Bad Air Days in Mercer County, North Dakota: 5 a Year
5 bad air days a year
More bad air days than three quarters of monitored counties. Ranked 246 of 996 monitored counties, where 1 is worst.
What makes them bad: mostly particles: smoke and dust (91% 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 August and September and July and June. 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.
- Upgrade the furnace or AC filter to MERV 13 so the whole house is filtered, not just one room.
The worst days on file
In 2000 to 2009 this county averaged under 1 bad days a year; in 2016 to 2025, 5. It has got worse. The worst recent year was 2023, with 16 bad days on 365 monitored days.
| Date | AQI | Main pollutant |
|---|---|---|
| 2023-05-17 | 322 | PM2.5 |
| 2025-05-31 | 283 | PM2.5 |
| 2025-06-11 | 196 | PM2.5 |
| 2021-08-16 | 174 | PM2.5 |
| 2025-06-01 | 172 | PM2.5 |
The air on a normal day
Across 3,653 monitored days from 2016 to 2025, the air in Mercer County rated Good on 84% of them, more often than the 72% typical of monitored counties, and Moderate on 15%. The median day sat at AQI 37; one day in ten went above 57.
The pollutant setting the AQI on an ordinary day here:
- ozone67%2,464 days
- fine particles (PM2.5)32%1,161 days
- nitrogen dioxide1%23 days
Mercer County by year
| Year | Days monitored | Good | Moderate | Over 100 | Over 150 | Median AQI | Highest AQI |
|---|---|---|---|---|---|---|---|
| 2025* | 365 | 293 | 62 | 10 | 4 | 37 | 283 |
| 2024 | 366 | 304 | 56 | 6 | 2 | 37 | 167 |
| 2023 | 365 | 252 | 97 | 16 | 6 | 41 | 322 |
| 2022 | 365 | 318 | 47 | 0 | 0 | 36 | 72 |
| 2021 | 365 | 279 | 77 | 9 | 4 | 38 | 174 |
| 2020 | 366 | 328 | 38 | 0 | 0 | 36 | 78 |
| 2019 | 365 | 301 | 64 | 0 | 0 | 38 | 72 |
| 2018 | 365 | 305 | 58 | 2 | 0 | 38 | 111 |
| 2017 | 365 | 317 | 46 | 2 | 1 | 35 | 159 |
| 2016 | 366 | 356 | 9 | 1 | 0 | 32 | 107 |
| 2015 | 365 | 297 | 62 | 6 | 2 | 37 | 152 |
| 2014 | 363 | 324 | 38 | 1 | 0 | 37 | 128 |
| 2013 | 365 | 300 | 65 | 0 | 0 | 39 | 76 |
| 2012 | 366 | 301 | 65 | 0 | 0 | 40 | 87 |
| 2011 | 365 | 262 | 103 | 0 | 0 | 44 | 74 |
| 2010 | 365 | 293 | 72 | 0 | 0 | 40 | 87 |
*2025 may be a partial year in EPA's file.
North Dakota compared
- Burleigh County7/yr
- Ward County7/yr
- Oliver County6/yr
- Burke County6/yr
- Dunn County5/yr
- Cass County5/yr
- McKenzie County4/yr
- Billings 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.