minnesota

Median AQI: 485yr Avg: 39↑ Worsening

Primary pollutant: PM2.5

C

#168Washoe, Nevada

Median AQI: 505yr Avg: 50→ Stable

Primary pollutant: Ozone

C

#169Hamilton, Ohio

Median AQI: 545yr Avg: 55↓ Improving

Primary pollutant: PM2.5

C

#170Montgomery, Ohio

Median AQI: 515yr Avg: 51→ Stable

Primary pollutant: PM2.5

C

#171Harrison, Texas

Median AQI: 475yr Avg: 46↑ Worsening

Primary pollutant: PM2.5

C

#172Montgomery, Texas

Median AQI: 535yr Avg: 48→ Stable

Primary pollutant: PM2.5

C

#173Tooele, Utah

Median AQI: 455yr Avg: 44↑ Worsening

Primary pollutant: Ozone

C

#174Richmond City, Virginia

Median AQI: 455yr Avg: 42↑ Worsening

Primary pollutant: PM2.5

C

#175Benton, Washington

Median AQI: 415yr Avg: 38↑ Worsening

Primary pollutant: PM2.5

C

#176Dane, Wisconsin

Median AQI: 505yr Avg: 46↑ Worsening

Primary pollutant: PM2.5

C

#177Grant, Wisconsin

Median AQI: 485yr Avg: 42↑ Worsening

Primary pollutant: PM2.5

C

#178Lincoln, Wyoming

Median AQI: 445yr Avg: 29↑ Worsening

Primary pollutant: PM10

C

#179Washington, Oklahoma

Median AQI: 515yr Avg: 47↑ Worsening

Primary pollutant: PM2.5

C

#180Gilpin, Colorado

Median AQI: 475yr Avg: 46↑ Worsening

Primary pollutant: Ozone

C

#181Pulaski, Arkansas

Median AQI: 555yr Avg: 53→ Stable

Primary pollutant: PM2.5

C

#182Orange, California

Median AQI: 525yr Avg: 54↓ Improving

Primary pollutant: PM2.5

C

#183El Paso, Colorado

Median AQI: 475yr Avg: 46→ Stable

Primary pollutant: Ozone

C

#184Bay, Florida

Median AQI: 515yr Avg: 47↑ Worsening

Primary pollutant: PM2.5

C

#185Holmes, Florida

Median AQI: 495yr Avg: 48↑ Worsening

Primary pollutant: PM2.5

C

#186Clarke, Georgia

Median AQI: 525yr Avg: 49↑ Worsening

Primary pollutant: PM2.5

C

#187Fulton, Georgia

Median AQI: 535yr Avg: 53→ Stable

Primary pollutant: PM2.5

C

#188Benewah, Idaho

Median AQI: 485yr Avg: 48→ Stable

Primary pollutant: PM2.5

C

#189Champaign, Illinois

Median AQI: 485yr Avg: 45↑ Worsening

Primary pollutant: PM2.5

C

#190Clark, Indiana

Median AQI: 525yr Avg: 50→ Stable

Primary pollutant: PM2.5

C

#191Lake, Indiana

Median AQI: 555yr Avg: 53→ Stable

Primary pollutant: PM2.5

C

#192Bossier, Louisiana

Median AQI: 535yr Avg: 47↑ Worsening

Primary pollutant: PM2.5

C

#193Calcasieu, Louisiana

Median AQI: 545yr Avg: 52→ Stable

Primary pollutant: PM2.5

C

#194Chippewa, Michigan

Median AQI: 435yr Avg: 43↑ Worsening

Primary pollutant: PM2.5

C

#195Queens, New York

Median AQI: 505yr Avg: 46→ Stable

Primary pollutant: PM2.5

C

#196Durham, North Carolina

Median AQI: 525yr Avg: 49↑ Worsening

Primary pollutant: PM2.5

C

#197Burleigh, North Dakota

Median AQI: 425yr Avg: 38↑ Worsening

Primary pollutant: PM2.5

C

#198Love, Oklahoma

Median AQI: 455yr Avg: 44↑ Worsening

Primary pollutant: Ozone

C

#199Sequoyah, Oklahoma

Median AQI: 465yr Avg: 41↑ Worsening

Primary pollutant: PM2.5

C

#200Lehigh, Pennsylvania

Median AQI: 435yr Avg: 43↑ Worsening

Primary pollutant: PM2.5

C

Frequently Asked Questions

What does it mean health-wise to live in one of these cities?

For people with asthma, COPD, cardiovascular disease, or pregnancy, sustained exposure to elevated PM2.5 and ozone is associated with measurable increases in hospitalization, ER visits, and pollution-attributable mortality. Cities in the bottom tier of this ranking average roughly 77 unhealthy-air days per year — meaning more than three weeks annually when sensitive groups are advised to limit outdoor exertion. The American Lung Association and the World Health Organization both publish dose-response evidence linking long-term PM2.5 exposure to reduced life expectancy.

Why do these cities score so poorly?

Three structural factors compound. First, geography: bowl-shaped valleys (Central Valley California, Wasatch Front Utah) trap pollution under temperature inversions. Second, emission sources: heavy freight corridors, refineries, and ports cluster vehicle and industrial pollution into specific metros. Third, wildfire smoke: in the Western U.S., a single bad fire season can swing a city's grade by a full letter and push annual unhealthy-day counts well above 100. Among the top 50 worst-air cities here, Ozone is the dominant pollutant in 27 of them.

Are any of these cities improving?

Many are, slowly. National PM2.5 has dropped substantially since 2010 thanks to cleaner vehicles, retired coal plants, and tighter EPA standards. The fastest-improving-air-quality ranking (which is a different list) captures cities where the trend is steepest. But on the worst-air list, sustained exposure remains a real concern even when the trend is flat or modestly improving — the absolute level matters as much as the direction.

How can residents reduce their personal exposure?

Three practical steps: (1) sign up for AirNow.gov alerts at your specific zip code so you know when to limit outdoor exertion; (2) run a HEPA air cleaner sized to your bedroom or family room — well-sized indoor HEPA can cut indoor PM2.5 by 80% during smoke or pollution episodes; (3) on flagged days, an N95 or KN95 mask provides meaningful protection for outdoor activity (surgical masks do not). The personal exposure estimator is at /tools/exposure-calculator.

How are these rankings calculated?

Each city's Air Quality Grade combines four EPA-derived signals: 5-year median AQI (40% of the score), 10-year trend direction (30%), the count of "Unhealthy for Sensitive Groups" days per year (20%), and the dominant pollutant type (10%). All inputs come from the EPA Air Quality System (AQS) Annual AQI by County dataset. Cities at the bottom of this ranking earned D or F grades — meaning multiple factors line up unfavorably. The top 50 cities on this list average a 5-year median AQI of 55, well above the national city-level average of 39. Full methodology at /methodology.

How These Ranks Are Calculated

For each city we compute a 5-year median AQI and a 10-year trend slope from EPA AQS Annual AQI by County data. Those feed a composite Air Quality Grade — 40% median AQI, 30% trend, 20% unhealthy days, 10% dominant pollutant — that produces both a 0–100 score and an A–F letter. Cities at the bottom of the distribution land at D or F. Read the full methodology.

Cleanest Air Cities →Fastest-Improving Cities →Compare Any Two Cities →

Worst air quality cities in America — bottom 200 ranked by EPA AQS Annual AQI by County data, with health-implication context for sensitive groups.