Bad Air Days in Clay County, South Dakota: 6 a Year
6 bad air days a year
More bad air days than three quarters of monitored counties. Ranked 190 of 996 monitored counties, where 1 is worst.
What makes them bad: a mix of particles and ozone (55% particle days).
When the bad days come in Clay
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Most bad days here fall in June and September and May and July. Averaged over 2016 to 2025.
What actually helps here
- Particles (wildfire smoke, dust) cause enough bad days here to matter. A HEPA purifier sized to your bedroom removes them; run it with windows shut on bad days.
Better or worse than it was
The worst recent year was 2023, with 18 bad days on 365 monitored days.
| Date | AQI | Main pollutant |
|---|---|---|
| 2023-05-18 | 173 | PM2.5 |
| 2023-07-16 | 165 | PM2.5 |
| 2023-09-06 | 159 | PM2.5 |
| 2024-10-20 | 137 | PM2.5 |
| 2023-09-07 | 135 | PM2.5 |
Most days, not the worst ones
Across 1,447 monitored days from 2022 to 2025, the air in Clay County rated Good on 80% of them, more often than the 72% typical of monitored counties, and Moderate on 18%. The median day sat at AQI 39; one day in ten went above 61.
The pollutant setting the AQI on an ordinary day here:
- ozone60%861 days
- fine particles (PM2.5)40%586 days
Year by year
| Year | Days monitored | Good | Moderate | Over 100 | Over 150 | Median AQI | Highest AQI |
|---|---|---|---|---|---|---|---|
| 2025* | 351 | 308 | 41 | 2 | 0 | 34 | 117 |
| 2024 | 366 | 289 | 75 | 2 | 0 | 39 | 137 |
| 2023 | 365 | 244 | 103 | 18 | 3 | 43 | 173 |
| 2022 | 365 | 320 | 45 | 0 | 0 | 38 | 87 |
*2025 may be a partial year in EPA's file.
Elsewhere in South Dakota
- Minnehaha County5/yr
- Pennington County4/yr
- Brown County3/yr
- Brookings County3/yr
- Custer County3/yr
- Codington County3/yr
- Jackson County2/yr
- Union County2/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.