Bad Air Days in Knox County, Ohio: under 1 a Year
under 1 bad air day a year
Fewer bad air days than most monitored US counties. Ranked 708 of 996 monitored counties, where 1 is worst.
What makes them bad: mostly ozone: summer smog (0% particle days).
Which months to watch
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Most bad days here fall in June and May and July. Averaged over 2016 to 2025.
What to buy, and what not to
- Bad air days are rare here. A standard furnace filter is enough; no purifier needed for outdoor air.
- On the odd bad day, check AirNow and keep windows shut.
The record for Knox
In 2000 to 2009 this county averaged 27 bad days a year; in 2016 to 2025, under 1. The air has improved. The worst recent year was 2025, with 2 bad days on 245 monitored days.
| Date | AQI | Main pollutant |
|---|---|---|
| 2025-06-12 | 159 | Ozone |
| 2022-06-21 | 119 | Ozone |
| 2018-05-25 | 115 | Ozone |
| 2023-06-18 | 105 | Ozone |
| 2024-06-13 | 101 | Ozone |
Most days, not the worst ones
Across 2,418 monitored days from 2016 to 2025, the air in Knox County rated Good on 88% of them, more often than the 72% typical of monitored counties, and Moderate on 12%. The median day sat at AQI 40; one day in ten went above 54.
The pollutant setting the AQI on an ordinary day here:
- ozone100%2,418 days
Every recent year on file
| Year | Days monitored | Good | Moderate | Over 100 | Over 150 | Median AQI | Highest AQI |
|---|---|---|---|---|---|---|---|
| 2025* | 245 | 209 | 34 | 2 | 1 | 39 | 159 |
| 2024 | 245 | 208 | 36 | 1 | 0 | 41 | 101 |
| 2023 | 245 | 200 | 44 | 1 | 0 | 42 | 105 |
| 2022 | 245 | 225 | 19 | 1 | 0 | 39 | 119 |
| 2021 | 245 | 225 | 20 | 0 | 0 | 38 | 97 |
| 2020 | 245 | 226 | 19 | 0 | 0 | 38 | 80 |
| 2019 | 245 | 218 | 27 | 0 | 0 | 41 | 93 |
| 2018 | 245 | 208 | 36 | 1 | 0 | 40 | 115 |
| 2017 | 245 | 223 | 22 | 0 | 0 | 38 | 100 |
| 2016 | 213 | 175 | 38 | 0 | 0 | 41 | 100 |
| 2015 | 210 | 178 | 28 | 4 | 0 | 40 | 119 |
| 2014 | 214 | 179 | 35 | 0 | 0 | 41 | 97 |
| 2013 | 214 | 182 | 30 | 2 | 0 | 40 | 108 |
| 2012 | 214 | 135 | 71 | 8 | 1 | 45 | 182 |
| 2011 | 214 | 166 | 41 | 7 | 0 | 42 | 147 |
| 2010 | 214 | 154 | 56 | 4 | 0 | 42 | 122 |
*2025 may be a partial year in EPA's file.
Nearby counties on file
- Hamilton County9/yr
- Cuyahoga County7/yr
- Lucas County7/yr
- Lake County7/yr
- Butler County6/yr
- Warren County5/yr
- Geauga County5/yr
- Ashtabula County4/yr
How this is counted
A bad air day is a day the county's daily AQI from EPA AirData went above 100, the level where EPA tells children, older adults and people with asthma or heart disease to cut back outdoors. Monitors do not run every day, so yearly counts are scaled to 365 days. This is the record, not today's air: for that, check AirNow. More on the method in how the county numbers are made, on the AQI 100 line in what counts as a bad air day, and on why a purifier does not touch ozone in smoke vs ozone.