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2024 monitoring year Public dataset EPA AQS

Ohio Air Quality Rankings

County-level AQI rollup using EPA Air Quality System monitor records. Refreshed as new EPA AQS data lands.

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County-by-county air quality data for Ohio based on EPA AQS annual AQI readings. Data covers 40 monitored counties for 2024.

Ohio (2024): 40 counties monitored. State average median AQI: 42 (national average: 38.8). 73% of monitored days rated "Good."

Ohio air quality on this page is drawn from the EPA Air Quality System (AQS), which aggregates daily readings from federal, state, tribal, and local monitors into annual summaries per county. The current dataset covers 40 Ohio counties with at least ten days of valid AQI readings in 2024, out of the state's total monitored counties.

The state-average median AQI across those counties is 42, compared with a national average of 38.8 in the same reporting period. On average, 73% of monitored days fell into the "Good" AQI bucket (0–50). The heaviest burden of unhealthy days lands on Columbiana County (0 days above AQI 100).

AQI values translate ambient concentrations of pollutants (ozone, PM2.5, PM10, NO₂, SO₂, CO) onto a single 0–500 scale with six health-based bands. A low median AQI reflects typical daily conditions; peak values matter separately because short-term exposure drives most acute health effects. Counties without monitors are not "clean" - they are simply unmeasured by EPA AQS. For site-specific exposure guidance, check AirNow.gov alongside the county detail links below.

Counties with Data
40
State Avg Median AQI
42
National Avg Median AQI
38.8
Avg Good Days %
73%

Which Ohio counties have the worst air quality?

Ranked by median AQI (higher = worse). Click a county for full environmental data.

# County Median AQI Unhealthy Days
1 Cuyahoga 54 0
2 Franklin 53 0
3 Butler 53 0
4 Lucas 52 0
5 Hamilton 52 0
6 Stark 48 0
7 Montgomery 47 0
8 Jefferson 45 0
9 Trumbull 45 0
10 Clark 45 0
11 Madison 44 0
12 Summit 44 0
13 Medina 44 0
14 Mahoning 44 0
15 Clinton 44 0
16 Preble 44 0
17 Portage 43 0
18 Warren 43 0
19 Greene 43 0
20 Miami 43 0
21 Lawrence 43 0
22 Delaware 42 0
23 Licking 42 0
24 Allen 42 0
25 Knox 41 0
26 Lake 41 0
27 Wood 41 0
28 Ashtabula 41 0
29 Geauga 41 0
30 Washington 41 0
31 Noble 40 0
32 Scioto 40 0
33 Lorain 39 0
34 Clermont 39 0
35 Adams 39 0
36 Fayette 35 0
37 Harrison 33 0
38 Belmont 32 0
39 Athens 28 0
40 Columbiana 12 0

Frequently Asked Questions

What is the air quality like in Ohio?

In 2024, Ohio had an average median AQI of 42 across 40 monitored counties, with 73% of monitored days rated "Good" (AQI 0–50). The national average median AQI is 38.8.

Which county in Ohio has the worst air quality?

Based on 2024 EPA AQS data, Columbiana County had the most unhealthy air days in Ohio - 0 days above AQI 100, with a median AQI of 12.

Explore More

National AQI Rankings → Ohio Full Profile → Ohio Water Quality →

About This Data

Air quality data is from the EPA Air Quality System (AQS), Annual AQI by County dataset. Counties with fewer than 10 monitored days are excluded. "Unhealthy days" counts days with AQI above 100 (Unhealthy for Sensitive Groups or worse). All data is for 2024.

Source: U.S. Environmental Protection Agency, Air Quality System (AQS) U.S. Environmental Protection Agency, Air Quality System (AQS)

Read our methodology - how this data is sourced, computed, and verified.

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Data sourced from the U.S. Environmental Protection Agency (EPA). See our methodology for details. Retrieved and formatted by PlainEnviro Editorial