Bad Air Days in DuPage County, Illinois: 5 a Year
5 bad air days a year
More bad air days than three quarters of monitored counties. Ranked 211 of 996 monitored counties, where 1 is worst.
What makes them bad: mostly ozone: summer smog (17% particle days).
When the bad days come in DuPage
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Most bad days here fall in June and July and August and May. Averaged over 2016 to 2025.
Is a purifier worth it 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.
The worst days on file
In 2000 to 2009 this county averaged 5 bad days a year; in 2016 to 2025, 5. Not much has changed. The worst recent year was 2023, with 17 bad days on 365 monitored days.
| Date | AQI | Main pollutant |
|---|---|---|
| 2023-06-27 | 234 | PM2.5 |
| 2023-06-28 | 227 | PM2.5 |
| 2019-08-03 | 174 | Ozone |
| 2023-06-29 | 159 | PM2.5 |
| 2025-07-31 | 158 | PM2.5 |
The air on a normal day
Across 3,457 monitored days from 2016 to 2025, the air in DuPage County rated Good on 55% of them, less often than the 72% typical of monitored counties, and Moderate on 43%. The median day sat at AQI 47; one day in ten went above 68.
The pollutant setting the AQI on an ordinary day here:
- fine particles (PM2.5)64%2,203 days
- ozone36%1,254 days
Every recent year on file
| Year | Days monitored | Good | Moderate | Over 100 | Over 150 | Median AQI | Highest AQI |
|---|---|---|---|---|---|---|---|
| 2025* | 365 | 233 | 126 | 6 | 1 | 42 | 158 |
| 2024 | 366 | 230 | 136 | 0 | 0 | 45 | 97 |
| 2023 | 365 | 146 | 202 | 17 | 6 | 53 | 234 |
| 2022 | 365 | 199 | 165 | 1 | 0 | 47 | 129 |
| 2021 | 365 | 179 | 184 | 2 | 0 | 51 | 105 |
| 2020 | 366 | 213 | 149 | 4 | 1 | 47 | 154 |
| 2019 | 352 | 196 | 153 | 3 | 1 | 48 | 174 |
| 2018 | 361 | 136 | 221 | 4 | 0 | 53 | 112 |
| 2017 | 311 | 210 | 99 | 2 | 0 | 44 | 129 |
| 2016 | 241 | 176 | 56 | 9 | 0 | 42 | 136 |
| 2015 | 259 | 196 | 62 | 1 | 0 | 42 | 115 |
| 2014 | 234 | 183 | 49 | 2 | 0 | 39 | 101 |
| 2013 | 301 | 177 | 123 | 1 | 0 | 45 | 115 |
| 2012 | 366 | 158 | 201 | 7 | 0 | 52 | 136 |
| 2011 | 365 | 110 | 252 | 3 | 0 | 56 | 119 |
| 2010 | 365 | 132 | 230 | 3 | 0 | 54 | 110 |
*2025 may be a partial year in EPA's file.
Nearby counties on file
- Cook County18/yr
- Lake County9/yr
- Madison County8/yr
- Kane County7/yr
- McHenry County7/yr
- Jersey 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.