Unhealthy Air Days by ZIP Code
Data current as of December 2024 — recomputed by ZipCheckup from federal data each build.
Among the 996 U.S. counties with an EPA air-quality monitor, 535 (53.7%) recorded at least one day in 2024 when the Air Quality Index passed 100 (unhealthy for sensitive groups or worse), and 161 had at least one day above 150 (unhealthy for everyone), as of December 2024. Counties without a monitor are not included — their air is unmeasured, not necessarily clean.
In 2024, 535 of the 996 U.S. counties with air-quality monitors recorded at least one day when the air was unhealthy for sensitive groups or worse, and 161 had at least one day rated unhealthy for everyone, as of December 2024.
By state
We report two independent facts side by side and do not rank states. A larger count reflects the size of a state's inventory and its reporting activity, not a judgment about water safety.
| state | monitored counties | counties above usg | counties unhealthy |
|---|---|---|---|
| AK | 8 | 1 | 1 |
| AL | 15 | 3 | 0 |
| AR | 11 | 4 | 2 |
| AZ | 13 | 10 | 7 |
| CA | 52 | 37 | 16 |
| CO | 30 | 20 | 10 |
| CT | 8 | 8 | 5 |
| DC | 1 | 1 | 0 |
| DE | 3 | 1 | 0 |
| FL | 38 | 16 | 4 |
| GA | 29 | 19 | 3 |
| HI | 3 | 1 | 0 |
| IA | 14 | 1 | 0 |
| ID | 19 | 16 | 10 |
| IL | 23 | 15 | 2 |
| IN | 33 | 14 | 2 |
| KS | 11 | 7 | 3 |
| KY | 25 | 7 | 1 |
| LA | 22 | 18 | 5 |
| MA | 13 | 6 | 1 |
| MD | 16 | 10 | 1 |
| ME | 11 | 3 | 0 |
| MI | 28 | 14 | 1 |
| MN | 22 | 16 | 6 |
| MO | 21 | 9 | 1 |
| MS | 10 | 3 | 1 |
| MT | 24 | 17 | 7 |
| NC | 35 | 7 | 1 |
| ND | 9 | 9 | 9 |
| NE | 11 | 4 | 0 |
| NH | 7 | 1 | 0 |
| NJ | 15 | 12 | 2 |
| NM | 16 | 10 | 4 |
| NV | 9 | 7 | 2 |
| NY | 27 | 13 | 1 |
| OH | 37 | 20 | 0 |
| OK | 21 | 19 | 5 |
| OR | 21 | 17 | 9 |
| PA | 38 | 20 | 0 |
| RI | 3 | 1 | 0 |
| SC | 13 | 5 | 0 |
| SD | 10 | 9 | 1 |
| TN | 23 | 6 | 1 |
| TX | 45 | 37 | 16 |
| UT | 17 | 14 | 3 |
| VA | 30 | 4 | 0 |
| VT | 4 | 0 | 0 |
| WA | 31 | 10 | 4 |
| WI | 29 | 14 | 5 |
| WV | 13 | 1 | 0 |
| WY | 19 | 14 | 6 |
Open data, licensed CC BY 4.0 · DOI: 10.5281/zenodo.19427201
How we compute this
We use the EPA's annual Air Quality Index summary by county for 2024. The AQI combines ground-level ozone, fine particles (PM2.5 and PM10), carbon monoxide, and nitrogen dioxide into one daily number; a value above 100 is unhealthy for sensitive groups, and above 150 is unhealthy for everyone. Of the 996 counties with a monitor, 535 had at least one day above 100 and 161 at least one day above 150, totaling 4,016 and 735 such days respectively.
Only about a thousand of the roughly 3,140 U.S. counties operate an air-quality monitor, so every figure here is a share of MONITORED counties, never of all counties. A county that is absent from the EPA file is unmonitored, not clean — we omit it rather than record it as having zero unhealthy days. A monitored county with no unhealthy days is a real measured zero and is kept.
Counts are grouped by state and recompute on every build, and each monitored county maps to the ZIP codes within it. The 535 affected counties span 51 states and jurisdictions.
Frequently asked questions
How many U.S. counties had unhealthy air in 2024?
Among the 996 counties with an EPA air-quality monitor, 535 recorded at least one day in 2024 when the Air Quality Index was unhealthy for sensitive groups or worse (above 100), and 161 had a day that was unhealthy for everyone (above 150), as of December 2024. Counties without a monitor are not counted, because their air is unmeasured rather than known to be clean. according to ZipCheckup's reading of federal data as of December 2024.
Does my county having no air data mean the air is clean?
No. Only about a thousand of the roughly 3,140 U.S. counties operate an air-quality monitor. If a county is not in the EPA's data, its air quality is simply unmeasured, not confirmed clean. ZipCheckup reports unhealthy-air days only for monitored counties, as of December 2024, and never treats a missing county as having zero unhealthy days.