Bad Air Days in Ozaukee County, Wisconsin: 9 a Year
9 bad air days a year
Among the worst tenth of monitored US counties. Ranked 98 of 996 monitored counties, where 1 is worst.
What makes them bad: mostly ozone: summer smog (15% particle days).
The bad-air season here
- 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.
What to buy, and what not to
- 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 record for Ozaukee
In 2000 to 2009 this county averaged 21 bad days a year; in 2016 to 2025, 9. The air has improved. The worst recent year was 2023, with 18 bad days on 363 monitored days.
| Date | AQI | Main pollutant |
|---|---|---|
| 2023-06-27 | 210 | PM2.5 |
| 2023-07-25 | 202 | Ozone |
| 2023-06-28 | 185 | PM2.5 |
| 2023-06-29 | 179 | Ozone |
| 2016-08-04 | 172 | Ozone |
An ordinary day in Ozaukee
Across 3,559 monitored days from 2016 to 2025, the air in Ozaukee County rated Good on 73% of them, close to the 72% typical of monitored counties, and Moderate on 25%. The median day sat at AQI 40; one day in ten went above 66.
The pollutant setting the AQI on an ordinary day here:
- fine particles (PM2.5)51%1,818 days
- ozone49%1,741 days
Every recent year on file
| Year | Days monitored | Good | Moderate | Over 100 | Over 150 | Median AQI | Highest AQI |
|---|---|---|---|---|---|---|---|
| 2025* | 365 | 277 | 73 | 15 | 2 | 36 | 167 |
| 2024 | 366 | 296 | 61 | 9 | 2 | 37 | 161 |
| 2023 | 363 | 219 | 126 | 18 | 4 | 45 | 210 |
| 2022 | 307 | 228 | 74 | 5 | 1 | 41 | 159 |
| 2021 | 364 | 241 | 116 | 7 | 0 | 43 | 129 |
| 2020 | 365 | 269 | 91 | 5 | 1 | 40 | 164 |
| 2019 | 363 | 271 | 89 | 3 | 0 | 40 | 108 |
| 2018 | 363 | 254 | 102 | 7 | 2 | 43 | 169 |
| 2017 | 348 | 276 | 64 | 8 | 0 | 40 | 136 |
| 2016 | 355 | 269 | 77 | 9 | 1 | 38 | 172 |
| 2015 | 365 | 260 | 100 | 5 | 0 | 40 | 122 |
| 2014 | 358 | 258 | 94 | 6 | 0 | 41 | 119 |
| 2013 | 352 | 230 | 118 | 4 | 0 | 42 | 112 |
| 2012 | 364 | 201 | 139 | 24 | 6 | 47 | 192 |
| 2011 | 235 | 174 | 53 | 8 | 1 | 40 | 182 |
| 2010 | 253 | 183 | 64 | 6 | 1 | 42 | 161 |
*2025 may be a partial year in EPA's file.
Nearby counties on file
- Sheboygan County16/yr
- Racine County15/yr
- Kenosha County12/yr
- Milwaukee County8/yr
- Manitowoc County7/yr
- Door County7/yr
- Walworth County6/yr
- Rock County6/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.