Bad Air Days in Jersey County, Illinois: 5 a Year
5 bad air days a year
More bad air days than three quarters of monitored counties. Ranked 238 of 996 monitored counties, where 1 is worst.
What makes them bad: mostly ozone: summer smog (9% particle days).
When the bad days come in Jersey
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Most bad days here fall in June and May. Averaged over 2016 to 2025.
What actually helps here
- Ozone drives many bad days here. Purifiers and filters do not remove ozone, so do not buy one for that. Ozone peaks on hot afternoons: exercise outside in the morning.
Better or worse than it was
In 2000 to 2009 this county averaged 23 bad days a year; in 2016 to 2025, 5. The air has improved. The worst recent year was 2023, with 18 bad days on 365 monitored days.
| Date | AQI | Main pollutant |
|---|---|---|
| 2023-06-28 | 166 | PM2.5 |
| 2025-09-18 | 156 | Ozone |
| 2016-08-04 | 150 | Ozone |
| 2023-05-31 | 147 | Ozone |
| 2023-06-03 | 147 | Ozone |
The air on a normal day
Across 3,446 monitored days from 2016 to 2025, the air in Jersey County rated Good on 65% of them, less often than the 72% typical of monitored counties, and Moderate on 34%. The median day sat at AQI 45; one day in ten went above 64.
The pollutant setting the AQI on an ordinary day here:
- fine particles (PM2.5)57%1,979 days
- ozone43%1,467 days
Jersey County by year
| Year | Days monitored | Good | Moderate | Over 100 | Over 150 | Median AQI | Highest AQI |
|---|---|---|---|---|---|---|---|
| 2025* | 358 | 259 | 95 | 4 | 1 | 42 | 156 |
| 2024 | 333 | 248 | 84 | 1 | 0 | 42 | 112 |
| 2023 | 365 | 199 | 148 | 18 | 1 | 48 | 166 |
| 2022 | 365 | 240 | 120 | 5 | 0 | 45 | 112 |
| 2021 | 360 | 225 | 133 | 2 | 0 | 45 | 112 |
| 2020 | 358 | 258 | 99 | 1 | 0 | 44 | 112 |
| 2019 | 347 | 221 | 124 | 2 | 0 | 46 | 119 |
| 2018 | 356 | 208 | 145 | 3 | 0 | 47 | 122 |
| 2017 | 309 | 170 | 136 | 3 | 0 | 48 | 119 |
| 2016 | 295 | 202 | 88 | 5 | 0 | 44 | 150 |
| 2015 | 240 | 190 | 49 | 1 | 0 | 41 | 112 |
| 2014 | 233 | 178 | 54 | 1 | 0 | 40 | 101 |
| 2013 | 211 | 168 | 41 | 2 | 1 | 41 | 151 |
| 2012 | 212 | 120 | 65 | 27 | 5 | 49 | 202 |
| 2011 | 213 | 156 | 47 | 10 | 1 | 44 | 156 |
| 2010 | 262 | 197 | 61 | 4 | 0 | 38 | 108 |
*2025 may be a partial year in EPA's file.
Illinois compared
- Cook County18/yr
- Lake County9/yr
- Madison County8/yr
- Kane County7/yr
- McHenry County7/yr
- DuPage County5/yr
- Peoria County4/yr
- Winnebago 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.