Where the air is cleanest in the US

13 counties that measure both ozone and particles all year had no bad-air days at all from 2021 to 2025. Among counties of 1 million people or more, Honolulu County, HI had the fewest: 0.2 bad-air days a year, about 1 every 5 years.

Every county

Fewest bad-air days a year first, 2021 to 2025. Ties go to the county with the lower AQI on a typical day.

#CountyBad-air days a year Typical-day AQIMain cause
1 Carbon County, WYRarely bad 0 9 Rarely bad
2 San Mateo County, CASan MateoRarely bad 0 32 Rarely bad
3 Denali Borough, AKRarely bad 0 34 Rarely bad
4 Washington County, MERarely bad 0 34 Rarely bad
5 Marin County, CASan RafaelRarely bad 0 34 Rarely bad
6 Tucker County, WVRarely bad 0 36 Rarely bad
7 Sumter County, ALRarely bad 0 37 Rarely bad
8 Edgecombe County, NCRocky MountRarely bad 0 38 Rarely bad
9 Buncombe County, NCAshevilleRarely bad 0 41 Rarely bad
10 Edgefield County, SCRarely bad 0 43 Rarely bad
11 Etowah County, ALGadsdenRarely bad 0 45 Rarely bad
12 Columbia County, FLLake CityRarely bad 0 46 Rarely bad
13 Holmes County, FLRarely bad 0 47 Rarely bad
14 Apache County, AZRarely bad 0.2 17 Rarely bad
15 Honolulu County, HIHonoluluRarely bad 0.2 30 Rarely bad
16 Navajo County, AZShow LowRarely bad 0.2 31 Rarely bad
17 Santa Cruz County, CASanta CruzRarely bad 0.2 36 Rarely bad
18 Newton County, ARRarely bad 0.2 38 Rarely bad
19 Lee County, FLCape CoralRarely bad 0.2 39 Rarely bad
20 Alachua County, FLGainesvilleRarely bad 0.2 39 Rarely bad
21 Ouachita Parish, LAMonroeRarely bad 0.2 39 Rarely bad
22 Monterey County, CASalinasRarely bad 0.2 40 Rarely bad
23 Wakulla County, FLRarely bad 0.2 41 Rarely bad
24 Loudon County, TNLenoir CityRarely bad 0.2 41 Rarely bad
25 Glynn County, GABrunswickRarely bad 0.2 41 Rarely bad

Counties of 250,000 people or more

Fewest bad-air days a year first, 2021 to 2025. Ties go to the county with the lower AQI on a typical day.

#CountyBad-air days a year Typical-day AQIMain cause
1 San Mateo County, CASan MateoRarely bad 0 32 Rarely bad
2 Marin County, CASan RafaelRarely bad 0 34 Rarely bad
3 Buncombe County, NCAshevilleRarely bad 0 41 Rarely bad
4 Honolulu County, HIHonoluluRarely bad 0.2 30 Rarely bad
5 Santa Cruz County, CASanta CruzRarely bad 0.2 36 Rarely bad
6 Lee County, FLCape CoralRarely bad 0.2 39 Rarely bad
7 Alachua County, FLGainesvilleRarely bad 0.2 39 Rarely bad
8 Monterey County, CASalinasRarely bad 0.2 40 Rarely bad
9 Palm Beach County, FLWest Palm BeachRarely bad 0.2 42 Rarely bad
10 Brevard County, FLPalm BayRarely bad 0.2 42 Rarely bad
11 Collier County, FLNaplesRarely bad 0.2 42 Rarely bad
12 Volusia County, FLDeltonaRarely bad 0.2 43 Rarely bad
13 Mobile County, ALMobileRarely bad 0.2 46 Rarely bad
14 Charleston County, SCCharlestonRarely bad 0.2 46 Rarely bad
15 San Francisco County, CARarely bad 0.2 35 Rarely bad
16 Sonoma County, CASanta RosaRarely bad 0.4 27 Rarely bad
17 Osceola County, FLKissimmeeRarely bad 0.4 36 Rarely bad
18 Polk County, FLLakelandRarely bad 0.4 41 Rarely bad
19 Seminole County, FLSanfordRarely bad 0.4 41 Rarely bad
20 Sarasota County, FLNorth PortRarely bad 0.4 45 Rarely bad
21 Durham County, NCSummer smoke 0.6 45 Summer smoke
22 Marion County, FLOcalaOzone 0.6 45 Ozone
23 Leon County, FLTallahasseeSummer smoke 0.6 47 Summer smoke
24 Escambia County, FLPensacolaOzone 0.6 47 Ozone
25 Santa Barbara County, CASanta MariaOzone and particles 0.6 48 Ozone and particles

Counties of 1 million people or more

Fewest bad-air days a year first, 2021 to 2025. Ties go to the county with the lower AQI on a typical day.

