| County | Ozone scores | ||
| 2014-2016 | 2015-2017 | 2016-2018 | |
| Cook | 9.8 | 14.0 | 19.2 |
| DuPage | 3.7 | 3.7 | 5.0 |
| Kane | 3.0 | 3.0 | 4.7 |
| Lake | 5.3 | 6.0 | 8.0 |
| McHenry | 3.3 | 3.3 | 5.7 |