#CountyBad-air days a year Typical-day AQIMain cause
1 Honolulu County, HIHonoluluRarely bad 0.2 30 Rarely bad
2 Palm Beach County, FLWest Palm BeachRarely bad 0.2 42 Rarely bad
3 Middlesex County, MACambridgeOzone 0.8 38 Ozone
4 Orange County, FLOrlandoOzone 1.0 40 Ozone
5 Broward County, FLFort LauderdaleOzone and particles 1.0 48 Ozone and particles
6 Wake County, NCRaleighSummer smoke 1.4 46 Summer smoke
7 Montgomery County, MDGaithersburgOzone 1.8 41 Ozone
8 Hillsborough County, FLTampaOzone 2.2 50 Ozone
9 Contra Costa County, CAConcordSummer smoke 2.2 49 Summer smoke
10 Miami-Dade County, FLMiamiOzone and particles 2.4 47 Ozone and particles
11 Mecklenburg County, NCHuntersvilleOzone 2.8 50 Ozone
12 Fairfax County, VAMcLeanOzone 3.6 45 Ozone
13 Santa Clara County, CASan JoseSummer smoke 4.2 48 Summer smoke
14 Franklin County, OHColumbusOzone and particles 4.4 52 Ozone and particles
15 Westchester County, NYYonkersOzone 5.0 38 Ozone
16 New York County, NYManhattanOzone 5.2 45 Ozone
17 Fulton County, GAAtlantaOzone 5.4 51 Ozone
18 Bronx County, NYNew York CityOzone 5.6 45 Ozone
19 St. Louis County, MOFlorissantOzone 6.0 44 Ozone
20 Travis County, TXAustinOzone 6.4 52 Ozone
21 Queens County, NYNew York CityOzone 6.6 47 Ozone
22 King County, WASeattleSummer smoke 6.6 44 Summer smoke
23 Hennepin County, MNMinneapolisSummer smoke 6.8 45 Summer smoke
24 Cuyahoga County, OHClevelandOzone 7.0 55 Ozone
25 Alameda County, CAOaklandOzone and particles 7.2 50 Ozone and particles

How we rank

Every number comes from the EPA's AirData county summaries for 2021 to 2025. A bad-air day is a day when a county's worst monitor shows an AQI over 100, the point where the EPA says children, older adults and people with asthma or heart or lung disease should cut back outdoors. The typical-day AQI is the median: half of days are cleaner, half are worse. 50 or under is the green "good" range.

We rank only the 527 counties whose monitors measure both ozone and fine particles and report on at least 340 days a year. A county that measures only one can't record the other's bad days, and a monitor that runs only in ozone season can miss bad days, so either could look cleaner than it is. Counties without monitors aren't ranked; their state page and the map have CDC estimates.

The American Lung Association's State of the Air report ranks counties too. It uses 3 years of data and gives more weight to worse days, so its order differs from ours.

See the worst air · States ranked · How we count · Download every county's numbers

Questions people ask

Which US county has the cleanest air?

Going by EPA monitors from 2021 to 2025, Carbon County, WY ranks first, with no bad-air days and a typical-day AQI of about 9, well inside the green range. 13 counties had no bad-air days at all; we break ties by the typical day's AQI.

Which big city has the cleanest air?

We rank counties, because the EPA reports air quality by county. Among counties of 1 million people or more, the fewest bad-air days were in Honolulu County, HI (Honolulu), Palm Beach County, FL (West Palm Beach) and Middlesex County, MA (Cambridge).

Sources: EPA AirData county AQI summaries, 2021 to 2025. Updated November 8, 2026.